NAME
posix_spawn,
posix_spawnp —
spawn a process
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <spawn.h>
int
posix_spawn(
pid_t
*restrict pid,
const char
*restrict path,
const
posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *restrict
attrp,
char *const
argv[restrict],
char *const
envp[restrict]);
int
posix_spawnp(
pid_t
*restrict pid,
const char
*restrict file,
const
posix_spawn_file_actions_t *file_actions,
const posix_spawnattr_t *restrict
attrp,
char *const
argv[restrict],
char *const
envp[restrict]);
DESCRIPTION
The
posix_spawn() and
posix_spawnp()
functions create a new process (child process) from the specified process
image. The new process image is constructed from a regular executable file
called the new process image file.
When a C program is executed as the result of this call, it is entered as a
C-language function call as follows:
int main(int argc, char *argv[]);
where
argc is the argument count and
argv is an array of character pointers to the arguments
themselves. In addition, the variable:
points to an array of character pointers to the environment strings.
The argument
argv is an array of character pointers to
null-terminated strings. The last member of this array is a null pointer and
is not counted in
argc. These strings constitute the
argument list available to the new process image. The value in
argv[0] should point to a filename that is associated
with the process image being started by the
posix_spawn() or
posix_spawnp() function.
The argument
envp is an array of character pointers to
null-terminated strings. These strings constitute the environment for the new
process image. The environment array is terminated by a null pointer.
The
path argument to
posix_spawn() is a
pathname that identifies the new process image file to execute.
The
file parameter to
posix_spawnp() is
used to construct a pathname that identifies the new process image file. If
the file parameter contains a slash character, the file parameter is used as
the pathname for the new process image file. Otherwise, the path prefix for
this file is obtained by a search of the directories passed as the environment
variable “
PATH
”. If this variable is not
specified, the default path is set according to the
_PATH_DEFPATH
definition in
<paths.h>, which is set to
“
/usr/bin:/bin
”.
If
file_actions is a null pointer, then file descriptors
open in the calling process remain open in the child process, except for those
whose close-on-exec flag
FD_CLOEXEC
is set (see
fcntl()). For those file descriptors that remain open, all
attributes of the corresponding open file descriptions, including file locks
(see
fcntl()), remain unchanged.
If
file_actions is not
NULL
, then
the file descriptors open in the child process are those open in the calling
process as modified by the spawn file actions object pointed to by
file_actions and the
FD_CLOEXEC
flag of each remaining open file descriptor after the spawn file actions have
been processed. The effective order of processing the spawn file actions are:
- The set of open file descriptors for the child process
initially are the same set as is open for the calling process. All
attributes of the corresponding open file descriptions, including file
locks (see fcntl()), remain unchanged.
- The signal mask, signal default actions, and the effective
user and group IDs for the child process are changed as specified in the
attributes object referenced by attrp.
- The file actions specified by the spawn file actions
object are performed in the order in which they were added to the spawn
file actions object.
- Any file descriptor that has its
FD_CLOEXEC
flag set (see
fcntl()) is closed.
The maximum number of
file_actions objects is limited to
the
RLIMIT_NOFILE
rlimit times 2.
The
posix_spawnattr_t spawn attributes object type is
defined in
<spawn.h>. It contains
the attributes defined below.
If the
POSIX_SPAWN_SETPGROUP
flag is set in the
spawn-flags attribute of the object referenced by
attrp,
and the spawn-pgroup attribute of the same object is non-zero, then the
child's process group is as specified in the spawn-pgroup attribute of the
object referenced by
attrp.
As a special case, if the
POSIX_SPAWN_SETPGROUP
flag is
set in the spawn-flags attribute of the object referenced by
attrp, and the spawn-pgroup attribute of the same object
is set to zero, then the child is in a new process group with a process group
ID equal to its process ID.
If the
POSIX_SPAWN_SETPGROUP
flag is not set in the
spawn-flags attribute of the object referenced by
attrp,
the new child process inherits the parent's process group.
If the
POSIX_SPAWN_SETSCHEDPARAM
flag is set in the
spawn-flags attribute of the object referenced by
attrp,
but
POSIX_SPAWN_SETSCHEDULER
is not set, the new
process image initially has the scheduling policy of the calling process with
the scheduling parameters specified in the spawn-schedparam attribute of the
object referenced by
attrp.
If the
POSIX_SPAWN_SETSCHEDULER
flag is set in the
spawn-flags attribute of the object referenced by
attrp
(regardless of the setting of the
POSIX_SPAWN_SETSCHEDPARAM
flag), the new process image
initially has the scheduling policy specified in the spawn-schedpolicy
attribute of the object referenced by
attrp and the
scheduling parameters specified in the spawn-schedparam attribute of the same
object.
The
POSIX_SPAWN_RESETIDS
flag in the spawn-flags
attribute of the object referenced by
attrp governs the
effective user ID of the child process. If this flag is not set, the child
process inherits the parent process' effective user ID. If this flag is set,
the child process' effective user ID is reset to the parent's real user ID. In
either case, if the set-user-ID mode bit of the new process image file is set,
the effective user ID of the child process becomes that file's owner ID before
the new process image begins execution.
The
POSIX_SPAWN_RESETIDS
flag in the spawn-flags
attribute of the object referenced by
attrp also governs
the effective group ID of the child process. If this flag is not set, the
child process inherits the parent process' effective group ID. If this flag is
set, the child process' effective group ID is reset to the parent's real group
ID. In either case, if the set-group-ID mode bit of the new process image file
is set, the effective group ID of the child process becomes that file's group
ID before the new process image begins execution.
