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);
/* POSIX.1 version */
pid_t getpgrp( void);  
/* BSD version */
pid_t getpgrp( psid_t   pid);
/* System V version */
int setpgrp( void);  
/* BSD version */
int setpgrp( pid_t   pid,
  pid_t   pgid);
[Note] Note
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, the process ID of the calling process is used. If pgid is zero, the process ID of the process specified by pid is used. 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 argumennts 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 send 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 2.79 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/.


  Copyright (c) 1983, 1991 Regents of the University of California.
and Copyright (C) 2007, Michael Kerrisk <mtk.manpagesgmail.com>
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
This product includes software developed by the University of
California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
   may be used to endorse or promote products derived from this software
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.

    (#)getpgrp.2 6.4 (Berkeley) 3/10/91

Modified 1993-07-24 by Rik Faith <faithcs.unc.edu>
Modified 1995-04-15 by Michael Chastain <mecshell.portal.com>:
  Added 'getpgid'.
Modified 1996-07-21 by Andries Brouwer <aebcwi.nl>
Modified 1996-11-06 by Eric S. Raymond <esrthyrsus.com>
Modified 1999-09-02 by Michael Haardt <michaelmoria.de>
Modified 2002-01-18 by Michael Kerrisk <mtk.manpagesgmail.com>
Modified 2003-01-20 by Andries Brouwer <aebcwi.nl>
2007-07-25, mtk, fairly substantial rewrites and rearrangements
of text.