Upgrade Debian 11 Bullseye to Debian 12 Bookworm

How to upgrade from Debian 11 Bullseye to Debian 12 Bookworm

1 Before you begin

In this guide, we will upgrade a Debian 11 server to Debian 12

Backup

Before we get started, we'll take a full backup of the server

Check disk space

Also check there is enough free disk space to do the upgrade

df -h

Check Debian OS version

cat /etc/*-release

cat /etc/debian_version

Check third party repositories 

Any third party repositories will also need to be updated for Debian 12 sources and the applications upgraded

ls /etc/apt/sources.list.d/

Install updates and reboot

Refresh apt sources, install updates and restart

# install updates
apt update
apt upgrade

# restart
systemctl reboot

2 Edit apt sources

Edit apt sources and change to Debian 12 Bookworm

nano /etc/apt/sources.list

apt sources.list before changes

# main
deb http://archive.debian.org/debian bullseye main contrib non-free
deb-src http://archive.debian.org/debian bullseye main contrib non-free

# security
deb http://archive.debian.org/debian-security bullseye-security main contrib non-free
deb-src http://archive.debian.org/debian-security bullseye-security main contrib non-free

# bullseye-updates, previously known as 'volatile'
deb http://archive.debian.org/debian bullseye-updates main contrib
deb-src http://archive.debian.org/debian bullseye-updates main contrib

# bullseye-backports
deb http://archive.debian.org/debian bullseye-backports main

main

replace archive.debian.org with deb.debian.org
replace bullseye with bookworm

# main
deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

security

replace archive.debian.org with security.debian.org
replace bullseye-security with bookworm-security

# security
deb http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

updates

replace archive.debian.org with deb.debian.org
replace bullseye-updates with bookworm-updates

# bookworm-updates, previously known as 'volatile'
deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

backports

replace archive.debian.org with deb.debian.org
replace bullseye-backports with bullseye-backports

# bookworm-backports
deb http://deb.debian.org/debian bookworm-backports main contrib non-free
deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free

New apt sources.list for Bullseye

# main
deb http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm main contrib non-free non-free-firmware

# security
deb http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
deb-src http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware

# bookworm-updates, previously known as 'volatile'
deb http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware
deb-src http://deb.debian.org/debian bookworm-updates main contrib non-free non-free-firmware

# bookworm-backports
deb http://deb.debian.org/debian bookworm-backports main contrib non-free
deb-src http://deb.debian.org/debian bookworm-backports main contrib non-free

3 Update third party repos

Edit apt sources for any third party repositories and make sure they are pointing to the latest version that is compatible with Debian 12

ls /etc/apt/sources.list.d/

We're not covering these step by step in this guide because each application will be different

4 Run minimal upgrade

Run minimal upgrade first before running the full OS upgrade

# refresh apt packages
apt update

# run minimal upgrade
apt upgrade --without-new-pkgs

You will get prompted to confirm any package changes or changes to config files

Installation finished. No error reported. 

Restart

systemctl reboot

5 Run full upgrade

Run the full OS upgrade

apt full-upgrade

Again, you will get prompted for any package changes that need you to confirm 

Full upgrade completed

Restart

# reboot
systemctl reboot

Check OS version

cat /etc/debian_version
cat /etc/*-release

6 Clean up apt packages

Clean up old apt packages using apt autoremove

apt update
apt upgrade

The following packages were automatically installed and are no longer required

apt autoremove

 Package clean up completed