If the
POSIX_SPAWN_SETSIGMASK
flag is set in the
spawn-flags attribute of the object referenced by
attrp,
the child process initially has the signal mask specified in the spawn-sigmask
attribute of the object referenced by
attrp.
If the
POSIX_SPAWN_SETSIGDEF
flag is set in the
spawn-flags attribute of the object referenced by
attrp,
the signals specified in the spawn-sigdefault attribute of the same object is
set to their default actions in the child process. Signals set to the default
action in the parent process is set to the default action in the child
process.
Signals set to be caught by the calling process is set to the default action in
the child process.
Signals set to be ignored by the calling process image is set to be ignored by
the child process, unless otherwise specified by the
POSIX_SPAWN_SETSIGDEF
flag being set in the
spawn-flags attribute of the object referenced by
attrp
and the signals being indicated in the spawn-sigdefault attribute of the
object referenced by
attrp.
If the value of the
attrp pointer is
NULL
, then the default values are used.
All process attributes, other than those influenced by the attributes set in the
object referenced by
attrp as specified above or by the
file descriptor manipulations specified in
file_actions,
appear in the new process image as though
vfork() had been
called to create a child process and then
execve() had been
called by the child process to execute the new process image.
The implementation uses vfork(), thus the fork handlers are not run when
posix_spawn() or
posix_spawnp() is called.
RETURN VALUES
Upon successful completion,
posix_spawn() and
posix_spawnp() return the process ID of the child process to
the parent process, in the variable pointed to by a
non-
NULL
pid argument, and
return zero as the function return value. Otherwise, no child process is
created, no value is stored into the variable pointed to by
pid, and an error number is returned as the function
return value to indicate the error. If the
pid argument
is a null pointer, the process ID of the child is not returned to the caller.
ERRORS
- If posix_spawn() and
posix_spawnp() fail for any of the reasons that would
cause vfork() or one of the exec to
fail, an error value is returned as described by vfork()
and exec, respectively (or, if the error occurs after
the calling process successfully returns, the child process exits with
exit status 127).
- If POSIX_SPAWN_SETPGROUP is set in the
spawn-flags attribute of the object referenced by attrp, and
posix_spawn() or posix_spawnp() fails
while changing the child's process group, an error value is returned as
described by setpgid() (or, if the error occurs after
the calling process successfully returns, the child process exits with
exit status 127).
- If POSIX_SPAWN_SETSCHEDPARAM is set and
POSIX_SPAWN_SETSCHEDULER is not set in the spawn-flags
attribute of the object referenced by attrp, then if
posix_spawn() or posix_spawnp() fails
for any of the reasons that would cause sched_setparam()
to fail, an error value is returned as described by
sched_setparam() (or, if the error occurs after the
calling process successfully returns, the child process exits with exit
status 127).
- If POSIX_SPAWN_SETSCHEDULER is set in
the spawn-flags attribute of the object referenced by attrp, and if
posix_spawn() or posix_spawnp() fails
for any of the reasons that would cause
sched_setscheduler() to fail, an error value is returned
as described by sched_setscheduler() (or, if the error
occurs after the calling process successfully returns, the child process
exits with exit status 127).
- If the file_actions argument is not
NULL
, and specifies any close(),
dup2(), or open() actions to be
performed, and if posix_spawn() or
posix_spawnp() fails for any of the reasons that would
cause close(), dup2(), or
open() to fail, an error value is returned as described
by close(), dup2(), and
open(), respectively (or, if the error occurs after the
calling process successfully returns, the child process exits with exit
status 127). An open file action may, by itself, result in any of the
errors described by close() or dup2(),
in addition to those described by open(). Finally, if
the number of file_actions objects exceeds the
allowed limit, EINVAL
is returned.
SEE ALSO
close(2),
dup2(2),
execve(2),
fcntl(2),
open(2),
setpgid(2),
vfork(2),
posix_spawn_file_actions_addclose(3),
posix_spawn_file_actions_adddup2(3),
posix_spawn_file_actions_addopen(3),
posix_spawn_file_actions_destroy(3),
posix_spawn_file_actions_init(3),
posix_spawnattr_destroy(3),
posix_spawnattr_getflags(3),
posix_spawnattr_getpgroup(3),
posix_spawnattr_getschedparam(3),
posix_spawnattr_getschedpolicy(3),
posix_spawnattr_getsigdefault(3),
posix_spawnattr_getsigmask(3),
posix_spawnattr_init(3),
posix_spawnattr_setflags(3),
posix_spawnattr_setpgroup(3),
posix_spawnattr_setschedparam(3),
posix_spawnattr_setschedpolicy(3),
posix_spawnattr_setsigdefault(3),
posix_spawnattr_setsigmask(3),
sched_setparam(3),
sched_setscheduler(3)
STANDARDS
The
posix_spawn() and
posix_spawnp()
functions conform to
IEEE Std 1003.1-2001
(“POSIX.1”).
HISTORY
The
posix_spawn() and
posix_spawnp()
functions first appeared in
FreeBSD 8.0. The library
parts were ported and a kernel implementation of
posix_spawn() added for
NetBSD 6.0
during Google Summer of Code by Charles Zhang and Martin Husemann.
AUTHORS
Ed Schouten
<
ed@FreeBSD.org>