BTRFS How to make a snapshot and rollback

I’ve mentioned earlier on how to fix the root FS filling up with snapshots generated by apt-get upgrade

Now assume I do need to rollback because of whatever went wrong.

First, if you haven’t installed yet apt-btrfs-snapshot (because of this) we do it now and then we upgrade.

apt-get install apt-btrfs-snapshot

# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
 evolution-data-server evolution-data-server-common evolution-data-server-online-accounts gir1.2-ebook-1.2 gir1.2-ebookcontacts-1.2 gir1.2-edataserver-1.2 google-chrome-beta libcamel-1.2-45
 libebackend-1.2-7 libebook-1.2-14 libebook-contacts-1.2-0 libecal-1.2-16 libedata-book-1.2-20 libedata-cal-1.2-23 libedataserver-1.2-18 locales
16 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 52.4 MB of archives.
After this operation, 8,133 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
........

Done. see the snapshots we now have

# btrfs subvolume list /
ID 257 gen 8126 top level 5 path @
ID 258 gen 8126 top level 5 path @home
ID 325 gen 8123 top level 5 path @apt-snapshot-2014-05-23_22:14:26

# apt-btrfs-snapshot list
Available snapshots:
@apt-snapshot-2014-05-23_22:14:26

Lets do a manual one cause I know I’m going to do a few silly things now.

# btrfs subvolume snapshot / /andreas_doing_silly_things
Create a snapshot of '/' in '//andreas_doing_silly_things'

I can see it here.

# ls -al /
total 25
drwxr-xr-x 1 root root 228 May 23 22:29 .
drwxr-xr-x 1 root root 228 May 23 22:29 ..
drwxr-xr-x 1 root root 176 May 23 22:29 andreas_doing_silly_things

Now we want to rollback. Identify the deice where btrfs is on and mount it

# df -h /
 Filesystem Size Used Avail Use% Mounted on
 /dev/sdb4 25G 9.4G 15G 40% /
 root@USB-DISK:/#

mount /dev/sdb4 /mnt

# ls -al
total 16
drwxr-xr-x 1 root root 78 May 23 22:14 .
drwxr-xr-x 1 root root 228 May 23 22:29 ..
drwxr-xr-x 1 root root 228 May 23 22:29 @
drwxr-xr-x 1 root root 176 May 2 21:15 @apt-snapshot-2014-05-23_22:14:26
drwxr-xr-x 1 root root 14 May 2 21:13 @home

# btrfs subvolume list /mnt
ID 257 gen 8201 top level 5 path @
ID 258 gen 8128 top level 5 path @home
ID 325 gen 8123 top level 5 path @apt-snapshot-2014-05-23_22:14:26
ID 329 gen 8201 top level 5 path @/andreas_doing_silly_things

Ideally we want to go back to before the patching cause I feel that upgrade made some mess. I first create a markr to see that this is my pre-upgrade FS

# cd /mnt
root@USB-DISK:/mnt# ls -al
total 16
drwxr-xr-x 1 root root 78 May 23 22:14 .
drwxr-xr-x 1 root root 228 May 23 23:23 ..
drwxr-xr-x 1 root root 228 May 23 23:23 @
drwxr-xr-x 1 root root 226 May 23 23:33 @apt-snapshot-2014-05-23_22:14:26
drwxr-xr-x 1 root root 14 May 2 21:13 @home

