Leopard login blue screen fixed by deleting CUPS Cache single user mode

No question here, just a troubleshooting tip to share.

About a week ago our 10.5.8 (Leopard) G5 iMac was misbehaving. It was SPODng (Spinning PIzza of Death) when woken from sleep to login. On reboot it blue screened before the multiuser login screen. I could move the cursor about, but that was it.

A safe boot restart didn't work. Still blue screen. I tried a lot of different troubleshooting techniques, which I detail in a blog posting [1]. I thought my old G5 was failing, but this turned out to be software, not hardware.

The machine had been well behaved for some time. There were no recent software updates. The only thing that was new was that my son was sending a lot of print jobs to the connected printer. Reinstalling 10.5 (archive and install) fixed it for a day or two, but then it recurred.

After two days of struggle, I did fix the problem. It was related to a bad print. This is what I did to fix it [2]

1. Startup in single user mode (cmd-S on startup)
2. Run the command that allows me to modify the file system (you see it on startup prompt)
3. Navigate to where OS X stores the CUPS printer spool (I knew the driver was CUPS): ~\var\spool\cups\cache (to use the cd command to get here you have to do sudo -s first to get a root shell).
4. Delete all the files - rm *
5. exit

I suspect the following combination is not stable: OS X 10.5.8 as a print server over a WiFi AirPort network with Epson HL-2140 printer drivers.

I rearranged my home network and made my 10.6 machine the print server, and the 10.5 machine a client. It's been fine since.

[1] http://tech.kateva.org/2011/06/g5-imac-blue-screen-on-logout-and.html. I thought I'd solved the problem once, but it recurred. It's been fixed since the update. This blog post is also a general introduction to G5 issues and troubleshooting.
[2] it would have been easier to put the machine in target disk mode and do the same thing from my laptop.