bsd/man/man2/posix_spawn.2

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  27 .\"
  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 .El
 328 .Sh CAVEAT
 329 If a program is
 330 .Em setuid
 331 to a non-super-user, but is executed when
 332 the real
 333 .Em uid
 334 is ``root'', then the program has some of the powers
 335 of a super-user as well.
 336 .Sh SEE ALSO
 337 .Xr exit 2 ,
 338 .Xr fork 2 ,
 339 .Xr execl 3 ,
 340 .Xr sysctl 3 ,
 341 .Xr environ 7 ,
 342 .Xr posix_spawnattr_init 3 ,
 343 .Xr posix_spawn_file_actions_init 3 ,
 344 .Sh STANDARDS
 345 .St -susv3 [SPN]
 346 .Sh HISTORY
 347 The
 348 .Fn posix_spawn
 349 and
 350 .Fn posix_spawnp
 351 function calls appeared in
 352 .St -susv3 [SPN] .