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28 .\" @(#)wait.2 8.2 (Berkeley) 4/19/94
41 .Nd wait for processes to change status
48 .Fn wait "int *status"
50 .Fn waitpid "pid_t wpid" "int *status" "int options"
53 .Fn waitid "idtype_t idtype" "id_t id" "siginfo_t *info" "int options"
57 .Fn wait3 "int *status" "int options" "struct rusage *rusage"
59 .Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
61 .Fn wait6 "idtype_t idtype" "id_t id" "int *status" "int options" "struct __wrusage *wrusage" "siginfo_t *infop"
65 function suspends execution of its calling thread until
67 information is available for a child process
68 or a signal is received.
69 On return from a successful
74 area contains information about the process that reported a status change
81 system calls provide a more general interface for programs
82 that need to wait for specific child processes,
83 that need resource utilization statistics accumulated by child processes,
84 or that require options.
85 The other wait functions are implemented using either
92 function is the most general function in this family and its distinct
95 All of the desired process statuses to be waited on must be explicitly
104 functions all implicitly wait for exited and trapped processes,
109 functions require the corresponding
113 flags to be explicitly specified.
114 This allows waiting for processes which have experienced other
115 status changes without having to also handle the exit status from
116 terminated processes.
122 argument which points to a structure defined as:
125 struct rusage wru_self;
126 struct rusage wru_children;
130 This allows the calling process to collect resource usage statistics
131 from both its own child process as well as from its grand children.
132 When no resource usage statistics are needed this pointer can be
144 the structure is filled with the same data as for a
146 signal delivered when the process changed state.
148 The set of child processes to be queried is specified by the arguments
156 arguments support many other types of
157 identifers in addition to process IDs and process group IDs.
158 .Bl -bullet -offset indent
167 wait for the child process with a process ID equal to
177 wait for the child process with a process group ID equal to
187 wait for any child process and the
203 wait for any child process in the same process group as the caller.
206 Non-standard identifier types supported by this
212 .Bl -tag -width P_JAILID
214 Wait for processes whose effective user ID is equal to
217 Wait for processes whose effective group ID is equal to
220 Wait for processes whose session ID is equal to
222 .\" This is just how sessions work, not sure this needs to be documented here
223 If the child process started its own session,
224 its session ID will be the same as its process ID.
225 Otherwise the session ID of a child process will match the caller's session ID.
227 Waits for processes within a jail whose jail identifier is equal to
235 functions, the single
237 argument specifies the set of child processes for which to wait.
238 .Bl -bullet -offset indent
242 is -1, the call waits for any child process.
247 the call waits for any child process in the process group of the caller.
251 is greater than zero, the call waits for the process with process ID
256 is less than -1, the call waits for any process whose process group ID
257 equals the absolute value of
263 argument is defined below.
267 argument contains the bitwise OR of any of the following options.
268 .Bl -tag -width WCONTINUED
270 Report the status of selected processes that
271 have continued from a job control stop by receiving a
276 there are no processes wishing to report status.
278 Report the status of selected processes which are stopped due to a
279 .Dv SIGTTIN , SIGTTOU , SIGTSTP ,
287 Report the status of selected processes which are being traced via
289 and have trapped or reached a breakpoint.
290 This flag is implicitly set for the functions
301 functions, the flag has to be explicitly included in
303 if status reports from trapped processes are expected.
305 Report the status of selected processes which have terminated.
306 This flag is implicitly set for the functions
317 functions, the flag has to be explicitly included in
319 if status reports from terminated processes are expected.
321 Keep the process whose status is returned in a waitable state.
322 The process may be waited for again after this call completes.
329 functions, at least one of the options
337 Otherwise there will be no events for the call to report.
338 To avoid hanging indefinitely in such a case these functions
346 is non-NULL, a summary of the resources used by the terminated
347 process and all its children is returned.
351 is non-NULL, separate summaries are returned for the resources used
352 by the terminated process and the resources used by all its children.
358 structure is returned with the
364 field set to the process ID of the process reporting status.
368 option is specified and no processes
369 wish to report status,
378 Checking these fields is the only way to know if a status change was reported.
382 option is specified and no processes
383 wish to report status,
407 function is identical to
422 function is identical to
435 The following macros may be used to test the current status of the process.
436 Exactly one of the following four macros will evaluate to a non-zero
440 .It Fn WIFCONTINUED status
441 True if the process has not terminated, and
442 has continued after a job control stop.
443 This macro can be true only if the wait call specified the
446 .It Fn WIFEXITED status
447 True if the process terminated normally by a call to
451 .It Fn WIFSIGNALED status
452 True if the process terminated due to receipt of a signal.
453 .It Fn WIFSTOPPED status
454 True if the process has not terminated, but has stopped and can be restarted.
455 This macro can be true only if the wait call specified the
458 or if the child process is being traced (see
462 Depending on the values of those macros, the following macros
463 produce the remaining status information about the child process:
465 .It Fn WEXITSTATUS status
468 is true, evaluates to the low-order 8 bits
469 of the argument passed to
474 .It Fn WTERMSIG status
476 .Fn WIFSIGNALED status
477 is true, evaluates to the number of the signal
478 that caused the termination of the process.
479 .It Fn WCOREDUMP status
481 .Fn WIFSIGNALED status
482 is true, evaluates as true if the termination
483 of the process was accompanied by the creation of a core file
484 containing an image of the process when the signal was received.
485 .It Fn WSTOPSIG status
487 .Fn WIFSTOPPED status
488 is true, evaluates to the number of the signal
489 that caused the process to stop.
494 for a list of termination signals.
495 A status of 0 indicates normal termination.
497 If a parent process terminates without
498 waiting for all of its child processes to terminate,
499 the remaining child processes are assigned the parent
500 process 1 ID (the init process ID).
502 If a signal is caught while any of the
505 the call may be interrupted or restarted when the signal-catching routine
507 depending on the options in effect for the signal;
513 The implementation queues one
515 signal for each child process whose
516 status has changed; if
518 returns because the status of a child process is available, the pending
519 SIGCHLD signal associated with the process ID of the child process will
523 signals remain pending.
529 returns because the status of a child process is available, the pending
531 signal will be cleared unless another status of the child process
536 returns due to a stopped, continued,
537 or terminated child process, the process ID of the child
538 is returned to the calling process.
539 Otherwise, a value of \-1
542 is set to indicate the error.
550 returns due to a stopped, continued,
551 or terminated child process, the process ID of the child
552 is returned to the calling process.
553 If there are no children not previously awaited,
560 is specified and there are
561 no stopped, continued or exited children,
563 If an error is detected or a caught signal aborts the call,
567 is set to indicate the error.
571 returns because one or more processes have a state change to report,
573 If an error is detected,
577 is set to indicate the error.
580 is specified and there are
581 no stopped, continued or exited children,
589 must be checked against zero to determine if a process reported status.
594 will fail and return immediately if:
597 The calling process has no existing unwaited-for
600 No status from the terminated child process is available
601 because the calling process has asked the system to discard
602 such status by ignoring the signal
612 argument points to an illegal address.
613 (May not be detected before exit of a child process.)
615 The call was interrupted by a caught signal,
616 or the signal did not have the
620 An invalid value was specified for
626 do not specify a valid set of processes.
640 functions are defined by POSIX;
645 are not specified by POSIX.
649 is an extension to the POSIX interface.
651 The ability to use the
657 only permits this flag with
663 to return the full 32 bits passed to
665 this implementation only returns 8 bits like the other calls.