This is libc.info, produced by makeinfo version 7.1.1 from libc.texinfo. This is ‘The GNU C Library Reference Manual’, for version 2.41 (Buildroot). Copyright © 1993-2025 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being "Free Software Needs Free Documentation" and "GNU Lesser General Public License", the Front-Cover texts being "A GNU Manual", and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled "GNU Free Documentation License". (a) The FSF's Back-Cover Text is: "You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom." INFO-DIR-SECTION Software libraries START-INFO-DIR-ENTRY * Libc: (libc). C library. END-INFO-DIR-ENTRY INFO-DIR-SECTION GNU C library functions and macros START-INFO-DIR-ENTRY * ALTWERASE: (libc)Local Modes. * ARGP_ERR_UNKNOWN: (libc)Argp Parser Functions. * ARG_MAX: (libc)General Limits. * BC_BASE_MAX: (libc)Utility Limits. * BC_DIM_MAX: (libc)Utility Limits. * BC_SCALE_MAX: (libc)Utility Limits. * BC_STRING_MAX: (libc)Utility Limits. * BRKINT: (libc)Input Modes. * BUFSIZ: (libc)Controlling Buffering. * CCTS_OFLOW: (libc)Control Modes. * CHAR_BIT: (libc)Width of Type. * CHILD_MAX: (libc)General Limits. * CIGNORE: (libc)Control Modes. * CLK_TCK: (libc)Processor Time. * CLOCAL: (libc)Control Modes. * CLOCKS_PER_SEC: (libc)CPU Time. * CLOCK_MONOTONIC: (libc)Getting the Time. * CLOCK_REALTIME: (libc)Getting the Time. * COLL_WEIGHTS_MAX: (libc)Utility Limits. * CPU_CLR: (libc)CPU Affinity. * CPU_FEATURE_ACTIVE: (libc)X86. * CPU_FEATURE_PRESENT: (libc)X86. * CPU_ISSET: (libc)CPU Affinity. * CPU_SET: (libc)CPU Affinity. * CPU_SETSIZE: (libc)CPU Affinity. * CPU_ZERO: (libc)CPU Affinity. * CREAD: (libc)Control Modes. * CRTS_IFLOW: (libc)Control Modes. * CS5: (libc)Control Modes. * CS6: (libc)Control Modes. * CS7: (libc)Control Modes. * CS8: (libc)Control Modes. * CSIZE: (libc)Control Modes. * CSTOPB: (libc)Control Modes. * DLFO_EH_SEGMENT_TYPE: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_COUNT: (libc)Dynamic Linker Introspection. * DLFO_STRUCT_HAS_EH_DBASE: (libc)Dynamic Linker Introspection. * DTTOIF: (libc)Directory Entries. * E2BIG: (libc)Error Codes. * EACCES: (libc)Error Codes. * EADDRINUSE: (libc)Error Codes. * EADDRNOTAVAIL: (libc)Error Codes. * EADV: (libc)Error Codes. * EAFNOSUPPORT: (libc)Error Codes. * EAGAIN: (libc)Error Codes. * EALREADY: (libc)Error Codes. * EAUTH: (libc)Error Codes. * EBACKGROUND: (libc)Error Codes. * EBADE: (libc)Error Codes. * EBADF: (libc)Error Codes. * EBADFD: (libc)Error Codes. * EBADMSG: (libc)Error Codes. * EBADR: (libc)Error Codes. * EBADRPC: (libc)Error Codes. * EBADRQC: (libc)Error Codes. * EBADSLT: (libc)Error Codes. * EBFONT: (libc)Error Codes. * EBUSY: (libc)Error Codes. * ECANCELED: (libc)Error Codes. * ECHILD: (libc)Error Codes. * ECHO: (libc)Local Modes. * ECHOCTL: (libc)Local Modes. * ECHOE: (libc)Local Modes. * ECHOK: (libc)Local Modes. * ECHOKE: (libc)Local Modes. * ECHONL: (libc)Local Modes. * ECHOPRT: (libc)Local Modes. * ECHRNG: (libc)Error Codes. * ECOMM: (libc)Error Codes. * ECONNABORTED: (libc)Error Codes. * ECONNREFUSED: (libc)Error Codes. * ECONNRESET: (libc)Error Codes. * ED: (libc)Error Codes. * EDEADLK: (libc)Error Codes. * EDEADLOCK: (libc)Error Codes. * EDESTADDRREQ: (libc)Error Codes. * EDIED: (libc)Error Codes. * EDOM: (libc)Error Codes. * EDOTDOT: (libc)Error Codes. * EDQUOT: (libc)Error Codes. * EEXIST: (libc)Error Codes. * EFAULT: (libc)Error Codes. * EFBIG: (libc)Error Codes. * EFTYPE: (libc)Error Codes. * EGRATUITOUS: (libc)Error Codes. * EGREGIOUS: (libc)Error Codes. * EHOSTDOWN: (libc)Error Codes. * EHOSTUNREACH: (libc)Error Codes. * EHWPOISON: (libc)Error Codes. * EIDRM: (libc)Error Codes. * EIEIO: (libc)Error Codes. * EILSEQ: (libc)Error Codes. * EINPROGRESS: (libc)Error Codes. * EINTR: (libc)Error Codes. * EINVAL: (libc)Error Codes. * EIO: (libc)Error Codes. * EISCONN: (libc)Error Codes. * EISDIR: (libc)Error Codes. * EISNAM: (libc)Error Codes. * EKEYEXPIRED: (libc)Error Codes. * EKEYREJECTED: (libc)Error Codes. * EKEYREVOKED: (libc)Error Codes. * EL2HLT: (libc)Error Codes. * EL2NSYNC: (libc)Error Codes. * EL3HLT: (libc)Error Codes. * EL3RST: (libc)Error Codes. * ELIBACC: (libc)Error Codes. * ELIBBAD: (libc)Error Codes. * ELIBEXEC: (libc)Error Codes. * ELIBMAX: (libc)Error Codes. * ELIBSCN: (libc)Error Codes. * ELNRNG: (libc)Error Codes. * ELOOP: (libc)Error Codes. * EMEDIUMTYPE: (libc)Error Codes. * EMFILE: (libc)Error Codes. * EMLINK: (libc)Error Codes. * EMSGSIZE: (libc)Error Codes. * EMULTIHOP: (libc)Error Codes. * ENAMETOOLONG: (libc)Error Codes. * ENAVAIL: (libc)Error Codes. * ENEEDAUTH: (libc)Error Codes. * ENETDOWN: (libc)Error Codes. * ENETRESET: (libc)Error Codes. * ENETUNREACH: (libc)Error Codes. * ENFILE: (libc)Error Codes. * ENOANO: (libc)Error Codes. * ENOBUFS: (libc)Error Codes. * ENOCSI: (libc)Error Codes. * ENODATA: (libc)Error Codes. * ENODEV: (libc)Error Codes. * ENOENT: (libc)Error Codes. * ENOEXEC: (libc)Error Codes. * ENOKEY: (libc)Error Codes. * ENOLCK: (libc)Error Codes. * ENOLINK: (libc)Error Codes. * ENOMEDIUM: (libc)Error Codes. * ENOMEM: (libc)Error Codes. * ENOMSG: (libc)Error Codes. * ENONET: (libc)Error Codes. * ENOPKG: (libc)Error Codes. * ENOPROTOOPT: (libc)Error Codes. * ENOSPC: (libc)Error Codes. * ENOSR: (libc)Error Codes. * ENOSTR: (libc)Error Codes. * ENOSYS: (libc)Error Codes. * ENOTBLK: (libc)Error Codes. * ENOTCONN: (libc)Error Codes. * ENOTDIR: (libc)Error Codes. * ENOTEMPTY: (libc)Error Codes. * ENOTNAM: (libc)Error Codes. * ENOTRECOVERABLE: (libc)Error Codes. * ENOTSOCK: (libc)Error Codes. * ENOTSUP: (libc)Error Codes. * ENOTTY: (libc)Error Codes. * ENOTUNIQ: (libc)Error Codes. * ENXIO: (libc)Error Codes. * EOF: (libc)EOF and Errors. * EOPNOTSUPP: (libc)Error Codes. * EOVERFLOW: (libc)Error Codes. * EOWNERDEAD: (libc)Error Codes. * EPERM: (libc)Error Codes. * EPFNOSUPPORT: (libc)Error Codes. * EPIPE: (libc)Error Codes. * EPROCLIM: (libc)Error Codes. * EPROCUNAVAIL: (libc)Error Codes. * EPROGMISMATCH: (libc)Error Codes. * EPROGUNAVAIL: (libc)Error Codes. * EPROTO: (libc)Error Codes. * EPROTONOSUPPORT: (libc)Error Codes. * EPROTOTYPE: (libc)Error Codes. * EQUIV_CLASS_MAX: (libc)Utility Limits. * ERANGE: (libc)Error Codes. * EREMCHG: (libc)Error Codes. * EREMOTE: (libc)Error Codes. * EREMOTEIO: (libc)Error Codes. * ERESTART: (libc)Error Codes. * ERFKILL: (libc)Error Codes. * EROFS: (libc)Error Codes. * ERPCMISMATCH: (libc)Error Codes. * ESHUTDOWN: (libc)Error Codes. * ESOCKTNOSUPPORT: (libc)Error Codes. * ESPIPE: (libc)Error Codes. * ESRCH: (libc)Error Codes. * ESRMNT: (libc)Error Codes. * ESTALE: (libc)Error Codes. * ESTRPIPE: (libc)Error Codes. * ETIME: (libc)Error Codes. * ETIMEDOUT: (libc)Error Codes. * ETOOMANYREFS: (libc)Error Codes. * ETXTBSY: (libc)Error Codes. * EUCLEAN: (libc)Error Codes. * EUNATCH: (libc)Error Codes. * EUSERS: (libc)Error Codes. * EWOULDBLOCK: (libc)Error Codes. * EXDEV: (libc)Error Codes. * EXFULL: (libc)Error Codes. * EXIT_FAILURE: (libc)Exit Status. * EXIT_SUCCESS: (libc)Exit Status. * EXPR_NEST_MAX: (libc)Utility Limits. * FD_CLOEXEC: (libc)Descriptor Flags. * FD_CLR: (libc)Waiting for I/O. * FD_ISSET: (libc)Waiting for I/O. * FD_SET: (libc)Waiting for I/O. * FD_SETSIZE: (libc)Waiting for I/O. * FD_ZERO: (libc)Waiting for I/O. * FE_SNANS_ALWAYS_SIGNAL: (libc)Infinity and NaN. * FILENAME_MAX: (libc)Limits for Files. * FLUSHO: (libc)Local Modes. * FOPEN_MAX: (libc)Opening Streams. * FP_ILOGB0: (libc)Exponents and Logarithms. * FP_ILOGBNAN: (libc)Exponents and Logarithms. * FP_LLOGB0: (libc)Exponents and Logarithms. * FP_LLOGBNAN: (libc)Exponents and Logarithms. * F_DUPFD: (libc)Duplicating Descriptors. * F_GETFD: (libc)Descriptor Flags. * F_GETFL: (libc)Getting File Status Flags. * F_GETLK: (libc)File Locks. * F_GETOWN: (libc)Interrupt Input. * F_OFD_GETLK: (libc)Open File Description Locks. * F_OFD_SETLK: (libc)Open File Description Locks. * F_OFD_SETLKW: (libc)Open File Description Locks. * F_OK: (libc)Testing File Access. * F_SETFD: (libc)Descriptor Flags. * F_SETFL: (libc)Getting File Status Flags. * F_SETLK: (libc)File Locks. * F_SETLKW: (libc)File Locks. * F_SETOWN: (libc)Interrupt Input. * HUGE_VAL: (libc)Math Error Reporting. * HUGE_VALF: (libc)Math Error Reporting. * HUGE_VALL: (libc)Math Error Reporting. * HUGE_VAL_FN: (libc)Math Error Reporting. * HUGE_VAL_FNx: (libc)Math Error Reporting. * HUPCL: (libc)Control Modes. * I: (libc)Complex Numbers. * ICANON: (libc)Local Modes. * ICRNL: (libc)Input Modes. * IEXTEN: (libc)Local Modes. * IFNAMSIZ: (libc)Interface Naming. * IFTODT: (libc)Directory Entries. * IGNBRK: (libc)Input Modes. * IGNCR: (libc)Input Modes. * IGNPAR: (libc)Input Modes. * IMAXBEL: (libc)Input Modes. * INADDR_ANY: (libc)Host Address Data Type. * INADDR_BROADCAST: (libc)Host Address Data Type. * INADDR_LOOPBACK: (libc)Host Address Data Type. * INADDR_NONE: (libc)Host Address Data Type. * INFINITY: (libc)Infinity and NaN. * INLCR: (libc)Input Modes. * INPCK: (libc)Input Modes. * IPPORT_RESERVED: (libc)Ports. * IPPORT_USERRESERVED: (libc)Ports. * ISIG: (libc)Local Modes. * ISTRIP: (libc)Input Modes. * IXANY: (libc)Input Modes. * IXOFF: (libc)Input Modes. * IXON: (libc)Input Modes. * LINE_MAX: (libc)Utility Limits. * LINK_MAX: (libc)Limits for Files. * L_ctermid: (libc)Identifying the Terminal. * L_cuserid: (libc)Who Logged In. * L_tmpnam: (libc)Temporary Files. * MAXNAMLEN: (libc)Limits for Files. * MAXSYMLINKS: (libc)Symbolic Links. * MAX_CANON: (libc)Limits for Files. * MAX_INPUT: (libc)Limits for Files. * MB_CUR_MAX: (libc)Selecting the Conversion. * MB_LEN_MAX: (libc)Selecting the Conversion. * MDMBUF: (libc)Control Modes. * MSG_DONTROUTE: (libc)Socket Data Options. * MSG_OOB: (libc)Socket Data Options. * MSG_PEEK: (libc)Socket Data Options. * NAME_MAX: (libc)Limits for Files. * NAN: (libc)Infinity and NaN. * NCCS: (libc)Mode Data Types. * NGROUPS_MAX: (libc)General Limits. * NOFLSH: (libc)Local Modes. * NOKERNINFO: (libc)Local Modes. * NSIG: (libc)Standard Signals. * NULL: (libc)Null Pointer Constant. * ONLCR: (libc)Output Modes. * ONOEOT: (libc)Output Modes. * OPEN_MAX: (libc)General Limits. * OPOST: (libc)Output Modes. * OXTABS: (libc)Output Modes. * O_ACCMODE: (libc)Access Modes. * O_APPEND: (libc)Operating Modes. * O_ASYNC: (libc)Operating Modes. * O_CREAT: (libc)Open-time Flags. * O_DIRECTORY: (libc)Open-time Flags. * O_EXCL: (libc)Open-time Flags. * O_EXEC: (libc)Access Modes. * O_EXLOCK: (libc)Open-time Flags. * O_FSYNC: (libc)Operating Modes. * O_IGNORE_CTTY: (libc)Open-time Flags. * O_NDELAY: (libc)Operating Modes. * O_NOATIME: (libc)Operating Modes. * O_NOCTTY: (libc)Open-time Flags. * O_NOFOLLOW: (libc)Open-time Flags. * O_NOLINK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Open-time Flags. * O_NONBLOCK: (libc)Operating Modes. * O_NOTRANS: (libc)Open-time Flags. * O_PATH: (libc)Access Modes. * O_RDONLY: (libc)Access Modes. * O_RDWR: (libc)Access Modes. * O_READ: (libc)Access Modes. * O_SHLOCK: (libc)Open-time Flags. * O_SYNC: (libc)Operating Modes. * O_TMPFILE: (libc)Open-time Flags. * O_TRUNC: (libc)Open-time Flags. * O_WRITE: (libc)Access Modes. * O_WRONLY: (libc)Access Modes. * PARENB: (libc)Control Modes. * PARMRK: (libc)Input Modes. * PARODD: (libc)Control Modes. * PATH_MAX: (libc)Limits for Files. * PA_FLAG_MASK: (libc)Parsing a Template String. * PENDIN: (libc)Local Modes. * PF_FILE: (libc)Local Namespace Details. * PF_INET6: (libc)Internet Namespace. * PF_INET: (libc)Internet Namespace. * PF_LOCAL: (libc)Local Namespace Details. * PF_UNIX: (libc)Local Namespace Details. * PIPE_BUF: (libc)Limits for Files. * PTHREAD_ATTR_NO_SIGMASK_NP: (libc)Initial Thread Signal Mask. * P_tmpdir: (libc)Temporary Files. * RAND_MAX: (libc)ISO Random. * RE_DUP_MAX: (libc)General Limits. * RLIM_INFINITY: (libc)Limits on Resources. * RSEQ_SIG: (libc)Restartable Sequences. * R_OK: (libc)Testing File Access. * SA_NOCLDSTOP: (libc)Flags for Sigaction. * SA_NOCLDWAIT: (libc)Flags for Sigaction. * SA_NODEFER: (libc)Flags for Sigaction. * SA_ONSTACK: (libc)Flags for Sigaction. * SA_RESETHAND: (libc)Flags for Sigaction. * SA_RESTART: (libc)Flags for Sigaction. * SA_SIGINFO: (libc)Flags for Sigaction. * SEEK_CUR: (libc)File Positioning. * SEEK_END: (libc)File Positioning. * SEEK_SET: (libc)File Positioning. * SIGABRT: (libc)Program Error Signals. * SIGALRM: (libc)Alarm Signals. * SIGBUS: (libc)Program Error Signals. * SIGCHLD: (libc)Job Control Signals. * SIGCLD: (libc)Job Control Signals. * SIGCONT: (libc)Job Control Signals. * SIGEMT: (libc)Program Error Signals. * SIGFPE: (libc)Program Error Signals. * SIGHUP: (libc)Termination Signals. * SIGILL: (libc)Program Error Signals. * SIGINFO: (libc)Miscellaneous Signals. * SIGINT: (libc)Termination Signals. * SIGIO: (libc)Asynchronous I/O Signals. * SIGIOT: (libc)Program Error Signals. * SIGKILL: (libc)Termination Signals. * SIGLOST: (libc)Operation Error Signals. * SIGPIPE: (libc)Operation Error Signals. * SIGPOLL: (libc)Asynchronous I/O Signals. * SIGPROF: (libc)Alarm Signals. * SIGQUIT: (libc)Termination Signals. * SIGSEGV: (libc)Program Error Signals. * SIGSTOP: (libc)Job Control Signals. * SIGSYS: (libc)Program Error Signals. * SIGTERM: (libc)Termination Signals. * SIGTRAP: (libc)Program Error Signals. * SIGTSTP: (libc)Job Control Signals. * SIGTTIN: (libc)Job Control Signals. * SIGTTOU: (libc)Job Control Signals. * SIGURG: (libc)Asynchronous I/O Signals. * SIGUSR1: (libc)Miscellaneous Signals. * SIGUSR2: (libc)Miscellaneous Signals. * SIGVTALRM: (libc)Alarm Signals. * SIGWINCH: (libc)Miscellaneous Signals. * SIGXCPU: (libc)Operation Error Signals. * SIGXFSZ: (libc)Operation Error Signals. * SIG_ERR: (libc)Basic Signal Handling. * SNAN: (libc)Infinity and NaN. * SNANF: (libc)Infinity and NaN. * SNANFN: (libc)Infinity and NaN. * SNANFNx: (libc)Infinity and NaN. * SNANL: (libc)Infinity and NaN. * SOCK_DGRAM: (libc)Communication Styles. * SOCK_RAW: (libc)Communication Styles. * SOCK_RDM: (libc)Communication Styles. * SOCK_SEQPACKET: (libc)Communication Styles. * SOCK_STREAM: (libc)Communication Styles. * SOL_SOCKET: (libc)Socket-Level Options. * SSIZE_MAX: (libc)General Limits. * STREAM_MAX: (libc)General Limits. * SUN_LEN: (libc)Local Namespace Details. * S_IFMT: (libc)Testing File Type. * S_ISBLK: (libc)Testing File Type. * S_ISCHR: (libc)Testing File Type. * S_ISDIR: (libc)Testing File Type. * S_ISFIFO: (libc)Testing File Type. * S_ISLNK: (libc)Testing File Type. * S_ISREG: (libc)Testing File Type. * S_ISSOCK: (libc)Testing File Type. * S_TYPEISMQ: (libc)Testing File Type. * S_TYPEISSEM: (libc)Testing File Type. * S_TYPEISSHM: (libc)Testing File Type. * TIME_UTC: (libc)Getting the Time. * TMP_MAX: (libc)Temporary Files. * TOSTOP: (libc)Local Modes. * TZNAME_MAX: (libc)General Limits. * VDISCARD: (libc)Other Special. * VDSUSP: (libc)Signal Characters. * VEOF: (libc)Editing Characters. * VEOL2: (libc)Editing Characters. * VEOL: (libc)Editing Characters. * VERASE: (libc)Editing Characters. * VINTR: (libc)Signal Characters. * VKILL: (libc)Editing Characters. * VLNEXT: (libc)Other Special. * VMIN: (libc)Noncanonical Input. * VQUIT: (libc)Signal Characters. * VREPRINT: (libc)Editing Characters. * VSTART: (libc)Start/Stop Characters. * VSTATUS: (libc)Other Special. * VSTOP: (libc)Start/Stop Characters. * VSUSP: (libc)Signal Characters. * VTIME: (libc)Noncanonical Input. * VWERASE: (libc)Editing Characters. * WCHAR_MAX: (libc)Extended Char Intro. * WCHAR_MIN: (libc)Extended Char Intro. * WCOREDUMP: (libc)Process Completion Status. * WEOF: (libc)EOF and Errors. * WEOF: (libc)Extended Char Intro. * WEXITSTATUS: (libc)Process Completion Status. * WIFEXITED: (libc)Process Completion Status. * WIFSIGNALED: (libc)Process Completion Status. * WIFSTOPPED: (libc)Process Completion Status. * WSTOPSIG: (libc)Process Completion Status. * WTERMSIG: (libc)Process Completion Status. * W_OK: (libc)Testing File Access. * X_OK: (libc)Testing File Access. * _Complex_I: (libc)Complex Numbers. * _Exit: (libc)Termination Internals. * _Fork: (libc)Creating a Process. * _IOFBF: (libc)Controlling Buffering. * _IOLBF: (libc)Controlling Buffering. * _IONBF: (libc)Controlling Buffering. * _Imaginary_I: (libc)Complex Numbers. * _PATH_UTMP: (libc)Manipulating the Database. * _PATH_WTMP: (libc)Manipulating the Database. * _POSIX2_C_DEV: (libc)System Options. * _POSIX2_C_VERSION: (libc)Version Supported. * _POSIX2_FORT_DEV: (libc)System Options. * _POSIX2_FORT_RUN: (libc)System Options. * _POSIX2_LOCALEDEF: (libc)System Options. * _POSIX2_SW_DEV: (libc)System Options. * _POSIX_CHOWN_RESTRICTED: (libc)Options for Files. * _POSIX_JOB_CONTROL: (libc)System Options. * _POSIX_NO_TRUNC: (libc)Options for Files. * _POSIX_SAVED_IDS: (libc)System Options. * _POSIX_VDISABLE: (libc)Options for Files. * _POSIX_VERSION: (libc)Version Supported. * __fbufsize: (libc)Controlling Buffering. * __flbf: (libc)Controlling Buffering. * __fpending: (libc)Controlling Buffering. * __fpurge: (libc)Flushing Buffers. * __freadable: (libc)Opening Streams. * __freading: (libc)Opening Streams. * __fsetlocking: (libc)Streams and Threads. * __fwritable: (libc)Opening Streams. * __fwriting: (libc)Opening Streams. * __gconv_end_fct: (libc)glibc iconv Implementation. * __gconv_fct: (libc)glibc iconv Implementation. * __gconv_init_fct: (libc)glibc iconv Implementation. * __ppc_get_timebase: (libc)PowerPC. * __ppc_get_timebase_freq: (libc)PowerPC. * __ppc_mdoio: (libc)PowerPC. * __ppc_mdoom: (libc)PowerPC. * __ppc_set_ppr_low: (libc)PowerPC. * __ppc_set_ppr_med: (libc)PowerPC. * __ppc_set_ppr_med_high: (libc)PowerPC. * __ppc_set_ppr_med_low: (libc)PowerPC. * __ppc_set_ppr_very_low: (libc)PowerPC. * __ppc_yield: (libc)PowerPC. * __riscv_flush_icache: (libc)RISC-V. * __va_copy: (libc)Argument Macros. * __x86_get_cpuid_feature_leaf: (libc)X86. * _dl_find_object: (libc)Dynamic Linker Introspection. * _exit: (libc)Termination Internals. * _flushlbf: (libc)Flushing Buffers. * _tolower: (libc)Case Conversion. * _toupper: (libc)Case Conversion. * a64l: (libc)Encode Binary Data. * abort: (libc)Aborting a Program. * abs: (libc)Absolute Value. * accept: (libc)Accepting Connections. * access: (libc)Testing File Access. * acos: (libc)Inverse Trig Functions. * acosf: (libc)Inverse Trig Functions. * acosfN: (libc)Inverse Trig Functions. * acosfNx: (libc)Inverse Trig Functions. * acosh: (libc)Hyperbolic Functions. * acoshf: (libc)Hyperbolic Functions. * acoshfN: (libc)Hyperbolic Functions. * acoshfNx: (libc)Hyperbolic Functions. * acoshl: (libc)Hyperbolic Functions. * acosl: (libc)Inverse Trig Functions. * acospi: (libc)Inverse Trig Functions. * acospif: (libc)Inverse Trig Functions. * acospifN: (libc)Inverse Trig Functions. * acospifNx: (libc)Inverse Trig Functions. * acospil: (libc)Inverse Trig Functions. * addmntent: (libc)mtab. * addseverity: (libc)Adding Severity Classes. * adjtime: (libc)Setting and Adjusting the Time. * adjtimex: (libc)Setting and Adjusting the Time. * aio_cancel64: (libc)Cancel AIO Operations. * aio_cancel: (libc)Cancel AIO Operations. * aio_error64: (libc)Status of AIO Operations. * aio_error: (libc)Status of AIO Operations. * aio_fsync64: (libc)Synchronizing AIO Operations. * aio_fsync: (libc)Synchronizing AIO Operations. * aio_init: (libc)Configuration of AIO. * aio_read64: (libc)Asynchronous Reads/Writes. * aio_read: (libc)Asynchronous Reads/Writes. * aio_return64: (libc)Status of AIO Operations. * aio_return: (libc)Status of AIO Operations. * aio_suspend64: (libc)Synchronizing AIO Operations. * aio_suspend: (libc)Synchronizing AIO Operations. * aio_write64: (libc)Asynchronous Reads/Writes. * aio_write: (libc)Asynchronous Reads/Writes. * alarm: (libc)Setting an Alarm. * aligned_alloc: (libc)Aligned Memory Blocks. * alloca: (libc)Variable Size Automatic. * alphasort64: (libc)Scanning Directory Content. * alphasort: (libc)Scanning Directory Content. * arc4random: (libc)High Quality Random. * arc4random_buf: (libc)High Quality Random. * arc4random_uniform: (libc)High Quality Random. * argp_error: (libc)Argp Helper Functions. * argp_failure: (libc)Argp Helper Functions. * argp_help: (libc)Argp Help. * argp_parse: (libc)Argp. * argp_state_help: (libc)Argp Helper Functions. * argp_usage: (libc)Argp Helper Functions. * argz_add: (libc)Argz Functions. * argz_add_sep: (libc)Argz Functions. * argz_append: (libc)Argz Functions. * argz_count: (libc)Argz Functions. * argz_create: (libc)Argz Functions. * argz_create_sep: (libc)Argz Functions. * argz_delete: (libc)Argz Functions. * argz_extract: (libc)Argz Functions. * argz_insert: (libc)Argz Functions. * argz_next: (libc)Argz Functions. * argz_replace: (libc)Argz Functions. * argz_stringify: (libc)Argz Functions. * asctime: (libc)Formatting Calendar Time. * asctime_r: (libc)Formatting Calendar Time. * asin: (libc)Inverse Trig Functions. * asinf: (libc)Inverse Trig Functions. * asinfN: (libc)Inverse Trig Functions. * asinfNx: (libc)Inverse Trig Functions. * asinh: (libc)Hyperbolic Functions. * asinhf: (libc)Hyperbolic Functions. * asinhfN: (libc)Hyperbolic Functions. * asinhfNx: (libc)Hyperbolic Functions. * asinhl: (libc)Hyperbolic Functions. * asinl: (libc)Inverse Trig Functions. * asinpi: (libc)Inverse Trig Functions. * asinpif: (libc)Inverse Trig Functions. * asinpifN: (libc)Inverse Trig Functions. * asinpifNx: (libc)Inverse Trig Functions. * asinpil: (libc)Inverse Trig Functions. * asprintf: (libc)Dynamic Output. * assert: (libc)Consistency Checking. * assert_perror: (libc)Consistency Checking. * atan2: (libc)Inverse Trig Functions. * atan2f: (libc)Inverse Trig Functions. * atan2fN: (libc)Inverse Trig Functions. * atan2fNx: (libc)Inverse Trig Functions. * atan2l: (libc)Inverse Trig Functions. * atan2pi: (libc)Inverse Trig Functions. * atan2pif: (libc)Inverse Trig Functions. * atan2pifN: (libc)Inverse Trig Functions. * atan2pifNx: (libc)Inverse Trig Functions. * atan2pil: (libc)Inverse Trig Functions. * atan: (libc)Inverse Trig Functions. * atanf: (libc)Inverse Trig Functions. * atanfN: (libc)Inverse Trig Functions. * atanfNx: (libc)Inverse Trig Functions. * atanh: (libc)Hyperbolic Functions. * atanhf: (libc)Hyperbolic Functions. * atanhfN: (libc)Hyperbolic Functions. * atanhfNx: (libc)Hyperbolic Functions. * atanhl: (libc)Hyperbolic Functions. * atanl: (libc)Inverse Trig Functions. * atanpi: (libc)Inverse Trig Functions. * atanpif: (libc)Inverse Trig Functions. * atanpifN: (libc)Inverse Trig Functions. * atanpifNx: (libc)Inverse Trig Functions. * atanpil: (libc)Inverse Trig Functions. * atexit: (libc)Cleanups on Exit. * atof: (libc)Parsing of Floats. * atoi: (libc)Parsing of Integers. * atol: (libc)Parsing of Integers. * atoll: (libc)Parsing of Integers. * backtrace: (libc)Backtraces. * backtrace_symbols: (libc)Backtraces. * backtrace_symbols_fd: (libc)Backtraces. * basename: (libc)Finding Tokens in a String. * basename: (libc)Finding Tokens in a String. * bcmp: (libc)String/Array Comparison. * bcopy: (libc)Copying Strings and Arrays. * bind: (libc)Setting Address. * bind_textdomain_codeset: (libc)Charset conversion in gettext. * bindtextdomain: (libc)Locating gettext catalog. * brk: (libc)Resizing the Data Segment. * bsearch: (libc)Array Search Function. * btowc: (libc)Converting a Character. * bzero: (libc)Copying Strings and Arrays. * cabs: (libc)Absolute Value. * cabsf: (libc)Absolute Value. * cabsfN: (libc)Absolute Value. * cabsfNx: (libc)Absolute Value. * cabsl: (libc)Absolute Value. * cacos: (libc)Inverse Trig Functions. * cacosf: (libc)Inverse Trig Functions. * cacosfN: (libc)Inverse Trig Functions. * cacosfNx: (libc)Inverse Trig Functions. * cacosh: (libc)Hyperbolic Functions. * cacoshf: (libc)Hyperbolic Functions. * cacoshfN: (libc)Hyperbolic Functions. * cacoshfNx: (libc)Hyperbolic Functions. * cacoshl: (libc)Hyperbolic Functions. * cacosl: (libc)Inverse Trig Functions. * call_once: (libc)Call Once. * calloc: (libc)Allocating Cleared Space. * canonicalize: (libc)FP Bit Twiddling. * canonicalize_file_name: (libc)Symbolic Links. * canonicalizef: (libc)FP Bit Twiddling. * canonicalizefN: (libc)FP Bit Twiddling. * canonicalizefNx: (libc)FP Bit Twiddling. * canonicalizel: (libc)FP Bit Twiddling. * carg: (libc)Operations on Complex. * cargf: (libc)Operations on Complex. * cargfN: (libc)Operations on Complex. * cargfNx: (libc)Operations on Complex. * cargl: (libc)Operations on Complex. * casin: (libc)Inverse Trig Functions. * casinf: (libc)Inverse Trig Functions. * casinfN: (libc)Inverse Trig Functions. * casinfNx: (libc)Inverse Trig Functions. * casinh: (libc)Hyperbolic Functions. * casinhf: (libc)Hyperbolic Functions. * casinhfN: (libc)Hyperbolic Functions. * casinhfNx: (libc)Hyperbolic Functions. * casinhl: (libc)Hyperbolic Functions. * casinl: (libc)Inverse Trig Functions. * catan: (libc)Inverse Trig Functions. * catanf: (libc)Inverse Trig Functions. * catanfN: (libc)Inverse Trig Functions. * catanfNx: (libc)Inverse Trig Functions. * catanh: (libc)Hyperbolic Functions. * catanhf: (libc)Hyperbolic Functions. * catanhfN: (libc)Hyperbolic Functions. * catanhfNx: (libc)Hyperbolic Functions. * catanhl: (libc)Hyperbolic Functions. * catanl: (libc)Inverse Trig Functions. * catclose: (libc)The catgets Functions. * catgets: (libc)The catgets Functions. * catopen: (libc)The catgets Functions. * cbrt: (libc)Exponents and Logarithms. * cbrtf: (libc)Exponents and Logarithms. * cbrtfN: (libc)Exponents and Logarithms. * cbrtfNx: (libc)Exponents and Logarithms. * cbrtl: (libc)Exponents and Logarithms. * ccos: (libc)Trig Functions. * ccosf: (libc)Trig Functions. * ccosfN: (libc)Trig Functions. * ccosfNx: (libc)Trig Functions. * ccosh: (libc)Hyperbolic Functions. * ccoshf: (libc)Hyperbolic Functions. * ccoshfN: (libc)Hyperbolic Functions. * ccoshfNx: (libc)Hyperbolic Functions. * ccoshl: (libc)Hyperbolic Functions. * ccosl: (libc)Trig Functions. * ceil: (libc)Rounding Functions. * ceilf: (libc)Rounding Functions. * ceilfN: (libc)Rounding Functions. * ceilfNx: (libc)Rounding Functions. * ceill: (libc)Rounding Functions. * cexp: (libc)Exponents and Logarithms. * cexpf: (libc)Exponents and Logarithms. * cexpfN: (libc)Exponents and Logarithms. * cexpfNx: (libc)Exponents and Logarithms. * cexpl: (libc)Exponents and Logarithms. * cfgetispeed: (libc)Line Speed. * cfgetospeed: (libc)Line Speed. * cfmakeraw: (libc)Noncanonical Input. * cfsetispeed: (libc)Line Speed. * cfsetospeed: (libc)Line Speed. * cfsetspeed: (libc)Line Speed. * chdir: (libc)Working Directory. * chmod: (libc)Setting Permissions. * chown: (libc)File Owner. * cimag: (libc)Operations on Complex. * cimagf: (libc)Operations on Complex. * cimagfN: (libc)Operations on Complex. * cimagfNx: (libc)Operations on Complex. * cimagl: (libc)Operations on Complex. * clearenv: (libc)Environment Access. * clearerr: (libc)Error Recovery. * clearerr_unlocked: (libc)Error Recovery. * clock: (libc)CPU Time. * clock_getres: (libc)Getting the Time. * clock_gettime: (libc)Getting the Time. * clock_settime: (libc)Setting and Adjusting the Time. * clog10: (libc)Exponents and Logarithms. * clog10f: (libc)Exponents and Logarithms. * clog10fN: (libc)Exponents and Logarithms. * clog10fNx: (libc)Exponents and Logarithms. * clog10l: (libc)Exponents and Logarithms. * clog: (libc)Exponents and Logarithms. * clogf: (libc)Exponents and Logarithms. * clogfN: (libc)Exponents and Logarithms. * clogfNx: (libc)Exponents and Logarithms. * clogl: (libc)Exponents and Logarithms. * close: (libc)Opening and Closing Files. * close_range: (libc)Opening and Closing Files. * closedir: (libc)Reading/Closing Directory. * closefrom: (libc)Opening and Closing Files. * closelog: (libc)closelog. * cnd_broadcast: (libc)ISO C Condition Variables. * cnd_destroy: (libc)ISO C Condition Variables. * cnd_init: (libc)ISO C Condition Variables. * cnd_signal: (libc)ISO C Condition Variables. * cnd_timedwait: (libc)ISO C Condition Variables. * cnd_wait: (libc)ISO C Condition Variables. * confstr: (libc)String Parameters. * conj: (libc)Operations on Complex. * conjf: (libc)Operations on Complex. * conjfN: (libc)Operations on Complex. * conjfNx: (libc)Operations on Complex. * conjl: (libc)Operations on Complex. * connect: (libc)Connecting. * copy_file_range: (libc)Copying File Data. * copysign: (libc)FP Bit Twiddling. * copysignf: (libc)FP Bit Twiddling. * copysignfN: (libc)FP Bit Twiddling. * copysignfNx: (libc)FP Bit Twiddling. * copysignl: (libc)FP Bit Twiddling. * cos: (libc)Trig Functions. * cosf: (libc)Trig Functions. * cosfN: (libc)Trig Functions. * cosfNx: (libc)Trig Functions. * cosh: (libc)Hyperbolic Functions. * coshf: (libc)Hyperbolic Functions. * coshfN: (libc)Hyperbolic Functions. * coshfNx: (libc)Hyperbolic Functions. * coshl: (libc)Hyperbolic Functions. * cosl: (libc)Trig Functions. * cospi: (libc)Trig Functions. * cospif: (libc)Trig Functions. * cospifN: (libc)Trig Functions. * cospifNx: (libc)Trig Functions. * cospil: (libc)Trig Functions. * cpow: (libc)Exponents and Logarithms. * cpowf: (libc)Exponents and Logarithms. * cpowfN: (libc)Exponents and Logarithms. * cpowfNx: (libc)Exponents and Logarithms. * cpowl: (libc)Exponents and Logarithms. * cproj: (libc)Operations on Complex. * cprojf: (libc)Operations on Complex. * cprojfN: (libc)Operations on Complex. * cprojfNx: (libc)Operations on Complex. * cprojl: (libc)Operations on Complex. * creal: (libc)Operations on Complex. * crealf: (libc)Operations on Complex. * crealfN: (libc)Operations on Complex. * crealfNx: (libc)Operations on Complex. * creall: (libc)Operations on Complex. * creat64: (libc)Opening and Closing Files. * creat: (libc)Opening and Closing Files. * csin: (libc)Trig Functions. * csinf: (libc)Trig Functions. * csinfN: (libc)Trig Functions. * csinfNx: (libc)Trig Functions. * csinh: (libc)Hyperbolic Functions. * csinhf: (libc)Hyperbolic Functions. * csinhfN: (libc)Hyperbolic Functions. * csinhfNx: (libc)Hyperbolic Functions. * csinhl: (libc)Hyperbolic Functions. * csinl: (libc)Trig Functions. * csqrt: (libc)Exponents and Logarithms. * csqrtf: (libc)Exponents and Logarithms. * csqrtfN: (libc)Exponents and Logarithms. * csqrtfNx: (libc)Exponents and Logarithms. * csqrtl: (libc)Exponents and Logarithms. * ctan: (libc)Trig Functions. * ctanf: (libc)Trig Functions. * ctanfN: (libc)Trig Functions. * ctanfNx: (libc)Trig Functions. * ctanh: (libc)Hyperbolic Functions. * ctanhf: (libc)Hyperbolic Functions. * ctanhfN: (libc)Hyperbolic Functions. * ctanhfNx: (libc)Hyperbolic Functions. * ctanhl: (libc)Hyperbolic Functions. * ctanl: (libc)Trig Functions. * ctermid: (libc)Identifying the Terminal. * ctime: (libc)Formatting Calendar Time. * ctime_r: (libc)Formatting Calendar Time. * cuserid: (libc)Who Logged In. * daddl: (libc)Misc FP Arithmetic. * dcgettext: (libc)Translation with gettext. * dcngettext: (libc)Advanced gettext functions. * ddivl: (libc)Misc FP Arithmetic. * dfmal: (libc)Misc FP Arithmetic. * dgettext: (libc)Translation with gettext. * difftime: (libc)Calculating Elapsed Time. * dirfd: (libc)Opening a Directory. * dirname: (libc)Finding Tokens in a String. * div: (libc)Integer Division. * dlinfo: (libc)Dynamic Linker Introspection. * dmull: (libc)Misc FP Arithmetic. * dngettext: (libc)Advanced gettext functions. * dprintf: (libc)Formatted Output Functions. * drand48: (libc)SVID Random. * drand48_r: (libc)SVID Random. * drem: (libc)Remainder Functions. * dremf: (libc)Remainder Functions. * dreml: (libc)Remainder Functions. * dsqrtl: (libc)Misc FP Arithmetic. * dsubl: (libc)Misc FP Arithmetic. * dup2: (libc)Duplicating Descriptors. * dup3: (libc)Duplicating Descriptors. * dup: (libc)Duplicating Descriptors. * ecvt: (libc)System V Number Conversion. * ecvt_r: (libc)System V Number Conversion. * endfsent: (libc)fstab. * endgrent: (libc)Scanning All Groups. * endhostent: (libc)Host Names. * endmntent: (libc)mtab. * endnetent: (libc)Networks Database. * endnetgrent: (libc)Lookup Netgroup. * endprotoent: (libc)Protocols Database. * endpwent: (libc)Scanning All Users. * endservent: (libc)Services Database. * endutent: (libc)Manipulating the Database. * endutxent: (libc)XPG Functions. * envz_add: (libc)Envz Functions. * envz_entry: (libc)Envz Functions. * envz_get: (libc)Envz Functions. * envz_merge: (libc)Envz Functions. * envz_remove: (libc)Envz Functions. * envz_strip: (libc)Envz Functions. * epoll_create: (libc)Other Low-Level I/O APIs. * epoll_wait: (libc)Other Low-Level I/O APIs. * erand48: (libc)SVID Random. * erand48_r: (libc)SVID Random. * erf: (libc)Special Functions. * erfc: (libc)Special Functions. * erfcf: (libc)Special Functions. * erfcfN: (libc)Special Functions. * erfcfNx: (libc)Special Functions. * erfcl: (libc)Special Functions. * erff: (libc)Special Functions. * erffN: (libc)Special Functions. * erffNx: (libc)Special Functions. * erfl: (libc)Special Functions. * err: (libc)Error Messages. * errno: (libc)Checking for Errors. * error: (libc)Error Messages. * error_at_line: (libc)Error Messages. * errx: (libc)Error Messages. * execl: (libc)Executing a File. * execle: (libc)Executing a File. * execlp: (libc)Executing a File. * execv: (libc)Executing a File. * execve: (libc)Executing a File. * execvp: (libc)Executing a File. * exit: (libc)Normal Termination. * exp10: (libc)Exponents and Logarithms. * exp10f: (libc)Exponents and Logarithms. * exp10fN: (libc)Exponents and Logarithms. * exp10fNx: (libc)Exponents and Logarithms. * exp10l: (libc)Exponents and