SETPGID(2) Linux Programmer s Manual SETPGID(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(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)

DESCRIPTION All of these interfaces are available on Linux, and are used for get- ting and setting the process group ID (PGID) of a process. The pre- ferred, POSIX.1-specified ways of doing this are: getpgrp(void), for retrieving the calling processs PGID; and setpgid(), for setting a processs 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 equivalent to setpgid(pid, pgid).

The BSD-specific getpgrp() call, which takes a single pid argument, is equivalent to getpgid(pid).

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 per- formed 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 dif- ferent 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 parents 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 mem- ber 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 back- ground. If a signal is generated from the terminal (e.g., typing the interrupt key to generate SIGINT), that signal is sent to the fore- ground process group. (See termios(3) for a description of the charac- ters 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 SIGTSTP signal, which suspends it. The tcgetpgrp(3) and tcsetpgrp(3) functions are used to get/set the foreground process group of the controlling termi- nal.

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.

SEE ALSO getuid(2), setsid(2), tcgetpgrp(3), tcsetpgrp(3), termios(3), creden- tials(7)

COLOPHON This page is part of release 3.22 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.

Linux 2008-08-06 SETPGID(2)