F_GETFD - get/set file descriptor flags

NAME LIBRARY SYNOPSIS DESCRIPTION RETURN VALUE ERRORS STANDARDS HISTORY CAVEATS SEE ALSO

NAME

F_GETFD, F_SETFD − get/set file descriptor flags

SYNOPSIS

#include <fcntl.h>

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

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.1-2024.

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.