1.\" $NetBSD: wait.2,v 1.18 2002/04/29 01:41:46 simonb Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993, 1994 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)wait.2 8.2 (Berkeley) 4/19/94 35.\" 36.Dd April 19, 1994 37.Dt WAIT 2 38.Os 39.Sh NAME 40.Nm wait , 41.Nm waitpid , 42.Nm wait4 , 43.Nm wait3 44.Nd wait for process termination 45.Sh LIBRARY 46.Lb libc 47.Sh SYNOPSIS 48.Fd #include \*[Lt]sys/wait.h\*[Gt] 49.Ft pid_t 50.Fn wait "int *status" 51.Ft pid_t 52.Fn waitpid "pid_t wpid" "int *status" "int options" 53.Fd #include \*[Lt]sys/resource.h\*[Gt] 54.Ft pid_t 55.Fn wait3 "int *status" "int options" "struct rusage *rusage" 56.Ft pid_t 57.Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage" 58.Sh DESCRIPTION 59The 60.Fn wait 61function suspends execution of its calling process until 62.Fa status 63information is available for a terminated child process, 64or a signal is received. 65On return from a successful 66.Fn wait 67call, 68the 69.Fa status 70area contains termination information about the process that exited 71as defined below. 72.Pp 73The 74.Fn wait4 75call provides a more general interface for programs 76that need to wait for certain child processes, 77that need resource utilization statistics accumulated by child processes, 78or that require options. 79The other wait functions are implemented using 80.Fn wait4 . 81.Pp 82The 83.Fa wpid 84parameter specifies the set of child processes for which to wait. 85If 86.Fa wpid 87is -1, the call waits for any child process. 88If 89.Fa wpid 90is 0, 91the call waits for any child process in the process group of the caller. 92If 93.Fa wpid 94is greater than zero, the call waits for the process with process id 95.Fa wpid . 96If 97.Fa wpid 98is less than -1, the call waits for any process whose process group id 99equals the absolute value of 100.Fa wpid . 101.Pp 102The 103.Fa status 104parameter is defined below. The 105.Fa options 106parameter contains the bitwise OR of any of the following options: 107.Bl -tag -width WUNTRACED 108.It Dv WNOHANG 109This option is used to indicate that the call should not block if 110there are no processes that wish to report status. 111.It Dv WUNTRACED 112If this option is set, children of the current process that are stopped 113due to a 114.Dv SIGTTIN , SIGTTOU , SIGTSTP , 115or 116.Dv SIGSTOP 117signal also have their status reported. 118.It Dv WALTSIG 119If this option is specified, the call will wait only for processes that 120are configured to post a signal other than 121.Dv SIGCHLD 122when they exit. If 123.Dv WALTSIG 124is not specified, the call will wait only for processes that 125are configured to post 126.Dv SIGCHLD . 127.It Dv __WCLONE 128This is an alias for 129.Dv WALTSIG . 130It is provided for compatibility with the Linux 131.Xr clone 2 132API. 133.It Dv WALLSIG 134If this option is specified, the call will wait for all children regardless 135of what exit signal they post. 136.It Dv __WALL 137This is an alias for 138.Dv WALLSIG . 139It is provided for compatibility with the Linux 140.Xr clone 2 141API . 142.El 143.Pp 144If 145.Fa rusage 146is non-zero, a summary of the resources used by the terminated 147process and all its 148children is returned (this information is currently not available 149for stopped processes). 150.Pp 151When the 152.Dv WNOHANG 153option is specified and no processes 154wish to report status, 155.Fn wait4 156returns a 157process id 158of 0. 159.Pp 160The 161.Fn waitpid 162call is identical to 163.Fn wait4 164with an 165.Fa rusage 166value of zero. 167The older 168.Fn wait3 169call is the same as 170.Fn wait4 171with a 172.Fa wpid 173value of -1. 174.Pp 175The following macros may be used to test the manner of exit of the process. 176One of the first three macros will evaluate to a non-zero (true) value: 177.Bl -tag -width Ds 178.It Fn WIFEXITED status 179True if the process terminated normally by a call to 180.Xr _exit 2 181or 182.Xr exit 3 . 