Safely Upgrading Proxmox Backup Server from Version 3 to 4

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October 16, 2025

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2 min read

This walkthrough explains how to safely upgrade your Proxmox Backup Server (PBS) from version 3.4 to 4.0. The process also moves your system from Debian 12 (Bookworm) to Debian 13 (Trixie). Follow each step carefully for a smooth upgrade.

Before you begin make sure you have:

PBS version 3.4.2-1 or newer
A full configuration backup
At least 10 GB free on your root filesystem
Physical console or IPMI access
Local access in case of network issues

If you’re using Proxmox Backup Server version 3.0, 3.1, 3.2, or 3.3, you’ll need to upgrade to version 3.4 first. This can be done easily through the web interface before proceeding with the main upgrade.

Click Administration > Updates > Refresh > Upgrade (See screenshot below)

The following commands will be run directly from the Proxmox Backup Server shell. You can access it through the web interface under Shell or by connecting via SSH. Make sure you have root privileges before starting so each step completes without permission issues.

Verify Your Current PBS Version

proxmox-backup-manager versions

Backup Your Configuration

tar czf "pbs3-etc-backup-$(date -I).tar.gz" -C /etc proxmox-backup

Run the Upgrade Readiness Check

pbs3to4 --full

Fix any issues it reports and rerun the command until it passes.

Update PBS 3.4 to the Latest Release

apt update
apt dist-upgrade
proxmox-backup-manager versions

Add the Proxmox Archive Keyring for Debian Trixie

wget https://enterprise.proxmox.com/debian/proxmox-archive-keyring-trixie.gpg -O /usr/share/keyrings/proxmox-archive-keyring.gpg

Switch Your Debian Repositories to Trixie

Copy and paste each repository link one by one into your terminal.

sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
sed -i 's/bookworm/trixie/g' /etc/apt/sources.list.d/*.list || true
grep -R "bookworm" /etc/apt/sources.list || true

Configure the PBS 4 Repositories

Most people use the "No Subscription" repository so be sure to choose the right one below if you do.

No-Subscription Repository:

cat > /etc/apt/sources.list.d/proxmox.sources <<EOF
Types: deb
URIs: http://download.proxmox.com/debian/pbs
Suites: trixie
Components: pbs-no-subscription
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
EOF

Enterprise Repository:

cat > /etc/apt/sources.list.d/pbs-enterprise.sources <<EOF
Types: deb
URIs: https://enterprise.proxmox.com/debian/pbs
Suites: trixie
Components: pbs-enterprise
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
EOF

Perform the System Upgrade

apt update
apt dist-upgrade

You’ll be prompted with a few setup screens asking about configuration files, language, and other options. I just went with the defaults and continued.