exit

_exit(2)                       System Calls Manual                      _exit(2)

NAME
       _exit, _Exit - terminate the calling process

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #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
       _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
       These functions do not return.

STANDARDS
       _exit()
              POSIX.1-2024.

       _Exit()
              C11, POSIX.1-2024.

HISTORY
       _exit()
              POSIX.1-2001, SVr4, 4.3BSD.

       _Exit()
              C99, POSIX.1-2001.

NOTES
       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
       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 6.16               2025-10-29                           _exit(2)