F_GETFD(2const) - Linux manual page (original) (raw)

FGETFD(2const) FGETFD(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)](../man2/execve.2.html).  (If the [execve(2)](../man2/execve.2.html) 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)](../man2/execve.2.html).

   **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](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   See [fcntl(2)](../man2/fcntl.2.html).

STANDARDS top

   POSIX.1-2008.

HISTORY top

   SVr4, 4.3BSD, POSIX.1-2001.

CAVEATS top

   In multithreaded programs, using [fcntl(2)](../man2/fcntl.2.html) **F_SETFD** to set the
   close-on-exec flag at the same time as another thread performs a
   [fork(2)](../man2/fork.2.html) plus [execve(2)](../man2/execve.2.html) 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)](../man2/open.2.html) for details and a remedy to the problem.

SEE ALSO top

   [fcntl(2)](../man2/fcntl.2.html)

COLOPHON top

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

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