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[thirdparty/man-pages.git] / 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@gmx.net>
.\" Modified 2003-01-20 by Andries Brouwer <aeb@cwi.nl>
.\"
.TH SETPGID 2 2003-01-20 "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 );
.br
.B int setpgrp(void);
.br
.B pid_t getpgrp(void);
.SH DESCRIPTION
.BR setpgid ()
sets the process group ID of the process specified by
.I pid
to
.IR pgid .
If
.I pid
is zero, the process ID of the current process is used.  If
.I pgid
is zero, the process ID of the process specified by
.I pid
is used.  If \fBsetpgid\fP() 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.  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.

.BR getpgid ()
returns the process group ID of the process specified by
.IR pid .
If
.I pid
is zero, the process ID of the current process is used.

The call
.BR setpgrp ()
is equivalent to
.BR setpgid(0,0) .

Similarly,
.BR getpgrp ()
is equivalent to
.BR getpgid(0) .
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.

Process groups are used for distribution of signals, and by terminals to
arbitrate requests for their input: Processes that have the same process
group as the terminal are foreground and may read, while others will
block with a signal if they attempt to read.
These calls are thus used by programs such as
.BR csh (1)
to create process groups in implementing job control.  The
.B TIOCGPGRP
and
.B TIOCSPGRP
calls described in
.BR termios (3)
are used to get/set the process group of the control terminal.

If a session has a controlling terminal, CLOCAL is not set and a hangup
occurs, then the session leader is sent a SIGHUP.  If the session leader
exits, the SIGHUP signal will 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.
.SH "RETURN VALUE"
On success,
.BR setpgid ()
and 
.BR setpgrp ()
return zero.  On error, \-1 is returned, and
.I errno
is set appropriately.

.BR getpgid ()
returns a process group on success.
On error, \-1 is returned, and
.I errno
is set appropriately.

.BR getpgrp ()
always returns the current process group.
.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 \fBexecve\fP()
(\fBsetpgid\fP(), \fBsetpgrp\fP()).
.TP
.B EINVAL
.I pgid
is less than 0
(\fBsetpgid\fP(), \fBsetpgrp\fP()).
.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
(\fBsetpgid\fP(), \fBsetpgrp\fP()).
.TP
.B ESRCH
For
.BR getpgid ():
.I pid
does not match any process.
For
.BR setpgid ():
.I pid
is not the current process and not a child of the current process.
.SH "CONFORMING TO"
The functions
.BR setpgid ()
and
.BR getpgrp ()
conform to POSIX.1-2001.
The function
.BR setpgrp ()
is from 4.2BSD.
The function
.BR getpgid ()
conforms to SVr4.
.SH NOTES
A child created via 
.BR fork (2)
inherits its parent's process group ID.
The process group ID is preserved across an
.BR execve (2).

POSIX took
.BR setpgid ()
from the BSD function
.BR setpgrp ().
Also System V has a function with the same name, but it is identical to
.BR setsid (2).
.LP
To get the prototypes under glibc, define both _XOPEN_SOURCE and
_XOPEN_SOURCE_EXTENDED, or use "#define _XOPEN_SOURCE \fIn\fP"
for some integer \fIn\fP larger than or equal to 500.
.SH "SEE ALSO"
.BR getuid (2),
.BR setsid (2),
.BR tcgetpgrp (3),
.BR tcsetpgrp (3),
.BR termios (3),
.BR feature_test_macros (7)