I've recently caused xdm to start on bootup. Went fine for a couple of
days, but something funny has started happening over the last couple of
days. After exiting the first session started, the machine locks up
tight -- it's stuck in graphics mode, the mouse pointer doesn't move,
and I can't ping the machine from elsewhere.

Thinking it might be xdm3d, I disabled it and went back to stock xdm
(xdm3d wasn't an improvement in my books anyways), where I noticed a
warning on the console that getty was going nuts on /dev/console.
Disabled the entry in /etc/ttys and it seems to be sane once more.

Why is this?