Fedora BTRFS+Snapper PART 2: Full System Snapshot/Rollback

History

In part 1 of this series I discussed why I desired a computer setup where I can do full system snapshots so I could seamlessly roll back at will. I also gave an overview of how I went about setting up a system so it could take advantage of BTRFS and snapper to do full system snapshotting and recovery. In this final post of the series I will give an overview of how to get snapper installed and configured on the system and walk through using it to do a rollback.

Installing and Configuring Snapper

First things first, as part of this whole setup I want to be able to tell how much space each one of my snapshots are taking up. I covered how to do this in a previous post, but the way you do it is by enabled quota on the BTRFS filesystem:

[root@localhost ~]# btrfs quota enable /
[root@localhost ~]#
[root@localhost ~]# btrfs subvolume list /
ID 258 gen 50 top level 5 path var/lib/machines
[root@localhost ~]# btrfs qgroup show /
WARNING: Rescan is running, qgroup data may be incorrect
qgroupid         rfer         excl
--------         ----         ----
0/5         975.90MiB    975.90MiB
0/258        16.00KiB     16.00KiB

You can see from the output that we currently have two subvolumes. One of them is the root subvolume while the other is a subvolume automatically created by systemd for systemd-nspawn container images.

Now that we have quota enabled let's get snapper installed and configured:

[root@localhost ~]# dnf install -y snapper
...
Complete!
[root@localhost ~]# snapper --config=root create-config /
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+------+------+---------+-------------+---------
single | 0 |       |      | root |         | current     |
[root@localhost ~]# snapper list-configs
Config | Subvolume
-------+----------
root   | /
[root@localhost ~]#
[root@localhost ~]# btrfs subvolume list /
ID 258 gen 50 top level 5 path var/lib/machines
ID 260 gen 83 top level 5 path .snapshots

So we used the snapper command to create a configuration for BTRFS filesystem mounted at /. As part of this process we can see from the btrfs subvolume list / command that snapper also created a .snapshots subvolume. This subvolume will be used to house the COW snapshots that are taken of the system.

The next thing we want to do is add an entry to fstab to make it so that regardless of what subvolume we are actually booted into we will always be able to view the .snapshots subvolume and all nested subvolumes (snapshots):

[root@localhost ~]# echo '/dev/vgroot/lvroot /.snapshots btrfs subvol=.snapshots 0 0' >> /etc/fstab

Taking Snapshots

OK, now that we have snapper installed and the .snapshots subvolume in /etc/fstab we can start creating snapshots:

[root@localhost ~]# btrfs subvolume get-default /
ID 5 (FS_TREE)
[root@localhost ~]# snapper create --description "BigBang"
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date                     | User | Cleanup | Description | Userdata
-------+---+-------+--------------------------+------+---------+-------------+---------
single | 0 |       |                          | root |         | current     |
single | 1 |       | Tue Jul 14 23:07:42 2015 | root |         | BigBang     |
[root@localhost ~]#
[root@localhost ~]# btrfs subvolume list /
ID 258 gen 50 top level 5 path var/lib/machines
ID 260 gen 90 top level 5 path .snapshots
ID 261 gen 88 top level 260 path .snapshots/1/snapshot
[root@localhost ~]#
[root@localhost ~]# ls /.snapshots/1/snapshot/
bin  boot  dev  etc  home  lib  lib64  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var

We made our first snapshot called BigBang and then ran a btrfs subvolume list / to view that a new snapshot was actually created. Notice at the top of the output of the sections that we ran a btrfs subvolume get-default /. This outputs what the currently set default subvolume is for the BTRFS filesystem. Right now we are booted into the root subvolume but that will change as soon as we decide we want to use one of the snapshots for rollback.

Since we took a snapshot let's go ahead and make some changes to the system:

[root@localhost ~]# dnf install -y htop
[root@localhost ~]# rpm -q htop
htop-1.0.3-4.fc22.x86_64
[root@localhost ~]#
[root@localhost ~]# snapper status 1..0  | grep htop
+..... /usr/bin/htop
+..... /usr/share/doc/htop
+..... /usr/share/doc/htop/AUTHORS
+..... /usr/share/doc/htop/COPYING
+..... /usr/share/doc/htop/ChangeLog
+..... /usr/share/doc/htop/README
+..... /usr/share/man/man1/htop.1.gz
+..... /usr/share/pixmaps/htop.png
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/checksum_data
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/checksum_type
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/command_line
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/from_repo
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/installed_by
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/reason
+..... /var/lib/dnf/yumdb/h/2cd64300c204b0e1ecc9ad185259826852226561-htop-1.0.3-4.fc22-x86_64/releasever

So from this we installed htop and then compared the current running system (0) with snapshot 1.

Rolling Back

Now that we have taken a previous snapshot and have since made a change to the system we can use the snapper rollback functionality to get back to the state the system was in before we made the change. Let's do the rollback to get back to the snapshot 1 BigBang state:

[root@localhost ~]# snapper rollback 1
Creating read-only snapshot of current system. (Snapshot 2.)
Creating read-write snapshot of snapshot 1. (Snapshot 3.)
Setting default subvolume to snapshot 3.
[root@localhost ~]# reboot

As part of the rollback process you specify to snapper which snapshot you want to go back to. It then creates a read-only snapshot of the current system (in case you change your mind and want to get back to where you currently are) and then a new read-write subvolume based on the snapshot you specified to go back to. It then sets the default subvolume to be the newly created read-write subvolume it just created. After a reboot you will be booted into the new read-write subvolume and your state should be exactly as it was at the time you made the original snapshot.

