It is possible that you'll need to reinstall GRUB at some point after Window$ had force-upgraded itself, and apparently wiped any trace of your Linux installation. Or you might have installed Window$ after installing Linux, despite all the warnings, and now Linux is unbootable. Do not worry, your system is still there, and intact, only there is no way to boot into it just now.
If you encounter problems on an EFI this Debian Wiki article might have some solutions. Unfortunately (U)EFI implementations are random at best, mostly depending on the manufacturer. This Arch Wiki article has a good collection of vendor-specific (U)EFI implementations and their details, but you need to remember this is an Arch Linux specific page, so some commands might need to be changed for Debian.
Fortunately reinstalling the Grub bootloader is rather straightforward, and quick. All you need is your original Debian install CD, DVD or USB pendrive.
From the advanced menu, you will need to start the installer in "rescuse mode". There are two ways to do this, graphical, or CLI, just like when you have the installed Debian.
The installer will start, and go through the same steps as in normal mode. This means it will try to collect information about the hardware and even connect to the network. Don't worry, it will not install anything.
The next steps will be identical to the regular installation steps, in the following order:
After you've gone through these initial steps, you will be presented with a list of available partition. You will need to select the one on which your Linux installation's root filesystem is located.
A typical non-EFI Window$ installation would have created at least two partitions for itself, and if you went with the default options during the installation, your Debian system should occupy two. If that is the case, you should select the one before the last, and click Continue.
Or, ideally, you should remember the partitioning layout. The good news is, you don't actually have to. When you select a partition, the installer will look or an existing Debian (or other Linux) installation. If it cannot find one, you'll get the following error:
Click Continue to go back to the partition selector screen
You will then be presented with further choices:
There are a few options here, but one of them is called option called Reinstall GRUB boot loader. Can you guess which one you need to reinstall the GRUB boot loader?
You will then be explained what happens next. Typically, you would have installed GRUB on the MBR of the first disk. It's easy enough to assume that your first disk is called /dev/sda
because your first disk will be called /dev/sda
.
/dev/sda
into the input field, and click Continue. (Unless you've had GRUB (manually) installed somewhere else, in which case you should probably know what else to write there.)A progress bar will briefly appear, after which you will find yourself in the previous menu. Nothing will tell you that the installation succeeded, but if you are back where you've started from without an error message, you might as well assume it did.
The installer will start, and go through the same steps as in normal mode. This means it will try to collect information about the hardware and even connect to the network. Don't worry, it will not install anything.
The next steps will be identical to the regular installation steps, in the following order:
After you've gone through these initial steps, you will be presented with a list of available partition. You will need to select the one on which your Linux installation's root filesystem is located.
A typical non-EFI Window$ installation would have created at least two partitions for itself, and if you went with the default options during the installation, your Debian system should occupy two. If that is the case, you should select the one before the last, and press Enter.
Or, ideally, you should remember the partitioning layout. The good news is, you don't actually have to. When you select a partition, the installer will look or an existing Debian (or other Linux) installation. If it cannot find one, you'll get the following scary-looking error:
Select Continue with the Tab key if it's not already selected, and press Enter to go back to the partition selector screen.
You will then be presented with further choices:
There are a few options here, but one of them is called option called Reinstall GRUB boot loader. Can you guess which one you need to reinstall the GRUB boot loader?
You will then be explained what happens next. Typically, you would have installed GRUB on the MBR of the first disk. It's easy enough to assume that your first disk is called /dev/sda
because your first disk will be called /dev/sda
.
/dev/sda
into the input field, and press Enter. (Unless you've had GRUB (manually) installed somewhere else, in which case you should probably know what else to write there.)A progress bar will briefly appear, after which you will find yourself in the previous menu. Nothing will tell you that the installation succeeded, but if you are back where you've started from without an error message, you might as well assume it did.
And you're done. GRUB should be restored, your Debian installations should be bootable once again.