671 lines
14 KiB
Groff
671 lines
14 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993, 1994
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)wait.2 8.2 (Berkeley) 4/19/94
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.\" $FreeBSD$
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.\"
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.Dd December 3, 2013
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.Dt WAIT 2
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.Os
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.Sh NAME
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.Nm wait ,
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.Nm waitid ,
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.Nm waitpid ,
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.Nm wait3 ,
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.Nm wait4 ,
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.Nm wait6
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.Nd wait for processes to change status
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In sys/types.h
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.In sys/wait.h
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.Ft pid_t
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.Fn wait "int *status"
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.Ft pid_t
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.Fn waitpid "pid_t wpid" "int *status" "int options"
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.In signal.h
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.Ft int
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.Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options"
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.In sys/time.h
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.In sys/resource.h
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.Ft pid_t
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.Fn wait3 "int *status" "int options" "struct rusage *rusage"
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.Ft pid_t
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.Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
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.Ft pid_t
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.Fn wait6 "idtype_t idtype" "id_t id" "int *status" "int options" "struct __wrusage *wrusage" "siginfo_t *infop"
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.Sh DESCRIPTION
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The
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.Fn wait
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function suspends execution of its calling thread until
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.Fa status
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information is available for a child process
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or a signal is received.
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On return from a successful
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.Fn wait
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call,
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the
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.Fa status
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area contains information about the process that reported a status change
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as defined below.
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.Pp
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The
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.Fn wait4
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and
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.Fn wait6
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system calls provide a more general interface for programs
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that need to wait for specific child processes,
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that need resource utilization statistics accumulated by child processes,
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or that require options.
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The other wait functions are implemented using either
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.Fn wait4
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or
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.Fn wait6 .
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.Pp
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The
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.Fn wait6
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function is the most general function in this family and its distinct
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features are:
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.Pp
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All of the desired process statuses to be waited on must be explicitly
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specified in
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.Fa options .
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The
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.Fn wait ,
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.Fn waitpid ,
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.Fn wait3 ,
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and
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.Fn wait4
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functions all implicitly wait for exited and trapped processes,
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but the
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.Fn waitid
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and
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.Fn wait6
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functions require the corresponding
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.Dv WEXITED
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and
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.Dv WTRAPPED
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flags to be explicitly specified.
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This allows waiting for processes which have experienced other
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status changes without having to also handle the exit status from
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terminated processes.
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.Pp
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The
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.Fn wait6
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function accepts a
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.Fa wrusage
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argument which points to a structure defined as:
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.Bd -literal
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struct __wrusage {
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struct rusage wru_self;
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struct rusage wru_children;
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};
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.Ed
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.Pp
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This allows the calling process to collect resource usage statistics
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from both its own child process as well as from its grand children.
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When no resource usage statistics are needed this pointer can be
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.Dv NULL .
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.Pp
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The last argument
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.Fa infop
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must be either
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.Dv NULL
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or a pointer to a
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.Fa siginfo_t
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structure.
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If
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.Pf non- Dv NULL ,
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the structure is filled with the same data as for a
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.Dv SIGCHLD
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signal delivered when the process changed state.
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.Pp
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The set of child processes to be queried is specified by the arguments
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.Fa idtype
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and
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.Fa id .
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The separate
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.Fa idtype
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and
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.Fa id
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arguments support many other types of
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identifers in addition to process IDs and process group IDs.
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.Bl -bullet -offset indent
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.It
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If
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.Fa idtype
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is
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.Dv P_PID ,
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.Fn waitid
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and
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.Fn wait6
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wait for the child process with a process ID equal to
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.Dv (pid_t)id .
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.It
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If
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.Fa idtype
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is
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.Dv P_PGID ,
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.Fn waitid
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and
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.Fn wait6
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wait for the child process with a process group ID equal to
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.Dv (pid_t)id .
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.It
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If
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.Fa idtype
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is
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.Dv P_ALL ,
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.Fn waitid
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and
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.Fn wait6
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wait for any child process and the
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.Dv id
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is ignored.
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.It
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If
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.Fa idtype
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is
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.Dv P_PID
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or
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.Dv P_PGID
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and the
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.Dv id
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is zero,
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.Fn waitid
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and
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.Fn wait6
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wait for any child process in the same process group as the caller.
