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Upgrading to Debian 11 Bullseye

Introduction

Although Debian 11 codenamed Bullseye was released almost 7 months back on 14th August, 2021, it was only in January, 2022 that I upgraded all my computers running Debian 10 to Debian 11. Admittedly a little late to the party, I like to take a cautious approach to upgrading my systems, which is not very difficult to predict given my Linux distribution of choice! In this post, I am going to share my experience and the steps I used while doing the actual upgrade.


Table of Contents


A word of caution

This post should not be considered as a guide about how to do Debian upgrades. The simple reason is that every system is configured differently and there is no one guide that can cover all types of system configurations. So what worked for me may not work for your systems. This post should give you some practical experience on how to go about it and the obvious pitfalls. But it is strongly suggested that you go through the Official Debian guide to upgrade from Debian 10 before you actually do the upgrade.

Plan for the worst

Even the best-laid plans can sometimes fail spectacularly. So I can’t stress enough on the importance of taking backup of important files and directories before starting the upgrade process. Additionally download the Live Install CD image for Debian 11 and follow the instructions to prepare a USB stick with the CD image. If things go sideways, you can always use the USB to live boot your system and diagnose the problems and even recover.

Remove the third party packages and sources

If you have installed any third party packages (packages that do not come from the official Debian repositories) in your system, it’s always a good idea to uninstall them before doing the upgrade so that there are least chances of surprises. You can install them back once your upgrade is complete.

To find out such packages, use the following command (you may need to install aptitude if not already installed):

aptitude search '?narrow(?installed, ?not(?origin(Debian)))'

Uninstall the packages from the output list using the following command:

sudo apt remove <package-name(s)>

Also disable the third party sources. The third party sources should have their own .sources files in the /etc/apt/sources.list.d directory or added to the /etc/apt/sources.list file. Rename the *.sources files under the /etc/apt/sources.list.d directory by appending .disabled at the end of the file names. If any third party sources are added in the /etc/apt/sources.list file, comment out the lines by prefixing them with a #.

Update the Buster system

Run the following commands to make sure that the Buster system is fully updated before continuing with the upgrade.

sudo apt update
sudo apt upgrade

Remove the obsolete packages

To search for the obsolete packages, use following the command:

sudo aptitude search '~o'

And to remove, use:

sudo aptitude purge '~o'

Modify the apt sources

Before modifying the apt sources to point to the bullseye release, make a copy of the existing /etc/apt/sources.list file.

sudo cp /etc/apt/sources.list /etc/apt/sources.list.buster

After this, open the /etc/apt/sources.list file as root with your favourite text editor and replace the following:

Start recording the session

It’s a good idea to record the terminal session when the upgrade is running. If something goes wrong, the session can be replayed to debug the issue. To record the session, an utility called script will be used. Install it if it is not already installed.

To start the recording, use this command:

script -t 2>~/upgrade-bullseye.time -a ~/upgrade-bullseye.script

After this all the commands are run from the same terminal session and their outputs will be recorded in those two files. To exit the recording, simply enter exit. After that, to replay the session later, use the following command:

scriptreplay ~/upgrade-bullseye.time ~/upgrade-bullseye.script

Update the package cache

Update the APT’s package cache with the bullseye package information:

sudo apt update

Dry run upgrade

Before running the actual upgrade, do a dry run of the upgrade process to make sure that there are sufficient disk spaces for doing the upgrade.

sudo apt -o APT::Get::Trivial-Only=true full-upgrade

Minimal system upgrade

While the upgrade can be done in one go, I prefer to do it in two steps. In the first step, do minimal system upgrade where only the installed packages are upgraded and no new packages are installed or existing packages are removed.

sudo apt upgrade --without-new-pkgs

Full system upgrade

Finally to fully upgrade the system, run this command:

sudo apt full-upgrade

Purge removed packages

The last two commands may take a long time to complete depending on the Internet speed. But once complete, use the following command to remove the left-over configuration files from the removed packages during the upgrade:

dpkg -l | awk '/^rc/ { print $2 }'; sudo apt purge $(dpkg -l | awk '/^rc/ { print $2 }')

Restart the system

You should restart the system at the end of the upgrade so that the system can boot with the shiny new packages and the kernel.

Conclusion

That’s it. Run the command: cat /etc/debian_version to print the Debian version you are currently on and hopefully it will print 11.

The upgrade process in Debian is not as straight forward as you would see in many other Linux distributions that ship with specific tools that hide the complexities and automatically take care of the system upgrades. But in my opinion the Debian way gives you greater control and more insight into how your system is upgraded, which in turn will help you diagnose the problems should something go wrong.



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