Debian Linux 12 Bookworm has been released. As of 23 July 2023, Debian 12.6 point was released on the 29 june 2024.

The new version offers updated packages and five years of support. This page provides a step-by-step guide to updating Debian 11 Bullseye to Debian 12 Bookworm using command-line options, including upgrading all installed packages.

The procedure is as follows:

1. Backup the system.
2. Update existing packages and reboot the Debian 11 system.
3. Edit the file /etc/apt/sources.list using a text editor and replace each instance of bullseye with bookworm. Next find the update line, replace keyword bullseye-updates with bookworm-updates. Finally, search the security line, replace keyword bullseye-security with bookworm-security.
4. Update the packages index on Debian Linux, run:

   frater@host:~$ sudo apt update

5. Prepare for the operating system minimal system upgrade, run:

   frater@host:~$ sudo apt upgrade --without-new-pkgs

6. Finally, update Debian 11 to Debian 12 Bookworm by running:

   frater@host:~$ sudo apt full-upgrade

7. Reboot the Linux system so that you can boot into Debian 12 Bookworm
8. Verify that everything is working correctly.

Let us see all commands step by step to upgrade Debian 11 Bullseye to Debian 12 Bookworm safely running in the cloud or bare metal environment.

Backing up all data and system configurations is extremely important. To do this efficiently, cloud-based virtual machines can be quickly backed up and restored using snapshots. Check os version in Linux using the lsb_release command.

frater@host:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Debian
Description:	Debian GNU/Linux 11 (bullseye)
Release:	11
Codename:	bullseye

Note down the Linux kernel version too. Try the uname command:

frater@host:~$ uname -mrs
Linux 5.10.0-23-amd64 x86_64

Also note down the Debian version using the cat command:

frater@host:~$ cat /etc/debian_version
11.7

To make the upgrade safer, you must remove non-Debian packages.

For example, Google Chrome or VirtualBox is a non-Debian package installed using 3rd party repo. Those can create a problem. Here is how to find such pages:

frater@host:~$ sudo apt list '?narrow(?installed, ?not(?origin(Debian)))'
frater@host:~$ sudo apt-forktracer | sort

Fortunately, I don’t rely on Google Chrome, VirtualBox, or any third-party applications on Debian.

However, if you use these apps, you should back up your data before upgrading. After upgrading, you can reinstall these packages if the Bookworm release supports them. Also, any package in hold status will create a problem with the upgrade procedure. Therefore, list all packages hold from upgrades using the apt-mark command as follows:

frater@host:~$ sudo apt-mark showhold | more

## OR ##

frater@host:~$ sudo dpkg --get-selections | grep 'hold$' | more

Then you must delete or remove the host status for all listed packages one by one with the help of the following command:

frater@host:~$ sudo apt-mark unhold package_name

## OR ##

frater@host:~$ echo 'package_name install' | sudo dpkg --set-selections

Before you upgrade your Debian version to 12, you must apply all security patches and pending upgrades to Debian 11 itself. Therefore, type the following apt command or apt-get command:

frater@host:~$ sudo apt update
Hit:1 http://deb.debian.org/debian bullseye InRelease
Get:2 http://deb.debian.org/debian bullseye-updates InRelease [44.1 kB]
Hit:3 http://deb.debian.org/debian bullseye-security InRelease [48.4 kB]
Fetched 92.4 kB in 2s (138 kB/s)
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
frater@host:~$ sudo apt upgrade
frater@host:~$ sudo apt full-upgrade

frater@host:~$ sudo apt --purge autoremove

Reboot the Debian 11.x bullseye to apply the kernel and other updates using the “reboot” or “shutdown” command. For instance:

frater@host:~$ sudo systemctl reboot

To begin the upgrade process, it is necessary to reconfigure the source-list files of APT.

You can view the current settings by using the commands cat command or more command. This will display the list of Debian 11 repo URLs.

frater@host:~$ sudo cat /etc/apt/sources.list

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

The keyword bullseye indicates we are using an older version, 11. Hence, we must change all the references in this file from bullseye to bookworm using a text editor such as Vim or Nano. For example:

frater@host:~$ sudo cp -v /etc/apt/sources.list /root/sources.list-bakup.11.bullseye
frater@host:~$ sudo vim /etc/apt/sources.list

From:

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

To:

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

Save and close the file. You can also use the sed command to find and replace bullseye with bookworm as follows:

frater@host:~$ sudo sed -i'.bak' 's/bullseye/bookworm/g' /etc/apt/sources.list

If you intend to use Debian 12 on either a desktop or server that requires non-free firmware for hardware such as WiFi, GPU, Sound, Nvida/AMD GPU, NIC and more, it is recommended to include the non-free firmware repository. Below is the updated file /etc/apt/sources.list file.

