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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SETPGID(2) Linux Programmer's Manual SETPGID(2)
setpgid, getpgid, setpgrp, getpgrp - set/get process group
#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
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
setpgrp() (POSIX.1):
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_SOURCE
setpgrp() (BSD), getpgrp() (BSD):
[These are available only before glibc 2.19]
_BSD_SOURCE &&
! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
_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 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 a wrapper function that calls
setpgid(pid, pgid)
Since glibc 2.19, the BSD-specific setpgrp() function is no longer
exposed by <unistd.h>; calls should be replaced with the setpgid()
call shown above.
The BSD-specific getpgrp() call, which takes a single pid argument,
is a wrapper function that calls
getpgid(pid)
Since glibc 2.19, the BSD-specific getpgrp() function is no longer
exposed by <unistd.h>; calls should be replaced with calls to the
POSIX.1 getpgrp() which takes no arguments (if the intent is to
obtain the caller's PGID), or with the getpgid() call shown above.
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.
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.
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. (See
credentials(7).)
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 the termination of a 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)).
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3),
credentials(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2016-10-08 SETPGID(2)
Pages that refer to this page: gawk(1), fork(2), getsid(2), setsid(2), syscalls(2), exit(3), killpg(3), posix_spawn(3), tcgetpgrp(3), credentials(7), pthreads(7), signal-safety(7)