What makes Ubuntu crash? I try to isolate the problem

tried to SSH into the box from another to see if the machine is really locked up or if it is just X...

I'd have commented directly, but it wants me to sign up to do that, and I've already got way too many accounts and passwords to remember...

I've often seen newbie linux users assume (from their windows experience) that linux has crashed, when it's actually just the X display that is hung.

Sometimes, you can get to a virtual console to restart X Sometimes, you'll have to ssh in to restart X, if the KB is well and truly wedged. Sometimes, there is a known issue with certain hardware or 3rd party drivers. Sometimes, there is a kernel panic, which prompts me to start checking hardware. Once in a blue moon, there is an actual kernel bug that should be reported.

SSHing into the box is an excellent idea, as would be looking at the relevant log files.

So far, things have gone well on a second day of using Xfce as the WM (after adding xubuntu-desktop) instead of GNOME. The problem, I think, has something to do with power-management issues, perhaps a daemon or daemons that are waiting to go into screen-saver mode or suspend.

There was an 8.04 bug that caused a crash when suspending. I upgraded to 8.04 from 7.10 on my xubuntu laptop about a month ago. The fix arrived arrived about 1 week after I did my upgrade. So if you have the latest patches, you have that fix. Besides it was a classic kernel panic, displaying its dump at the terminal.

You are using XFCE as your desktop. Are you using xfwm4 or Metacity as your WM? XFCE works well on multiple WM's. I've used it on Metacity and xfwm4.

My guess is that you are now on xfwm4 having gone from Ubuntu to Xubuntu. It may be that the bug is in the WM metacity and not in Gnome(just a guess).

fusion-icon is a compiz related program available in the ubuntu repositories. It puts an icon in your xfce systray that lets you switch window managers between those installed on your system. I have a choice of xfwm4, metacity and 'Compiz'. You may not want compiz on your system, but if you have it it is easier to switch WM and restart WM using the icon, otherwise you can do it from the command line.

You may find that you get the freezes using Metacity, and not using xfwm4. Then the bug is in Metacity. If you use Xfce on Metacity and have no freezes, then the bug is probably in Gnome and not Metacity.

I'm sure you have tons of free time to do all this :)

If you do try, happy bug hunting!

No crashes with Xfce. When logged out, with the login screen displaying, if the PC goes into screen-saver mode, the screen blanks and I need to do ctrl-alt-backspace to log in again. I've had that issue in Ubuntu for a long time, but it's not too much for me to put up with.

But either something in Ubuntu's GNOME build is causing the crashes, or miraculously the offending package has been replaced. I'll have to go back to GNOME to find out, since the past two days in Xfce have gone just about perfectly.