I am installing Ubuntu (latest version 64 bits) on Macbook Pro 2015. Before Ubuntu, I have already installed Win 10 using bootcamp, and I am installing Ubuntu on an external hard-drive. At the Ubuntu installation page, I have clicked install boot-loader to the external hard-drive (/dev/Sdb) as well.
But here comes the problem. Every time when I start my Macbook after a shutdown, it will automatically going into the GNU Grub command line.
If I do
grub>exit, then it will boot into Mac-OS.
If I hold "Alt option" key during boot-up, I will see only two systems: Mac and Windows. No Ubuntu.
I have to select Windows and then select Ubuntu in order to get into the linux system. The boot-loader setup must have been messed up. How do I fix this?