2

Please note the following commands:

user@ubuntu:~$ sudo btrfs subvolume create /srv/audio
Create subvolume '/srv/audio'
user@ubuntu:~$ sudo btrfs fi show
Label: 'BTRFS_STORAGE'  uuid: 0042d7c1-6850-42d2-9de8-3d408642b397
    Total devices 3 FS bytes used 886.08GB
    devid    1 size 931.51GB used 478.00GB path /dev/sdd
    devid    3 size 1.82TB used 955.03GB path /dev/sde
    devid    2 size 931.51GB used 477.03GB path /dev/sdc

Label: 'home'  uuid: 5a869b17-5d30-462f-9abb-7095532a1994
    Total devices 3 FS bytes used 3.70GB
    devid    1 size 27.33GB used 0.00 path /dev/dm-1
    devid    2 size 111.79GB used 5.03GB path /dev/sdb
    devid    3 size 59.63GB used 1.03GB path /dev/sda
Btrfs v0.20-rc1
user@ubuntu:~$ sudo btrfs subvolume list /
ID 256 gen 17101 top level 5 path @
ID 258 gen 17064 top level 5 path @home
ID 261 gen 17079 top level 5 path @apt-snapshot-release-upgrade-saucy-2013-10-20_11:17:04
ID 269 gen 17100 top level 256 path srv/audio
user@ubuntu:~$ 

So, this is my first fresh installation with a btrfs root, ive used btrfs in the past with an ext4 root with mounted btrfs disks.

Its obvious that they are subvolumes of some sort, but I am unfamiliar with the "@" symbols in the pathname. What does it signify?

1 Answer 1

3

When you install Ubuntu on btrfs partition, the system automatically creates the @ and @home subvolumes. If it didn't it would be much more difficult to take advantage of backups of the whole system with snapshots. You can also use them to install more then one system on a single BTRFS partition: see also my answer to Can I have two distros on the same partition using btrfs?

I have no idea, why the Ubuntu team did chose names @ and @home for these subvolumes. Maybe so they can stand out and will not be confused easily with directories? Keep in mind, that when you forget about the snapshooting stuff, the subvolume indeed behave very much like a standard directory.

3
  • So, the use of the "@" symbol is completely arbitrary and makes no difference to anything else?
    – Ace
    Feb 27, 2014 at 23:56
  • 1
    @ace For all purposes that I know of - yes. It is arbitrary. Feb 28, 2014 at 7:46
  • Through recent experiences with mounting and otherwise manipulating these subvolumes, i have concluded that you are right, @Adam.
    – Ace
    Mar 1, 2014 at 17:22

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .