Ubuntu Installer doesn't detect Windows 10

Solution 1:

Make sure that you have turned off quick startup in Windows and do a full shutdown by holding shift when you click shutdown to disable quick startup. If you dont do this, the Windows partition cannot be mounted by linux to see that there is a Windows partition.

Solution 2:

I solved this issue for my own laptop after many hours. My problem was that the existing Windows installation used UEFI boot mode. So when I used rufus to install the Ubuntu 16.04 ISO image onto a USB memory stick, I needed to choose the "UEFI (non CSM)" option (rather than BIOS/legacy boot which was the default in rufus).

Then I had to boot my laptop from the USB drive (which in my case required first booting into BIOS setup mode and adding a temporary boot option for the USB drive), then install Ubuntu from the USB drive.

Only by installing Ubuntu in EFI mode was I able to get the Ubuntu installer to recognise the existing Windows installation and get it to create a dual boot menu with Windows and Ubuntu on it.

To check if Ubuntu is running in EFI mode (e.g. in try without installing mode), look in the /sys/firmware folder and there will be an EFI file if it is. Otherwise its running in legacy mode.

Solution 3:

I know this is too late for OP, but for anyone googling, for me it was secure boot being the issue. I tried to disable secure boot initially via the BIOS, but for some reason the option was hidden behind CSM (which I later googled and found out meant Compatibility Support Module) which I disabled, and then I could disable secure boot. I was then allowed to install Ubuntu alongside Windows.