SETPGID(2) Linux Programmer's Manual SETPGID(2)
setpgid, getpgid, setpgrp, getpgrp - set/get process group
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)):
_XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
_SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
setpgrp() (BSD), getpgrp() (BSD):
! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
_XOPEN_SOURCE_EXTENDED || _GNU_SOURCE || _SVID_SOURCE)
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 pipe-
lines), both process groups must be part of the same session (see setsid(2) and creden-
tials(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 call-
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 call-
er 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
The BSD-specific getpgrp() call, which takes a single pid argument, is equivalent to
On success, setpgid() and setpgrp() return zero. On error, -1 is returned, and errno is
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.
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(), setp-
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 ses-
sion leader (setpgid(), setpgrp()).
ESRCH For getpgid(): pid does not match any process. For setpgid(): pid is not the call-
ing 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 argu-
ments. (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.
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 sig-
nals.) 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 ses-
sion (see also credentials(7)).
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), credentials(7)
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2013-07-31 SETPGID(2)