For some reason, I can't reply to my previous post as it's marked as locked:
Latest XPS BIOS updates 2.4.2 & 2.5 will cause rebooting issues, and overwrite GRUB if you are using it for a Linux dual-boot system.
Over a month later and still no fix. As I also mentioned, downgrading the BIOS firmware to an older version is not possible.
Thanks Dell Update, for breaking a previously perfectly working system and not allowing a BIOS downgrade!
The recent BIOS update also stopped my XPS15 from booting with GRUB. I was able to restore GRUB by entering the BOOT MENU (i.e. holding the F12 key down when DELL flashed on the screen while booting the computer). From the BOOT MENU, I was able to select the GRUB MENU after a bit of trial and error since the GRUB MENU was named after the USB stick I had used to install Ubuntu Linux rather than being called GRUB. Once I was in Linux, I was able to fix GRUB by running the following command: sudo grub-install.
Before the update, I also had a problem in which I couldn't Shutdown my computer from Windows, although I was able to Restart and enter GRUB. To fix this problem, I had to turn off the FAST STARTUP option in Windows. The following is one way of finding the FAST STARTUP option:
Settings->System->Power & sleep: Additional power settings
Choose what the power buttons do->Change settings that are currently unavailable:
unselect "Turn on fast startup (recommended)"
select "Save changes"
I was able to restore GRUB as well, but if I restart in Windows it is deleted again.
One option of course is to avoid restarting, which is OK until Windows decides to install updates ...
My current solution is moving Linux to a VM, which works, but not as well.
I had the same issue on my XPS 9550. I fixed it with the help of this thread. It's so disappointing. I love my XPS, but these Linux-related issues are disheartening. I go to a lot of It&Tech conferences and I see a lot of ppl with XPS laptops there. And guess what? They never use Windows unless they are .NET engineers! This is an amazing machine and is a great match for Tech professionals. Dell should really pay more attention to Linux support.
Anyway, to sum it up: what worked for me is:
1) Add another boot option in the Boot Sequence in BIOS.
2) Disable Secure Boot.
Thanks for your reply.
I have always had SecureBoot disabled.
I'm afraid I still have this problem - I am indeed able to restore Grub2 and my partition fine, but if the machine reboots, it gets deleted!