man2/_exit.2

   1 .\" This manpage is Copyright (C) 1992 Drew Eckhardt;
   2 .\"             and Copyright (C) 1993 Michael Haardt, Ian Jackson.
   3 .\"
   4 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   5 .\"
   6 .\" Modified Wed Jul 21 23:02:38 1993 by Rik Faith <faith@cs.unc.edu>
   7 .\" Modified 2001-11-17, aeb
   8 .\"
   9 .TH _EXIT 2 2022-09-09 "Linux man-pages (unreleased)"
  10 .SH NAME
  11 _exit, _Exit \- terminate the calling process
  12 .SH LIBRARY
  13 Standard C library
  14 .RI ( libc ", " \-lc )
  15 .SH SYNOPSIS
  16 .nf
  17 .B #include <unistd.h>
  18 .PP
  19 .BI "noreturn void _exit(int " status );
  20 .PP
  21 .B #include <stdlib.h>
  22 .PP
  23 .BI "noreturn void _Exit(int " status );
  24 .fi
  25 .PP
  26 .RS -4
  27 Feature Test Macro Requirements for glibc (see
  28 .BR feature_test_macros (7)):
  29 .RE
  30 .PP
  31 .BR _Exit ():
  32 .nf
  33     _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
  34 .fi
  35 .SH DESCRIPTION
  36 .BR _exit ()
  37 terminates the calling process "immediately".
  38 Any open file descriptors belonging to the process are closed.
  39 Any children of the process are inherited by
  40 .BR init (1)
  41 (or by the nearest "subreaper" process as defined through the use of the
  42 .BR prctl (2)
  43 .B PR_SET_CHILD_SUBREAPER
  44 operation).
  45 The process's parent is sent a
  46 .B SIGCHLD
  47 signal.
  48 .PP
  49 The value
  50 .I "status & 0xFF"
  51 is returned to the parent process as the process's exit status, and
  52 can be collected by the parent using one of the
  53 .BR wait (2)
  54 family of calls.
  55 .PP
  56 The function
  57 .BR _Exit ()
  58 is equivalent to
  59 .BR _exit ().
  60 .SH RETURN VALUE
  61 These functions do not return.
  62 .SH STANDARDS
  63 POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
  64 The function
  65 .BR _Exit ()
  66 was introduced by C99.
  67 .SH NOTES
  68 For a discussion on the effects of an exit, the transmission of
  69 exit status, zombie processes, signals sent, and so on, see
  70 .BR exit (3).
  71 .PP
  72 The function
  73 .BR _exit ()
  74 is like
  75 .BR exit (3),
  76 but does not call any
  77 functions registered with
  78 .BR atexit (3)
  79 or
  80 .BR on_exit (3).
  81 Open
  82 .BR stdio (3)
  83 streams are not flushed.
  84 On the other hand,
  85 .BR _exit ()
  86 does close open file descriptors, and this may cause an unknown delay,
  87 waiting for pending output to finish.
  88 If the delay is undesired,
  89 it may be useful to call functions like
  90 .BR tcflush (3)
  91 before calling
  92 .BR _exit ().
  93 Whether any pending I/O is canceled, and which pending I/O may be
  94 canceled upon
  95 .BR _exit (),
  96 is implementation-dependent.
  97 .SS C library/kernel differences
  98 The text above in DESCRIPTION describes the traditional effect of
  99 .BR _exit (),
 100 which is to terminate a process,
 101 and these are the semantics specified by POSIIX.1 and implemented
 102 by the C library wrapper function.
 103 On modern systems, this means termination of all threads in the process.
 104 .PP
 105 By contrast with the C library wrapper function, the raw Linux
 106 .BR _exit ()
 107 system call terminates only the calling thread, and actions such as
 108 reparenting child processes or sending
 109 .B SIGCHLD
 110 to the parent process are performed only if this is
 111 the last thread in the thread group.
 112 .\" _exit() is used by pthread_exit() to terminate the calling thread
 113 .PP
 114 In glibc up to version 2.3, the
 115 .BR _exit ()
 116 wrapper function invoked the kernel system call of the same name.
 117 Since glibc 2.3, the wrapper function invokes
 118 .BR exit_group (2),
 119 in order to terminate all of the threads in a process.
 120 .SH SEE ALSO
 121 .BR execve (2),
 122 .BR exit_group (2),
 123 .BR fork (2),
 124 .BR kill (2),
 125 .BR wait (2),
 126 .BR wait4 (2),
 127 .BR waitpid (2),
 128 .BR atexit (3),
 129 .BR exit (3),
 130 .BR on_exit (3),
 131 .BR termios (3)