Upgrading Debian Buster to Bullseye

Debian 11 (codename Bullseye) was released on August 14th, 2021 with the latest stable packages. In this post I will show how easy it is to upgrade it.

1. Backup before doing anything! While this is a simple process, things always can go wrong.

2. Confirm the existing installation runs on Debian Buster:

lsb_release -c
(out)Codename:	buster

3. As root, edit the apt sources by commenting the existing entries and adding the new repositories:

apt edit-sources
(out)#deb http://deb.debian.org/debian buster main contrib non-free
(out)#deb http://deb.debian.org/debian buster-updates main contrib non-free
(out)#deb http://security.debian.org/debian-security buster-security main
(out)#deb http://ftp.debian.org/debian buster-backports main contrib non-free
(out)
(out)deb http://deb.debian.org/debian bullseye main contrib non-free
(out)deb http://deb.debian.org/debian bullseye-updates main contrib non-free
(out)deb http://security.debian.org/debian-security bullseye-security main
(out)deb http://ftp.debian.org/debian bullseye-backports main contrib non-free

4. Update the repository list:

apt update

5. Then, upgrade the packages:

apt full-upgrade

Depending on the customizations made in the system, this step may ask to replace configuration files or keeping the existing ones. There's an option to compare the files but when in doubt, prefer to keep the existing ones.

6. If completed without any errors, I'd encourage a reboot just to make sure the latest Linux Kernel image is loaded as well:

reboot

7. And finally, to confirm it's now running Debian Bullseye:

lsb_release -c
(out)Codename:	bullseye

More details on how to upgrade from Debian 10 (Buster) can be found here.