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28 .\" @(#)posix_spawn.2
29 .
30 .Dd November 2, 2010
31 .Dt POSIX_SPAWN 2
32 .Os "Mac OS X"
33 .Sh NAME
34 .Nm posix_spawn
35 .Nm posix_spawnp
36 .Nd spawn a process
37 .Sh SYNOPSIS
38 .Fd #include <spawn.h>
39 .Ft int
40 .Fo posix_spawn
41 .Fa "pid_t *restrict pid"
42 .Fa "const char *restrict path"
43 .Fa "const posix_spawn_file_actions_t *file_actions"
44 .Fa "const posix_spawnattr_t *restrict attrp"
45 .Fa "char *const argv[restrict]"
46 .Fa "char *const envp[restrict]"
47 .Fc
48 .Ft int
49 .Fo posix_spawnp
50 .Fa "pid_t *restrict pid"
51 .Fa "const char *restrict file"
52 .Fa "const posix_spawn_file_actions_t *file_actions"
53 .Fa "const posix_spawnattr_t *restrict attrp"
54 .Fa "char *const argv[restrict]"
55 .Fa "char *const envp[restrict]"
56 .Fc
57 .Sh DESCRIPTION
58 The
59 .Fn posix_spawn
60 function creates a new process from the executable file, called the
61 .Em new process file ,
62 specified by
63 .Em path ,
64 which is an absolute or relative path to the file.
65 The
66 .Fn posix_spawnp
67 function is identical to the
68 .Fn posix_spawn
69 function if the
70 .Em file
71 specified contains a slash character; otherwise, the
72 .Em file
73 parameter is used to construct a pathname, with its path prefix being
74 obtained by a search of the path specified in the environment by the
75 .Dq Ev PATH variable .
76 If this variable isn't specified, the default path is set according
77 to the
78 .Dv _PATH_DEFPATH
79 definition in
80 .In paths.h ,
81 which is set to
82 .Dq Ev /usr/bin:/bin .
83 This pathname either refers to an executable object file,
84 or a file of data for an interpreter;
85 .Xr execve 2
86 for more details.
87 .Pp
88 The argument
89 .Fa pid
90 is a pointer to a pid_t variable to receive the pid of the spawned
91 process; if this is NULL, then the pid of the spawned process is
92 not returned. If this pointer is non-NULL, then on successful
93 completion, the variable will be modified to contain the pid of the
94 spawned process. The value is undefined in the case of a failure.
95 .Pp
96 The argument
97 .Fa file_actions
98 is either NULL, or it is a pointer to a file actions object that was
99 initialized by a call to
100 .Xr posix_spawn_file_actions_init 3
101 and represents zero or more file actions.
102 .Pp
103 File descriptors open in the calling process image remain open in
104 the new process image, except for those for which the close-on-exec
105 flag is set (see
106 .Xr close 2
107 and
108 .Xr fcntl 2 ) .
109 Descriptors that remain open are unaffected by
110 .Fn posix_spawn
111 unless their behaviour is modified by particular spawn flags
112 or a file action; see
113 .Xr posix_spawnattr_setflags 3
114 and
115 .Xr posix_spawn_file_actions_init 3
116 for additional information.
117 .Pp
118 The argument
119 .Fa attrp
120 is either NULL, or it is a pointer to an attributes object that was
121 initialized by a call to
122 .Xr posix_spawnattr_init 3
123 and represents a set of spawn attributes to apply. If NULL, then the
124 default attributes are applied; otherwise, these attributes can control
125 various aspects of the spawned process, and are applied prior to the
126 spawned process beginning execution; see
127 .Xr posix_spawnattr_init 3
128 for more information.
129 .Pp
130 The argument
131 .Fa argv
132 is a pointer to a null-terminated array of
133 character pointers to null-terminated character strings.
