getpgid(0)



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 || _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 get-
       ting and setting the process group ID (PGID) of a  process.   The  pre-
       ferred,  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
       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  per-
              formed 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 dif-
              ferent 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 mem-
       ber 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  back-
       ground.   If  a signal is generated from the terminal (e.g., typing the
       interrupt key to generate SIGINT), that signal is  sent  to  the  fore-
       ground process group.  (See termios(3) for a description of the charac-
       ters 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  termi-
       nal.

       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),  creden-
       tials(7)

COLOPHON
       This  page  is  part of release 3.71 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/.

Linux                             2014-01-07                        SETPGID(2)

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