A few decades ago I bought a used IBM as a *nix server, but it would lock up at nearly random intervals like you describe. Tried a different Linux distro… same issues. Tried BSD - same issues!

It wasn’t until after I learned of the 1999-2007 capacitor plague that I inspected the motherboard and saw that yes, several of the capacitories were bulging.

https://www.robotroom.com/Faulty-Capacitors-1.html

I mailed the motherboard to a servicer who replaced all the capacitors for a nominal fee. After that it was a rock solid system. You mention that this is recent hardware, but I would still suggest taking a peek at those caps.

Iirc the original steamOS was Debian based and you really had to be an experienced Linux user to use and enjoy it.

With the new steamOS (arch based?) it’s a much more streamlined experience and opens up the user base because of it

On my machine, the L2 cache is 256KiB

Is this a typo or are they running on a Pentium 3?

In the future, you should look into using LVMs for your partitions. I ran into a similar problem recently where my /var needed to be increased - I was able to run a simple lvextend -L+4G /dev/myvg/var --resizefs to grow my /var by 4 gigabytes.

Before I was using LVMs though I used a gparted live disk a lot

I’ve been a decades long Gentoo user, but now I’m experimenting with NixOS as I’ve gotten older and value my time more. The 12+ hours of compiling when there’s a chromium / QT update is no longer a badge of honor. I haven’t fully converted though, Gentoo binary packages are working as an acceptable stopgap