I was installing and setting up Cacti recently and faced following error:

“FATAL: Cannot connect to MySQL server on ‘localhost’.”

This post includes debugging steps and solution for the issue.

Along with the Cacti’s web-interface, the poller.php was generating the same error as follows:

root@ubuntu:/var/www/cacti# php /var/www/cacti/poller.php
FATAL: Cannot connect to MySQL server on 'localhost'. Please make sure you have specified a valid MySQL database name in 'include/config.php'

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