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SETPGID
Section: Linux Programmer's Manual (2)
Updated: 2007-07-26
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NAME
setpgid, getpgid, setpgrp, getpgrp - set/get process group
SYNOPSIS
#include <unistd.h>
int setpgid(pid_t pid, pid_t pgid);
pid_t getpgid(pid_t pid);
pid_t getpgrp(void); /* POSIX.1 version */
pid_t getpgrp(psid_t pid);
/* BSD version */
int setpgrp(void); /* System V version */
int setpgrp(pid_t pid, pid_t pgid);
/* BSD version */
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
getpgid():
_XOPEN_SOURCE >= 500
setpgrp()
(POSIX.1): _SVID_SOURCE || _XOPEN_SOURCE >= 500
setpgrp() (BSD),
getpgrp() (BSD):
_BSD_SOURCE && ! (_POSIX_SOURCE || _POSIX_C_SOURCE ||
_XOPEN_SOURCE || _XOPEN_SOURCE_EXTENDED || _GNU_SOURCE || _SVID_SOURCE)
DESCRIPTION
All of these interfaces are available on Linux,
and are used for getting and setting the
process group ID (PGID) of a process.
The preferred, POSIX.1-specified ways of doing this are:
getpgrp(void),
for retrieving the calling process's PGID; and
setpgid(),
for setting a process's PGID.
setpgid()
sets the PGID of the process specified by
pid
to
pgid.
If
pid
is zero, then the process ID of the calling process is used.
If
pgid
is zero, then the PGID of the process specified by
pid
is made the same as its process ID.
If
setpgid()
is used to move a process from one process
group to another (as is done by some shells when creating pipelines),
both process groups must be part of the same session (see
setsid(2)
and
credentials(7)).
In this case,
the pgid specifies an existing process group to be joined and the
session ID of that group must match the session ID of the joining process.
The POSIX.1 version of
getpgrp(),
which takes no arguments,
returns the PGID of the calling process.
getpgid()
returns the PGID of the process specified by
pid.
If
pid
is zero, the process ID of the calling process is used.
(Retrieving the PGID of a process other than the caller is rarely
necessary, and the POSIX.1
getpgrp()
is preferred for that task.)
The System V-style
setpgrp(),
which takes no arguments, is equivalent to
setpgid(0, 0).
The BSD-specific
setpgrp()
call, which takes arguments
pid
and
pgid,
is equivalent to
setpgid(pid, pgid).
The BSD-specific
getpgrp()
call, which takes a single
pid
argument, is equivalent to
getpgid(pid).
RETURN VALUE
On success,
setpgid()
and
setpgrp()
return zero.
On error, -1 is returned, and
errno
is set appropriately.
The POSIX.1
getpgrp()
always returns the PGID of the caller.
getpgid(),
and the BSD-specific
getpgrp()
return a process group on success.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
- EACCES
-
An attempt was made to change the process group ID
of one of the children of the calling process and the child had
already performed an
execve(2)
(setpgid(),
setpgrp()).
- EINVAL
-
pgid
is less than 0
(setpgid(),
setpgrp()).
- EPERM
-
An attempt was made to move a process into a process group in a
different session, or to change the process
group ID of one of the children of the calling process and the
child was in a different session, or to change the process group ID of
a session leader
(setpgid(),
setpgrp()).
- ESRCH
-
For
getpgid():
pid
does not match any process.
For
setpgid():
pid
is not the calling process and not a child of the calling process.
CONFORMING TO
setpgid()
and the version of
getpgrp()
with no arguments
conform to POSIX.1-2001.
POSIX.1-2001 also specifies
getpgid()
and the version of
setpgrp()
that takes no arguments.
The version of
getpgrp()
with one argument and the version of
setpgrp()
that takes two arguments derive from 4.2BSD,
and are not specified by POSIX.1.
NOTES
A child created via
fork(2)
inherits its parent's process group ID.
The PGID is preserved across an
execve(2).
Each process group is a member of a session and each process is a
member of the session of which its process group is a member.
A session can have a controlling terminal.
At any time, one (and only one) of the process groups
in the session can be the foreground process group
for the terminal;
the remaining process groups are in the background.
If a signal is generated from the terminal (e.g., typing the
interrupt key to generate
SIGINT),
that signal is sent to the foreground process group.
(See
termios(3)
for a description of the characters that generate signals.)
Only the foreground process group may
read(2)
from the terminal;
if a background process group tries to
read(2)
from the terminal, then the group is sent a
SIGTSTP
signal, which suspends it.
The
tcgetpgrp(3)
and
tcsetpgrp(3)
functions are used to get/set the foreground
process group of the controlling terminal.
The
setpgid()
and
getpgrp()
calls are used by programs such as
bash(1)
to create process groups in order to implement shell job control.
If a session has a controlling terminal, and the
CLOCAL
flag for that terminal is not set,
and a terminal hangup occurs, then the session leader is sent a
SIGHUP.
If the session leader exits, then a
SIGHUP
signal will also be sent to each process in the foreground
process group of the controlling terminal.
If the exit of the process causes a process group to become orphaned,
and if any member of the newly orphaned process group is stopped, then a
SIGHUP
signal followed by a
SIGCONT
signal will be sent to each process
in the newly orphaned process group.
SEE ALSO
getuid(2),
setsid(2),
tcgetpgrp(3),
tcsetpgrp(3),
termios(3),
credentials(7)
COLOPHON
This page is part of release 3.05 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
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