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.El
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.Pp
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Non-standard identifier types supported by this
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implementation of
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.Fn waitid
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and
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.Fn wait6
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are:
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.Bl -tag -width P_JAILID
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.It Dv P_UID
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Wait for processes whose effective user ID is equal to
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.Dv (uid_t) Fa id .
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.It Dv P_GID
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Wait for processes whose effective group ID is equal to
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.Dv (gid_t) Fa id .
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.It Dv P_SID
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Wait for processes whose session ID is equal to
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.Fa id .
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.\" This is just how sessions work, not sure this needs to be documented here
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If the child process started its own session,
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its session ID will be the same as its process ID.
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Otherwise the session ID of a child process will match the caller's session ID.
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.It Dv P_JAILID
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Waits for processes within a jail whose jail identifier is equal to
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.Fa id .
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.El
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.Pp
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For the
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.Fn waitpid
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and
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.Fn wait4
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functions, the single
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.Fa wpid
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argument specifies the set of child processes for which to wait.
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.Bl -bullet -offset indent
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.It
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If
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.Fa wpid
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is -1, the call waits for any child process.
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.It
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If
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.Fa wpid
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is 0,
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the call waits for any child process in the process group of the caller.
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.It
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If
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.Fa wpid
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is greater than zero, the call waits for the process with process ID
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.Fa wpid .
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.It
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If
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.Fa wpid
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is less than -1, the call waits for any process whose process group ID
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equals the absolute value of
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.Fa wpid .
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.El
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.Pp
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The
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.Fa status
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argument is defined below.
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.Pp
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The
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.Fa options
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argument contains the bitwise OR of any of the following options.
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.Bl -tag -width WCONTINUED
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.It Dv WCONTINUED
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Report the status of selected processes that
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have continued from a job control stop by receiving a
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.Dv SIGCONT
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signal.
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.It Dv WNOHANG
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Do not block when
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there are no processes wishing to report status.
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.It Dv WUNTRACED
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Report the status of selected processes which are stopped due to a
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.Dv SIGTTIN , SIGTTOU , SIGTSTP ,
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or
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.Dv SIGSTOP
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signal.
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.It Dv WSTOPPED
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An alias for
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.Dv WUNTRACED .
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.It Dv WTRAPPED
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Report the status of selected processes which are being traced via
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.Xr ptrace 2
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and have trapped or reached a breakpoint.
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This flag is implicitly set for the functions
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.Fn wait ,
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.Fn waitpid ,
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.Fn wait3 ,
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and
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.Fn wait4 .
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.br
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For the
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.Fn waitid
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and
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.Fn wait6
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functions, the flag has to be explicitly included in
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.Fa options
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if status reports from trapped processes are expected.
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.It Dv WEXITED
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Report the status of selected processes which have terminated.
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This flag is implicitly set for the functions
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.Fn wait ,
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.Fn waitpid ,
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.Fn wait3 ,
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and
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.Fn wait4 .
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.br
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For the
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.Fn waitid
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and
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.Fn wait6
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functions, the flag has to be explicitly included in
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.Fa options
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if status reports from terminated processes are expected.
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.It Dv WNOWAIT
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Keep the process whose status is returned in a waitable state.
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The process may be waited for again after this call completes.
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.El
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.sp
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For the
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.Fn waitid
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and
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.Fn wait6
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functions, at least one of the options
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.Dv WEXITED ,
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.Dv WUNTRACED ,
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.Dv WSTOPPED ,
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.Dv WTRAPPED ,
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or
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.Dv WCONTINUED
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must be specified.
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Otherwise there will be no events for the call to report.
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To avoid hanging indefinitely in such a case these functions
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return -1 with
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.Dv errno
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set to
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.Dv EINVAL .
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.Pp
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If
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.Fa rusage
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is non-NULL, a summary of the resources used by the terminated
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process and all its children is returned.
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.Pp
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If
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.Fa wrusage
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is non-NULL, separate summaries are returned for the resources used
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by the terminated process and the resources used by all its children.
