xref: /dragonfly/lib/libc/sys/wait.2 (revision b7367ef6)
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32.\"     @(#)wait.2	8.2 (Berkeley) 4/19/94
33.\" $FreeBSD: src/lib/libc/sys/wait.2,v 1.6.2.6 2001/12/14 18:34:02 ru Exp $
34.\" $DragonFly: src/lib/libc/sys/wait.2,v 1.4 2007/08/30 20:58:35 pavalos Exp $
35.\"
36.Dd August 30, 2007
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.In sys/types.h
49.In sys/wait.h
50.Ft pid_t
51.Fn wait "int *status"
52.In sys/time.h
53.In sys/resource.h
54.Ft pid_t
55.Fn waitpid "pid_t wpid" "int *status" "int options"
56.Ft pid_t
57.Fn wait3 "int *status" "int options" "struct rusage *rusage"
58.Ft pid_t
59.Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
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
77call provides a more general interface for programs
78that need to wait for certain child processes,
79that need resource utilization statistics accumulated by child processes,
80or that require options.
81The other wait functions are implemented using
82.Fn wait4 .
83.Pp
84The
85.Fa wpid
86parameter specifies the set of child processes for which to wait.
87If
88.Fa wpid
89is -1, the call waits for any child process.
90If
91.Fa wpid
92is 0,
93the call waits for any child process in the process group of the caller.
94If
95.Fa wpid
96is greater than zero, the call waits for the process with process id
97.Fa wpid .
98If
99.Fa wpid
100is less than -1, the call waits for any process whose process group id
101equals the absolute value of
102.Fa wpid .
103.Pp
104The
105.Fa status
106parameter is defined below.  The
107.Fa options
108parameter contains the bitwise OR of any of the following options.
109The
110.Dv WCONTINUED
111option indicates that children of the current process that
112have continued from a job control stop, by receiving a
113.Dv SIGCONT
114signal, should also have their status reported.
115The
116.Dv WNOHANG
117option
118is used to indicate that the call should not block if
119there are no processes that wish to report status.
120If the
121.Dv WUNTRACED
122option is set,
123children of the current process that are stopped
124due to a
125.Dv SIGTTIN , SIGTTOU , SIGTSTP ,
126or
127.Dv SIGSTOP
128signal also have
129their status reported.
130.Pp
131If
132.Fa rusage
133is non-zero, a summary of the resources used by the terminated
134process and all its
135children is returned (this information is currently not available
136for stopped processes).
137.Pp
138When the
139.Dv WNOHANG
140option is specified and no processes
141wish to report status,
142.Fn wait4
143returns a
144process id
145of 0.
146.Pp
147The
148.Fn waitpid
149call is identical to
150.Fn wait4
151with an
152.Fa rusage
153value of zero.
154The older
155.Fn wait3
156call is the same as
157.Fn wait4
158with a
159.Fa wpid
160value of -1.
161.Pp
162The following macros may be used to test the manner of exit of the process.
163One of the first three macros will evaluate to a non-zero (true) value:
164.Bl -tag -width Ds
165.It Fn WIFEXITED status
166True if the process terminated normally by a call to
167.Xr _exit 2
168or
169.Xr exit 3 .
170.It Fn WIFSIGNALED status
171True if the process terminated due to receipt of a signal.
172.It Fn WIFSTOPPED status
173True if the process has not terminated, but has stopped and can be restarted.
174This macro can be true only if the wait call specified the
175.Dv WUNTRACED
176option
177or if the child process is being traced (see
178.Xr ptrace 2 ) .
179.El
180.Pp
181Depending on the values of those macros, the following macros
182produce the remaining status information about the child process:
183.Bl -tag -width Ds
184.It Fn WIFCONTINUED status
185True if the process has not terminated, and
186has continued after a job control stop.
187This macro can be true only if the wait call specified the
188.Dv WCONTINUED
189option).
190.It Fn WEXITSTATUS status
191If
192.Fn WIFEXITED status
193is true, evaluates to the low-order 8 bits
194of the argument passed to
195.Xr _exit 2
196or
197.Xr exit 3
198by the child.
199.It Fn WTERMSIG status
200If
201.Fn WIFSIGNALED status
202is true, evaluates to the number of the signal
203that caused the termination of the process.
204.It Fn WCOREDUMP status
205If
206.Fn WIFSIGNALED status
207is true, evaluates as true if the termination
208of the process was accompanied by the creation of a core file
209containing an image of the process when the signal was received.
210.It Fn WSTOPSIG status
211If
212.Fn WIFSTOPPED status
213is true, evaluates to the number of the signal
214that caused the process to stop.
215.El
216.Sh NOTES
217See
218.Xr sigaction 2
219for a list of termination signals.
220A status of 0 indicates normal termination.
221.Pp
222If a parent process terminates without
223waiting for all of its child processes to terminate,
224the remaining child processes are assigned the parent
225process 1 ID (the init process ID).
226.Pp
227If a signal is caught while any of the
228.Fn wait
229calls are pending,
230the call may be interrupted or restarted when the signal-catching routine
231returns,
232depending on the options in effect for the signal;
233see
234.Xr intro 2 ,
235System call restart.
236.Sh RETURN VALUES
237If
238.Fn wait
239returns due to a stopped
240or terminated child process, the process ID of the child
241is returned to the calling process.  Otherwise, a value of -1
242is returned and
243.Va errno
244is set to indicate the error.
245.Pp
246If
247.Fn wait4 ,
248.Fn wait3 ,
249or
250.Fn waitpid
251returns due to a stopped
252or terminated child process, the process ID of the child
253is returned to the calling process.
254If there are no children not previously awaited,
255-1 is returned with
256.Va errno
257set to
258.Er ECHILD .
259Otherwise, if
260.Dv WNOHANG
261is specified and there are
262no stopped or exited children,
2630 is returned.
264If an error is detected or a caught signal aborts the call,
265a value of -1
266is returned and
267.Va errno
268is set to indicate the error.
269.Sh ERRORS
270.Fn Wait
271will fail and return immediately if:
272.Bl -tag -width Er
273.It Bq Er ECHILD
274The calling process has no existing unwaited-for
275child processes.
276.It Bq Er EFAULT
277The
278.Fa status
279or
280.Fa rusage
281arguments point to an illegal address.
282(May not be detected before exit of a child process.)
283.It Bq Er EINTR
284The call was interrupted by a caught signal,
285or the signal did not have the
286.Dv SA_RESTART
287flag set.
288.El
289.Sh SEE ALSO
290.Xr ptrace 2 ,
291.Xr sigaction 2 ,
292.Xr _exit 2 ,
293.Xr exit 3
294.Sh STANDARDS
295The
296.Fn wait
297and
298.Fn waitpid
299functions are defined by POSIX;
300.Fn wait4
301and
302.Fn wait3
303are not specified by POSIX.
304The
305.Fn WCOREDUMP
306macro
307and the ability to restart a pending
308.Fn wait
309call are extensions to the POSIX interface.
310.Sh HISTORY
311A
312.Fn wait
313function call appeared in
314.At v6 .
315