134 These strings construct the argument list to be made available to the new
135 process. At least
136 .Fa argv[0]
137 must be present in the array, and should contain the file name of the
138 program being spawned, e.g. the last component of the
139 .Em path
140 or
141 .Em file
142 argument.
143 .Pp
144 The argument
145 .Fa envp
146 is a pointer to a null-terminated array of character pointers to
147 null-terminated strings. A pointer to this array is normally stored
148 in the global variable
149 .Va environ.
150 These strings pass information to the
151 new process that is not directly an argument to the command (see
152 .Xr environ 7 ) .
153 .Pp
154 Signals set to be ignored in the calling process are set to be ignored in
155 the new process, unless the behaviour is modified by user specified
156 .Em spawn attributes .
157 Signals which are set to be caught in the calling process image are set to
158 default action in the new process image.
159 Blocked signals remain blocked regardless of changes to the signal action,
160 unless the mask is overridden by user specified
161 .Em spawn attributes .
162 The signal stack is reset to be undefined (see
163 .Xr sigaction 2
164 for more information).
165 .Pp
166 By default, the effective user ID and group ID will be the same as those of
167 the calling process image; however, this may be overridden to force them to
168 be the real user ID and group ID of the parent process by user specified
169 .Em spawn attributes
170 (see
171 .Xr posix_spawnattr_init 3
172 for more information).
173 .Pp
174 If the set-user-ID mode bit of the new process image file is set
175 (see
176 .Xr chmod 2 ) ,
177 the effective user ID of the new process image is set to the owner ID
178 of the new process image file.
179 If the set-group-ID mode bit of the new process image file is set,
180 the effective group ID of the new process image is set to the group ID
181 of the new process image file.
182 (The effective group ID is the first element of the group list.)
183 The real user ID, real group ID and supplementary group IDs of the new
184 process image remain the same as the calling process image.
185 After any set-user-ID and set-group-ID processing,
186 the effective user ID is recorded as the saved set-user-ID,
187 and the effective group ID is recorded as the saved set-group-ID.
188 These values may be used in changing the effective IDs later (see
189 .Xr setuid 2 ) .
190 .Pp
191 The new process also inherits the following attributes from
192 the calling process:
193 .Pp
194 .Bl -column parent_process_ID -offset indent -compact
195 .It parent process ID Ta see Xr getppid 2
196 .It process group ID Ta see Xr getpgrp 2 , Xr posix_spawnattr_init 3
197 .It access groups Ta see Xr getgroups 2
198 .It working directory Ta see Xr chdir 2
199 .It root directory Ta see Xr chroot 2
200 .It control terminal Ta see Xr termios 4
201 .It resource usages Ta see Xr getrusage 2
202 .It interval timers Ta see Xr getitimer 2
203 .It resource limits Ta see Xr getrlimit 2
204 .It file mode mask Ta see Xr umask 2
205 .It signal mask Ta see Xr sigaction 2 , Xr sigsetmask 2 ,
206 .Xr posix_spawnattr_init 3
207 .El
208 .Pp
209 When a program is executed as a result of a
210 .Fn posix_spawn
211 or
212 .Fn posix_spawnp
213 call, it is entered as follows:
214 .Bd -literal -offset indent
215 main(argc, argv, envp)
216 int argc;
217 char **argv, **envp;
218 .Ed
219 .Pp
220 where
221 .Fa argc
222 is the number of elements in
223 .Fa argv
224 (the ``arg count'')
225 and
226 .Fa argv
227 points to the array of character pointers
228 to the arguments themselves.
229 .Sh RETURN VALUES
230 If the
231 .Em pid
232 argument is NULL, no pid is returned to the calling process; if it is
233 non-NULL, then
234 .Fn posix_spawn
235 and
236 .Fn posix_spawnp
237 functions return the process ID of the child process into the pid_t
238 variable pointed to by the
239 .Em pid
240 argument and return a 0 on success. If an error occurs, they return
241 a non-zero error code as the function return value, and no child process
242 is created.
