Proxmox Update 8 to 9 does not boot anymore - black screen

Problem

After I updated my Asus/Intel NUC from proxmox v8.4.14 to 9.1.6, it did not boot anymore. I followed the instructions of https://pve.proxmox.com/wiki/Upgrade_from_8_to_9 and used the update checker tool:

1. Update checker with pve8to9 
   --> all green ✅
2. Updated from 8.4.14 to 9.1.6 complete using this 
   --> GUI & CLI showed new version ✅
   --> VMs and Containers continued to run normally ✅
3. Reboot 
   --> does not boot anymore ❌
4. BIOS Update of the Asus/Intel NUC did not help ❌

Solution

I found Dustin Rues awesome blog entry: https://dustinrue.com/2025/12/recovering-from-a-failed-proxmox-upgrade/

1. Boot from live linux via USB stick (in my case linux mint)

2. In the live linux terminal, run the following commands:

mount /dev/mapper/pve-root /mnt
mount /dev/sda2 /mnt/boot/efi
mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount --bind /proc /mnt/proc
mount --bind /dev/pts /mnt/dev/pts
chroot /mnt
mount -t efivarfs efivarfs /sys/firmware/efi/efivars
grub-install --target x86_64-efi --no-floppy --bootloader-id proxmox /dev/sda
grub-install --target x86_64-efi --no-floppy --bootloader-id proxmox --removable /dev/sda
echo 'grub-efi-amd64 grub2/force_efi_extra_removable boolean true' | debconf-set-selections -v -u
apt install --reinstall grub-efi-amd64
update-initramfs -u -k all

Once this finished I did the following

umount /mnt/dev/pts
umount /mnt/proc
umount /mnt/dev
umount /mnt/sys/firmware/efi/efivars
umount /mnt/sys
umount /mnt/boot/efi
umount /mnt/
reboot

Example

root@mint:~#
root@mint:~#
root@mint:~# mount /dev/mapper/pve-root /mnt
root@mint:~# mount /dev/sda2 /mnt/boot/efi/
root@mint:~# mount --bind /dev /mnt/dev
root@mint:~# mount --bind /sys /mnt/sys
root@mint:~# mount --bind /proc /mnt/proc
root@mint:~# mount --bind /dev/pts /mnt/dev/pts
root@mint:~#
root@mint:~# chroot /mnt
root@mint:/#
root@mint:/# mount -t efivarfs efivarfs /sys/firmware/efi/efivars/
root@mint:/#
root@mint:/# grub-install --target x86_64-efi --no-floppy --bootloader-id proxmox /dev/sda
Installing for x86_64-efi platform.
Installation finished. No error reported.
root@mint:/#
root@mint:/# grub-install --target x86_64-efi --no-floppy --bootloader-id proxmox --removable /dev/sda
Installing for x86_64-efi platform.
Installation finished. No error reported.
root@mint:/#
root@mint:/#
root@mint:/# echo 'grub-efi-amd64 grub2/force_efi_extra_removable boolean true' | debconf-set-selections -v -u
info: Trying to set 'grub2/force_efi_extra_removable' [boolean] to 'true'
info: Loading answer for 'grub2/force_efi_extra_removable'
root@mint:/#
root@mint:/# apt install --reinstall grub-efi-amd64
The following packages were automatically installed and are no longer required:
  bsdmainutils                    libdav1d6               libllvm15               libpython3.9-stdlib  perl-modules-5.32                   python3-soupsieve
  gcc-12-base                     libdns-export1110       libmpdec3               librav1e0            perl-modules-5.36                   python3-talloc
  libabsl20220623                 libdrm-nouveau2         libnsl-dev              libsubid4            proxmox-kernel-6.8.12-1-pve-signed  python3-tempita
  libapt-pkg6.0                   libdrm-radeon1          libnumber-compare-perl  libsvtav1enc1        pve-kernel-5.15                     python3-tz
  libavif15                       libfile-find-rule-perl  libopts25               libtext-glob-perl    pve-kernel-5.15.126-1-pve           python3-waitress
  libboost-context1.74.0          libflac12               libperl5.32             libthrift-0.17.0     pve-kernel-5.15.158-2-pve           python3-webtest
  libboost-coroutine1.74.0        libfmt9                 libperl5.36             libtiff5             python3-bs4                         python3.11
  libboost-filesystem1.74.0       libglusterd0            libprocps8              libtirpc-dev         python3-jaraco.classes              python3.11-minimal
  libboost-iostreams1.74.0        libicu67                libprotobuf23           liburing1            python3-ldb                         python3.9
  libboost-program-options1.74.0  libicu72                libpython3.11           libwebp6             python3-paste                       python3.9-minimal
  libboost-thread1.74.0           libisc-export1105       libpython3.11-minimal   libx265-199          python3-pastedeploy                 sgml-base
  libbpf0                         libjs-sencha-touch      libpython3.11-stdlib    libxcb-dri2-0        python3-pastedeploy-tpl             telnet
  libcbor0                        libldap-2.5-0           libpython3.9            libzpool5linux       python3-pytz                        usrmerge
  libcbor0.8                      libleveldb1d            libpython3.9-minimal    lua-lpeg             python3-singledispatch
Use 'apt autoremove' to remove them.

