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.Dd July 24, 2024
.Dt EXIT 3
.Os
.Sh NAME
.Nm exit , _Exit
.Nd perform normal program termination
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft void
.Fn exit "int status"
.Ft void
.Fn _Exit "int status"
.Sh DESCRIPTION
The
.Fn exit
and
.Fn _Exit
functions terminate a process.
.Pp
Before termination,
.Fn exit
performs the following functions in the order listed:
.Bl -enum -offset indent
.It
Call all functions registered with the
.Xr __cxa_atexit 3
function
(which are typically destructors from the loaded dynamic objects),
and the functions registered with the
.Xr atexit 3
function, in the reverse order of their registration.
.It
Flush all open output streams.
.It
Close all open streams.
.El
.Pp
The
.Fn _Exit
function terminates without calling the functions registered with the
.Xr atexit 3
function, and may or may not perform the other actions listed.
The
.Fx
implementation of the
.Fn _Exit
function does not call destructors registered with
.Xr __cxa_atexit 3 ,
does not flush buffers, and does not close streams.
.Pp
Both functions make the low-order eight bits of the
.Fa status
argument available to a parent process which has called a
.Xr wait 2 Ns -family
function.
.Pp
The C Standard
.Pq St -isoC-99
defines the values
.Li 0 ,
.Dv EXIT_SUCCESS ,
and
.Dv EXIT_FAILURE
as possible values of
.Fa status .
Cooperating processes may use other values;
in a program which might be called by a mail transfer agent, the
values described in
.Xr sysexits 3
may be used to provide more information to the parent process.
.Pp
The complete
.Fa status
value is avaliable as
.Va si_status
member of the
.Vt siginfo_t
structure, to the
.Xr wait6 2
and
.Xr sigwaitinfo 2
callers, and
.Va SIGCHLD
signal handlers.
.Pp
Calls to the
.Fn exit
function are serialized.
All functions registered by
.Xr atexit 3
are executed in the first thread that called
.Nm exit .
If any other thread of the process calls
.Nm exit
before all registered functions have completed or before the process
terminates, the thread is blocked until the process terminates.
The exit status of the process is the
.Fa status
argument of the first
.Nm exit
call which thread proceeds the atexit handlers.
.Pp
Note that
.Fn exit
does nothing to prevent bottomless recursion should a function registered
using
.Xr atexit 3
itself call
.Fn exit .
Such functions must call
.Fn _Exit
instead (although this has other effects as well which may not be desired).
.Sh RETURN VALUES
The
.Fn exit
and
.Fn _Exit
functions
never return.
.Sh SEE ALSO
.Xr _exit 2 ,
.Xr abort2 2 ,
.Xr wait 2 ,
.Xr at_quick_exit 3 ,
.Xr atexit 3 ,
.Xr intro 3 ,
.Xr quick_exit 3 ,
.Xr sysexits 3 ,
.Xr tmpfile 3
.Sh STANDARDS
The
.Fn exit
and
.Fn _Exit
functions conform to
.St -isoC-99 .
.Sh HISTORY
The
.Fn exit
function appeared in
.At v1 .