fcntl.h(0p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

fcntl.h(0P)             POSIX Programmer's Manual            fcntl.h(0P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       fcntl.h — file control options

SYNOPSIS         top

       #include <fcntl.h>

DESCRIPTION         top

       The <fcntl.h> header shall define the following symbolic
       constants for the cmd argument used by fcntl().  The values shall
       be unique and shall be suitable for use in #if preprocessing
       directives.

       F_DUPFD     Duplicate file descriptor.

       F_DUPFD_CLOEXEC
                   Duplicate file descriptor with the close-on-exec flag
                   FD_CLOEXEC set.

       F_GETFD     Get file descriptor flags.

       F_SETFD     Set file descriptor flags.

       F_GETFL     Get file status flags and file access modes.

       F_SETFL     Set file status flags.

       F_GETLK     Get record locking information.

       F_SETLK     Set record locking information.

       F_SETLKW    Set record locking information; wait if blocked.

       F_GETOWN    Get process or process group ID to receive SIGURG
                   signals.

       F_SETOWN    Set process or process group ID to receive SIGURG
                   signals.

       The <fcntl.h> header shall define the following symbolic constant
       used for the fcntl() file descriptor flags, which shall be
       suitable for use in #if preprocessing directives.

       FD_CLOEXEC  Close the file descriptor upon execution of an exec
                   family function.

       The <fcntl.h> header shall also define the following symbolic
       constants for the l_type argument used for record locking with
       fcntl().  The values shall be unique and shall be suitable for
       use in #if preprocessing directives.

       F_RDLCK     Shared or read lock.

       F_UNLCK     Unlock.

       F_WRLCK     Exclusive or write lock.

       The <fcntl.h> header shall define the values used for l_whence,
       SEEK_SET, SEEK_CUR, and SEEK_END as described in <stdio.h>.

       The <fcntl.h> header shall define the following symbolic
       constants as file creation flags for use in the oflag value to
       open() and openat().  The values shall be bitwise-distinct and
       shall be suitable for use in #if preprocessing directives.

       O_CLOEXEC   The FD_CLOEXEC flag associated with the new
                   descriptor shall be set to close the file descriptor
                   upon execution of an exec family function.

       O_CREAT     Create file if it does not exist.

       O_DIRECTORY Fail if file is a non-directory file.

       O_EXCL      Exclusive use flag.

       O_NOCTTY    Do not assign controlling terminal.

       O_NOFOLLOW  Do not follow symbolic links.

       O_TRUNC     Truncate flag.

       O_TTY_INIT  Set the termios structure terminal parameters to a
                   state that provides conforming behavior; see Section
                   11.2, Parameters that Can be Set.

       The O_TTY_INIT flag can have the value zero and in this case it
       need not be bitwise-distinct from the other flags.

       The <fcntl.h> header shall define the following symbolic
       constants for use as file status flags for open(), openat(), and
       fcntl().  The values shall be suitable for use in #if
       preprocessing directives.

       O_APPEND    Set append mode.

       O_DSYNC     Write according to synchronized I/O data integrity
                   completion.

       O_NONBLOCK  Non-blocking mode.

       O_RSYNC     Synchronized read I/O operations.

       O_SYNC      Write according to synchronized I/O file integrity
                   completion.

       The <fcntl.h> header shall define the following symbolic constant
       for use as the mask for file access modes. The value shall be
       suitable for use in #if preprocessing directives.

       O_ACCMODE   Mask for file access modes.

       The <fcntl.h> header shall define the following symbolic
       constants for use as the file access modes for open(), openat(),
       and fcntl().  The values shall be unique, except that O_EXEC and
       O_SEARCH may have equal values. The values shall be suitable for
       use in #if preprocessing directives.

       O_EXEC      Open for execute only (non-directory files). The
                   result is unspecified if this flag is applied to a
                   directory.

       O_RDONLY    Open for reading only.

       O_RDWR      Open for reading and writing.

       O_SEARCH    Open directory for search only. The result is
                   unspecified if this flag is applied to a non-
                   directory file.

       O_WRONLY    Open for writing only.

       The <fcntl.h> header shall define the symbolic constants for file
       modes for use as values of mode_t as described in <sys/stat.h>.

