Using Crouton, it is possible to install a second operating system on your chromebook.
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Pro Keeps Chrome operating system
This method will keep your chrome operating system installed; so you can use both on your device.
Pro Will not void warranty
This is a software method, no hardware will have to be modified, so your warranty will stay intact.
Con Developer Mode
In doing this method, you will have to put your chrome book in developer mode, while not a huge downside, some security considerations will have to be given to that fact. Developer mode on most chrome books are insecure by design.
Con Ram usage
Due to the nature of Chroots (what Crouton does) you will be running both Chrome OS and your Linux operating system of choice at the same time. On lower end chrome books this may cause issues with RAM usage.