I want to install an Ubuntu Server with a btrfs filesystem (in a RAID1 way).

The problem is that I can't see the option in the installer to make more subvolumes. The installer creates two by default: @ and @home, and I want to separate also @var, @tmp, ...

Is there any option to do this? Maybe with the shell... but I think the installer doesn't understand the subvolumes feature of btrfs, so you can't mount each partition in each subvolume...


This should be easy enough to change after you have finished your initial install.

  • One neat way is to take two snapshots of @, calling them @var and @tmp.
  • Then delete everything in @var except for @var/var, them move the contents of @var/var/* up to @var/* and delete @var/var. Same for @tmp/tmp/.
  • Then modify /etc/fstab with the new subvolume mount points for /var and /tmp.
  • Reboot.
  • Finally (I'm not so sure about this last bit) you should be able to delete the original contents of @/var and @/tmp by mounting the subvolume @ under /mnt (so the same subvolume is mounted twice, once as / and once as /mnt) and deleting /mnt/var and /mnt/tmp.

You're right, the installer is not aware of BTRFS subvolumes, and this is still the case for 18.04.

Using a separate subvolume for /var/log/ allows to restore a snapshot of / without loosing the logs.

  • Do the server setup as usual, at the Finish installation step, select Go Back and Execute a shell.
  • List all your target file systems:

    mount | grep target
    /dev/md-0 on /target type btrfs (rw,noatime,space_cache,subvolid=257,subvol=/@)
    /dev/md-0 on /target/home type btrfs (rw,noatime,space_cache,subvolid=258,subvol=/@home)
    proc on /target/proc type proc (rw,nosuid,nodev,noexec,relatime)
    devtmpfs on /target/dev type devtmpfs (rw,nosuid,relatime,size=475608k,nr_inodes=118902,mode=755)
  • Take a note of the btrfs device, in this example /dev/dm-0.

  • Now un-mount all of your mounted file systems.

    umount /target/dev
    umount /target/proc
    umount /target/boot/efi
    umount /target/home
    umount /target/
  • Mount your flat btrfs filesystem :

    cd /tmp
    mkdir work
    mount /dev/dm-0 work
    cd work
  • Verify the mount is correct (should show @ and @home):

    @ @home
  • Create your additional subvolumes (@tmp, @var, @var-log)

    btrfs subvolume create @tmp
    btrfs subvolume create @var
    btrfs subvolume create @var-log
  • Move the data

    mv @/var/log/* @var-log/
    mv @/var/* @var/
    # Remove data from tmp
    rm @/tmp/* @/tmp/.*
    # For 18.04, remove the swapfile since it won't work on btrfs
    rm @/swapfile
  • Add the new subvolumes to fstab, the device part may be different than the previous mount command, copy the device part from the already existing mount points.

    /dev/mapper/root-root /               btrfs   noatime,subvol=@ 0       1
    /dev/mapper/root-root /home           btrfs   noatime,subvol=@home 0       2
    /dev/mapper/root-root /var            btrfs   noatime,subvol=@var 0       2
    /dev/mapper/root-root /var/log        btrfs   noatime,subvol=@var-log 0       2
  • Unmount

    cd /tmp
    umount work
  • exit, then Finish the installation

  • Install and configure snapper, a great tool for automatizing snapshots.

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