Unity already comes with several keyboard shortcuts, but you can customize these shortcuts or even create new ones through Ubuntu's own graphical interface. The simple procedure: 1. Click the gear icon in the upper right corner next to your user name. 2.Click System Settings (Will open Ubuntu Control Panel) 3.In Hardware section, click keyboard 4.In Keyboard Properties, click 'shortcuts' tab 
In this part you can edit any system shortcut and create your own, to create a new shortcut, click the last option in the left column, "Custom shortcuts"
Clicking the "+" button will open this dialog box from the image above, enter the name of your shortcut and the command it should execute when triggered, in which case the shortcut is being configured to open the system monitor with the command. gnome-system-monitor.
Okay, your shortcut has been added, just now just choose which keys will open the command you typed in the previous step, at the top right of the frame, there is a line written 'disabled' indicating that your shortcut is not working yet .
Double-click this sentence and then press the keys you want to be used as a shortcut to the command.
In this example I used the combination, Alt + M, so each time I press, "alt + M" on my keyboard will open the system monitor.
A hug, see you next time.
