Debug Multisite WP

Hello,

I’m trying the following code, but the file debug.log is not created. (http://codex.wordpress.org/Debugging_in_WordPress)

// Enable WP_DEBUG mode
define('WP_DEBUG', true);

// Enable Debug logging to the /wp-content/debug.log file
define('WP_DEBUG_LOG', true);

// Disable display of errors and warnings
define('WP_DEBUG_DISPLAY', false);
@ini_set('display_errors',0);

How do you usually debug your network?

thanks!