.\" $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. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. 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 April 19, 1994 .Dt WAIT 2 .Os BSD 4 .Sh NAME .Nm wait , .Nm wait3 , .Nm wait4 , .Nm waitpid .Nd wait for process termination .Sh SYNOPSIS .Fd #include <sys/wait.h> .Ft pid_t .Fo wait .Fa "int *stat_loc" .Fc .Ft pid_t .Fo wait3 .Fa "int *stat_loc" .Fa "int options" .Fa "struct rusage *rusage" .Fc .Ft pid_t .Fo wait4 .Fa "pid_t pid" .Fa "int *stat_loc" .Fa "int options" .Fa "struct rusage *rusage" .Fc .Ft pid_t .Fo waitpid .Fa "pid_t pid" .Fa "int *stat_loc" .Fa "int options" .Fc .Sh DESCRIPTION The .Fn wait function suspends execution of its calling process until .Fa stat_loc information is available for a terminated child process, or a signal is received. On return from a successful .Fn wait call, the .Fa stat_loc area contains termination information about the process that exited as defined 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 pid parameter specifies the set of child processes for which to wait. If .Fa pid is -1, the call waits for any child process. If .Fa pid is 0, the call waits for any child process in the process group of the caller. If .Fa pid is greater than zero, the call waits for the process with process id .Fa pid . If .Fa pid is less than -1, the call waits for any process whose process group id equals the absolute value of .Fa pid . .Pp The .Fa stat_loc parameter is defined below. The .Fa options parameter contains the bitwise OR of any of the following options. The .Dv WNOHANG option is used to indicate that the call should not block if there are no processes that wish to report status. If the .Dv WUNTRACED option is 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. .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 pid 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 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; see .Xr intro 2 , System call restart. .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 wait3 , .Fn wait4 , 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 The .Fn wait system call 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 argument points to an illegal address (may not be detected before the exit of a child process). .\" =========== .It Bq Er EINVAL Invalid or undefined flags are passed in the .Fa options argument. .El .Pp The .Fn wait3 and .Fn waitpid calls will fail and return immediately if: .Bl -tag -width Er .\" =========== .It Bq Er ECHILD The process specified by .Fa pid does not exist or is not a child of the calling process, or the process group specified by .Fa pid does not exist or does not have any member process that is a child of the calling process. .El .Pp The .Fn waitpid call will fail and return immediately if: .Bl -tag -width Er .\" =========== .It Bq Er EINVAL The options argument is not valid. .El .Pp Any of these calls will fail and return immediately if: .Bl -tag -width Er .\" =========== .It Bq Er EINTR The call is interrupted by a caught signal or the signal does not have the .Dv SA_RESTART flag set. .El .Sh STANDARDS The .Fn wait and .Fn waitpid functions are defined by POSIX; .Fn wait3 and .Fn wait4 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 LEGACY SYNOPSIS .Fd #include <sys/types.h> .Fd #include <sys/wait.h> .Pp The include file .In sys/types.h is necessary. .Sh SEE ALSO .Xr sigaction 2 , .Xr exit 3 , .Xr compat 5 .Sh HISTORY A .Fn wait function call appeared in .At v6 .