Create snapshots

To create a snapshot use

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sudo btrfs subvolume snapshot /mnt/@ /mnt/@_snapshot

# or

cd /btrfs
btrfs subvolume snapshot @ @_snapshot

this will create a snapshot of the @ subvolume named @_snapshot located also in the top of the btrfs tree.

Rollback to a snapshot

To roll back to a snapshot, you simply need to change its name to the name that ubuntu mounts, using

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sudo mv /mnt/@ /mnt/@_badroot
sudo mv /mnt/@_snapshot /mnt/@

and reboot.

Delete a snapshot To delete a snapshot use

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sudo btrfs subvolume delete /mnt/@_badroot

btrfs snapshots are subvolumes in themselves, and self-contained, deleting the old @ subvolume like this is fine, provided we have a replacement.

Resize

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btrfs filesystem resize max /btrfs/@