       The <fcntl.h> header shall define the following symbolic constant
       as a special value used in place of a file descriptor for the
       *at() functions which take a directory file descriptor as a
       parameter:

       AT_FDCWD    Use the current working directory to determine the
                   target of relative file paths.

       The <fcntl.h> header shall define the following symbolic constant
       as a value for the flag used by faccessat():

       AT_EACCESS  Check access using effective user and group ID.

       The <fcntl.h> header shall define the following symbolic constant
       as a value for the flag used by fstatat(), fchmodat(),
       fchownat(), and utimensat():

       AT_SYMLINK_NOFOLLOW
                   Do not follow symbolic links.

       The <fcntl.h> header shall define the following symbolic constant
       as a value for the flag used by linkat():

       AT_SYMLINK_FOLLOW
                   Follow symbolic link.

       The <fcntl.h> header shall define the following symbolic constant
       as a value for the flag used by unlinkat():

       AT_REMOVEDIR
                   Remove directory instead of file.

       The <fcntl.h> header shall define the following symbolic
       constants for the advice argument used by posix_fadvise():

       POSIX_FADV_DONTNEED
             The application expects that it will not access the
             specified data in the near future.

       POSIX_FADV_NOREUSE
             The application expects to access the specified data once
             and then not reuse it thereafter.

       POSIX_FADV_NORMAL
             The application has no advice to give on its behavior with
             respect to the specified data. It is the default
             characteristic if no advice is given for an open file.

       POSIX_FADV_RANDOM
             The application expects to access the specified data in a
             random order.

       POSIX_FADV_SEQUENTIAL
             The application expects to access the specified data
             sequentially from lower offsets to higher offsets.

       POSIX_FADV_WILLNEED
             The application expects to access the specified data in the
             near future.

       The <fcntl.h> header shall define the flock structure describing
       a file lock. It shall include the following members:

           short  l_type   Type of lock; F_RDLCK, F_WRLCK, F_UNLCK.
           short  l_whence Flag for starting offset.
           off_t  l_start  Relative offset in bytes.
           off_t  l_len    Size; if 0 then until EOF.
           pid_t  l_pid    Process ID of the process holding the lock; returned with F_GETLK.

       The <fcntl.h> header shall define the mode_t, off_t, and pid_t
       types as described in <sys/types.h>.

       The following shall be declared as functions and may also be
       defined as macros. Function prototypes shall be provided.

           int  creat(const char *, mode_t);
           int  fcntl(int, int, ...);
           int  open(const char *, int, ...);
           int  openat(int, const char *, int, ...);
           int  posix_fadvise(int, off_t, off_t, int);
           int  posix_fallocate(int, off_t, off_t);

       Inclusion of the <fcntl.h> header may also make visible all
       symbols from <sys/stat.h> and <unistd.h>.

       The following sections are informative.

APPLICATION USAGE         top

       Although no existing implementation defines AT_SYMLINK_FOLLOW and
       AT_SYMLINK_NOFOLLOW as the same numeric value, POSIX.1‐2008 does
       not prohibit that as the two constants are not used with the same
       interfaces.

RATIONALE         top

       While many of the symbolic constants introduced in the <fcntl.h>
       header do not strictly need to be used in #if preprocessor
       directives, widespread historic practice has defined them as
       macros that are usable in such constructs, and examination of
       existing applications has shown that they are occasionally used
       in such a way. Therefore it was decided to retain this
       requirement on an implementation in POSIX.1‐2008.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       stdio.h(0p), sys_stat.h(0p), sys_types.h(0p), unistd.h(0p)

       The System Interfaces volume of POSIX.1‐2017, creat(3p),
       exec(1p), fcntl(3p), futimens(3p), open(3p), posix_fadvise(3p),
       posix_fallocate(3p), posix_madvise(3p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                       fcntl.h(0P)

Pages that refer to this page: aio.h(0p)mqueue.h(0p)semaphore.h(0p)access(3p)catopen(3p)chmod(3p)chown(3p)creat(3p)fcntl(3p)fstatat(3p)futimens(3p)iconv_open(3p)link(3p)mkdir(3p)mkfifo(3p)mknod(3p)open(3p)pipe(3p)posix_fadvise(3p)posix_fallocate(3p)posix_openpt(3p)posix_typed_mem_open(3p)readlink(3p)rename(3p)shm_open(3p)symlink(3p)unlink(3p)