Logarithms. * exp10m1: (libc)Exponents and Logarithms. * exp10m1f: (libc)Exponents and Logarithms. * exp10m1fN: (libc)Exponents and Logarithms. * exp10m1fNx: (libc)Exponents and Logarithms. * exp10m1l: (libc)Exponents and Logarithms. * exp2: (libc)Exponents and Logarithms. * exp2f: (libc)Exponents and Logarithms. * exp2fN: (libc)Exponents and Logarithms. * exp2fNx: (libc)Exponents and Logarithms. * exp2l: (libc)Exponents and Logarithms. * exp2m1: (libc)Exponents and Logarithms. * exp2m1f: (libc)Exponents and Logarithms. * exp2m1fN: (libc)Exponents and Logarithms. * exp2m1fNx: (libc)Exponents and Logarithms. * exp2m1l: (libc)Exponents and Logarithms. * exp: (libc)Exponents and Logarithms. * expf: (libc)Exponents and Logarithms. * expfN: (libc)Exponents and Logarithms. * expfNx: (libc)Exponents and Logarithms. * expl: (libc)Exponents and Logarithms. * explicit_bzero: (libc)Erasing Sensitive Data. * expm1: (libc)Exponents and Logarithms. * expm1f: (libc)Exponents and Logarithms. * expm1fN: (libc)Exponents and Logarithms. * expm1fNx: (libc)Exponents and Logarithms. * expm1l: (libc)Exponents and Logarithms. * fMaddfN: (libc)Misc FP Arithmetic. * fMaddfNx: (libc)Misc FP Arithmetic. * fMdivfN: (libc)Misc FP Arithmetic. * fMdivfNx: (libc)Misc FP Arithmetic. * fMfmafN: (libc)Misc FP Arithmetic. * fMfmafNx: (libc)Misc FP Arithmetic. * fMmulfN: (libc)Misc FP Arithmetic. * fMmulfNx: (libc)Misc FP Arithmetic. * fMsqrtfN: (libc)Misc FP Arithmetic. * fMsqrtfNx: (libc)Misc FP Arithmetic. * fMsubfN: (libc)Misc FP Arithmetic. * fMsubfNx: (libc)Misc FP Arithmetic. * fMxaddfN: (libc)Misc FP Arithmetic. * fMxaddfNx: (libc)Misc FP Arithmetic. * fMxdivfN: (libc)Misc FP Arithmetic. * fMxdivfNx: (libc)Misc FP Arithmetic. * fMxfmafN: (libc)Misc FP Arithmetic. * fMxfmafNx: (libc)Misc FP Arithmetic. * fMxmulfN: (libc)Misc FP Arithmetic. * fMxmulfNx: (libc)Misc FP Arithmetic. * fMxsqrtfN: (libc)Misc FP Arithmetic. * fMxsqrtfNx: (libc)Misc FP Arithmetic. * fMxsubfN: (libc)Misc FP Arithmetic. * fMxsubfNx: (libc)Misc FP Arithmetic. * fabs: (libc)Absolute Value. * fabsf: (libc)Absolute Value. * fabsfN: (libc)Absolute Value. * fabsfNx: (libc)Absolute Value. * fabsl: (libc)Absolute Value. * fadd: (libc)Misc FP Arithmetic. * faddl: (libc)Misc FP Arithmetic. * fchdir: (libc)Working Directory. * fchmod: (libc)Setting Permissions. * fchown: (libc)File Owner. * fclose: (libc)Closing Streams. * fcloseall: (libc)Closing Streams. * fcntl: (libc)Control Operations. * fcvt: (libc)System V Number Conversion. * fcvt_r: (libc)System V Number Conversion. * fdatasync: (libc)Synchronizing I/O. * fdim: (libc)Misc FP Arithmetic. * fdimf: (libc)Misc FP Arithmetic. * fdimfN: (libc)Misc FP Arithmetic. * fdimfNx: (libc)Misc FP Arithmetic. * fdiml: (libc)Misc FP Arithmetic. * fdiv: (libc)Misc FP Arithmetic. * fdivl: (libc)Misc FP Arithmetic. * fdopen: (libc)Descriptors and Streams. * fdopendir: (libc)Opening a Directory. * feclearexcept: (libc)Status bit operations. * fedisableexcept: (libc)Control Functions. * feenableexcept: (libc)Control Functions. * fegetenv: (libc)Control Functions. * fegetexcept: (libc)Control Functions. * fegetexceptflag: (libc)Status bit operations. * fegetmode: (libc)Control Functions. * fegetround: (libc)Rounding. * feholdexcept: (libc)Control Functions. * feof: (libc)EOF and Errors. * feof_unlocked: (libc)EOF and Errors. * feraiseexcept: (libc)Status bit operations. * ferror: (libc)EOF and Errors. * ferror_unlocked: (libc)EOF and Errors. * fesetenv: (libc)Control Functions. * fesetexcept: (libc)Status bit operations. * fesetexceptflag: (libc)Status bit operations. * fesetmode: (libc)Control Functions. * fesetround: (libc)Rounding. * fetestexcept: (libc)Status bit operations. * fetestexceptflag: (libc)Status bit operations. * feupdateenv: (libc)Control Functions. * fexecve: (libc)Executing a File. * fflush: (libc)Flushing Buffers. * fflush_unlocked: (libc)Flushing Buffers. * ffma: (libc)Misc FP Arithmetic. * ffmal: (libc)Misc FP Arithmetic. * fgetc: (libc)Character Input. * fgetc_unlocked: (libc)Character Input. * fgetgrent: (libc)Scanning All Groups. * fgetgrent_r: (libc)Scanning All Groups. * fgetpos64: (libc)Portable Positioning. * fgetpos: (libc)Portable Positioning. * fgetpwent: (libc)Scanning All Users. * fgetpwent_r: (libc)Scanning All Users. * fgets: (libc)Line Input. * fgets_unlocked: (libc)Line Input. * fgetwc: (libc)Character Input. * fgetwc_unlocked: (libc)Character Input. * fgetws: (libc)Line Input. * fgetws_unlocked: (libc)Line Input. * fileno: (libc)Descriptors and Streams. * fileno_unlocked: (libc)Descriptors and Streams. * finite: (libc)Floating Point Classes. * finitef: (libc)Floating Point Classes. * finitel: (libc)Floating Point Classes. * flockfile: (libc)Streams and Threads. * floor: (libc)Rounding Functions. * floorf: (libc)Rounding Functions. * floorfN: (libc)Rounding Functions. * floorfNx: (libc)Rounding Functions. * floorl: (libc)Rounding Functions. * fma: (libc)Misc FP Arithmetic. * fmaf: (libc)Misc FP Arithmetic. * fmafN: (libc)Misc FP Arithmetic. * fmafNx: (libc)Misc FP Arithmetic. * fmal: (libc)Misc FP Arithmetic. * fmax: (libc)Misc FP Arithmetic. * fmaxf: (libc)Misc FP Arithmetic. * fmaxfN: (libc)Misc FP Arithmetic. * fmaxfNx: (libc)Misc FP Arithmetic. * fmaximum: (libc)Misc FP Arithmetic. * fmaximum_mag: (libc)Misc FP Arithmetic. * fmaximum_mag_num: (libc)Misc FP Arithmetic. * fmaximum_mag_numf: (libc)Misc FP Arithmetic. * fmaximum_mag_numfN: (libc)Misc FP Arithmetic. * fmaximum_mag_numfNx: (libc)Misc FP Arithmetic. * fmaximum_mag_numl: (libc)Misc FP Arithmetic. * fmaximum_magf: (libc)Misc FP Arithmetic. * fmaximum_magfN: (libc)Misc FP Arithmetic. * fmaximum_magfNx: (libc)Misc FP Arithmetic. * fmaximum_magl: (libc)Misc FP Arithmetic. * fmaximum_num: (libc)Misc FP Arithmetic. * fmaximum_numf: (libc)Misc FP Arithmetic. * fmaximum_numfN: (libc)Misc FP Arithmetic. * fmaximum_numfNx: (libc)Misc FP Arithmetic. * fmaximum_numl: (libc)Misc FP Arithmetic. * fmaximumf: (libc)Misc FP Arithmetic. * fmaximumfN: (libc)Misc FP Arithmetic. * fmaximumfNx: (libc)Misc FP Arithmetic. * fmaximuml: (libc)Misc FP Arithmetic. * fmaxl: (libc)Misc FP Arithmetic. * fmaxmag: (libc)Misc FP Arithmetic. * fmaxmagf: (libc)Misc FP Arithmetic. * fmaxmagfN: (libc)Misc FP Arithmetic. * fmaxmagfNx: (libc)Misc FP Arithmetic. * fmaxmagl: (libc)Misc FP Arithmetic. * fmemopen: (libc)String Streams. * fmin: (libc)Misc FP Arithmetic. * fminf: (libc)Misc FP Arithmetic. * fminfN: (libc)Misc FP Arithmetic. * fminfNx: (libc)Misc FP Arithmetic. * fminimum: (libc)Misc FP Arithmetic. * fminimum_mag: (libc)Misc FP Arithmetic. * fminimum_mag_num: (libc)Misc FP Arithmetic. * fminimum_mag_numf: (libc)Misc FP Arithmetic. * fminimum_mag_numfN: (libc)Misc FP Arithmetic. * fminimum_mag_numfNx: (libc)Misc FP Arithmetic. * fminimum_mag_numl: (libc)Misc FP Arithmetic. * fminimum_magf: (libc)Misc FP Arithmetic. * fminimum_magfN: (libc)Misc FP Arithmetic. * fminimum_magfNx: (libc)Misc FP Arithmetic. * fminimum_magl: (libc)Misc FP Arithmetic. * fminimum_num: (libc)Misc FP Arithmetic. * fminimum_numf: (libc)Misc FP Arithmetic. * fminimum_numfN: (libc)Misc FP Arithmetic. * fminimum_numfNx: (libc)Misc FP Arithmetic. * fminimum_numl: (libc)Misc FP Arithmetic. * fminimumf: (libc)Misc FP Arithmetic. * fminimumfN: (libc)Misc FP Arithmetic. * fminimumfNx: (libc)Misc FP Arithmetic. * fminimuml: (libc)Misc FP Arithmetic. * fminl: (libc)Misc FP Arithmetic. * fminmag: (libc)Misc FP Arithmetic. * fminmagf: (libc)Misc FP Arithmetic. * fminmagfN: (libc)Misc FP Arithmetic. * fminmagfNx: (libc)Misc FP Arithmetic. * fminmagl: (libc)Misc FP Arithmetic. * fmod: (libc)Remainder Functions. * fmodf: (libc)Remainder Functions. * fmodfN: (libc)Remainder Functions. * fmodfNx: (libc)Remainder Functions. * fmodl: (libc)Remainder Functions. * fmtmsg: (libc)Printing Formatted Messages. * fmul: (libc)Misc FP Arithmetic. * fmull: (libc)Misc FP Arithmetic. * fnmatch: (libc)Wildcard Matching. * fopen64: (libc)Opening Streams. * fopen: (libc)Opening Streams. * fopencookie: (libc)Streams and Cookies. * fork: (libc)Creating a Process. * forkpty: (libc)Pseudo-Terminal Pairs. * fpathconf: (libc)Pathconf. * fpclassify: (libc)Floating Point Classes. * fprintf: (libc)Formatted Output Functions. * fputc: (libc)Simple Output. * fputc_unlocked: (libc)Simple Output. * fputs: (libc)Simple Output. * fputs_unlocked: (libc)Simple Output. * fputwc: (libc)Simple Output. * fputwc_unlocked: (libc)Simple Output. * fputws: (libc)Simple Output. * fputws_unlocked: (libc)Simple Output. * fread: (libc)Block Input/Output. * fread_unlocked: (libc)Block Input/Output. * free: (libc)Freeing after Malloc. * freopen64: (libc)Opening Streams. * freopen: (libc)Opening Streams. * frexp: (libc)Normalization Functions. * frexpf: (libc)Normalization Functions. * frexpfN: (libc)Normalization Functions. * frexpfNx: (libc)Normalization Functions. * frexpl: (libc)Normalization Functions. * fromfp: (libc)Rounding Functions. * fromfpf: (libc)Rounding Functions. * fromfpfN: (libc)Rounding Functions. * fromfpfNx: (libc)Rounding Functions. * fromfpl: (libc)Rounding Functions. * fromfpx: (libc)Rounding Functions. * fromfpxf: (libc)Rounding Functions. * fromfpxfN: (libc)Rounding Functions. * fromfpxfNx: (libc)Rounding Functions. * fromfpxl: (libc)Rounding Functions. * fscanf: (libc)Formatted Input Functions. * fseek: (libc)File Positioning. * fseeko64: (libc)File Positioning. * fseeko: (libc)File Positioning. * fsetpos64: (libc)Portable Positioning. * fsetpos: (libc)Portable Positioning. * fsqrt: (libc)Misc FP Arithmetic. * fsqrtl: (libc)Misc FP Arithmetic. * fstat64: (libc)Reading Attributes. * fstat: (libc)Reading Attributes. * fstatat64: (libc)Reading Attributes. * fstatat: (libc)Reading Attributes. * fsub: (libc)Misc FP Arithmetic. * fsubl: (libc)Misc FP Arithmetic. * fsync: (libc)Synchronizing I/O. * ftell: (libc)File Positioning. * ftello64: (libc)File Positioning. * ftello: (libc)File Positioning. * ftruncate64: (libc)File Size. * ftruncate: (libc)File Size. * ftrylockfile: (libc)Streams and Threads. * ftw64: (libc)Working with Directory Trees. * ftw: (libc)Working with Directory Trees. * funlockfile: (libc)Streams and Threads. * futimes: (libc)File Times. * fwide: (libc)Streams and I18N. * fwprintf: (libc)Formatted Output Functions. * fwrite: (libc)Block Input/Output. * fwrite_unlocked: (libc)Block Input/Output. * fwscanf: (libc)Formatted Input Functions. * gamma: (libc)Special Functions. * gammaf: (libc)Special Functions. * gammal: (libc)Special Functions. * gcvt: (libc)System V Number Conversion. * get_avphys_pages: (libc)Query Memory Parameters. * get_current_dir_name: (libc)Working Directory. * get_nprocs: (libc)Processor Resources. * get_nprocs_conf: (libc)Processor Resources. * get_phys_pages: (libc)Query Memory Parameters. * getauxval: (libc)Auxiliary Vector. * getc: (libc)Character Input. * getc_unlocked: (libc)Character Input. * getchar: (libc)Character Input. * getchar_unlocked: (libc)Character Input. * getcontext: (libc)System V contexts. * getcpu: (libc)CPU Affinity. * getcwd: (libc)Working Directory. * getdate: (libc)General Time String Parsing. * getdate_r: (libc)General Time String Parsing. * getdelim: (libc)Line Input. * getdents64: (libc)Low-level Directory Access. * getdomainnname: (libc)Host Identification. * getegid: (libc)Reading Persona. * getentropy: (libc)Unpredictable Bytes. * getenv: (libc)Environment Access. * geteuid: (libc)Reading Persona. * getfsent: (libc)fstab. * getfsfile: (libc)fstab. * getfsspec: (libc)fstab. * getgid: (libc)Reading Persona. * getgrent: (libc)Scanning All Groups. * getgrent_r: (libc)Scanning All Groups. * getgrgid: (libc)Lookup Group. * getgrgid_r: (libc)Lookup Group. * getgrnam: (libc)Lookup Group. * getgrnam_r: (libc)Lookup Group. * getgrouplist: (libc)Setting Groups. * getgroups: (libc)Reading Persona. * gethostbyaddr: (libc)Host Names. * gethostbyaddr_r: (libc)Host Names. * gethostbyname2: (libc)Host Names. * gethostbyname2_r: (libc)Host Names. * gethostbyname: (libc)Host Names. * gethostbyname_r: (libc)Host Names. * gethostent: (libc)Host Names. * gethostid: (libc)Host Identification. * gethostname: (libc)Host Identification. * getitimer: (libc)Setting an Alarm. * getline: (libc)Line Input. * getloadavg: (libc)Processor Resources. * getlogin: (libc)Who Logged In. * getmntent: (libc)mtab. * getmntent_r: (libc)mtab. * getnetbyaddr: (libc)Networks Database. * getnetbyname: (libc)Networks Database. * getnetent: (libc)Networks Database. * getnetgrent: (libc)Lookup Netgroup. * getnetgrent_r: (libc)Lookup Netgroup. * getopt: (libc)Using Getopt. * getopt_long: (libc)Getopt Long Options. * getopt_long_only: (libc)Getopt Long Options. * getpagesize: (libc)Query Memory Parameters. * getpass: (libc)getpass. * getpayload: (libc)FP Bit Twiddling. * getpayloadf: (libc)FP Bit Twiddling. * getpayloadfN: (libc)FP Bit Twiddling. * getpayloadfNx: (libc)FP Bit Twiddling. * getpayloadl: (libc)FP Bit Twiddling. * getpeername: (libc)Who is Connected. * getpgid: (libc)Process Group Functions. * getpgrp: (libc)Process Group Functions. * getpid: (libc)Process Identification. * getppid: (libc)Process Identification. * getpriority: (libc)Traditional Scheduling Functions. * getprotobyname: (libc)Protocols Database. * getprotobynumber: (libc)Protocols Database. * getprotoent: (libc)Protocols Database. * getpt: (libc)Allocation. * getpwent: (libc)Scanning All Users. * getpwent_r: (libc)Scanning All Users. * getpwnam: (libc)Lookup User. * getpwnam_r: (libc)Lookup User. * getpwuid: (libc)Lookup User. * getpwuid_r: (libc)Lookup User. * getrandom: (libc)Unpredictable Bytes. * getrlimit64: (libc)Limits on Resources. * getrlimit: (libc)Limits on Resources. * getrusage: (libc)Resource Usage. * gets: (libc)Line Input. * getservbyname: (libc)Services Database. * getservbyport: (libc)Services Database. * getservent: (libc)Services Database. * getsid: (libc)Process Group Functions. * getsockname: (libc)Reading Address. * getsockopt: (libc)Socket Option Functions. * getsubopt: (libc)Suboptions. * gettext: (libc)Translation with gettext. * gettid: (libc)Process Identification. * gettimeofday: (libc)Getting the Time. * getuid: (libc)Reading Persona. * getumask: (libc)Setting Permissions. * getutent: (libc)Manipulating the Database. * getutent_r: (libc)Manipulating the Database. * getutid: (libc)Manipulating the Database. * getutid_r: (libc)Manipulating the Database. * getutline: (libc)Manipulating the Database. * getutline_r: (libc)Manipulating the Database. * getutmp: (libc)XPG Functions. * getutmpx: (libc)XPG Functions. * getutxent: (libc)XPG Functions. * getutxid: (libc)XPG Functions. * getutxline: (libc)XPG Functions. * getw: (libc)Character Input. * getwc: (libc)Character Input. * getwc_unlocked: (libc)Character Input. * getwchar: (libc)Character Input. * getwchar_unlocked: (libc)Character Input. * getwd: (libc)Working Directory. * glob64: (libc)Calling Glob. * glob: (libc)Calling Glob. * globfree64: (libc)More Flags for Globbing. * globfree: (libc)More Flags for Globbing. * gmtime: (libc)Broken-down Time. * gmtime_r: (libc)Broken-down Time. * grantpt: (libc)Allocation. * gsignal: (libc)Signaling Yourself. * gtty: (libc)BSD Terminal Modes. * hasmntopt: (libc)mtab. * hcreate: (libc)Hash Search Function. * hcreate_r: (libc)Hash Search Function. * hdestroy: (libc)Hash Search Function. * hdestroy_r: (libc)Hash Search Function. * hsearch: (libc)Hash Search Function. * hsearch_r: (libc)Hash Search Function. * htonl: (libc)Byte Order. * htons: (libc)Byte Order. * hypot: (libc)Exponents and Logarithms. * hypotf: (libc)Exponents and Logarithms. * hypotfN: (libc)Exponents and Logarithms. * hypotfNx: (libc)Exponents and Logarithms. * hypotl: (libc)Exponents and Logarithms. * iconv: (libc)Generic Conversion Interface. * iconv_close: (libc)Generic Conversion Interface. * iconv_open: (libc)Generic Conversion Interface. * if_freenameindex: (libc)Interface Naming. * if_indextoname: (libc)Interface Naming. * if_nameindex: (libc)Interface Naming. * if_nametoindex: (libc)Interface Naming. * ilogb: (libc)Exponents and Logarithms. * ilogbf: (libc)Exponents and Logarithms. * ilogbfN: (libc)Exponents and Logarithms. * ilogbfNx: (libc)Exponents and Logarithms. * ilogbl: (libc)Exponents and Logarithms. * imaxabs: (libc)Absolute Value. * imaxdiv: (libc)Integer Division. * in6addr_any: (libc)Host Address Data Type. * in6addr_loopback: (libc)Host Address Data Type. * index: (libc)Search Functions. * inet_addr: (libc)Host Address Functions. * inet_aton: (libc)Host Address Functions. * inet_lnaof: (libc)Host Address Functions. * inet_makeaddr: (libc)Host Address Functions. * inet_netof: (libc)Host Address Functions. * inet_network: (libc)Host Address Functions. * inet_ntoa: (libc)Host Address Functions. * inet_ntop: (libc)Host Address Functions. * inet_pton: (libc)Host Address Functions. * initgroups: (libc)Setting Groups. * initstate: (libc)BSD Random. * initstate_r: (libc)BSD Random. * innetgr: (libc)Netgroup Membership. * ioctl: (libc)IOCTLs. * isalnum: (libc)Classification of Characters. * isalpha: (libc)Classification of Characters. * isascii: (libc)Classification of Characters. * isatty: (libc)Is It a Terminal. * isblank: (libc)Classification of Characters. * iscanonical: (libc)Floating Point Classes. * iscntrl: (libc)Classification of Characters. * isdigit: (libc)Classification of Characters. * iseqsig: (libc)FP Comparison Functions. * isfinite: (libc)Floating Point Classes. * isgraph: (libc)Classification of Characters. * isgreater: (libc)FP Comparison Functions. * isgreaterequal: (libc)FP Comparison Functions. * isinf: (libc)Floating Point Classes. * isinff: (libc)Floating Point Classes. * isinfl: (libc)Floating Point Classes. * isless: (libc)FP Comparison Functions. * islessequal: (libc)FP Comparison Functions. * islessgreater: (libc)FP Comparison Functions. * islower: (libc)Classification of Characters. * isnan: (libc)Floating Point Classes. * isnan: (libc)Floating Point Classes. * isnanf: (libc)Floating Point Classes. * isnanl: (libc)Floating Point Classes. * isnormal: (libc)Floating Point Classes. * isprint: (libc)Classification of Characters. * ispunct: (libc)Classification of Characters. * issignaling: (libc)Floating Point Classes. * isspace: (libc)Classification of Characters. * issubnormal: (libc)Floating Point Classes. * isunordered: (libc)FP Comparison Functions. * isupper: (libc)Classification of Characters. * iswalnum: (libc)Classification of Wide Characters. * iswalpha: (libc)Classification of Wide Characters. * iswblank: (libc)Classification of Wide Characters. * iswcntrl: (libc)Classification of Wide Characters. * iswctype: (libc)Classification of Wide Characters. * iswdigit: (libc)Classification of Wide Characters. * iswgraph: (libc)Classification of Wide Characters. * iswlower: (libc)Classification of Wide Characters. * iswprint: (libc)Classification of Wide Characters. * iswpunct: (libc)Classification of Wide Characters. * iswspace: (libc)Classification of Wide Characters. * iswupper: (libc)Classification of Wide Characters. * iswxdigit: (libc)Classification of Wide Characters. * isxdigit: (libc)Classification of Characters. * iszero: (libc)Floating Point Classes. * j0: (libc)Special Functions. * j0f: (libc)Special Functions. * j0fN: (libc)Special Functions. * j0fNx: (libc)Special Functions. * j0l: (libc)Special Functions. * j1: (libc)Special Functions. * j1f: (libc)Special Functions. * j1fN: (libc)Special Functions. * j1fNx: (libc)Special Functions. * j1l: (libc)Special Functions. * jn: (libc)Special Functions. * jnf: (libc)Special Functions. * jnfN: (libc)Special Functions. * jnfNx: (libc)Special Functions. * jnl: (libc)Special Functions. * jrand48: (libc)SVID Random. * jrand48_r: (libc)SVID Random. * kill: (libc)Signaling Another Process. * killpg: (libc)Signaling Another Process. * l64a: (libc)Encode Binary Data. * labs: (libc)Absolute Value. * lcong48: (libc)SVID Random. * lcong48_r: (libc)SVID Random. * ldexp: (libc)Normalization Functions. * ldexpf: (libc)Normalization Functions. * ldexpfN: (libc)Normalization Functions. * ldexpfNx: (libc)Normalization Functions. * ldexpl: (libc)Normalization Functions. * ldiv: (libc)Integer Division. * lfind: (libc)Array Search Function. * lgamma: (libc)Special Functions. * lgamma_r: (libc)Special Functions. * lgammaf: (libc)Special Functions. * lgammafN: (libc)Special Functions. * lgammafN_r: (libc)Special Functions. * lgammafNx: (libc)Special Functions. * lgammafNx_r: (libc)Special Functions. * lgammaf_r: (libc)Special Functions. * lgammal: (libc)Special Functions. * lgammal_r: (libc)Special Functions. * link: (libc)Hard Links. * linkat: (libc)Hard Links. * lio_listio64: (libc)Asynchronous Reads/Writes. * lio_listio: (libc)Asynchronous Reads/Writes. * listen: (libc)Listening. * llabs: (libc)Absolute Value. * lldiv: (libc)Integer Division. * llogb: (libc)Exponents and Logarithms. * llogbf: (libc)Exponents and Logarithms. * llogbfN: (libc)Exponents and Logarithms. * llogbfNx: (libc)Exponents and Logarithms. * llogbl: (libc)Exponents and Logarithms. * llrint: (libc)Rounding Functions. * llrintf: (libc)Rounding Functions. * llrintfN: (libc)Rounding Functions. * llrintfNx: (libc)Rounding Functions. * llrintl: (libc)Rounding Functions. * llround: (libc)Rounding Functions. * llroundf: (libc)Rounding Functions. * llroundfN: (libc)Rounding Functions. * llroundfNx: (libc)Rounding Functions. * llroundl: (libc)Rounding Functions. * localeconv: (libc)The Lame Way to Locale Data. * localtime: (libc)Broken-down Time. * localtime_r: (libc)Broken-down Time. * log10: (libc)Exponents and Logarithms. * log10f: (libc)Exponents and Logarithms. * log10fN: (libc)Exponents and Logarithms. * log10fNx: (libc)Exponents and Logarithms. * log10l: (libc)Exponents and Logarithms. * log10p1: (libc)Exponents and Logarithms. * log10p1f: (libc)Exponents and Logarithms. * log10p1fN: (libc)Exponents and Logarithms. * log10p1fNx: (libc)Exponents and Logarithms. * log10p1l: (libc)Exponents and Logarithms. * log1p: (libc)Exponents and Logarithms. * log1pf: (libc)Exponents and Logarithms. * log1pfN: (libc)Exponents and Logarithms. * log1pfNx: (libc)Exponents and Logarithms. * log1pl: (libc)Exponents and Logarithms. * log2: (libc)Exponents and Logarithms. * log2f: (libc)Exponents and Logarithms. * log2fN: (libc)Exponents and Logarithms. * log2fNx: (libc)Exponents and Logarithms. * log2l: (libc)Exponents and Logarithms. * log2p1: (libc)Exponents and Logarithms. * log2p1f: (libc)Exponents and Logarithms. * log2p1fN: (libc)Exponents and Logarithms. * log2p1fNx: (libc)Exponents and Logarithms. * log2p1l: (libc)Exponents and Logarithms. * log: (libc)Exponents and Logarithms. * logb: (libc)Exponents and Logarithms. * logbf: (libc)Exponents and Logarithms. * logbfN: (libc)Exponents and Logarithms. * logbfNx: (libc)Exponents and Logarithms. * logbl: (libc)Exponents and Logarithms. * logf: (libc)Exponents and Logarithms. * logfN: (libc)Exponents and Logarithms. * logfNx: (libc)Exponents and Logarithms. * login: (libc)Logging In and Out. * login_tty: (libc)Logging In and Out. * logl: (libc)Exponents and Logarithms. * logout: (libc)Logging In and Out. * logp1: (libc)Exponents and Logarithms. * logp1f: (libc)Exponents and Logarithms. * logp1fN: (libc)Exponents and Logarithms. * logp1fNx: (libc)Exponents and Logarithms. * logp1l: (libc)Exponents and Logarithms. * logwtmp: (libc)Logging In and Out. * longjmp: (libc)Non-Local Details. * lrand48: (libc)SVID Random. * lrand48_r: (libc)SVID Random. * lrint: (libc)Rounding Functions. * lrintf: (libc)Rounding Functions. * lrintfN: (libc)Rounding Functions. * lrintfNx: (libc)Rounding Functions. * lrintl: (libc)Rounding Functions. * lround: (libc)Rounding Functions. * lroundf: (libc)Rounding Functions. * lroundfN: (libc)Rounding Functions. * lroundfNx: (libc)Rounding Functions. * lroundl: (libc)Rounding Functions. * lsearch: (libc)Array Search Function. * lseek64: (libc)File Position Primitive. * lseek: (libc)File Position Primitive. * lstat64: (libc)Reading Attributes. * lstat: (libc)Reading Attributes. * lutimes: (libc)File Times. * madvise: (libc)Memory-mapped I/O. * makecontext: (libc)System V contexts. * mallinfo2: (libc)Statistics of Malloc. * malloc: (libc)Basic Allocation. * mallopt: (libc)Malloc Tunable Parameters. * mblen: (libc)Non-reentrant Character Conversion. * mbrlen: (libc)Converting a Character. * mbrtowc: (libc)Converting a Character. * mbsinit: (libc)Keeping the state. * mbsnrtowcs: (libc)Converting Strings. * mbsrtowcs: (libc)Converting Strings. * mbstowcs: (libc)Non-reentrant String Conversion. * mbtowc: (libc)Non-reentrant Character Conversion. * mcheck: (libc)Heap Consistency Checking. * memalign: (libc)Aligned Memory Blocks. * memccpy: (libc)Copying Strings and Arrays. * memchr: (libc)Search Functions. * memcmp: (libc)String/Array Comparison. * memcpy: (libc)Copying Strings and Arrays. * memfd_create: (libc)Memory-mapped I/O. * memfrob: (libc)Obfuscating Data. * memmem: (libc)Search Functions. * memmove: (libc)Copying Strings and Arrays. * mempcpy: (libc)Copying Strings and Arrays. * memrchr: (libc)Search Functions. * memset: (libc)Copying Strings and Arrays. * mkdir: (libc)Creating Directories. * mkdtemp: (libc)Temporary Files. * mkfifo: (libc)FIFO Special Files. * mknod: (libc)Making Special Files. * mkstemp: (libc)Temporary Files. * mktemp: (libc)Temporary Files. * mktime: (libc)Broken-down Time. * mlock2: (libc)Page Lock Functions. * mlock: (libc)Page Lock Functions. * mlockall: (libc)Page Lock Functions. * mmap64: (libc)Memory-mapped I/O. * mmap: (libc)Memory-mapped I/O. * modf: (libc)Rounding Functions. * modff: (libc)Rounding Functions. * modffN: (libc)Rounding Functions. * modffNx: (libc)Rounding Functions. * modfl: (libc)Rounding Functions. * mount: (libc)Mount-Unmount-Remount. * mprobe: (libc)Heap Consistency Checking. * mprotect: (libc)Memory Protection. * mrand48: (libc)SVID Random. * mrand48_r: (libc)SVID Random. * mremap: (libc)Memory-mapped I/O. * msync: (libc)Memory-mapped I/O. * mtrace: (libc)Tracing malloc. * mtx_destroy: (libc)ISO C Mutexes. * mtx_init: (libc)ISO C Mutexes. * mtx_lock: (libc)ISO C Mutexes. * mtx_timedlock: (libc)ISO C Mutexes. * mtx_trylock: (libc)ISO C Mutexes. * mtx_unlock: (libc)ISO C Mutexes. * munlock: (libc)Page Lock Functions. * munlockall: (libc)Page Lock Functions. * munmap: (libc)Memory-mapped I/O. * muntrace: (libc)Tracing malloc. * nan: (libc)FP Bit Twiddling. * nanf: (libc)FP Bit Twiddling. * nanfN: (libc)FP Bit Twiddling. * nanfNx: (libc)FP Bit Twiddling. * nanl: (libc)FP Bit Twiddling. * nanosleep: (libc)Sleeping. * nearbyint: (libc)Rounding Functions. * nearbyintf: (libc)Rounding Functions. * nearbyintfN: (libc)Rounding Functions. * nearbyintfNx: (libc)Rounding Functions. * nearbyintl: (libc)Rounding Functions. * nextafter: (libc)FP Bit Twiddling. * nextafterf: (libc)FP Bit Twiddling. * nextafterfN: (libc)FP Bit Twiddling. * nextafterfNx: (libc)FP Bit Twiddling. * nextafterl: (libc)FP Bit Twiddling. * nextdown: (libc)FP Bit Twiddling. * nextdownf: (libc)FP Bit Twiddling. * nextdownfN: (libc)FP Bit Twiddling. * nextdownfNx: (libc)FP Bit Twiddling. * nextdownl: (libc)FP Bit Twiddling. * nexttoward: (libc)FP Bit Twiddling. * nexttowardf: (libc)FP Bit Twiddling. * nexttowardl: (libc)FP Bit Twiddling. * nextup: (libc)FP Bit Twiddling. * nextupf: (libc)FP Bit Twiddling. * nextupfN: (libc)FP Bit Twiddling. * nextupfNx: (libc)FP Bit Twiddling. * nextupl: (libc)FP Bit Twiddling. * nftw64: (libc)Working with Directory Trees. * nftw: (libc)Working with Directory Trees. * ngettext: (libc)Advanced gettext functions. * nice: (libc)Traditional Scheduling Functions. * nl_langinfo: (libc)The Elegant and Fast Way. * nrand48: (libc)SVID Random. * nrand48_r: (libc)SVID Random. * ntohl: (libc)Byte Order. * ntohs: (libc)Byte Order. * ntp_adjtime: (libc)Setting and Adjusting the Time. * ntp_gettime: (libc)Setting and Adjusting the Time. * obstack_1grow: (libc)Growing Objects. * obstack_1grow_fast: (libc)Extra Fast Growing. * obstack_alignment_mask: (libc)Obstacks Data Alignment. * obstack_alloc: (libc)Allocation in an Obstack. * obstack_base: (libc)Status of an Obstack. * obstack_blank: (libc)Growing Objects. * obstack_blank_fast: (libc)Extra Fast Growing. * obstack_chunk_size: (libc)Obstack Chunks. * obstack_copy0: (libc)Allocation in an Obstack. * obstack_copy: (libc)Allocation in an Obstack. * obstack_finish: (libc)Growing Objects. * obstack_free: (libc)Freeing Obstack Objects. * obstack_grow0: (libc)Growing Objects. * obstack_grow: (libc)Growing Objects. * obstack_init: (libc)Preparing for Obstacks. * obstack_int_grow: (libc)Growing Objects. * obstack_int_grow_fast: (libc)Extra Fast Growing. * obstack_next_free: (libc)Status of an Obstack. * obstack_object_size: (libc)Growing Objects. * obstack_object_size: (libc)Status of an Obstack. * obstack_printf: (libc)Dynamic Output. * obstack_ptr_grow: (libc)Growing Objects. * obstack_ptr_grow_fast: (libc)Extra Fast Growing. * obstack_room: (libc)Extra Fast Growing. * obstack_vprintf: (libc)Variable Arguments Output. * offsetof: (libc)Structure Measurement. * on_exit: (libc)Cleanups on Exit. * open64: (libc)Opening and Closing Files. * open: (libc)Opening and Closing Files. * open_memstream: (libc)String Streams. * openat64: (libc)Opening and Closing Files. * openat: (libc)Opening and Closing Files. * opendir: (libc)Opening a Directory. * openlog: (libc)openlog. * openpty: (libc)Pseudo-Terminal Pairs. * parse_printf_format: (libc)Parsing a Template String. * pathconf: (libc)Pathconf. * pause: (libc)Using Pause. * pclose: (libc)Pipe to a Subprocess. * perror: (libc)Error Messages. * pidfd_getpid: (libc)Querying a Process. * pipe: (libc)Creating a Pipe. * pkey_alloc: (libc)Memory Protection. * pkey_free: (libc)Memory Protection. * pkey_get: (libc)Memory Protection. * pkey_mprotect: (libc)Memory Protection. * pkey_set: (libc)Memory Protection. * poll: (libc)Other Low-Level I/O APIs. * popen: (libc)Pipe to a Subprocess. * posix_fallocate64: (libc)Storage Allocation. * posix_fallocate: (libc)Storage Allocation. * posix_memalign: (libc)Aligned Memory Blocks. * posix_openpt: (libc)Allocation. * pow: (libc)Exponents and Logarithms. * powf: (libc)Exponents and Logarithms. * powfN: (libc)Exponents and Logarithms. * powfNx: (libc)Exponents and Logarithms. * powl: (libc)Exponents and Logarithms. * pread64: (libc)I/O Primitives. * pread: (libc)I/O Primitives. * preadv2: (libc)Scatter-Gather. * preadv64: (libc)Scatter-Gather. * preadv64v2: (libc)Scatter-Gather. * preadv: (libc)Scatter-Gather. * printf: (libc)Formatted Output Functions. * printf_size: (libc)Predefined Printf Handlers. * printf_size_info: (libc)Predefined Printf Handlers. * psignal: (libc)Signal Messages. * pthread_attr_getsigmask_np: (libc)Initial Thread Signal Mask. * pthread_attr_setsigmask_np: (libc)Initial Thread Signal Mask. * pthread_clockjoin_np: (libc)Waiting with Explicit Clocks. * pthread_cond_clockwait: (libc)Waiting with Explicit Clocks. * pthread_getattr_default_np: (libc)Default Thread Attributes. * pthread_getspecific: (libc)Thread-specific Data. * pthread_key_create: (libc)Thread-specific Data. * pthread_key_delete: (libc)Thread-specific Data. * pthread_rwlock_clockrdlock: (libc)Waiting with Explicit Clocks. * pthread_rwlock_clockwrlock: (libc)Waiting with Explicit Clocks. * pthread_setattr_default_np: (libc)Default Thread Attributes. * pthread_setspecific: (libc)Thread-specific Data. * pthread_timedjoin_np: (libc)Waiting with Explicit Clocks. * pthread_tryjoin_np: (libc)Waiting with Explicit Clocks. * ptsname: (libc)Allocation. * ptsname_r: (libc)Allocation. * putc: (libc)Simple Output. * putc_unlocked: (libc)Simple Output. * putchar: (libc)Simple Output. * putchar_unlocked: (libc)Simple Output. * putenv: (libc)Environment Access. * putpwent: (libc)Writing a User Entry. * puts: (libc)Simple Output. * pututline: (libc)Manipulating the Database. * pututxline: (libc)XPG Functions. * putw: (libc)Simple Output. * putwc: (libc)Simple Output. * putwc_unlocked: (libc)Simple Output. * putwchar: (libc)Simple Output. * putwchar_unlocked: (libc)Simple Output. * pwrite64: (libc)I/O Primitives. * pwrite: (libc)I/O Primitives. * pwritev2: (libc)Scatter-Gather. * pwritev64: (libc)Scatter-Gather. * pwritev64v2: (libc)Scatter-Gather. * pwritev: (libc)Scatter-Gather. * qecvt: (libc)System V Number Conversion. * qecvt_r: (libc)System V Number Conversion. * qfcvt: (libc)System V Number Conversion. * qfcvt_r: (libc)System V Number Conversion. * qgcvt: (libc)System V Number Conversion. * qsort: (libc)Array Sort Function. * raise: (libc)Signaling Yourself. * rand: (libc)ISO Random. * rand_r: (libc)ISO Random. * random: (libc)BSD Random. * random_r: (libc)BSD Random. * rawmemchr: (libc)Search Functions. * read: (libc)I/O Primitives. * readdir64: (libc)Reading/Closing Directory. * readdir64_r: (libc)Reading/Closing Directory. * readdir: (libc)Reading/Closing Directory. * readdir_r: (libc)Reading/Closing Directory. * readlink: (libc)Symbolic Links. * readv: (libc)Scatter-Gather. * realloc: (libc)Changing Block Size. * reallocarray: (libc)Changing Block Size. * realpath: (libc)Symbolic Links. * recv: (libc)Receiving Data. * recvfrom: (libc)Receiving Datagrams. * recvmsg: (libc)Other Socket APIs. * regcomp: (libc)POSIX Regexp Compilation. * regerror: (libc)Regexp Cleanup. * regexec: (libc)Matching POSIX Regexps. * regfree: (libc)Regexp Cleanup. * register_printf_function: (libc)Registering New Conversions. * remainder: (libc)Remainder Functions. * remainderf: (libc)Remainder Functions. * remainderfN: (libc)Remainder Functions. * remainderfNx: (libc)Remainder Functions. * remainderl: (libc)Remainder Functions. * remove: (libc)Deleting Files. * rename: (libc)Renaming Files. * rewind: (libc)File Positioning. * rewinddir: (libc)Random Access Directory. * rindex: (libc)Search Functions. * rint: (libc)Rounding Functions. * rintf: (libc)Rounding Functions. * rintfN: (libc)Rounding Functions. * rintfNx: (libc)Rounding Functions. * rintl: (libc)Rounding Functions. * rmdir: (libc)Deleting Files. * round: (libc)Rounding Functions. * roundeven: (libc)Rounding Functions. * roundevenf: (libc)Rounding Functions. * roundevenfN: (libc)Rounding Functions. * roundevenfNx: (libc)Rounding Functions. * roundevenl: (libc)Rounding Functions. * roundf: (libc)Rounding Functions. * roundfN: (libc)Rounding Functions. * roundfNx: (libc)Rounding Functions. * roundl: (libc)Rounding Functions. * rpmatch: (libc)Yes-or-No Questions. * sbrk: (libc)Resizing the Data Segment. * scalb: (libc)Normalization Functions. * scalbf: (libc)Normalization Functions. * scalbl: (libc)Normalization Functions. * scalbln: (libc)Normalization Functions. * scalblnf: (libc)Normalization Functions. * scalblnfN: (libc)Normalization Functions. * scalblnfNx: (libc)Normalization Functions. * scalblnl: (libc)Normalization Functions. * scalbn: (libc)Normalization Functions. * scalbnf: (libc)Normalization Functions. * scalbnfN: (libc)Normalization Functions. * scalbnfNx: (libc)Normalization Functions. * scalbnl: (libc)Normalization Functions. * scandir64: (libc)Scanning Directory Content. * scandir: (libc)Scanning Directory Content. * scanf: (libc)Formatted Input Functions. * sched_get_priority_max: (libc)Basic Scheduling Functions. * sched_get_priority_min: (libc)Basic Scheduling Functions. * sched_getaddr: (libc)Extensible Scheduling. * sched_getaffinity: (libc)CPU Affinity. * sched_getparam: (libc)Basic Scheduling Functions. * sched_getscheduler: (libc)Basic Scheduling Functions. * sched_rr_get_interval: (libc)Basic Scheduling Functions. * sched_setaddr: (libc)Extensible Scheduling. * sched_setaffinity: (libc)CPU Affinity. * sched_setparam: (libc)Basic Scheduling Functions. * sched_setscheduler: (libc)Basic Scheduling Functions. * sched_yield: (libc)Basic Scheduling Functions. * secure_getenv: (libc)Environment Access. * seed48: (libc)SVID Random. * seed48_r: (libc)SVID Random. * seekdir: (libc)Random Access Directory. * select: (libc)Waiting for I/O. * sem_clockwait: (libc)Waiting with Explicit Clocks. * sem_close: (libc)Semaphores. * sem_destroy: (libc)Semaphores. * sem_getvalue: (libc)Semaphores. * sem_init: (libc)Semaphores. * sem_open: (libc)Semaphores. * sem_post: (libc)Semaphores. * sem_timedwait: (libc)Semaphores. * sem_trywait: (libc)Semaphores. * sem_unlink: (libc)Semaphores. * sem_wait: (libc)Semaphores. * semctl: (libc)Semaphores. * semget: (libc)Semaphores. * semop: (libc)Semaphores. * semtimedop: (libc)Semaphores. * send: (libc)Sending Data. * sendmsg: (libc)Other Socket APIs. * sendto: (libc)Sending Datagrams. * setbuf: (libc)Controlling Buffering. * setbuffer: (libc)Controlling Buffering. * setcontext: (libc)System V contexts. * setdomainname: (libc)Host Identification. * setegid: (libc)Setting Groups. * setenv: (libc)Environment Access. * seteuid: (libc)Setting User ID. * setfsent: (libc)fstab. * setgid: (libc)Setting Groups. * setgrent: (libc)Scanning All Groups. * setgroups: (libc)Setting Groups. * sethostent: (libc)Host Names. * sethostid: (libc)Host Identification. * sethostname: (libc)Host Identification. * setitimer: (libc)Setting an Alarm. * setjmp: (libc)Non-Local Details. * setlinebuf: (libc)Controlling Buffering. * setlocale: (libc)Setting the Locale. * setlogmask: (libc)setlogmask. * setmntent: (libc)mtab. * setnetent: (libc)Networks Database. * setnetgrent: (libc)Lookup Netgroup. * setpayload: (libc)FP Bit Twiddling. * setpayloadf: (libc)FP Bit Twiddling. * setpayloadfN: (libc)FP Bit Twiddling. * setpayloadfNx: (libc)FP Bit Twiddling. * setpayloadl: (libc)FP Bit Twiddling. * setpayloadsig: (libc)FP Bit Twiddling. * setpayloadsigf: (libc)FP Bit Twiddling. * setpayloadsigfN: (libc)FP Bit Twiddling. * setpayloadsigfNx: (libc)FP Bit Twiddling. * setpayloadsigl: (libc)FP Bit Twiddling. * setpgid: (libc)Process Group Functions. * setpgrp: (libc)Process Group Functions. * setpriority: (libc)Traditional Scheduling Functions. * setprotoent: (libc)Protocols Database. * setpwent: (libc)Scanning All Users. * setregid: (libc)Setting Groups. * setreuid: (libc)Setting User ID. * setrlimit64: (libc)Limits on Resources. * setrlimit: (libc)Limits on Resources. * setservent: (libc)Services Database. * setsid: (libc)Process Group Functions. * setsockopt: (libc)Socket Option Functions. * setstate: (libc)BSD Random. * setstate_r: (libc)BSD Random. * settimeofday: (libc)Setting and Adjusting the Time. * setuid: (libc)Setting User ID. * setutent: (libc)Manipulating the Database. * setutxent: (libc)XPG Functions. * setvbuf: (libc)Controlling Buffering. * shm_open: (libc)Memory-mapped I/O. * shm_unlink: (libc)Memory-mapped I/O. * shutdown: (libc)Closing a Socket. * sigabbrev_np: (libc)Signal Messages. * sigaction: (libc)Advanced Signal Handling. * sigaddset: (libc)Signal Sets. * sigaltstack: (libc)Signal Stack. * sigblock: (libc)BSD Signal Handling. * sigdelset: (libc)Signal Sets. * sigdescr_np: (libc)Signal Messages. * sigemptyset: (libc)Signal Sets. * sigfillset: (libc)Signal Sets. * siginterrupt: (libc)BSD Signal Handling. * sigismember: (libc)Signal Sets. * siglongjmp: (libc)Non-Local Exits and Signals. * sigmask: (libc)BSD Signal Handling. * signal: (libc)Basic Signal Handling. * signbit: (libc)FP Bit Twiddling. * significand: (libc)Normalization Functions. * significandf: (libc)Normalization Functions. * significandl: (libc)Normalization Functions. * sigpause: (libc)BSD Signal Handling. * sigpending: (libc)Checking for Pending Signals. * sigprocmask: (libc)Process Signal Mask. * sigsetjmp: (libc)Non-Local Exits and Signals. * sigsetmask: (libc)BSD Signal Handling. * sigstack: (libc)Signal Stack. * sigsuspend: (libc)Sigsuspend. * sin: (libc)Trig Functions. * sincos: (libc)Trig Functions. * sincosf: (libc)Trig Functions. * sincosfN: (libc)Trig Functions. * sincosfNx: (libc)Trig Functions. * sincosl: (libc)Trig Functions. * sinf: (libc)Trig Functions. * sinfN: (libc)Trig Functions. * sinfNx: (libc)Trig Functions. * sinh: (libc)Hyperbolic Functions. * sinhf: (libc)Hyperbolic Functions. * sinhfN: (libc)Hyperbolic Functions. * sinhfNx: (libc)Hyperbolic Functions. * sinhl: (libc)Hyperbolic Functions. * sinl: (libc)Trig Functions. * sinpi: (libc)Trig Functions. * sinpif: (libc)Trig Functions. * sinpifN: (libc)Trig Functions. * sinpifNx: (libc)Trig Functions. * sinpil: (libc)Trig Functions. * sleep: (libc)Sleeping. * snprintf: (libc)Formatted Output Functions. * socket: (libc)Creating a Socket. * socketpair: (libc)Socket Pairs. * sprintf: (libc)Formatted Output Functions. * sqrt: (libc)Exponents and Logarithms. * sqrtf: (libc)Exponents and Logarithms. * sqrtfN: (libc)Exponents and Logarithms. * sqrtfNx: (libc)Exponents and Logarithms. * sqrtl: (libc)Exponents and Logarithms. * srand48: (libc)SVID Random. * srand48_r: (libc)SVID Random. * srand: (libc)ISO Random. * srandom: (libc)BSD Random. * srandom_r: (libc)BSD Random. * sscanf: (libc)Formatted Input Functions. * ssignal: (libc)Basic Signal Handling. * stat64: (libc)Reading Attributes. * stat: (libc)Reading Attributes. * stdc_bit_ceil_uc: (libc)Bit Manipulation. * stdc_bit_ceil_ui: (libc)Bit Manipulation. * stdc_bit_ceil_ul: (libc)Bit Manipulation. * stdc_bit_ceil_ull: (libc)Bit Manipulation. * stdc_bit_ceil_us: (libc)Bit Manipulation. * stdc_bit_floor_uc: (libc)Bit Manipulation. * stdc_bit_floor_ui: (libc)Bit Manipulation. * stdc_bit_floor_ul: (libc)Bit Manipulation. * stdc_bit_floor_ull: (libc)Bit Manipulation. * stdc_bit_floor_us: (libc)Bit Manipulation. * stdc_bit_width_uc: (libc)Bit Manipulation. * stdc_bit_width_ui: (libc)Bit Manipulation. * stdc_bit_width_ul: (libc)Bit Manipulation. * stdc_bit_width_ull: (libc)Bit Manipulation. * stdc_bit_width_us: (libc)Bit Manipulation. * stdc_count_ones_uc: (libc)Bit Manipulation. * stdc_count_ones_ui: (libc)Bit Manipulation. * stdc_count_ones_ul: (libc)Bit Manipulation. * stdc_count_ones_ull: (libc)Bit Manipulation. * stdc_count_ones_us: (libc)Bit Manipulation. * stdc_count_zeros_uc: (libc)Bit Manipulation. * stdc_count_zeros_ui: (libc)Bit Manipulation. * stdc_count_zeros_ul: (libc)Bit Manipulation. * stdc_count_zeros_ull: (libc)Bit Manipulation. * stdc_count_zeros_us: (libc)Bit Manipulation. * stdc_first_leading_one_uc: (libc)Bit Manipulation. * stdc_first_leading_one_ui: (libc)Bit Manipulation. * stdc_first_leading_one_ul: (libc)Bit Manipulation. * stdc_first_leading_one_ull: (libc)Bit Manipulation. * stdc_first_leading_one_us: (libc)Bit Manipulation. * stdc_first_leading_zero_uc: (libc)Bit Manipulation. * stdc_first_leading_zero_ui: (libc)Bit Manipulation. * stdc_first_leading_zero_ul: (libc)Bit Manipulation. * stdc_first_leading_zero_ull: (libc)Bit Manipulation. * stdc_first_leading_zero_us: (libc)Bit Manipulation. * stdc_first_trailing_one_uc: (libc)Bit Manipulation. * stdc_first_trailing_one_ui: (libc)Bit Manipulation. * stdc_first_trailing_one_ul: (libc)Bit Manipulation. * stdc_first_trailing_one_ull: (libc)Bit Manipulation. * stdc_first_trailing_one_us: (libc)Bit Manipulation. * stdc_first_trailing_zero_uc: (libc)Bit Manipulation. * stdc_first_trailing_zero_ui: (libc)Bit Manipulation. * stdc_first_trailing_zero_ul: (libc)Bit Manipulation. * stdc_first_trailing_zero_ull: (libc)Bit Manipulation. * stdc_first_trailing_zero_us: (libc)Bit Manipulation. * stdc_has_single_bit_uc: (libc)Bit Manipulation. * stdc_has_single_bit_ui: (libc)Bit Manipulation. * stdc_has_single_bit_ul: (libc)Bit Manipulation. * stdc_has_single_bit_ull: (libc)Bit Manipulation. * stdc_has_single_bit_us: (libc)Bit Manipulation. * stdc_leading_ones_uc: (libc)Bit Manipulation. * stdc_leading_ones_ui: (libc)Bit Manipulation. * stdc_leading_ones_ul: (libc)Bit Manipulation. * stdc_leading_ones_ull: (libc)Bit Manipulation. * stdc_leading_ones_us: (libc)Bit Manipulation. * stdc_leading_zeros_uc: (libc)Bit Manipulation. * stdc_leading_zeros_ui: (libc)Bit Manipulation. * stdc_leading_zeros_ul: (libc)Bit Manipulation. * stdc_leading_zeros_ull: (libc)Bit Manipulation. * stdc_leading_zeros_us: (libc)Bit Manipulation. * stdc_trailing_ones_uc: (libc)Bit Manipulation. * stdc_trailing_ones_ui: (libc)Bit Manipulation. * stdc_trailing_ones_ul: (libc)Bit Manipulation. * stdc_trailing_ones_ull: (libc)Bit Manipulation. * stdc_trailing_ones_us: (libc)Bit Manipulation. * stdc_trailing_zeros_uc: (libc)Bit Manipulation. * stdc_trailing_zeros_ui: (libc)Bit Manipulation. * stdc_trailing_zeros_ul: (libc)Bit Manipulation. * stdc_trailing_zeros_ull: (libc)Bit Manipulation. * stdc_trailing_zeros_us: (libc)Bit Manipulation. * stime: (libc)Setting and Adjusting the Time. * stpcpy: (libc)Copying Strings and Arrays. * stpncpy: (libc)Truncating Strings. * strcasecmp: (libc)String/Array Comparison. * strcasestr: (libc)Search Functions. * strcat: (libc)Concatenating Strings. * strchr: (libc)Search Functions. * strchrnul: (libc)Search Functions. * strcmp: (libc)String/Array Comparison. * strcoll: (libc)Collation Functions. * strcpy: (libc)Copying Strings and Arrays. * strcspn: (libc)Search Functions. * strdup: (libc)Copying Strings and Arrays. * strdupa: (libc)Copying Strings and Arrays. * strerror: (libc)Error Messages. * strerror_l: (libc)Error Messages. * strerror_r: (libc)Error Messages. * strerror_r: (libc)Error Messages. * strerrordesc_np: (libc)Error Messages. * strerrorname_np: (libc)Error Messages. * strfmon: (libc)Formatting Numbers. * strfromd: (libc)Printing of Floats. * strfromf: (libc)Printing of Floats. * strfromfN: (libc)Printing of Floats. * strfromfNx: (libc)Printing of Floats. * strfroml: (libc)Printing of Floats. * strfry: (libc)Shuffling Bytes. * strftime: (libc)Formatting Calendar Time. * strftime_l: (libc)Formatting Calendar Time. * strlcat: (libc)Truncating Strings. * strlcpy: (libc)Truncating Strings. * strlen: (libc)String Length. * strncasecmp: (libc)String/Array Comparison. * strncat: (libc)Truncating Strings. * strncmp: (libc)String/Array Comparison. * strncpy: (libc)Truncating Strings. * strndup: (libc)Truncating Strings. * strndupa: (libc)Truncating Strings. * strnlen: (libc)String Length. * strpbrk: (libc)Search Functions. * strptime: (libc)Low-Level Time String Parsing. * strrchr: (libc)Search Functions. * strsep: (libc)Finding Tokens in a String. * strsignal: (libc)Signal Messages. * strspn: (libc)Search Functions. * strstr: (libc)Search Functions. * strtod: (libc)Parsing of Floats. * strtof: (libc)Parsing of Floats. * strtofN: (libc)Parsing of Floats. * strtofNx: (libc)Parsing of Floats. * strtoimax: (libc)Parsing of Integers. * strtok: (libc)Finding Tokens in a String. * strtok_r: (libc)Finding Tokens in a String. * strtol: (libc)Parsing of Integers. * strtold: (libc)Parsing of Floats. * strtoll: (libc)Parsing of Integers. * strtoq: (libc)Parsing of Integers. * strtoul: (libc)Parsing of Integers. * strtoull: (libc)Parsing of Integers. * strtoumax: (libc)Parsing of Integers. * strtouq: (libc)Parsing of Integers. * strverscmp: (libc)String/Array Comparison. * strxfrm: (libc)Collation Functions. * stty: (libc)BSD Terminal Modes. * swapcontext: (libc)System V contexts. * swprintf: (libc)Formatted Output Functions. * swscanf: (libc)Formatted Input Functions. * symlink: (libc)Symbolic Links. * sync: (libc)Synchronizing I/O. * syscall: (libc)System Calls. * sysconf: (libc)Sysconf Definition. * syslog: (libc)syslog; vsyslog. * system: (libc)Running a Command. * sysv_signal: (libc)Basic Signal Handling. * tan: (libc)Trig Functions. * tanf: (libc)Trig Functions. * tanfN: (libc)Trig Functions. * tanfNx: (libc)Trig Functions. * tanh: (libc)Hyperbolic Functions. * tanhf: (libc)Hyperbolic Functions. * tanhfN: (libc)Hyperbolic Functions. * tanhfNx: (libc)Hyperbolic Functions. * tanhl: (libc)Hyperbolic Functions. * tanl: (libc)Trig Functions. * tanpi: (libc)Trig Functions. * tanpif: (libc)Trig Functions. * tanpifN: (libc)Trig Functions. * tanpifNx: (libc)Trig Functions. * tanpil: (libc)Trig Functions. * tcdrain: (libc)Line Control. * tcflow: (libc)Line Control. * tcflush: (libc)Line Control. * tcgetattr: (libc)Mode Functions. * tcgetpgrp: (libc)Terminal Access Functions. * tcgetsid: (libc)Terminal Access Functions. * tcsendbreak: (libc)Line Control. * tcsetattr: (libc)Mode Functions. * tcsetpgrp: (libc)Terminal Access Functions. * tdelete: (libc)Tree Search Function. * tdestroy: (libc)Tree Search Function. * telldir: (libc)Random Access Directory. * tempnam: (libc)Temporary Files. * textdomain: (libc)Locating gettext catalog. * tfind: (libc)Tree Search Function. * tgamma: (libc)Special Functions. * tgammaf: (libc)Special Functions. * tgammafN: (libc)Special Functions. * tgammafNx: (libc)Special Functions. * tgammal: (libc)Special Functions. * tgkill: (libc)Signaling Another Process. * thrd_create: (libc)ISO C Thread Management. * thrd_current: (libc)ISO C Thread Management. * thrd_detach: (libc)ISO C Thread Management. * thrd_equal: (libc)ISO C Thread Management. * thrd_exit: (libc)ISO C Thread Management. * thrd_join: (libc)ISO C Thread Management. * thrd_sleep: (libc)ISO C Thread Management. * thrd_yield: (libc)ISO C Thread Management. * time: (libc)Getting the Time. * timegm: (libc)Broken-down Time. * timelocal: (libc)Broken-down Time. * times: (libc)Processor Time. * timespec_get: (libc)Getting the Time. * timespec_getres: (libc)Getting the Time. * tmpfile64: (libc)Temporary Files. * tmpfile: (libc)Temporary Files. * tmpnam: (libc)Temporary Files. * tmpnam_r: (libc)Temporary Files. * toascii: (libc)Case Conversion. * tolower: (libc)Case Conversion. * totalorder: (libc)FP Comparison Functions. * totalorderf: (libc)FP Comparison Functions. * totalorderfN: (libc)FP Comparison Functions. * totalorderfNx: (libc)FP Comparison Functions. * totalorderl: (libc)FP Comparison Functions. * totalordermag: (libc)FP Comparison Functions. * totalordermagf: (libc)FP Comparison Functions. * totalordermagfN: (libc)FP Comparison Functions. * totalordermagfNx: (libc)FP Comparison Functions. * totalordermagl: (libc)FP Comparison Functions. * toupper: (libc)Case Conversion. * towctrans: (libc)Wide Character Case Conversion. * towlower: (libc)Wide Character Case Conversion. * towupper: (libc)Wide Character Case Conversion. * trunc: (libc)Rounding Functions. * truncate64: (libc)File Size. * truncate: (libc)File Size. * truncf: (libc)Rounding Functions. * truncfN: (libc)Rounding Functions. * truncfNx: (libc)Rounding Functions. * truncl: (libc)Rounding Functions. * tsearch: (libc)Tree Search Function. * tss_create: (libc)ISO C Thread-local Storage. * tss_delete: (libc)ISO C Thread-local Storage. * tss_get: (libc)ISO C Thread-local Storage. * tss_set: (libc)ISO C Thread-local Storage. * ttyname: (libc)Is It a Terminal. * ttyname_r: (libc)Is It a Terminal. * twalk: (libc)Tree Search Function. * twalk_r: (libc)Tree Search Function. * tzset: (libc)Time Zone State. * ufromfp: (libc)Rounding Functions. * ufromfpf: (libc)Rounding Functions. * ufromfpfN: (libc)Rounding Functions. * ufromfpfNx: (libc)Rounding Functions. * ufromfpl: (libc)Rounding Functions. * ufromfpx: (libc)Rounding Functions. * ufromfpxf: (libc)Rounding Functions. * ufromfpxfN: (libc)Rounding Functions. * ufromfpxfNx: (libc)Rounding Functions. * ufromfpxl: (libc)Rounding Functions. * ulimit: (libc)Limits on Resources. * umask: (libc)Setting Permissions. * umount2: (libc)Mount-Unmount-Remount. * umount: (libc)Mount-Unmount-Remount. * uname: (libc)Platform Type. * ungetc: (libc)How Unread. * ungetwc: (libc)How Unread. * unlink: (libc)Deleting Files. * unlockpt: (libc)Allocation. * unsetenv: (libc)Environment Access. * updwtmp: (libc)Manipulating the Database. * utime: (libc)File Times. * utimes: (libc)File Times. * utmpname: (libc)Manipulating the Database. * utmpxname: (libc)XPG Functions. * va_arg: (libc)Argument Macros. * va_copy: (libc)Argument Macros. * va_end: (libc)Argument Macros. * va_start: (libc)Argument Macros. * valloc: (libc)Aligned Memory Blocks. * vasprintf: (libc)Variable Arguments Output. * vdprintf: (libc)Variable Arguments Output. * verr: (libc)Error Messages. * verrx: (libc)Error Messages. * versionsort64: (libc)Scanning Directory Content. * versionsort: (libc)Scanning Directory Content. * vfork: (libc)Creating a Process. * vfprintf: (libc)Variable Arguments Output. * vfscanf: (libc)Variable Arguments Input. * vfwprintf: (libc)Variable Arguments Output. * vfwscanf: (libc)Variable Arguments Input. * vlimit: (libc)Limits on Resources. * vprintf: (libc)Variable Arguments Output. * vscanf: (libc)Variable Arguments Input. * vsnprintf: (libc)Variable Arguments Output. * vsprintf: (libc)Variable Arguments Output. * vsscanf: (libc)Variable Arguments Input. * vswprintf: (libc)Variable Arguments Output. * vswscanf: (libc)Variable Arguments Input. * vsyslog: (libc)syslog; vsyslog. * vwarn: (libc)Error Messages. * vwarnx: (libc)Error Messages. * vwprintf: (libc)Variable Arguments Output. * vwscanf: (libc)Variable Arguments Input. * wait3: (libc)BSD Wait Functions. * wait4: (libc)Process Completion. * wait: (libc)Process Completion. * waitpid: (libc)Process Completion. * warn: (libc)Error Messages. * warnx: (libc)Error Messages. * wcpcpy: (libc)Copying Strings and Arrays. * wcpncpy: (libc)Truncating Strings. * wcrtomb: (libc)Converting a Character. * wcscasecmp: (libc)String/Array Comparison. * wcscat: (libc)Concatenating Strings. * wcschr: (libc)Search Functions. * wcschrnul: (libc)Search Functions. * wcscmp: (libc)String/Array Comparison. * wcscoll: (libc)Collation Functions. * wcscpy: (libc)Copying Strings and Arrays. * wcscspn: (libc)Search Functions. * wcsdup: (libc)Copying Strings and Arrays. * wcsftime: (libc)Formatting Calendar Time. * wcslcat: (libc)Truncating Strings. * wcslcpy: (libc)Truncating Strings. * wcslen: (libc)String Length. * wcsncasecmp: (libc)String/Array Comparison. * wcsncat: (libc)Truncating Strings. * wcsncmp: (libc)String/Array Comparison. * wcsncpy: (libc)Truncating Strings. * wcsnlen: (libc)String Length. * wcsnrtombs: (libc)Converting Strings. * wcspbrk: (libc)Search Functions. * wcsrchr: (libc)Search Functions. * wcsrtombs: (libc)Converting Strings. * wcsspn: (libc)Search Functions. * wcsstr: (libc)Search Functions. * wcstod: (libc)Parsing of Floats. * wcstof: (libc)Parsing of Floats. * wcstofN: (libc)Parsing of Floats. * wcstofNx: (libc)Parsing of Floats. * wcstoimax: (libc)Parsing of Integers. * wcstok: (libc)Finding Tokens in a String. * wcstol: (libc)Parsing of Integers. * wcstold: (libc)Parsing of Floats. * wcstoll: (libc)Parsing of Integers. * wcstombs: (libc)Non-reentrant String Conversion. * wcstoq: (libc)Parsing of Integers. * wcstoul: (libc)Parsing of Integers. * wcstoull: (libc)Parsing of Integers. * wcstoumax: (libc)Parsing of Integers. * wcstouq: (libc)Parsing of Integers. * wcswcs: (libc)Search Functions. * wcsxfrm: (libc)Collation Functions. * wctob: (libc)Converting a Character. * wctomb: (libc)Non-reentrant Character Conversion. * wctrans: (libc)Wide Character Case Conversion. * wctype: (libc)Classification of Wide Characters. * wmemchr: (libc)Search Functions. * wmemcmp: (libc)String/Array Comparison. * wmemcpy: (libc)Copying Strings and Arrays. * wmemmove: (libc)Copying Strings and Arrays. * wmempcpy: (libc)Copying Strings and Arrays. * wmemset: (libc)Copying Strings and Arrays. * wordexp: (libc)Calling Wordexp. * wordfree: (libc)Calling Wordexp. * wprintf: (libc)Formatted Output Functions. * write: (libc)I/O Primitives. * writev: (libc)Scatter-Gather. * wscanf: (libc)Formatted Input Functions. * y0: (libc)Special Functions. * y0f: (libc)Special Functions. * y0fN: (libc)Special Functions. * y0fNx: (libc)Special Functions. * y0l: (libc)Special Functions. * y1: (libc)Special Functions. * y1f: (libc)Special Functions. * y1fN: (libc)Special Functions. * y1fNx: (libc)Special Functions. * y1l: (libc)Special Functions. * yn: (libc)Special Functions. * ynf: (libc)Special Functions. * ynfN: (libc)Special Functions. * ynfNx: (libc)Special Functions. * ynl: (libc)Special Functions. END-INFO-DIR-ENTRY  File: libc.info, Node: Open File Description Locks, Next: Open File Description Locks Example, Prev: File Locks, Up: Low-Level I/O 13.17 Open File Description Locks ================================= In contrast to process-associated record locks (*note File Locks::), open file description record locks are associated with an open file description rather than a process. Using ‘fcntl’ to apply an open file description lock on a region that already has an existing open file description lock that was created via the same file descriptor will never cause a lock conflict. Open file description locks are also inherited by child processes across ‘fork’, or ‘clone’ with ‘CLONE_FILES’ set (*note Creating a Process::), along with the file descriptor. It is important to distinguish between the open file _description_ (an instance of an open file, usually created by a call to ‘open’) and an open file _descriptor_, which is a numeric value that refers to the open file description. The locks described here are associated with the open file _description_ and not the open file _descriptor_. Using ‘dup’ (*note Duplicating Descriptors::) to copy a file descriptor does not give you a new open file description, but rather copies a reference to an existing open file description and assigns it to a new file descriptor. Thus, open file description locks set on a file descriptor cloned by ‘dup’ will never conflict with open file description locks set on the original descriptor since they refer to the same open file description. Depending on the range and type of lock involved, the original lock may be modified by a ‘F_OFD_SETLK’ or ‘F_OFD_SETLKW’ command in this situation however. Open file description locks always conflict with process-associated locks, even if acquired by the same process or on the same open file descriptor. Open file description locks use the same ‘struct flock’ as process-associated locks as an argument (*note File Locks::) and the macros for the ‘command’ values are also declared in the header file ‘fcntl.h’. To use them, the macro ‘_GNU_SOURCE’ must be defined prior to including any header file. In contrast to process-associated locks, any ‘struct flock’ used as an argument to open file description lock commands must have the ‘l_pid’ value set to 0. Also, when returning information about an open file description lock in a ‘F_GETLK’ or ‘F_OFD_GETLK’ request, the ‘l_pid’ field in ‘struct flock’ will be set to -1 to indicate that the lock is not associated with a process. When the same ‘struct flock’ is reused as an argument to a ‘F_OFD_SETLK’ or ‘F_OFD_SETLKW’ request after being used for an ‘F_OFD_GETLK’ request, it is necessary to inspect and reset the ‘l_pid’ field to 0. -- Macro: int F_OFD_GETLK This macro is used as the COMMAND argument to ‘fcntl’, to specify that it should get information about a lock. This command requires a third argument of type ‘struct flock *’ to be passed to ‘fcntl’, so that the form of the call is: fcntl (FILEDES, F_OFD_GETLK, LOCKP) If there is a lock already in place that would block the lock described by the LOCKP argument, information about that lock is written to ‘*LOCKP’. Existing locks are not reported if they are compatible with making a new lock as specified. Thus, you should specify a lock type of ‘F_WRLCK’ if you want to find out about both read and write locks, or ‘F_RDLCK’ if you want to find out about write locks only. There might be more than one lock affecting the region specified by the LOCKP argument, but ‘fcntl’ only returns information about one of them. Which lock is returned in this situation is undefined. The ‘l_whence’ member of the LOCKP structure are set to ‘SEEK_SET’ and the ‘l_start’ and ‘l_len’ fields are set to identify the locked region. If no conflicting lock exists, the only change to the LOCKP structure is to update the ‘l_type’ field to the value ‘F_UNLCK’. The normal return value from ‘fcntl’ with this command is either 0 on success or -1, which indicates an error. The following ‘errno’ error conditions are defined for this command: ‘EBADF’ The FILEDES argument is invalid. ‘EINVAL’ Either the LOCKP argument doesn't specify valid lock information, the operating system kernel doesn't support open file description locks, or the file associated with FILEDES doesn't support locks. -- Macro: int F_OFD_SETLK This macro is used as the COMMAND argument to ‘fcntl’, to specify that it should set or clear a lock. This command requires a third argument of type ‘struct flock *’ to be passed to ‘fcntl’, so that the form of the call is: fcntl (FILEDES, F_OFD_SETLK, LOCKP) If the open file already has a lock on any part of the region, the old lock on that part is replaced with the new lock. You can remove a lock by specifying a lock type of ‘F_UNLCK’. If the lock cannot be set, ‘fcntl’ returns immediately with a value of -1. This command does not wait for other tasks to release locks. If ‘fcntl’ succeeds, it returns 0. The following ‘errno’ error conditions are defined for this command: ‘EAGAIN’ The lock cannot be set because it is blocked by an existing lock on the file. ‘EBADF’ Either: the FILEDES argument is invalid; you requested a read lock but the FILEDES is not open for read access; or, you requested a write lock but the FILEDES is not open for write access. ‘EINVAL’ Either the LOCKP argument doesn't specify valid lock information, the operating system kernel doesn't support open file description locks, or the file associated with FILEDES doesn't support locks. ‘ENOLCK’ The system has run out of file lock resources; there are already too many file locks in place. Well-designed file systems never report this error, because they have no limitation on the number of locks. However, you must still take account of the possibility of this error, as it could result from network access to a file system on another machine. -- Macro: int F_OFD_SETLKW This macro is used as the COMMAND argument to ‘fcntl’, to specify that it should set or clear a lock. It is just like the ‘F_OFD_SETLK’ command, but causes the process to wait until the request can be completed. This command requires a third argument of type ‘struct flock *’, as for the ‘F_OFD_SETLK’ command. The ‘fcntl’ return values and errors are the same as for the ‘F_OFD_SETLK’ command, but these additional ‘errno’ error conditions are defined for this command: ‘EINTR’ The function was interrupted by a signal while it was waiting. *Note Interrupted Primitives::. Open file description locks are useful in the same sorts of situations as process-associated locks. They can also be used to synchronize file access between threads within the same process by having each thread perform its own ‘open’ of the file, to obtain its own open file description. Because open file description locks are automatically freed only upon closing the last file descriptor that refers to the open file description, this locking mechanism avoids the possibility that locks are inadvertently released due to a library routine opening and closing a file without the application being aware. As with process-associated locks, open file description locks are advisory.  File: libc.info, Node: Open File Description Locks Example, Next: Interrupt Input, Prev: Open File Description Locks, Up: Low-Level I/O 13.18 Open File Description Locks Example ========================================= Here is an example of using open file description locks in a threaded program. If this program used process-associated locks, then it would be subject to data corruption because process-associated locks are shared by the threads inside a process, and thus cannot be used by one thread to lock out another thread in the same process. Proper error handling has been omitted in the following program for brevity. #define _GNU_SOURCE #include #include #include #include #include #include #define FILENAME "/tmp/foo" #define NUM_THREADS 3 #define ITERATIONS 5 void * thread_start (void *arg) { int i, fd, len; long tid = (long) arg; char buf[256]; struct flock lck = { .l_whence = SEEK_SET, .l_start = 0, .l_len = 1, }; fd = open ("/tmp/foo", O_RDWR | O_CREAT, 0666); for (i = 0; i < ITERATIONS; i++) { lck.l_type = F_WRLCK; fcntl (fd, F_OFD_SETLKW, &lck); len = sprintf (buf, "%d: tid=%ld fd=%d\n", i, tid, fd); lseek (fd, 0, SEEK_END); write (fd, buf, len); fsync (fd); lck.l_type = F_UNLCK; fcntl (fd, F_OFD_SETLK, &lck); /* sleep to ensure lock is yielded to another thread */ usleep (1); } pthread_exit (NULL); } int main (int argc, char **argv) { long i; pthread_t threads[NUM_THREADS]; truncate (FILENAME, 0); for (i = 0; i < NUM_THREADS; i++) pthread_create (&threads[i], NULL, thread_start, (void *) i); pthread_exit (NULL); return 0; } This example creates three threads each of which loops five times, appending to the file. Access to the file is serialized via open file description locks. If we compile and run the above program, we'll end up with /tmp/foo that has 15 lines in it. If we, however, were to replace the ‘F_OFD_SETLK’ and ‘F_OFD_SETLKW’ commands with their process-associated lock equivalents, the locking essentially becomes a noop since it is all done within the context of the same process. That leads to data corruption (typically manifested as missing lines) as some threads race in and overwrite the data written by others.  File: libc.info, Node: Interrupt Input, Next: IOCTLs, Prev: Open File Description Locks Example, Up: Low-Level I/O 13.19 Interrupt-Driven Input ============================ If you set the ‘O_ASYNC’ status flag on a file descriptor (*note File Status Flags::), a ‘SIGIO’ signal is sent whenever input or output becomes possible on that file descriptor. The process or process group to receive the signal can be selected by using the ‘F_SETOWN’ command to the ‘fcntl’ function. If the file descriptor is a socket, this also selects the recipient of ‘SIGURG’ signals that are delivered when out-of-band data arrives on that socket; see *note Out-of-Band Data::. (‘SIGURG’ is sent in any situation where ‘select’ would report the socket as having an "exceptional condition". *Note Waiting for I/O::.) If the file descriptor corresponds to a terminal device, then ‘SIGIO’ signals are sent to the foreground process group of the terminal. *Note Job Control::. The symbols in this section are defined in the header file ‘fcntl.h’. -- Macro: int F_GETOWN This macro is used as the COMMAND argument to ‘fcntl’, to specify that it should get information about the process or process group to which ‘SIGIO’ signals are sent. (For a terminal, this is actually the foreground process group ID, which you can get using ‘tcgetpgrp’; see *note Terminal Access Functions::.) The return value is interpreted as a process ID; if negative, its absolute value is the process group ID. The following ‘errno’ error condition is defined for this command: ‘EBADF’ The FILEDES argument is invalid. -- Macro: int F_SETOWN This macro is used as the COMMAND argument to ‘fcntl’, to specify that it should set the process or process group to which ‘SIGIO’ signals are sent. This command requires a third argument of type ‘pid_t’ to be passed to ‘fcntl’, so that the form of the call is: fcntl (FILEDES, F_SETOWN, PID) The PID argument should be a process ID. You can also pass a negative number whose absolute value is a process group ID. The return value from ‘fcntl’ with this command is -1 in case of error and some other value if successful. The following ‘errno’ error conditions are defined for this command: ‘EBADF’ The FILEDES argument is invalid. ‘ESRCH’ There is no process or process group corresponding to PID.  