I need to apologise for CPU usage on dallas723.

I'll be submitting this as a support request too, but I feel I need to post this in the forums.

For a while, I've been developing a script to help me simulate what bash would be like running through a low-baud connection. I did this on my local computer, but when it didn't work (it was outputting random files, and I wondered if maybe the method I was using was one Cygwin didn't like), I tried uploading and running it on my Linode on March 9th. No such luck, it didn't work either.

What I didn't realise was that it wasn't just outputting random files, it was spawning processes named them, too. On March 9th, it spawned four copies of /usr/bin/not (which is a program testing tool included with "llvm", as I later discovered), which were passed invalid arguments (my program had basically tried to run "not found"; yeah, my program was really buggy and I still don't understand why it did that). In response, it seems /usr/bin/not went into an infinite loop and used 100% CPU on all four processes. As the system has four simulated cores, this caused the VM to take up a full 100% of its allocated CPU.

I didn't notice this until last night due to unrelated reasons, and seeing an unknown executable (at the time) combined with taking 100% CPU caused me to believe my server had had a major security breach. After taking some forensics, I took networking offline and started looking into it with a friend of mine, who offered to help. 3 hours later, we had together determined exactly what was going on. At that point I killed the processes.

My main point with this post, though, was to apologise for hogging my portion of the CPU time for the last month-and-a-half. That was irresponsible of me. I've now enabled the email alert thresholds in the LPM so I'll know if that starts happening again a lot sooner.

It also frightens me that I had apparently not noticed these runaway processes before. I will pay a lot more attention to my server in future.

Thanks for reading, and again, I'm sorry.

2 Replies

If you didn't get contacted by Linode about it I doubt anybody cared. :)

I'm curious, though — what exactly was not running? All the not command does is invert the exit status of the command passed to it on the command line, and I can't think of any system where found is a command!

Yeah, I never got contacted by Linode.

As for what 'not' was doing exactly, I seriously have no idea. When I was taking forensics I did use 'gcore' to take a core dump of each of the four processes, so I should hopefully be able to analyse those to work out exactly what it was doing. But for now, I don't know.

I got a response to my support ticket, btw, just letting me know that it didn't look like I caused noticeable issues for anyone else on the same host. I'm really glad about that, and that makes me all the more impressed with how far Linode has come!


Please enter an answer

You can mention users to notify them: @username

You can use Markdown to format your question. For more examples see the Markdown Cheatsheet.

> I’m a blockquote.

I’m a blockquote.

[I'm a link] (https://www.google.com)

I'm a link

**I am bold** I am bold

*I am italicized* I am italicized

Community Code of Conduct