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.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH wait4 2 2025-05-17 "Linux man-pages (unreleased)"
.SH NAME
wait3, wait4 \- wait for process to change state, BSD style
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.B #include <sys/wait.h>
.P
.BI "pid_t wait3(int *_Nullable " "wstatus" ", int " options ,
.BI " struct rusage *_Nullable " rusage );
.BI "pid_t wait4(pid_t " pid ", int *_Nullable " wstatus ", int " options ,
.BI " struct rusage *_Nullable " rusage );
.fi
.P
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.P
.BR wait3 ():
.nf
Since glibc 2.26:
_DEFAULT_SOURCE
|| (_XOPEN_SOURCE >= 500 &&
! (_POSIX_C_SOURCE >= 200112L
|| _XOPEN_SOURCE >= 600))
From glibc 2.19 to glibc 2.25:
_DEFAULT_SOURCE || _XOPEN_SOURCE >= 500
glibc 2.19 and earlier:
_BSD_SOURCE || _XOPEN_SOURCE >= 500
.\" || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
.fi
.P
.BR wait4 ():
.nf
Since glibc 2.19:
_DEFAULT_SOURCE
glibc 2.19 and earlier:
_BSD_SOURCE
.fi
.SH DESCRIPTION
These functions are nonstandard; in new programs, the use of
.BR waitpid (2)
or
.BR waitid (2)
is preferable.
.P
The
.BR wait3 ()
and
.BR wait4 ()
system calls are similar to
.BR waitpid (2),
but additionally return resource usage information about the
child in the structure pointed to by
.IR rusage .
.P
Other than the use of the
.I rusage
argument, the following
.BR wait3 ()
call:
.P
.in +4n
.EX
wait3(wstatus, options, rusage);
.EE
.in
.P
is equivalent to:
.P
.in +4n
.EX
waitpid(\-1, wstatus, options);
.EE
.in
.P
Similarly, the following
.BR wait4 ()
call:
.P
.in +4n
.EX
wait4(pid, wstatus, options, rusage);
.EE
.in
.P
is equivalent to:
.P
.in +4n
.EX
waitpid(pid, wstatus, options);
.EE
.in
.P
In other words,
.BR wait3 ()
waits of any child, while
.BR wait4 ()
can be used to select a specific child, or children, on which to wait.
See
.BR wait (2)
for further details.
.P
If
.I rusage
is not NULL, the
.I struct rusage
to which it points will be filled with accounting information
about the child.
See
.BR getrusage (2)
for details.
.SH RETURN VALUE
As for
.BR waitpid (2).
.SH ERRORS
As for
.BR waitpid (2).
.SH STANDARDS
None.
.SH HISTORY
4.3BSD.
.P
SUSv1 included a specification of
.BR wait3 ();
SUSv2 included
.BR wait3 (),
but marked it LEGACY;
SUSv3 removed it.
.P
Including
.I <sys/time.h>
is not required these days, but increases portability.
(Indeed,
.I <sys/resource.h>
defines the
.I rusage
structure with fields of type
.I struct timeval
defined in
.IR <sys/time.h> .)
.SS C library/kernel differences
On Linux,
.BR wait3 ()
is a library function implemented on top of the
.BR wait4 ()
system call.
.SH SEE ALSO
.BR fork (2),
.BR getrusage (2),
.BR sigaction (2),
.BR signal (2),
.BR wait (2),
.BR signal (7)
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