F_GETFD(2const)                                                F_GETFD(2const)

NAME
       F_GETFD, F_SETFD - get/set file descriptor flags

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <fcntl.h>

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

DESCRIPTION
       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
       F_GETFD
              Value of file descriptor flags.

       F_SETFD
              Zero.

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

ERRORS
       See fcntl(2).

STANDARDS
       POSIX.1-2008.

HISTORY
       SVr4, 4.3BSD, POSIX.1-2001.

CAVEATS
       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
       fcntl(2)

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