function drupal_error_levels() {
  $types = array(
    E_ERROR => array('Error', WATCHDOG_ERROR),
    E_WARNING => array('Warning', WATCHDOG_WARNING),
    E_PARSE => array('Parse error', WATCHDOG_ERROR),
    E_NOTICE => array('Notice', WATCHDOG_NOTICE),
    E_CORE_ERROR => array('Core error', WATCHDOG_ERROR),
    E_CORE_WARNING => array('Core warning', WATCHDOG_WARNING),
    E_COMPILE_ERROR => array('Compile error', WATCHDOG_ERROR),
    E_COMPILE_WARNING => array('Compile warning', WATCHDOG_WARNING),
    E_USER_ERROR => array('User error', WATCHDOG_ERROR),
    E_USER_WARNING => array('User warning', WATCHDOG_WARNING),
    E_USER_NOTICE => array('User notice', WATCHDOG_NOTICE),
    E_RECOVERABLE_ERROR => array('Recoverable fatal error', WATCHDOG_ERROR),
  );
  // E_DEPRECATED and E_USER_DEPRECATED were added in PHP 5.3.0.
  if (defined('E_DEPRECATED')) {
    $types[E_DEPRECATED] = array('Deprecated function', WATCHDOG_DEBUG);
    $types[E_USER_DEPRECATED] = array('User deprecated function', WATCHDOG_DEBUG);
  }
  return $types;
}
<br />
<b>Fatal error</b>:  Uncaught Error: Call to undefined function _drupal_log_error() in /var/www/ozyegin/public_html/includes/bootstrap.inc:2670
Stack trace:
#0 [internal function]: _drupal_exception_handler()
#1 {main}
  thrown in <b>/var/www/ozyegin/public_html/includes/bootstrap.inc</b> on line <b>2670</b><br />