Warning: include_once(./_common.php): failed to open stream: No such file or directory in /volume1/web/so/bbs/board.php on line 2

Warning: include_once(): Failed opening './_common.php' for inclusion (include_path='.:/usr/share/pear') in /volume1/web/so/bbs/board.php on line 2

Fatal error: Uncaught Error: Call to undefined function alert() in /volume1/web/so/bbs/board.php:5
Stack trace:
#0 {main}
  thrown in /volume1/web/so/bbs/board.php on line 5