ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock' (2)

[native-api]

Looks like a duplicate of

Failures installing MariaDB 10.2 on Xenial

Okay, I found the cause of the discrepancy. In Xenial, all 4 MySQL packages are marked as manually installed. So I’d have to supply all the 4 corresponding MariaDB packages on the command line manually, too, for them to override the MySQL ones. @BanzaiMan I could make a workaround PR so that MariaDB addon starts working in Xenial+ before https://github.com/travis-ci/travis-cookbooks/pull/1057 is deployed. But I would rather help you resolve whatever problem you are having with updating VM …