I am having a problem doing this as the Ubuntu installer will not see any partitions except /dev/sda1 in the 3rd step when it asks for Installation Type:
EDIT from comments: In Windows 10, I shrinked current C partition used by Windows and made 40GB free for Ubuntu.
I followed number of articles and changed settings on Windows to disable Secure Boot and enable Legacy boot and that allowed me to boot from bootable USB with Ubuntu 14.04 on it.
Once I boot from USB, I get the menu to Test Ubuntu or Install it. I click on Test and that opens Ubuntu from where I can click on desktop M icon "Install Ubuntu". But that takes me only up to this step.
I have tried same with Ubuntu 15.10 (both are 64 bits as recommended for Windows 10).
Once in Test Ubuntu, here is what gdisk returns. Not sure if that can help though:
Best Answer
The first thing you should do is install windows 10. From there Using disk management you spit a portion of your harddrive and leave it as free space. Then with you efi bootable usb you run the linux install process. Make sure that the installer has launched in efi mode and not bios mode. To do this on the installation you can type [ -d /sys/firmware/efi ] && echo UEFI || echo BIOS If it launched in UEFI after you hit installation you should get the option to install Ubuntu alongside window.
So important things: