163 lines
4.4 KiB
Groff
163 lines
4.4 KiB
Groff
|
.\" Copyright (c) 1980 Regents of the University of California.
|
||
|
|
.\" All rights reserved. The Berkeley software License Agreement
|
||
|
|
.\" specifies the terms and conditions for redistribution.
|
||
|
|
.\"
|
||
|
|
.\" @(#)wait.2 6.2 (Berkeley) 6/30/85
|
||
|
|
.\"
|
||
|
|
.TH WAIT 2 "June 30, 1985"
|
||
|
|
.UC 4
|
||
|
|
.SH NAME
|
||
|
|
wait, waitpid \- wait for process to terminate
|
||
|
|
.SH SYNOPSIS
|
||
|
|
.ft B
|
||
|
|
.nf
|
||
|
|
#include <sys/types.h>
|
||
|
|
#include <sys/wait.h>
|
||
|
|
|
||
|
|
pid_t wait(int *\fIstatus\fP)
|
||
|
|
pid_t waitpid(pid_t \fIpid\fP, int *\fIstatus\fP, int \fIoptions\fP)
|
||
|
|
.fi
|
||
|
|
.SH DESCRIPTION
|
||
|
|
.B Wait
|
||
|
|
causes its caller to delay until a signal is received or
|
||
|
|
one of its child
|
||
|
|
processes terminates.
|
||
|
|
If any child has died since the last
|
||
|
|
.BR wait ,
|
||
|
|
return is immediate, returning the process id and
|
||
|
|
exit status of one of the terminated
|
||
|
|
children.
|
||
|
|
If there are no children, return is immediate with
|
||
|
|
the value \-1 returned.
|
||
|
|
.PP
|
||
|
|
On return from a successful
|
||
|
|
.B wait
|
||
|
|
call,
|
||
|
|
.I status
|
||
|
|
is nonzero, and the high byte of
|
||
|
|
.I status
|
||
|
|
contains the low byte of the argument to
|
||
|
|
.B exit
|
||
|
|
supplied by the child process;
|
||
|
|
the low byte of
|
||
|
|
.I status
|
||
|
|
contains the termination status of the process.
|
||
|
|
A more precise definition of the
|
||
|
|
.I status
|
||
|
|
word is given in
|
||
|
|
.RI < sys/wait.h >.
|
||
|
|
.B Wait
|
||
|
|
can be called with a null pointer argument to indicate that no status need
|
||
|
|
be returned.
|
||
|
|
.PP
|
||
|
|
.B Waitpid
|
||
|
|
provides an alternate interface for programs
|
||
|
|
that must not block when collecting the status
|
||
|
|
of child processes, or that wish to wait for
|
||
|
|
one particular child. The pid parameter is
|
||
|
|
the process ID of the child to wait for, \-1
|
||
|
|
for any child. The
|
||
|
|
.I status
|
||
|
|
parameter is defined as above. The
|
||
|
|
.I options
|
||
|
|
parameter is used to indicate the call should not block if
|
||
|
|
there are no processes that wish to report status (WNOHANG),
|
||
|
|
and/or that children of the current process that are stopped
|
||
|
|
due to a SIGTTIN, SIGTTOU, SIGTSTP, or SIGSTOP signal should also have
|
||
|
|
their status reported (WUNTRACED). (Job control is not implemented for
|
||
|
|
MINIX 3, but these symbols and signals are.)
|
||
|
|
.PP
|
||
|
|
When the WNOHANG option is specified and no processes
|
||
|
|
wish to report status,
|
||
|
|
.B waitpid
|
||
|
|
either returns 0 under some implementations, or \-1 with
|
||
|
|
.B errno
|
||
|
|
set to
|
||
|
|
.B EAGAIN
|
||
|
|
under others.
|
||
|
|
(Under MINIX 3 it returns 0.)
|
||
|
|
The WNOHANG and WUNTRACED options may be combined by
|
||
|
|
.IR or 'ing
|
||
|
|
the two values.