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.Pp
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If
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.Fa infop
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is non-NULL, a
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.Dv siginfo_t
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structure is returned with the
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.Fa si_signo
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field set to
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.Dv SIGCHLD
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and the
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.Fa si_pid
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field set to the process ID of the process reporting status.
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.Pp
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When the
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.Dv WNOHANG
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option is specified and no processes
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wish to report status,
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.Fn waitid
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sets the
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.Fa si_signo
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and
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.Fa si_pid
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fields in
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.Fa infop
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to zero.
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Checking these fields is the only way to know if a status change was reported.
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.Pp
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When the
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.Dv WNOHANG
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option is specified and no processes
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wish to report status,
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.Fn wait4
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and
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.Fn wait6
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return a
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process id
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of 0.
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.Pp
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The
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.Fn wait
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call is the same as
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.Fn wait4
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with a
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.Fa wpid
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value of -1,
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with an
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.Fa options
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value of zero,
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and a
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.Fa rusage
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value of
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.Dv NULL .
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The
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.Fn waitpid
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function is identical to
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.Fn wait4
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with an
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.Fa rusage
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value of
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.Dv NULL .
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The older
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.Fn wait3
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call is the same as
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.Fn wait4
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with a
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.Fa wpid
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value of -1.
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The
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.Fn wait4
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function is identical to
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.Fn wait6
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with the flags
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.Dv WEXITED
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and
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.Dv WTRAPPED
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set in
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.Fa options
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and
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.Fa infop
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set to
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.Dv NULL .
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.Pp
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The following macros may be used to test the current status of the process.
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Exactly one of the following four macros will evaluate to a non-zero
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.Pq true
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value:
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.Bl -tag -width Ds
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.It Fn WIFCONTINUED status
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True if the process has not terminated, and
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has continued after a job control stop.
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This macro can be true only if the wait call specified the
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.Dv WCONTINUED
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option.
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.It Fn WIFEXITED status
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True if the process terminated normally by a call to
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.Xr _exit 2
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or
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.Xr exit 3 .
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.It Fn WIFSIGNALED status
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True if the process terminated due to receipt of a signal.
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.It Fn WIFSTOPPED status
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True if the process has not terminated, but has stopped and can be restarted.
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This macro can be true only if the wait call specified the
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.Dv WUNTRACED
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option
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or if the child process is being traced (see
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.Xr ptrace 2 ) .
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.El
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.Pp
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Depending on the values of those macros, the following macros
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produce the remaining status information about the child process:
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.Bl -tag -width Ds
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.It Fn WEXITSTATUS status
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If
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.Fn WIFEXITED status
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is true, evaluates to the low-order 8 bits
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of the argument passed to
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.Xr _exit 2
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or
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.Xr exit 3
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by the child.
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.It Fn WTERMSIG status
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If
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.Fn WIFSIGNALED status
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is true, evaluates to the number of the signal
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that caused the termination of the process.
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.It Fn WCOREDUMP status
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|
If
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|
.Fn WIFSIGNALED status
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|
is true, evaluates as true if the termination
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of the process was accompanied by the creation of a core file
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containing an image of the process when the signal was received.
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.It Fn WSTOPSIG status
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If
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.Fn WIFSTOPPED status
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is true, evaluates to the number of the signal
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that caused the process to stop.
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.El
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.Sh NOTES
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See
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.Xr sigaction 2
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for a list of termination signals.
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A status of 0 indicates normal termination.
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.Pp
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If a parent process terminates without
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waiting for all of its child processes to terminate,
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the remaining child processes are assigned the parent
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process 1 ID (the init process ID).
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.Pp
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If a signal is caught while any of the
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.Fn wait
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calls are pending,
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the call may be interrupted or restarted when the signal-catching routine
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returns,
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depending on the options in effect for the signal;
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|
see discussion of
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.Dv SA_RESTART
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in
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.Xr sigaction 2 .
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.Pp
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The implementation queues one
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.Dv SIGCHLD
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signal for each child process whose
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status has changed; if
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.Fn wait
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returns because the status of a child process is available, the pending
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SIGCHLD signal associated with the process ID of the child process will
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be discarded.
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Any other pending
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.Dv SIGCHLD
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signals remain pending.
