How to upgrade to Debian Bullseye from Buster in WSL?

If we installed a Debian WSL distro on our computer, there is a chance that in 6-9 months a new release will come out. We want to keep our system updated, so a distribution upgrade should happen in our WSL ecosystem.

The distribution upgrade happens the same way as on other ordinary virtual and physical platforms.

In the time of writing this post the current Debian oldstable is 10.12 (buster), and I upgrade to 11.03 (bullseye).

My approach is the following:

preparation -> backup -> upgrade -> clean up -> checks

Preparation

Before we start the process let’s check the current Debian version of our system:

cat /etc/debian_version
10.12

On the releases page of the Debian homepage we can double-check the release names and version numbers.

Debian 10 == buster
Debian 11 == bullseye

Now we know that we want to upgrade from 10 to 11.

Let’s read the release notes and make sure we understand the consequences of the upgrade!

Backup

Taking a backup of a WSL distro is relatively easy: we export the distro to a tar archive.

Terminate the WSL distro and take a backup of it!

In case of emergency we can simply import back the the current state of the machine with its data.

Upgrade

The actual Debian distribution upgrade happens as the upgrade documentation states it. In the first phase the minimal system is being changed, then in the second phase the full upgrade happens.

Let’s make sure we start with the latest Debian 10 version!

Update the current Debian buster version with the latest patches:

sudo apt update && sudo apt full-upgrade -y

Remove the unnecessary packages:

sudo apt autoremove -y

At this point we have a clean state of the freshest Debian Buster, so we are ready to change the package repository configuration, and point it to the new release.

sudo sed -i 's/buster/bullseye/g' /etc/apt/sources.list

The bullseye security repo follows a different convention than the buster repo did. Find the following line in the /etc/apt/sources.list file:

deb http://security.debian.org/debian-security bullseye/updates main

And change it to:

deb http://security.debian.org/debian-security bullseye-security main

Thus the /etc/apt/sources.list file should look something like this:

deb http://deb.debian.org/debian bullseye main
deb http://deb.debian.org/debian bullseye-updates main
deb http://security.debian.org/debian-security bullseye-security main
deb http://ftp.debian.org/debian bullseye-backports main

Let’s update the package repository cache!

sudo apt update

Hit:1 http://ftp.debian.org/debian bullseye-backports InRelease
Hit:2 http://deb.debian.org/debian bullseye InRelease
Hit:3 http://security.debian.org/debian-security bullseye-security InRelease
Hit:4 http://deb.debian.org/debian bullseye-updates InRelease
Reading package lists… Done
Building dependency tree
Reading state information… Done
396 packages can be upgraded. Run 'apt list --upgradable' to see them.

If everything is fine and the command ran without any error then the upgrade should happen in two phases:

Minimal upgrade

Upgrade the base system with the bullseye packages:

sudo apt upgrade --without-new-pkgs

If the upgrade ran without any errors, then let’s clean up the unnecessary packages:

sudo apt autoremove -y

Full upgrade

The full upgrade happens with the following command:

sudo apt full-upgrade

Again if everything ran without any issue, let’s clean up the packages again:

sudo apt autoremove -y

The distribution upgrade is done at this point, checks and monitoring can be done depending on the function of the system.

Post checks

Let’s see if the upgrade was successful and we have Debian 11:

cat /etc/debian_version
11.3

The further checks depend on the system’s function and on our taste.

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