File: libc.info, Node: IOCTLs, Next: Other Low-Level I/O APIs, Prev: Interrupt Input, Up: Low-Level I/O 13.20 Generic I/O Control operations ==================================== GNU systems can handle most input/output operations on many different devices and objects in terms of a few file primitives - ‘read’, ‘write’ and ‘lseek’. However, most devices also have a few peculiar operations which do not fit into this model. Such as: • Changing the character font used on a terminal. • Telling a magnetic tape system to rewind or fast forward. (Since they cannot move in byte increments, ‘lseek’ is inapplicable). • Ejecting a disk from a drive. • Playing an audio track from a CD-ROM drive. • Maintaining routing tables for a network. Although some such objects such as sockets and terminals (1) have special functions of their own, it would not be practical to create functions for all these cases. Instead these minor operations, known as “IOCTL”s, are assigned code numbers and multiplexed through the ‘ioctl’ function, defined in ‘sys/ioctl.h’. The code numbers themselves are defined in many different headers. -- Function: int ioctl (int FILEDES, int COMMAND, ...) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘ioctl’ function performs the generic I/O operation COMMAND on FILEDES. A third argument is usually present, either a single number or a pointer to a structure. The meaning of this argument, the returned value, and any error codes depends upon the command used. Often -1 is returned for a failure. On some systems, IOCTLs used by different devices share the same numbers. Thus, although use of an inappropriate IOCTL _usually_ only produces an error, you should not attempt to use device-specific IOCTLs on an unknown device. Most IOCTLs are OS-specific and/or only used in special system utilities, and are thus beyond the scope of this document. For an example of the use of an IOCTL, see *note Out-of-Band Data::. ---------- Footnotes ---------- (1) Actually, the terminal-specific functions are implemented with IOCTLs on many platforms.  File: libc.info, Node: Other Low-Level I/O APIs, Prev: IOCTLs, Up: Low-Level I/O 13.21 Other low-level-I/O-related functions =========================================== -- Data Type: struct pollfd -- Data Type: struct epoll_event -- Function: int poll (struct pollfd *FDS, nfds_t NFDS, int TIMEOUT) This documentation is a stub. For additional information on this function, consult the manual page . *Note Linux Kernel::. -- Function: int epoll_create (int SIZE) This documentation is a stub. For additional information on this function, consult the manual page . *Note Linux Kernel::. -- Function: int epoll_wait (int EPFD, struct epoll_event *EVENTS, int MAXEVENTS, int TIMEOUT) This documentation is a stub. For additional information on this function, consult the manual page . *Note Linux Kernel::.  File: libc.info, Node: File System Interface, Next: Pipes and FIFOs, Prev: Low-Level I/O, Up: Top 14 File System Interface ************************ This chapter describes the GNU C Library's functions for manipulating files. Unlike the input and output functions (*note I/O on Streams::; *note Low-Level I/O::), these functions are concerned with operating on the files themselves rather than on their contents. Among the facilities described in this chapter are functions for examining or modifying directories, functions for renaming and deleting files, and functions for examining and setting file attributes such as access permissions and modification times. * Menu: * Working Directory:: This is used to resolve relative file names. * Descriptor-Relative Access:: Ways to control file name lookup. * Accessing Directories:: Finding out what files a directory contains. * Working with Directory Trees:: Apply actions to all files or a selectable subset of a directory hierarchy. * Hard Links:: Adding alternate names to a file. * Symbolic Links:: A file that "points to" a file name. * Deleting Files:: How to delete a file, and what that means. * Renaming Files:: Changing a file's name. * Creating Directories:: A system call just for creating a directory. * File Attributes:: Attributes of individual files. * Making Special Files:: How to create special files. * Temporary Files:: Naming and creating temporary files.  File: libc.info, Node: Working Directory, Next: Descriptor-Relative Access, Up: File System Interface 14.1 Working Directory ====================== Each process has associated with it a directory, called its “current working directory” or simply “working directory”, that is used in the resolution of relative file names (*note File Name Resolution::). When you log in and begin a new session, your working directory is initially set to the home directory associated with your login account in the system user database. You can find any user's home directory using the ‘getpwuid’ or ‘getpwnam’ functions; see *note User Database::. Users can change the working directory using shell commands like ‘cd’. The functions described in this section are the primitives used by those commands and by other programs for examining and changing the working directory. Prototypes for these functions are declared in the header file ‘unistd.h’. -- Function: char * getcwd (char *BUFFER, size_t SIZE) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘getcwd’ function returns an absolute file name representing the current working directory, storing it in the character array BUFFER that you provide. The SIZE argument is how you tell the system the allocation size of BUFFER. The GNU C Library version of this function also permits you to specify a null pointer for the BUFFER argument. Then ‘getcwd’ allocates a buffer automatically, as with ‘malloc’ (*note Unconstrained Allocation::). If the SIZE is greater than zero, then the buffer is that large; otherwise, the buffer is as large as necessary to hold the result. The return value is BUFFER on success and a null pointer on failure. The following ‘errno’ error conditions are defined for this function: ‘EINVAL’ The SIZE argument is zero and BUFFER is not a null pointer. ‘ERANGE’ The SIZE argument is less than the length of the working directory name. You need to allocate a bigger array and try again. ‘EACCES’ Permission to read or search a component of the file name was denied. You could implement the behavior of GNU's ‘getcwd (NULL, 0)’ using only the standard behavior of ‘getcwd’: char * gnu_getcwd () { size_t size = 100; while (1) { char *buffer = (char *) xmalloc (size); if (getcwd (buffer, size) == buffer) return buffer; free (buffer); if (errno != ERANGE) return 0; size *= 2; } } *Note Malloc Examples::, for information about ‘xmalloc’, which is not a library function but is a customary name used in most GNU software. -- Deprecated Function: char * getwd (char *BUFFER) Preliminary: | MT-Safe | AS-Unsafe heap i18n | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. This is similar to ‘getcwd’, but has no way to specify the size of the buffer. The GNU C Library provides ‘getwd’ only for backwards compatibility with BSD. The BUFFER argument should be a pointer to an array at least ‘PATH_MAX’ bytes long (*note Limits for Files::). On GNU/Hurd systems there is no limit to the size of a file name, so this is not necessarily enough space to contain the directory name. That is why this function is deprecated. -- Function: char * get_current_dir_name (void) Preliminary: | MT-Safe env | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘get_current_dir_name’ function is basically equivalent to ‘getcwd (NULL, 0)’, except the value of the ‘PWD’ environment variable is first examined, and if it does in fact correspond to the current directory, that value is returned. This is a subtle difference which is visible if the path described by the value in ‘PWD’ is using one or more symbolic links, in which case the value returned by ‘getcwd’ would resolve the symbolic links and therefore yield a different result. This function is a GNU extension. -- Function: int chdir (const char *FILENAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is used to set the process's working directory to FILENAME. The normal, successful return value from ‘chdir’ is ‘0’. A value of ‘-1’ is returned to indicate an error. The ‘errno’ error conditions defined for this function are the usual file name syntax errors (*note File Name Errors::), plus ‘ENOTDIR’ if the file FILENAME is not a directory. -- Function: int fchdir (int FILEDES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is used to set the process's working directory to directory associated with the file descriptor FILEDES. The normal, successful return value from ‘fchdir’ is ‘0’. A value of ‘-1’ is returned to indicate an error. The following ‘errno’ error conditions are defined for this function: ‘EACCES’ Read permission is denied for the directory named by ‘dirname’. ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘ENOTDIR’ The file descriptor FILEDES is not associated with a directory. ‘EINTR’ The function call was interrupt by a signal. ‘EIO’ An I/O error occurred.  File: libc.info, Node: Descriptor-Relative Access, Next: Accessing Directories, Prev: Working Directory, Up: File System Interface 14.2 Descriptor-Relative Access =============================== Many functions that accept file names have ‘...at’ variants which accept a file descriptor and a file name argument instead of just a file name argument. For example, ‘fstatat’ is the descriptor-based variant of the ‘fstat’ function. Most such functions also accept an additional flags argument which changes the behavior of the file name lookup based on the passed ‘AT_...’ flags. There are several reasons to use descriptor-relative access: • The working directory is a process-wide resource, so individual threads cannot change it without affecting other threads in the process. Explicitly specifying the directory against which relative paths are resolved can be a thread-safe alternative to changing the working directory. • If a program wishes to access a directory tree which is being modified concurrently, perhaps even by a different user on the system, the program must avoid looking up file names with multiple components, in order to detect symbolic links, using the ‘O_NOFOLLOW’ flag (*note Open-time Flags::) or the ‘AT_SYMLINK_FOLLOW’ flag (described below). Without directory-relative access, it is necessary to use the ‘fchdir’ function to change the working directory (*note Working Directory::), which is not thread-safe. • Listing directory contents using the ‘readdir’ or ‘readdir64’ functions (*note Reading/Closing Directory::) does not provide full file name paths. Using ‘...at’ functions, it is possible to use the file names directly, without having to construct such full paths. • Additional flags available with some of the ‘...at’ functions provide access to functionality which is not available otherwise. The file descriptor used by these ‘...at’ functions has the following uses: • It can be a file descriptor referring to a directory. Such a descriptor can be created explicitly using the ‘open’ function and the ‘O_RDONLY’ file access mode, with or without the ‘O_DIRECTORY’ flag. *Note Opening and Closing Files::. Or it can be created implicitly by ‘opendir’ and retrieved using the ‘dirfd’ function. *Note Opening a Directory::. If a directory descriptor is used with one of the ‘...at’ functions, a relative file name argument is resolved relative to directory referred to by the file descriptor, just as if that directory were the current working directory. Absolute file name arguments (starting with ‘/’) are resolved against the file system root, and the descriptor argument is effectively ignored. This means that file name lookup is not constrained to the directory of the descriptor. For example, it is possible to access a file ‘example’ in the descriptor's parent directory using a file name argument ‘"../example"’, or in the root directory using ‘"/example"’. If the file descriptor refers to a directory, the empty string ‘""’ is not a valid file name argument. It is possible to use ‘"."’ to refer to the directory itself. Also see ‘AT_EMPTY_PATH’ below. • The special value ‘AT_FDCWD’. This means that the current working directory is used for the lookup if the file name is a relative. For ‘...at’ functions with an ‘AT_...’ flags argument, this provides a shortcut to use those flags with regular (not descriptor-based) file name lookups. If ‘AT_FDCWD’ is used, the empty string ‘""’ is not a valid file name argument. • An arbitrary file descriptor, along with an empty string ‘""’ as the file name argument, and the ‘AT_EMPTY_PATH’ flag. In this case, the operation uses the file descriptor directly, without further file name resolution. On Linux, this allows operations on descriptors opened with the ‘O_PATH’ flag. For regular descriptors (opened without ‘O_PATH’), the same functionality is also available through the plain descriptor-based functions (for example, ‘fstat’ instead of ‘fstatat’). This is a GNU extension. The flags argument in ‘...at’ functions can be a combination of the following flags, defined in ‘fcntl.h’. Not all such functions support all flags, and some (such as ‘openat’) do not accept a flags argument at all. In the flag descriptions below, the “effective final path component” refers to the final component (basename) of the full path constructed from the descriptor and file name arguments, using file name lookup, as described above. ‘AT_EMPTY_PATH’ This flag is used with an empty file name ‘""’ and a descriptor which does not necessarily refer to a directory. It is most useful with ‘O_PATH’ descriptors, as described above. This flag is a GNU extension. ‘AT_NO_AUTOMOUNT’ If the effective final path component refers to a potential file system mount point controlled by an auto-mounting service, the operation does not trigger auto-mounting and refers to the unmounted mount point instead. *Note Mount-Unmount-Remount::. If a file system has already been mounted at the effective final path component, the operation applies to the file or directory in the mounted file system, not the underlying file system that was mounted over. This flag is a GNU extension. ‘AT_SYMLINK_FOLLOW’ If the effective final path component is a symbolic link, the operation follows the symbolic link and operates on its target. (For most functions, this is the default behavior.) ‘AT_SYMLINK_NOFOLLOW’ If the effective final path component is a symbolic link, the operation operates on the symbolic link, without following it. The difference in behavior enabled by this flag is similar to the difference between the ‘lstat’ and ‘stat’ functions, or the behavior activated by the ‘O_NOFOLLOW’ argument to the ‘open’ function. Even with the ‘AT_SYMLINK_NOFOLLOW’ flag present, symbolic links in a non-final component of the file name are still followed. *Note:* There is no relationship between these flags and the type argument to the ‘getauxval’ function (with ‘AT_...’ constants defined in ‘elf.h’). *Note Auxiliary Vector::.  File: libc.info, Node: Accessing Directories, Next: Working with Directory Trees, Prev: Descriptor-Relative Access, Up: File System Interface 14.3 Accessing Directories ========================== The facilities described in this section let you read the contents of a directory file. This is useful if you want your program to list all the files in a directory, perhaps as part of a menu. The ‘opendir’ function opens a “directory stream” whose elements are directory entries. Alternatively ‘fdopendir’ can be used which can have advantages if the program needs to have more control over the way the directory is opened for reading. This allows, for instance, to pass the ‘O_NOATIME’ flag to ‘open’. You use the ‘readdir’ function on the directory stream to retrieve these entries, represented as ‘struct dirent’ objects. The name of the file for each entry is stored in the ‘d_name’ member of this structure. There are obvious parallels here to the stream facilities for ordinary files, described in *note I/O on Streams::. * Menu: * Directory Entries:: Format of one directory entry. * Opening a Directory:: How to open a directory stream. * Reading/Closing Directory:: How to read directory entries from the stream. * Simple Directory Lister:: A very simple directory listing program. * Random Access Directory:: Rereading part of the directory already read with the same stream. * Scanning Directory Content:: Get entries for user selected subset of contents in given directory. * Simple Directory Lister Mark II:: Revised version of the program. * Low-level Directory Access:: AS-Safe functions for directory access.  File: libc.info, Node: Directory Entries, Next: Opening a Directory, Up: Accessing Directories 14.3.1 Format of a Directory Entry ---------------------------------- This section describes what you find in a single directory entry, as you might obtain it from a directory stream. All the symbols are declared in the header file ‘dirent.h’. -- Data Type: struct dirent This is a structure type used to return information about directory entries. It contains the following fields: ‘char d_name[]’ This is the null-terminated file name component. This is the only field you can count on in all POSIX systems. ‘ino_t d_fileno’ This is the file serial number. For BSD compatibility, you can also refer to this member as ‘d_ino’. On GNU/Linux and GNU/Hurd systems and most POSIX systems, for most files this the same as the ‘st_ino’ member that ‘stat’ will return for the file. *Note File Attributes::. ‘unsigned char d_namlen’ This is the length of the file name, not including the terminating null character. Its type is ‘unsigned char’ because that is the integer type of the appropriate size. This member is a BSD extension. The symbol ‘_DIRENT_HAVE_D_NAMLEN’ is defined if this member is available. ‘unsigned char d_type’ This is the type of the file, possibly unknown. The following constants are defined for its value: ‘DT_UNKNOWN’ The type is unknown. Only some filesystems have full support to return the type of the file, others might always return this value. ‘DT_REG’ A regular file. ‘DT_DIR’ A directory. ‘DT_FIFO’ A named pipe, or FIFO. *Note FIFO Special Files::. ‘DT_SOCK’ A local-domain socket. ‘DT_CHR’ A character device. ‘DT_BLK’ A block device. ‘DT_LNK’ A symbolic link. This member is a BSD extension. The symbol ‘_DIRENT_HAVE_D_TYPE’ is defined if this member is available. On systems where it is used, it corresponds to the file type bits in the ‘st_mode’ member of ‘struct stat’. If the value cannot be determined the member value is DT_UNKNOWN. These two macros convert between ‘d_type’ values and ‘st_mode’ values: -- Function: int IFTODT (mode_t MODE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This returns the ‘d_type’ value corresponding to MODE. -- Function: mode_t DTTOIF (int DTYPE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This returns the ‘st_mode’ value corresponding to DTYPE. This structure may contain additional members in the future. Their availability is always announced in the compilation environment by a macro named ‘_DIRENT_HAVE_D_XXX’ where XXX is replaced by the name of the new member. For instance, the member ‘d_reclen’ available on some systems is announced through the macro ‘_DIRENT_HAVE_D_RECLEN’. When a file has multiple names, each name has its own directory entry. The only way you can tell that the directory entries belong to a single file is that they have the same value for the ‘d_fileno’ field. File attributes such as size, modification times etc., are part of the file itself, not of any particular directory entry. *Note File Attributes::.  File: libc.info, Node: Opening a Directory, Next: Reading/Closing Directory, Prev: Directory Entries, Up: Accessing Directories 14.3.2 Opening a Directory Stream --------------------------------- This section describes how to open a directory stream. All the symbols are declared in the header file ‘dirent.h’. -- Data Type: DIR The ‘DIR’ data type represents a directory stream. You shouldn't ever allocate objects of the ‘struct dirent’ or ‘DIR’ data types, since the directory access functions do that for you. Instead, you refer to these objects using the pointers returned by the following functions. Directory streams are a high-level interface. On Linux, alternative interfaces for accessing directories using file descriptors are available. *Note Low-level Directory Access::. -- Function: DIR * opendir (const char *DIRNAME) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘opendir’ function opens and returns a directory stream for reading the directory whose file name is DIRNAME. The stream has type ‘DIR *’. If unsuccessful, ‘opendir’ returns a null pointer. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ Read permission is denied for the directory named by ‘dirname’. ‘EMFILE’ The process has too many files open. ‘ENFILE’ The entire system, or perhaps the file system which contains the directory, cannot support any additional open files at the moment. (This problem cannot happen on GNU/Hurd systems.) ‘ENOMEM’ Not enough memory available. The ‘DIR’ type is typically implemented using a file descriptor, and the ‘opendir’ function in terms of the ‘open’ function. *Note Low-Level I/O::. Directory streams and the underlying file descriptors are closed on ‘exec’ (*note Executing a File::). The directory which is opened for reading by ‘opendir’ is identified by the name. In some situations this is not sufficient. Or the way ‘opendir’ implicitly creates a file descriptor for the directory is not the way a program might want it. In these cases an alternative interface can be used. -- Function: DIR * fdopendir (int FD) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘fdopendir’ function works just like ‘opendir’ but instead of taking a file name and opening a file descriptor for the directory the caller is required to provide a file descriptor. This file descriptor is then used in subsequent uses of the returned directory stream object. The caller must make sure the file descriptor is associated with a directory and it allows reading. If the ‘fdopendir’ call returns successfully the file descriptor is now under the control of the system. It can be used in the same way the descriptor implicitly created by ‘opendir’ can be used but the program must not close the descriptor. In case the function is unsuccessful it returns a null pointer and the file descriptor remains to be usable by the program. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The file descriptor is not valid. ‘ENOTDIR’ The file descriptor is not associated with a directory. ‘EINVAL’ The descriptor does not allow reading the directory content. ‘ENOMEM’ Not enough memory available. In some situations it can be desirable to get hold of the file descriptor which is created by the ‘opendir’ call. For instance, to switch the current working directory to the directory just read the ‘fchdir’ function could be used. Historically the ‘DIR’ type was exposed and programs could access the fields. This does not happen in the GNU C Library. Instead a separate function is provided to allow access. -- Function: int dirfd (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The function ‘dirfd’ returns the file descriptor associated with the directory stream DIRSTREAM. This descriptor can be used until the directory is closed with ‘closedir’. If the directory stream implementation is not using file descriptors the return value is ‘-1’.  File: libc.info, Node: Reading/Closing Directory, Next: Simple Directory Lister, Prev: Opening a Directory, Up: Accessing Directories 14.3.3 Reading and Closing a Directory Stream --------------------------------------------- This section describes how to read directory entries from a directory stream, and how to close the stream when you are done with it. All the symbols are declared in the header file ‘dirent.h’. -- Function: struct dirent * readdir (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note POSIX Safety Concepts::. This function reads the next entry from the directory. It normally returns a pointer to a structure containing information about the file. This structure is associated with the DIRSTREAM handle and can be rewritten by a subsequent call. *Portability Note:* On some systems ‘readdir’ may not return entries for ‘.’ and ‘..’, even though these are always valid file names in any directory. *Note File Name Resolution::. If there are no more entries in the directory or an error is detected, ‘readdir’ returns a null pointer. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The DIRSTREAM argument is not valid. To distinguish between an end-of-directory condition or an error, you must set ‘errno’ to zero before calling ‘readdir’. To avoid entering an infinite loop, you should stop reading from the directory after the first error. *Caution:* The pointer returned by ‘readdir’ points to a buffer within the ‘DIR’ object. The data in that buffer will be overwritten by the next call to ‘readdir’. You must take care, for instance, to copy the ‘d_name’ string if you need it later. Because of this, it is not safe to share a ‘DIR’ object among multiple threads, unless you use your own locking to ensure that no thread calls ‘readdir’ while another thread is still using the data from the previous call. In the GNU C Library, it is safe to call ‘readdir’ from multiple threads as long as each thread uses its own ‘DIR’ object. POSIX.1-2008 does not require this to be safe, but we are not aware of any operating systems where it does not work. ‘readdir_r’ allows you to provide your own buffer for the ‘struct dirent’, but it is less portable than ‘readdir’, and has problems with very long filenames (see below). We recommend you use ‘readdir’, but do not share ‘DIR’ objects. -- Function: int readdir_r (DIR *DIRSTREAM, struct dirent *ENTRY, struct dirent **RESULT) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note POSIX Safety Concepts::. This function is a version of ‘readdir’ which performs internal locking. Like ‘readdir’ it returns the next entry from the directory. To prevent conflicts between simultaneously running threads the result is stored inside the ENTRY object. *Portability Note:* ‘readdir_r’ is deprecated. It is recommended to use ‘readdir’ instead of ‘readdir_r’ for the following reasons: • On systems which do not define ‘NAME_MAX’, it may not be possible to use ‘readdir_r’ safely because the caller does not specify the length of the buffer for the directory entry. • On some systems, ‘readdir_r’ cannot read directory entries with very long names. If such a name is encountered, the GNU C Library implementation of ‘readdir_r’ returns with an error code of ‘ENAMETOOLONG’ after the final directory entry has been read. On other systems, ‘readdir_r’ may return successfully, but the ‘d_name’ member may not be NUL-terminated or may be truncated. • POSIX-1.2008 does not guarantee that ‘readdir’ is thread-safe, even when access to the same DIRSTREAM is serialized. But in current implementations (including the GNU C Library), it is safe to call ‘readdir’ concurrently on different DIRSTREAMs, so there is no need to use ‘readdir_r’ in most multi-threaded programs. In the rare case that multiple threads need to read from the same DIRSTREAM, it is still better to use ‘readdir’ and external synchronization. • It is expected that future versions of POSIX will obsolete ‘readdir_r’ and mandate the level of thread safety for ‘readdir’ which is provided by the GNU C Library and other implementations today. Normally ‘readdir_r’ returns zero and sets ‘*RESULT’ to ENTRY. If there are no more entries in the directory or an error is detected, ‘readdir_r’ sets ‘*RESULT’ to a null pointer and returns a nonzero error code, also stored in ‘errno’, as described for ‘readdir’. It is also important to look at the definition of the ‘struct dirent’ type. Simply passing a pointer to an object of this type for the second parameter of ‘readdir_r’ might not be enough. Some systems don't define the ‘d_name’ element sufficiently long. In this case the user has to provide additional space. There must be room for at least ‘NAME_MAX + 1’ characters in the ‘d_name’ array. Code to call ‘readdir_r’ could look like this: union { struct dirent d; char b[offsetof (struct dirent, d_name) + NAME_MAX + 1]; } u; if (readdir_r (dir, &u.d, &res) == 0) ... To support large filesystems on 32-bit machines there are LFS variants of the last two functions. -- Function: struct dirent64 * readdir64 (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note POSIX Safety Concepts::. The ‘readdir64’ function is just like the ‘readdir’ function except that it returns a pointer to a record of type ‘struct dirent64’. Some of the members of this data type (notably ‘d_ino’) might have a different size to allow large filesystems. In all other aspects this function is equivalent to ‘readdir’. -- Function: int readdir64_r (DIR *DIRSTREAM, struct dirent64 *ENTRY, struct dirent64 **RESULT) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note POSIX Safety Concepts::. The deprecated ‘readdir64_r’ function is equivalent to the ‘readdir_r’ function except that it takes parameters of base type ‘struct dirent64’ instead of ‘struct dirent’ in the second and third position. The same precautions mentioned in the documentation of ‘readdir_r’ also apply here. -- Function: int closedir (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Unsafe heap lock/hurd | AC-Unsafe mem fd lock/hurd | *Note POSIX Safety Concepts::. This function closes the directory stream DIRSTREAM. It returns ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The DIRSTREAM argument is not valid.  File: libc.info, Node: Simple Directory Lister, Next: Random Access Directory, Prev: Reading/Closing Directory, Up: Accessing Directories 14.3.4 Simple Program to List a Directory ----------------------------------------- Here's a simple program that prints the names of the files in the current working directory: #include #include #include int main (void) { DIR *dp; struct dirent *ep; dp = opendir ("./"); if (dp != NULL) { while (ep = readdir (dp)) puts (ep->d_name); (void) closedir (dp); } else perror ("Couldn't open the directory"); return 0; } The order in which files appear in a directory tends to be fairly random. A more useful program would sort the entries (perhaps by alphabetizing them) before printing them; see *note Scanning Directory Content::, and *note Array Sort Function::.  File: libc.info, Node: Random Access Directory, Next: Scanning Directory Content, Prev: Simple Directory Lister, Up: Accessing Directories 14.3.5 Random Access in a Directory Stream ------------------------------------------ This section describes how to reread parts of a directory that you have already read from an open directory stream. All the symbols are declared in the header file ‘dirent.h’. -- Function: void rewinddir (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock | *Note POSIX Safety Concepts::. The ‘rewinddir’ function is used to reinitialize the directory stream DIRSTREAM, so that if you call ‘readdir’ it returns information about the first entry in the directory again. This function also notices if files have been added or removed to the directory since it was opened with ‘opendir’. (Entries for these files might or might not be returned by ‘readdir’ if they were added or removed since you last called ‘opendir’ or ‘rewinddir’.) -- Function: long int telldir (DIR *DIRSTREAM) Preliminary: | MT-Safe | AS-Unsafe heap/bsd lock/bsd | AC-Unsafe mem/bsd lock/bsd | *Note POSIX Safety Concepts::. The ‘telldir’ function returns the file position of the directory stream DIRSTREAM. You can use this value with ‘seekdir’ to restore the directory stream to that position. -- Function: void seekdir (DIR *DIRSTREAM, long int POS) Preliminary: | MT-Safe | AS-Unsafe heap/bsd lock/bsd | AC-Unsafe mem/bsd lock/bsd | *Note POSIX Safety Concepts::. The ‘seekdir’ function sets the file position of the directory stream DIRSTREAM to POS. The value POS must be the result of a previous call to ‘telldir’ on this particular stream; closing and reopening the directory can invalidate values returned by ‘telldir’.  