Every now and then (I haven't been able to figure out a pattern), X stops responding to any input and no video updates occur anymore. The mouse pointer can still be moved, but has no effect.

If I switch to a tty (ctrl+alt+f1), both top and htop show 100% CPU usage and little RAM usage (right now 168). However, no process is shown to use more than 4% CPU. No process accounts for the 100% cpu usage.

Also, I can no longer switch back to X's vty (with ctrl+alt+f7 or f8).

Even if I restart X, htop still shows 100% cpu usage, without any process accounting for it.

Any ideas?

Yes, htop is a little misleading sometimes.

What does normal "top" say? Is there significant time being used by "Sys" rather than anything else?

htop sometimes misorders tasks for some reason, I see it a lot with heavily threaded items, and also even with "Sort By CPU%" the top CPU using process is actually at the bottom of the UI about 3 pages down.

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Matt Sealey

I can't reproduce this at will, I should've captured top's output. It'll likely lock up again if I keep using it, I'll capture it then.

What I do remember is that top and htop agreed in that no process used more than 4-5% CPU.

Locked up again, but unfortunately I forgot to capture top's output. It showed 20% as the highest CPU usage, and that was gnome-system-monitor (I had just opened it when it locked up).

In X11 screen was unresponsive, but mouse could be moved. No clicks or keyboard bindings worked, except for X11 ones (ctrl+alt+f#).