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