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

   setpgrp() (POSIX.1):
       _XOPEN_SOURCE >= 500
           || /* Since glibc 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE

   setpgrp() (BSD), getpgrp() (BSD):
       [These are available only before glibc 2.19]
       _BSD_SOURCE &&
           ! (_POSIX_SOURCE || _POSIX_C_SOURCE || _XOPEN_SOURCE ||
               _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.   (See
   credentials(7).)

   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  the  termination  of  a  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 4.09 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
   https://www.kernel.org/doc/man-pages/.

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