Background

On August 05, 2025 – Leading open-source server solutions provider Proxmox Server Solutions GmbH (henceforth “Proxmox”), celebrating its 20th year of innovation, announced the release of Proxmox Virtual Environment (VE) 9.0. The main highlight of this update is a modernized core built upon Debian 13 “Trixie”, ensuring a robust foundation for the platform.

While on August 6, 2025 – Proxmox announced the release of Proxmox Backup Server (PBS) 4.0. The main highlight of this update is a modernized core built upon Debian 13 “Trixie”, just like Proxmox Virtual Environment (VE) 9.0, as well as expanding its backup options by introducing native support for S3-compatible object storage.

The release post for Proxmox Virtual Environment (VE) 9.0 can be found here on the Proxmox website, while the release post for Proxmox Backup Server 4.0 can also be found here on the Proxmox website.

Preparation

It goes without saying but before embarking on the upgrade you should read the section on “Known issues” on the Proxmox Wiki page for upgrading Proxmox 8 to 9.

I also recommend running the following command to run through some pre-upgrade checks recommended by Proxmox…

pve8to9 --full

Once you are satisified that you can safely proceed with the upgrade you MUST BACKUP all LXC containers and KVM Virtual Machines (VM’s) on the Proxmox node being upgraded.

If you haven’t run a full BACKUP on all your containers and VM’s AND you haven’t TESTED your backups you’re in for a VERY bad time if the upgrade fails.

I’ve simplified the process down to 3 main steps described below but again I recommend reading the official upgrade wiki page before beginning.

Step 1: Update the current Node

NOTE: All these instructions are based on my experience following the instructions on the official upgrade wiki page.

To upgrade to the latest “Trixie” based versions of Proxmox you MUST update your Node to the current latest version. This is very simple and can be achieved by running the following commands from a Shell as root

/usr/bin/apt update
/usr/bin/apt dist-upgrade -y
/usr/bin/apt autoremove -y

This may take a while depending on how often you update your Proxmox Nodes. At the time of writing this should upgrade the node to 8.4.9.

Step 2: Update apt to new repositories

Proxmox Virtual Environment (VE) 9 and Proxmox Backup Server (PBS) 4 both move the apt configuration from the old-style .list format to the new deb822 format so we need to create some new .sources files for the upgrade.

Common Debian Repository

To create the new Debian repository sources file simply run the following command as root…

cat > /etc/apt/sources.list.d/debian.sources << EOF
Types: deb
URIs: http://deb.debian.org/debian/
Suites: trixie trixie-updates
Components: main contrib non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg

Types: deb
URIs: http://security.debian.org/debian-security/
Suites: trixie-security
Components: main contrib non-free-firmware
Signed-By: /usr/share/keyrings/debian-archive-keyring.gpg
EOF

Create the Enterprise repositories

To enable the Enterprise Repositories file simply run the following commands as root…

# Remove the # from ONE of the following lines depending on the Node type.
#PROXMOX_TYPE=pve # Proxmox Virtual Environment
#PROXMOX_TYPE=pbs # Proxmox Backup Server

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

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

“No subscription” Users Only AKA Homelabbers

There are a few extra steps required in order to enable the “No Subscription” repositories and disable the Enterprise repositories.

These changes can be done simply by running the following commands as root…

# Remove the # from ONE of the following lines depending on the Node type.
#PROXMOX_TYPE=pve # Proxmox Virtual Environment
#PROXMOX_TYPE=pbs # Proxmox Backup Server

echo "Enabled: false" >> /etc/apt/sources.list.d/${PROXMOX_TYPE}-enterprise.sources
echo "Enabled: false" >> /etc/apt/sources.list.d/ceph.sources

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

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

Remove old repositories.

We now need to remove the old “Bookworm” repositores in order to upgrade safely. Failure to do so will corrupt the apt cahce resulting in a broken and possibly unbootable system.

This can be done simply by running the following commands as root…

> /etc/apt/sources.list
rm /etc/apt/sources.list.d/*.list

NOTE: This will also remove any custom repositories added to the system. Custom repositories should only bve added AFTER the upgrade and a clean reboot.

Step 3: Update the current Node

With all that preparation complete we can now upgrade to the latest “Trixie” based versions of Proxmox. To do this simply run the following commands from a Shell as root

/usr/bin/apt update
/usr/bin/apt dist-upgrade -y
/usr/bin/apt autoremove -y

This WILL take a long time to run. Several questions will be asked along the way.

In my experience upgrading my 3 Proxmox servers I chose the following.

• I chose NOT to restart services
• I chose NOT to overwrite /etc/issue
• I chose NOT to overwrite /etc/lvm/lvm.conf as it is based on how your node is installed.
• I chose not to overwrite /etc/apt/sources.list.d/pve-enterprise.sources as I’m using the “No-Subscription” repositories.
• Once the upgrade was complet I rebooted the Node to ensure all services were running the new versions.

That being said I’ll leave it to your own judgement as to how to answer those questions based on your particular setup.

Semi-automated Script

I also created a simple script, which encapsulates the 3 steps outlined above, to automate the process as much as possible.

The script will set the system for the “No-Subscription” repositories by default.

If the script is to be run on a Proxmox node with a licence then create a file called /etc/default/proxmox-setup with the following contents…

PROXMOX_ENV=LIVE

This file MUST be created BEFORE running the upgrade script.

Then, to run this script simply run the following command as root…

bash -c "$(wget -qLO - https://github.com/alandoyle/proxmox-setup/raw/main/upgrade-proxmox)"

Conclusion

Overall the process is really simple. Although, my setup is very simple so thnakfully I’ve managed to update all 3 of my Proxmox Virtual Environment Nodes from 8.4 to 9.0 without issue.