setpgid, getpgid, setpgrp, getpgrp - set/get process group
pid_t getpgrp(void); /* POSIX.1 version */
pid); /* BSD
int setpgrp(void); /* System V version */
pgid); /* BSD version */
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_XOPEN_SOURCE >= 500 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
_XOPEN_SOURCE >= 500 || /* Since glibc 2.19: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _SVID_SOURCE
[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 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
pgid specifies an existing process group to be joined
and the session ID of that group must match the session ID of the
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
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
The BSD-specific setpgrp() call, which takes
pgid, is a wrapper function that
The BSD-specific getpgrp() call, which takes a
pid argument, is a wrapper function that calls
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.
The POSIX.1 getpgrp() always returns the PGID of the caller.
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()).
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.
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)).
This page is part of release 5.10 of the Linux
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