If the shutdown of your computer is taking too long time, maybe it's because of the default timeout that is set to 90 seconds. You can change it like this: 

1. Open your terminal and write: 
<code>sudo xed /etc/systemd/system.conf</code>

2. Find #DefaultTimeoutStopSec=90s and change it to **DefaultTimeoutStopSec=4s**. \\
Remember to remove the "#". :)