Dusty Mabe: Fedora BTRFS+Snapper – The Fedora 25 Edition

History

I’m back again with the Fedora 25 edition of my Fedora BTRFS+Snapper series. As you know, in the past I have configured my computers to be able to snapshot and rollback the entire system by leveraging BTRFS snapshots, a tool called snapper, and a patched version of Fedora’s grub2 package. I have updated the patchset (patches taken from SUSE) for Fedora 25’s version of grub and the results are available in this git repo.

This setup is not new. I have fully documented the steps I took in the past for my Fedora 22 systems in two blog posts: part1 and part2. This is a condensed continuation of those posts for Fedora 25.

Setting up System with LUKS + LVM + BTRFS

The manual steps for setting up the system are detailed in the part1 blog post from Fedora 22. This time around I have created a script that will quickly configure the system with LUKS + LVM + BTRFS. The script will need to be run in an Anaconda environment just like the manual steps were done in part1 last time.

You can easily enable ssh access to your Anaconda booted machine by adding inst.sshd to the kernel command line arguments. After booting up you can scp the script over and then execute it to build the system. Please read over the script and modify it to your liking.

Alternatively, for an automated install I have embedded that same script into a kickstart file that you can use. The kickstart file doesn’t really leverage Anaconda at all because it simply runs a %pre script and then reboots the box. It’s basically like just telling Anaconda to run a bash script, but allows you to do it in an automated way. None of the kickstart directives at the top of the kickstart file actually get used.

Installing and Configuring Snapper

After the system has booted for the first time, let’s configure the system for doing snapshots. I still want to be able to track how much size each snapshot has taken so I’ll go ahead and enable quota support on BTRFS. I covered how to do this in a previous post:

[root@localhost ~]# btrfs quota enable /
[root@localhost ~]# btrfs qgroup show /
qgroupid         rfer         excl 
--------         ----         ---- 
0/5         999.80MiB    999.80MiB

Next up is installing/configuring snapper. I am also going to install the dnf plugin for snapper so that rpm transactions will automatically get snapshotted:

[root@localhost ~]# dnf install -y snapper python3-dnf-plugins-extras-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 ~]# btrfs subvolume list /
ID 260 gen 44 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.

Next, we’ll add an entry to fstab so that regardless of what subvolume we are actually booted in 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 |       | Mon 13 Feb 2017 12:50:51 AM UTC | root |         | BigBang     |         
[root@localhost ~]# btrfs subvolume list /
ID 260 gen 48 top level 5 path .snapshots
ID 261 gen 48 top level 260 path .snapshots/1/snapshot
[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 by updating the kernel:

[root@localhost ~]# dnf update -y kernel
...
Complete!
[root@localhost ~]# rpm -q kernel
kernel-4.8.6-300.fc25.x86_64
kernel-4.9.8-201.fc25.x86_64
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date                            | User | Cleanup | Description                   | Userdata
-------+---+-------+---------------------------------+------+---------+-------------------------------+---------
single | 0 |       |                                 | root |         | current                       |         
single | 1 |       | Mon 13 Feb 2017 12:50:51 AM UTC | root |         | BigBang                       |         
single | 2 |       | Mon 13 Feb 2017 12:52:38 AM UTC | root | number  | /usr/bin/dnf update -y kernel |

So we updated the kernel and the snapper dnf plugin automatically created a snapshot for us. Let’s reboot the system and see if the new kernel boots properly:

[root@localhost ~]# reboot 
...
[dustymabe@media ~]$ ssh root@192.168.122.177
Warning: Permanently added '192.168.122.177' (ECDSA) to the list of known hosts.
root@192.168.122.177's password: 
Last login: Mon Feb 13 00:41:40 2017 from 192.168.122.1
[root@localhost ~]# 
[root@localhost ~]# uname -r
4.9.8-201.fc25.x86_64

Rolling Back

Say we don’t like that new kernel. Let’s go back to the earlier snapshot we made:

[root@localhost ~]# snapper rollback 1
Creating read-only snapshot of current system. (Snapshot 3.)
Creating read-write snapshot of snapshot 1. (Snapshot 4.)
Setting default subvolume to snapshot 4.
[root@localhost ~]# reboot

snapper created a read-only snapshot of the current system and then a new read-write subvolume based on the snapshot we wanted to go back to. It then sets the default subvolume to be the newly created read-write subvolume. After reboot you’ll be in the newly created read-write subvolume and exactly back in the state you system was in at the time the snapshot was created.

In our case, after reboot we should now be booted into snapshot 4 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 264 gen 66 top level 260 path .snapshots/4/snapshot
[root@localhost ~]# snapper ls
Type   | # | Pre # | Date                     | User | Cleanup | Description                   | Userdata
-------+---+-------+--------------------------+------+---------+-------------------------------+---------
single | 0 |       |                          | root |         | current                       |         
single | 1 |       | Mon Feb 13 00:50:51 2017 | root |         | BigBang                       |         
single | 2 |       | Mon Feb 13 00:52:38 2017 | root | number  | /usr/bin/dnf update -y kernel |         
single | 3 |       | Mon Feb 13 00:56:13 2017 | root |         |                               |         
single | 4 |       | Mon Feb 13 00:56:13 2017 | root |         |                               |         
[root@localhost ~]# ls /.snapshots/
1  2  3  4
[root@localhost ~]# btrfs subvolume list /
ID 260 gen 67 top level 5 path .snapshots
ID 261 gen 61 top level 260 path .snapshots/1/snapshot
ID 262 gen 53 top level 260 path .snapshots/2/snapshot
ID 263 gen 60 top level 260 path .snapshots/3/snapshot
ID 264 gen 67 top level 260 path .snapshots/4/snapshot

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

[root@localhost ~]# uname -r 
4.8.6-300.fc25.x86_64
[root@localhost ~]# rpm -q kernel
kernel-4.8.6-300.fc25.x86_64

Enjoy!

Dusty


Source From: fedoraplanet.org.
Original article title: Dusty Mabe: Fedora BTRFS+Snapper – The Fedora 25 Edition.
This full article can be read at: Dusty Mabe: Fedora BTRFS+Snapper – The Fedora 25 Edition.

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