Installing:
  grub-efi-amd64

REMOVING:
  grub-pc

Summary:
  Upgrading: 0, Installing: 1, Removing: 1, Not Upgrading: 0
  Download size: 46.7 kB
  Freed space: 349 kB

Continue? [Y/n]
Get:1 http://download.proxmox.com/debian/pve trixie/pve-no-subscription amd64 grub-efi-amd64 amd64 2.12-9+pmx2 [46.7 kB]
Fetched 46.7 kB in 0s (398 kB/s)          
Preconfiguring packages ...
(Reading database ... 119801 files and directories currently installed.)
Removing grub-pc (2.12-9+pmx2) ...
Selecting previously unselected package grub-efi-amd64.
(Reading database ... 119792 files and directories currently installed.)
Preparing to unpack .../grub-efi-amd64_2.12-9+pmx2_amd64.deb ...
Unpacking grub-efi-amd64 (2.12-9+pmx2) ...
Setting up grub-efi-amd64 (2.12-9+pmx2) ...
Installing for x86_64-efi platform.
File descriptor 3 (pipe:[43286]) leaked on vgs invocation. Parent PID 3806: grub-install.real
File descriptor 3 (pipe:[43286]) leaked on vgs invocation. Parent PID 3806: grub-install.real
Installation finished. No error reported.
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-6.17.13-1-pve
Found initrd image: /boot/initrd.img-6.17.13-1-pve
Found linux image: /boot/vmlinuz-6.8.12-17-pve
Found initrd image: /boot/initrd.img-6.8.12-17-pve
Found linux image: /boot/vmlinuz-6.8.12-1-pve
Found initrd image: /boot/initrd.img-6.8.12-1-pve
Found linux image: /boot/vmlinuz-5.15.158-2-pve
Found initrd image: /boot/initrd.img-5.15.158-2-pve
Found linux image: /boot/vmlinuz-5.15.126-1-pve
Found initrd image: /boot/initrd.img-5.15.126-1-pve
Found linux image: /boot/vmlinuz-5.4.203-1-pve
Found initrd image: /boot/initrd.img-5.4.203-1-pve
Found linux image: /boot/vmlinuz-5.4.73-1-pve
Found initrd image: /boot/initrd.img-5.4.73-1-pve
Found memtest86+ 64bit EFI image: /boot/memtest86+x64.efi
Found memtest86+ 32bit EFI image: /boot/memtest86+ia32.efi
Found memtest86+ 64bit image: /boot/memtest86+x64.bin
Found memtest86+ 32bit image: /boot/memtest86+ia32.bin
Warning: os-prober will not be executed to detect other bootable partitions.
Systems on them will not be added to the GRUB boot configuration.
Check GRUB_DISABLE_OS_PROBER documentation entry.
Adding boot menu entry for UEFI Firmware Settings ...
done
Processing triggers for man-db (2.13.1-1) ...
root@mint:/#
root@mint:/#
root@mint:/# 
root@mint:/# 
root@mint:/# 
root@mint:/# 
root@mint:/# update-initramfs -u -k all
update-initramfs: Generating /boot/initrd.img-6.17.13-1-pve
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-6.8.12-17-pve
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-6.8.12-1-pve
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-5.15.158-2-pve
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-5.15.126-1-pve
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-5.4.203-1-pve
W: zstd compression (CONFIG_RD_ZSTD) not supported by kernel, using gzip
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
update-initramfs: Generating /boot/initrd.img-5.4.73-1-pve
W: zstd compression (CONFIG_RD_ZSTD) not supported by kernel, using gzip
Running hook script 'zz-proxmox-boot'..
Re-executing '/etc/kernel/postinst.d/zz-proxmox-boot' in new private mount namespace..
No /etc/kernel/proxmox-boot-uuids found, skipping ESP sync.
root@mint:/#
root@mint:/#
root@mint:/#
root@mint:/# exit
exit
root@mint:~#
root@mint:~# ls /mnt
bin  boot  dev  etc  home  lib  lib64  lost+found  media  mnt  opt  proc  root  run  sbin  srv  sys  tmp  usr  var
root@mint:~#
root@mint:~# umount /mnt/dev/pts
root@mint:~# umount /mnt/proc
root@mint:~# umount /mnt/dev
root@mint:~# umount /mnt/sys/firmware/efi/efivars
root@mint:~# umount /mnt/sys
root@mint:~# umount /mnt/boot/efi
root@mint:~# umount /mnt/
root@mint:~#
root@mint:~# reboot