F_GETFD(2const) — Linux manual page

F_GETFD(2const)                                           F_GETFD(2const)

NAME         top

       F_GETFD, F_SETFD - get/set file descriptor flags

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <fcntl.h>

       int fcntl(int fd, F_GETFD);
       int fcntl(int fd, F_SETFD, int arg);

DESCRIPTION         top

       These operations manipulate the flags associated with a file
       descriptor.  Currently, only one such flag is defined: FD_CLOEXEC,
       the close-on-exec flag.  If the FD_CLOEXEC bit is set, the file
       descriptor will automatically be closed during a successful
       execve(2).  (If the execve(2) fails, the file descriptor is left
       open.)  If the FD_CLOEXEC bit is not set, the file descriptor will
       remain open across an execve(2).

       F_GETFD
              Return (as the function result) the file descriptor flags;
              arg is ignored.

       F_SETFD
              Set the file descriptor flags to the value specified by
              arg.

RETURN VALUE         top

       F_GETFD
              Value of file descriptor flags.

       F_SETFD
              Zero.

       On error, -1 is returned, and errno is set to indicate the error.

ERRORS         top

       See fcntl(2).

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       SVr4, 4.3BSD, POSIX.1-2001.

CAVEATS         top

       In multithreaded programs, using fcntl(2) F_SETFD to set the
       close-on-exec flag at the same time as another thread performs a
       fork(2) plus execve(2) is vulnerable to a race condition that may
       unintentionally leak the file descriptor to the program executed
       in the child process.  See the discussion of the O_CLOEXEC flag in
       open(2) for details and a remedy to the problem.

SEE ALSO         top

       fcntl(2)

COLOPHON         top

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Linux man-pages 6.15            2025-07-19                F_GETFD(2const)

Pages that refer to this page: fcntl(2),  F_DUPFD(2const)

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