Owncloud cannot connect to mysql. What to do?

Question

MySQL

Installed and configured Owncloud and the necessary components. Apache, PHP7, mysql.
The browser launches the installation interface, where it asks to enter a user who can in the database. this is an owncloud user. He has all the permissions. Rechecked.
However, it won't let me in and gives me an SQLSTATE[H000] [2002] Connection refused error.
When trying to enable mysql logs, the service refuses to start.
The only thing I found was error.log, which stopped being written.
Tell me, please, where to dig?