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(pid_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 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
setpgrp() (POSIX.1):
_SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
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.
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. (POSIX.1-2008 marks this
setpgrp()
specification as obsolete.)
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. 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
credentials(7)).
SEE ALSO¶
getuid(2),
setsid(2),
tcgetpgrp(3),
tcsetpgrp(3),
termios(3),
credentials(7)
COLOPHON¶
This page is part of release 3.44 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/.
