So I'm running Ubuntu 18.04 on a btrfs root. I recently rebooted because I got a notification about "restart required" after an update. The last few times I restarted this server, I had an issue where the kernel wouldn't load and I ended up in grub, and loaded the last kernel manually. This time (I had definitely run update-grub since last time) I'm in
grub rescue and the usual commands don't work, so I looked at a tutorial, but when I get to
insmod normal, I get the error "Compression type 0x3 not supported", and then
command not found. I'm writing this post because apparently nobody has ever seen this error* and I can't figure out what it means or how to fix it. My system works fine with kernel 4.15.0-23 but not at all with 4.15.0-24, which somehow got reinstalled after I removed it.
*A web search for the error message in quotes comes up empty