NAME¶

exit - cause normal process termination

LIBRARY¶

Standard C library (libc, -lc)

SYNOPSIS¶

#include <stdlib.h>

[[noreturn]] void exit(int status);

DESCRIPTION¶

The exit() function causes normal process termination and the least significant byte of status (i.e., status & 0xFF) is returned to the parent (see wait(2)).

All functions registered with atexit(3) and on_exit(3) are called, in the reverse order of their registration. (It is possible for one of these functions to use atexit(3) or on_exit(3) to register an additional function to be executed during exit processing; the new registration is added to the front of the list of functions that remain to be called.) If one of these functions does not return (e.g., it calls _exit(2), or kills itself with a signal), then none of the remaining functions is called, and further exit processing (in particular, flushing of stdio(3) streams) is abandoned. If a function has been registered multiple times using atexit(3) or on_exit(3), then it is called as many times as it was registered.

All open stdio(3) streams are flushed and closed. Files created by tmpfile(3) are removed.

The C standard specifies two constants, EXIT_SUCCESS and EXIT_FAILURE, that may be passed to exit() to indicate successful or unsuccessful termination, respectively.

RETURN VALUE¶

The exit() function does not return.

ATTRIBUTES¶

For an explanation of the terms used in this section, see attributes(7).

The exit() function uses a global variable that is not protected, so it is not thread-safe.

STANDARDS¶

C11, POSIX.1-2008.

HISTORY¶

C89, POSIX.1-2001, SVr4, 4.3BSD.

NOTES¶

The behavior is undefined if one of the functions registered using atexit(3) and on_exit(3) calls either exit() or longjmp(3). Note that a call to execve(2) removes registrations created using atexit(3) and on_exit(3).

The use of EXIT_SUCCESS and EXIT_FAILURE is slightly more portable (to non-UNIX environments) than the use of 0 and some nonzero value like 1 or -1. In particular, VMS uses a different convention.

BSD has attempted to standardize exit codes (which some C libraries such as the GNU C library have also adopted); see the file <sysexits.h>.

After exit(), the exit status must be transmitted to the parent process. There are three cases:

•

If the parent has set SA_NOCLDWAIT, or has set the SIGCHLD handler to SIG_IGN, the status is discarded and the child dies immediately.

•

If the parent was waiting on the child, it is notified of the exit status and the child dies immediately.

•

Otherwise, the child becomes a "zombie" process: most of the process resources are recycled, but a slot containing minimal information about the child process (termination status, resource usage statistics) is retained in process table. This allows the parent to subsequently use waitpid(2) (or similar) to learn the termination status of the child; at that point the zombie process slot is released.

If the implementation supports the SIGCHLD signal, this signal is sent to the parent. If the parent has set SA_NOCLDWAIT, it is undefined whether a SIGCHLD signal is sent.

SEE ALSO¶

_exit(2), get_robust_list(2), setpgid(2), wait(2), atexit(3), on_exit(3), tmpfile(3)