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.Volsung. : If you mean UEFI boot with secure boot disabled - it's relatively easy. New Debian installer (for Jessie) already supports setting up UEFI boot, though I didn't try using Jessie installer with UEFI yet, since when I was installing Debian on my computer with UEFI boot I was using Wheezy installer and that required way more manual steps.
In my case "Other OS" setting in the BIOS means that you are booting with UEFI (which for example requires to use grub-efi and to have EFI partition set up), but simply disables secure boot feature which requires signing your kernel and all the applications (never tried doing that, but it should be possible on Linux by now).
The basic idea for installation with the modern boot - use GPT partitioning (not MBR) and set the EFI partition as frist (it should be FAT32). See
https://wiki.archlinux.org/index.php/UEFI#EFI_System_Partition
Jessie installer should offer various automation for doing this I think. You can experiment with it using some empty hard drive in order not to ruin your working installation.
Just keep in mind, Debian testing can bork your EFI boot entries in the BIOS. Which happened to me recently with grub-efi-amd64 package upgrade. I had to unplug the hard drive (for some reason I had also hard time booting any live images), insert it into another computer and fiddle with the EFI partition to copy EFI/debian/grubx64.efi from there as EFI/boot/bootx64.efi
bootx64.efi is a default file picked by the EFI boot process if nothing else is known (that's the standard). Luckily in my case grub package created grubx64.efi properly, but it just wiped the boot entries in the motherboard flash memory. So copying that as a default fallback entry helped, and later I added grubx64.efi back using efibootmgr tool (in order to use it, make sure that you have efivars kernel module enabled. It can be done as:
And then using something like:
Code:
efibootmgr -c -l "\\EFI\\debian\\grubx64.efi" -L "Debian Linux"
Just be careful with that tool - it modifies motherboard memory to store boot entries. And don't panic if your computer doesn't boot
Most of the time things are fixable, but it can be annoying and required me some time to figure things out.
Situation can be worse when you have no proper *.efi file to boot at all. In such case you need to resort to a more elaborate trick. Insert your hard drive in any working Linux system (either live on the same machine or on another), and mount your partitions for chroot access. And then chroot into your broken system and rerun grub-install and update-grub. Make sure to do that properly, like for example provide the disk device for grub-install. I once forgot to do it and it also borked my boot ;D
Here is an example:
http://www.sysresccd.org/Sysresccd-Partitioning-EN-Repairing-a-damaged-Grub
(Though they for some reason forgot to mention that you also should run update-grub).