In the final part of our Debian 11 to 12 upgrade process, we focus on resolving the deepest technical challenges and reviving services. We take a detailed look at how to fix a stubborn Grub/OpenSSL issue that was blocking package management using a unique "Dummy Script" trick. Next comes fine-tuning the server environment: setting the system's default PHP versions, then running the ISPConfig upgrade script to restore website and control panel availability, correcting Apache configuration changes. Finally, we verify phpMyAdmin functionality and fix the Roundcube webmail 404 error, completing the system's operation in the new Debian 12 environment.

After a successful reboot of the Debian 11 to 12 upgrade, we will perform a system health assessment and mandatory post-installation tasks on this page. We will verify that the new kernel and services are running, and then perform a thorough system cleanup to remove unnecessary dependencies and "orphaned" configuration files. We will demonstrate in detail how to restore previously disabled external package repositories (e.g. Ásbrú, Sublime Text) and how to fix errors (GPG keys, 404 paths) from the command line. Finally, we will use aptitude to find and selectively remove obsolete packages that are no longer in the Debian 12 repositories, thus ensuring complete system cleanliness and stability.

In the process of a major system upgrade from Debian 11 to 12, after the preparations, we have reached the most critical stage: performing a full distribution upgrade (dist-upgrade). On this page, we will start the process by switching to the Konsole terminal and go through all the configuration file conflicts in detail. We will pay special attention to the services that are vital for ISPConfig servers (MariaDB, Pure-FTPd, Dovecot, Apache), showing in which cases we should stick to our own settings to maintain functionality, and when we can safely accept new versions (e.g. Jailkit, Roundcube, GRUB). At the end of the steps, we will close the stage with a successful reboot, entering the world of Debian 12.

Another era has come, when our Debian 10 (Buster) server has also reached its peak, and it has become a pressing task to do something about this problem. In this article, we will upgrade a perfect Debian 10 (Buster) server to Debian 11 (Bullseye system). On this page, we will review the basic system, as well as our higher-level server services, and perform the necessary post-configurations. The article has been updated with fixes for network interface (systemd) bugs encountered in Debian 11, as well as new GPG key management (signed-by) settings for external repositories (e.g. Sury PHP).

Another era has come again, when our Debian 10 (Buster) server has also run out of time, and it has become a burning task to do something about this problem. In this tutorial, we will upgrade a perfect Debian 10 (Buster) server to Debian 11 (Bullseye). On this page we will update the distribution to Debian 11 (Bullseye).