Grub2

To see the grub menu on boot, edit the default grub config and decomment the following line:

1
2

vim /etc/default/grub
#GRUB_HIDDEN_TIMEOUT=0

This is the default setting with only one identified operating system.

By the way, to force Grub 2 to show the menu on boot just hold down the Shift key while Grub is starting.