Standard C Library Functions posixspawn(3C)
NAME
posixspawn, posixspawnp - spawn a process
SYNOPSIS
#include
int posixspawn(pidt *restrict pid, const char *restrict path,
const posixspawnfileactionst *fileactions,
const posixspawnattrt *restrict attrp,
char *const argv[restrict], char *const envp[restrict]);
int posixspawnp(pidt *restrict pid, const char *restrict file,
const posixspawnfileactionst *fileactions,
const posixspawnattrt *restrict attrp,
char *const argv[restrict], char *const envp[restrict]);
DESCRIPTION
The posixspawn() and posixspawnp() functions create a new
process (child process) from the specified process image.
The new process image is constructed from a regular execut-
able 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 following variable
extern char **environ;
is initialized as a pointer 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 con-
stitute 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
posixspawn() or posixspawnp() function.
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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 number of bytes available for the child process's com-
bined argument and environment lists is {ARGMAX}, counting
all character pointers, the strings they point to, the
trailing null bytes in the strings, and the list-terminating
null pointers. There is no additional system overhead
included in this total.
The path argument to posixspawn() is a pathname that iden-
tifies the new process image file to execute.
The file parameter to posixspawnp() is used to construct a
pathname that identifies the new process image file. If the
file parameter contains a slash character, the file parame-
ter 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 environment variable is not defined, the
results of the search are implementation-defined.
If fileactions is a null pointer, then file descriptors
open in the calling process remain open in the child pro-
cess, except for those whose close-on-exec flag FDCLOEXEC
is set (see fcntl(2)). For those file descriptors that
remain open, all attributes of the corresponding open file
descriptions, including file locks (see fcntl(2)), remain
unchanged.
If fileactions is not NUL, 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
fileactions and the FDCLOEXEC flag of each remaining open
file descriptor after the spawn file actions have been pro-
cessed. The effective order of processing the spawn file
actions are:
1. The set of open file descriptors for the child pro-
cess are initially the same set as is open for the
calling process. All attributes of the correspond-
ing open file descriptions, including file locks
(see fcntl(2)), remain unchanged.
2. The signal mask, signal default or ignore actions,
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and the effective user and group IDs for the child
process are changed as specified in the attributes
object referenced by attrp.
3. 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.
4. Any file descriptor that has its FDCLOEXEC flag
set (see fcntl(2)) is closed.
The posixspawnattrt spawn attributes object type is
defined in . It contains at least the attributes
defined below.
If the POSIXSPAWNSETPGROUP 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 POSIXSPAWNSETPGROUP 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 will be in a new process group
with a process group ID equal to its process ID.
If the POSIXSPAWNSETPGROUP 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 POSIXSPAWNSETSCHEDPARAM flag is set in the spawn-
flags attribute of the object referenced by attrp, but
POSIXSPAWNSETSCHEDULER 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 POSIXSPAWNSETSCHEDULER flag is set in spawn-flags
attribute of the object referenced by attrp (regardless of
the setting of the POSIXSPAWNSETSCHEDPARAM 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.
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The POSIXSPAWNRESETIDS 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's effective user ID. If
this flag is set, the child process's 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 execu-
tion. If this flag is set, the child process's 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 POSIXSPAWNRESETIDS 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's effective group
ID. If this flag is set, the child process's 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 POSIXSPAWNSETSIGMASK flag is set in the spawn-flags
attribute of the object referenced by attrp, the child pro-
cess initially has the signal mask specified in the spawn-
sigmask attribute of the object referenced by attrp.
If the POSIXSPAWNSETSIGDEF 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.
If the POSIXSPAWNSETSIGIGNP flag is set in the spawn-
flags attribute of the object referenced by attrp, the sig-
nals specified in the spawn-sigignore attribute of the same
object are set to be ignored in the child process.
If both POSIXSPAWNSETSIGDEF and POSIXSPAWNSETSIGIGNP
flags are set in the spawn-flags attribute of the object
referenced by attrp, the actions for POSIXSPAWNSETSIGDEF
take precedence over the actions for
POSIXSPAWNSETSIGIGNP.
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If the POSIXSPAWNOSIGCHLDNP flag is set in the spawn-
flags attribute of the object referenced by attrp, no
SIGCHLD signal will be posted to the parent process when the
child process terminates, regardless of the disposition of
the SIGCHLD signal in the parent. SIGCHLD signals are still
possible for job control stop and continue actions if the
parent has requested them.
If the POSIXSPAWNWAITPIDNP flag is set in the spawn-flags
attribute of the object referenced by attrp, no wait-for-
multiple-pids operation by the parent, as in wait(),
waitid(PAL), or waitid(PGID), will succeed in reaping
the child, and the child will not be reaped automatically
due the disposition of the SIGCHLD signal being set to be
ignored in the parent. Only a specific wait for the child,
as in waitid(PID, pid), is allowed and it is required,
else when the child exits it will remain a zombie until the
parent exits.
If the POSIXSPAWNOEXECERNP flag is set in the spawn-
flags attribute of the object referenced by attrp, and if
the specified process image file cannot be executed, then
the posixspawn() and posixspawnp() functions do not fail
with one of the exec(2) error codes, as is normal, but
rather return successfully having created a child process
that exits immediately with exit status 127. This flag per-
mits system(3C) and popen(3C) to be implemented with
posixspawn() and still conform strictly to their POSIX
specifications.
Signals set to be caught or set to the default action in the
calling process are set to the default action in the child
process, unless the POSIXSPAWNSETSIGIGNP flag is set in
the spawn-flags attribute of the object referenced by attrp
and the signals are specified in the spawn-sigignore attri-
bute of the same object.
