bsd/man/man2/posix_spawn.2

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  28 .\"     @(#)posix_spawn.2
  29 .
  30 .Dd August 9, 2007
  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 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 a file action; see
 112 .Xr posix_spawn_file_actions_init 3
 113 for more information.
 114 .Pp
 115 The argument
 116 .Fa attrp
 117 is either NULL, or it is a pointer to an attributes object that was
 118 initialized by a call to
 119 .Xr posix_spawnattr_init 3
 120 and represents a set of spawn attributes to apply.  If NULL, then the
 121 default attributes are applied; otherwise, these attributes can control
 122 various aspects of the spawned process, and are applied prior to the
 123 spawned process beginning execution; see
 124 .Xr posix_spawnattr_init 3
 125 for more information.
 126 .Pp
 127 The argument
 128 .Fa argv
 129 is a pointer to a null-terminated array of
 130 character pointers to null-terminated character strings.
 131 These strings construct the argument list to be made available to the new
 132 process.  At least
 133 .Fa argv[0]
 134 must be present in the array, and should contain the file name of the
 135 program being spawned, e.g. the last component of the
 136 .Em path
 137 or
 138 .Em file
 139 argument.
 140 .Pp
 141 The argument
 142 .Fa envp
 143 is a pointer to a null-terminated array of character pointers to
 144 null-terminated strings.  A pointer to this array is normally stored
 145 in the global variable
 146 .Va environ.
 147 These strings pass information to the
 148 new process that is not directly an argument to the command (see
 149 .Xr environ 7 ) .
 150 .Pp
 151 Signals set to be ignored in the calling process are set to be ignored in
 152 the new process, unless the behaviour is modified by user specified
 153 .Em spawn attributes .
 154 Signals which are set to be caught in the calling process image are set to
 155 default action in the new process image.
 156 Blocked signals remain blocked regardless of changes to the signal action,
 157 unless the mask is overridden by user specified
 158 .Em spawn attributes .
 159 The signal stack is reset to be undefined (see
 160 .Xr sigaction 2
 161 for more information).
 162 .Pp
 163 By default, the effective user ID and group ID will be the same as those of
 164 the calling process image; however, this may be overridden to force them to
 165 be the real user ID and group ID of the parent process by user specified
 166 .Em spawn attributes
 167 (see
 168 .Xr posix_spawnattr_init 3
 169 for more information).
 170 .Pp
 171 If the set-user-ID mode bit of the new process image file is set
 172 (see
 173 .Xr chmod 2 ) ,
 174 the effective user ID of the new process image is set to the owner ID
 175 of the new process image file.
 176 If the set-group-ID mode bit of the new process image file is set,
 177 the effective group ID of the new process image is set to the group ID
 178 of the new process image file.
 179 (The effective group ID is the first element of the group list.)
 180 The real user ID, real group ID and supplementary group IDs of the new
 181 process image remain the same as the calling process image.
 182 After any set-user-ID and set-group-ID processing,
 183 the effective user ID is recorded as the saved set-user-ID,
 184 and the effective group ID is recorded as the saved set-group-ID.
 185 These values may be used in changing the effective IDs later (see
 186 .Xr setuid 2 ) .
 187 .Pp
 188 The new process also inherits the following attributes from
 189 the calling process:
 190 .Pp
 191 .Bl -column parent_process_ID -offset indent -compact
 192 .It parent process ID Ta see Xr getppid 2
 193 .It process group ID Ta see Xr getpgrp 2 , Xr posix_spawnattr_init 3
 194 .It access groups Ta see Xr getgroups 2
 195 .It working directory Ta see Xr chdir 2
 196 .It root directory Ta see Xr chroot 2
 197 .It control terminal Ta see Xr termios 4
 198 .It resource usages Ta see Xr getrusage 2
 199 .It interval timers Ta see Xr getitimer 2
 200 .It resource limits Ta see Xr getrlimit 2
 201 .It file mode mask Ta see Xr umask 2
 202 .It signal mask Ta see Xr sigaction 2 , Xr sigsetmask 2 ,
 203 .Xr posix_spawnattr_init 3
 204 .El
 205 .Pp
 206 When a program is executed as a result of a
 207 .Fn posix_spawn
 208 or
 209 .Fn posix_spawnp
 210 call, it is entered as follows:
 211 .Bd -literal -offset indent
 212 main(argc, argv, envp)
 213 int argc;
 214 char **argv, **envp;
 215 .Ed
 216 .Pp
 217 where
 218 .Fa argc
 219 is the number of elements in
 220 .Fa argv
 221 (the ``arg count'')
 222 and
 223 .Fa argv
 224 points to the array of character pointers
 225 to the arguments themselves.
