Make Grub Menu Appear for Dual Boot Systems

Open the grub config file:

sudo vim /etc/default/grub

Change the lines:

GRUB_TIMEOUT_STYLE=hidden
GRUB_TIMEOUT=0

to

GRUB_TIMEOUT_STYLE=menu
#GRUB_TIMEOUT=0

Exit the file, then run the command

sudo update-grub

So that the changes can be registered. If you have a drive with another OS on it, it should be detected and displayed in the grub menu the next time you boot up. Good luck!