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  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  pipe-
       lines),  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  join-
       ing 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  pre-
       ferred 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() 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.

       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 gener-
       ated 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
       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)