File: libc.info, Node: Scanning Directory Content, Next: Simple Directory Lister Mark II, Prev: Random Access Directory, Up: Accessing Directories 14.3.6 Scanning the Content of a Directory ------------------------------------------ A higher-level interface to the directory handling functions is the ‘scandir’ function. With its help one can select a subset of the entries in a directory, possibly sort them and get a list of names as the result. -- Function: int scandir (const char *DIR, struct dirent ***NAMELIST, int (*SELECTOR) (const struct dirent *), int (*CMP) (const struct dirent **, const struct dirent **)) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘scandir’ function scans the contents of the directory selected by DIR. The result in *NAMELIST is an array of pointers to structures of type ‘struct dirent’ which describe all selected directory entries and which is allocated using ‘malloc’. Instead of always getting all directory entries returned, the user supplied function SELECTOR can be used to decide which entries are in the result. Only the entries for which SELECTOR returns a non-zero value are selected. Finally the entries in *NAMELIST are sorted using the user-supplied function CMP. The arguments passed to the CMP function are of type ‘struct dirent **’, therefore one cannot directly use the ‘strcmp’ or ‘strcoll’ functions; instead see the functions ‘alphasort’ and ‘versionsort’ below. The return value of the function is the number of entries placed in *NAMELIST. If it is ‘-1’ an error occurred (either the directory could not be opened for reading or memory allocation failed) and the global variable ‘errno’ contains more information on the error. As described above, the fourth argument to the ‘scandir’ function must be a pointer to a sorting function. For the convenience of the programmer the GNU C Library contains implementations of functions which are very helpful for this purpose. -- Function: int alphasort (const struct dirent **A, const struct dirent **B) Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. The ‘alphasort’ function behaves like the ‘strcoll’ function (*note String/Array Comparison::). The difference is that the arguments are not string pointers but instead they are of type ‘struct dirent **’. The return value of ‘alphasort’ is less than, equal to, or greater than zero depending on the order of the two entries A and B. -- Function: int versionsort (const struct dirent **A, const struct dirent **B) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘versionsort’ function is like ‘alphasort’ except that it uses the ‘strverscmp’ function internally. If the filesystem supports large files we cannot use the ‘scandir’ anymore since the ‘dirent’ structure might not able to contain all the information. The LFS provides the new type ‘struct dirent64’. To use this we need a new function. -- Function: int scandir64 (const char *DIR, struct dirent64 ***NAMELIST, int (*SELECTOR) (const struct dirent64 *), int (*CMP) (const struct dirent64 **, const struct dirent64 **)) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘scandir64’ function works like the ‘scandir’ function except that the directory entries it returns are described by elements of type ‘struct dirent64’. The function pointed to by SELECTOR is again used to select the desired entries, except that SELECTOR now must point to a function which takes a ‘struct dirent64 *’ parameter. Similarly the CMP function should expect its two arguments to be of type ‘struct dirent64 **’. As CMP is now a function of a different type, the functions ‘alphasort’ and ‘versionsort’ cannot be supplied for that argument. Instead we provide the two replacement functions below. -- Function: int alphasort64 (const struct dirent64 **A, const struct dirent **B) Preliminary: | MT-Safe locale | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. The ‘alphasort64’ function behaves like the ‘strcoll’ function (*note String/Array Comparison::). The difference is that the arguments are not string pointers but instead they are of type ‘struct dirent64 **’. Return value of ‘alphasort64’ is less than, equal to, or greater than zero depending on the order of the two entries A and B. -- Function: int versionsort64 (const struct dirent64 **A, const struct dirent64 **B) Preliminary: | MT-Safe locale | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘versionsort64’ function is like ‘alphasort64’, excepted that it uses the ‘strverscmp’ function internally. It is important not to mix the use of ‘scandir’ and the 64-bit comparison functions or vice versa. There are systems on which this works but on others it will fail miserably.  File: libc.info, Node: Simple Directory Lister Mark II, Next: Low-level Directory Access, Prev: Scanning Directory Content, Up: Accessing Directories 14.3.7 Simple Program to List a Directory, Mark II -------------------------------------------------- Here is a revised version of the directory lister found above (*note Simple Directory Lister::). Using the ‘scandir’ function we can avoid the functions which work directly with the directory contents. After the call the returned entries are available for direct use. #include #include static int one (const struct dirent *unused) { return 1; } int main (void) { struct dirent **eps; int n; n = scandir ("./", &eps, one, alphasort); if (n >= 0) { int cnt; for (cnt = 0; cnt < n; ++cnt) puts (eps[cnt]->d_name); } else perror ("Couldn't open the directory"); return 0; } Note the simple selector function in this example. Since we want to see all directory entries we always return ‘1’.  File: libc.info, Node: Low-level Directory Access, Prev: Simple Directory Lister Mark II, Up: Accessing Directories 14.3.8 Low-level Directory Access --------------------------------- The stream-based directory functions are not AS-Safe and cannot be used after ‘vfork’. *Note POSIX Safety Concepts::. The functions below provide an alternative that can be used in these contexts. Directory data is obtained from a file descriptor, as created by the ‘open’ function, with or without the ‘O_DIRECTORY’ flag. *Note Opening and Closing Files::. -- Function: ssize_t getdents64 (int FD, void *BUFFER, size_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘getdents64’ function reads at most LENGTH bytes of directory entry data from the file descriptor FD and stores it into the byte array starting at BUFFER. On success, the function returns the number of bytes written to the buffer. This number is zero if FD is already at the end of the directory stream. On error, the function returns ‘-1’ and sets ‘errno’ to the appropriate error code. The data is stored as a sequence of ‘struct dirent64’ records, which can be traversed using the ‘d_reclen’ member. The buffer should be large enough to hold the largest possible directory entry. Note that some file systems support file names longer than ‘NAME_MAX’ bytes (e.g., because they support up to 255 Unicode characters), so a buffer size of at least 1024 is recommended. This function is specific to Linux.  File: libc.info, Node: Working with Directory Trees, Next: Hard Links, Prev: Accessing Directories, Up: File System Interface 14.4 Working with Directory Trees ================================= The functions described so far for handling the files in a directory have allowed you to either retrieve the information bit by bit, or to process all the files as a group (see ‘scandir’). Sometimes it is useful to process whole hierarchies of directories and their contained files. The X/Open specification defines two functions to do this. The simpler form is derived from an early definition in System V systems and therefore this function is available on SVID-derived systems. The prototypes and required definitions can be found in the ‘ftw.h’ header. There are four functions in this family: ‘ftw’, ‘nftw’ and their 64-bit counterparts ‘ftw64’ and ‘nftw64’. These functions take as one of their arguments a pointer to a callback function of the appropriate type. -- Data Type: __ftw_func_t int (*) (const char *, const struct stat *, int) The type of callback functions given to the ‘ftw’ function. The first parameter points to the file name, the second parameter to an object of type ‘struct stat’ which is filled in for the file named in the first parameter. The last parameter is a flag giving more information about the current file. It can have the following values: ‘FTW_F’ The item is either a normal file or a file which does not fit into one of the following categories. This could be special files, sockets etc. ‘FTW_D’ The item is a directory. ‘FTW_NS’ The ‘stat’ call failed and so the information pointed to by the second parameter is invalid. ‘FTW_DNR’ The item is a directory which cannot be read. ‘FTW_SL’ The item is a symbolic link. Since symbolic links are normally followed seeing this value in a ‘ftw’ callback function means the referenced file does not exist. The situation for ‘nftw’ is different. This value is only available if the program is compiled with ‘_XOPEN_EXTENDED’ defined before including the first header. The original SVID systems do not have symbolic links. If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this type is in fact ‘__ftw64_func_t’ since this mode changes ‘struct stat’ to be ‘struct stat64’. For the LFS interface and for use in the function ‘ftw64’, the header ‘ftw.h’ defines another function type. -- Data Type: __ftw64_func_t int (*) (const char *, const struct stat64 *, int) This type is used just like ‘__ftw_func_t’ for the callback function, but this time is called from ‘ftw64’. The second parameter to the function is a pointer to a variable of type ‘struct stat64’ which is able to represent the larger values. -- Data Type: __nftw_func_t int (*) (const char *, const struct stat *, int, struct FTW *) The first three arguments are the same as for the ‘__ftw_func_t’ type. However for the third argument some additional values are defined to allow finer differentiation: ‘FTW_DP’ The current item is a directory and all subdirectories have already been visited and reported. This flag is returned instead of ‘FTW_D’ if the ‘FTW_DEPTH’ flag is passed to ‘nftw’ (see below). ‘FTW_SLN’ The current item is a stale symbolic link. The file it points to does not exist. The last parameter of the callback function is a pointer to a structure with some extra information as described below. If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this type is in fact ‘__nftw64_func_t’ since this mode changes ‘struct stat’ to be ‘struct stat64’. For the LFS interface there is also a variant of this data type available which has to be used with the ‘nftw64’ function. -- Data Type: __nftw64_func_t int (*) (const char *, const struct stat64 *, int, struct FTW *) This type is used just like ‘__nftw_func_t’ for the callback function, but this time is called from ‘nftw64’. The second parameter to the function is this time a pointer to a variable of type ‘struct stat64’ which is able to represent the larger values. -- Data Type: struct FTW The information contained in this structure helps in interpreting the name parameter and gives some information about the current state of the traversal of the directory hierarchy. ‘int base’ The value is the offset into the string passed in the first parameter to the callback function of the beginning of the file name. The rest of the string is the path of the file. This information is especially important if the ‘FTW_CHDIR’ flag was set in calling ‘nftw’ since then the current directory is the one the current item is found in. ‘int level’ Whilst processing, the code tracks how many directories down it has gone to find the current file. This nesting level starts at 0 for files in the initial directory (or is zero for the initial file if a file was passed). -- Function: int ftw (const char *FILENAME, __ftw_func_t FUNC, int DESCRIPTORS) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘ftw’ function calls the callback function given in the parameter FUNC for every item which is found in the directory specified by FILENAME and all directories below. The function follows symbolic links if necessary but does not process an item twice. If FILENAME is not a directory then it itself is the only object returned to the callback function. The file name passed to the callback function is constructed by taking the FILENAME parameter and appending the names of all passed directories and then the local file name. So the callback function can use this parameter to access the file. ‘ftw’ also calls ‘stat’ for the file and passes that information on to the callback function. If this ‘stat’ call is not successful the failure is indicated by setting the third argument of the callback function to ‘FTW_NS’. Otherwise it is set according to the description given in the account of ‘__ftw_func_t’ above. The callback function is expected to return 0 to indicate that no error occurred and that processing should continue. If an error occurred in the callback function or it wants ‘ftw’ to return immediately, the callback function can return a value other than 0. This is the only correct way to stop the function. The program must not use ‘setjmp’ or similar techniques to continue from another place. This would leave resources allocated by the ‘ftw’ function unfreed. The DESCRIPTORS parameter to ‘ftw’ specifies how many file descriptors it is allowed to consume. The function runs faster the more descriptors it can use. For each level in the directory hierarchy at most one descriptor is used, but for very deep ones any limit on open file descriptors for the process or the system may be exceeded. Moreover, file descriptor limits in a multi-threaded program apply to all the threads as a group, and therefore it is a good idea to supply a reasonable limit to the number of open descriptors. The return value of the ‘ftw’ function is 0 if all callback function calls returned 0 and all actions performed by the ‘ftw’ succeeded. If a function call failed (other than calling ‘stat’ on an item) the function returns -1. If a callback function returns a value other than 0 this value is returned as the return value of ‘ftw’. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is in fact ‘ftw64’, i.e., the LFS interface transparently replaces the old interface. -- Function: int ftw64 (const char *FILENAME, __ftw64_func_t FUNC, int DESCRIPTORS) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. This function is similar to ‘ftw’ but it can work on filesystems with large files. File information is reported using a variable of type ‘struct stat64’ which is passed by reference to the callback function. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is available under the name ‘ftw’ and transparently replaces the old implementation. -- Function: int nftw (const char *FILENAME, __nftw_func_t FUNC, int DESCRIPTORS, int FLAG) Preliminary: | MT-Safe cwd | AS-Unsafe heap | AC-Unsafe mem fd cwd | *Note POSIX Safety Concepts::. The ‘nftw’ function works like the ‘ftw’ functions. They call the callback function FUNC for all items found in the directory FILENAME and below. At most DESCRIPTORS file descriptors are consumed during the ‘nftw’ call. One difference is that the callback function is of a different type. It is of type ‘struct FTW *’ and provides the callback function with the extra information described above. A second difference is that ‘nftw’ takes a fourth argument, which is 0 or a bitwise-OR combination of any of the following values. ‘FTW_PHYS’ While traversing the directory symbolic links are not followed. Instead symbolic links are reported using the ‘FTW_SL’ value for the type parameter to the callback function. If the file referenced by a symbolic link does not exist ‘FTW_SLN’ is returned instead. ‘FTW_MOUNT’ The callback function is only called for items which are on the same mounted filesystem as the directory given by the FILENAME parameter to ‘nftw’. ‘FTW_CHDIR’ If this flag is given the current working directory is changed to the directory of the reported object before the callback function is called. When ‘ntfw’ finally returns the current directory is restored to its original value. ‘FTW_DEPTH’ If this option is specified then all subdirectories and files within them are processed before processing the top directory itself (depth-first processing). This also means the type flag given to the callback function is ‘FTW_DP’ and not ‘FTW_D’. ‘FTW_ACTIONRETVAL’ If this option is specified then return values from callbacks are handled differently. If the callback returns ‘FTW_CONTINUE’, walking continues normally. ‘FTW_STOP’ means walking stops and ‘FTW_STOP’ is returned to the caller. If ‘FTW_SKIP_SUBTREE’ is returned by the callback with ‘FTW_D’ argument, the subtree is skipped and walking continues with next sibling of the directory. If ‘FTW_SKIP_SIBLINGS’ is returned by the callback, all siblings of the current entry are skipped and walking continues in its parent. No other return values should be returned from the callbacks if this option is set. This option is a GNU extension. The return value is computed in the same way as for ‘ftw’. ‘nftw’ returns 0 if no failures occurred and all callback functions returned 0. In case of internal errors, such as memory problems, the return value is -1 and ‘errno’ is set accordingly. If the return value of a callback invocation was non-zero then that value is returned. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is in fact ‘nftw64’, i.e., the LFS interface transparently replaces the old interface. -- Function: int nftw64 (const char *FILENAME, __nftw64_func_t FUNC, int DESCRIPTORS, int FLAG) Preliminary: | MT-Safe cwd | AS-Unsafe heap | AC-Unsafe mem fd cwd | *Note POSIX Safety Concepts::. This function is similar to ‘nftw’ but it can work on filesystems with large files. File information is reported using a variable of type ‘struct stat64’ which is passed by reference to the callback function. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is available under the name ‘nftw’ and transparently replaces the old implementation.  File: libc.info, Node: Hard Links, Next: Symbolic Links, Prev: Working with Directory Trees, Up: File System Interface 14.5 Hard Links =============== In POSIX systems, one file can have many names at the same time. All of the names are equally real, and no one of them is preferred to the others. To add a name to a file, use the ‘link’ function. (The new name is also called a “hard link” to the file.) Creating a new link to a file does not copy the contents of the file; it simply makes a new name by which the file can be known, in addition to the file's existing name or names. One file can have names in several directories, so the organization of the file system is not a strict hierarchy or tree. In most implementations, it is not possible to have hard links to the same file in multiple file systems. ‘link’ reports an error if you try to make a hard link to the file from another file system when this cannot be done. The prototype for the ‘link’ function is declared in the header file ‘unistd.h’. -- Function: int link (const char *OLDNAME, const char *NEWNAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘link’ function makes a new link to the existing file named by OLDNAME, under the new name NEWNAME. This function returns a value of ‘0’ if it is successful and ‘-1’ on failure. In addition to the usual file name errors (*note File Name Errors::) for both OLDNAME and NEWNAME, the following ‘errno’ error conditions are defined for this function: ‘EACCES’ You are not allowed to write to the directory in which the new link is to be written. ‘EEXIST’ There is already a file named NEWNAME. If you want to replace this link with a new link, you must remove the old link explicitly first. ‘EMLINK’ There are already too many links to the file named by OLDNAME. (The maximum number of links to a file is ‘LINK_MAX’; see *note Limits for Files::.) ‘ENOENT’ The file named by OLDNAME doesn't exist. You can't make a link to a file that doesn't exist. ‘ENOSPC’ The directory or file system that would contain the new link is full and cannot be extended. ‘EPERM’ On GNU/Linux and GNU/Hurd systems and some others, you cannot make links to directories. Many systems allow only privileged users to do so. This error is used to report the problem. ‘EROFS’ The directory containing the new link can't be modified because it's on a read-only file system. ‘EXDEV’ The directory specified in NEWNAME is on a different file system than the existing file. ‘EIO’ A hardware error occurred while trying to read or write the to filesystem. -- Function: int linkat (int oldfd, const char *OLDNAME, int newfd, const char *NEWNAME, int flags) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘linkat’ function is analogous to the ‘link’ function, except that it identifies its source and target using a combination of a file descriptor (referring to a directory) and a file name. *Note Descriptor-Relative Access::. For ‘linkat’, if a file name is not absolute, it is resolved relative to the corresponding file descriptor. As usual, the special value ‘AT_FDCWD’ denotes the current directory. The FLAGS argument is a combination of the following flags: ‘AT_SYMLINK_FOLLOW’ If the source path identified by OLDFD and OLDNAME is a symbolic link, ‘linkat’ follows the symbolic link and creates a link to its target. If the flag is not set, a link for the symbolic link itself is created; this is not supported by all file systems and ‘linkat’ can fail in this case. ‘AT_EMPTY_PATH’ If this flag is specified, OLDNAME can be an empty string. In this case, a new link to the file denoted by the descriptor OLDFD is created, which may have been opened with ‘O_PATH’ or ‘O_TMPFILE’. This flag is a GNU extension.  File: libc.info, Node: Symbolic Links, Next: Deleting Files, Prev: Hard Links, Up: File System Interface 14.6 Symbolic Links =================== GNU systems support “soft links” or “symbolic links”. This is a kind of "file" that is essentially a pointer to another file name. Unlike hard links, symbolic links can be made to directories or across file systems with no restrictions. You can also make a symbolic link to a name which is not the name of any file. (Opening this link will fail until a file by that name is created.) Likewise, if the symbolic link points to an existing file which is later deleted, the symbolic link continues to point to the same file name even though the name no longer names any file. The reason symbolic links work the way they do is that special things happen when you try to open the link. The ‘open’ function realizes you have specified the name of a link, reads the file name contained in the link, and opens that file name instead. The ‘stat’ function likewise operates on the file that the symbolic link points to, instead of on the link itself. By contrast, other operations such as deleting or renaming the file operate on the link itself. The functions ‘readlink’ and ‘lstat’ also refrain from following symbolic links, because their purpose is to obtain information about the link. ‘link’, the function that makes a hard link, does too. It makes a hard link to the symbolic link, which one rarely wants. Some systems have, for some functions operating on files, a limit on how many symbolic links are followed when resolving a path name. The limit if it exists is published in the ‘sys/param.h’ header file. -- Macro: int MAXSYMLINKS The macro ‘MAXSYMLINKS’ specifies how many symlinks some function will follow before returning ‘ELOOP’. Not all functions behave the same and this value is not the same as that returned for ‘_SC_SYMLOOP’ by ‘sysconf’. In fact, the ‘sysconf’ result can indicate that there is no fixed limit although ‘MAXSYMLINKS’ exists and has a finite value. Prototypes for most of the functions listed in this section are in ‘unistd.h’. -- Function: int symlink (const char *OLDNAME, const char *NEWNAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘symlink’ function makes a symbolic link to OLDNAME named NEWNAME. The normal return value from ‘symlink’ is ‘0’. A return value of ‘-1’ indicates an error. In addition to the usual file name syntax errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EEXIST’ There is already an existing file named NEWNAME. ‘EROFS’ The file NEWNAME would exist on a read-only file system. ‘ENOSPC’ The directory or file system cannot be extended to make the new link. ‘EIO’ A hardware error occurred while reading or writing data on the disk. -- Function: ssize_t readlink (const char *FILENAME, char *BUFFER, size_t SIZE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘readlink’ function gets the value of the symbolic link FILENAME. The file name that the link points to is copied into BUFFER. This file name string is _not_ null-terminated; ‘readlink’ normally returns the number of characters copied. The SIZE argument specifies the maximum number of characters to copy, usually the allocation size of BUFFER. If the return value equals SIZE, you cannot tell whether or not there was room to return the entire name. So make a bigger buffer and call ‘readlink’ again. Here is an example: char * readlink_malloc (const char *filename) { size_t size = 50; char *buffer = NULL; while (1) { buffer = xreallocarray (buffer, size, 2); size *= 2; ssize_t nchars = readlink (filename, buffer, size); if (nchars < 0) { free (buffer); return NULL; } if (nchars < size) return buffer; } } A value of ‘-1’ is returned in case of error. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EINVAL’ The named file is not a symbolic link. ‘EIO’ A hardware error occurred while reading or writing data on the disk. In some situations it is desirable to resolve all the symbolic links to get the real name of a file where no prefix names a symbolic link which is followed and no filename in the path is ‘.’ or ‘..’. This is for instance desirable if files have to be compared in which case different names can refer to the same inode. -- Function: char * canonicalize_file_name (const char *NAME) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. The ‘canonicalize_file_name’ function returns the absolute name of the file named by NAME which contains no ‘.’, ‘..’ components nor any repeated path separators (‘/’) or symlinks. The result is passed back as the return value of the function in a block of memory allocated with ‘malloc’. If the result is not used anymore the memory should be freed with a call to ‘free’. If any of the path components are missing the function returns a NULL pointer. This is also what is returned if the length of the path reaches or exceeds ‘PATH_MAX’ characters. In any case ‘errno’ is set accordingly. ‘ENAMETOOLONG’ The resulting path is too long. This error only occurs on systems which have a limit on the file name length. ‘EACCES’ At least one of the path components is not readable. ‘ENOENT’ The input file name is empty. ‘ENOENT’ At least one of the path components does not exist. ‘ELOOP’ More than ‘MAXSYMLINKS’ many symlinks have been followed. This function is a GNU extension and is declared in ‘stdlib.h’. The Unix standard includes a similar function which differs from ‘canonicalize_file_name’ in that the user has to provide the buffer where the result is placed in. -- Function: char * realpath (const char *restrict NAME, char *restrict RESOLVED) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem fd | *Note POSIX Safety Concepts::. A call to ‘realpath’ where the RESOLVED parameter is ‘NULL’ behaves exactly like ‘canonicalize_file_name’. The function allocates a buffer for the file name and returns a pointer to it. If RESOLVED is not ‘NULL’ it points to a buffer into which the result is copied. It is the callers responsibility to allocate a buffer which is large enough. On systems which define ‘PATH_MAX’ this means the buffer must be large enough for a pathname of this size. For systems without limitations on the pathname length the requirement cannot be met and programs should not call ‘realpath’ with anything but ‘NULL’ for the second parameter. One other difference is that the buffer RESOLVED (if nonzero) will contain the part of the path component which does not exist or is not readable if the function returns ‘NULL’ and ‘errno’ is set to ‘EACCES’ or ‘ENOENT’. This function is declared in ‘stdlib.h’. The advantage of using this function is that it is more widely available. The drawback is that it reports failures for long paths on systems which have no limits on the file name length.  File: libc.info, Node: Deleting Files, Next: Renaming Files, Prev: Symbolic Links, Up: File System Interface 14.7 Deleting Files =================== You can delete a file with ‘unlink’ or ‘remove’. Deletion actually deletes a file name. If this is the file's only name, then the file is deleted as well. If the file has other remaining names (*note Hard Links::), it remains accessible under those names. -- Function: int unlink (const char *FILENAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘unlink’ function deletes the file name FILENAME. If this is a file's sole name, the file itself is also deleted. (Actually, if any process has the file open when this happens, deletion is postponed until all processes have closed the file.) The function ‘unlink’ is declared in the header file ‘unistd.h’. This function returns ‘0’ on successful completion, and ‘-1’ on error. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ Write permission is denied for the directory from which the file is to be removed, or the directory has the sticky bit set and you do not own the file. ‘EBUSY’ This error indicates that the file is being used by the system in such a way that it can't be unlinked. For example, you might see this error if the file name specifies the root directory or a mount point for a file system. ‘ENOENT’ The file name to be deleted doesn't exist. ‘EPERM’ On some systems ‘unlink’ cannot be used to delete the name of a directory, or at least can only be used this way by a privileged user. To avoid such problems, use ‘rmdir’ to delete directories. (On GNU/Linux and GNU/Hurd systems ‘unlink’ can never delete the name of a directory.) ‘EROFS’ The directory containing the file name to be deleted is on a read-only file system and can't be modified. -- Function: int rmdir (const char *FILENAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘rmdir’ function deletes a directory. The directory must be empty before it can be removed; in other words, it can only contain entries for ‘.’ and ‘..’. In most other respects, ‘rmdir’ behaves like ‘unlink’. There are two additional ‘errno’ error conditions defined for ‘rmdir’: ‘ENOTEMPTY’ ‘EEXIST’ The directory to be deleted is not empty. These two error codes are synonymous; some systems use one, and some use the other. GNU/Linux and GNU/Hurd systems always use ‘ENOTEMPTY’. The prototype for this function is declared in the header file ‘unistd.h’. -- Function: int remove (const char *FILENAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This is the ISO C function to remove a file. It works like ‘unlink’ for files and like ‘rmdir’ for directories. ‘remove’ is declared in ‘stdio.h’.  File: libc.info, Node: Renaming Files, Next: Creating Directories, Prev: Deleting Files, Up: File System Interface 14.8 Renaming Files =================== The ‘rename’ function is used to change a file's name. -- Function: int rename (const char *OLDNAME, const char *NEWNAME) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘rename’ function renames the file OLDNAME to NEWNAME. The file formerly accessible under the name OLDNAME is afterwards accessible as NEWNAME instead. (If the file had any other names aside from OLDNAME, it continues to have those names.) The directory containing the name NEWNAME must be on the same file system as the directory containing the name OLDNAME. One special case for ‘rename’ is when OLDNAME and NEWNAME are two names for the same file. The consistent way to handle this case is to delete OLDNAME. However, in this case POSIX requires that ‘rename’ do nothing and report success--which is inconsistent. We don't know what your operating system will do. If OLDNAME is not a directory, then any existing file named NEWNAME is removed during the renaming operation. However, if NEWNAME is the name of a directory, ‘rename’ fails in this case. If OLDNAME is a directory, then either NEWNAME must not exist or it must name a directory that is empty. In the latter case, the existing directory named NEWNAME is deleted first. The name NEWNAME must not specify a subdirectory of the directory ‘oldname’ which is being renamed. One useful feature of ‘rename’ is that the meaning of NEWNAME changes "atomically" from any previously existing file by that name to its new meaning (i.e., the file that was called OLDNAME). There is no instant at which NEWNAME is non-existent "in between" the old meaning and the new meaning. If there is a system crash during the operation, it is possible for both names to still exist; but NEWNAME will always be intact if it exists at all. If ‘rename’ fails, it returns ‘-1’. