1.\" $NetBSD: wait.2,v 1.36 2016/06/30 17:00:55 abhinav 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. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)wait.2 8.2 (Berkeley) 4/19/94 31.\" 32.Dd June 27, 2016 33.Dt WAIT 2 34.Os 35.Sh NAME 36.Nm wait , 37.Nm waitid , 38.Nm waitpid , 39.Nm wait6 , 40.Nm wait4 , 41.Nm wait3 42.Nd wait for process termination 43.Sh LIBRARY 44.Lb libc 45.Sh SYNOPSIS 46.In sys/wait.h 47.Ft pid_t 48.Fn wait "int *status" 49.Ft pid_t 50.Fn waitpid "pid_t wpid" "int *status" "int options" 51.Ft int 52.Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options" 53.In sys/resource.h 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.Ft pid_t 59.Fn wait6 "idtype_t idtype" "id_t id" "int *status" "int options" "struct wrusage *wrusage" "siginfo_t *infop" 60.Sh DESCRIPTION 61The 62.Fn wait 63function suspends execution of its calling process until 64.Fa status 65information is available for a terminated child process, 66or a signal is received. 67On return from a successful 68.Fn wait 69call, 70the 71.Fa status 72area contains termination information about the process that exited 73as defined below. 74.Pp 75The 76.Fn wait4 77and 78.Fn wait6 79call provides a more general interface for programs 80that need to wait for certain child processes, 81that need resource utilization statistics accumulated by child processes, 82or that require options. 83The other wait functions are implemented using 84.Fn wait4 . 85or 86.Fn wait6 . 87.Pp 88The 89.Fn wait6 90function is the most general function in this family and its distinct 91features are: 92.Pp 93All of the desired process statuses to be waited on must be explicitly 94specified in 95.Fa options . 96The 97.Fn wait , 98.Fn waitpid , 99.Fn wait3 , 100and 101.Fn wait4 102functions all implicitly wait for exited and trapped processes, 103but the 104.Fn waitid 105and 106.Fn wait6 107functions require the corresponding 108.Dv WEXITED 109and 110.Dv WTRAPPED 111flags to be explicitly specified. 112This allows waiting for processes which have experienced other 113status changes without having to also handle the exit status from 114terminated processes. 115.Pp 116The 117.Fn wait6 118function accepts a 119.Fa wrusage 120argument which points to a structure defined as: 121.Bd -literal 122struct wrusage { 123 struct rusage wru_self; 124 struct rusage wru_children; 125}; 126.Ed 127.Pp 128This allows the calling process to collect resource usage statistics 129from both its own child process as well as from its grand children. 130When no resource usage statistics are needed this pointer can be 131.Dv NULL . 132.Pp 133The last argument 134.Fa infop 135must be either 136.Dv NULL 137or a pointer to a 138.Fa siginfo_t 139structure. 140If 141.Pf non- Dv NULL , 142the structure is filled with the same data as for a 143.Dv SIGCHLD 144signal delivered when the process changed state. 145.Pp 146The set of child processes to be queried is specified by the arguments 147.Fa idtype 148and 149.Fa id . 150The separate 151.Fa idtype 152and 153.Fa id 154arguments support many other types of 155identifiers in addition to process IDs and process group IDs. 156.Bl -bullet -offset indent 157.It 158If 159.Fa idtype 160is 161.Dv P_PID , 162.Fn waitid 163and 164.Fn wait6 165wait for the child process with a process ID equal to 166.Dv (pid_t)id . 167.It 168If 169.Fa idtype 170is 171.Dv P_PGID , 172.Fn waitid 173and 174.Fn wait6 175wait for the child process with a process group ID equal to 176.Dv (pid_t)id . 177.It 178If 179.Fa idtype 180is 181.Dv P_ALL , 182.Fn waitid 183and 184.Fn wait6 185wait for any child process and the 186.Dv id 187is ignored. 188.It 189If 190.Fa idtype 191is 192.Dv P_PID 193or 194.Dv P_PGID 195and the 196.Dv id 197is zero, 198.Fn waitid 199and 200.Fn wait6 201wait for any child process in the same process group as the caller. 