setpgrp(2)
NAME
setpgid, getpgid, setpgrp, getpgrp - set/get process group
SYNOPSIS
#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)
DESCRIPTION
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.
RETURN VALUE
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.
ERRORS
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.
CONFORMING TO
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.
NOTES
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)).
SEE ALSO
getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), credentials(7)
COLOPHON
This page is part of release 4.09 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/.
Opportunity
Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.
Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.
Free Software
Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.
Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.
Free Books
The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.
Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.
Education
Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.
Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.
