Installing/Creating Bootable USB
Creating bootable GalliumOS media is very similar to other Linux distributions. Unfortunately, that doesn't mean it's easy. The goal of this guide is to make it as straightforward as possible.
First, you need to download the GalliumOS iso for your Chromebook.
Once the iso is finished downloading (you MUST wait for it to finish), open up your favourite Terminal emulator.
cd to the place where you downloaded the iso. It's probably ~/Downloads.
Plug in your USB device, identify it, and unmount it. This is a little tricky. You can use
lsblk to get a list of storage devices attatched to your system. Try to find out which one is your USB flash drive. It is very important to not get this wrong, as it could cause catastrophic data loss. Once you've figured it out, make sure the USB flash drive is unmounted.
sudo umount -f /dev/sdb1
Be sure to replace sdb1 with the actual partition name as listed in lsblk. Next, use dd to copy the ISO to the USB flash drive.
dd bs=1M if=galliumos.iso of=/dev/sdb
Be sure to replace galliumos.iso with the filename of the iso you want to write. Usually typing "galliumos" and hitting tab will autocomplete it for you. Also be sure to replace sdb with the actual device as listed in lsblk. Make sure to write to the DEVICE and NOT the partition. This process can take a long time depending on the speed of your flash drive, USB connection, and hard drive. Be patient. Once the prompt comes back, the ISO should be written. If you're getting errors, try adding sudo to the beginning of the command. Before you unplug your flash drive, be sure to run
On Mac OS X
This process is very similar to Linux, but not identical. I will write a proper guide as soon as I have access to a Mac.
Windows is a little tricky. I will write a few guides once I have access to a Windows box.