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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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setpgid(2) System Calls Manual setpgid(2)
setpgid, getpgid, setpgrp, getpgrp - set/get process group
Standard C library (libc, -lc)
#include <unistd.h>
int setpgid(pid_t pid, pid_t pgid);
pid_t getpgid(pid_t pid);
pid_t getpgrp(void); /* POSIX.1 version */
[[deprecated]] pid_t getpgrp(pid_t pid); /* BSD version */
int setpgrp(void); /* System V version */
[[deprecated]] 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 <= 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 to indicate the error.
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 to
indicate the error.
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()).
EPERM The target process group does not exist. (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.
getpgid()
setpgid()
getpgrp() (no args)
setpgrp() (no args)
POSIX.1-2008 (but see HISTORY).
setpgrp() (2 args)
getpgrp() (1 arg)
None.
getpgid()
setpgid()
getpgrp() (no args)
POSIX.1-2001.
setpgrp() (no args)
POSIX.1-2001. POSIX.1-2008 marks it as obsolete.
setpgrp() (2 args)
getpgrp() (1 arg)
4.2BSD.
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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 setpgid(2)
Pages that refer to this page: setpgid(1), strace(1), fork(2), getsid(2), setsid(2), syscalls(2), exit(3), id_t(3type), killpg(3), posix_spawn(3), tcgetpgrp(3), credentials(7), pthreads(7), signal-safety(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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