.\" Copyright 1992, Drew Eckhardt <drew@cs.colorado.edu>
.\" Copyright 1993, Ian Jackson <iwj10@cus.cam.ac.uk>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH _exit 3 2026-07-02 "Linux man-pages 6.19"
.SH NAME
_exit, _Exit \- terminate the calling process
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <unistd.h>
.P
.BI "[[noreturn]] void _exit(int " status );
.P
.B #include <stdlib.h>
.P
.BI "[[noreturn]] void _Exit(int " status );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR _Exit ():
.nf
    _ISOC99_SOURCE || _POSIX_C_SOURCE >= 200112L
.fi
.SH DESCRIPTION
.BR _exit ()
terminates the calling process "immediately".
Any open file descriptors belonging to the process are closed.
Any children of the process are inherited by
.BR init (1)
(or by the nearest "subreaper" process as defined through the use of the
.BR prctl (2)
.B PR_SET_CHILD_SUBREAPER
operation).
The process's parent is sent a
.B SIGCHLD
signal.
.P
The value
.I "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
.BR wait (2)
family of calls.
.P
The function
.BR _Exit ()
is equivalent to
.BR _exit ().
.SH RETURN VALUE
These functions do not return.
.SH STANDARDS
.TP
.BR _exit ()
POSIX.1-2024.
.TP
.BR _Exit ()
C11, POSIX.1-2024.
.SH HISTORY
.TP
.BR _exit ()
4.3BSD,
SVr4,
POSIX.1-1988.
.TP
.BR _Exit ()
C99, POSIX.1-2001.
.P
Up to glibc 2.3,
these functions invoked
.BR exit (2).
Since glibc 2.3,
they invoke
.BR exit_group (2),
in order to terminate all of the threads in a process.
.SH NOTES
For a discussion on the effects of an exit, the transmission of
exit status, zombie processes, signals sent, and so on, see
.BR exit (3).
.P
The function
.BR _exit ()
is like
.BR exit (3),
but does not call any
functions registered with
.BR atexit (3)
or
.BR on_exit (3).
Open
.BR stdio (3)
streams are not flushed.
On the other hand,
.BR _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
.BR tcflush (3)
before calling
.BR _exit ().
Whether any pending I/O is canceled, and which pending I/O may be
canceled upon
.BR _exit (),
is implementation-dependent.
.SH SEE ALSO
.BR execve (2),
.BR exit (2),
.BR exit_group (2),
.BR fork (2),
.BR kill (2),
.BR wait (2),
.BR wait4 (2),
.BR waitpid (2),
.BR atexit (3),
.BR exit (3),
.BR on_exit (3),
.BR termios (7)