History
It’s almost 2020. Fedora 31 came out a month back and I’m just getting
around to converting my desktop system to Fedora 31. As mentioned before,
for my laptop systems I’ve moved on to
Fedora Silverblue. As I
continue to containerize my workflows I’m moving more and more of my
daily workflows into Flatpaks from
the Fedora registry, pet containers (via toolbox)
and, single purpose containers. As I continue to convert my workflows into
containers I’ll stick with the BTRFS+snapper setup for my desktop
system, which still has the benefits of being able to snapshot and rollback
the entire system by leveraging BTRFS snapshots, and a tool called snapper.
In the past I have documented this setup and all the steps I took in detail for Fedora 22 (part1 and part2), 24, 25, 27, and 29. This is a condensed continuation of those posts for Fedora 31.
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 the first 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 more or less like having
Anaconda 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.
Note that this time I did run into a problem because the default for
LUKS now is to use the version 2 of the header format.
GRUB2 doesn’t support this yet
so I had to change the command to specify --type luks1.
Installing and Configuring Snapper
NOTE: systemd creates some btrfs subvolumes automatically. They have been omitted from the logged output from commands below.
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 1.33GiB 1.33GiB
Next up is installing 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!
Use snapper command to create a configuration for
BTRFS filesystem mounted at /:
[root@localhost ~]# snapper --config=root create-config /
Now we can look at the snapshot setup and the current configuration:
[root@localhost ~]# snapper ls
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
---+--------+-------+------+------+------------+---------+-------------+---------
0 | single | | | root | | | current |
[root@localhost ~]# snapper list-configs
Config | Subvolume
-------+----------
root | /
[root@localhost ~]# btrfs subvolume list /
ID 262 gen 1811 top level 5 path .snapshots
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 | Used Space | Cleanup | Description | Userdata
---+--------+-------+---------------------------------+------+------------+---------+-------------+---------
0 | single | | | root | | | current |
1 | single | | Sun 29 Dec 2019 05:49:25 PM UTC | root | 120.00 KiB | | BigBang |
[root@localhost ~]# btrfs subvolume list /
ID 262 gen 1823 top level 5 path .snapshots
ID 263 gen 1820 top level 262 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-5.3.7-301.fc31.x86_64
kernel-5.3.16-300.fc31.x86_64
[root@localhost ~]# snapper ls
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
---+--------+-------+---------------------------------+------+------------+---------+-------------------------------+---------
0 | single | | | root | | | current |
1 | single | | Sun 29 Dec 2019 05:49:25 PM UTC | root | 8.82 MiB | | BigBang |
2 | pre | | Sun 29 Dec 2019 05:51:24 PM UTC | root | 8.96 MiB | number | /usr/bin/dnf update -y kernel |
3 | post | 2 | Sun 29 Dec 2019 05:52:01 PM UTC | root | 640.00 KiB | 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
Connection to 192.168.122.183 closed by remote host.
Connection to 192.168.122.183 closed.
[dustymabe@media ~]$ ssh root@192.168.122.183
root@192.168.122.183's password:
Last login: Sun Dec 29 17:43:16 2019 from 192.168.122.1
[root@localhost ~]# uname -r
5.3.16-300.fc31.x86_64
Rolling Back
Want to go back to the earlier snapshot? No problem!
[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 267 gen 1913 top level 262 path .snapshots/5/snapshot
[root@localhost ~]# snapper ls
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
---+--------+-------+---------------------------------+------+------------+---------+-------------------------------+--------------
0 | single | | | root | | | current |
1 | single | | Sun 29 Dec 2019 05:49:25 PM UTC | root | 1.89 MiB | | BigBang |
2 | pre | | Sun 29 Dec 2019 05:51:24 PM UTC | root | 8.96 MiB | number | /usr/bin/dnf update -y kernel |
3 | post | 2 | Sun 29 Dec 2019 05:52:01 PM UTC | root | 4.66 MiB | number | /usr/bin/dnf update -y kernel |
4 | single | | Sun 29 Dec 2019 06:00:11 PM UTC | root | 1.68 MiB | number | rollback backup | important=yes
5* | single | | Sun 29 Dec 2019 06:00:11 PM UTC | root | 46.23 MiB | | |
[root@localhost ~]# ls /.snapshots/
1 2 3 4 5
[root@localhost ~]# btrfs subvolume list /
ID 262 gen 1914 top level 5 path .snapshots
ID 263 gen 1886 top level 262 path .snapshots/1/snapshot
ID 264 gen 1829 top level 262 path .snapshots/2/snapshot
ID 265 gen 1847 top level 262 path .snapshots/3/snapshot
ID 266 gen 1886 top level 262 path .snapshots/4/snapshot
ID 267 gen 1916 top level 262 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
5.3.7-301.fc31.x86_64
[root@localhost ~]# rpm -q kernel
kernel-5.3.7-301.fc31.x86_64
It worked!