Ubuntu won't detect windows 10 when I try to install it, so I'm assuming it is because my BIOS is not in UEFI mode, but rather, in Legacy mode. Is there any way for me to still be able to install ubuntu alongside my windows installation?
2 Answers
Well, I am a new 'Ubuntuan' (permit me to use that word) too!
This is my first answer on the forum, I hope to give it a good try.
From what you said, i presume you have a working windows 10 OS!
Download the Ubuntu ISO image from the Ubuntu website here.
Download Rufus to setup a USB drive to be used as boot manager.
Open rufus after download
Select the drive you want to install on.
Select the partition scheme for both legacy and UEFI modes
Leave file system and cluster size as default
In the Create bootable disk using
option, select ISO Image, then click the icon beside to pick the Ubuntu ISO Image you downloaded.
Then click start
to start the operation.
You should know when the process is done.
However, due to Windows Fast Boot options, your computer might boot directly into Windows 10 without booting from the Ubuntu Boot manager you created (Which i assume is connected to your system). You can force your system to load your external drives by Reordering the Boot Options in your BIOS setup. And some computers will give you access to select which drive to boot from when you press a specific key (mostly F12 or ESC key) immediately your computer powers on.
Then select the USB Bootable manager you created, and UBUNTU should load then. Follow the download process to install Ubuntu and enjoy freedom for life! Thanks.

- 56
Correction
@philsegeler 's comment in the question is not true.
Windows 10 supports both UEFI and Legacy mode. You need to check your Windows installation BIOS mode following this answer.
Answer
You need to boot Ubuntu image from Generic Flash Disk (NOT UEFI: Generic Flash Disk) in BIOS boot option to install alongside with Windows in Legacy mode.
According to the documentation, the Secure Boot is only available in UEFI. If you have Windows in Legacy mode, I think you don't need to turn that off in your BIOS setting. As you could see the "Secure Boot State" in System Information Utility will be "Unsupported".
-
If I use a Ubuntu Installation usb, I should find 'Generic flash disk' from BIOS menu ? I installed Ubuntu in UEFI and windows is in BIOS, now I can't boot to any... Is there a way to boot back to windows? – June Wang Jan 10 '21 at 06:08
@philsegeler I see, thank you! And you too!
– Dominik H Jan 09 '16 at 23:39