To my embarrassment, I had not known that 4.0 had been released.
In preparation for incorporating an OpenID module into Xoops, which runs this site, I was trying to bring everything up to date. As I watched the output scroll by while running an automatic upgrade with aptitude, I suddenly thought:
“Ah! MySQL has become 5.0…”
What a shock.
Everything other than MySQL upgraded smoothly, but MySQL failed, perhaps because settings for debian-sys-maint and similar items were not properly configured. The database had been inherited from RedHat…
In the end, I had to do everything manually… although all I actually did was run mysql_upgrade and Repair Table. Still, it took some effort.
I should seriously set up a development machine first… How many months has it been since the development machine died…?