mirror of https://github.com/GnoConsortium/gno.git
330 lines
8.5 KiB
Groff
330 lines
8.5 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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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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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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.\"
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.TH WAIT 2 "19 January 1997" GNO "System Calls"
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.SH NAME
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.BR wait ,
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.BR waitpid ,
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.BR wait4 ,
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.BR wait3
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\- wait for process termination
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.SH SYNOPSIS
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#include <sys/types.h>
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.br
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#include <sys/wait.h>
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.sp 1
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pid_t
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\fBwait\fR (union wait *\fIstatus\fR);
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.sp 1
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#include <sys/time.h>
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.br
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#include <sys/resource.h>
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.sp 1
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pid_t
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\fBwaitpid\fR (pid_t \fIwpid\fR, union wait *\fIstatus\fR, int \fIoptions\fR);
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.sp 1
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pid_t
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\fBwait3\fR (union wait *\fIstatus\fR, int \fIoptions\fR, struct rusage *\fIrusage\fR);
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.sp 1
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pid_t
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\fBwait4\fR (pid_t \fIwpid\fR, union wait *\fIstatus\fR, int \fIoptions\fR, struct rusage *\fIrusage\fR);
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.SH DESCRIPTION
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The
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.BR wait
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function suspends execution of its calling process until
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.I status
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information is available for a terminated child process,
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or a signal is received.
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On return from a successful
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.BR wait
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call,
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the
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.I status
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area contains termination information about the process that exited
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as defined below.
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.LP
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The
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.BR wait4
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call provides a more general interface for programs
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that need to wait for certain 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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.LP
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The
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.I wpid
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parameter specifies the set of child processes for which to wait.
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If
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.I wpid
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is -1, the call waits for any child process.
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If
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.I 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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If
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.I wpid
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is greater than zero, the call waits for the process with process id
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.IR wpid .
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If
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.I 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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.IR wpid .
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.LP
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The
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.I status
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parameter is defined below. The
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.I options
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parameter contains the bitwise OR of any of the following options.
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The
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.BR WNOHANG
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option
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is used to indicate that the call should not block if
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there are no processes that wish to report status.
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If the
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.BR WUNTRACED
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option is set,
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children of the current process that are stopped
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due to a
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.BR SIGTTIN ,
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.BR SIGTTOU ,
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.BR SIGTSTP ,
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or
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.BR SIGSTOP
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signal also have
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their status reported.
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.LP
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If
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.I rusage
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is non-zero, a summary of the resources used by the terminated
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process and all its
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children is returned (this information is currently not available
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for stopped processes).
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.LP
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When the
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.BR WNOHANG
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option is specified and no processes
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wish to report status,
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.BR wait4
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returns a process id of 0.
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.LP
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The
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.BR waitpid
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call is identical to
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.BR wait4
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with an
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.I rusage
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value of zero.
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The older
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.BR wait3
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call is the same as
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.BR wait4
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with a
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.I wpid
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value of -1.
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.LP
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The following macros may be used to test the manner of exit of the process.
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One of the first three macros will evaluate to a non-zero (true) value:
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.RS
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.IP \fBWIFEXITED\fR(\fIstatus\fR)
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True if the process terminated normally by a call to
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.BR _exit (2),
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.BR exit (3),
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.BR rexit (3),
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or a GS/OS quit call.
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.IP \fBWIFSIGNALED\fR(\fIstatus\fR)
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True if the process terminated due to receipt of a signal.
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.IP \fBWIFSTOPPED\fR(\fIstatus\fR)
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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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.BR WUNTRACED
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option
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or if the child process is being traced (see
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.BR ptrace (2)).
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.RE
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.LP
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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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.RS
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.IP \fBWEXITSTATUS\fR(\fIstatus\fR)
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If
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\fBWIFEXITED\fR(\fIstatus\fR)
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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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.BR _exit (2),
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.BR exit (3),
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.BR rexit (3),
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or a GS/OS Quit call
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by the child.
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.IP \fBWTERMSIG\fR(\fIstatus\fR)
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If
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\fBWIFSIGNALED\fR(\fIstatus\fR)
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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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.IP \fBWCOREDUMP\fR(\fIstatus\fR)
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If
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\fBWIFSIGNALED\fR(\fIstatus\fR)
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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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.I "This feature is not available under GNO."
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.IP \fBWSTOPSIG\fR(\fIstatus\fR)
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If
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\fBWIFSTOPPED\fR(\fIstatus\fR)
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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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.RE
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.SH NOTES
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See
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.BR signal (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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.LP
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Some Unix uses of these functions expect
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.IR status
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to be a pointer to an
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.BR int
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rather than to a
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.BR "union wait" .
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It is safe to use a cast under such circumstances.
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.LP
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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
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are inherited by the Kernel Null Process (pid zero).
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.LP
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If a signal is caught while any of the
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.BR wait
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calls is 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
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.BR intro (2),
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System call restart.
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.SH BUGS
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Currently, only
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.BR wait
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is implemented in the GNO kernel. There is a minimal version of
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.BR waitpid
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in the libraries, but that version of
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.BR waitpid
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ignores its
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.IR options
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parameter
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(making it impossible to make a non-blocking wait).
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It may also give unexpected results when there is more than one
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child task being waited upon.
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.LP
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.BR wait4
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and
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.BR wait3
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are not implemented.
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.SH RETURN VALUES
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If
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.BR wait
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returns due to a stopped
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or terminated child process, the process ID of the child
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is returned to the calling process. Otherwise, a value of -1
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is returned and
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.IR errno
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is set to indicate the error.
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.LP
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If
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.BR wait4 ,
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.BR wait3
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or
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.BR waitpid
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returns due to a stopped
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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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.IR errno
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set to ECHILD.
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Otherwise, if
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.BR WNOHANG
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is specified and there are
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no stopped 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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.IR errno
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is set to indicate the error.
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.SH ERRORS
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.BR Wait
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will fail and return immediately if:
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.RS
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.IP \fBECHILD\fR
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The calling process has no existing unwaited-for
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child processes.
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.IP \fBEFAULT\fR
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The
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.I status
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or
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.I rusage
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arguments point to an illegal address.
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(May not be detected before exit of a child process.)
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.IP \fBEINTR\fR
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The call was interrupted by a caught signal,
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or the signal did not have the
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.BR SA_RESTART
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flag set.
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.RE
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.SH STANDARDS
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The
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.BR wait
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and
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.BR waitpid
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functions are defined by POSIX;
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.BR wait4
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and
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.BR wait3
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are not specified by POSIX.
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The
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.BR WCOREDUMP
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macro
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and the ability to restart a pending
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.BR wait
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call are extensions to the POSIX interface.
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.SH SEE ALSO
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.BR _exit (2),
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.BR execve (2),
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.BR signal (2),
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.BR exit (3)
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.BR rexit (3)
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.SH HISTORY
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A
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.BR wait3
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function call appeared in Version 6 AT&T UNIX.
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