In-Place Upgrade to Proxmox Backup Server 4.0 (Homelab Edition)

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If your homelab matters, your backups matter more. Proxmox Backup Server (PBS) 4.0 is out now on Debian 13 “Trixie”, with a Linux 6.14 kernel and ZFS 2.3.3. Headline upgrades include native S3-compatible object storage, live RAIDZ expansion, and automatic sync on mount for removable datastores. Below is a straightforward, no-subscription in-place upgrade from PBS 3.4 → 4.0, with homelab-friendly notes.On this page:

From the field: I upgraded my PBS instance in-place and it went smoothly — but only because I took a backup of the backup server first (yes, the irony is not lost on me). In-place upgrades on infrastructure you depend on always warrant caution.

Why upgrade?

Before you start

Why upgrade?

  • Modern base (Debian 13 “Trixie”) + Kernel 6.14 — better hardware support, performance, and security on mixed homelab gear.
  • ZFS 2.3.3 with live RAIDZ expansion — grow existing RAIDZ vdevs with minimal downtime.
  • Native S3-compatible object storage — point PBS at public or private S3-API storage; smart local caching reduces API calls and cost. Contents remain reusable for DR.
  • Automatic sync on mount — run sync jobs whenever a removable datastore is mounted; great for USB/offsite copies.

Before you start (quick checks)

Tip: Use SSH with tmux or screen. Don’t rely on the web console during the upgrade.

  1. Be on PBS 3.4 latest apt update && apt dist-upgrade proxmox-backup-manager versions # expect 3.4.2-1 or newer
  2. Back up your config tar czf ~/pbs3-etc-backup-$(date -I).tar.gz -C /etc proxmox-backup
  3. Free space: aim for ≥ 10 GB free on /. df -h /
  4. If PBS and PVE live on the same box, review the PVE 8→9 upgrade and switch both repos in sync.

Step 1 — Run the checklist

Fix what it flags, then re-run until clean. It’s advisory (no changes made) but catches common issues.

pbs3to4 --full

Step 2 — (Optional) Enable maintenance mode

Stop new backups starting mid-upgrade while keeping existing ones readable:

proxmox-backup-manager datastore update <DATASTORE-ID> --maintenance-mode read-only

Step 3 — Point APT at Trixie and the no-subscription PBS repo

No-subscription users: This adds the correct PBS 4 pbs-no-subscription repository in the modern deb822 format.

1) Flip Debian to Trixie

sed -i 's/bookworm/trixie/g' /etc/apt/sources.list

Also check files under /etc/apt/sources.list.d/ and comment out any remaining Bookworm entries.

2) Add the PBS 4 no-subscription repo (deb822 format)

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

apt update && apt policy   # ensure only Trixie repos are active

Remove or disable older PBS repo entries once apt policy shows only Trixie sources.

Step 4 — Upgrade

apt dist-upgrade

Expect prompts about service restarts and some config diffs (e.g., /etc/ssh/sshd_config, /etc/default/grub). If unsure, defaults are fine — you’ll reboot anyway.

Step 5 — Reboot and verify

systemctl reboot
# after boot:
systemctl status proxmox-backup.service proxmox-backup-proxy.service

Force-reload the web UI after the upgrade (Ctrl+Shift+R on Windows/Linux or ⌘+Alt+R on macOS).

Step 6 — Tidy up

  • Turn off maintenance mode if you enabled it: proxmox-backup-manager datastore update <DATASTORE-ID> --delete maintenance-mode
  • (Optional) Modernise APT sources to deb822: apt modernize-sources # Answer "n" to preview changes, then run again and "Y" to apply

Gotchas & homelab notes

Heads-up: Keep iKVM/IPMI or physical access handy during any major OS upgrade.

  • NIC names may change with the newer kernel; check your network config if links don’t come up as expected. Consider proxmox-network-interface-pinning to pin interface names and update config.
  • Older hardware: Kernel 6.14 brings changes; test on similar kit if you’re running decade-old controllers.
  • Bootloader: If your system historically pulled the systemd-boot meta-package, remove it (Proxmox manages boot via proxmox-boot-tool).

New features worth trying next

  • S3-compatible datastores for budget-friendly offsite copies with caching to reduce API calls.
  • Live RAIDZ expansion to grow your pool gradually without a rebuild.
  • USB/offsite drive workflows using run-on-mount sync jobs for an easy 3-2-1 backup strategy.
The RTM Essential Stack - Gear I Actually Use

Watch out for this: If your PBS datastore is on ZFS, check the pool status before upgrading. A degraded pool combined with a version upgrade is asking for trouble. Run `zpool status` and resolve any issues first.

FAQ

Can I do this upgrade without an enterprise subscription?

Yes. Use the pbs-no-subscription repository (shown above). PBS is free and open-source; paid support is optional.

Will my existing backups still work after upgrading?

Yes. The datastore format remains compatible. Always keep a tested config backup and ensure you reboot into the new kernel.

What’s the safest way to handle the upgrade on a busy homelab?

Enable read-only maintenance mode on your datastores, complete the upgrade, reboot, verify services, then disable maintenance mode.

Do I have to use S3 in PBS 4.0?

No. S3 support is optional. You can continue with local/ZFS storage only and adopt S3 later for offsite/DR benefits.

My NIC name changed after reboot. What now?

Have out-of-band access ready. Update your network config to the new interface names or use the interface-pinning tool provided by Proxmox to keep names stable.

Written for homelab & hobbyist users. As always, make sure you’ve got verified backups before any major upgrade.

Read more at the official pages

Proxmox Backup Server 4.0 available

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