Crash goes the system

[GreyGeek]

Thanks yet again. I think my problem was in using mkdir to create @old and @homeold. I didn't know the uses of @ and thought I needed to create those new directories in order to make the think work. If I remember right, I think I deleted those two directories before I finished, and thus grub couldn't find my file system when I rebooted.

On a freshly installed, or clean, system @ is the subvolume that contains / and everything under it except another subvolumes. @home contains /home.

If you browse through @ (while you have /dev/sda1 mounted to /mnt) you will see / and all of its subdirectories, including /home, but browsing into /home there will be NOTHING in /home under @. Nothing. Not your home account name nor any files that would be under it in a normal EXT4 based system. If you browse into @home you will find /home and /home/youracctname and under your accountname will be all of the folders and files in your account.

The same will be true of snapshots of @ and @home. If you browsed through a @home20180802 (for example) snapshot of @home you will notice everything that was in your account the day you took the snapshot. If you accidentally delete some folder or file from your /home/aacountname you can browse into @home20180802 and drag and drop what you deleted out into your home account where it should be. One of the many nice features of Btrfs!

Now, if you use the 'mv' command to move @ to, say, @old, and forget to replace @ with a rw copy of another @snapshot then when you reboot fstab won't be able to find @ and you'll get a hang. If that happens you'll need to boot a LiveUSB, modprobe btrfs, and mount /dev/sda1 to /mnt and recover @ using a @snapshot ... if you have one. If not, then it's time to reinstall.