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30 .\" @(#)wait.2 8.2 (Berkeley) 4/19/94
31 .\"
32 .Dd April 3, 2010
33 .Dt WAIT 2
34 .Os
35 .Sh NAME
36 .Nm wait ,
37 .Nm waitpid ,
38 .Nm wait4 ,
39 .Nm wait3
40 .Nd wait for process termination
41 .Sh LIBRARY
42 .Lb libc
43 .Sh SYNOPSIS
44 .In sys/wait.h
45 .Ft pid_t
46 .Fn wait "int *status"
47 .Ft pid_t
48 .Fn waitpid "pid_t wpid" "int *status" "int options"
49 .In sys/resource.h
50 .Ft pid_t
51 .Fn wait3 "int *status" "int options" "struct rusage *rusage"
52 .Ft pid_t
53 .Fn wait4 "pid_t wpid" "int *status" "int options" "struct rusage *rusage"
54 .Sh DESCRIPTION
55 The
56 .Fn wait
57 function suspends execution of its calling process until
58 .Fa status
59 information is available for a terminated child process,
60 or a signal is received.
61 On return from a successful
62 .Fn wait
63 call,
64 the
65 .Fa status
66 area contains termination information about the process that exited
67 as defined below.
68 .Pp
69 The
70 .Fn wait4
71 call provides a more general interface for programs
72 that need to wait for certain child processes,
73 that need resource utilization statistics accumulated by child processes,
74 or that require options.
75 The other wait functions are implemented using
76 .Fn wait4 .
77 .Pp
78 The
79 .Fa wpid
80 parameter specifies the set of child processes for which to wait.
81 If
82 .Fa wpid
83 is \-1, the call waits for any child process.
84 If
85 .Fa wpid
86 is 0,
87 the call waits for any child process in the process group of the caller.
88 If
89 .Fa wpid
90 is greater than zero, the call waits for the process with process id
91 .Fa wpid .
92 If
93 .Fa wpid
94 is less than \-1, the call waits for any process whose process group id
95 equals the absolute value of
96 .Fa wpid .
97 .Pp
98 The
99 .Fa status
100 parameter is defined below.
101 .Pp
102 The
103 .Fa options
104 parameter contains the bitwise OR of any of the following options:
105 .Bl -tag -width WUNTRACED
106 .It Dv WNOHANG
107 This option is used to indicate that the call should not block if
108 there are no processes that wish to report status.
109 .It Dv WUNTRACED
110 If this option is set, children of the current process that are stopped
111 due to a
112 .Dv SIGTTIN , SIGTTOU , SIGTSTP ,
113 or
114 .Dv SIGSTOP
115 signal also have their status reported.
116 .It Dv WALTSIG
117 If this option is specified, the call will wait only for processes that
118 are configured to post a signal other than
119 .Dv SIGCHLD
120 when they exit.
121 If
122 .Dv WALTSIG
123 is not specified, the call will wait only for processes that
124 are configured to post
125 .Dv SIGCHLD .
126 .It Dv __WCLONE
127 This is an alias for
128 .Dv WALTSIG .
129 It is provided for compatibility with the Linux
130 .Xr clone 2
131 API.
132 .It Dv WALLSIG
133 If this option is specified, the call will wait for all children regardless
134 of what exit signal they post.
135 .It Dv __WALL
136 This is an alias for
137 .Dv WALLSIG .
138 It is provided for compatibility with the Linux
139 .Xr clone 2
140 API .
141 .El
142 .Pp
143 If
144 .Fa rusage
145 is non-zero, a summary of the resources used by the terminated
146 process and all its
147 children is returned (this information is currently not available
148 for stopped processes).
149 .Pp
150 When the
151 .Dv WNOHANG
152 option is specified and no processes
153 wish to report status,
154 .Fn wait4
155 returns a
156 process id
157 of 0.
158 .Pp
159 The
160 .Fn waitpid
161 call is identical to
162 .Fn wait4
163 with an
164 .Fa rusage
165 value of zero.
166 The older
167 .Fn wait3
168 call is the same as
169 .Fn wait4
170 with a
171 .Fa wpid
172 value of \-1.
173 .Pp
174 The following macros may be used to test the manner of exit of the process.
175 Note that these macros expect the
176 .Fa status
177 value itself, not a pointer to the
178 .Fa status
179 value.
180 One of the first three macros will evaluate to a non-zero (true) value:
181 .Bl -tag -width Ds
182 .It Fn WIFEXITED status
183 True if the process terminated normally by a call to
184 .Xr _exit 2
185 or
186 .Xr exit 3 .
