Install Ubuntu Server 20.04 on Btrfs

Install Ubuntu Server 20.04 on Btrfs

I have summarized the procedure when the root file system of Ubuntu Server 20.04 is set to Btrfs.

About Btrfs subvolumes

Btrfs subvolumes can be mounted individually and displayed as subdirectories. In addition, Btrfs snapshots can be quickly created with the copy-on-write (CoW) function.

About the layout of Btrfs subvolumes

OpenSUSE is a good reference for the layout of Btrfs subvolumes. The default file system for openSUSE uses Btrfs.

Storage layout settings

In the storage layout settings, select Custom storage layout.

Create a partition for the boot device.

Add a GPT partition.

Format with btrfs and mount point to /.

Write the partition table to disk and continue the installation.

After the installation is complete, proceed to the next step without rebooting.

Creating a Btrfs subvolume

After the installation is complete, press ALT + F2 without rebooting to switch to the console. Here is the route.

sudo -i

Shows the mounted devices. Ubuntu is installed in / target.

mount -l | grep /target

Unmount / target and mount the disk on / mnt.

umount -l /target
mount /dev/vda2 /mnt

You can view the list of block devices with lsblk.

Create a subvolume.

cd /mnt
btrfs subvolume create @
btrfs subvolume create @/home
btrfs subvolume create @/opt
btrfs subvolume create @/root
btrfs subvolume create @/srv
btrfs subvolume create @/tmp
chmod 1777 @/tmp
mkdir @/usr
btrfs subvolume create @/usr/local
btrfs subvolume create @/var
btrfs subvolume create @/swap

Disable copy-on-write (CoW) on / var to improve performance.

chattr +C /mnt/@/var

Move all files and folders to a subvolume.

shopt -s dotglob
mv home/* @/home
mv root/* @/root
mv usr/local/* @/usr/local
mv var/* @/var
rmdir home opt root srv usr/local tmp var
ls | grep -v @ | xargs mv -t @

Unmount / mnt to mount all the devices needed for your system.

umount /mnt
mount -o subvol=@ /dev/vda2 /target
mount /dev/vda2 /target/boot/efi
mount --bind /proc /target/proc
mount --bind /dev  /target/dev
mount --bind /sys  /target/sys

Press ALT + F3 to switch to the third window and chroot to switch the system.

sudo -i
chroot /target

Edit fstab to set the appropriate mount point for the subvolume.

vi /etc/fstab

UUID=xxxx / btrfs defaults,ssd,noatime,space_cache,commit=120,compress=zstd,subvol=@ 0 1
/swap/swapfile none swap sw 0 0

Creating a swap file

Copy-on-write (CoW) must be disabled to create a swap file on a Btrfs subvolume. However, if there are files with copy-on-write (CoW) disabled, you will not be able to take snapshots. Therefore, create a subvolume for the swap file and create a swap file there.

touch /swap/swapfile
chmod 0600 /swap/swapfile
chattr +C /swap/swapfile
fallocate /swap/swapfile -l 2g
mkswap /swap/swapfile

Finally update GRUB.

update-initramfs -u -k all
grub-install --recheck /dev/sda
update-grub

Press ALT + F1 to switch to the first window and reboot.

References

1. Install Ubuntu 18.04 Server on btrfs - work-work.work
2. 18.04 - Where are my BTRFS subvolumes? - Ask Ubuntu
3. Ubuntu 20.04 with btrfs-luks-RAID1 full disk encryption including /boot and auto-apt snapshots with Timeshift | Willi Mutschler
4. Using Btrfs for Easy Backup and Rollback | John Ramsden
5. Creating openSUSE-style btrfs root partition & subvolumes
6. SDB:BTRFS - openSUSE Wiki
7. swap - Can I have a swapfile on btrfs? - Ask Ubuntu