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ One of the directories containing NEWNAME or OLDNAME refuses write permission; or NEWNAME and OLDNAME are directories and write permission is refused for one of them. ‘EBUSY’ A directory named by OLDNAME or NEWNAME is being used by the system in a way that prevents the renaming from working. This includes directories that are mount points for filesystems, and directories that are the current working directories of processes. ‘ENOTEMPTY’ ‘EEXIST’ The directory NEWNAME isn't empty. GNU/Linux and GNU/Hurd systems always return ‘ENOTEMPTY’ for this, but some other systems return ‘EEXIST’. ‘EINVAL’ OLDNAME is a directory that contains NEWNAME. ‘EISDIR’ NEWNAME is a directory but the OLDNAME isn't. ‘EMLINK’ The parent directory of NEWNAME would have too many links (entries). ‘ENOENT’ The file OLDNAME doesn't exist. ‘ENOSPC’ The directory that would contain NEWNAME has no room for another entry, and there is no space left in the file system to expand it. ‘EROFS’ The operation would involve writing to a directory on a read-only file system. ‘EXDEV’ The two file names NEWNAME and OLDNAME are on different file systems.  File: libc.info, Node: Creating Directories, Next: File Attributes, Prev: Renaming Files, Up: File System Interface 14.9 Creating Directories ========================= Directories are created with the ‘mkdir’ function. (There is also a shell command ‘mkdir’ which does the same thing.) -- Function: int mkdir (const char *FILENAME, mode_t MODE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘mkdir’ function creates a new, empty directory with name FILENAME. The argument MODE specifies the file permissions for the new directory file. *Note Permission Bits::, for more information about this. A return value of ‘0’ indicates successful completion, and ‘-1’ indicates failure. In addition to the usual file name syntax errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ Write permission is denied for the parent directory in which the new directory is to be added. ‘EEXIST’ A file named FILENAME already exists. ‘EMLINK’ The parent directory has too many links (entries). Well-designed file systems never report this error, because they permit more links than your disk could possibly hold. However, you must still take account of the possibility of this error, as it could result from network access to a file system on another machine. ‘ENOSPC’ The file system doesn't have enough room to create the new directory. ‘EROFS’ The parent directory of the directory being created is on a read-only file system and cannot be modified. To use this function, your program should include the header file ‘sys/stat.h’.  File: libc.info, Node: File Attributes, Next: Making Special Files, Prev: Creating Directories, Up: File System Interface 14.10 File Attributes ===================== When you issue an ‘ls -l’ shell command on a file, it gives you information about the size of the file, who owns it, when it was last modified, etc. These are called the “file attributes”, and are associated with the file itself and not a particular one of its names. This section contains information about how you can inquire about and modify the attributes of a file. * Menu: * Attribute Meanings:: The names of the file attributes, and what their values mean. * Reading Attributes:: How to read the attributes of a file. * Testing File Type:: Distinguishing ordinary files, directories, links... * File Owner:: How ownership for new files is determined, and how to change it. * Permission Bits:: How information about a file's access mode is stored. * Access Permission:: How the system decides who can access a file. * Setting Permissions:: How permissions for new files are assigned, and how to change them. * Testing File Access:: How to find out if your process can access a file. * File Times:: About the time attributes of a file. * File Size:: Manually changing the size of a file. * Storage Allocation:: Allocate backing storage for files.  File: libc.info, Node: Attribute Meanings, Next: Reading Attributes, Up: File Attributes 14.10.1 The meaning of the File Attributes ------------------------------------------ When you read the attributes of a file, they come back in a structure called ‘struct stat’. This section describes the names of the attributes, their data types, and what they mean. For the functions to read the attributes of a file, see *note Reading Attributes::. The header file ‘sys/stat.h’ declares all the symbols defined in this section. -- Data Type: struct stat The ‘stat’ structure type is used to return information about the attributes of a file. It contains at least the following members: ‘mode_t st_mode’ Specifies the mode of the file. This includes file type information (*note Testing File Type::) and the file permission bits (*note Permission Bits::). ‘ino_t st_ino’ The file serial number, which distinguishes this file from all other files on the same device. ‘dev_t st_dev’ Identifies the device containing the file. The ‘st_ino’ and ‘st_dev’, taken together, uniquely identify the file. The ‘st_dev’ value is not necessarily consistent across reboots or system crashes, however. ‘nlink_t st_nlink’ The number of hard links to the file. This count keeps track of how many directories have entries for this file. If the count is ever decremented to zero, then the file itself is discarded as soon as no process still holds it open. Symbolic links are not counted in the total. ‘uid_t st_uid’ The user ID of the file's owner. *Note File Owner::. ‘gid_t st_gid’ The group ID of the file. *Note File Owner::. ‘off_t st_size’ This specifies the size of a regular file in bytes. For files that are really devices this field isn't usually meaningful. For symbolic links this specifies the length of the file name the link refers to. ‘time_t st_atime’ This is the last access time for the file. *Note File Times::. ‘unsigned long int st_atime_usec’ This is the fractional part of the last access time for the file. *Note File Times::. ‘time_t st_mtime’ This is the time of the last modification to the contents of the file. *Note File Times::. ‘unsigned long int st_mtime_usec’ This is the fractional part of the time of the last modification to the contents of the file. *Note File Times::. ‘time_t st_ctime’ This is the time of the last modification to the attributes of the file. *Note File Times::. ‘unsigned long int st_ctime_usec’ This is the fractional part of the time of the last modification to the attributes of the file. *Note File Times::. ‘blkcnt_t st_blocks’ This is the amount of disk space that the file occupies, measured in units of 512-byte blocks. The number of disk blocks is not strictly proportional to the size of the file, for two reasons: the file system may use some blocks for internal record keeping; and the file may be sparse--it may have "holes" which contain zeros but do not actually take up space on the disk. You can tell (approximately) whether a file is sparse by comparing this value with ‘st_size’, like this: (st.st_blocks * 512 < st.st_size) This test is not perfect because a file that is just slightly sparse might not be detected as sparse at all. For practical applications, this is not a problem. ‘unsigned int st_blksize’ The optimal block size for reading or writing this file, in bytes. You might use this size for allocating the buffer space for reading or writing the file. (This is unrelated to ‘st_blocks’.) The extensions for the Large File Support (LFS) require, even on 32-bit machines, types which can handle file sizes up to 2^63. Therefore a new definition of ‘struct stat’ is necessary. -- Data Type: struct stat64 The members of this type are the same and have the same names as those in ‘struct stat’. The only difference is that the members ‘st_ino’, ‘st_size’, and ‘st_blocks’ have a different type to support larger values. ‘mode_t st_mode’ Specifies the mode of the file. This includes file type information (*note Testing File Type::) and the file permission bits (*note Permission Bits::). ‘ino64_t st_ino’ The file serial number, which distinguishes this file from all other files on the same device. ‘dev_t st_dev’ Identifies the device containing the file. The ‘st_ino’ and ‘st_dev’, taken together, uniquely identify the file. The ‘st_dev’ value is not necessarily consistent across reboots or system crashes, however. ‘nlink_t st_nlink’ The number of hard links to the file. This count keeps track of how many directories have entries for this file. If the count is ever decremented to zero, then the file itself is discarded as soon as no process still holds it open. Symbolic links are not counted in the total. ‘uid_t st_uid’ The user ID of the file's owner. *Note File Owner::. ‘gid_t st_gid’ The group ID of the file. *Note File Owner::. ‘off64_t st_size’ This specifies the size of a regular file in bytes. For files that are really devices this field isn't usually meaningful. For symbolic links this specifies the length of the file name the link refers to. ‘time_t st_atime’ This is the last access time for the file. *Note File Times::. ‘unsigned long int st_atime_usec’ This is the fractional part of the last access time for the file. *Note File Times::. ‘time_t st_mtime’ This is the time of the last modification to the contents of the file. *Note File Times::. ‘unsigned long int st_mtime_usec’ This is the fractional part of the time of the last modification to the contents of the file. *Note File Times::. ‘time_t st_ctime’ This is the time of the last modification to the attributes of the file. *Note File Times::. ‘unsigned long int st_ctime_usec’ This is the fractional part of the time of the last modification to the attributes of the file. *Note File Times::. ‘blkcnt64_t st_blocks’ This is the amount of disk space that the file occupies, measured in units of 512-byte blocks. ‘unsigned int st_blksize’ The optimal block size for reading of writing this file, in bytes. You might use this size for allocating the buffer space for reading of writing the file. (This is unrelated to ‘st_blocks’.) Some of the file attributes have special data type names which exist specifically for those attributes. (They are all aliases for well-known integer types that you know and love.) These typedef names are defined in the header file ‘sys/types.h’ as well as in ‘sys/stat.h’. Here is a list of them. -- Data Type: mode_t This is an integer data type used to represent file modes. In the GNU C Library, this is an unsigned type no narrower than ‘unsigned int’. -- Data Type: ino_t This is an unsigned integer type used to represent file serial numbers. (In Unix jargon, these are sometimes called “inode numbers”.) In the GNU C Library, this type is no narrower than ‘unsigned int’. If the source is compiled with ‘_FILE_OFFSET_BITS == 64’ this type is transparently replaced by ‘ino64_t’. -- Data Type: ino64_t This is an unsigned integer type used to represent file serial numbers for the use in LFS. In the GNU C Library, this type is no narrower than ‘unsigned int’. When compiling with ‘_FILE_OFFSET_BITS == 64’ this type is available under the name ‘ino_t’. -- Data Type: dev_t This is an arithmetic data type used to represent file device numbers. In the GNU C Library, this is an integer type no narrower than ‘int’. -- Data Type: nlink_t This is an integer type used to represent file link counts. -- Data Type: blkcnt_t This is a signed integer type used to represent block counts. In the GNU C Library, this type is no narrower than ‘int’. If the source is compiled with ‘_FILE_OFFSET_BITS == 64’ this type is transparently replaced by ‘blkcnt64_t’. -- Data Type: blkcnt64_t This is a signed integer type used to represent block counts for the use in LFS. In the GNU C Library, this type is no narrower than ‘int’. When compiling with ‘_FILE_OFFSET_BITS == 64’ this type is available under the name ‘blkcnt_t’.  File: libc.info, Node: Reading Attributes, Next: Testing File Type, Prev: Attribute Meanings, Up: File Attributes 14.10.2 Reading the Attributes of a File ---------------------------------------- To examine the attributes of files, use the functions ‘stat’, ‘fstat’ and ‘lstat’. They return the attribute information in a ‘struct stat’ object. All three functions are declared in the header file ‘sys/stat.h’. -- Function: int stat (const char *FILENAME, struct stat *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘stat’ function returns information about the attributes of the file named by FILENAME in the structure pointed to by BUF. If FILENAME is the name of a symbolic link, the attributes you get describe the file that the link points to. If the link points to a nonexistent file name, then ‘stat’ fails reporting a nonexistent file. The return value is ‘0’ if the operation is successful, or ‘-1’ on failure. In addition to the usual file name errors (*note File Name Errors::, the following ‘errno’ error conditions are defined for this function: ‘ENOENT’ The file named by FILENAME doesn't exist. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is in fact ‘stat64’ since the LFS interface transparently replaces the normal implementation. -- Function: int stat64 (const char *FILENAME, struct stat64 *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘stat’ but it is also able to work on files larger than 2^31 bytes on 32-bit systems. To be able to do this the result is stored in a variable of type ‘struct stat64’ to which BUF must point. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is available under the name ‘stat’ and so transparently replaces the interface for small files on 32-bit machines. -- Function: int fstat (int FILEDES, struct stat *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘fstat’ function is like ‘stat’, except that it takes an open file descriptor as an argument instead of a file name. *Note Low-Level I/O::. Like ‘stat’, ‘fstat’ returns ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for ‘fstat’: ‘EBADF’ The FILEDES argument is not a valid file descriptor. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is in fact ‘fstat64’ since the LFS interface transparently replaces the normal implementation. -- Function: int fstat64 (int FILEDES, struct stat64 *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘fstat’ but is able to work on large files on 32-bit platforms. For large files the file descriptor FILEDES should be obtained by ‘open64’ or ‘creat64’. The BUF pointer points to a variable of type ‘struct stat64’ which is able to represent the larger values. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is available under the name ‘fstat’ and so transparently replaces the interface for small files on 32-bit machines. -- Function: int fstatat (int FILEDES, const char *FILENAME, struct stat *BUF, int FLAGS) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is a descriptor-relative version of the ‘fstat’ function above. *Note Descriptor-Relative Access::. The FLAGS argument can contain a combination of the flags ‘AT_EMPTY_PATH’, ‘AT_NO_AUTOMOUNT’, ‘AT_SYMLINK_NOFOLLOW’. Compared to ‘fstat’, the following additional error conditions can occur: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EINVAL’ The FLAGS argument is not valid for this function. ‘ENOTDIR’ The descriptor FILEDES is not associated with a directory, and FILENAME is a relative file name. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is in fact ‘fstatat64’ since the LFS interface transparently replaces the normal implementation. -- Function: int fstatat64 (int FILEDES, const char *FILENAME, struct stat64 *BUF, int FLAGS) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is the large-file variant of ‘fstatat’, similar to how ‘fstat64’ is the variant of ‘fstat’. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is available under the name ‘fstatat’ and so transparently replaces the interface for small files on 32-bit machines. -- Function: int lstat (const char *FILENAME, struct stat *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘lstat’ function is like ‘stat’, except that it does not follow symbolic links. If FILENAME is the name of a symbolic link, ‘lstat’ returns information about the link itself; otherwise ‘lstat’ works like ‘stat’. *Note Symbolic Links::. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is in fact ‘lstat64’ since the LFS interface transparently replaces the normal implementation. -- Function: int lstat64 (const char *FILENAME, struct stat64 *BUF) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to ‘lstat’ but it is also able to work on files larger than 2^31 bytes on 32-bit systems. To be able to do this the result is stored in a variable of type ‘struct stat64’ to which BUF must point. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ this function is available under the name ‘lstat’ and so transparently replaces the interface for small files on 32-bit machines.  File: libc.info, Node: Testing File Type, Next: File Owner, Prev: Reading Attributes, Up: File Attributes 14.10.3 Testing the Type of a File ---------------------------------- The “file mode”, stored in the ‘st_mode’ field of the file attributes, contains two kinds of information: the file type code, and the access permission bits. This section discusses only the type code, which you can use to tell whether the file is a directory, socket, symbolic link, and so on. For details about access permissions see *note Permission Bits::. There are two ways you can access the file type information in a file mode. Firstly, for each file type there is a “predicate macro” which examines a given file mode and returns whether it is of that type or not. Secondly, you can mask out the rest of the file mode to leave just the file type code, and compare this against constants for each of the supported file types. All of the symbols listed in this section are defined in the header file ‘sys/stat.h’. The following predicate macros test the type of a file, given the value M which is the ‘st_mode’ field returned by ‘stat’ on that file: -- Macro: int S_ISDIR (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a directory. -- Macro: int S_ISCHR (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a character special file (a device like a terminal). -- Macro: int S_ISBLK (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a block special file (a device like a disk). -- Macro: int S_ISREG (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a regular file. -- Macro: int S_ISFIFO (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a FIFO special file, or a pipe. *Note Pipes and FIFOs::. -- Macro: int S_ISLNK (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a symbolic link. *Note Symbolic Links::. -- Macro: int S_ISSOCK (mode_t M) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro returns non-zero if the file is a socket. *Note Sockets::. An alternate non-POSIX method of testing the file type is supported for compatibility with BSD. The mode can be bitwise AND-ed with ‘S_IFMT’ to extract the file type code, and compared to the appropriate constant. For example, S_ISCHR (MODE) is equivalent to: ((MODE & S_IFMT) == S_IFCHR) -- Macro: int S_IFMT This is a bit mask used to extract the file type code from a mode value. These are the symbolic names for the different file type codes: ‘S_IFDIR’ This is the file type constant of a directory file. ‘S_IFCHR’ This is the file type constant of a character-oriented device file. ‘S_IFBLK’ This is the file type constant of a block-oriented device file. ‘S_IFREG’ This is the file type constant of a regular file. ‘S_IFLNK’ This is the file type constant of a symbolic link. ‘S_IFSOCK’ This is the file type constant of a socket. ‘S_IFIFO’ This is the file type constant of a FIFO or pipe. The POSIX.1b standard introduced a few more objects which possibly can be implemented as objects in the filesystem. These are message queues, semaphores, and shared memory objects. To allow differentiating these objects from other files the POSIX standard introduced three new test macros. But unlike the other macros they do not take the value of the ‘st_mode’ field as the parameter. Instead they expect a pointer to the whole ‘struct stat’ structure. -- Macro: int S_TYPEISMQ (struct stat *S) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. If the system implements POSIX message queues as distinct objects and the file is a message queue object, this macro returns a non-zero value. In all other cases the result is zero. -- Macro: int S_TYPEISSEM (struct stat *S) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. If the system implements POSIX semaphores as distinct objects and the file is a semaphore object, this macro returns a non-zero value. In all other cases the result is zero. -- Macro: int S_TYPEISSHM (struct stat *S) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. If the system implements POSIX shared memory objects as distinct objects and the file is a shared memory object, this macro returns a non-zero value. In all other cases the result is zero.  File: libc.info, Node: File Owner, Next: Permission Bits, Prev: Testing File Type, Up: File Attributes 14.10.4 File Owner ------------------ Every file has an “owner” which is one of the registered user names defined on the system. Each file also has a “group” which is one of the defined groups. The file owner can often be useful for showing you who edited the file (especially when you edit with GNU Emacs), but its main purpose is for access control. The file owner and group play a role in determining access because the file has one set of access permission bits for the owner, another set that applies to users who belong to the file's group, and a third set of bits that applies to everyone else. *Note Access Permission::, for the details of how access is decided based on this data. When a file is created, its owner is set to the effective user ID of the process that creates it (*note Process Persona::). The file's group ID may be set to either the effective group ID of the process, or the group ID of the directory that contains the file, depending on the system where the file is stored. When you access a remote file system, it behaves according to its own rules, not according to the system your program is running on. Thus, your program must be prepared to encounter either kind of behavior no matter what kind of system you run it on. You can change the owner and/or group owner of an existing file using the ‘chown’ function. This is the primitive for the ‘chown’ and ‘chgrp’ shell commands. The prototype for this function is declared in ‘unistd.h’. -- Function: int chown (const char *FILENAME, uid_t OWNER, gid_t GROUP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘chown’ function changes the owner of the file FILENAME to OWNER, and its group owner to GROUP. Changing the owner of the file on certain systems clears the set-user-ID and set-group-ID permission bits. (This is because those bits may not be appropriate for the new owner.) Other file permission bits are not changed. The return value is ‘0’ on success and ‘-1’ on failure. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EPERM’ This process lacks permission to make the requested change. Only privileged users or the file's owner can change the file's group. On most file systems, only privileged users can change the file owner; some file systems allow you to change the owner if you are currently the owner. When you access a remote file system, the behavior you encounter is determined by the system that actually holds the file, not by the system your program is running on. *Note Options for Files::, for information about the ‘_POSIX_CHOWN_RESTRICTED’ macro. ‘EROFS’ The file is on a read-only file system. -- Function: int fchown (int FILEDES, uid_t OWNER, gid_t GROUP) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This is like ‘chown’, except that it changes the owner of the open file with descriptor FILEDES. The return value from ‘fchown’ is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error codes are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EINVAL’ The FILEDES argument corresponds to a pipe or socket, not an ordinary file. ‘EPERM’ This process lacks permission to make the requested change. For details see ‘chmod’ above. ‘EROFS’ The file resides on a read-only file system.  File: libc.info, Node: Permission Bits, Next: Access Permission, Prev: File Owner, Up: File Attributes 14.10.5 The Mode Bits for Access Permission ------------------------------------------- The “file mode”, stored in the ‘st_mode’ field of the file attributes, contains two kinds of information: the file type code, and the access permission bits. This section discusses only the access permission bits, which control who can read or write the file. *Note Testing File Type::, for information about the file type code. All of the symbols listed in this section are defined in the header file ‘sys/stat.h’. These symbolic constants are defined for the file mode bits that control access permission for the file: ‘S_IRUSR’ ‘S_IREAD’ Read permission bit for the owner of the file. On many systems this bit is 0400. ‘S_IREAD’ is an obsolete synonym provided for BSD compatibility. ‘S_IWUSR’ ‘S_IWRITE’ Write permission bit for the owner of the file. Usually 0200. ‘S_IWRITE’ is an obsolete synonym provided for BSD compatibility. ‘S_IXUSR’ ‘S_IEXEC’ Execute (for ordinary files) or search (for directories) permission bit for the owner of the file. Usually 0100. ‘S_IEXEC’ is an obsolete synonym provided for BSD compatibility. ‘S_IRWXU’ This is equivalent to ‘(S_IRUSR | S_IWUSR | S_IXUSR)’. ‘S_IRGRP’ Read permission bit for the group owner of the file. Usually 040. ‘S_IWGRP’ Write permission bit for the group owner of the file. Usually 020. ‘S_IXGRP’ Execute or search permission bit for the group owner of the file. Usually 010. ‘S_IRWXG’ This is equivalent to ‘(S_IRGRP | S_IWGRP | S_IXGRP)’. ‘S_IROTH’ Read permission bit for other users. Usually 04. ‘S_IWOTH’ Write permission bit for other users. Usually 02. ‘S_IXOTH’ Execute or search permission bit for other users. Usually 01. ‘S_IRWXO’ This is equivalent to ‘(S_IROTH | S_IWOTH | S_IXOTH)’. ‘S_ISUID’ This is the set-user-ID on execute bit, usually 04000. *Note How Change Persona::. ‘S_ISGID’ This is the set-group-ID on execute bit, usually 02000. *Note How Change Persona::. ‘S_ISVTX’ This is the “sticky” bit, usually 01000. For a directory it gives permission to delete a file in that directory only if you own that file. Ordinarily, a user can either delete all the files in a directory or cannot delete any of them (based on whether the user has write permission for the directory). The same restriction applies--you must have both write permission for the directory and own the file you want to delete. The one exception is that the owner of the directory can delete any file in the directory, no matter who owns it (provided the owner has given himself write permission for the directory). This is commonly used for the ‘/tmp’ directory, where anyone may create files but not delete files created by other users. Originally the sticky bit on an executable file modified the swapping policies of the system. Normally, when a program terminated, its pages in core were immediately freed and reused. If the sticky bit was set on the executable file, the system kept the pages in core for a while as if the program were still running. This was advantageous for a program likely to be run many times in succession. This usage is obsolete in modern systems. When a program terminates, its pages always remain in core as long as there is no shortage of memory in the system. When the program is next run, its pages will still be in core if no shortage arose since the last run. On some modern systems where the sticky bit has no useful meaning for an executable file, you cannot set the bit at all for a non-directory. If you try, ‘chmod’ fails with ‘EFTYPE’; *note Setting Permissions::. Some systems (particularly SunOS) have yet another use for the sticky bit. If the sticky bit is set on a file that is _not_ executable, it means the opposite: never cache the pages of this file at all. The main use of this is for the files on an NFS server machine which are used as the swap area of diskless client machines. The idea is that the pages of the file will be cached in the client's memory, so it is a waste of the server's memory to cache them a second time. With this usage the sticky bit also implies that the filesystem may fail to record the file's modification time onto disk reliably (the idea being that no-one cares for a swap file). This bit is only available on BSD systems (and those derived from them). Therefore one has to use the ‘_GNU_SOURCE’ feature select macro, or not define any feature test macros, to get the definition (*note Feature Test Macros::). The actual bit values of the symbols are listed in the table above so you can decode file mode values when debugging your programs. These bit values are correct for most systems, but they are not guaranteed. *Warning:* Writing explicit numbers for file permissions is bad practice. Not only is it not portable, it also requires everyone who reads your program to remember what the bits mean. To make your program clean use the symbolic names.  File: libc.info, Node: Access Permission, Next: Setting Permissions, Prev: Permission Bits, Up: File Attributes 14.10.6 How Your Access to a File is Decided -------------------------------------------- Recall that the operating system normally decides access permission for a file based on the effective user and group IDs of the process and its supplementary group IDs, together with the file's owner, group and permission bits. These concepts are discussed in detail in *note Process Persona::. If the effective user ID of the process matches the owner user ID of the file, then permissions for read, write, and execute/search are controlled by the corresponding "user" (or "owner") bits. Likewise, if any of the effective group ID or supplementary group IDs of the process matches the group owner ID of the file, then permissions are controlled by the "group" bits. Otherwise, permissions are controlled by the "other" bits. Privileged users, like ‘root’, can access any file regardless of its permission bits. As a special case, for a file to be executable even by a privileged user, at least one of its execute bits must be set.  File: libc.info, Node: Setting Permissions, Next: Testing File Access, Prev: Access Permission, Up: File Attributes 14.10.7 Assigning File Permissions ---------------------------------- The primitive functions for creating files (for example, ‘open’ or ‘mkdir’) take a MODE argument, which specifies the file permissions to give the newly created file. This mode is modified by the process's “file creation mask”, or “umask”, before it is used. The bits that are set in the file creation mask identify permissions that are always to be disabled for newly created files. For example, if you set all the "other" access bits in the mask, then newly created files are not accessible at all to processes in the "other" category, even if the MODE argument passed to the create function would permit such access. In other words, the file creation mask is the complement of the ordinary access permissions you want to grant. Programs that create files typically specify a MODE argument that includes all the permissions that make sense for the particular file. For an ordinary file, this is typically read and write permission for all classes of users. These permissions are then restricted as specified by the individual user's own file creation mask. To change the permission of an existing file given its name, call ‘chmod’. This function uses the specified permission bits and ignores the file creation mask. In normal use, the file creation mask is initialized by the user's login shell (using the ‘umask’ shell command), and inherited by all subprocesses. Application programs normally don't need to worry about the file creation mask. It will automatically do what it is supposed to do. When your program needs to create a file and bypass the umask for its access permissions, the easiest way to do this is to use ‘fchmod’ after opening the file, rather than changing the umask. In fact, changing the umask is usually done only by shells. They use the ‘umask’ function. The functions in this section are declared in ‘sys/stat.h’. -- Function: mode_t umask (mode_t MASK) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘umask’ function sets the file creation mask of the current process to MASK, and returns the previous value of the file creation mask. Here is an example showing how to read the mask with ‘umask’ without changing it permanently: mode_t read_umask (void) { mode_t mask = umask (0); umask (mask); return mask; } However, on GNU/Hurd systems it is better to use ‘getumask’ if you just want to read the mask value, because it is reentrant. -- Function: mode_t getumask (void) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Return the current value of the file creation mask for the current process. This function is a GNU extension and is only available on GNU/Hurd systems. -- Function: int chmod (const char *FILENAME, mode_t MODE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘chmod’ function sets the access permission bits for the file named by FILENAME to MODE. If FILENAME is a symbolic link, ‘chmod’ changes the permissions of the file pointed to by the link, not those of the link itself. This function returns ‘0’ if successful and ‘-1’ if not. