When the unpleasant brown stuff hits the fan...
I've been doing Ubuntu upgrades since version 5 on my UML Linode. No surprises with each version I've done. Well, until I upgraded to karmic (9.10) and rebooted. mountall failed. WTF? Show-stopper issue. My Linode's services were completely down until I resolved this.
After much head-scratching and quick research, realized I needed a 2.6.31 kernel for karmic. Nothing newer than 2.6.18 or so for UML guests. But there was a Xen 2.6.31 kernel. Hmmmm. Solution: migrate from UML to Xen super duper quick. Had to be done within the same data center so I could keep my IP because I run a public DNS nameserver.
Opened a ticket. 8 minutes later, I had a migration running - wow! 15 minutes later, I was booted into a working Xenode with ALL of my settings and data intact. Now THAT's service!!! Not only that, the documentation someone put up helped me through a few specific places where I had to change a few config files, Profile setting, and make device nodes to boot properly under Xen:
Thanks, Danny (who assisted with the ticket), the original doc author, and the helpful #linode folks who helped out with migration tips! I'm celebrating my 5th anniversary with Linode in a few weeks.