187 .It Fn WIFSIGNALED status
188 True if the process terminated due to receipt of a signal.
189 .It Fn WIFSTOPPED status
190 True if the process has not terminated, but has stopped and can be restarted.
191 This macro can be true only if the wait call specified the
192 .Dv WUNTRACED
193 option
194 or if the child process is being traced (see
195 .Xr ptrace 2 ) .
196 .El
197 .Pp
198 Depending on the values of those macros, the following macros
199 produce the remaining status information about the child process:
200 .Bl -tag -width Ds
201 .It Fn WEXITSTATUS status
202 If
203 .Fn WIFEXITED status
204 is true, evaluates to the low-order 8 bits
205 of the argument passed to
206 .Xr _exit 2
207 or
208 .Xr exit 3
209 by the child.
210 .It Fn WTERMSIG status
211 If
212 .Fn WIFSIGNALED status
213 is true, evaluates to the number of the signal
214 that caused the termination of the process.
215 .It Fn WCOREDUMP status
216 If
217 .Fn WIFSIGNALED status
218 is true, evaluates as true if the termination
219 of the process was accompanied by the creation of a core file
220 containing an image of the process when the signal was received.
221 .It Fn WSTOPSIG status
222 If
223 .Fn WIFSTOPPED status
224 is true, evaluates to the number of the signal
225 that caused the process to stop.
226 .El
227 .Sh NOTES
228 See
229 .Xr sigaction 2
230 for a list of termination signals.
231 A status of 0 indicates normal termination.
232 .Pp
233 If a parent process terminates without
234 waiting for all of its child processes to terminate,
235 the remaining child processes are assigned the parent
236 process 1 ID (the init process ID).
237 .Pp
238 If a signal is caught while any of the
239 .Fn wait
240 calls is pending,
241 the call may be interrupted or restarted when the signal-catching routine
242 returns,
243 depending on the options in effect for the signal;
244 see
245 .Xr intro 2 ,
246 System call restart.
247 .Sh RETURN VALUES
248 If
249 .Fn wait
250 returns due to a stopped
251 or terminated child process, the process ID of the child
252 is returned to the calling process.
253 Otherwise, a value of \-1 is returned and
254 .Va errno
255 is set to indicate the error.
256 .Pp
257 If
258 .Fn wait4 ,
259 .Fn wait3
260 or
261 .Fn waitpid
262 returns due to a stopped
263 or terminated child process, the process ID of the child
264 is returned to the calling process.
265 If there are no children not previously awaited,
266 \-1 is returned with
267 .Va errno
268 set to
269 .Bq Er ECHILD .
270 Otherwise, if
271 .Dv WNOHANG
272 is specified and there are
273 no stopped or exited children, 0 is returned.
274 If an error is detected or a caught signal aborts the call,
275 a value of \-1 is returned and
276 .Va errno
277 is set to indicate the error.
278 .Sh ERRORS
279 .Fn wait
280 will fail and return immediately if:
281 .Bl -tag -width Er
282 .It Bq Er ECHILD
283 The calling process has no existing unwaited-for child processes.
284 .It Bq Er EFAULT
285 The
286 .Fa status
287 or
288 .Fa rusage
289 arguments point to an illegal address.
290 (May not be detected before exit of a child process.)
291 .It Bq Er EINTR
292 The call was interrupted by a caught signal,
293 or the signal did not have the
294 .Dv SA_RESTART
295 flag set.
296 .El
297 .Pp
298 In addition,
299 .Fn wait3 ,
300 .Fn wait4 ,
301 and
302 .Fn waitpid
303 will fail and return immediately if:
304 .Bl -tag -width Er
305 .It Bq Er EINVAL
306 An invalid value was specified for
307 .Fa options .
308 .El
309 .Sh SEE ALSO
310 .Xr _exit 2 ,
311 .Xr sigaction 2
312 .Sh STANDARDS
313 The
314 .Fn wait
315 and
316 .Fn waitpid
317 functions conform to
318 .St -p1003.1-90 ;
319 the
320 .Fn wait3
321 function conforms to
322 .St -xpg4 ;
323 .Fn wait4
324 is an extension.
325 The
326 .Fn WCOREDUMP
327 macro
328 and the ability to restart a pending
329 .Fn wait
330 call are extensions to the POSIX interface.
331 .Sh HISTORY
332 A
333 .Fn wait
334 function call appeared in
335 .At v2 .