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘ENOENT’ The named file doesn't exist. ‘EPERM’ This process does not have permission to change the access permissions of this file. Only the file's owner (as judged by the effective user ID of the process) or a privileged user can change them. ‘EROFS’ The file resides on a read-only file system. ‘EFTYPE’ MODE has the ‘S_ISVTX’ bit (the "sticky bit") set, and the named file is not a directory. Some systems do not allow setting the sticky bit on non-directory files, and some do (and only some of those assign a useful meaning to the bit for non-directory files). You only get ‘EFTYPE’ on systems where the sticky bit has no useful meaning for non-directory files, so it is always safe to just clear the bit in MODE and call ‘chmod’ again. *Note Permission Bits::, for full details on the sticky bit. -- Function: int fchmod (int FILEDES, mode_t MODE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This is like ‘chmod’, except that it changes the permissions of the currently open file given by FILEDES. The return value from ‘fchmod’ is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error codes are defined for this function: ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EINVAL’ The FILEDES argument corresponds to a pipe or socket, or something else that doesn't really have access permissions. ‘EPERM’ This process does not have permission to change the access permissions of this file. Only the file's owner (as judged by the effective user ID of the process) or a privileged user can change them. ‘EROFS’ The file resides on a read-only file system.  File: libc.info, Node: Testing File Access, Next: File Times, Prev: Setting Permissions, Up: File Attributes 14.10.8 Testing Permission to Access a File ------------------------------------------- In some situations it is desirable to allow programs to access files or devices even if this is not possible with the permissions granted to the user. One possible solution is to set the setuid-bit of the program file. If such a program is started the _effective_ user ID of the process is changed to that of the owner of the program file. So to allow write access to files like ‘/etc/passwd’, which normally can be written only by the super-user, the modifying program will have to be owned by ‘root’ and the setuid-bit must be set. But besides the files the program is intended to change the user should not be allowed to access any file to which s/he would not have access anyway. The program therefore must explicitly check whether _the user_ would have the necessary access to a file, before it reads or writes the file. To do this, use the function ‘access’, which checks for access permission based on the process's _real_ user ID rather than the effective user ID. (The setuid feature does not alter the real user ID, so it reflects the user who actually ran the program.) There is another way you could check this access, which is easy to describe, but very hard to use. This is to examine the file mode bits and mimic the system's own access computation. This method is undesirable because many systems have additional access control features; your program cannot portably mimic them, and you would not want to try to keep track of the diverse features that different systems have. Using ‘access’ is simple and automatically does whatever is appropriate for the system you are using. ‘access’ is _only_ appropriate to use in setuid programs. A non-setuid program will always use the effective ID rather than the real ID. The symbols in this section are declared in ‘unistd.h’. -- Function: int access (const char *FILENAME, int HOW) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘access’ function checks to see whether the file named by FILENAME can be accessed in the way specified by the HOW argument. The HOW argument either can be the bitwise OR of the flags ‘R_OK’, ‘W_OK’, ‘X_OK’, or the existence test ‘F_OK’. This function uses the _real_ user and group IDs of the calling process, rather than the _effective_ IDs, to check for access permission. As a result, if you use the function from a ‘setuid’ or ‘setgid’ program (*note How Change Persona::), it gives information relative to the user who actually ran the program. The return value is ‘0’ if the access is permitted, and ‘-1’ otherwise. (In other words, treated as a predicate function, ‘access’ returns true if the requested access is _denied_.) In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ The access specified by HOW is denied. ‘ENOENT’ The file doesn't exist. ‘EROFS’ Write permission was requested for a file on a read-only file system. These macros are defined in the header file ‘unistd.h’ for use as the HOW argument to the ‘access’ function. The values are integer constants. -- Macro: int R_OK Flag meaning test for read permission. -- Macro: int W_OK Flag meaning test for write permission. -- Macro: int X_OK Flag meaning test for execute/search permission. -- Macro: int F_OK Flag meaning test for existence of the file.  File: libc.info, Node: File Times, Next: File Size, Prev: Testing File Access, Up: File Attributes 14.10.9 File Times ------------------ Each file has three time stamps associated with it: its access time, its modification time, and its attribute modification time. These correspond to the ‘st_atime’, ‘st_mtime’, and ‘st_ctime’ members of the ‘stat’ structure; see *note File Attributes::. All of these times are represented in calendar time format, as ‘time_t’ objects. This data type is defined in ‘time.h’. For more information about representation and manipulation of time values, see *note Calendar Time::. Reading from a file updates its access time attribute, and writing updates its modification time. When a file is created, all three time stamps for that file are set to the current time. In addition, the attribute change time and modification time fields of the directory that contains the new entry are updated. Adding a new name for a file with the ‘link’ function updates the attribute change time field of the file being linked, and both the attribute change time and modification time fields of the directory containing the new name. These same fields are affected if a file name is deleted with ‘unlink’, ‘remove’ or ‘rmdir’. Renaming a file with ‘rename’ affects only the attribute change time and modification time fields of the two parent directories involved, and not the times for the file being renamed. Changing the attributes of a file (for example, with ‘chmod’) updates its attribute change time field. You can also change some of the time stamps of a file explicitly using the ‘utime’ function--all except the attribute change time. You need to include the header file ‘utime.h’ to use this facility. -- Data Type: struct utimbuf The ‘utimbuf’ structure is used with the ‘utime’ function to specify new access and modification times for a file. It contains the following members: ‘time_t actime’ This is the access time for the file. ‘time_t modtime’ This is the modification time for the file. -- Function: int utime (const char *FILENAME, const struct utimbuf *TIMES) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is used to modify the file times associated with the file named FILENAME. If TIMES is a null pointer, then the access and modification times of the file are set to the current time. Otherwise, they are set to the values from the ‘actime’ and ‘modtime’ members (respectively) of the ‘utimbuf’ structure pointed to by TIMES. The attribute modification time for the file is set to the current time in either case (since changing the time stamps is itself a modification of the file attributes). The ‘utime’ function returns ‘0’ if successful and ‘-1’ on failure. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EACCES’ There is a permission problem in the case where a null pointer was passed as the TIMES argument. In order to update the time stamp on the file, you must either be the owner of the file, have write permission for the file, or be a privileged user. ‘ENOENT’ The file doesn't exist. ‘EPERM’ If the TIMES argument is not a null pointer, you must either be the owner of the file or be a privileged user. ‘EROFS’ The file lives on a read-only file system. Each of the three time stamps has a corresponding microsecond part, which extends its resolution. These fields are called ‘st_atime_usec’, ‘st_mtime_usec’, and ‘st_ctime_usec’; each has a value between 0 and 999,999, which indicates the time in microseconds. They correspond to the ‘tv_usec’ field of a ‘timeval’ structure; see *note Time Types::. The ‘utimes’ function is like ‘utime’, but also lets you specify the fractional part of the file times. The prototype for this function is in the header file ‘sys/time.h’. -- Function: int utimes (const char *FILENAME, const struct timeval TVP[2]) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function sets the file access and modification times of the file FILENAME. The new file access time is specified by ‘TVP[0]’, and the new modification time by ‘TVP[1]’. Similar to ‘utime’, if TVP is a null pointer then the access and modification times of the file are set to the current time. This function comes from BSD. The return values and error conditions are the same as for the ‘utime’ function. -- Function: int lutimes (const char *FILENAME, const struct timeval TVP[2]) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is like ‘utimes’, except that it does not follow symbolic links. If FILENAME is the name of a symbolic link, ‘lutimes’ sets the file access and modification times of the symbolic link special file itself (as seen by ‘lstat’; *note Symbolic Links::) while ‘utimes’ sets the file access and modification times of the file the symbolic link refers to. This function comes from FreeBSD, and is not available on all platforms (if not available, it will fail with ‘ENOSYS’). The return values and error conditions are the same as for the ‘utime’ function. -- Function: int futimes (int FD, const struct timeval TVP[2]) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is like ‘utimes’, except that it takes an open file descriptor as an argument instead of a file name. *Note Low-Level I/O::. This function comes from FreeBSD, and is not available on all platforms (if not available, it will fail with ‘ENOSYS’). Like ‘utimes’, ‘futimes’ returns ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for ‘futimes’: ‘EACCES’ There is a permission problem in the case where a null pointer was passed as the TIMES argument. In order to update the time stamp on the file, you must either be the owner of the file, have write permission for the file, or be a privileged user. ‘EBADF’ The FILEDES argument is not a valid file descriptor. ‘EPERM’ If the TIMES argument is not a null pointer, you must either be the owner of the file or be a privileged user. ‘EROFS’ The file lives on a read-only file system.  File: libc.info, Node: File Size, Next: Storage Allocation, Prev: File Times, Up: File Attributes 14.10.10 File Size ------------------ Normally file sizes are maintained automatically. A file begins with a size of 0 and is automatically extended when data is written past its end. It is also possible to empty a file completely by an ‘open’ or ‘fopen’ call. However, sometimes it is necessary to _reduce_ the size of a file. This can be done with the ‘truncate’ and ‘ftruncate’ functions. They were introduced in BSD Unix. ‘ftruncate’ was later added to POSIX.1. Some systems allow you to extend a file (creating holes) with these functions. This is useful when using memory-mapped I/O (*note Memory-mapped I/O::), where files are not automatically extended. However, it is not portable but must be implemented if ‘mmap’ allows mapping of files (i.e., ‘_POSIX_MAPPED_FILES’ is defined). Using these functions on anything other than a regular file gives _undefined_ results. On many systems, such a call will appear to succeed, without actually accomplishing anything. -- Function: int truncate (const char *FILENAME, off_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘truncate’ function changes the size of FILENAME to LENGTH. If LENGTH is shorter than the previous length, data at the end will be lost. The file must be writable by the user to perform this operation. If LENGTH is longer, holes will be added to the end. However, some systems do not support this feature and will leave the file unchanged. When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ the ‘truncate’ function is in fact ‘truncate64’ and the type ‘off_t’ has 64 bits which makes it possible to handle files up to 2^63 bytes in length. The return value is 0 for success, or -1 for an error. In addition to the usual file name errors, the following errors may occur: ‘EACCES’ The file is a directory or not writable. ‘EINVAL’ LENGTH is negative. ‘EFBIG’ The operation would extend the file beyond the limits of the operating system. ‘EIO’ A hardware I/O error occurred. ‘EPERM’ The file is "append-only" or "immutable". ‘EINTR’ The operation was interrupted by a signal. -- Function: int truncate64 (const char *NAME, off64_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to the ‘truncate’ function. The difference is that the LENGTH argument is 64 bits wide even on 32 bits machines, which allows the handling of files with sizes up to 2^63 bytes. When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32 bits machine this function is actually available under the name ‘truncate’ and so transparently replaces the 32 bits interface. -- Function: int ftruncate (int FD, off_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This is like ‘truncate’, but it works on a file descriptor FD for an opened file instead of a file name to identify the object. The file must be opened for writing to successfully carry out the operation. The POSIX standard leaves it implementation defined what happens if the specified new LENGTH of the file is bigger than the original size. The ‘ftruncate’ function might simply leave the file alone and do nothing or it can increase the size to the desired size. In this later case the extended area should be zero-filled. So using ‘ftruncate’ is no reliable way to increase the file size but if it is possible it is probably the fastest way. The function also operates on POSIX shared memory segments if these are implemented by the system. ‘ftruncate’ is especially useful in combination with ‘mmap’. Since the mapped region must have a fixed size one cannot enlarge the file by writing something beyond the last mapped page. Instead one has to enlarge the file itself and then remap the file with the new size. The example below shows how this works. When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ the ‘ftruncate’ function is in fact ‘ftruncate64’ and the type ‘off_t’ has 64 bits which makes it possible to handle files up to 2^63 bytes in length. The return value is 0 for success, or -1 for an error. The following errors may occur: ‘EBADF’ FD does not correspond to an open file. ‘EACCES’ FD is a directory or not open for writing. ‘EINVAL’ LENGTH is negative. ‘EFBIG’ The operation would extend the file beyond the limits of the operating system. ‘EIO’ A hardware I/O error occurred. ‘EPERM’ The file is "append-only" or "immutable". ‘EINTR’ The operation was interrupted by a signal. -- Function: int ftruncate64 (int ID, off64_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is similar to the ‘ftruncate’ function. The difference is that the LENGTH argument is 64 bits wide even on 32 bits machines which allows the handling of files with sizes up to 2^63 bytes. When the source file is compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32 bits machine this function is actually available under the name ‘ftruncate’ and so transparently replaces the 32 bits interface. As announced here is a little example of how to use ‘ftruncate’ in combination with ‘mmap’: int fd; void *start; size_t len; int add (off_t at, void *block, size_t size) { if (at + size > len) { /* Resize the file and remap. */ size_t ps = sysconf (_SC_PAGESIZE); size_t ns = (at + size + ps - 1) & ~(ps - 1); void *np; if (ftruncate (fd, ns) < 0) return -1; np = mmap (NULL, ns, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0); if (np == MAP_FAILED) return -1; start = np; len = ns; } memcpy ((char *) start + at, block, size); return 0; } The function ‘add’ writes a block of memory at an arbitrary position in the file. If the current size of the file is too small it is extended. Note that it is extended by a whole number of pages. This is a requirement of ‘mmap’. The program has to keep track of the real size, and when it has finished a final ‘ftruncate’ call should set the real size of the file.  File: libc.info, Node: Storage Allocation, Prev: File Size, Up: File Attributes 14.10.11 Storage Allocation --------------------------- Most file systems support allocating large files in a non-contiguous fashion: the file is split into _fragments_ which are allocated sequentially, but the fragments themselves can be scattered across the disk. File systems generally try to avoid such fragmentation because it decreases performance, but if a file gradually increases in size, there might be no other option than to fragment it. In addition, many file systems support _sparse files_ with _holes_: regions of null bytes for which no backing storage has been allocated by the file system. When the holes are finally overwritten with data, fragmentation can occur as well. Explicit allocation of storage for yet-unwritten parts of the file can help the system to avoid fragmentation. Additionally, if storage pre-allocation fails, it is possible to report the out-of-disk error early, often without filling up the entire disk. However, due to deduplication, copy-on-write semantics, and file compression, such pre-allocation may not reliably prevent the out-of-disk-space error from occurring later. Checking for write errors is still required, and writes to memory-mapped regions created with ‘mmap’ can still result in ‘SIGBUS’. -- Function: int posix_fallocate (int FD, off_t OFFSET, off_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. Allocate backing store for the region of LENGTH bytes starting at byte OFFSET in the file for the descriptor FD. The file length is increased to ‘LENGTH + OFFSET’ if necessary. FD must be a regular file opened for writing, or ‘EBADF’ is returned. If there is insufficient disk space to fulfill the allocation request, ‘ENOSPC’ is returned. *Note:* If ‘fallocate’ is not available (because the file system does not support it), ‘posix_fallocate’ is emulated, which has the following drawbacks: • It is very inefficient because all file system blocks in the requested range need to be examined (even if they have been allocated before) and potentially rewritten. In contrast, with proper ‘fallocate’ support (see below), the file system can examine the internal file allocation data structures and eliminate holes directly, maybe even using unwritten extents (which are pre-allocated but uninitialized on disk). • There is a race condition if another thread or process modifies the underlying file in the to-be-allocated area. Non-null bytes could be overwritten with null bytes. • If FD has been opened with the ‘O_WRONLY’ flag, the function will fail with an ‘errno’ value of ‘EBADF’. • If FD has been opened with the ‘O_APPEND’ flag, the function will fail with an ‘errno’ value of ‘EBADF’. • If LENGTH is zero, ‘ftruncate’ is used to increase the file size as requested, without allocating file system blocks. There is a race condition which means that ‘ftruncate’ can accidentally truncate the file if it has been extended concurrently. On Linux, if an application does not benefit from emulation or if the emulation is harmful due to its inherent race conditions, the application can use the Linux-specific ‘fallocate’ function, with a zero flag argument. For the ‘fallocate’ function, the GNU C Library does not perform allocation emulation if the file system does not support allocation. Instead, an ‘EOPNOTSUPP’ is returned to the caller. -- Function: int posix_fallocate64 (int FD, off64_t OFFSET, off64_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is a variant of ‘posix_fallocate64’ which accepts 64-bit file offsets on all platforms.  File: libc.info, Node: Making Special Files, Next: Temporary Files, Prev: File Attributes, Up: File System Interface 14.11 Making Special Files ========================== The ‘mknod’ function is the primitive for making special files, such as files that correspond to devices. The GNU C Library includes this function for compatibility with BSD. The prototype for ‘mknod’ is declared in ‘sys/stat.h’. -- Function: int mknod (const char *FILENAME, mode_t MODE, dev_t DEV) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘mknod’ function makes a special file with name FILENAME. The MODE specifies the mode of the file, and may include the various special file bits, such as ‘S_IFCHR’ (for a character special file) or ‘S_IFBLK’ (for a block special file). *Note Testing File Type::. The DEV argument specifies which device the special file refers to. Its exact interpretation depends on the kind of special file being created. The return value is ‘0’ on success and ‘-1’ on error. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EPERM’ The calling process is not privileged. Only the superuser can create special files. ‘ENOSPC’ The directory or file system that would contain the new file is full and cannot be extended. ‘EROFS’ The directory containing the new file can't be modified because it's on a read-only file system. ‘EEXIST’ There is already a file named FILENAME. If you want to replace this file, you must remove the old file explicitly first.  File: libc.info, Node: Temporary Files, Prev: Making Special Files, Up: File System Interface 14.12 Temporary Files ===================== If you need to use a temporary file in your program, you can use the ‘tmpfile’ function to open it. Or you can use the ‘tmpnam’ (better: ‘tmpnam_r’) function to provide a name for a temporary file and then you can open it in the usual way with ‘fopen’. The ‘tempnam’ function is like ‘tmpnam’ but lets you choose what directory temporary files will go in, and something about what their file names will look like. Important for multi-threaded programs is that ‘tempnam’ is reentrant, while ‘tmpnam’ is not since it returns a pointer to a static buffer. These facilities are declared in the header file ‘stdio.h’. -- Function: FILE * tmpfile (void) Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem fd lock | *Note POSIX Safety Concepts::. This function creates a temporary binary file for update mode, as if by calling ‘fopen’ with mode ‘"wb+"’. The file is deleted automatically when it is closed or when the program terminates. (On some other ISO C systems the file may fail to be deleted if the program terminates abnormally). This function is reentrant. When the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32-bit system this function is in fact ‘tmpfile64’, i.e., the LFS interface transparently replaces the old interface. -- Function: FILE * tmpfile64 (void) Preliminary: | MT-Safe | AS-Unsafe heap lock | AC-Unsafe mem fd lock | *Note POSIX Safety Concepts::. This function is similar to ‘tmpfile’, but the stream it returns a pointer to was opened using ‘tmpfile64’. Therefore this stream can be used for files larger than 2^31 bytes on 32-bit machines. Please note that the return type is still ‘FILE *’. There is no special ‘FILE’ type for the LFS interface. If the sources are compiled with ‘_FILE_OFFSET_BITS == 64’ on a 32 bits machine this function is available under the name ‘tmpfile’ and so transparently replaces the old interface. -- Function: char * tmpnam (char *RESULT) Preliminary: | MT-Unsafe race:tmpnam/!result | AS-Unsafe | AC-Safe | *Note POSIX Safety Concepts::. This function constructs and returns a valid file name that does not refer to any existing file. If the RESULT argument is a null pointer, the return value is a pointer to an internal static string, which might be modified by subsequent calls and therefore makes this function non-reentrant. Otherwise, the RESULT argument should be a pointer to an array of at least ‘L_tmpnam’ characters, and the result is written into that array. It is possible for ‘tmpnam’ to fail if you call it too many times without removing previously-created files. This is because the limited length of the temporary file names gives room for only a finite number of different names. If ‘tmpnam’ fails it returns a null pointer. *Warning:* Between the time the pathname is constructed and the file is created another process might have created a file with the same name using ‘tmpnam’, leading to a possible security hole. The implementation generates names which can hardly be predicted, but when opening the file you should use the ‘O_EXCL’ flag. Using ‘tmpfile’ or ‘mkstemp’ is a safe way to avoid this problem. -- Function: char * tmpnam_r (char *RESULT) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This function is nearly identical to the ‘tmpnam’ function, except that if RESULT is a null pointer it returns a null pointer. This guarantees reentrancy because the non-reentrant situation of ‘tmpnam’ cannot happen here. *Warning*: This function has the same security problems as ‘tmpnam’. -- Macro: int L_tmpnam The value of this macro is an integer constant expression that represents the minimum size of a string large enough to hold a file name generated by the ‘tmpnam’ function. -- Macro: int TMP_MAX The macro ‘TMP_MAX’ is a lower bound for how many temporary names you can create with ‘tmpnam’. You can rely on being able to call ‘tmpnam’ at least this many times before it might fail saying you have made too many temporary file names. With the GNU C Library, you can create a very large number of temporary file names. If you actually created the files, you would probably run out of disk space before you ran out of names. Some other systems have a fixed, small limit on the number of temporary files. The limit is never less than ‘25’. -- Function: char * tempnam (const char *DIR, const char *PREFIX) Preliminary: | MT-Safe env | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. This function generates a unique temporary file name. If PREFIX is not a null pointer, up to five characters of this string are used as a prefix for the file name. The return value is a string newly allocated with ‘malloc’, so you should release its storage with ‘free’ when it is no longer needed. Because the string is dynamically allocated this function is reentrant. The directory prefix for the temporary file name is determined by testing each of the following in sequence. The directory must exist and be writable. • The environment variable ‘TMPDIR’, if it is defined. For security reasons this only happens if the program is not SUID or SGID enabled. • The DIR argument, if it is not a null pointer. • The value of the ‘P_tmpdir’ macro. • The directory ‘/tmp’. This function is defined for SVID compatibility. *Warning:* Between the time the pathname is constructed and the file is created another process might have created a file with the same name using ‘tempnam’, leading to a possible security hole. The implementation generates names which can hardly be predicted, but when opening the file you should use the ‘O_EXCL’ flag. Using ‘tmpfile’ or ‘mkstemp’ is a safe way to avoid this problem. -- SVID Macro: char * P_tmpdir This macro is the name of the default directory for temporary files. Older Unix systems did not have the functions just described. Instead they used ‘mktemp’ and ‘mkstemp’. Both of these functions work by modifying a file name template string you pass. The last six characters of this string must be ‘XXXXXX’. These six ‘X’s are replaced with six characters which make the whole string a unique file name. Usually the template string is something like ‘/tmp/PREFIXXXXXXX’, and each program uses a unique PREFIX. *NB:* Because ‘mktemp’ and ‘mkstemp’ modify the template string, you _must not_ pass string constants to them. String constants are normally in read-only storage, so your program would crash when ‘mktemp’ or ‘mkstemp’ tried to modify the string. These functions are declared in the header file ‘stdlib.h’. -- Function: char * mktemp (char *TEMPLATE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘mktemp’ function generates a unique file name by modifying TEMPLATE as described above. If successful, it returns TEMPLATE as modified. If ‘mktemp’ cannot find a unique file name, it makes TEMPLATE an empty string and returns that. If TEMPLATE does not end with ‘XXXXXX’, ‘mktemp’ returns a null pointer. *Warning:* Between the time the pathname is constructed and the file is created another process might have created a file with the same name using ‘mktemp’, leading to a possible security hole. The implementation generates names which can hardly be predicted, but when opening the file you should use the ‘O_EXCL’ flag. Using ‘mkstemp’ is a safe way to avoid this problem. -- Function: int mkstemp (char *TEMPLATE) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. The ‘mkstemp’ function generates a unique file name just as ‘mktemp’ does, but it also opens the file for you with ‘open’ (*note Opening and Closing Files::). If successful, it modifies TEMPLATE in place and returns a file descriptor for that file open for reading and writing. If ‘mkstemp’ cannot create a uniquely-named file, it returns ‘-1’. If TEMPLATE does not end with ‘XXXXXX’, ‘mkstemp’ returns ‘-1’ and does not modify TEMPLATE. The file is opened using mode ‘0600’. If the file is meant to be used by other users this mode must be changed explicitly. Unlike ‘mktemp’, ‘mkstemp’ is actually guaranteed to create a unique file that cannot possibly clash with any other program trying to create a temporary file. This is because it works by calling ‘open’ with the ‘O_EXCL’ flag, which says you want to create a new file and get an error if the file already exists. -- Function: char * mkdtemp (char *TEMPLATE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘mkdtemp’ function creates a directory with a unique name. If it succeeds, it overwrites TEMPLATE with the name of the directory, and returns TEMPLATE. As with ‘mktemp’ and ‘mkstemp’, TEMPLATE should be a string ending with ‘XXXXXX’. If ‘mkdtemp’ cannot create an uniquely named directory, it returns ‘NULL’ and sets ‘errno’ appropriately. If TEMPLATE does not end with ‘XXXXXX’, ‘mkdtemp’ returns ‘NULL’ and does not modify TEMPLATE. ‘errno’ will be set to ‘EINVAL’ in this case. The directory is created using mode ‘0700’. The directory created by ‘mkdtemp’ cannot clash with temporary files or directories created by other users. This is because directory creation always works like ‘open’ with ‘O_EXCL’. *Note Creating Directories::. The ‘mkdtemp’ function comes from OpenBSD.  File: libc.info, Node: Pipes and FIFOs, Next: Sockets, Prev: File System Interface, Up: Top 15 Pipes and FIFOs ****************** A “pipe” is a mechanism for interprocess communication; data written to the pipe by one process can be read by another process. The data is handled in a first-in, first-out (FIFO) order. The pipe has no name; it is created for one use and both ends must be inherited from the single process which created the pipe. A “FIFO special file” is similar to a pipe, but instead of being an anonymous, temporary connection, a FIFO has a name or names like any other file. Processes open the FIFO by name in order to communicate through it. A pipe or FIFO has to be open at both ends simultaneously. If you read from a pipe or FIFO file that doesn't have any processes writing to it (perhaps because they have all closed the file, or exited), the read returns end-of-file. Writing to a pipe or FIFO that doesn't have a reading process is treated as an error condition; it generates a ‘SIGPIPE’ signal, and fails with error code ‘EPIPE’ if the signal is handled or blocked. Neither pipes nor FIFO special files allow file positioning. Both reading and writing operations happen sequentially; reading from the beginning of the file and writing at the end. * Menu: * Creating a Pipe:: Making a pipe with the ‘pipe’ function. * Pipe to a Subprocess:: Using a pipe to communicate with a child process. * FIFO Special Files:: Making a FIFO special file. * Pipe Atomicity:: When pipe (or FIFO) I/O is atomic.  