Upgrade Debian 11 to Debian 12

Step-by-step guide to upgrade from Debian 11 (Bullseye) to Debian 12 (Bookworm)

This guide walks you through upgrading your Debian 11 (Bullseye) system to Debian 12 (Bookworm).

Before you begin:

• Backup all important data
• Create a snapshot of your VPS
• Ensure you have console access in case of issues

Pre-Upgrade Preparation

1. Update Debian 11

   Ensure your current system is fully updated:

   sudo apt update && sudo apt dist-upgrade -y
   
2. Disable third-party repositories

   Comment out or remove third-party repository entries in /etc/apt/sources.list and /etc/apt/sources.list.d/.

Upgrade Process

1. Update sources list

   Replace bullseye with bookworm:

   sudo sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list
   
2. Update package lists

   sudo apt update
   
3. Upgrade packages

   sudo apt upgrade -y
   
4. Perform distribution upgrade

   sudo apt dist-upgrade -y
   

   Follow any on-screen prompts to resolve conflicts.

5. Reboot

   sudo reboot
   
6. Verify upgrade

   After rebooting, check the new version:

   lsb_release -a
   

Post-Upgrade Steps

1. Re-enable third-party repositories

   Update third-party repositories to their Debian 12 versions if available.

2. Clean up

   Remove obsolete packages:

   sudo apt autoremove
   sudo apt clean
   
3. Verify services

   Check that all essential services are running correctly.

If you encounter issues during upgrade, use the KVM Console to access your server and troubleshoot.