Hello, I have a weird problem. I successfully use one bootable USB to install Debian/Grub2/EFI to a second, blank USB. After installation, the USB boots to Debian in multiple reboot and full shutdown cycles. Then, I boot into Windows once without the USB target inserted, shut down, and the target USB no longer boots.
I am blind, so I cannot review any on-screen messages at boot-time. I will describe my setup, install and troubleshooting steps. Motherboard: Asus Maximus VIII GENE; Chipset: Intel Z170 I have two built-in hard drives, /dev/sda and /dev/sdb. According to the partition utilities, I have a non-EFI, or legacy, boot sector (partition type 07, not EF) on /dev/sda1. I do not want to modify the bootloader on /dev/sda. I start with a Debian ISO image and use the Rufus tool to make a bootable USB from Windows. The target USB is also inserted. The installation USB boots (two beeps) and I use the Debian text installer to install Debian to the target USB. During the installation, the target USB is at /dev/sdc and the installation media is at /dev/sdd. The Debian documentation says that two beeps means an EFI boot. After install, I can boot and reboot from the target USB multiple times, and I have a wonderful Linux system to work and play with. If I remove the target USB, boot into Windows from a cold boot, then immediately shut down, then re-insert the target USB, Linux no longer boots. I still boot into Windows. There are no beeps with the target USB inserted. While I am running Linux, the target USB is still at /dev/sdc. I ran a few checks [1]: # [ -d /sys/firmware/efi ] && echo "EFI boot on HDD" || echo "Legacy boot on HDD" EFI boot on HDD The EFI system partition (/dev/sdc1) is in fact mounted at /boot/efi. Reinstall the grub-efi package: # apt-get install --reinstall grub-efi # grub-install /dev/sdc # update-grub There is in fact a file at /boot/efi/EFI/debian/grubx64.efi # efibootmgr --verbose | grep debian There was a line displayed. I am really stumped here. I can boot the Debian install USB (syslinux bootloader) on demand, but if I boot into Windows once, the target USB with Grub doesn't boot anymore. I could desparately use some hints. Alan [1] https://wiki.debian.org/GrubEFIReinstall
