some times, seemingly random, my system stops being interactive. The cursor moves as it should, but stays locked in a single shape, depending on what I was doing. num lock also responds, but I have no communication with the system. sometimes this lasts a few seconds, other times several minutes. The kernel is fine, logging in from another computer usually works fine, no delay. Right now it has been about 10 minutes and counting. 'top' over ssh tells me there is plenty of idle cpu and free memory, and no sluggish processes.

anyone else encountered something similar?

Kubuntu 10.04/x64

Hi,

I've seen similar behaviour, although not lasting as long as you describe (10 minutes). This behaviour could be caused by high disk I/O.

If I start multiple encode/decode processes (change movies from X to Y format) and start un-rarring files at the same time my system does become temporarily unresponsive. These time-outs lasts seconds (1-3 secs. max) and happen 3 to 4 times over a 15 minute period. This happens because the processes started are very disk intensive (reads and writes) and all is done to the same physical disk.

Have a look at the iostat command (link provided explains the command and output), which can tell you if disk I/O is the problem you are encountering. If this is the case have a look at the processes that are running. Check if you can spread them around and/or check to see if you can let them work on a different physical disks (if you have that luxury).

Hope this helps.

This time it appears that linuxdcpp (a port of DC++) was responsible. I killed that, and the system returned to normal. I saw a glimpse of it using 9999 CPU in top, which gave me a clue. I was resizing a column on one of the tabs there when things locked up.

I had that on x64 when I was short of memory. The other things that spring to mind are:
Firefox running some script can take over, but usually not for 10 minutes. Adobe Reader's zero day flaw is known, and exploits for that are out in the wild. Things took forever on my amd64 with an ubuntu kernel. Everybody will jump in and attack that, but that was my experience.

Pin it down a bit more. Free? lsof? Logs? I don't want to see any of that, but you check them. also try to associate this misbehaviour with something.