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 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, the process ID of the calling process is used.  If pgid is
       zero,  the  process  ID	of  the  process specified by pid is used.  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  creden-
       tials(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  argumennts  conform  to
       POSIX.1-2001.

       POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
       takes no arguments.

       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 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  send  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  pro-
       cess 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 2.77 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				  2007-07-26			    SETPGID(2)