This article is translated from Chinese to English by ChatGPT. There might be errors.

I recently bought a small J1900 mini PC to give to a friend as a soft router. As usual, I tried to install Proxmox on it, but ran into an issue I’d never seen before: when the progress bar reached 100%, it threw this error: failed to prepare EFI boot using Grub on '/dev/sda2': unable to install the EFI boot loader on '/dev/sda'. I then spent the whole afternoon wrestling with it before finally fixing the problem.

After searching the web and trying various suggestions, none of the following worked:

  • According to this thread, I tried running rm /sys/firmware/efi/efivars/dump-* to free up efivarfs space, but I found there were no dump-* files at all on my machine, and efivarfs still had 60% free space, so it was probably unrelated
  • Used wipefs and dd to completely clear the partition table and file systems
  • Tweaked various BIOS parameters
  • Reset BIOS settings to default
  • Opened the mini PC and tried to locate NVRAM-related jumpers, but couldn’t find any (idea inspired by this thread)
  • Gave up on EFI boot and tried using CSM instead, but CSM couldn’t even boot the installer

After digging into it for quite a while, I could almost conclude that the BIOS of this industrial PC has a bug that causes EFI boot entry writes to fail. In the first thread mentioned above, a guru in reply #15 provided a manual boot installation method: the idea is to use the default EFI boot file BOOTX64.EFI, so the system can boot normally even without writing EFI boot entries. However, step 4 of his procedure requires entering Rescue boot, which I simply couldn’t access from the installer, so I got stuck again.

In the end, the problem was solved thanks to a clutch hint from ChatGPT, which suggested using chroot. After some trial and error, it worked. Here are the exact steps:

  1. First install PVE as usual; it will throw an error at the end. Reboot into the installer again, then press Ctrl+Shift+F3 to enter the console.

  2. Run the following commands to mount the file systems on the hard drive (assuming the default partition layout):

    vgchange -ay
mount /dev/pve/root /mnt
mount /dev/sda2 /mnt/boot/efi
mount --bind /dev /mnt/dev
mount --bind /proc /mnt/proc
mount --bind /sys /mnt/sys
chroot /mnt

  3. Then follow the guru’s steps from the thread:

    cp /boot/efi/EFI/proxmox/grubx64.efi /boot/efi/EFI/BOOT/BOOTX64.EFI
cp -r /boot/grub/x86_64-efi /boot/efi/EFI/BOOT/
grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=proxmox --removable --recheck
update-grub

After rebooting, the system can boot normally. Many thanks to the forum guru and to ChatGPT. 🙏