_exit
Section: System Calls (2)
Updated: 2023-01-22
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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
POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.
The function
_Exit()
was introduced by C99.
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)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- STANDARDS
-
- NOTES
-
- C library/kernel differences
-
- SEE ALSO
-
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