.\" $OpenBSD: wait.2,v 1.24 2013/04/03 03:15:59 guenther Exp $ .\" $NetBSD: wait.2,v 1.6 1995/02/27 12:39:37 cgd Exp $ .\" .\" Copyright (c) 1980, 1991, 1993, 1994 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)wait.2 8.2 (Berkeley) 4/19/94 .\" .Dd $Mdocdate: April 3 2013 $ .Dt WAIT 2 .Os .Sh NAME .Nm wait , .Nm waitpid , .Nm wait4 , .Nm wait3 .Nd wait for process termination .Sh SYNOPSIS .Fd #include .Ft pid_t .Fn wait "int *status" .Ft pid_t .Fn waitpid "pid_t wpid" "int *status" "int options" .Fd #include .Fd #include .Ft pid_t .Fn wait3 "int *status" "int options" "struct rusage *rusage" .Ft pid_t .Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage" .Sh DESCRIPTION The .Fn wait function suspends execution of its calling process until .Fa status information is available for a terminated child process, or a signal is received. On return from a successful .Fn wait call, the .Fa status area, if non-zero, is filled in with termination information about the process that exited (see below). .Pp The .Fn wait4 call provides a more general interface for programs that need to wait for certain child processes, that need resource utilization statistics accumulated by child processes, or that require options. The other wait functions are implemented using .Fn wait4 . .Pp The .Fa wpid parameter specifies the set of child processes for which to wait. The following symbolic constants are currently defined in .Aq Pa sys/wait.h : .Bd -unfilled -offset indent #define WAIT_ANY (-1) /* any process */ #define WAIT_MYPGRP 0 /* any process in my process group */ .Ed .Pp If .Fa wpid is set to .Dv WAIT_ANY , the call waits for any child process. If .Fa wpid is set to .Dv WAIT_MYPGRP , the call waits for any child process in the process group of the caller. If .Fa wpid is greater than zero, the call waits for the process with process ID .Fa wpid . If .Fa wpid is less than \-1, the call waits for any process whose process group ID equals the absolute value of .Fa wpid . .Pp The .Fa status parameter is defined below. The .Fa options parameter contains the bitwise .Tn OR of any of the following options: .Bl -tag -width "WCONTINUED" .It Dv WCONTINUED Causes status to be reported for stopped child processes that have been continued by receipt of a .Dv SIGCONT signal. .It Dv WNOHANG Indicates that the call should not block if there are no processes that wish to report status. .It Dv WUNTRACED If set, children of the current process that are stopped due to a .Dv SIGTTIN , SIGTTOU , SIGTSTP , or .Dv SIGSTOP signal also have their status reported. .El .Pp If .Fa rusage is non-zero, a summary of the resources used by the terminated process and all its children is returned (this information is currently not available for stopped processes). .Pp When the .Dv WNOHANG option is specified and no processes wish to report status, .Fn wait4 returns a process ID of 0. .Pp The .Fn waitpid call is identical to .Fn wait4 with an .Fa rusage value of zero. The older .Fn wait3 call is the same as .Fn wait4 with a .Fa wpid value of \-1. .Pp The following macros may be used to test the manner of exit of the process. One of the first three macros will evaluate to a non-zero (true) value: .Bl -tag -width Ds .It Fn WIFCONTINUED status True if the process has not terminated, and has continued after a job control stop. This macro can be true only if the wait call specified the .Dv WCONTINUED option. .It Fn WIFEXITED status True if the process terminated normally by a call to .Xr _exit 2 or .Xr exit 3 . .It Fn WIFSIGNALED status True if the process terminated due to receipt of a signal. .It Fn WIFSTOPPED status True if the process has not terminated, but has stopped and can be restarted. This macro can be true only if the wait call specified the .Dv WUNTRACED option or if the child process is being traced (see .Xr ptrace 2 ) . .El .Pp Depending on the values of those macros, the following macros produce the remaining status information about the child process: .Bl -tag -width Ds .It Fn WEXITSTATUS status If .Fn WIFEXITED status is true, evaluates to the low-order 8 bits of the argument passed to .Xr _exit 2 or .Xr exit 3 by the child. .It Fn WTERMSIG status If .Fn WIFSIGNALED status is true, evaluates to the number of the signal that caused the termination of the process. .It Fn WCOREDUMP status If .Fn WIFSIGNALED status is true, evaluates as true if the termination of the process was accompanied by the creation of a core file containing an image of the process when the signal was received. .It Fn WSTOPSIG status If .Fn WIFSTOPPED status is true, evaluates to the number of the signal that caused the process to stop. .El .Sh NOTES See .Xr sigaction 2 for a list of termination signals. A status of 0 indicates normal termination. .Pp If a parent process terminates without waiting for all of its child processes to terminate, the remaining child processes are assigned the parent process 1 ID (the init process ID). .Pp If a signal is caught while any of the .Fn wait calls is pending, the call may be interrupted or restarted when the signal-catching routine returns, depending on the options in effect for the signal; for further information, see .Xr siginterrupt 3 . .Sh RETURN VALUES If .Fn wait 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 .Va errno is set to indicate the error. .Pp If .Fn wait4 , .Fn wait3 or .Fn waitpid returns due to a stopped or terminated child process, the process ID of the child is returned to the calling process. If there are no children not previously awaited, \-1 is returned with .Va errno set to .Bq Er ECHILD . Otherwise, if .Dv WNOHANG is specified and there are no stopped or exited children, 0 is returned. If an error is detected or a caught signal aborts the call, a value of \-1 is returned and .Va errno is set to indicate the error. .Sh ERRORS .Fn wait 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 EFAULT The .Fa status or .Fa rusage arguments point 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 Invalid or undefined flags were passed in the .Fa options argument. .El .Sh SEE ALSO .Xr _exit 2 , .Xr sigaction 2 , .Xr exit 3 .Sh STANDARDS The .Fn wait and .Fn waitpid functions are defined by POSIX; .Fn wait4 and .Fn wait3 are not specified by POSIX. The .Fn WCOREDUMP macro and the ability to restart a pending .Fn wait call are extensions to the POSIX interface. .Sh HISTORY A .Fn wait system call first appeared in .At v1 . The .Fa status argument is accepted since .At v2 . A .Fn wait3 system call first appeared in .Bx 4 , but the final calling convention was only established in .Bx 4.2 . The .Fn wait4 and .Fn waitpid function calls first appeared in .Bx 4.3 Reno .