Dual boot Linux and windows (separate disks) using Grub2 SHOULDN'T BE THIS TRICKY
ISSUE: has the grub menu disappeared? does your system boot straight into windows? Explanation Each disk has its own OS, and efI bootloader 1) Linux bootlader (xubuntu) is sda1 2) Windows 10 bootloader is sdb2 Now, the grub2 files that matter are: /etc/default/grub in which you need to make sure GRUB_TIMEOUT_STYLE=menu and doesn't say GRUB_TIMEOUT_STYLE=hidden This makes sure you see the grub menu and /etc/grub.d/40_custom (see https://linuxvox.com/blog/grub-config-file-ubuntu /) where we add our extra menu option for Windows 10 (see https://askubuntu.com/questions/661947/add-windows-10-to-grub-os-list ) viz: type lsblk to identify your windows EFI partition, then blkid /dev/sda1 (with the partition /dev name) to find the UUID of the EFI (call that YOUR_WIN_EFI_UUID) then FINALLY, the code to add in the /etc/grub.d/40_custom\ is menuentry 'Windows 10' { search --fs-uuid --no-floppy --set=root YOUR_WIN_EFI_UUID chainloader (${root}...