Except for SIGCHLD, signals set to be ignored by the calling
process image are set to be ignored by the child process,
unless otherwise specified by the POSIXSPAWNSETSIGDEF flag
being set in the spawn-flags attribute of the object refer-
enced by attrp and the signals being indicated in the
spawn-sigdefault attribute of the object referenced by
attrp.
If the SIGCHLD signal is set to be ignored by the calling
process, it is unspecified whether the SIGCHLD signal is set
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to be ignored or to the default action in the child process,
unless otherwise specified by the POSIXSPAWNSETSIGDEF flag
being set in the spawn-flags attribute of the object refer-
enced by attrp and the SIGCHLD signal being indicated in the
spawn-sigdefault attribute of the object referenced by
attrp.
If the value of the attrp pointer is NUL, then the default
values are used.
All process attributes, other than those influenced by the
attributes set in the object referenced by attrp as speci-
fied above or by the file descriptor manipulations specified
in fileactions appear in the new process image as though
fork() had been called to create a child process and then a
member of the exec family of functions had been called by
the child process to execute the new process image.
The fork handlers are not run when posixspawn() or
posixspawnp() is called.
RETURN VALUES
Upon successful completion, posixspawn() and posixspawnp()
return the process ID of the child process to the parent
process in the variable pointed to by a non-null pid argu-
ment, and return zero as the function return value. Other-
wise, no child process is created, the value stored into the
variable pointed to by a non-null pid is unspecified, 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.
ERORS
The posixspawn() and posixspawnp() functions will fail if:
EINVAL The value specified by fileactions or attrp is
invalid.
If posixspawn() or posixspawnp() fails for any of the rea-
sons that would cause fork() or one of the exec family of
functions to fail, an error value is returned as described
by fork(2) and exec(2), respectively
If POSIXSPAWNSETPGROUP is set in the spawn-flags attribute
of the object referenced by attrp, and posixspawn() or
posixspawnp() fails while changing the child's process
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group, an error value is returned as described by
setpgid(2).
If POSIXSPAWNSETSCHEDPARAM is set and
POSIXSPAWNSETSCHEDULER is not set in the spawn-flags
attribute of the object referenced by attrp, then if
posixspawn() or posixspawnp() fails for any of the reasons
that would cause schedsetparam() to fail, an error value is
returned as described by schedsetparam(3C).
If POSIXSPAWNSETSCHEDULER is set in the spawn-flags attri-
bute of the object referenced by attrp, and if posixspawn()
or posixspawnp() fails for any of the reasons that would
cause schedsetscheduler() to fail, an error value is
returned as described by schedsetscheduler(3C).
If the fileactions argument is not NUL and specifies any
close(), dup2(), or open() actions to be performed, and if
posixspawn() or posixspawnp() fails for any of the reasons
that would cause close(), dup2(), or open() to fail, an
error value is returned as described by close(2), dup2(3C),
or open(2), respectively. An open file action might, by
itself, result in any of the errors described by close() or
dup2(), in addition to those described by open().
If a close(2) operation is specified to be performed for a
file descriptor that is not open at the time of the call to
posixspawn() or posixspawnp(), the action does not cause
posixspawn() or posixspawnp() to fail.
ATRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
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Standard C Library Functions posixspawn(3C)
ATRIBUTE TYPE ATRIBUTE VALUE
Interface Stability Committed
MT-Level MT-Safe
Standard See standards(5).
SEE ALSO
alarm(2), chmod(2), close(2), dup(2), exec(2), exit(2),
fcntl(2), fork(2), kill(2), open(2), setpgid(2), setuid(2),
stat(2), times(2), dup2(3C), popen(3C),
posixspawnfileactionsaddclose(3C),
posixspawnfileactionsadddup2(3C),
posixspawnfileactionsaddopen(3C),
posixspawnfileactionsdestroy(3C),
posixspawnfileactionsinit(3C),
posixspawnattrdestroy(3C), posixspawnattrgetflags(3C),
posixspawnattrgetpgroup(3C),
posixspawnattrgetschedparam(3C),
posixspawnattrgetschedpolicy(3C),
posixspawnattrgetsigdefault(3C),
posixspawnattrgetsigignorenp(3C),
posixspawnattrgetsigmask(3C), posixspawnattrinit(3C),
posixspawnattrsetflags(3C), posixspawnattrsetpgroup(3C),
posixspawnattrsetschedparam(3C),
posixspawnattrsetschedpolicy(3C),
posixspawnattrsetsigdefault(3C),
posixspawnattrsetsigignorenp(3C),
posixspawnattrsetsigmask(3C), schedsetparam(3C),
schedsetscheduler(3C), system(3C), wait(3C), attributes(5),
standards(5)
NOTES
The SUSv3 POSIX standard (The Open Group Base Specifications
Issue 6, IE Std 1003.1-2001) permits the posixspawn() and
posixspawnp() functions to return successfully before some
of the above-described errors are detected, allowing the
child process to fail instead:
... if the error occurs after the calling process
successfully returns, the child process exits with
exit status 127.
With the one exception of when the POSIXSPAWNOEXECERNP
flag is passed in the attributes structure, this behavior is
not present in the Solaris implementation. Any error that
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Standard C Library Functions posixspawn(3C)
occurs before the new process image is successfully con-
structed causes the posixspawn() and posixspawnp() func-
tions to return the corresponding non-zero error value
without creating a child process.
The POSIXSPAWNOSIGCHLDNP, POSIXSPAWNWAITPIDNP,
POSIXSPAWNOEXECERNP, and POSIXSPAWNSETSIGIGNP flags
and the posixspawnattrgetsigignorenp() and
posixspawnattrsetsigignorenp() functions are non-portable
Solaris extensions to the posixspawn() and posixspawnp()
interfaces.
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