I use kde neon and dual boot into windows every now and then, well my laptop receives firmware updates and I decided to get those updated on windows. I haven't had good luck on the linux fwupdate... Well it hosed my efi, windows boot still worked but my linux side was no longer booting. Thanks windows updates for forcing me to do them.
I scoured the internet for a solution. I tried boot-repair, no go. I downloaded KDE Neon live iso, put it on a usb and then finally found a solution.
I mounted the necessary folders and then chrooted into the mnt. I noticed my /boot was readonly..thats odd., unmounted it and ran
sudo dosfsck -t -a -w /dev/sda1 <--change /dev/sdx to your /boot partition disk
Then do this:
/dev/sda8 in this example is the / partition
/dev/sda1 in this example is the efi partition
sudo mount /dev/sda8 /mnt sudo mount /dev/sda1 /mnt/boot/efi for i in /dev /dev/pts /proc /sys /run; do sudo mount -B $i /mnt$i; done sudo chroot /mnt grub-install /dev/sda update-grub
This might help someone, it's definitely a bookmark for me.