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.\"     @(#)posix_spawn.2
.
.Dd August 9, 2007
.Dt POSIX_SPAWN 2
.Os "Mac OS X"
.Sh NAME
.Nm posix_spawn
.Nm posix_spawnp
.Nd spawn a process
.Sh SYNOPSIS
.Fd #include <spawn.h>
.Ft int
.Fo posix_spawn
.Fa "pid_t *restrict pid"
.Fa "const char *restrict path"
.Fa "const posix_spawn_file_actions_t *file_actions"
.Fa "const posix_spawnattr_t *restrict attrp"
.Fa "char *const argv[restrict]"
.Fa "char *const envp[restrict]"
.Fc
.Ft int
.Fo posix_spawnp
.Fa "pid_t *restrict pid"
.Fa "const char *restrict file"
.Fa "const posix_spawn_file_actions_t *file_actions"
.Fa "const posix_spawnattr_t *restrict attrp"
.Fa "char *const argv[restrict]"
.Fa "char *const envp[restrict]"
.Fc
.Sh DESCRIPTION
The
.Fn posix_spawn
function creates a new process from the executable file, called the
.Em new process file ,
specified by
.Em path ,
which is an absolute or relative path to the file.
The
.Fn posix_spawnp
function is identical to the
.Fn posix_spawn
function if the
.Em file
specified contains a slash character; otherwise, the
.Em file
parameter is used to construct a pathname, with its path prefix being
obtained by a search of the path specified in the environment by the
.Dq Ev PATH variable .
If this variable isn't specified, the default path is set according
to the
.Dv _PATH_DEFPATH
definition in
.In paths.h ,
which is set to
.Dq Ev /usr/bin:/bin .
This pathname either refers to an executable object file,
or a file of data for an interpreter;
.Xr execve 2
for more details.
.Pp
The argument
.Fa pid
is a pointer to a pid_t variable to receive the pid of the spawned
process; if this is NULL, then the pid of the spawned process is
not returned.  If this pointer is non-NULL, then on successful
completion, the variable will be modified to contain the pid of the
spawned process.  The value is undefined in the case of a failure.
.Pp
The argument
.Fa file_actions
is either NULL, or it is a a pointer to a file actions object that was
initialized by a call to
.Xr posix_spawn_file_actions_init 3
and represents zero or more file actions.
.Pp
File descriptors open in the calling process image remain open in
the new process image, except for those for which the close-on-exec
flag is set (see
.Xr close 2
and
.Xr fcntl 2 ) .
Descriptors that remain open are unaffected by
.Fn posix_spawn
unless their behaviour is modified by a file action; see
.Xr posix_spawn_file_actions_init 3
for more information.
.Pp
The argument
.Fa attrp
is either NULL, or it is a pointer to an attributes object that was
initialized by a call to
.Xr posix_spawnattr_init 3
and represents a set of spawn attributes to apply.  If NULL, then the
default attributes are applied; otherwise, these attributes can control
various aspects of the spawned process, and are applied prior to the
spawned process beginning execution; see
.Xr posix_spawnattr_init 3
for more information.
.Pp
The argument
.Fa argv
is a pointer to a null-terminated array of
character pointers to null-terminated character strings.
These strings construct the argument list to be made available to the new
process.  At least
.Fa argv[0]
must be present in the array, and should contain the file name of the
program being spawned, e.g. the last component of the
.Em path
or
.Em file
argument.
.Pp
The argument
.Fa envp
is a pointer to a null-terminated array of character pointers to
null-terminated strings.  A pointer to this array is normally stored
in the global variable
.Va environ.
These strings pass information to the
new process that is not directly an argument to the command (see
.Xr environ 7 ) .
.Pp
Signals set to be ignored in the calling process are set to be ignored in
the new process, unless the behaviour is modified by user specified
.Em spawn attributes .
Signals which are set to be caught in the calling process image are set to
default action in the new process image.
Blocked signals remain blocked regardless of changes to the signal action,
unless the mask is overridden by user specified
.Em spawn attributes .
The signal stack is reset to be undefined (see
.Xr sigaction 2
for more information).
.Pp
By default, the effective user ID and group ID will be the same as those of
the calling process image; however, this may be overridden to force them to
be the real user ID and group ID of the parent process by user specified
.Em spawn attributes
(see
.Xr posix_spawnattr_init 3
for more information).
.Pp
If the set-user-ID mode bit of the new process image file is set
(see
.Xr chmod 2 ) ,
the effective user ID of the new process image is set to the owner ID
of the new process image file.
If the set-group-ID mode bit of the new process image file is set,
the effective group ID of the new process image is set to the group ID
of the new process image file.
