path: root/man2/setpgid.2

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.\"     @(#)getpgrp.2	6.4 (Berkeley) 3/10/91
.\"
.\" Modified 1993-07-24 by Rik Faith <faith@cs.unc.edu>
.\" Modified 1995-04-15 by Michael Chastain <mec@shell.portal.com>:
.\"   Added 'getpgid'.
.\" Modified 1996-07-21 by Andries Brouwer <aeb@cwi.nl>
.\" Modified 1996-11-06 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 1999-09-02 by Michael Haardt <michael@moria.de>
.\" Modified 2002-01-18 by Michael Kerrisk <mtk.manpages@gmail.com>
.\" Modified 2003-01-20 by Andries Brouwer <aeb@cwi.nl>
.\" 2007-07-25, mtk, fairly substantial rewrites and rearrangements
.\" of text.
.\"
.TH SETPGID 2 2009-09-20 "Linux" "Linux Programmer's Manual"
.SH NAME
setpgid, getpgid, setpgrp, getpgrp \- set/get process group
.SH SYNOPSIS
.B #include <unistd.h>
.sp
.BI "int setpgid(pid_t " pid ", pid_t " pgid );
.br
.BI "pid_t getpgid(pid_t " pid );
.sp
.BR "pid_t getpgrp(void);" "                 /* POSIX.1 version */"
.br
.BI "pid_t getpgrp(pid_t " pid ");\ \ \ \ \ \ \ \ \ \ \ "
/* BSD version */
.sp
.BR "int setpgrp(void);" "                   /* System V version */"
.br
.BI "int setpgrp(pid_t " pid ", pid_t " pgid ");\ "
/* BSD version */
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.ad l
.PD 0
.BR getpgid ():
.RS 4
.TP 4
Since glibc 2.12:
_POSIX_C_SOURCE\ >=\ 200809L ||
_XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.TP
Before glibc 2.12:
_XOPEN_SOURCE\ >=\ 500 ||
_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.RE
.sp
.BR setpgrp "() (POSIX.1):"
.nf
    _SVID_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
    _XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
.fi
.sp
.BR setpgrp "()\ (BSD),"
.BR getpgrp "()\ (BSD):"
.nf
    _BSD_SOURCE &&
        !\ (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
           _XOPEN_SOURCE_EXTENDED || _GNU_SOURCE || _SVID_SOURCE)
.fi
.PD
.ad
.SH 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:
.BR getpgrp (void),
for retrieving the calling process's PGID; and
.BR setpgid (),
for setting a process's PGID.

.BR setpgid ()
sets the PGID of the process specified by
.I pid
to
.IR pgid .
If
.I pid
is zero, then the process ID of the calling process is used.
If
.I pgid
is zero, then the PGID of the process specified by
.I pid
is made the same as its process ID.
If
.BR 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
.BR setsid (2)
and
.BR credentials (7)).
In this case,
the \fIpgid\fP 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
.BR getpgrp (),
which takes no arguments,
returns the PGID of the calling process.

.BR getpgid ()
returns the PGID of the process specified by
.IR pid .
If
.I 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
.BR getpgrp ()
is preferred for that task.)

The System V-style
.BR setpgrp (),
which takes no arguments, is equivalent to
.IR "setpgid(0,\ 0)" .

The BSD-specific
.BR setpgrp ()
call, which takes arguments
.I pid
and
.IR pgid ,
is equivalent to
.IR "setpgid(pid, pgid)" .
.\" The true BSD setpgrp() system call differs in allowing the PGID
.\" to be set to arbitrary values, rather than being restricted to
.\" PGIDs in the same session.

The BSD-specific
.BR getpgrp ()
call, which takes a single
.I pid
argument, is equivalent to
.IR "getpgid(pid)" .
.SH "RETURN VALUE"
On success,
.BR setpgid ()
and
.BR setpgrp ()
return zero.
On error, \-1 is returned, and
.I errno
is set appropriately.

The POSIX.1
.BR getpgrp ()
always returns the PGID of the caller.

.BR getpgid (),
and the BSD-specific
.BR getpgrp ()
return a process group on success.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B 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
.BR execve (2)
.RB ( setpgid (),
.BR setpgrp ()).
.TP
.B EINVAL
.I pgid
is less than 0
.RB ( setpgid (),
.BR setpgrp ()).
.TP
.B 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
.RB ( setpgid (),
.BR setpgrp ()).
.TP
.B ESRCH
For
.BR getpgid ():
.I pid
does not match any process.
For
.BR setpgid ():
.I pid
is not the calling process and not a child of the calling process.
.SH "CONFORMING TO"
.BR setpgid ()
and the version of
.BR getpgrp ()
with no arguments
conform to POSIX.1-2001.

POSIX.1-2001 also specifies
.BR getpgid ()
and the version of
.BR setpgrp ()
that takes no arguments.
(POSIX.1-2008 marks this
.BR setpgrp ()
specification as obsolete.)

The version of
.BR getpgrp ()
with one argument and the version of
.BR setpgrp ()
that takes two arguments derive from 4.2BSD,
and are not specified by POSIX.1.
.SH NOTES
A child created via
.BR fork (2)
inherits its parent's process group ID.
The PGID is preserved across an
.BR 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
.BR SIGINT ),
that signal is sent to the foreground process group.
(See
.BR termios (3)
for a description of the characters that generate signals.)
Only the foreground process group may
.BR read (2)
from the terminal;
if a background process group tries to
.BR read (2)
from the terminal, then the group is sent a
.B SIGTSTP
signal, which suspends it.
The
.BR tcgetpgrp (3)
and
.BR tcsetpgrp (3)
functions are used to get/set the foreground
process group of the controlling terminal.

The
.BR setpgid ()
and
.BR getpgrp ()
calls are used by programs such as
.BR bash (1)
to create process groups in order to implement shell job control.

If a session has a controlling terminal, and the
.B CLOCAL
flag for that terminal is not set,
and a terminal hangup occurs, then the session leader is sent a
.BR SIGHUP .
If the session leader exits, then a
.B 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
.B SIGHUP
signal followed by a
.B SIGCONT
signal will be sent to each process
in the newly orphaned process group.
.\" exit.3 refers to the following text:
An orphaned process group is one in which the parent of
every member of process group is either itself also a member
of the process group or is a member of a process group
in a different session (see also
.BR credentials (7)).
.SH "SEE ALSO"
.BR getuid (2),
.BR setsid (2),
.BR tcgetpgrp (3),
.BR tcsetpgrp (3),
.BR termios (3),
.BR credentials (7)