|
||
|
|
.SH NOTES
|
||
|
|
The call
|
||
|
|
.BI "wait(&" status ")"
|
||
|
|
is equivalent to
|
||
|
|
.BI "waitpid(\-1, &" status ", 0)\fR."
|
||
|
|
.PP
|
||
|
|
See
|
||
|
|
.BR sigaction (2)
|
||
|
|
for a list of termination statuses (signals);
|
||
|
|
0 status indicates normal termination.
|
||
|
|
A special status (0177) is returned for a stopped process
|
||
|
|
that has not terminated and can be restarted;
|
||
|
|
see
|
||
|
|
.BR ptrace (2).
|
||
|
|
If the 0200 bit of the termination status
|
||
|
|
is set,
|
||
|
|
a core image of the process was produced
|
||
|
|
by the system.
|
||
|
|
.PP
|
||
|
|
If the parent process terminates without
|
||
|
|
waiting on its children,
|
||
|
|
the initialization process
|
||
|
|
(process ID = 1)
|
||
|
|
inherits the children.
|
||
|
|
.PP
|
||
|
|
.I <sys/wait.h>
|
||
|
|
defines a number of macros that operate on a status word:
|
||
|
|
.TP 5
|
||
|
|
.BI "WIFEXITED(" status ")"
|
||
|
|
True if normal exit.
|
||
|
|
.TP 5
|
||
|
|
.BI "WEXITSTATUS(" status ")"
|
||
|
|
Exit status if the process returned by a normal exit, zero otherwise.
|
||
|
|
.TP 5
|
||
|
|
.BI "WTERMSIG(" status ")"
|
||
|
|
Signal number if the process died by a signal, zero otherwise.
|
||
|
|
.TP 5
|
||
|
|
.BI "WIFSIGNALED(" status ")"
|
||
|
|
True if the process died by a signal.
|
||
|
|
.TP 5
|
||
|
|
.BI "WIFSTOPPED(" status ")"
|
||
|
|
True if the process is stopped. (Never true under MINIX 3.)
|
||
|
|
.TP 5
|
||
|
|
.BI "WSTOPSIG(" status ")"
|
||
|
|
Signal number of the signal that stopped the process.
|
||
|
|
.SH "RETURN VALUE
|
||
|
|
If \fBwait\fP returns due to a stopped
|
||
|
|
or terminated child process, the process ID of the child
|
||
|
|
is returned to the calling process. Otherwise, a value of \-1
|
||
|
|
is returned and \fBerrno\fP is set to indicate the error.
|
||
|
|
.PP
|
||
|
|
.B Waitpid
|
||
|
|
returns \-1 if there are no children not previously waited for or if
|
||
|
|
the process that it wants to wait for doesn't exist.
|
||
|
|
.PP
|
||
|
|
.B Waitpid
|
||
|
|
returns 0 if WNOHANG is specified and there are no stopped or exited
|
||
|
|
children. (Under other implementations it may return \-1 instead. Portable
|
||
|
|
code should test for both possibilities.)
|
||
|
|
.SH ERRORS
|
||
|
|
.B Wait
|
||
|
|
will fail and return immediately if one or more of the following
|
||
|
|
are true:
|
||
|
|
.TP 15
|
||
|
|
[ECHILD]
|
||
|
|
The calling process has no existing unwaited-for
|
||
|
|
child processes.
|
||
|
|
.TP 15
|
||
|
|
[EFAULT]
|
||
|
|
The \fIstatus\fP argument points to an illegal address.
|
||
|
|
.TP 15
|
||
|
|
[EAGAIN]
|
||
|
|
.B Waitpid
|
||
|
|
is called with the WNOHANG option and no child has exited yet. (Not under
|
||
|
|
MINIX 3, it'll return 0 in this case and leave
|
||
|
|
.B errno
|
||
|
|
alone.)
|
||
|
|
.SH "SEE ALSO"
|
||
|
|
.BR execve (2),
|
||
|
|
.BR exit (2),
|
||
|
|
.BR sigaction (2).
|