In our case, after reboot we should now be booted into snapshot 3 as indicated by the output of the snapper rollback command above and we should be able to inspect information about all of the snapshots on the system:

[root@localhost ~]# btrfs subvolume get-default /
ID 263 gen 104 top level 260 path .snapshots/3/snapshot
[root@localhost ~]#
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date                     | User | Cleanup | Description | Userdata
-------+---+-------+--------------------------+------+---------+-------------+---------
single | 0 |       |                          | root |         | current     |
single | 1 |       | Tue Jul 14 23:07:42 2015 | root |         | BigBang     |
single | 2 |       | Tue Jul 14 23:14:12 2015 | root |         |             |
single | 3 |       | Tue Jul 14 23:14:12 2015 | root |         |             |
[root@localhost ~]#
[root@localhost ~]# ls /.snapshots/
1  2  3
[root@localhost ~]# btrfs subvolume list /
ID 258 gen 50 top level 5 path var/lib/machines
ID 260 gen 100 top level 5 path .snapshots
ID 261 gen 98 top level 260 path .snapshots/1/snapshot
ID 262 gen 97 top level 260 path .snapshots/2/snapshot
ID 263 gen 108 top level 260 path .snapshots/3/snapshot

And the big test is to see if the change we made to the system was actually reverted:

[root@localhost ~]# rpm -q htop
package htop is not installed

Bliss!!

Now in my case I like to have more descriptive notes on my snapshots so I'll go back now and give some notes for snapshots 2 and 3:

[root@localhost ~]# snapper modify --description "installed htop" 2
[root@localhost ~]# snapper modify --description "rollback to 1 - read/write" 3
[root@localhost ~]#
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date                     | User | Cleanup | Description                | Userdata
-------+---+-------+--------------------------+------+---------+----------------------------+---------
single | 0 |       |                          | root |         | current                    |
single | 1 |       | Tue Jul 14 23:07:42 2015 | root |         | BigBang                    |
single | 2 |       | Tue Jul 14 23:14:12 2015 | root |         | installed htop             |
single | 3 |       | Tue Jul 14 23:14:12 2015 | root |         | rollback to 1 - read/write |

We can also see how much space (shared and exclusive each of the snapshots are taking up:

[root@localhost ~]# btrfs qgroup show /
WARNING: Qgroup data inconsistent, rescan recommended
qgroupid         rfer         excl
--------         ----         ----
0/5           1.08GiB      7.53MiB
0/258        16.00KiB     16.00KiB
0/260        16.00KiB     16.00KiB
0/261         1.07GiB      2.60MiB
0/262         1.07GiB    740.00KiB
0/263         1.08GiB     18.91MiB

Now that is useful info so you can know how much space you will be recovering when you delete snapshots in the future.

Updating The Kernel

I mentioned in part 1 that I had to get a special rebuild of GRUB with some patches from the SUSE guys in order to get booting from the default subvolume to work. This was all needed so that I can update the kernel as normal and have the GRUB files that get used be the ones that are in the actual subvolume I am currently using. So let's test it out by doing a full system update (including a kernel update):

[root@localhost ~]# dnf update -y
...
Install    8 Packages
Upgrade  173 Packages
...
Complete!
[root@localhost ~]# rpm -q kernel
kernel-4.0.4-301.fc22.x86_64
kernel-4.0.7-300.fc22.x86_64
[root@localhost ~]#
[root@localhost ~]# btrfs qgroup show /
WARNING: Qgroup data inconsistent, rescan recommended
qgroupid         rfer         excl
--------         ----         ----
0/5           1.08GiB      7.53MiB
0/258        16.00KiB     16.00KiB
0/260        16.00KiB     16.00KiB
0/261         1.07GiB     11.96MiB
0/262         1.07GiB    740.00KiB
0/263         1.19GiB    444.35MiB

So we did a full system upgrade that upgraded 173 packages and installed a few others. We can see now that the current subvolume (snapshot 3 with ID 263) now has 444MiB of exclusive data. This makes sense since all of the other snapshots were from before the full system update.

Let's create a new snapshot that represents the state of the system right after we did the full system update and then reboot:

[root@localhost ~]# snapper create --description "full system upgrade"
[root@localhost ~]# reboot

After reboot we can now check to see if we have properly booted the recently installed kernel:

[root@localhost ~]# rpm -q kernel
kernel-4.0.4-301.fc22.x86_64
kernel-4.0.7-300.fc22.x86_64
[root@localhost ~]# uname -r
4.0.7-300.fc22.x86_64

Bliss again. Yay! And I'm Done.

Enjoy!

Dusty

4 Responses to “Fedora BTRFS+Snapper PART 2: Full System Snapshot/Rollback”


  • Do you think this version of Grub will eventually make it to Fedora? Because this sounds like something I’d like to setup next time I install Fedora from scratch.

    • Hi Eric,

      I don’t really know if this version of GRUB will make it into Fedora. If we were able to make a convincing argument GRUB upstream may consider this as a valid use case and add it back as optional behavior for GRUB. If it were upstreamed then Fedora would definitely pick it up :). I might send a note to grub-devel but I’m not sure if it will be well received or not as I think they have had this conversation in the past with other people.

  • Hi!

    Thank you for this very good article.

    I gave this a try with Fedora 24 beta, but I after a snapper rollback & reboot, it looks like I don’t get the default btrfs submodule.

    I did install grub from your github repo. Is there something I’m missing?

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