History
I’m back again with the Fedora 27 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 some great news this time! You no longer need
a patched version of Fedora’s grub package in order to pull this off.
Recently Fedora developer Peter Jones, Fedora contributor Neal Gompa
and I got together and managed to get
these patches
into Fedora’s grub.
In the past I have documented this setup and all the steps I took in detail for Fedora 22 (part1 and part2), Fedora 24 and Fedora 25. This is a condensed continuation of those posts for Fedora 27.
Alternatives: Fedora Atomic Workstation
Before I continue with this blog post I think it is worth noting that the project I work on every day is now producing and delivering updates to Fedora Atomic Workstation (iso here). It offers Fedora Workstation content via an OSTree and thus Atomic Upgrades and Rollbacks for the system software delivered in the Ostree. The next time I write one of these posts it may be about Atomic Workstation and not BTRFS snapshots.
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 1.24GiB 1.24GiB
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 41 top level 5 path .snapshots
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 | | Sun 17 Dec 2017 08:21:00 PM UTC | root | | BigBang |
[root@localhost ~]# btrfs subvolume list /
ID 260 gen 47 top level 5 path .snapshots
ID 261 gen 47 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-4.13.9-300.fc27.x86_64
kernel-4.14.5-300.fc27.x86_64
[root@localhost ~]# snapper ls
Type | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+---------------------------------+------+---------+-------------------------------+---------
single | 0 | | | root | | current |
single | 1 | | Sun 17 Dec 2017 08:21:00 PM UTC | root | | BigBang |
pre | 2 | | Sun 17 Dec 2017 08:23:32 PM UTC | root | number | /usr/bin/dnf update -y kernel |
post | 3 | 2 | Sun 17 Dec 2017 08:24:00 PM UTC | root | number | /usr/bin/dnf update -y kernel |
So we updated the kernel and the snapper dnf plugin automatically
created a pre and post snapshot for us. Let’s reboot the system and
see if the new kernel boots properly:
[root@localhost ~]# reboot
...
+[dustymabe@media ~]$ ssh root@192.168.122.105
root@192.168.122.105's password:
Last login: Sun Dec 17 20:12:57 2017 from 192.168.122.1
[root@localhost ~]#
[root@localhost ~]#
[root@localhost ~]# uname -r
4.14.5-300.fc27.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 4.)
Creating read-write snapshot of snapshot 1. (Snapshot 5.)
Setting default subvolume to snapshot 5.
[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 5 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 265 gen 67 top level 260 path .snapshots/5/snapshot
[root@localhost ~]# snapper ls
Type | # | Pre # | Date | User | Cleanup | Description | Userdata
-------+---+-------+---------------------------------+------+---------+-------------------------------+--------------
single | 0 | | | root | | current |
single | 1 | | Sun 17 Dec 2017 08:21:00 PM UTC | root | | BigBang |
pre | 2 | | Sun 17 Dec 2017 08:23:32 PM UTC | root | number | /usr/bin/dnf update -y kernel |
post | 3 | 2 | Sun 17 Dec 2017 08:24:00 PM UTC | root | number | /usr/bin/dnf update -y kernel |
single | 4 | | Sun 17 Dec 2017 08:29:14 PM UTC | root | number | rollback backup | important=yes
single | 5 | | Sun 17 Dec 2017 08:29:14 PM UTC | root | | |
[root@localhost ~]# ls /.snapshots/
1 2 3 4 5
[root@localhost ~]# btrfs subvolume list /
ID 260 gen 68 top level 5 path .snapshots
ID 261 gen 61 top level 260 path .snapshots/1/snapshot
ID 262 gen 50 top level 260 path .snapshots/2/snapshot
ID 263 gen 51 top level 260 path .snapshots/3/snapshot
ID 264 gen 61 top level 260 path .snapshots/4/snapshot
ID 265 gen 68 top level 260 path .snapshots/5/snapshot
And the big test is to see if the change we made to the system was actually reverted:
[root@localhost ~]# uname -r
4.13.9-300.fc27.x86_64
[root@localhost ~]# rpm -q kernel
kernel-4.13.9-300.fc27.x86_64
Enjoy!