Run the pve8to9 script first to do some sanity checks (it should already be installed if the system is up to date).
Update the box to latest 8.x with apt update etc. Change the package sources to the new ones and update the system.
The packages databases can be a bit confusing: You have two lots - stock Debian and Proxmox (enterprise OR no-subscription).
Stock Debian is in the single file /etc/apt/sources.list - change "bookworm" to "trixie".
Proxmox sources is in a file in /etc/apt/sources.list.d/ Remove all of the Proxmox related ones you have there and run this (or do it yourself with an editor). This example is no-sub - the official doc notes the enterprise equivalent:
cat > /etc/apt/sources.list.d/proxmox.sources << EOF
Types: deb
URIs: http://download.proxmox.com/debian/pve
Suites: trixie
Components: pve-no-subscription
Signed-By: /usr/share/keyrings/proxmox-archive-keyring.gpg
EOF
Job done.
I had put off the upgrade for a while figuring it would be a breaking change. But it went so smoothly I’ll probably be upgrading to 9.1 pretty soon.
I was (still am sadly) a VMware consultant for about 25 years. It makes me laugh when I hear breathless "enterprise noises" with regards VMware and how PVE isn't quite ready yet.
PVE is just so easy and accommodating. It's Linux on Debian with a few nobs on. The web interface is so quick and uncluttered and simple. The clustering arrangements are superb and simple. The biggest issue for me and many like me was how to deal with iSCSI SANS (no snapshots - long story) It turns out you can pull the SSDs out of a Dell Msomething SAN and wack them into the hosts and you have a hyperconverged Ceph thingie with little effort.
VMware rapidly gets very expensive. Nowadays with Broadcom you have to fork out for the full enterprise thing to get DRS and vDS - that's auto balancing clusters and funky networking. PVE gifts you Open vSwitch support out of the box and all clusters are equal. Storage DRS (migrate virty hard discs on the fly) is free on PVE too. Oh and you get containers too on PVE - VMware Tanzu is seriously expensive.
Anyway, I could grind on about this for quite some time but in my opinion, PVE is a far better base product in general for your VMs. A vCentre is a horrendous waste of resources and the rest of VMware's appliances are pretty tubby too. I recall evaluating their first efforts at SDN with edge firewalls and so on - no thanks!
too bad SUSE is doing the rancher prime stuff now as well.
In the end, Proxmox is based on KVM and KVM does run a workload or two across the world. VMware isn't KVM and I watched both be born and grow up oh and I should mention Xen but I can't be arsed. Most of the rest are Johnny come latelys.
If I need a massive cloud then I'll go all in on K8s or whatever and get my orchestration hat on big time but for my needs and my customer needs, PVE is more than enough, whilst being just enough.
5 host cluster; rebooted them all at completion and all of the containers came back up without issue (combination of VMs and LXC)
Im still on 8.x -- it was a fun way to consolidate my different hacky projects -- home assistant, frigate, wireguard, qbittorrent etc
Kinda scared to think of what it would take to upgrade to 9.1 :)
https://www.hackerneue.com/item?id=45980005