183.It Fn WIFSIGNALED status 184True if the process terminated due to receipt of a signal. 185.It Fn WIFSTOPPED status 186True if the process has not terminated, but has stopped and can be restarted. 187This macro can be true only if the wait call specified the 188.Dv WUNTRACED 189option 190or if the child process is being traced (see 191.Xr ptrace 2 ) . 192.El 193.Pp 194Depending on the values of those macros, the following macros 195produce the remaining status information about the child process: 196.Bl -tag -width Ds 197.It Fn WEXITSTATUS status 198If 199.Fn WIFEXITED status 200is true, evaluates to the low-order 8 bits 201of the argument passed to 202.Xr _exit 2 203or 204.Xr exit 3 205by the child. 206.It Fn WTERMSIG status 207If 208.Fn WIFSIGNALED status 209is true, evaluates to the number of the signal 210that caused the termination of the process. 211.It Fn WCOREDUMP status 212If 213.Fn WIFSIGNALED status 214is true, evaluates as true if the termination 215of the process was accompanied by the creation of a core file 216containing an image of the process when the signal was received. 217.It Fn WSTOPSIG status 218If 219.Fn WIFSTOPPED status 220is true, evaluates to the number of the signal 221that caused the process to stop. 222.El 223.Sh NOTES 224See 225.Xr sigaction 2 226for a list of termination signals. 227A status of 0 indicates normal termination. 228.Pp 229If a parent process terminates without 230waiting for all of its child processes to terminate, 231the remaining child processes are assigned the parent 232process 1 ID (the init process ID). 233.Pp 234If a signal is caught while any of the 235.Fn wait 236calls is pending, 237the call may be interrupted or restarted when the signal-catching routine 238returns, 239depending on the options in effect for the signal; 240see 241.Xr intro 2 , 242System call restart. 243.Sh RETURN VALUES 244If 245.Fn wait 246returns due to a stopped 247or terminated child process, the process ID of the child 248is returned to the calling process. Otherwise, a value of -1 249is returned and 250.Va errno 251is set to indicate the error. 252.Pp 253If 254.Fn wait4 , 255.Fn wait3 256or 257.Fn waitpid 258returns due to a stopped 259or terminated child process, the process ID of the child 260is returned to the calling process. 261If there are no children not previously awaited, 262-1 is returned with 263.Va errno 264set to 265.Bq Er ECHILD . 266Otherwise, if 267.Dv WNOHANG 268is specified and there are 269no stopped or exited children, 2700 is returned. 271If an error is detected or a caught signal aborts the call, 272a value of -1 273is returned and 274.Va errno 275is set to indicate the error. 276.Sh ERRORS 277.Fn wait 278will fail and return immediately if: 279.Bl -tag -width Er 280.It Bq Er ECHILD 281The calling process has no existing unwaited-for 282child processes. 283.It Bq Er EFAULT 284The 285.Fa status 286or 287.Fa rusage 288arguments point to an illegal address. 289(May not be detected before exit of a child process.) 290.It Bq Er EINTR 291The call was interrupted by a caught signal, 292or the signal did not have the 293.Dv SA_RESTART 294flag set. 295.El 296.Pp 297In addition, 298.Fn wait3 , 299.Fn wait4 , 300and 301.Fn waitpid 302will fail and return immediately if: 303.Bl -tag -width Er 304.It Bq Er EINVAL 305An invalid value was specified for 306.Fa options . 307.El 308.Sh SEE ALSO 309.Xr _exit 2 , 310.Xr sigaction 2 311.Sh STANDARDS 312The 313.Fn wait 314and 315.Fn waitpid 316functions conform to 317.St -p1003.1-90 ; 318the 319.Fn wait3 320function conforms to 321.St -xpg4 ; 322.Fn wait4 323is an extension. 324The 325.Fn WCOREDUMP 326macro 327and the ability to restart a pending 328.Fn wait 329call are extensions to the POSIX interface. 330.Sh HISTORY 331A 332.Fn wait 333function call appeared in 334.At v6 . 335