202.El 203.Pp 204Non-standard identifier types supported by this 205implementation of 206.Fn waitid 207and 208.Fn wait6 209are: 210.Bl -tag -width P_JAILID 211.It Dv P_UID 212Wait for processes whose effective user ID is equal to 213.Dv (uid_t) Fa id . 214.It Dv P_GID 215Wait for processes whose effective group ID is equal to 216.Dv (gid_t) Fa id . 217.It Dv P_SID 218Wait for processes whose session ID is equal to 219.Fa id . 220.\" This is just how sessions work, not sure this needs to be documented here 221If the child process started its own session, 222its session ID will be the same as its process ID. 223Otherwise the session ID of a child process will match the caller's session ID. 224.\" .It Dv P_JAILID 225.\" Waits for processes within a jail whose jail identifier is equal to 226.\" .Fa id . 227.El 228.Pp 229For the 230.Fn waitpid 231and 232.Fn wait4 233functions, the single 234.Fa wpid 235argument specifies the set of child processes for which to wait. 236The following symbolic constants are defined in 237.In sys/wait.h 238.Bd -literal -offset indent 239#define WAIT_ANY (-1) /* any process */ 240#define WAIT_MYPGRP 0 /* any process in my process group */ 241.Ed 242.Bl -bullet -offset indent 243.It 244If 245.Fa wpid 246is 247.Dv WAIT_ANY , 248the call waits for any child process. 249.It 250If 251.Fa wpid 252is 253.Dv WAIT_MYPGRP , 254the call waits for any child process in the process group of the caller. 255.It 256If 257.Fa wpid 258is greater than zero, the call waits for the process with process ID 259.Fa wpid . 260.It 261If 262.Fa wpid 263is less than \-1, the call waits for any process whose process group ID 264equals the absolute value of 265.Fa wpid . 266.El 267.Pp 268The 269.Fa status 270argument is defined below. 271.Pp 272The 273.Fa options 274argument contains the bitwise OR of any of the following options. 275.Bl -tag -width WCONTINUED 276.It Dv WALLSIG 277If this option is specified, the call will wait for all children regardless 278of what exit signal they post. 279.It Dv WALTSIG 280If this option is specified, the call will wait only for processes that 281are configured to post a signal other than 282.Dv SIGCHLD 283when they exit. 284If 285.Dv WALTSIG 286is not specified, the call will wait only for processes that 287are configured to post 288.Dv SIGCHLD . 289.It Dv WCONTINUED 290Report the status of selected processes that 291have continued from a job control stop by receiving a 292.Dv SIGCONT 293signal. 294.It Dv WEXITED 295Report the status of selected processes which have terminated. 296This flag is implicitly set for the functions 297.Fn wait , 298.Fn waitpid , 299.Fn wait3 , 300and 301.Fn wait4 . 302.br 303For the 304.Fn waitid 305and 306.Fn wait6 307functions, the flag has to be explicitly included in 308.Fa options 309if status reports from terminated processes are expected. 310.It Dv WNOHANG 311Do not block when 312there are no processes wishing to report status. 313.It Dv WNOWAIT 314Keep the process whose status is returned in a waitable state. 315The process may be waited for again after this call completes. 316.It Dv WSTOPPED 317An alias for 318.Dv WUNTRACED . 319.It Dv WTRAPPED 320Report the status of selected processes which are being traced via 321.Xr ptrace 2 322and have trapped or reached a breakpoint. 323This flag is implicitly set for the functions 324.Fn wait , 325.Fn waitpid , 326.Fn wait3 , 327and 328.Fn wait4 . 329.br 330For the 331.Fn waitid 332and 333.Fn wait6 334functions, the flag has to be explicitly included in 335.Fa options 336if status reports from trapped processes are expected. 337.It Dv WUNTRACED 338Report the status of selected processes which are stopped due to a 339.Dv SIGTTIN , SIGTTOU , SIGTSTP , 340or 341.Dv SIGSTOP 342signal. 343.It Dv __WALL 344This is an alias for 345.Dv WALLSIG . 346It is provided for compatibility with the Linux 347.Xr clone 2 348API . 349.It Dv __WCLONE 350This is an alias for 351.Dv WALTSIG . 352It is provided for compatibility with the Linux 353.Xr clone 2 354API. 355.El 356.sp 357For the 358.Fn waitid 359and 360.Fn wait6 361functions, at least one of the options 362.Dv WEXITED , 363.Dv WUNTRACED , 364.Dv WSTOPPED , 365.Dv WTRAPPED , 366or 367.Dv WCONTINUED 368must be specified. 369Otherwise there will be no events for the call to report. 370To avoid hanging indefinitely in such a case these functions 371return \-1 with 372.Dv errno 373set to 374.Dv EINVAL . 375.Pp 376If 377.Fa rusage 378is 379.Pf non- Dv NULL , 380a summary of the resources used by the terminated 381process and all its children is returned. 382.Pp 383If 384.Fa wrusage 385is 386.Pf non- Dv NULL , 387separate summaries are returned for the resources used 388by the terminated process and the resources used by all its children. 389.Pp 390If 391.Fa infop 392is 393.Pf non- Dv NULL , 394a 395.Dv siginfo_t 396structure is returned with the 397.Fa si_signo 398field set to 399.Dv SIGCHLD 400and the 401.Fa si_pid 402field set to the process ID of the process reporting status. 403For the exited process, the 404.Fa si_status 405field of the 406.Dv siginfo_t 407structure contains the full 32 bit exit status passed to 408.Xr _exit 2 ; 409the 410.Fa status 411argument of other calls only returns 8 lowest bits of the exit status. 412.Pp 413When the 414.Dv WNOHANG 415option is specified and no processes 416wish to report status, 417.Fn waitid 418sets the 419.Fa si_signo 420and 421.Fa si_pid 422fields in 423.Fa infop 424to zero. 425Checking these fields is the only way to know if a status change was reported. 426.Pp 427When the 428.Dv WNOHANG 429option is specified and no processes 430wish to report status, 431.Fn wait4 432returns a 433process id 434of 0. 435.Pp 436The 437.Fn waitpid 438call is identical to 439.Fn wait4 440with an 441.Fa rusage 442value of zero. 443The older 444.Fn wait3 445call is the same as 446.Fn wait4 447with a 448.Fa wpid 449value of \-1. 450.Pp 451The following macros may be used to test the manner of exit of the process. 452Note that these macros expect the 453.Fa status 454value itself, not a pointer to the 455.Fa status 456value. 457One of the first three macros will evaluate to a non-zero (true) value: 458.Bl -tag -width Ds 459.It Fn WIFEXITED status 460True if the process terminated normally by a call to 461.Xr _exit 2 462or 463.Xr exit 3 . 464.It Fn WIFSIGNALED status 465True if the process terminated due to receipt of a signal. 466.It Fn WIFSTOPPED status 467True if the process has not terminated, but has stopped and can be restarted. 468This macro can be true only if the wait call specified the 469.Dv WUNTRACED 470option 471or if the child process is being traced (see 472.Xr ptrace 2 ) . 473.It Fn WIFCONTINUED status 474True if the process has not terminated, but has been continued via the 475delivery of the 476.Dv SIGCONT 477signal. 478This macro can be true only if the wait call specified the 479.Dv WCONTINUED 480option. 481.El 482.Pp 483Depending on the values of those macros, the following macros 484produce the remaining status information about the child process: 485.Bl -tag -width Ds 486.It Fn WEXITSTATUS status 487If 488.Fn WIFEXITED status 489is true, evaluates to the low-order 8 bits 490of the argument passed to 491.Xr _exit 2 492or 493.Xr exit 3 494by the child. 495.It Fn WTERMSIG status 496If 497.Fn WIFSIGNALED status 498is true, evaluates to the number of the signal 499that caused the termination of the process. 