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— Written by Triangles on September 12, 2017 • updated on September 23, 2018 • ID 56 —
Having multiple OSes on a single machine is convenient. It is also great to choose what OS to boot on startup.
Lately I went through the struggle of installing Debian alongside a pre-existing Windows 10 on a UEFI-powered machine (Acer Aspire E15). The Debian installation went fine, but I wasn't able to boot into Debian: no OS selection menu came up upon boot. What to do?
Different tutorials on the Net suggest different routes. In general, you need to tweak two things before installing Debian: disable the fast startup on Windows 10 and disable secure boot in UEFI.
Fast startup is sort of partial hibernation of files and data. Unfortunately this creates a problem when you want to copy stuff from Debian to Windows. So let's disable it:
Secure boot is a way to stop malicious software to replace your boot loader. Unfortunately this makes Linux difficult (or impossible) to install. How to disable it:
Now you can install Debian as usual. Once finished, the new OS will be correctly installed but not yet accessible at startup. So head back to the UEFI settings (i.e. reboot and press F2) and in the "Security" tab select select an UEFI file as trusted for executing, as shown in picture 2. below. Here you are telling UEFI that there's another OS to take into account.
The interface will display a directory: browse it down until you find a file named
BOOTx64.EFI, then select it. You will be able to choose a name too: that's what will be displayed in the boot order list later on.
The menu seen in picture 2. might be greyed out. If so, temporarily re-enable the secure boot as you did in the previous point: it should unlock the menu. Remember to disable secure boot once finished.
Save, exit and restart.
Take a look at picture 1. above: you will see how my boot order still gives priority to Windows Boot Manager (#9) over Debian (#10). Unfortunately the Windows Boot Manager is unable to see other OSes such as Debian and the like. If you leave it as it is you will boot straight into Windows 10 with no OS selection. You need to switch to grub, the smarter Linux boot loader which is able to handle a wider selection of operating systems.
To change that, enter the UEFI settings again (reboot + F2) and flip the boot order of Windows Boot Manager with EFI File Boot 0: Debian. Save and exit. This way, the next boot you will be prompted with the OS selection managed by grub.