Now that was hard to find. Had to get the full manual at https://pve.proxmox.com/pve-docs/pve-admin-guide.html and search for update.

Better update first to 8.4.9. Then the upgrade pve8to9 is available.

Run "pve8to9 --full"

There is "Update Debian Base Repositories to Trixie" to do the first line, if you like me, does not have enterprise updates.

Then the update shows a long list... update. Keyboard and few things more, restart services... bla bla bla... Debian 13...

A side note from me: Proxmox is not Vmware. If it really wants for people to move to Proxmox, put the update process to be simple. Nobody in a company will do this manual update, it is too complex and dangerous. Make it possible for us to test this in lab and feel confortable to do it in production.

But the upgrade was done by the web interface. Reboot... nothing, errors.

Check update, still had loads of updates to do. Did second time and now it booted.

But stand a few times booting the kernel, had to turn off the server.

Like I was suspecting, dangerous updates... reconsidering Proxmox even for my lab.

There were many erros during upgrade, that probably are because of Debian, not Proxmox. At least one service openipmi fails. I have to check this out.

End of log.