[CentOS] system unresponsive

Ok, we used to get this occasionally on cluster nodes, and we just got it on a fileserver (very bad). The system is discovered to be unresponsive: it doesn't ping, and plugging a console in, you can see that it's not dead, but there nothing at all on the screen, nor does it respond to even <ctrl-alt-del>. The only answer is to power cycle it; it comes up fine.

Nothing in /var/log/dmesg or /var/log/messages. No abrts I can find. sar tells me it went unredponsive between 18:10 and 10:20 yesterday. Note that there are no further entries in sar, either, for yesterday, after the event, and nothing till I power cycled it.

Has anyone else seen this - I can't imagine it's only us - or have any thoughts?

C 7, 7.6.1810

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