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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():
	   Since glibc 2.12:
	       _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 500 ||
	       _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
	   Before glibc 2.12:
	       _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

       setpgrp() (POSIX.1):
	   _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
	   _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

       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,  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	 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  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.  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),  creden‐
       tials(7)

COLOPHON
       This  page  is  part of release 3.27 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				  2010-09-20			    SETPGID(2)
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