Ttyjfyk

I read here, once, that installing a Debian 9 on a pendrive (well, in my case it's a SDCard adapter) directly would work, and it did. The problem came up, though, after i unplugged the adapter from the computer; when i wanted to boot into linux, all i had to do was to choose the boot device labelled 'UEFI: debian' on the bios setup, but as soon as i removed the adapter, that option disappeared.

I don't want to lose the debian installation, I want it working again. Could someone help me getting it booting again?

This smells like a BIOS problem. You've missed some information out of your question so I'm going to assume somethings:

• 
  UEFI: debian appears in a BIOS menu after install (not a grub menu)


• When you unplug and re-plug the USB drive, the BIOS no-longer shows UEFI: debian even after reboot
  


• Your main hard disk uses EFI to boot your other operating system (Windows?)

It would be very difficult to give a direct solution without knowing a lot more about your BIOS. However the problem might be something to do with you having two EFI partitions; one on your internal HDD and one on your USB disk.

It may be possible to manually remind your BIOS about the USB EFI entries when you plug back in, but I couldn't tell you how.

A possible work around might be to copy your EFI entry from your USB drive onto your internal hard drive. This will be easier from Debian (if you can get back into it) but it can be done on windows.

EFI entries are basically just a few files in a directory on your EFI partition. So all you would need to do is to mount your internal HDD's EFI partition and copy the one from your USB drive (usually mounted to /boot/efi/EFI/debian)

My guess is that the root file system (with the Debian operating system) is damaged.

This can happen

• if the drive is unplugged before the operating system is fully shutdown or




• if connected when another operating system is running, you unplugged it without unmounting all partitions on the drive.

You can connect the drive to a computer running linux and try to repair the file system(s).

• Make sure that all partitions on the SD card are unmounted




• Repair the root file system on the SD card (and other file systems, that belong to Debian, for example home, if there is a separate home partition.



• 
  

  Run the following command line for each of these file systems (I assume ext4 here, modify if you use another file system),

  
  
  

  sudo e2fsck -f /dev/sdxn
  

  
  
  

  where x is the device letter for the SD card and n is the partition number, so for example /dev/sdb2

  
  

It is also possible, that Windows damaged the boot system for the SD card via USB. This can happen, if the card was connected, when you booted Windows or when Windows was running some update/upgrade process.

If this is the case, you can find methods to 'repair grub' or 'repair boot' via the internet. I know methods for Ubuntu, and I think but am not sure that the same methods work for Debian.

Please notice that the first part about damaged file systems and the second part about Windows damaging the boot system are describing independent problems. I don't know enough about your particular problem to be able to tell which of the problems that is affecting your Debian system on the SD card.