Dual booting Elementary OS on a Chromebook is relatively easy as long as your Chromebook uses the SeaBIOS and is setup in developer mode. Elementary OS gives you a Mac OS X like experience on a Chromebook. To accomplish this task I used my HP 14 Chromebook and an external USB Drive.
Download the Elementary OS iso
If you have not already done so, download the Elementary OS iso.
Create a boot-able USB Drive with Elementary OS
Note: This step can be accomplished on any device running Linux however; in this case I did this directly on the Chromebook.
Once the Chromebook is in developer mode press CTRL + ALT + T to open the CROSH terminal. Run the shell command. This will enter you into a Linux terminal. You should then run df -h to determine what the path to your USB Drive is. For me it was /dev/sdb. At this point we have already downloaded the ISO image so all we need to do is run the command:
sudo dd if=/path/to/the/downloaded/iso of=/path/to/the/USB/device
(Example: sudo dd if=~/Downloads/Elementary OS.iso of=/dev/sdb )
Once the command is complete I recommend running:
sudo umount /path/to/the/USB/device
This took some time from the Chromebook; be patient and wait until it is finished or you may end up with a corrupt USB.
Restart and boot from USB
Ensure the USB Drive is in the USB 2.0 slot. For some reason It does not work in the 2 USB 3.0 Slots.
Reboot the Chromebook and at the Dev mode screen (The first screen that opens on reboot) press CTRL+L (legacy boot mode). This will bring you into the Boot menu. You need to quickly press ESC before it auto loads the primary drive. This will allow you to choose your boot device. From here press 2 (to select the USB Drive) and Elementary OS will boot from the USB Drive.
This was my second encounter with Elementary OS and overall it appears to be a well thought out distribution. I had some issues getting the wireless adapter and touch-pad working. Suspend also seemed to lock the machine. I will create a follow up post detailing how to fix these issues.