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Cerin
Asked: 2013-05-25 06:31:31 +0800 CST

How to prioritize SSH to work in the event of high CPU load

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I'm encountering a weird problem where a Fedora Linux VPS server reports 100% CPU, and effectively becomes unusable, but I don't know why because the high load prevents me from SSHing into it to see what's wrong.

How do I prioritize or configure SSH so that I'm still able to connect even if some process is consuming all other CPU?

linux

4 Answers

  1. If this is for real a CPU / Load related problem you can (re)nice the sshd process on your server to give it a higher priority. To make that persistent you can add the nice inside the sshd init script.

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  2. Create a script which logs processes:

    #!/bin/bash
top -b -c -n 1 -d 1 > /tmp/top-$(date "+%Y-%m-%d_%H-%M-%S")

    Setup a cron job which runs the script every minute:

    */1 * * * * /path/to/script.sh

    Next time your system goes unresponsive, you'll have logging of what was doing it.

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  3. I was running the code that was hogging all the resources through Docker, so I just limited the amount of CPU that could be consumed by the container by starting it with

    --cpus=7.5

    Because I have 8 cores, this means I should always have half a core for processing SSH sessions into the actual server running the container (unless some other process takes up those resources too).

    For good measure I also limited the container's memory usage with

    --memory=4g

    https://docs.docker.com/config/containers/resource_constraints/#cpu

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  4. If you don't mind my saying, I think you're asking the wrong question. You really want to find out what is using so may resources to the point of your not being able to log in. I have come across this problem numerous times and the solution is to track what is going on the server constantly. I came up with this solution which is as light as possible, reducing its chances of being stopped by a resource hog:

    http://linuxtech.ie/wordpress/2012/09/05/finding-a-severe-resource-hog-on-your-server/

    I hope that helps

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