Hey guys! Let me ask for some advice from you...

I have an EFI capable box with two storage devices:

1. /dev/sda: 500GB HD, GPT, 100GB for windows 10 and its weird partition scheme, 400GB ext4 for transitory stuff (mostly video editing).

2. /dev/sdb: 256GB SSD, MBR, a 100MB FAT32 partition for unencrypted initrd boot and the rest with LUKS+LVM scheme where my Slackware lives.

This box has legacy bios set. After POST, lilo takes over from MBR and loads initrd from /dev/sdb1/, then moves to LUKS+LVM for the rest of the boot process and user space stuff.

Now I want to boot with EFI. This will require a GPT partition. So I ask:

1. Can I use the GPT drive at /dev/sda?
2. Is it possible to make these changes, add something like elilo from /dev/sda and keep both Slackware and Windows 10 booting at same time I do not loose any data change the partition schemes I have now?
3. If so, what are the general steps to achieve that?

My goal is to move from bios/lilo to EFI/elilo withou losing or rewriting any of my data.

Thanks in adavnce. 😉

In reply to @drgibbon:matrix.org
ahhh, not much experience with dual booting these days sorry, I've been doing all Windows required stuff in VMs for quite a while since all I really need is Office from time to time. Hopefully someone else can help!

In reply to@drgibbon:matrix.org
My preference would be that MS Word / did not even exist.

Em resposta a @drgibbon:matrix.org
ahhh, not much experience with dual booting these days sorry, I've been doing all Windows required stuff in VMs for quite a while since all I really need is Office from time to time. Hopefully someone else can help!

Yeah, yeah. I feel you... I have this windoze part because it came preinstalled in the HDD. I've managed to shrink it and leave the space for more useful stuff, so why not? Over the time it proved useful more than once with GPS and coporate stuff that I was only able to perform in a full windoze env... Things that wine or a capped VM running in a modest box couldn't provide. So I just let it be, boot into it once in a while to apply upgrades and that's it.

Maybe it could prove useful again if I could use its GPT to dual boot into Slackware from UFI. 😉

Em resposta a @lioh:feneas.org
http://slackware.osuosl.org/slackware64/README_UEFI.TXT

I've managed to convert /dev/sdb from DOS to GPT partition table withou brake anything or losing any data. gdisk is the tool for the job. The tricky part was to make grub boot in pure EFI mode (no legacy or CMS). To accomplish that, I've downloaded Slackware64 -current live (the smallest one with XFCE), burned it to a USB pen drive with a GPT partition and set the box to EFI. This makes efivars available to the kernel. Only then I could setup grub in a way it gets recognised by EFI boot manager.

To intall grub in the EFI boot partition (/dev/sdb1 in my case):

grub-install --target=x86_64-efi --efi-directory=/boot --bootloader-id=GRUB
`

Then, to create grub menu entries:

grub-mkconfig -o /boot/grub/grub.cfg

It worked perfectly with my LUKS/LVM setup and also provides full display resolution framebuffer since POST, which means core penguins are back, there's no KMS flickering during whole boot and X (or wayland) kicks in with the proper display resolution. Nice!