.\" $NetBSD: wait.2,v 1.39.16.1 2019/09/05 08:19:40 martin 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 September 2, 2019 .Dt WAIT 2 .Os .Sh NAME .Nm wait , .Nm waitid , .Nm waitpid , .Nm wait6 , .Nm wait4 , .Nm wait3 .Nd wait for process termination .Sh LIBRARY .Lb libc .Sh SYNOPSIS .In sys/wait.h .Ft pid_t .Fn wait "int *status" .Ft pid_t .Fn waitpid "pid_t wpid" "int *status" "int options" .Ft int .Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options" .In sys/resource.h .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" .Ft pid_t .Fn wait6 "idtype_t idtype" "id_t id" "int *status" "int options" "struct wrusage *wrusage" "siginfo_t *infop" .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 contains termination information about the process that exited as defined below. .Pp The .Fn wait4 and .Fn wait6 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 . or .Fn wait6 . .Pp The .Fn wait6 function is the most general function in this family and its distinct features are: .Pp All of the desired process statuses to be waited on must be explicitly specified in .Fa options . The .Fn wait , .Fn waitpid , .Fn wait3 , and .Fn wait4 functions all implicitly wait for exited and trapped processes, but the .Fn waitid and .Fn wait6 functions require the corresponding .Dv WEXITED and .Dv WTRAPPED flags to be explicitly specified. This allows waiting for processes which have experienced other status changes without having to also handle the exit status from terminated processes. .Pp The .Fn wait6 function accepts a .Fa wrusage argument which points to a structure defined as: .Bd -literal struct wrusage { struct rusage wru_self; struct rusage wru_children; }; .Ed .Pp This allows the calling process to collect resource usage statistics from both its own child process as well as from its grand children. When no resource usage statistics are needed this pointer can be .Dv NULL . .Pp The last argument .Fa infop must be either .Dv NULL or a pointer to a .Fa siginfo_t structure. If .Pf non- Dv NULL , the structure is filled with the same data as for a .Dv SIGCHLD signal delivered when the process changed state. .Pp The set of child processes to be queried is specified by the arguments .Fa idtype and .Fa id . The separate .Fa idtype and .Fa id arguments support many other types of identifiers in addition to process IDs and process group IDs. .Bl -bullet -offset indent .It If .Fa idtype is .Dv P_PID , .Fn waitid and .Fn wait6 wait for the child process with a process ID equal to .Dv (pid_t)id . .It If .Fa idtype is .Dv P_PGID , .Fn waitid and .Fn wait6 wait for the child process with a process group ID equal to .Dv (pid_t)id . .It If .Fa idtype is .Dv P_ALL , .Fn waitid and .Fn wait6 wait for any child process and the .Dv id is ignored. .It If .Fa idtype is .Dv P_PID or .Dv P_PGID and the .Dv id is zero, .Fn waitid and .Fn wait6 wait for any child process in the same process group as the caller. .El .Pp Non-standard identifier types supported by this implementation of .Fn waitid and .Fn wait6 are: .Bl -tag -width P_JAILID .It Dv P_UID Wait for processes whose effective user ID is equal to .Dv (uid_t) Fa id . .It Dv P_GID Wait for processes whose effective group ID is equal to .Dv (gid_t) Fa id . .It Dv P_SID Wait for processes whose session ID is equal to .Fa id . .\" This is just how sessions work, not sure this needs to be documented here If the child process started its own session, its session ID will be the same as its process ID. Otherwise the session ID of a child process will match the caller's session ID. .\" .It Dv P_JAILID .\" Waits for processes within a jail whose jail identifier is equal to .\" .Fa id . .El .Pp For the .Fn waitpid and .Fn wait4 functions, the single .Fa wpid argument specifies the set of child processes for which to wait. The following symbolic constants are defined in .In sys/wait.h .Bd -literal -offset indent #define WAIT_ANY (-1) /* any process */ #define WAIT_MYPGRP 0 /* any process in my process group */ .Ed .Bl -bullet -offset indent .It If .Fa wpid is .Dv WAIT_ANY , the call waits for any child process. .It If .Fa wpid is .Dv WAIT_MYPGRP , the call waits for any child process in the process group of the caller. .It If .Fa wpid is greater than zero, the call waits for the process with process ID .Fa wpid . .It If .Fa wpid is less than \-1, the call waits for any process whose process group ID equals the absolute value of .Fa wpid . .El .Pp The .Fa status argument is defined below. .Pp The .Fa options argument contains the bitwise OR of any of the following options. .Bl -tag -width WCONTINUED .It Dv WALLSIG If this option is specified, the call will wait for all children regardless of what exit signal they post. .It Dv WALTSIG If this option is specified, the call will wait only for processes that are configured to post a signal other than .Dv SIGCHLD when they exit. If .Dv WALTSIG is not specified, the call will