Your config.php does not contain all the required constant definitions. Please check config-sample.php and update your config accordingly, there are new stuffs!

'); // Define tables if( !defined('YOURLS_DB_TABLE_URL') ) define('YOURLS_DB_TABLE_URL', YOURLS_DB_PREFIX.'url'); if( !defined('YOURLS_DB_TABLE_OPTIONS') ) define('YOURLS_DB_TABLE_OPTIONS', YOURLS_DB_PREFIX.'options'); if( !defined('YOURLS_DB_TABLE_LOG') ) define('YOURLS_DB_TABLE_LOG', YOURLS_DB_PREFIX.'log'); // Create the YOURLS object $ydb that will contain everything we globally need if ( function_exists( 'yourls_db_connect' ) ) { global $ydb; yourls_db_connect(); } // Read option right from start yourls_get_all_options(); // Check if upgrade is needed. Note: this is bypassable with define('YOURLS_NO_VERSION_CHECK', true) if ( !defined('YOURLS_NO_VERSION_CHECK') || YOURLS_NO_VERSION_CHECK != true ) { if ( yourls_upgrade_is_needed() ) { yourls_redirect( YOURLS_SITE .'/admin/upgrade.php' ); } }