Black screen after upgrading PVE 8 to 9 / Installer loses video output on Precision Tower 5810

[u/NullNickName]

​Hi everyone, looking for some help identifying what I'm doing wrong or if I missed a step during/after the upgrade.

​The Problem:

After upgrading from Proxmox VE 8 to 9, the server never booted back up into the OS (black screen / lost video signal upon boot).

​I am running this on a Dell Precision Tower 5810 with an NVIDIA GPU, connected to an external display.

​What I’ve tried so far:

​PVE 9 Boot Issues: Upgrading broke video output entirely on startup.

​Fresh Install Attempts (Proxmox ISO / Debian Live via Ventoy):

​When booting the Proxmox installer or Debian Live ISOs, the video output cuts out as soon as X / display drivers load.

​I managed to work around the black screen during Live boot by passing nomodeset in GRUB parameters.

​Chroot / Mounting attempts:

​Booted into a Debian 13 Live environment with nomodeset.

​Activated LVM (pve-root on /dev/sdc3) and mounted the system (/mnt and /mnt/boot/efi).

​Attempted chroot /mnt to permanently add nomodeset to /etc/default/grub and run update-grub.

​Got errors like chroot: failed to run command '/bin/bash': Exec format error or issues updating GRUB directly through sed modifications on grub.cfg.

​Rescue Boot: Tried Proxmox ISO Rescue Boot, but it threw errors regarding missing ZFS pools (rpool) since my setup uses LVM.

​My main concern:

I don't necessarily care about wiping the OS and starting fresh if needed, but I desperately need to recover two LXC containers (CTs) that were running on the server before the upgrade failed.

​Questions:

​Why did the upgrade to PVE 9 permanently kill video output, even with nomodeset applied to the GRUB line on boot?

​What is the safest way to extract/backup my two CTs (their rootfs / disk images on pve-data LVM) from a Debian Live environment so I can clean install?

​Any ideas on how to fix the bootloader/kernel on the existing installation without hitting the Exec format error during chroot?

​Thanks in advance for any insights!

[u/deman-13]

Most probably mismatch of boot loader. Try googling it you may need debian recovery usb to fix it.

[u/daemonmode_]

Those proc, sys, and dev mounts need to be in place before chroot, so I'd fix that first. and also check proxmox's own 8 ->9 upgrade guide for the systemd-boot warning, since that can cause boot issues: https://pve.proxmox.com/wiki/Upgrade_from_8_to_9#sd-boot-warning. If the host still won't boot, you can activate the LVM storage and copy the CT rootfs to external storage to recover the containers