File: libc.info, Node: Creating a Pipe, Next: Pipe to a Subprocess, Up: Pipes and FIFOs 15.1 Creating a Pipe ==================== The primitive for creating a pipe is the ‘pipe’ function. This creates both the reading and writing ends of the pipe. It is not very useful for a single process to use a pipe to talk to itself. In typical use, a process creates a pipe just before it forks one or more child processes (*note Creating a Process::). The pipe is then used for communication either between the parent or child processes, or between two sibling processes. The ‘pipe’ function is declared in the header file ‘unistd.h’. -- Function: int pipe (int FILEDES[2]) Preliminary: | MT-Safe | AS-Safe | AC-Safe fd | *Note POSIX Safety Concepts::. The ‘pipe’ function creates a pipe and puts the file descriptors for the reading and writing ends of the pipe (respectively) into ‘FILEDES[0]’ and ‘FILEDES[1]’. An easy way to remember that the input end comes first is that file descriptor ‘0’ is standard input, and file descriptor ‘1’ is standard output. If successful, ‘pipe’ returns a value of ‘0’. On failure, ‘-1’ is returned. The following ‘errno’ error conditions are defined for this function: ‘EMFILE’ The process has too many files open. ‘ENFILE’ There are too many open files in the entire system. *Note Error Codes::, for more information about ‘ENFILE’. This error never occurs on GNU/Hurd systems. Here is an example of a simple program that creates a pipe. This program uses the ‘fork’ function (*note Creating a Process::) to create a child process. The parent process writes data to the pipe, which is read by the child process. #include #include #include #include /* Read characters from the pipe and echo them to ‘stdout’. */ void read_from_pipe (int file) { FILE *stream; int c; stream = fdopen (file, "r"); while ((c = fgetc (stream)) != EOF) putchar (c); fclose (stream); } /* Write some random text to the pipe. */ void write_to_pipe (int file) { FILE *stream; stream = fdopen (file, "w"); fprintf (stream, "hello, world!\n"); fprintf (stream, "goodbye, world!\n"); fclose (stream); } int main (void) { pid_t pid; int mypipe[2]; /* Create the pipe. */ if (pipe (mypipe)) { fprintf (stderr, "Pipe failed.\n"); return EXIT_FAILURE; } /* Create the child process. */ pid = fork (); if (pid == (pid_t) 0) { /* This is the child process. Close other end first. */ close (mypipe[1]); read_from_pipe (mypipe[0]); return EXIT_SUCCESS; } else if (pid < (pid_t) 0) { /* The fork failed. */ fprintf (stderr, "Fork failed.\n"); return EXIT_FAILURE; } else { /* This is the parent process. Close other end first. */ close (mypipe[0]); write_to_pipe (mypipe[1]); return EXIT_SUCCESS; } }  File: libc.info, Node: Pipe to a Subprocess, Next: FIFO Special Files, Prev: Creating a Pipe, Up: Pipes and FIFOs 15.2 Pipe to a Subprocess ========================= A common use of pipes is to send data to or receive data from a program being run as a subprocess. One way of doing this is by using a combination of ‘pipe’ (to create the pipe), ‘fork’ (to create the subprocess), ‘dup2’ (to force the subprocess to use the pipe as its standard input or output channel), and ‘exec’ (to execute the new program). Or, you can use ‘popen’ and ‘pclose’. The advantage of using ‘popen’ and ‘pclose’ is that the interface is much simpler and easier to use. But it doesn't offer as much flexibility as using the low-level functions directly. -- Function: FILE * popen (const char *COMMAND, const char *MODE) Preliminary: | MT-Safe | AS-Unsafe heap corrupt | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘popen’ function is closely related to the ‘system’ function; see *note Running a Command::. It executes the shell command COMMAND as a subprocess. However, instead of waiting for the command to complete, it creates a pipe to the subprocess and returns a stream that corresponds to that pipe. If you specify a MODE argument of ‘"r"’, you can read from the stream to retrieve data from the standard output channel of the subprocess. The subprocess inherits its standard input channel from the parent process. Similarly, if you specify a MODE argument of ‘"w"’, you can write to the stream to send data to the standard input channel of the subprocess. The subprocess inherits its standard output channel from the parent process. In the event of an error ‘popen’ returns a null pointer. This might happen if the pipe or stream cannot be created, if the subprocess cannot be forked, or if the program cannot be executed. -- Function: int pclose (FILE *STREAM) Preliminary: | MT-Safe | AS-Unsafe heap plugin corrupt lock | AC-Unsafe corrupt lock fd mem | *Note POSIX Safety Concepts::. The ‘pclose’ function is used to close a stream created by ‘popen’. It waits for the child process to terminate and returns its status value, as for the ‘system’ function. Here is an example showing how to use ‘popen’ and ‘pclose’ to filter output through another program, in this case the paging program ‘more’. #include #include void write_data (FILE * stream) { int i; for (i = 0; i < 100; i++) fprintf (stream, "%d\n", i); if (ferror (stream)) { fprintf (stderr, "Output to stream failed.\n"); exit (EXIT_FAILURE); } } int main (void) { FILE *output; output = popen ("more", "w"); if (!output) { fprintf (stderr, "incorrect parameters or too many files.\n"); return EXIT_FAILURE; } write_data (output); if (pclose (output) != 0) { fprintf (stderr, "Could not run more or other error.\n"); } return EXIT_SUCCESS; }  File: libc.info, Node: FIFO Special Files, Next: Pipe Atomicity, Prev: Pipe to a Subprocess, Up: Pipes and FIFOs 15.3 FIFO Special Files ======================= A FIFO special file is similar to a pipe, except that it is created in a different way. Instead of being an anonymous communications channel, a FIFO special file is entered into the file system by calling ‘mkfifo’. Once you have created a FIFO special file in this way, any process can open it for reading or writing, in the same way as an ordinary file. However, it has to be open at both ends simultaneously before you can proceed to do any input or output operations on it. Opening a FIFO for reading normally blocks until some other process opens the same FIFO for writing, and vice versa. The ‘mkfifo’ function is declared in the header file ‘sys/stat.h’. -- Function: int mkfifo (const char *FILENAME, mode_t MODE) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘mkfifo’ function makes a FIFO special file with name FILENAME. The MODE argument is used to set the file's permissions; see *note Setting Permissions::. The normal, successful return value from ‘mkfifo’ is ‘0’. In the case of an error, ‘-1’ is returned. In addition to the usual file name errors (*note File Name Errors::), the following ‘errno’ error conditions are defined for this function: ‘EEXIST’ The named file already exists. ‘ENOSPC’ The directory or file system cannot be extended. ‘EROFS’ The directory that would contain the file resides on a read-only file system.  File: libc.info, Node: Pipe Atomicity, Prev: FIFO Special Files, Up: Pipes and FIFOs 15.4 Atomicity of Pipe I/O ========================== Reading or writing pipe data is “atomic” if the size of data written is not greater than ‘PIPE_BUF’. This means that the data transfer seems to be an instantaneous unit, in that nothing else in the system can observe a state in which it is partially complete. Atomic I/O may not begin right away (it may need to wait for buffer space or for data), but once it does begin it finishes immediately. Reading or writing a larger amount of data may not be atomic; for example, output data from other processes sharing the descriptor may be interspersed. Also, once ‘PIPE_BUF’ characters have been written, further writes will block until some characters are read. *Note Limits for Files::, for information about the ‘PIPE_BUF’ parameter.  File: libc.info, Node: Sockets, Next: Low-Level Terminal Interface, Prev: Pipes and FIFOs, Up: Top 16 Sockets ********** This chapter describes the GNU facilities for interprocess communication using sockets. A “socket” is a generalized interprocess communication channel. Like a pipe, a socket is represented as a file descriptor. Unlike pipes sockets support communication between unrelated processes, and even between processes running on different machines that communicate over a network. Sockets are the primary means of communicating with other machines; ‘telnet’, ‘rlogin’, ‘ftp’, ‘talk’ and the other familiar network programs use sockets. Not all operating systems support sockets. In the GNU C Library, the header file ‘sys/socket.h’ exists regardless of the operating system, and the socket functions always exist, but if the system does not really support sockets these functions always fail. *Incomplete:* We do not currently document the facilities for broadcast messages or for configuring Internet interfaces. The reentrant functions and some newer functions that are related to IPv6 aren't documented either so far. * Menu: * Socket Concepts:: Basic concepts you need to know about. * Communication Styles::Stream communication, datagrams and other styles. * Socket Addresses:: How socket names ("addresses") work. * Interface Naming:: Identifying specific network interfaces. * Local Namespace:: Details about the local namespace. * Internet Namespace:: Details about the Internet namespace. * Misc Namespaces:: Other namespaces not documented fully here. * Open/Close Sockets:: Creating sockets and destroying them. * Connections:: Operations on sockets with connection state. * Datagrams:: Operations on datagram sockets. * Inetd:: Inetd is a daemon that starts servers on request. The most convenient way to write a server is to make it work with Inetd. * Socket Options:: Miscellaneous low-level socket options. * Networks Database:: Accessing the database of network names. * Other Socket APIs:: Other socket-related functions.  File: libc.info, Node: Socket Concepts, Next: Communication Styles, Up: Sockets 16.1 Socket Concepts ==================== When you create a socket, you must specify the style of communication you want to use and the type of protocol that should implement it. The “communication style” of a socket defines the user-level semantics of sending and receiving data on the socket. Choosing a communication style specifies the answers to questions such as these: • *What are the units of data transmission?* Some communication styles regard the data as a sequence of bytes with no larger structure; others group the bytes into records (which are known in this context as “packets”). • *Can data be lost during normal operation?* Some communication styles guarantee that all the data sent arrives in the order it was sent (barring system or network crashes); other styles occasionally lose data as a normal part of operation, and may sometimes deliver packets more than once or in the wrong order. Designing a program to use unreliable communication styles usually involves taking precautions to detect lost or misordered packets and to retransmit data as needed. • *Is communication entirely with one partner?* Some communication styles are like a telephone call--you make a “connection” with one remote socket and then exchange data freely. Other styles are like mailing letters--you specify a destination address for each message you send. You must also choose a “namespace” for naming the socket. A socket name ("address") is meaningful only in the context of a particular namespace. In fact, even the data type to use for a socket name may depend on the namespace. Namespaces are also called "domains", but we avoid that word as it can be confused with other usage of the same term. Each namespace has a symbolic name that starts with ‘PF_’. A corresponding symbolic name starting with ‘AF_’ designates the address format for that namespace. Finally you must choose the “protocol” to carry out the communication. The protocol determines what low-level mechanism is used to transmit and receive data. Each protocol is valid for a particular namespace and communication style; a namespace is sometimes called a “protocol family” because of this, which is why the namespace names start with ‘PF_’. The rules of a protocol apply to the data passing between two programs, perhaps on different computers; most of these rules are handled by the operating system and you need not know about them. What you do need to know about protocols is this: • In order to have communication between two sockets, they must specify the _same_ protocol. • Each protocol is meaningful with particular style/namespace combinations and cannot be used with inappropriate combinations. For example, the TCP protocol fits only the byte stream style of communication and the Internet namespace. • For each combination of style and namespace there is a “default protocol”, which you can request by specifying 0 as the protocol number. And that's what you should normally do--use the default. Throughout the following description at various places variables/parameters to denote sizes are required. And here the trouble starts. In the first implementations the type of these variables was simply ‘int’. On most machines at that time an ‘int’ was 32 bits wide, which created a _de facto_ standard requiring 32-bit variables. This is important since references to variables of this type are passed to the kernel. Then the POSIX people came and unified the interface with the words "all size values are of type ‘size_t’". On 64-bit machines ‘size_t’ is 64 bits wide, so pointers to variables were no longer possible. The Unix98 specification provides a solution by introducing a type ‘socklen_t’. This type is used in all of the cases that POSIX changed to use ‘size_t’. The only requirement of this type is that it be an unsigned type of at least 32 bits. Therefore, implementations which require that references to 32-bit variables be passed can be as happy as implementations which use 64-bit values.  File: libc.info, Node: Communication Styles, Next: Socket Addresses, Prev: Socket Concepts, Up: Sockets 16.2 Communication Styles ========================= The GNU C Library includes support for several different kinds of sockets, each with different characteristics. This section describes the supported socket types. The symbolic constants listed here are defined in ‘sys/socket.h’. -- Macro: int SOCK_STREAM The ‘SOCK_STREAM’ style is like a pipe (*note Pipes and FIFOs::). It operates over a connection with a particular remote socket and transmits data reliably as a stream of bytes. Use of this style is covered in detail in *note Connections::. -- Macro: int SOCK_DGRAM The ‘SOCK_DGRAM’ style is used for sending individually-addressed packets unreliably. It is the diametrical opposite of ‘SOCK_STREAM’. Each time you write data to a socket of this kind, that data becomes one packet. Since ‘SOCK_DGRAM’ sockets do not have connections, you must specify the recipient address with each packet. The only guarantee that the system makes about your requests to transmit data is that it will try its best to deliver each packet you send. It may succeed with the sixth packet after failing with the fourth and fifth packets; the seventh packet may arrive before the sixth, and may arrive a second time after the sixth. The typical use for ‘SOCK_DGRAM’ is in situations where it is acceptable to simply re-send a packet if no response is seen in a reasonable amount of time. *Note Datagrams::, for detailed information about how to use datagram sockets. -- Macro: int SOCK_RAW This style provides access to low-level network protocols and interfaces. Ordinary user programs usually have no need to use this style.  File: libc.info, Node: Socket Addresses, Next: Interface Naming, Prev: Communication Styles, Up: Sockets 16.3 Socket Addresses ===================== The name of a socket is normally called an “address”. The functions and symbols for dealing with socket addresses were named inconsistently, sometimes using the term "name" and sometimes using "address". You can regard these terms as synonymous where sockets are concerned. A socket newly created with the ‘socket’ function has no address. Other processes can find it for communication only if you give it an address. We call this “binding” the address to the socket, and the way to do it is with the ‘bind’ function. You need only be concerned with the address of a socket if other processes are to find it and start communicating with it. You can specify an address for other sockets, but this is usually pointless; the first time you send data from a socket, or use it to initiate a connection, the system assigns an address automatically if you have not specified one. Occasionally a client needs to specify an address because the server discriminates based on address; for example, the rsh and rlogin protocols look at the client's socket address and only bypass passphrase checking if it is less than ‘IPPORT_RESERVED’ (*note Ports::). The details of socket addresses vary depending on what namespace you are using. *Note Local Namespace::, or *note Internet Namespace::, for specific information. Regardless of the namespace, you use the same functions ‘bind’ and ‘getsockname’ to set and examine a socket's address. These functions use a phony data type, ‘struct sockaddr *’, to accept the address. In practice, the address lives in a structure of some other data type appropriate to the address format you are using, but you cast its address to ‘struct sockaddr *’ when you pass it to ‘bind’. * Menu: * Address Formats:: About ‘struct sockaddr’. * Setting Address:: Binding an address to a socket. * Reading Address:: Reading the address of a socket.  File: libc.info, Node: Address Formats, Next: Setting Address, Up: Socket Addresses 16.3.1 Address Formats ---------------------- The functions ‘bind’ and ‘getsockname’ use the generic data type ‘struct sockaddr *’ to represent a pointer to a socket address. You can't use this data type effectively to interpret an address or construct one; for that, you must use the proper data type for the socket's namespace. Thus, the usual practice is to construct an address of the proper namespace-specific type, then cast a pointer to ‘struct sockaddr *’ when you call ‘bind’ or ‘getsockname’. The one piece of information that you can get from the ‘struct sockaddr’ data type is the “address format designator”. This tells you which data type to use to understand the address fully. The symbols in this section are defined in the header file ‘sys/socket.h’. -- Data Type: struct sockaddr The ‘struct sockaddr’ type itself has the following members: ‘short int sa_family’ This is the code for the address format of this address. It identifies the format of the data which follows. ‘char sa_data[14]’ This is the actual socket address data, which is format-dependent. Its length also depends on the format, and may well be more than 14. The length 14 of ‘sa_data’ is essentially arbitrary. Each address format has a symbolic name which starts with ‘AF_’. Each of them corresponds to a ‘PF_’ symbol which designates the corresponding namespace. Here is a list of address format names: ‘AF_LOCAL’ This designates the address format that goes with the local namespace. (‘PF_LOCAL’ is the name of that namespace.) *Note Local Namespace Details::, for information about this address format. ‘AF_UNIX’ This is a synonym for ‘AF_LOCAL’. Although ‘AF_LOCAL’ is mandated by POSIX.1g, ‘AF_UNIX’ is portable to more systems. ‘AF_UNIX’ was the traditional name stemming from BSD, so even most POSIX systems support it. It is also the name of choice in the Unix98 specification. (The same is true for ‘PF_UNIX’ vs. ‘PF_LOCAL’). ‘AF_FILE’ This is another synonym for ‘AF_LOCAL’, for compatibility. (‘PF_FILE’ is likewise a synonym for ‘PF_LOCAL’.) ‘AF_INET’ This designates the address format that goes with the Internet namespace. (‘PF_INET’ is the name of that namespace.) *Note Internet Address Formats::. ‘AF_INET6’ This is similar to ‘AF_INET’, but refers to the IPv6 protocol. (‘PF_INET6’ is the name of the corresponding namespace.) ‘AF_UNSPEC’ This designates no particular address format. It is used only in rare cases, such as to clear out the default destination address of a "connected" datagram socket. *Note Sending Datagrams::. The corresponding namespace designator symbol ‘PF_UNSPEC’ exists for completeness, but there is no reason to use it in a program. ‘sys/socket.h’ defines symbols starting with ‘AF_’ for many different kinds of networks, most or all of which are not actually implemented. We will document those that really work as we receive information about how to use them.  File: libc.info, Node: Setting Address, Next: Reading Address, Prev: Address Formats, Up: Socket Addresses 16.3.2 Setting the Address of a Socket -------------------------------------- Use the ‘bind’ function to assign an address to a socket. The prototype for ‘bind’ is in the header file ‘sys/socket.h’. For examples of use, see *note Local Socket Example::, or see *note Inet Example::. -- Function: int bind (int SOCKET, struct sockaddr *ADDR, socklen_t LENGTH) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. The ‘bind’ function assigns an address to the socket SOCKET. The ADDR and LENGTH arguments specify the address; the detailed format of the address depends on the namespace. The first part of the address is always the format designator, which specifies a namespace, and says that the address is in the format of that namespace. The return value is ‘0’ on success and ‘-1’ on failure. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘EADDRNOTAVAIL’ The specified address is not available on this machine. ‘EADDRINUSE’ Some other socket is already using the specified address. ‘EINVAL’ The socket SOCKET already has an address. ‘EACCES’ You do not have permission to access the requested address. (In the Internet domain, only the super-user is allowed to specify a port number in the range 0 through ‘IPPORT_RESERVED’ minus one; see *note Ports::.) Additional conditions may be possible depending on the particular namespace of the socket.  File: libc.info, Node: Reading Address, Prev: Setting Address, Up: Socket Addresses 16.3.3 Reading the Address of a Socket -------------------------------------- Use the function ‘getsockname’ to examine the address of an Internet socket. The prototype for this function is in the header file ‘sys/socket.h’. -- Function: int getsockname (int SOCKET, struct sockaddr *ADDR, socklen_t *LENGTH-PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe mem/hurd | *Note POSIX Safety Concepts::. The ‘getsockname’ function returns information about the address of the socket SOCKET in the locations specified by the ADDR and LENGTH-PTR arguments. Note that the LENGTH-PTR is a pointer; you should initialize it to be the allocation size of ADDR, and on return it contains the actual size of the address data. The format of the address data depends on the socket namespace. The length of the information is usually fixed for a given namespace, so normally you can know exactly how much space is needed and can provide that much. The usual practice is to allocate a place for the value using the proper data type for the socket's namespace, then cast its address to ‘struct sockaddr *’ to pass it to ‘getsockname’. The return value is ‘0’ on success and ‘-1’ on error. The following ‘errno’ error conditions are defined for this function: ‘EBADF’ The SOCKET argument is not a valid file descriptor. ‘ENOTSOCK’ The descriptor SOCKET is not a socket. ‘ENOBUFS’ There are not enough internal buffers available for the operation. You can't read the address of a socket in the file namespace. This is consistent with the rest of the system; in general, there's no way to find a file's name from a descriptor for that file.  File: libc.info, Node: Interface Naming, Next: Local Namespace, Prev: Socket Addresses, Up: Sockets 16.4 Interface Naming ===================== Each network interface has a name. This usually consists of a few letters that relate to the type of interface, which may be followed by a number if there is more than one interface of that type. Examples might be ‘lo’ (the loopback interface) and ‘eth0’ (the first Ethernet interface). Although such names are convenient for humans, it would be clumsy to have to use them whenever a program needs to refer to an interface. In such situations an interface is referred to by its “index”, which is an arbitrarily-assigned small positive integer. The following functions, constants and data types are declared in the header file ‘net/if.h’. -- Constant: size_t IFNAMSIZ This constant defines the maximum buffer size needed to hold an interface name, including its terminating zero byte. -- Function: unsigned int if_nametoindex (const char *IFNAME) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note POSIX Safety Concepts::. This function yields the interface index corresponding to a particular name. If no interface exists with the name given, it returns 0. -- Function: char * if_indextoname (unsigned int IFINDEX, char *IFNAME) Preliminary: | MT-Safe | AS-Unsafe lock | AC-Unsafe lock fd | *Note POSIX Safety Concepts::. This function maps an interface index to its corresponding name. The returned name is placed in the buffer pointed to by ‘ifname’, which must be at least ‘IFNAMSIZ’ bytes in length. If the index was invalid, the function's return value is a null pointer, otherwise it is ‘ifname’. -- Data Type: struct if_nameindex This data type is used to hold the information about a single interface. It has the following members: ‘unsigned int if_index;’ This is the interface index. ‘char *if_name’ This is the null-terminated index name. -- Function: struct if_nameindex * if_nameindex (void) Preliminary: | MT-Safe | AS-Unsafe heap lock/hurd | AC-Unsafe lock/hurd fd mem | *Note POSIX Safety Concepts::. This function returns an array of ‘if_nameindex’ structures, one for every interface that is present. The end of the list is indicated by a structure with an interface of 0 and a null name pointer. If an error occurs, this function returns a null pointer. The returned structure must be freed with ‘if_freenameindex’ after use. -- Function: void if_freenameindex (struct if_nameindex *PTR) Preliminary: | MT-Safe | AS-Unsafe heap | AC-Unsafe mem | *Note POSIX Safety Concepts::. This function frees the structure returned by an earlier call to ‘if_nameindex’.  File: libc.info, Node: Local Namespace, Next: Internet Namespace, Prev: Interface Naming, Up: Sockets 16.5 The Local Namespace ======================== This section describes the details of the local namespace, whose symbolic name (required when you create a socket) is ‘PF_LOCAL’. The local namespace is also known as "Unix domain sockets". Another name is file namespace since socket addresses are normally implemented as file names. * Menu: * Concepts: Local Namespace Concepts. What you need to understand. * Details: Local Namespace Details. Address format, symbolic names, etc. * Example: Local Socket Example. Example of creating a socket.  File: libc.info, Node: Local Namespace Concepts, Next: Local Namespace Details, Up: Local Namespace 16.5.1 Local Namespace Concepts ------------------------------- In the local namespace socket addresses are file names. You can specify any file name you want as the address of the socket, but you must have write permission on the directory containing it. It's common to put these files in the ‘/tmp’ directory. One peculiarity of the local namespace is that the name is only used when opening the connection; once open the address is not meaningful and may not exist. Another peculiarity is that you cannot connect to such a socket from another machine-not even if the other machine shares the file system which contains the name of the socket. You can see the socket in a directory listing, but connecting to it never succeeds. Some programs take advantage of this, such as by asking the client to send its own process ID, and using the process IDs to distinguish between clients. However, we recommend you not use this method in protocols you design, as we might someday permit connections from other machines that mount the same file systems. Instead, send each new client an identifying number if you want it to have one. After you close a socket in the local namespace, you should delete the file name from the file system. Use ‘unlink’ or ‘remove’ to do this; see *note Deleting Files::. The local namespace supports just one protocol for any communication style; it is protocol number ‘0’.  File: libc.info, Node: Local Namespace Details, Next: Local Socket Example, Prev: Local Namespace Concepts, Up: Local Namespace 16.5.2 Details of Local Namespace --------------------------------- To create a socket in the local namespace, use the constant ‘PF_LOCAL’ as the NAMESPACE argument to ‘socket’ or ‘socketpair’. This constant is defined in ‘sys/socket.h’. -- Macro: int PF_LOCAL This designates the local namespace, in which socket addresses are local names, and its associated family of protocols. ‘PF_LOCAL’ is the macro used by POSIX.1g. -- Macro: int PF_UNIX This is a synonym for ‘PF_LOCAL’, for compatibility's sake. -- Macro: int PF_FILE This is a synonym for ‘PF_LOCAL’, for compatibility's sake. The structure for specifying socket names in the local namespace is defined in the header file ‘sys/un.h’: -- Data Type: struct sockaddr_un This structure is used to specify local namespace socket addresses. It has the following members: ‘short int sun_family’ This identifies the address family or format of the socket address. You should store the value ‘AF_LOCAL’ to designate the local namespace. *Note Socket Addresses::. ‘char sun_path[108]’ This is the file name to use. *Incomplete:* Why is 108 a magic number? RMS suggests making this a zero-length array and tweaking the following example to use ‘alloca’ to allocate an appropriate amount of storage based on the length of the filename. You should compute the LENGTH parameter for a socket address in the local namespace as the sum of the size of the ‘sun_family’ component and the string length (_not_ the allocation size!) of the file name string. This can be done using the macro ‘SUN_LEN’: -- Macro: int SUN_LEN (_struct sockaddr_un *_ PTR) Preliminary: | MT-Safe | AS-Safe | AC-Safe | *Note POSIX Safety Concepts::. This macro computes the length of the socket address in the local namespace.  File: libc.info, Node: Local Socket Example, Prev: Local Namespace Details, Up: Local Namespace 16.5.3 Example of Local-Namespace Sockets ----------------------------------------- Here is an example showing how to create and name a socket in the local namespace. #include #include #include #include #include #include #include int make_named_socket (const char *filename) { struct sockaddr_un name; int sock; size_t size; /* Create the socket. */ sock = socket (PF_LOCAL, SOCK_DGRAM, 0); if (sock < 0) { perror ("socket"); exit (EXIT_FAILURE); } /* Bind a name to the socket. */ name.sun_family = AF_LOCAL; strncpy (name.sun_path, filename, sizeof (name.sun_path)); name.sun_path[sizeof (name.sun_path) - 1] = '\0'; /* The size of the address is the offset of the start of the filename, plus its length (not including the terminating null byte). Alternatively you can just do: size = SUN_LEN (&name); */ size = (offsetof (struct sockaddr_un, sun_path) + strlen (name.sun_path)); if (bind (sock, (struct sockaddr *) &name, size) < 0) { perror ("bind"); exit (EXIT_FAILURE); } return sock; }  File: libc.info, Node: Internet Namespace, Next: Misc Namespaces, Prev: Local Namespace, Up: Sockets 16.6 The Internet Namespace =========================== This section describes the details of the protocols and socket naming conventions used in the Internet namespace. Originally the Internet namespace used only IP version 4 (IPv4). With the growing number of hosts on the Internet, a new protocol with a larger address space was necessary: IP version 6 (IPv6). IPv6 introduces 128-bit addresses (IPv4 has 32-bit addresses) and other features, and will eventually replace IPv4. To create a socket in the IPv4 Internet namespace, use the symbolic name ‘PF_INET’ of this namespace as the NAMESPACE argument to ‘socket’ or ‘socketpair’. For IPv6 addresses you need the macro ‘PF_INET6’. These macros are defined in ‘sys/socket.h’. -- Macro: int PF_INET This designates the IPv4 Internet namespace and associated family of protocols. -- Macro: int PF_INET6 This designates the IPv6 Internet namespace and associated family of protocols. A socket address for the Internet namespace includes the following components: • The address of the machine you want to connect to. Internet addresses can be specified in several ways; these are discussed in *note Internet Address Formats::, *note Host Addresses:: and *note Host Names::. • A port number for that machine. *Note Ports::. You must ensure that the address and port number are represented in a canonical format called “network byte order”. *Note Byte Order::, for information about this. * Menu: * Internet Address Formats:: How socket addresses are specified in the Internet namespace. * Host Addresses:: All about host addresses of Internet host. * Ports:: Internet port numbers. * Services Database:: Ports may have symbolic names. * Byte Order:: Different hosts may use different byte ordering conventions; you need to canonicalize host address and port number. * Protocols Database:: Referring to protocols by name. * Inet Example:: Putting it all together.