Manpages - exit.3
Table of Contents
NAME
exit - cause normal process termination
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).
| Interface | Attribute | Value |
| *exit*() | Thread safety | MT-Unsafe race:exit |
The *exit*() function uses a global variable that is not protected, so it is not thread-safe.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, 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.
Signals sent to other processes
If the exiting process is a session leader and its controlling terminal is the controlling terminal of the session, then each process in the foreground process group of this controlling terminal is sent a SIGHUP signal, and the terminal is disassociated from this session, allowing it to be acquired by a new controlling process.
If the exit of the process causes a process group to become orphaned, and if any member of the newly orphaned process group is stopped, then a SIGHUP signal followed by a SIGCONT signal will be sent to each process in this process group. See *setpgid*(2) for an explanation of orphaned process groups.
Except in the above cases, where the signalled processes may be children of the terminating process, termination of a process does not in general cause a signal to be sent to children of that process. However, a process can use the prctl*(2) *PR_SET_PDEATHSIG operation to arrange that it receives a signal if its parent terminates.
SEE ALSO
*_exit*(2), *get_robust_list*(2), *setpgid*(2), *wait*(2), *atexit*(3), *on_exit*(3), *tmpfile*(3)
COLOPHON
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