Access denied for user 'www-data'@'localhost - how to deal with that?

Question

I face with a strange problem yesterday. I have server running Debian with installed PHP 4.4.4-8 and mysql 5.5.9. That server serves a several websites. For some reason ran

Answer 1

Deactivating safe mode fixed it for me:

Notice: mysql_connect(): SQL safe mode in effect - ignoring host/user/password information in /var/www/html/test.php on line 4