Until the latest Kernel update to Ubuntu 22.04 LTS, Ubuntu Server ran nicely on 512 MB RAM, on a KVM VPS. Though I have not tested it on stand-alone hardware, I suspect the same holds true.
One of the (offending) update components is linux-headers-5.15.0-46. It does not fail until the Kernel is actually used, during the next boot, when the boot fails (hangs) with “end Kernel panic – not syncing: System is deadlocked on memory”.
This is not something that Ubuntu is going to fix, as their web site has been quietly updated at some point with a “recommended” minimum RAM of 1 GB.
Bottom line: Web Hosting companies are advised to no longer offer Ubuntu on anything less than 1 GB RAM. Even if they only offer older versions of Ubuntu, as some customers will, undoubtedly, try and upgrade themselves to 22.04 with the latest updates.
Anyone doing their own install on VPS or stand-alone hardware should be sure to have 1 GB RAM.
Caveat: Container VPS, e.g. – OpenVZ instead of KVM, may get away with 512 MB RAM. …for a while. I haven’t tested it in those environments.
But if you are installing or offering Ubuntu, better go with 1 GB RAM minimum.