Chromebooks with Android apps can be rooted now thanks to the aroc project recently posted to GitHub by developer nolirium. On the surface, rooting a Chrome OS device may seem mostly pointless since it runs as a subsystem underneath the browser-based operating system. That eliminates quite a few of the reasons many users choose to root a piece of hardware in the first place. Customizing the U.I. of the system using a ROM isn't necessarily going to accomplish much. However, there are still quite a few useful Android-specific changes that can be made with root access that wouldn't be easily done without it. For starters, users gain access to root-specific applications and while not every app works in Chrome OS, that could make it easier to save space by moving applications to an SD card or gaining access to the full Android file system. There are also a few more practical uses such as accessing deeper keyboard layout customizations. That's helpful in countries where a non-U.S. keyboard is more familiar but where some applications use the U.S. layout.
Getting started is easy enough; users need to ensure their Chromebook is running in developer mode and has at least 2GB of space available for a relatively large file download. Developer mode is accessible in the settings menu, hidden under the gear icon on the right-hand side of the app shelf. From there, tapping the three dash hamburger icon at the top and then navigating to "About Chrome OS" will allow users to switch channels under the "Detailed build information" section. Then, the rootfs verification checker needs to be disabled to prevent the system from blocking the root process. Nolirium's guide provides two easy ways to accomplish that. From there, the files to update can be either downloaded in advance for offline installation or installed directly via a few relatively straightforward terminal scripts. There's also a single shell command which will go through each script automatically to save time.
As always, there's no guarantee that everything will work as intended after rooting and some issues are known to exist. The scripts have been tested in Chrome OS versions 54 through 67. So the process should work on most devices running the latest version available as long as Android apps are supported but it really isn't possible to test all devices. Precautionary steps such as creating a backup to be restored in the event that things are broken should be taken since any future OS update could break everything and Chrome OS updates on a very frequent basis. Some non-English fonts are also broken by the root. Some Mods simply aren't supported and that includes one of the more popular ones, Xposed.