--- Process.getpgid(pid)
--- Process.getpgrp([pid])

    pid ΥץΥץ롼פ֤ޤpid  0 
    λά줿ϥȥץ̣ޤ

    ץ롼פμ˼Ԥϡ㳰 Errno::EXXX 
    ȯޤ
    

