man3/exit.3

   1 .\" Copyright (C) 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .\" FIXME . There are a lot of other process termination actions that
   6 .\" could be listed on this page. See, for example, the list in the
   7 .\" POSIX exit(3p) page.
   8 .\"
   9 .TH EXIT 3  2021-03-22 "Linux man-pages (unreleased)" "Linux Programmer's Manual"
  10 .SH NAME
  11 exit \- cause normal process termination
  12 .SH LIBRARY
  13 Standard C library
  14 .RI ( libc ", " \-lc )
  15 .SH SYNOPSIS
  16 .nf
  17 .B #include <stdlib.h>
  18 .PP
  19 .BI "noreturn void exit(int " status );
  20 .fi
  21 .SH DESCRIPTION
  22 The
  23 .BR exit ()
  24 function causes normal process termination and the least significant byte of
  25 .I status
  26 (i.e., \fIstatus & 0xFF\fP) is returned to the parent (see
  27 .BR wait (2)).
  28 .PP
  29 All functions registered with
  30 .BR atexit (3)
  31 and
  32 .BR on_exit (3)
  33 are called, in the reverse order of their registration.
  34 (It is possible for one of these functions to use
  35 .BR atexit (3)
  36 or
  37 .BR on_exit (3)
  38 to register an additional
  39 function to be executed during exit processing;
  40 the new registration is added to the front of the list of functions
  41 that remain to be called.)
  42 If one of these functions does not return
  43 (e.g., it calls
  44 .BR _exit (2),
  45 or kills itself with a signal),
  46 then none of the remaining functions is called,
  47 and further exit processing (in particular, flushing of
  48 .BR stdio (3)
  49 streams) is abandoned.
  50 If a function has been registered multiple times using
  51 .BR atexit (3)
  52 or
  53 .BR on_exit (3),
  54 then it is called as many times as it was registered.
  55 .PP
  56 All open
  57 .BR stdio (3)
  58 streams are flushed and closed.
  59 Files created by
  60 .BR tmpfile (3)
  61 are removed.
  62 .PP
  63 The C standard specifies two constants,
  64 \fBEXIT_SUCCESS\fP and \fBEXIT_FAILURE\fP,
  65 that may be passed to
  66 .BR exit ()
  67 to indicate successful or unsuccessful
  68 termination, respectively.
  69 .SH RETURN VALUE
  70 The
  71 .BR exit ()
  72 function does not return.
  73 .SH ATTRIBUTES
  74 For an explanation of the terms used in this section, see
  75 .BR attributes (7).
  76 .ad l
  77 .nh
  78 .TS
  79 allbox;
  80 lbx lb lb
  81 l l l.
  82 Interface       Attribute       Value
  83 T{
  84 .BR exit ()
  85 T}      Thread safety   MT-Unsafe race:exit
  86 .TE
  87 .hy
  88 .ad
  89 .sp 1
  90 .PP
  91 The
  92 .BR exit ()
  93 function uses a global variable that is not protected,
  94 so it is not thread-safe.
  95 .SH STANDARDS
  96 POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
  97 .SH NOTES
  98 The behavior is undefined if one of the functions registered using
  99 .BR atexit (3)
 100 and
 101 .BR on_exit (3)
 102 calls either
 103 .BR exit ()
 104 or
 105 .BR longjmp (3).
 106 Note that a call to
 107 .BR execve (2)
 108 removes registrations created using
 109 .BR atexit (3)
 110 and
 111 .BR on_exit (3).
 112 .PP
 113 The use of
 114 .B EXIT_SUCCESS
 115 and
 116 .B EXIT_FAILURE
 117 is slightly more portable
 118 (to non-UNIX environments) than the use of 0 and some nonzero value
 119 like 1 or \-1.
 120 In particular, VMS uses a different convention.
 121 .PP
 122 BSD has attempted to standardize exit codes
 123 (which some C libraries such as the GNU C library have also adopted);
 124 see the file
 125 .IR <sysexits.h> .
 126 .PP
 127 After
 128 .BR exit (),
 129 the exit status must be transmitted to the
 130 parent process.
 131 There are three cases:
 132 .IP \(bu 3
 133 If the parent has set
 134 .BR SA_NOCLDWAIT ,
 135 or has set the
 136 .B SIGCHLD
 137 handler to
 138 .BR SIG_IGN ,
 139 the status is discarded and the child dies immediately.
 140 .IP \(bu
 141 If the parent was waiting on the child,
 142 it is notified of the exit status and the child dies immediately.
 143 .IP \(bu
 144 Otherwise,
 145 the child becomes a "zombie" process:
 146 most of the process resources are recycled,
 147 but a slot containing minimal information about the child process
 148 (termination status, resource usage statistics) is retained in process table.
 149 This allows the parent to subsequently use
 150 .BR waitpid (2)
 151 (or similar) to learn the termination status of the child;
 152 at that point the zombie process slot is released.
 153 .PP
 154 If the implementation supports the
 155 .B SIGCHLD
 156 signal, this signal
 157 is sent to the parent.
 158 If the parent has set
 159 .BR SA_NOCLDWAIT ,
 160 it is undefined whether a
 161 .B SIGCHLD
 162 signal is sent.
 163 .\"
 164 .SS Signals sent to other processes
 165 If the exiting process is a session leader and its controlling terminal
 166 is the controlling terminal of the session, then each process in
 167 the foreground process group of this controlling terminal
 168 is sent a
 169 .B SIGHUP
 170 signal, and the terminal is disassociated
 171 from this session, allowing it to be acquired by a new controlling
 172 process.
 173 .PP
 174 If the exit of the process causes a process group to become orphaned,
 175 and if any member of the newly orphaned process group is stopped,
 176 then a
 177 .B SIGHUP
 178 signal followed by a
 179 .B SIGCONT
 180 signal will be
 181 sent to each process in this process group.
 182 See
 183 .BR setpgid (2)
 184 for an explanation of orphaned process groups.
 185 .PP
 186 Except in the above cases,
 187 where the signalled processes may be children of the terminating process,
 188 termination of a process does
 189 .I not
 190 in general cause a signal to be sent to children of that process.
 191 However, a process can use the
 192 .BR prctl (2)
 193 .B PR_SET_PDEATHSIG
 194 operation to arrange that it receives a signal if its parent terminates.
 195 .SH SEE ALSO
 196 .BR _exit (2),
 197 .BR get_robust_list (2),
 198 .BR setpgid (2),
 199 .BR wait (2),
 200 .BR atexit (3),
 201 .BR on_exit (3),
 202 .BR tmpfile (3)