In-Place Upgrade Proxmox VE from 7 to 8 🌱

💡 NOTE: These steps are for a single standalone Proxmox server. They have not been tested in a clustered environment

🚨 WARNING: Make sure to create external backups of all important VMs and CTs just in case something goes wrong. You've been warned.

1. Log into Proxmox VE, either at the console or the web UI and launch the web shell
2. Stop all running VMs and CTs
3. Run the following commands to make sure Proxmox VE is running the latest 7 updates
   # disable proxmox commmercial repo
   sed -i "s/^deb/\#deb/" /etc/apt/sources.list.d/pve-enterprise.list
   # add the proxmox community repo
   echo "deb http://download.proxmox.com/debian/pve $(grep "VERSION=" /etc/os-release | sed -n 's/.*(\(.*\)).*/\1/p') pve-no-subscription" > /etc/apt/sources.list.d/pve-community.list
   # update software repositories
   apt update
   # install software updates
   apt dist-upgrade -y
   # clean apt cache
   apt clean
   # run the upgrade checklist utility, resolve any issues reported before continuing
   pve7to8 --full
   # update apt repositories to bullseye
   sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list && sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list.d/pve-community.list && sed -i 's/bullseye/bookworm/g' /etc/apt/sources.list.d/pve-enterprise.list
   # update software repositories
   apt update
   # install software updates
   apt dist-upgrade -y
   # clean apt cache
   apt clean
   # reboot
   reboot now
4. That's it, Proxmox VE has now been updated to the latest v8.x

Source and Additional Info: https://pve.proxmox.com/wiki/Upgrade_from_7_to_8