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How to perform postmoterm analysis of high usage of CPU/RAM and nonresponsiveness on Ubuntu?

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Recently one of my dev server experienced very high usage of CPU (1 out of 2 cores completely used) and RAM(near 100%), and system didn't respond to either SSH, web requests(by apache), nor websocket(by apache and Rachet). From vendor's dashboard I could see the VPS was still running, and I was able to get it to work again after rebooting it from dashboard.

Once I was able to log in via SSH, I went through all system logs, the only thing out of order is entry in system/kern/ufw.log that has many NULs, something like the following:

NUL NUL NUL NUL NUL

The timestamp of that entry preceding the entry with many NULs matches the time when system started to have high usage of CPU and RAM(according to monitoring logs from vendor's dashboard).

Is there anything I can do to track down what caused the high usage of CPU/RAM, and essentially down of this server? I was not able to do anything while usage was still high because I cannot SSH into it.

Thanks.

mangohost

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