243 .Sh ERRORS
244 The
245 .Fn posix_spawn
246 and
247 .Fn posix_spawnp
248 functions will fail and return to the calling process if:
249 .Bl -tag -width Er
250 .\" ==========
251 .It Bq Er EINVAL
252 The value specified by
253 .Fa file_actions
254 or
255 .Fa attrp
256 is invalid.
257 .\" ==========
258 .It Bq Er E2BIG
259 The number of bytes in the new process's argument list
260 is larger than the system-imposed limit.
261 This limit is specified by the
262 .Xr sysctl 3
263 MIB variable
264 .Dv KERN_ARGMAX .
265 .\" ==========
266 .It Bq Er EACCES
267 Search permission is denied for a component of the path prefix.
268 .\" ==========
269 .It Bq Er EACCES
270 The new process file is not an ordinary file.
271 .\" ==========
272 .It Bq Er EACCES
273 The new process file mode denies execute permission.
274 .\" ==========
275 .It Bq Er EACCES
276 The new process file is on a filesystem mounted
277 with execution disabled
278 .Pf ( Dv MNT_NOEXEC
279 in
280 .Ao Pa sys/mount.h Ac ) .
281 .\" ==========
282 .It Bq Er EFAULT
283 The new process file is not as long as indicated by
284 the size values in its header.
285 .\" ==========
286 .It Bq Er EFAULT
287 .Fa Path ,
288 .Fa argv ,
289 or
290 .Fa envp
291 point
292 to an illegal address.
293 .\" ==========
294 .It Bq Er EIO
295 An I/O error occurred while reading from the file system.
296 .\" ==========
297 .It Bq Er ELOOP
298 Too many symbolic links were encountered in translating the pathname.
299 This is taken to be indicative of a looping symbolic link.
300 .\" ==========
301 .It Bq Er ENAMETOOLONG
302 A component of a pathname exceeded
303 .Dv {NAME_MAX}
304 characters, or an entire path name exceeded
305 .Dv {PATH_MAX}
306 characters.
307 .\" ==========
308 .It Bq Er ENOENT
309 The new process file does not exist.
310 .\" ==========
311 .It Bq Er ENOEXEC
312 The new process file has the appropriate access
313 permission, but has an unrecognized format
314 (e.g., an invalid magic number in its header).
315 .\" ==========
316 .It Bq Er ENOMEM
317 The new process requires more virtual memory than
318 is allowed by the imposed maximum
319 .Pq Xr getrlimit 2 .
320 .\" ==========
321 .It Bq Er ENOTDIR
322 A component of the path prefix is not a directory.
323 .\" ==========
324 .It Bq Er ETXTBSY
325 The new process file is a pure procedure (shared text)
326 file that is currently open for writing or reading by some process.
327 .\" ==========
328 .It Bq Er EBADARCH
329 The new process file has no architectures appropriate for the current system.
330 .\" ==========
331 .It Bq Er EBADF
332 Bad file descriptor for one or more
333 .Fa file_actions .
334 .El
335 .Pp
336 Additionally, they may fail for any of the reasons listed in
337 .Xr fork 2 or
338 .Xr exec 3 .
339 .Sh CAVEAT
340 If a program is
341 .Em setuid
342 to a non-super-user, but is executed when
343 the real
344 .Em uid
345 is ``root'', then the program has some of the powers
346 of a super-user as well.
347 .Sh SEE ALSO
348 .Xr exit 2 ,
349 .Xr fork 2 ,
350 .Xr execl 3 ,
351 .Xr sysctl 3 ,
352 .Xr environ 7 ,
353 .Xr posix_spawnattr_init 3 ,
354 .Xr posix_spawn_file_actions_init 3 ,
355 .Sh STANDARDS
356 .St -susv3 [SPN]
357 .Sh HISTORY
358 The
359 .Fn posix_spawn
360 and
361 .Fn posix_spawnp
362 function calls appeared in
363 .St -susv3 [SPN] .