If you’re unsure about your hardware, I suggest adding those repositories.

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

Finally, run the following command to get fresh apt repo data:

frater@host:~$ sudo apt update

The system provided the following message:

xxx packages can be upgraded. Run 'apt list --upgradable' to see them.

Therefore, a two-part process is necessary to avoid removing large numbers of packages you want to keep. Therefore, first, run the following command to apply:

frater@host:~$ sudo apt upgrade --without-new-pkgs

To complete the upgrade, please carefully follow the on-screen instructions. You may encounter questions such as “Would you like to restart the service?” or “Keep or erase configuration file options?” throughout the process.

Your system has some services that require a restart when specific libraries like libpam, libc, and libssl are updated.

These restarts might cause service disruptions, so you will usually be asked to choose which services to restart during each upgrade.

However, you can skip this prompt by selecting the “Yes” option. By doing so, all the necessary restarts will occur automatically, and you won’t be bothered with questions during each library upgrade.

Here is another example, about GRUB package. A new version (/tmp/grub.nSxPVErDRh) of the configuration file /etc/default/grub is available, but the version installed currently has been locally modified.

What do you want to do about the modified configuration file grub? Again review all options carefully. I typically chose the “keep the local version currently installed”.

To fully update from Debian 11 to Debian 12, it’s necessary to make complete upgrades, rather than just minimum ones. This step is crucial for the upgrade process. To do this, enter the following command to ensure that the latest versions of all packages are installed and any potential dependencies are resolved.

frater@host:~$ sudo apt full-upgrade

You might encounter more prompts that suggest restarting services or modifying existing configuration options. Make sure to review them carefully. For example, you may have the option to update or retain the OpenSSH configuration file, I've modified my setup (ssh port for example), so I decide to keep my local file.

And you are done with the whole updating procedure. It is time to reboot the Linux system to boot into Debian Linux 12 bookworm. Before we restart the system, ensure there are no errors in the SSHD config file for the remote server:

frater@host:~$ sudo sshd -t

If there are no errors, you can proceed with rebooting the system. However, if there are any errors, it is important to fix them before rebooting. To do so, run:

frater@host:~$ sudo vim /etc/ssh/sshd_config

Verify again:

frater@host:~$ sudo sshd -t

Now reboot it after fixing any errors:

frater@host:~$ sudo systemctl reboot
Connection to www.xxx.yyy.zzz closed by remote host.
Connection to www.xxx.yyy.zzz closed.

Try running the ping command to get notification when your server comes back online:

frater@local:~$ ping -a www.xxx.yyy.zzz

All done. It is time to confirm the upgrade. Type:

frater@host:~$ uname -mrs
Linux 6.1.0-21-amd64 x86_64

frater@host:~$ lsb_release -a
No LSB modules are available.
Distributor ID:	Debian
Description:	Debian GNU/Linux 12 (bookworm)
Release:	12
Codename:	bookworm

Check Debian major and minor version too:

frater@host:~$ cat /etc/debian_version
12.5

After the upgrade, look out for all your apps and services. Therefore, verify all TCP/UDP ports are opened and services are running using the tail command or ss command or grep command/egrep command:

frater@host:~$ sudo ss -tulpn
frater@host:~$ sudo tail -f /var/log/mail.log                    # depends on your config
frater@host:~$ sudo tail -f /var/log/apache2/access_log          # depends on your config

Check for service status

frater@host:~$ sudo systemctl status nginx.service      # depends on your config
frater@host:~$ sudo systemctl status apache2.service    # depends on your config
frater@host:~$ sudo systemctl status mariadb.service    # depends on your config

Use journalctl to query the contents of the systemd journal

frater@host:~$ sudo journalctl
frater@host:~$ sudo journalctl -u sshd.service

Finally, clean up outdated packages using the apt command/apt-get command as follows:

frater@local:~$ sudo apt --purge autoremove