Sets the current process group for the specified PID, 0 for the current process. Will produce a fatal error if used on a machine that doesn't implement POSIX setpgid(2) or BSD setpgrp(2). If the arguments are omitted, it defaults to 0,0 . Note that the BSD 4.2 version of setpgrp does not accept any arguments, so only setpgrp(0,0) is portable. See also POSIX::setsid() .