repair grub after installing windows

https://www.youtube.com/watch?v=Zr9oyWjD6IA
https://askubuntu.com/questions/88384/how-can-i-repair-grub-how-to-get-ubuntu-back-after-installing-windows

1. use ` sudo fdisk -l` to find efi and main linux partition
2. Mount linux partition to mnt. `sudo mount /dev/sdxy .mnt` and then mount efi partition to `/mnt/boot/efi`. `sudo mount /dev/sdab .mnt/boot/efi`.
3. chroot to /mnt to access linux partition and then `update-grub`. Though most probably have to do this step too `grub-install /dev/sda` sda here but it have to be the drive where efi is  installed
4. finally exit and reboot

and if installed distri is arch based then
while in chroot do following
`grub-mkconfig -o /boot/grub/grub.cfg`
then
`grub-install --target=x86_64-efi --efi-directory=/boot/efi --bootloader-id=GRUB`