Grub not recognizing btrfs partition after installation

Question

Recently I've installed Ubuntu 20.04 (ext4). On the same disk was installed Linux Mint 19 (btrfs). I was able to mount partition, copy files, etc. It wasn't corrupted.

After installing Ubuntu grub was unable to recognise files of Linux Mint system and make record in boot menu. I was running grub from ubuntu terminal.

Answer 1

There's problem with mounting partition in Ubuntu. Btrfs partition is mounted not in / but /@/. There's need to add symbolic links to /@/etc/ and /@/bin/ by executing

ln -s /@/etc/ /etc
ln -s /@/bin/ /bin

After this simple solution Grub recognises btrfs recognises Linux Mint system and after update appaired in boot menu.