Visit The New, Modern Unix Linux Community

Linux and UNIX Man Pages

Test Your Knowledge in Computers #116
Difficulty: Easy
Linux distributions are the most famous and healthiest example of the Unix derivatives; but macOS is currently the largest installed Unix user base (2019).
True or False?
Linux & Unix Commands - Search Man Pages

exit(3) [linux man page]

EXIT(3) 						     Linux Programmer's Manual							   EXIT(3)

NAME
exit - cause normal process termination SYNOPSIS
#include <stdlib.h> void exit(int status); DESCRIPTION
The exit() function causes normal process termination and the value of status & 0377 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 registra- tion 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. CONFORMING TO
SVr4, 4.3BSD, POSIX.1-2001, C89, C99. NOTES
It is undefined what happens if one of the functions registered using atexit(3) and on_exit(3) calls either exit() or longjmp(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; 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. If the parent was waiting on the child it is notified of the exit status. In both cases the exiting process dies immediately. If the parent has not indicated that it is not interested in the exit status, but is not waiting, the exiting process turns into a "zombie" process (which is nothing but a container for the single byte representing the exit status) so that the parent can learn the exit status when it later calls one of the wait(2) functions. 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. If the process is a session leader and its controlling terminal is the controlling terminal of the session, then each process in the fore- ground 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. SEE ALSO
_exit(2), setpgid(2), wait(2), atexit(3), on_exit(3), tmpfile(3) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/. Linux 2009-09-20 EXIT(3)

Check Out this Related Man Page

ATEXIT(3)						     Linux Programmer's Manual							 ATEXIT(3)

NAME
atexit - register a function to be called at normal process termination SYNOPSIS
#include <stdlib.h> int atexit(void (*function)(void)); DESCRIPTION
The atexit() function registers the given function to be called at normal process termination, either via exit(3) or via return from the program's main(). Functions so registered are called in the reverse order of their registration; no arguments are passed. The same function may be registered multiple times: it is called once for each registration. POSIX.1 requires that an implementation allow at least ATEXIT_MAX (32) such functions to be registered. The actual limit supported by an implementation can be obtained using sysconf(3). When a child process is created via fork(2), it inherits copies of its parent's registrations. Upon a successful call to one of the exec(3) functions, all registrations are removed. RETURN VALUE
The atexit() function returns the value 0 if successful; otherwise it returns a nonzero value. ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). +----------+---------------+---------+ |Interface | Attribute | Value | +----------+---------------+---------+ |atexit() | Thread safety | MT-Safe | +----------+---------------+---------+ CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD. NOTES
Functions registered using atexit() (and on_exit(3)) are not called if a process terminates abnormally because of the delivery of a signal. If one of the functions registered functions calls _exit(2), then any remaining functions are not invoked, and the other process termina- tion steps performed by exit(3) are not performed. POSIX.1 says that the result of calling exit(3) more than once (i.e., calling exit(3) within a function registered using atexit()) is unde- fined. On some systems (but not Linux), this can result in an infinite recursion; portable programs should not invoke exit(3) inside a function registered using atexit(). The atexit() and on_exit(3) functions register functions on the same list: at normal process termination, the registered functions are invoked in reverse order of their registration by these two functions. According to POSIX.1, the result is undefined if longjmp(3) is used to terminate execution of one of the functions registered using atexit(). Linux notes Since glibc 2.2.3, atexit() (and on_exit(3)) can be used within a shared library to establish functions that are called when the shared library is unloaded. EXAMPLE
#include <stdio.h> #include <stdlib.h> #include <unistd.h> void bye(void) { printf("That was all, folks "); } int main(void) { long a; int i; a = sysconf(_SC_ATEXIT_MAX); printf("ATEXIT_MAX = %ld ", a); i = atexit(bye); if (i != 0) { fprintf(stderr, "cannot set exit function "); exit(EXIT_FAILURE); } exit(EXIT_SUCCESS); } SEE ALSO
_exit(2), dlopen(3), exit(3), on_exit(3) COLOPHON
This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/. Linux 2017-09-15 ATEXIT(3)

Featured Tech Videos