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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(psid_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
setpgrp() (POSIX.1): _SVID_SOURCE || _XOPEN_SOURCE >= 500
setpgrp() (BSD), getpgrp() (BSD): _BSD_SOURCE && ! (_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
setpgid() sets the PGID of the process specified by pid to pgid. If
pid is zero, the process ID of the calling process is used. If pgid is
zero, the process ID of the process specified by pid is used. 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).
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
setpgid() and the version of getpgrp() with no argumennts conform to
POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
takes no arguments.
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
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 send 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
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.
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3),
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