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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(psid_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
       setpgrp() (POSIX.1): _SVID_SOURCE || _XOPEN_SOURCE >= 500

       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, the process ID of the calling process is used.  If pgid is
       zero,  the  process  ID  of  the  process specified by pid is used.  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  argumennts  conform  to
       POSIX.1-2001.

       POSIX.1-2001 also specifies getpgid() and the version of setpgrp() that
       takes no arguments.

       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  send  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.

SEE ALSO

       getuid(2),    setsid(2),    tcgetpgrp(3),   tcsetpgrp(3),   termios(3),
       credentials(7)

COLOPHON

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