Nextcloud - Error creating admin user

I installed nextcloud like described in the howto. Opening the nextcloud in the local network with a browser at http://IP/nextcloud I need to add user, password and the database credentials. First I don’t know, which port to use, so I left that open, just adding ‘localhost’. What I get is an error:

Error while trying to create admin user: Failed to connect to the database: An exception occured in driver: SQLSTATE[HY000][2002] Can’t connect to local MySQL server through socket ‘/tmp’ (111)

Any advises what I should do?

I have the same problem on my MOX. Today’s Turris update had been sucessful installed. But setting uo NExtcloud fails with the same error message as above. What to do?