I'm sitting on Ubuntu 9.04 with MySQL 5.0.75 installed.
The book states that error logging is enable by default and that the file called <host>.err is located in the data directory (on Ubuntu, that would be /var/lib/mysql) but this seems to be incorrect.
There is no such file in that directory and the only .err file that I can find on the system is a file called mysql.err located in the /var/log directory.
This file is empty and is not populated once I execute an erroneous command such as DROP USER noneexistinguser; It remains empty no matter what happens with MySQL.

So I added (like the book suggests) log-error=localhost.err which indeed created a file by that name, but it only contains when the server started and when it was shut down, and not the erroneous command. I assumed that the default behavior would be this since the example in the book has logged an attempt to remove a user that does not exists.

Furthermore, Query Logging records events such as server startup and shutdown. Since the localhost.err file I just created does exactly this, what is the point of the .err file?

Anyone care to enlighten me?