# cd @apt-snapshot-2014-05-23_22:14:26

# touch thatsbeforetheupgrade.txt

# ls -al
total 24
drwxr-xr-x 1 root root 226 May 23 23:33 .
drwxr-xr-x 1 root root 78 May 23 22:14 ..
drwxr-xr-x 1 root root 2052 May 15 21:07 bin
drwxrwxr-x 1 root root 0 May 2 21:09 boot
drwxrwxr-x 1 root root 0 May 2 21:12 cdrom
drwxr-xr-x 1 root root 902 Apr 17 02:26 dev
drwxr-xr-x 1 root root 4420 May 23 22:14 etc
drwxrwxr-x 1 root root 0 May 2 21:09 home
lrwxrwxrwx 1 root root 33 May 2 21:15 initrd.img -> boot/initrd.img-3.13.0-24-generic
drwxr-xr-x 1 root root 760 May 5 20:18 lib
drwxr-xr-x 1 root root 40 Apr 17 02:21 lib64
drwxr-xr-x 1 root root 14 May 2 21:24 media
drwxr-xr-x 1 root root 6 May 12 19:51 mnt
drwxr-xr-x 1 root root 34 May 3 10:06 opt
drwxr-xr-x 1 root root 0 Apr 10 23:12 proc
drwx------ 1 root root 100 May 9 20:30 root
drwxr-xr-x 1 root root 334 Apr 17 02:27 run
drwxr-xr-x 1 root root 4338 May 22 16:02 sbin
drwxr-xr-x 1 root root 0 Apr 17 02:21 srv
drwxr-xr-x 1 root root 0 Mar 13 01:41 sys
-rw-r--r-- 1 root root 0 May 23 23:33 thatsbeforetheupgrade.txt
drwxrwxrwt 1 root root 400 May 23 22:14 tmp
drwxr-xr-x 1 root root 70 Apr 17 02:21 usr
drwxr-xr-x 1 root root 114 Apr 17 02:29 var
lrwxrwxrwx 1 root root 30 May 2 21:15 vmlinuz -> boot/vmlinuz-3.13.0-24-generic

I’m not cheating

# ls -al /thatsbeforetheupgrade.txt
ls: cannot access /thatsbeforetheupgrade.txt: No such file or directory

Now we rollback before the update:

# mv /mnt/@ /mnt/@_badroot

# mv /mnt/@apt-snapshot-2014-05-23_22:14:26 /mnt/@

# ls -al
total 16
drwxr-xr-x 1 root root 30 May 24 00:09 .
drwxr-xr-x 1 root root 228 May 23 23:23 ..
drwxr-xr-x 1 root root 226 May 23 23:33 @
drwxr-xr-x 1 root root 228 May 23 23:23 @_badroot
drwxr-xr-x 1 root root 14 May 2 21:13 @home

# cd @
# ls
bin boot cdrom dev etc home initrd.img lib lib64 media mnt opt proc root run sbin srv sys thatsbeforetheupgrade.txt tmp usr var vmlinuz

which will set the new root partition (volume) as “@apt-snapshot-2014-05-23_22:14:26” which was before we run apt-get upgrade. Reboot the box.

reboot

After the reboot check what we have done.

 ls /
bin boot cdrom dev etc home initrd.img lib lib64 media mnt opt proc root run sbin srv sys thatsbeforetheupgrade.txt tmp usr var vmlinuz

That looks promising.

# btrfs subvolume list /
ID 257 gen 8257 top level 5 path @_badroot
ID 258 gen 8260 top level 5 path @home
ID 325 gen 8260 top level 5 path @
ID 329 gen 8201 top level 5 path @_badroot/andreas_doing_silly_things

And because I like to proof Einstein right I do the same again and expect it this time to work.

# apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
The following packages will be upgraded:
 evolution-data-server evolution-data-server-common evolution-data-server-online-accounts gir1.2-ebook-1.2 gir1.2-ebookcontacts-1.2 gir1.2-edataserver-1.2 google-chrome-beta libcamel-1.2-45
 libebackend-1.2-7 libebook-1.2-14 libebook-contacts-1.2-0 libecal-1.2-16 libedata-book-1.2-20 libedata-cal-1.2-23 libedataserver-1.2-18 locales
16 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B/52.4 MB of archives.
After this operation, 8,133 kB of additional disk space will be used.
Do you want to continue? [Y/n]

Now closing that theory lets do some cleanup.

# mount /dev/sdb4 /mnt

# btrfs subvolume list /mnt
ID 257 gen 8257 top level 5 path @_badroot
ID 258 gen 8266 top level 5 path @home
ID 325 gen 8266 top level 5 path @
ID 329 gen 8201 top level 5 path @_badroot/andreas_doing_silly_things

# btrfs subvolume delete /mnt/@_badroot/andreas_doing_silly_things
Delete subvolume '/mnt/@_badroot/andreas_doing_silly_things'

# btrfs subvolume delete /mnt/@_badroot
Delete subvolume '/mnt/@_badroot'

# btrfs subvolume list /mnt
ID 257 gen 8257 top level 0 path DELETED
ID 258 gen 8268 top level 5 path @home
ID 325 gen 8268 top level 5 path @
ID 329 gen 8201 top level 0 path DELETED

You can do the same with the manual created snapshot “andreas_doing_silly_things”. That’s why I put it into as informational.