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28 .\" @(#)wait.2 8.2 (Berkeley) 4/19/94
40 .Nd wait for processes to change status
46 .Fn wait "int *status"
48 .Fn waitpid "pid_t wpid" "int *status" "int options"
51 .Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options"
55 .Fn wait3 "int *status" "int options" "struct rusage *rusage"
57 .Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
60 .Fa "idtype_t idtype" "id_t id"
63 .Fa "struct __wrusage *wrusage"
64 .Fa "siginfo_t *infop"
69 function suspends execution of its calling thread until
71 information is available for a child process
72 or a signal is received.
73 On return from a successful
78 area contains information about the process that reported a status change
85 system calls provide a more general interface for programs
86 that need to wait for specific child processes,
87 that need resource utilization statistics accumulated by child processes,
88 or that require options.
89 The other wait functions are implemented using either
96 function is the most general function in this family and its distinct
99 All of the desired process statuses to be waited on must be explicitly
108 functions all implicitly wait for exited and trapped processes,
113 functions require the corresponding
117 flags to be explicitly specified.
118 This allows waiting for processes which have experienced other
119 status changes without having to also handle the exit status from
120 terminated processes.
126 argument which points to a structure defined as:
129 struct rusage wru_self;
130 struct rusage wru_children;
134 This allows the calling process to collect resource usage statistics
135 from both its own child process as well as from its grand children.
136 When no resource usage statistics are needed this pointer can be
148 the structure is filled with the same data as for a
150 signal delivered when the process changed state.
152 The set of child processes to be queried is specified by the arguments
160 arguments support many other types of
161 identifiers in addition to process IDs and process group IDs.
162 .Bl -bullet -offset indent
171 wait for the child process with a process ID equal to
181 wait for the child process with a process group ID equal to
191 wait for any child process and the
207 wait for any child process in the same process group as the caller.
210 Non-standard identifier types supported by this
216 .Bl -tag -width P_JAILID
218 Wait for processes whose effective user ID is equal to
221 Wait for processes whose effective group ID is equal to
224 Wait for processes whose session ID is equal to
226 .\" This is just how sessions work, not sure this needs to be documented here
227 If the child process started its own session,
228 its session ID will be the same as its process ID.
229 Otherwise the session ID of a child process will match the caller's session ID.
231 Waits for processes within a jail whose jail identifier is equal to
239 functions, the single
241 argument specifies the set of child processes for which to wait.
242 .Bl -bullet -offset indent
246 is -1, the call waits for any child process.
251 the call waits for any child process in the process group of the caller.
255 is greater than zero, the call waits for the process with process ID
260 is less than -1, the call waits for any process whose process group ID
261 equals the absolute value of
267 argument is defined below.
271 argument contains the bitwise OR of any of the following options.
272 .Bl -tag -width WCONTINUED
274 Report the status of selected processes that
275 have continued from a job control stop by receiving a
280 there are no processes wishing to report status.
282 Report the status of selected processes which are stopped due to a
283 .Dv SIGTTIN , SIGTTOU , SIGTSTP ,
291 Report the status of selected processes which are being traced via
293 and have trapped or reached a breakpoint.
294 This flag is implicitly set for the functions
305 functions, the flag has to be explicitly included in
307 if status reports from trapped processes are expected.
309 Report the status of selected processes which have terminated.
310 This flag is implicitly set for the functions
321 functions, the flag has to be explicitly included in
323 if status reports from terminated processes are expected.
325 Keep the process whose status is returned in a waitable state.
326 The process may be waited for again after this call completes.
333 functions, at least one of the options
341 Otherwise there will be no events for the call to report.
342 To avoid hanging indefinitely in such a case these functions
350 is non-NULL, a summary of the resources used by the terminated
351 process and all its children is returned.
355 is non-NULL, separate summaries are returned for the resources used
356 by the terminated process and the resources used by all its children.
362 structure is returned with the
368 field set to the process ID of the process reporting status.
