I just spent more time than I should have troubleshooting why the upgrade of MySQL from 5.0 to 5.1 on a Debian box resulted in a MySQL instance that wouldn’t start. Not a lot out there on this so hopefully this will save someone a bit of time in the future.

When upgrading from 5.0 to 5.1 using apt everything will install normally. Then when the MySQL service tries to restart you’ll see and init.d error and an error that looks something like this:

Errors were encountered while processing:mysql-server-5.1mysql-server

Not a lot to go on here but as it turns there is a deprecated entry in the my.cnf file called skip-bdb.  Comment this line out and you should be good to go.