The older Fix I.T. Phill Proxmox Backup Server tutorial covered installing Backup Server as a standalone system. This is the catch-up upgrade path for existing PBS 3.x systems. Do not jump from an old 3.1 or 3.2 box straight into Debian 13. First update to current PBS 3.4 on Bookworm, then follow the official 3-to-4 path, then update normally to current PBS 4.2.
The release chain since the older tutorial is important: PBS 3.3 arrived in November 2024, PBS 3.4 in April 2025, PBS 4.0 in August 2025 on Debian 13 Trixie, PBS 4.1 in November 2025, and PBS 4.2 on April 29, 2026. PBS 4.2 adds backup group and namespace moves, server-side encryption/decryption for sync jobs, concurrent group pull/push processing, improved sync logging, and official S3-compatible object storage support.
Preflight On PBS 3.4
Use SSH with tmux, a physical console, or remote management. Do not run the major upgrade from a web UI console that can disconnect mid-upgrade.
tmux new -s pbs4-upgrade
apt update
apt dist-upgrade
proxmox-backup-manager versions
df -h /
Back up the PBS configuration. This is not a replacement for backing up the data on the datastore, but it protects critical PBS configuration if the OS upgrade goes sideways.
tar czf "pbs3-etc-backup-$(date -I).tar.gz" -C "/etc" "proxmox-backup"
pbs3to4
pbs3to4 --full
Put Datastores In Read-Only Maintenance Mode
For busy backup servers, read-only maintenance mode prevents new backup jobs from starting during the upgrade while keeping existing backups readable. Replace DATASTORE-ID with each datastore name.
proxmox-backup-manager datastore list
proxmox-backup-manager datastore update DATASTORE-ID --maintenance-mode read-only
Switch PBS Repositories To Trixie
Update the Debian base repositories from Bookworm to Trixie and add the PBS 4 repository. Use the enterprise repository for production systems with a subscription, or no-subscription for labs.
apt install proxmox-archive-keyring
sed -i 's/bookworm/trixie/g' /etc/apt/sources.list
grep -R bookworm /etc/apt/sources.list /etc/apt/sources.list.d 2>/dev/null || true
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
No-subscription lab 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
Run The Upgrade
Run the upgrade, review configuration prompts, rerun the checker, and reboot into the new kernel.
apt update
apt policy
apt dist-upgrade
pbs3to4 --full
systemctl reboot
Verify PBS 4.2
After reboot, update again from the PBS 4 repository so the server lands on current 4.2 packages, then verify services and datastore access.
apt update
apt dist-upgrade
proxmox-backup-manager versions
systemctl status proxmox-backup-proxy.service proxmox-backup.service --no-pager
proxmox-backup-manager datastore list
Disable read-only maintenance mode after the upgrade is healthy:
proxmox-backup-manager datastore update DATASTORE-ID --delete maintenance-mode
Watch Points
- If PBS is co-installed on a Proxmox VE host, coordinate this with the Proxmox VE 8-to-9 upgrade instead of treating it as an isolated appliance.
- Network interface names can change under the newer kernel. Have console access before reboot.
- Old hardware should be tested first, especially if the backup server uses older storage controllers.
- Review sync jobs after 4.2. New encryption and concurrency options can improve offsite sync designs, but they should be staged deliberately.
Related Catch-Up Guides
- Proxmox VE 8.2 to 8.4 catch-up guide
- Proxmox VE 8.4 to 9.1 upgrade guide
- Proxmox Mail Gateway 8.2 to 9.0 upgrade guide