# Ubuntu – Installation disk is always uefi

bootdual-bootlive-usbuefi

I try to install Ubuntu 16.04 next to Windows 10. Windows is installed on legacy bios and then upgraded to Windows 10. When I try to install Ubuntu from USB stick, it shows a message titled "Force UEFI installation?". It says that the machine's firmware started the installer in UEFI mode but there is an OS installed using BIOS compatibility mode. If I force installation I won't be able to boot Windows.

How can I start the installer in legacy mode?

BIOS of the machine supports legacy and UEFI modes. Legacy support is enabled. But USB disk is always recognized as EFI. USB disk's name is shown as "EFI USB Disk" in BIOS. I cannot change that. I burned the USB with both startup disk creator on ubuntu 14.04 and pendrive software on Windows. Same result.

Thanks.

• Prepare a BIOS-only boot medium -- If you prepare the USB flash drive in a way that omits the EFI boot loader, it can't boot in EFI mode. Some tools for preparing bootable USB drives, like Rufus, give you good control over the boot loaders included on the disk. Others don't, although you can usually delete the EFI boot loaders from prepared USB drives. (The key file is EFI/BOOT/bootx64.efi for an x86-64 system.) If you're booting from an optical disc, adjusting the boot loaders on it is much more complex.