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(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
       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 getting 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 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 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 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() specifica-
       tion 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.

       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., typ-
       ing  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 SIGTSTP 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 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.  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 3.25 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								    2009-09-20								SETPGID(2)