wait only for processes that are configured to post .Dv SIGCHLD . .It Dv WCONTINUED Report the status of selected processes that have continued from a job control stop by receiving a .Dv SIGCONT signal. .It Dv WEXITED Report the status of selected processes which have terminated. This flag is implicitly set for the functions .Fn wait , .Fn waitpid , .Fn wait3 , and .Fn wait4 . .br For the .Fn waitid and .Fn wait6 functions, the flag has to be explicitly included in .Fa options if status reports from terminated processes are expected. .It Dv WNOHANG Do not block when there are no processes wishing to report status. .It Dv WNOWAIT Keep the process whose status is returned in a waitable state. The process may be waited for again after this call completes. .It Dv WNOZOMBIE Exclude zombie processes from the child selection criteria. .It Dv WSTOPPED An alias for .Dv WUNTRACED . .It Dv WTRAPPED Report the status of selected processes which are being traced via .Xr ptrace 2 and have trapped or reached a breakpoint. This flag is implicitly set for the functions .Fn wait , .Fn waitpid , .Fn wait3 , and .Fn wait4 . .br For the .Fn waitid and .Fn wait6 functions, the flag has to be explicitly included in .Fa options if status reports from trapped processes are expected. .It Dv WUNTRACED Report the status of selected processes which are stopped due to a .Dv SIGTTIN , SIGTTOU , SIGTSTP , or .Dv SIGSTOP signal. .It Dv __WALL This is an alias for .Dv WALLSIG . It is provided for compatibility with the Linux .Xr clone 2 API . .It Dv __WCLONE This is an alias for .Dv WALTSIG . It is provided for compatibility with the Linux .Xr clone 2 API. .El .sp For the .Fn waitid and .Fn wait6 functions, at least one of the options .Dv WEXITED , .Dv WUNTRACED , .Dv WSTOPPED , .Dv WTRAPPED , or .Dv WCONTINUED must be specified. Otherwise there will be no events for the call to report. To avoid hanging indefinitely in such a case these functions return \-1 with .Dv errno set to .Dv EINVAL . .Pp If .Fa rusage is .Pf non- Dv NULL , a summary of the resources used by the terminated process and all its children is returned. .Pp If .Fa wrusage is .Pf non- Dv NULL , separate summaries are returned for the resources used by the terminated process and the resources used by all its children. .Pp If .Fa infop is .Pf non- Dv NULL , a .Dv siginfo_t structure is returned with the .Fa si_signo field set to .Dv SIGCHLD and the .Fa si_pid field set to the process ID of the process reporting status. For the exited process, the .Fa si_status field of the .Dv siginfo_t structure contains the full 32 bit exit status passed to .Xr _exit 2 ; the .Fa status argument of other calls only returns 8 lowest bits of the exit status. .Pp When the .Dv WNOHANG option is specified and no processes wish to report status, .Fn waitid sets the .Fa si_signo and .Fa si_pid fields in .Fa infop to zero. Checking these fields is the only way to know if a status change was reported. .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. Note that these macros expect the .Fa status value itself, not a pointer to the .Fa status value. 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 ) . .It Fn WIFCONTINUED status True if the process has not terminated, but has been continued via the delivery of the .Dv SIGCONT signal. This macro can be true only if the wait call specified the .Dv WCONTINUED option. .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 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 wait6 , .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. .Pp If .Fn waitid returns because one or more processes have a state change to report, 0 is returned. If an error is detected, a value of -1 is returned and .Va errno is set to indicate the error. If .Dv WNOHANG is specified and there are no stopped, continued or exited children, 0 is returned. The .Fa si_signo and .Fa si_pid fields of .Fa infop must be checked against zero to determine if a process reported status. .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; or no status from the terminated child process is available because the calling process has asked the system to discard such status by ignoring the signal .Dv SIGCHLD or setting the flag .Dv SA_NOCLDWAIT for that signal. .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. .El .Pp In addition, .Fn wait6 , .Fn wait3 , .Fn wait4 , .Fn waitid , and .Fn waitpid will fail and return immediately if: .Bl -tag -width Er .It Bq Er EINVAL An invalid value was specified for .Fa options . .El .Sh SEE ALSO .Xr _exit 2 , .Xr fork 2 , .Xr ptrace 2 , .Xr sigaction 2 , .Xr siginfo 2 , .Xr exit 3 , .Xr siginterrupt 3 .Sh STANDARDS The .Fn wait and .Fn waitpid functions conform to .St -p1003.1-90 ; the .Fn waitid function conforms to .St -p1003.1-2004 ; the .Fn wait3 function conforms to .St -xpg4 ; .Fn wait4 is an extension. 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 function call appeared in .At v1 .