(The effective group ID is the first element of the group list.)
The real user ID, real group ID and supplementary group IDs of the new
process image remain the same as the calling process image.
After any set-user-ID and set-group-ID processing,
the effective user ID is recorded as the saved set-user-ID,
and the effective group ID is recorded as the saved set-group-ID.
These values may be used in changing the effective IDs later (see
.Xr setuid 2 ) .
.Pp
The new process also inherits the following attributes from
the calling process:
.Pp
.Bl -column parent_process_ID -offset indent -compact
.It parent process ID Ta see Xr getppid 2
.It process group ID Ta see Xr getpgrp 2 , Xr posix_spawnattr_init 3
.It access groups Ta see Xr getgroups 2
.It working directory Ta see Xr chdir 2
.It root directory Ta see Xr chroot 2
.It control terminal Ta see Xr termios 4
.It resource usages Ta see Xr getrusage 2
.It interval timers Ta see Xr getitimer 2
.It resource limits Ta see Xr getrlimit 2
.It file mode mask Ta see Xr umask 2
.It signal mask Ta see Xr sigaction 2 , Xr sigsetmask 2 ,
.Xr posix_spawnattr_init 3
.El
.Pp
When a program is executed as a result of a
.Fn posix_spawn
or
.Fn posix_spawnp
call, it is entered as follows:
.Bd -literal -offset indent
main(argc, argv, envp)
int argc;
char **argv, **envp;
.Ed
.Pp
where
.Fa argc
is the number of elements in
.Fa argv
(the ``arg count'')
and
.Fa argv
points to the array of character pointers
to the arguments themselves.
.Sh RETURN VALUES
If the
.Em pid
argument is NULL, no pid is returned to the calling process; if it is
non-NULL, then
.Fn posix_spawn
and
.Fn posix_spawnp
functions return the process ID of the child process into the pid_t
variable pointed to by the
.Em pid
argument and return a 0 on success.  If an error occurs, they return
a non-zero error code as the function return value, and no child process
is created.
.Sh ERRORS
The
.Fn posix_spawn
and
.Fn posix_spawnp
functions will fail and return to the calling process if:
.Bl -tag -width Er
.\" ==========
.It Bq Er EINVAL
The value specified by
.Fa file_actions
or
.Fa attrp
is invalid.
.\" ==========
.It Bq Er E2BIG
The number of bytes in the new process's argument list
is larger than the system-imposed limit.
This limit is specified by the
.Xr sysctl 3
MIB variable
.Dv KERN_ARGMAX .
.\" ==========
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.\" ==========
.It Bq Er EACCES
The new process file is not an ordinary file.
.\" ==========
.It Bq Er EACCES
The new process file mode denies execute permission.
.\" ==========
.It Bq Er EACCES
The new process file is on a filesystem mounted
with execution disabled
.Pf ( Dv MNT_NOEXEC
in
.Ao Pa sys/mount.h Ac ) .
.\" ==========
.It Bq Er EFAULT
The new process file is not as long as indicated by
the size values in its header.
.\" ==========
.It Bq Er EFAULT
.Fa Path ,
.Fa argv ,
or
.Fa envp
point
to an illegal address.
.\" ==========
.It Bq Er EIO
An I/O error occurred while reading from the file system.
.\" ==========
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
This is taken to be indicative of a looping symbolic link.
.\" ==========
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 
.Dv {NAME_MAX}
characters, or an entire path name exceeded 
.Dv {PATH_MAX}
characters.
.\" ==========
.It Bq Er ENOENT
The new process file does not exist.
.\" ==========
.It Bq Er ENOEXEC
The new process file has the appropriate access
permission, but has an unrecognized format
(e.g., an invalid magic number in its header).
.\" ==========
.It Bq Er ENOMEM
The new process requires more virtual memory than
is allowed by the imposed maximum
.Pq Xr getrlimit 2 .
.\" ==========
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.\" ==========
.It Bq Er ETXTBSY
The new process file is a pure procedure (shared text)
file that is currently open for writing or reading by some process.
.El
.Sh CAVEAT
If a program is
.Em setuid
to a non-super-user, but is executed when
the real
.Em uid
is ``root'', then the program has some of the powers
of a super-user as well.
.Sh SEE ALSO
.Xr exit 2 ,
.Xr fork 2 ,
.Xr execl 3 ,
.Xr sysctl 3 ,
.Xr environ 7 ,
.Xr posix_spawnattr_init 3 ,
.Xr posix_file_actions_init 3
.Sh STANDARDS
.St -susv3 [SPN]
.Sh HISTORY
The
.Fn posix_spawn
and
.Fn posix_spawnp
function calls appeared in
.St -susv3 [SPN] .