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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():
           Since glibc 2.12:
               _POSIX_C_SOURCE >= 200809L || _XOPEN_SOURCE >= 500 ||
               _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
           Before glibc 2.12:
               _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

       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  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.  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

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