Convert root ext4 to btrfs including subvolumes and snapper

ext4_to_btrfs

# on your ext4 distro
sudo su
apt install btrfs-progs
shutdown now

# switch to a linux live environment
sudo su
fsck -f /dev/vda3

# BTRFS convert
btrfs-convert /dev/vda3

# Move the Root filesystem from rescue
mount /dev/vda3 /mnt  
btrfs subvol create /mnt/@
btrfs subvolume delete /mnt/ext2_saved
mv /mnt/* /mnt/@/
btrfs subvol create /mnt/@home
mv /mnt/@/home/* /mnt/@home/

# FSTAB
blkid /dev/vda3 | awk '{print $2}'

vim /mnt/@/etc/fstab
--- comment the / ext4 line
UUID=9fb8437d-783c-4f2c-8c38-56290764b1ad / btrfs subvol=/@ 0 1 
UUID=9fb8437d-783c-4f2c-8c38-56290764b1ad /home btrfs subvol=/@home 0 2
---

# CHROOT
umount -l /mnt/
mount /dev/vda3 /mnt/ -t btrfs -o subvol=@
for fs in proc sys dev dev/pts; do mount --bind /$fs /mnt/$fs; done  
chroot /mnt /bin/bash

# GRUB
mount /boot/efi
grub-install --no-nvram /dev/vda
grub-mkconfig -o /boot/grub/grub.cfg

# list subvolumes
btrfs subvolume list / -t

# finish
exit
reboot

# check
sudo su
btrfs subvolume list / -t
btrfs filesystem df /

## SNAPPER:
sudo snapper -c root create-config /

sudo sed -i 's/^ALLOW_USERS=.*/ALLOW_USERS="pacadmin"/' /etc/snapper/configs/root

# Change permissions and ownership to snapshot directory:
sudo chmod a=rx /.snapshots/
sudo chown :pacadmin /.snapshots/

# Create snapshots:
snapper -c root create --description AfterMigration

# List snapshots under root config:
snapper -c root list

fstab

# fstab example from Manjaro forum: https://forum.manjaro.org/t/default-btrfs-mount-options-and-subvolume-layout/43250/17

# Swap
UUID=06686a06-c069-49f7-86e4-7a962740b364       none                    swap            defaults                                                                        0 0

# UEFI
UUID=447C-E2BC                                  /boot/efi               vfat            noatime,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8                   0 2

# System
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /btrfs                  btrfs           noatime,ssd,compress-force=zstd:5,subvolid=5                                    0 0
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /                       btrfs           noatime,ssd,compress-force=zstd:5,subvol=@                                      0 0
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /home                   btrfs           noatime,ssd,compress-force=zstd:5,subvol=@home                                  0 0
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /var                    btrfs           noatime,ssd,nodatacow,subvol=@var                                               0 0
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /.snapshots             btrfs           noatime,ssd,compress-force=zstd:5,subvol=@snapshots/root                        0 0
UUID=26c8751d-2747-4a4d-b857-32c82d67b20a       /home/.snapshots        btrfs           noatime,ssd,compress-force=zstd:5,subvol=@snapshots/home                        0 0

# var/lib mount into subvol=@
/usr/var/lib                                    /var/lib                none            defaults,bind                                                                   0 0

# Backup
UUID=d49e1730-5137-473c-8e28-a76cf14e9830       /media/Backups          btrfs           nofail,noatime,ssd,compress-force=zstd:5,subvol=@backups                        0 0