Ubuntu Manpage: setpgid, getpgid, setpgrp, getpgrp

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 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L

       setpgrp() (POSIX.1):
           _SVID_SOURCE || _XOPEN_SOURCE >= 500 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           || /* Since glibc 2.19: */ _BSD_SOURCE

       setpgrp() (BSD), getpgrp() (BSD) [before glibc 2.19]:
           _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 a wrapper function
       that calls

           setpgid(pid, pgid)

       Since glibc 2.19, the BSD-specific setpgrp() function is no longer exposed by  <unistd.h>;
       calls should be replaced with the setpgid() call shown above.

       The  BSD-specific getpgrp() call, which takes a single pid argument, is a wrapper function
       that calls

           getpgid(pid)

       Since glibc 2.19, the BSD-specific getpgrp() function is no longer exposed by  <unistd.h>;
       calls  should be replaced with calls to the POSIX.1 getpgrp() which takes no arguments (if
       the intent is to obtain the caller's PGID), or with the getpgid() call shown above.

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
SIGTTIN 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)).

COLOPHON

       This  page  is  part of release 4.04 of the Linux man-pages project.  A description of the
       project, information about reporting bugs, and the latest version of  this  page,  can  be
       found at http://www.kernel.org/doc/man-pages/.