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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(intfd, F_GETFD);int fcntl(intfd, F_SETFD, intarg);

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 theFD_CLOEXECbit is set, the file       descriptor will automatically be closed during a successfulexecve(2).  (If theexecve(2) fails, the file descriptor is left       open.)  If theFD_CLOEXECbit is not set, the file descriptor will       remain open across anexecve(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 byarg.

RETURN VALUE        top

F_GETFD              Value of file descriptor flags.F_SETFD              Zero.       On error, -1 is returned, anderrno is set to indicate the error.

ERRORS        top

       Seefcntl(2).

STANDARDS        top

       POSIX.1-2008.

HISTORY        top

       SVr4, 4.3BSD, POSIX.1-2001.

CAVEATS        top

       In multithreaded programs, usingfcntl(2)F_SETFDto set the       close-on-exec flag at the same time as another thread performs afork(2) plusexecve(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 theO_CLOEXECflag inopen(2) for details and a remedy to the problem.

SEE ALSO        top

fcntl(2)

COLOPHON        top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  If you discover any rendering problems in this HTML       version of the page, or you believe there is a better or more up-       to-date source for the page, or you have corrections or       improvements to the information in this COLOPHON (which isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-07-19F_GETFD(2const)

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

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