369 For the exited process, the
373 structure contains the full 32 bit exit status passed to
377 argument of other calls only returns 8 lowest bits of the exit status.
381 option is specified and no processes
382 wish to report status,
391 Checking these fields is the only way to know if a status change was reported.
395 option is specified and no processes
396 wish to report status,
420 function is identical to
435 function is identical to
448 The following macros may be used to test the current status of the process.
449 Exactly one of the following four macros will evaluate to a non-zero
453 .It Fn WIFCONTINUED status
454 True if the process has not terminated, and
455 has continued after a job control stop.
456 This macro can be true only if the wait call specified the
459 .It Fn WIFEXITED status
460 True if the process terminated normally by a call to
464 .It Fn WIFSIGNALED status
465 True if the process terminated due to receipt of a signal.
466 .It Fn WIFSTOPPED status
467 True if the process has not terminated, but has stopped and can be restarted.
468 This macro can be true only if the wait call specified the
471 or if the child process is being traced (see
475 Depending on the values of those macros, the following macros
476 produce the remaining status information about the child process:
478 .It Fn WEXITSTATUS status
481 is true, evaluates to the low-order 8 bits
482 of the argument passed to
487 .It Fn WTERMSIG status
489 .Fn WIFSIGNALED status
490 is true, evaluates to the number of the signal
491 that caused the termination of the process.
492 .It Fn WCOREDUMP status
494 .Fn WIFSIGNALED status
495 is true, evaluates as true if the termination
496 of the process was accompanied by the creation of a core file
497 containing an image of the process when the signal was received.
498 .It Fn WSTOPSIG status
500 .Fn WIFSTOPPED status
501 is true, evaluates to the number of the signal
502 that caused the process to stop.
507 for a list of termination signals.
508 A status of 0 indicates normal termination.
510 If a parent process terminates without
511 waiting for all of its child processes to terminate,
512 the remaining child processes are re-assigned to the reaper
513 of the exiting process as the parent, see
515 .Dv PROC_REAP_ACQUIRE .
516 If no specific reaper was assigned, the process with ID 1, the init process,
517 becomes the parent of the orphaned children by default.
519 If a signal is caught while any of the
522 the call may be interrupted or restarted when the signal-catching routine
524 depending on the options in effect for the signal;
530 The implementation queues one
532 signal for each child process whose
533 status has changed; if
535 returns because the status of a child process is available, the pending
536 SIGCHLD signal associated with the process ID of the child process will
540 signals remain pending.
546 returns because the status of a child process is available, the pending
548 signal will be cleared unless another status of the child process
553 returns due to a stopped, continued,
554 or terminated child process, the process ID of the child
555 is returned to the calling process.
556 Otherwise, a value of \-1
559 is set to indicate the error.
567 returns due to a stopped, continued,
568 or terminated child process, the process ID of the child
569 is returned to the calling process.
570 If there are no children not previously awaited,
577 is specified and there are
578 no stopped, continued or exited children,
580 If an error is detected or a caught signal aborts the call,
584 is set to indicate the error.
588 returns because one or more processes have a state change to report,
590 If an error is detected,
594 is set to indicate the error.
597 is specified and there are
598 no stopped, continued or exited children,
606 must be checked against zero to determine if a process reported status.
610 family of functions will not return a child process created with
612 unless specifically directed to do so by specifying its process ID.
617 will fail and return immediately if:
620 The calling process has no existing unwaited-for
623 No status from the terminated child process is available
624 because the calling process has asked the system to discard
625 such status by ignoring the signal
635 argument points to an illegal address.
636 (May not be detected before exit of a child process.)
638 The call was interrupted by a caught signal,
639 or the signal did not have the
643 An invalid value was specified for
649 do not specify a valid set of processes.
664 functions are defined by POSIX;
669 are not specified by POSIX.
673 is an extension to the POSIX interface.
675 The ability to use the
681 only permits this flag with