Lair Of The Multimedia Guru

Ive yesterday updated a 20.04 LTS ubuntu to 22.04. I expected it to just work but do-release-upgrade failed with something like
“The upgrade has aborted. The upgrade needs a total of 6XY M free space on disk ‘/boot’.”
Thats not nice of ubuntu considering the default /boot/ partition size was 500 M when this system was originally setup (i know because i know i left the default).
This system was also setup with disk encryption so simply resizing the partition is not as obvious and simple, not saying it cannot be done, just saying i felt more comfortable with making the update work with 500M /boot than trying to resize it.

So heres a list of solutions. For everyone who runs in this same issue. But before this a few words of caution.
Make a backup or have plan that you LIKE if it goes wrong.
The ubuntu tool is SHIT and this is polite. Its computation of needed space is at best a guess, it simply takes the current kernel size and the current initrd.img sizes and multiplies them by how many are expected to be needed and then asks for free space accordingly. Every number here is wrong. Its not using the actual kernel or initrd sizes, it doesnt use the current compression settings, it doesnt even seem to consider that the currently installed kernels will be removed. In practice for me it overestimated by 156mb but I think it can in corner cases also underestimate the needed space.

• Use your favorite partition resize tool, IFF you can.
• set /etc/initramfs-tools/initramfs.conf: COMPRESS to lzma (xz is slightly worse)
  then run update-initramfs -u, and remember ubuntu (no idea if others will too) will try to change this setting back during the update (it will ask) if you let it, and it changes it back then you may need more space during the update than what the tool computed
• uninstall all but one kernel
• uninstall anything you can from /boot/ like memtest
• Have the one installed kernel be the default standard not HWE in ubuntu IFF your system works with it. Why? its smaller and because if you use a HWE kernel then after the update you will have the current standard, previous standard and HWE kernels on /boot on ubuntu (I have not tested it but i ended with these 3 and i started with just the HWE one, assuming that was because HWE -> HWE + 2xstandard)
• If after all above you still dont have enough space but you are sure you actually have enough space, heres the sketchy solution, set MODULES=dep, run update-initramfs -u set MODULES back to most, run do-release-upgrade
  I did this, it worked for me. But what it effectively does is building a smaller initrd temporary to compensate ubuntus massive space overestimation. For me before, it asked still for around 360-370M free space which was 6M more than i had. In reality whenever i looked during the update there was 156+M remaining free space. You can also try to leave MODULES=dep during the upgrade if you are confident that the system will boot with that and the new kernel or maybe leave it at dep during the upgrade but just before rebooting set it back, removing unneeded kernels and running update-initramfs -u
• If something goes wrong and you run out of space and ubuntu sends you back to the command line (this didnt happen to me) simply try uninstalling some of the extra unneeded kernels with apt remove and do a apt -f install and apt update && apt dist-upgrade, If you have luck that might fix it
• Buy a new disk, install a new OS from scratch (that was my plan if what i did, didnt work)