Ubuntu Manpage: setpgid, getpgid, setpgrp, getpgrp

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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(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

       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 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

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       information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.