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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
       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
       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()  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 generated 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.

SEE ALSO

       getuid(2),   setsid(2),   tcgetpgrp(3),    tcsetpgrp(3),    termios(3),
       credentials(7)

COLOPHON

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