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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);
       int setpgrp(void);
       pid_t getpgrp(void);

DESCRIPTION

       setpgid()  sets the process group ID of the process specified by pid to
       pgid.  If pid is zero, the process ID of the current 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.   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.

       getpgid() returns the process group ID of the process specified by pid.
       If pid is zero, the process ID of the current process is used.

       The call setpgrp() is equivalent to setpgid(0,0).

       Similarly,  getpgrp()  is equivalent to getpgid(0).  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.

       Process  groups  are used for distribution of signals, and by terminals
       to arbitrate requests for their input: Processes  that  have  the  same
       process group as the terminal are foreground and may read, while others
       will block with a signal if they attempt to read.  These calls are thus
       used   by   programs  such  as  csh(1)  to  create  process  groups  in
       implementing job control.  The TIOCGPGRP and TIOCSPGRP calls  described
       in  termios(3)  are  used  to  get/set the process group of the control
       terminal.

       If a session has a controlling terminal, CLOCAL is not set and a hangup
       occurs,  then  the  session  leader  is  sent a SIGHUP.  If the session
       leader exits, the SIGHUP signal will 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.

RETURN VALUE

       On success, setpgid() and setpgrp()  return  zero.   On  error,  -1  is
       returned, and errno is set appropriately.

       getpgid()  returns  a  process  group  on  success.   On  error,  -1 is
       returned, and errno is set appropriately.

       getpgrp() always returns the current process group.

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() (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 current process and not a child of the current
              process.

CONFORMING TO

       The functions setpgid() and getpgrp() conform to POSIX.1.  The function
       setpgrp() is from 4.2BSD.  The function getpgid() conforms to SVr4.

NOTES

       POSIX  took setpgid() from the BSD function setpgrp().  Also SysV has a
       function with the same name, but it is identical to setsid(2).

       To get the  prototypes  under  glibc,  define  both  _XOPEN_SOURCE  and
       _XOPEN_SOURCE_EXTENDED,  or  use  "#define  _XOPEN_SOURCE  n"  for some
       integer n larger than or equal to 500.

SEE ALSO

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