 226 .Sh RETURN VALUES
 227 If the
 228 .Em pid
 229 argument is NULL, no pid is returned to the calling process; if it is
 230 non-NULL, then
 231 .Fn posix_spawn
 232 and
 233 .Fn posix_spawnp
 234 functions return the process ID of the child process into the pid_t
 235 variable pointed to by the
 236 .Em pid
 237 argument and return a 0 on success.  If an error occurs, they return
 238 a non-zero error code as the function return value, and no child process
 239 is created.
 240 .Sh ERRORS
 241 The
 242 .Fn posix_spawn
 243 and
 244 .Fn posix_spawnp
 245 functions will fail and return to the calling process if:
 246 .Bl -tag -width Er
 247 .\" ==========
 248 .It Bq Er EINVAL
 249 The value specified by
 250 .Fa file_actions
 251 or
 252 .Fa attrp
 253 is invalid.
 254 .\" ==========
 255 .It Bq Er E2BIG
 256 The number of bytes in the new process's argument list
 257 is larger than the system-imposed limit.
 258 This limit is specified by the
 259 .Xr sysctl 3
 260 MIB variable
 261 .Dv KERN_ARGMAX .
 262 .\" ==========
 263 .It Bq Er EACCES
 264 Search permission is denied for a component of the path prefix.
 265 .\" ==========
 266 .It Bq Er EACCES
 267 The new process file is not an ordinary file.
 268 .\" ==========
 269 .It Bq Er EACCES
 270 The new process file mode denies execute permission.
 271 .\" ==========
 272 .It Bq Er EACCES
 273 The new process file is on a filesystem mounted
 274 with execution disabled
 275 .Pf ( Dv MNT_NOEXEC
 276 in
 277 .Ao Pa sys/mount.h Ac ) .
 278 .\" ==========
 279 .It Bq Er EFAULT
 280 The new process file is not as long as indicated by
 281 the size values in its header.
 282 .\" ==========
 283 .It Bq Er EFAULT
 284 .Fa Path ,
 285 .Fa argv ,
 286 or
 287 .Fa envp
 288 point
 289 to an illegal address.
 290 .\" ==========
 291 .It Bq Er EIO
 292 An I/O error occurred while reading from the file system.
 293 .\" ==========
 294 .It Bq Er ELOOP
 295 Too many symbolic links were encountered in translating the pathname.
 296 This is taken to be indicative of a looping symbolic link.
 297 .\" ==========
 298 .It Bq Er ENAMETOOLONG
 299 A component of a pathname exceeded
 300 .Dv {NAME_MAX}
 301 characters, or an entire path name exceeded
 302 .Dv {PATH_MAX}
 303 characters.
 304 .\" ==========
 305 .It Bq Er ENOENT
 306 The new process file does not exist.
 307 .\" ==========
 308 .It Bq Er ENOEXEC
 309 The new process file has the appropriate access
 310 permission, but has an unrecognized format
 311 (e.g., an invalid magic number in its header).
 312 .\" ==========
 313 .It Bq Er ENOMEM
 314 The new process requires more virtual memory than
 315 is allowed by the imposed maximum
 316 .Pq Xr getrlimit 2 .
 317 .\" ==========
 318 .It Bq Er ENOTDIR
 319 A component of the path prefix is not a directory.
 320 .\" ==========
 321 .It Bq Er ETXTBSY
 322 The new process file is a pure procedure (shared text)
 323 file that is currently open for writing or reading by some process.
 324 .El
 325 .Sh CAVEAT
 326 If a program is
 327 .Em setuid
 328 to a non-super-user, but is executed when
 329 the real
 330 .Em uid
 331 is ``root'', then the program has some of the powers
 332 of a super-user as well.
 333 .Sh SEE ALSO
 334 .Xr exit 2 ,
 335 .Xr fork 2 ,
 336 .Xr execl 3 ,
 337 .Xr sysctl 3 ,
 338 .Xr environ 7 ,
 339 .Xr posix_spawnattr_init 3 ,
 340 .Xr posix_spawn_file_actions_init 3 ,
 341 .Sh STANDARDS
 342 .St -susv3 [SPN]
 343 .Sh HISTORY
 344 The
 345 .Fn posix_spawn
 346 and
 347 .Fn posix_spawnp
 348 function calls appeared in
 349 .St -susv3 [SPN] .