500.It Fn WCOREDUMP status 501If 502.Fn WIFSIGNALED status 503is true, evaluates as true if the termination 504of the process was accompanied by the creation of a core file 505containing an image of the process when the signal was received. 506.It Fn WSTOPSIG status 507If 508.Fn WIFSTOPPED status 509is true, evaluates to the number of the signal 510that caused the process to stop. 511.El 512.Sh NOTES 513See 514.Xr sigaction 2 515for a list of termination signals. 516A status of 0 indicates normal termination. 517.Pp 518If a parent process terminates without 519waiting for all of its child processes to terminate, 520the remaining child processes are assigned the parent 521process 1 ID (the init process ID). 522.Pp 523If a signal is caught while any of the 524.Fn wait 525calls is pending, 526the call may be interrupted or restarted when the signal-catching routine 527returns, 528depending on the options in effect for the signal; 529see 530.Xr siginterrupt 3 . 531.Sh RETURN VALUES 532If 533.Fn wait 534returns due to a stopped 535or terminated child process, the process ID of the child 536is returned to the calling process. 537Otherwise, a value of \-1 is returned and 538.Va errno 539is set to indicate the error. 540.Pp 541If 542.Fn wait6 , 543.Fn wait4 , 544.Fn wait3 545or 546.Fn waitpid 547returns due to a stopped 548or terminated child process, the process ID of the child 549is returned to the calling process. 550If there are no children not previously awaited, 551\-1 is returned with 552.Va errno 553set to 554.Bq Er ECHILD . 555Otherwise, if 556.Dv WNOHANG 557is specified and there are 558no stopped or exited children, 0 is returned. 559If an error is detected or a caught signal aborts the call, 560a value of \-1 is returned and 561.Va errno 562is set to indicate the error. 563.Pp 564If 565.Fn waitid 566returns because one or more processes have a state change to report, 5670 is returned. 568If an error is detected, 569a value of -1 570is returned and 571.Va errno 572is set to indicate the error. 573If 574.Dv WNOHANG 575is specified and there are 576no stopped, continued or exited children, 5770 is returned. 578The 579.Fa si_signo 580and 581.Fa si_pid 582fields of 583.Fa infop 584must be checked against zero to determine if a process reported status. 585.Sh ERRORS 586.Fn wait 587will fail and return immediately if: 588.Bl -tag -width Er 589.It Bq Er ECHILD 590The calling process has no existing unwaited-for child processes; or 591no status from the terminated child process is available 592because the calling process has asked the system to discard 593such status by ignoring the signal 594.Dv SIGCHLD 595or setting the flag 596.Dv SA_NOCLDWAIT 597for that signal. 598.It Bq Er EFAULT 599The 600.Fa status 601or 602.Fa rusage 603arguments point to an illegal address. 604(May not be detected before exit of a child process.) 605.It Bq Er EINTR 606The call was interrupted by a caught signal, 607or the signal did not have the 608.Dv SA_RESTART 609flag set. 610.El 611.Pp 612In addition, 613.Fn wait6 , 614.Fn wait3 , 615.Fn wait4 , 616.Fn waitid , 617and 618.Fn waitpid 619will fail and return immediately if: 620.Bl -tag -width Er 621.It Bq Er EINVAL 622An invalid value was specified for 623.Fa options . 624.El 625.Sh SEE ALSO 626.Xr _exit 2 , 627.Xr ptrace 2 , 628.Xr sigaction 2 , 629.Xr siginfo 2 , 630.Xr exit 3 , 631.Xr siginterrupt 3 632.Sh STANDARDS 633The 634.Fn wait 635and 636.Fn waitpid 637functions conform to 638.St -p1003.1-90 ; 639the 640.Fn waitid 641function conforms to 642.St -p1003.1-2004 ; 643the 644.Fn wait3 645function conforms to 646.St -xpg4 ; 647.Fn wait4 648is an extension. 649The 650.Fn WCOREDUMP 651macro 652and the ability to restart a pending 653.Fn wait 654call are extensions to the POSIX interface. 655.Sh HISTORY 656A 657.Fn wait 658function call appeared in 659.At v2 . 660