_exit(2) — Linux manual page

_exit(2)                   System Calls Manual                  _exit(2)

NAME         top

       _exit, _Exit - terminate the calling process

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #include <unistd.h>

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

       #include <stdlib.h>

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

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       _Exit():
           _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L

DESCRIPTION         top

       _exit() terminates the calling process "immediately".  Any open
       file descriptors belonging to the process are closed.  Any
       children of the process are inherited by init(1) (or by the
       nearest "subreaper" process as defined through the use of the
       prctl(2) PR_SET_CHILD_SUBREAPER operation).  The process's parent
       is sent a SIGCHLD signal.

       The value status & 0xFF is returned to the parent process as the
       process's exit status, and can be collected by the parent using
       one of the wait(2) family of calls.

       The function _Exit() is equivalent to _exit().

RETURN VALUE         top

       These functions do not return.

STANDARDS         top

       _exit()
              POSIX.1-2008.

       _Exit()
              C11, POSIX.1-2008.

HISTORY         top

       POSIX.1-2001, SVr4, 4.3BSD.

       _Exit() was introduced by C99.

NOTES         top

       For a discussion on the effects of an exit, the transmission of
       exit status, zombie processes, signals sent, and so on, see
       exit(3).

       The function _exit() is like exit(3), but does not call any
       functions registered with atexit(3) or on_exit(3).  Open stdio(3)
       streams are not flushed.  On the other hand, _exit() does close
       open file descriptors, and this may cause an unknown delay,
       waiting for pending output to finish.  If the delay is undesired,
       it may be useful to call functions like tcflush(3) before calling
       _exit().  Whether any pending I/O is canceled, and which pending
       I/O may be canceled upon _exit(), is implementation-dependent.

   C library/kernel differences
       The text above in DESCRIPTION describes the traditional effect of
       _exit(), which is to terminate a process, and these are the
       semantics specified by POSIX.1 and implemented by the C library
       wrapper function.  On modern systems, this means termination of
       all threads in the process.

       By contrast with the C library wrapper function, the raw Linux
       _exit() system call terminates only the calling thread, and
       actions such as reparenting child processes or sending SIGCHLD to
       the parent process are performed only if this is the last thread
       in the thread group.

       Up to glibc 2.3, the _exit() wrapper function invoked the kernel
       system call of the same name.  Since glibc 2.3, the wrapper
       function invokes exit_group(2), in order to terminate all of the
       threads in a process.

SEE ALSO         top

       execve(2), exit_group(2), fork(2), kill(2), wait(2), wait4(2),
       waitpid(2), atexit(3), exit(3), on_exit(3), termios(3)

Linux man-pages 6.04           2023-03-30                       _exit(2)

Pages that refer to this page: clone(2),  exit_group(2),  fork(2),  kill(2),  ptrace(2),  seccomp(2),  setsid(2),  shmop(2),  syscalls(2),  vfork(2),  wait(2),  atexit(3),  daemon(3),  exit(3),  on_exit(3),  pmgetconfig(3),  pmnomem(3),  system(3),  persistent-keyring(7),  signal-safety(7),  socket(7),  user-keyring(7),  user-session-keyring(7)

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