Debian OS Upgrade

Safe upgrade workflow (CLI)

This page documents a practical Debian upgrade process. The exact Debian versions (buster, bullseye, bookworm) can change, but the flow stays the same: backup, update, adjust sources, upgrade, reboot, verify.

Step 1) Backup your system

sudo cp -v /etc/apt/sources.list /root/
sudo cp -rv /etc/apt/sources.list.d/ /root/
sudo cp -rv /etc/nginx/ /root/

Tip: also back up your critical service configs (mail, firewall, VPN, DNS) before continuing.

Step 2) Update all installed packages

lsb_release -a
uname -mrs
sudo apt update
sudo apt upgrade -y
sudo apt full-upgrade -y
sudo apt --purge autoremove -y
sudo reboot

Step 3) Update apt sources

Example: replace old codename with new

cat /etc/apt/sources.list
# Replace "buster" with "bullseye" (example)
sudo sed -i 's/buster/bullseye/g' /etc/apt/sources.list
sudo sed -i 's/buster/bullseye/g' /etc/apt/sources.list.d/*
sudo apt update

If you use third party repositories, verify they support your target Debian release. Remove or disable unsupported ones before upgrading.

Step 4) Minimal system upgrade

sudo apt upgrade

During the upgrade you may be asked about config file changes. In most cases: keep your local config unless you are sure.

Step 5) Full upgrade

sudo apt full-upgrade
sudo reboot

Step 6) Verification and cleanup

sudo apt install -y lsb-release
lsb_release -a
uname -r
sudo apt --purge autoremove -y
sudo apt autoclean

Notes

Checklist

  • Backup configs
  • Disable unsupported repos
  • Upgrade + reboot
  • Verify version
  • Clean old packages