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.Pp
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If
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.Dv SIGCHLD
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is blocked and
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.Fn wait
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returns because the status of a child process is available, the pending
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.Dv SIGCHLD
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signal will be cleared unless another status of the child process
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is available.
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.Sh RETURN VALUES
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|
If
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.Fn wait
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|
returns due to a stopped, continued,
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or terminated child process, the process ID of the child
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is returned to the calling process.
|
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Otherwise, a value of \-1
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is returned and
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.Va errno
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is set to indicate the error.
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.Pp
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|
If
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.Fn wait6 ,
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|
.Fn wait4 ,
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.Fn wait3 ,
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or
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.Fn waitpid
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|
returns due to a stopped, continued,
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or terminated child process, the process ID of the child
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is returned to the calling process.
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|
If there are no children not previously awaited,
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-1 is returned with
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.Va errno
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set to
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.Er ECHILD .
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Otherwise, if
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.Dv WNOHANG
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is specified and there are
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no stopped, continued or exited children,
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0 is returned.
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|
If an error is detected or a caught signal aborts the call,
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a value of -1
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is returned and
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.Va errno
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is set to indicate the error.
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.Pp
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If
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.Fn waitid
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|
returns because one or more processes have a state change to report,
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0 is returned.
|
|
If an error is detected,
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a value of -1
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is returned and
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|
.Va errno
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is set to indicate the error.
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|
If
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|
.Dv WNOHANG
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is specified and there are
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no stopped, continued or exited children,
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0 is returned.
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The
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.Fa si_signo
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and
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.Fa si_pid
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|
fields of
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.Fa infop
|
|
must be checked against zero to determine if a process reported status.
|
|
.Sh ERRORS
|
|
The
|
|
.Fn wait
|
|
function
|
|
will fail and return immediately if:
|
|
.Bl -tag -width Er
|
|
.It Bq Er ECHILD
|
|
The calling process has no existing unwaited-for
|
|
child processes.
|
|
.It Bq Er ECHILD
|
|
No status from the terminated child process is available
|
|
because the calling process has asked the system to discard
|
|
such status by ignoring the signal
|
|
.Dv SIGCHLD
|
|
or setting the flag
|
|
.Dv SA_NOCLDWAIT
|
|
for that signal.
|
|
.It Bq Er EFAULT
|
|
The
|
|
.Fa status
|
|
or
|
|
.Fa rusage
|
|
argument points to an illegal address.
|
|
(May not be detected before exit of a child process.)
|
|
.It Bq Er EINTR
|
|
The call was interrupted by a caught signal,
|
|
or the signal did not have the
|
|
.Dv SA_RESTART
|
|
flag set.
|
|
.It Bq Er EINVAL
|
|
An invalid value was specified for
|
|
.Fa options ,
|
|
or
|
|
.Fa idtype
|
|
and
|
|
.Fa id
|
|
do not specify a valid set of processes.
|
|
.El
|
|
.Sh SEE ALSO
|
|
.Xr _exit 2 ,
|
|
.Xr ptrace 2 ,
|
|
.Xr sigaction 2 ,
|
|
.Xr exit 3 ,
|
|
.Xr siginfo 3
|
|
.Sh STANDARDS
|
|
The
|
|
.Fn wait ,
|
|
.Fn waitpid ,
|
|
and
|
|
.Fn waitid
|
|
functions are defined by POSIX;
|
|
.Fn wait6 ,
|
|
.Fn wait4 ,
|
|
and
|
|
.Fn wait3
|
|
are not specified by POSIX.
|
|
The
|
|
.Fn WCOREDUMP
|
|
macro
|
|
is an extension to the POSIX interface.
|
|
.Pp
|
|
The ability to use the
|
|
.Dv WNOWAIT
|
|
flag with
|
|
.Fn waitpid
|
|
is an extension;
|
|
.Tn POSIX
|
|
only permits this flag with
|
|
.Fn waitid .
|
|
.Pp
|
|
.Tn POSIX
|
|
requires
|
|
.Fn waitid
|
|
to return the full 32 bits passed to
|
|
.Xr _exit 2 ;
|
|
this implementation only returns 8 bits like the other calls.
|
|
.Sh HISTORY
|
|
The
|
|
.Fn wait
|
|
function appeared in
|
|
.At v6 .
|