In the last 24 hours, accessing a URL like above gives error:
Can't connect to local MySQL server
through socket '/var/lib/mysql/mysql.sock' (2)
That error is the result from mysql_db_query().
I can access the database through the phpMyAdmin web interface as normal.
Inspecting our config files via shell access shows that nothing seems to have changed.
I received two emails about project upgrades, but cannot see any information relevant to MySQL.
How can this be resolved?