Grub

Setting the default runlevel in Ubuntu 16.04

Mapping between runlevels and systemd targets

Runlevel / Target

0: poweroff.target
1: rescue.target
2, 3, 4: multi-user.target
5: graphical.target
6: reboot.target

To change runlevel:

sudo systemctl isolate multi-user.target

To set the default runlevel:

sudo systemctl enable multi-user.target
sudo systemctl set-default multi-user.target

Adding Operating Systems to Linux grub bootloader

Open a new terminal
Execute the following commands:

sudo os-prober		#this will search for the OSs
sudo update-grub	#this will update your grub bootloader