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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] .