SETPGID(2) |
Linux Programmer's Manual |
SETPGID(2) |
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.
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. (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
SIGTTIN 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 3.53 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/.