crouton: Chromium OS Universal Chroot Environment

crouton is a set of scripts that bundle up into an easy-to-use, Chromium OS-centric chroot generator. Currently Ubuntu and Debian are supported (using debootstrap behind the scenes), but "Chromium OS Debian, Ubuntu, and Probably Other Distros Eventually Chroot Environment" doesn't acronymize as well (crodupodece is admittedly pretty fun to say, though).

"crouton"...an acronym?

It stands for ChRomium Os Universal chrooT envirONment ...or something like that. Do capitals really matter if caps-lock has been (mostly) banished, and the keycaps are all lower-case?

Moving on...

Who's this for?

Anyone who wants to run straight Linux on their Chromium OS device, and doesn't care about physical security. You're also better off having some knowledge of Linux tools and the command line in case things go funny, but it's not strictly necessary.

What's a chroot?

Like virtualization, chroots provide the guest OS with their own, segregated file system to run in, allowing applications to run in a different binary environment from the host OS. Unlike virtualization, you are not booting a second OS; instead, the guest OS is running using the Chromium OS system. The benefit to this is that there is zero speed penalty since everything is run natively, and you aren't wasting RAM to boot two OSes at the same time. The downside is that you must be running the correct chroot for your hardware, the software must be compatible with Chromium OS's kernel, and machine resources are inextricably tied between the host Chromium OS and the guest OS. What this means is that while the chroot cannot directly access files outside of its view, it can access all of your hardware devices, including the entire contents of memory. A root exploit in your guest OS will essentially have unfettered access to the rest of Chromium OS.

...but hey, you can run TuxRacer!

Prerequisites

You need a device running Chromium OS that has been switched to developer mode. Note that developer mode, in its default configuration, is completely insecure, so don't expect a password in your chroot to keep anyone from your data. crouton does support encrypting chroots, but the encryption is only as strong as the quality of your passphrase. Consider this your warning.

That's it! Surprised?

Usage

crouton is a powerful tool, and there are a lot of features, but basic usage is as simple as possible by design.

If you're just here to use crouton, you can grab the latest release from goo.gl/fd3zc. Download it, pop open a shell (Ctrl+Alt+T, type shell and hit enter), and run sh ~/Downloads/crouton to see the help text. See the "examples" section for some usage examples.

If you're modifying crouton, you'll probably want to clone or download the repo and then either run installer/main.sh directly, or use make to build your very own crouton. You can also download the latest release, cd into the Downloads folder, and run sh crouton -x to extract out the juicy scripts contained within, but you'll be missing build-time stuff like the Makefile.

crouton uses the concept of "targets" to decide what to install. While you will have apt-get in your chroot, some targets may need minor hacks to avoid issues when running in the chrooted environment. As such, if you expect to want something that is fulfilled by a target, install that target when you make the chroot and you'll have an easier time. Don't worry if you forget to include a target; you can always update the chroot later and add it. You can see the list of available targets by running sh ~/Downloads/crouton -t help.

Once you've set up your chroot, you can easily enter it using the newly-installed enter-chroot command, or one of the target-specific start* commands. Ta-da! That was easy.

Examples

The easy way (assuming you want an Ubuntu LTS with Xfce)

1. Download crouton
2. Open a shell (Ctrl+Alt+T, type shell and hit enter) and run sudo sh ~/Downloads/crouton -t xfce
3. Wait patiently and answer the prompts like a good person.
4. Done! You can jump straight to your Xfce session by running sudo enter-chroot startxfce4 or, as a special shortcut, sudo startxfce4
5. Cycle through Chromium OS and your running graphical chroots using Ctrl+Alt+Shift+Back and Ctrl+Alt+Shift+Forward.
6. Exit the chroot by logging out of Xfce.

With encryption!

1. Add the -e parameter when you run crouton to create an encrypted chroot.
2. You can get some extra protection on your chroot by storing the decryption key separately from the place the chroot is stored. Use the -k parameter to specify a file or directory to store the keys in (such as a USB drive or SD card) when you create the chroot. Beware that if you lose this file, your chroot will not be decryptable. That's kind of the point, of course.

Hey now, Ubuntu 12.04 is pretty old; I'm young and hip

1. The -r parameter specifies which distro release you want to use.
2. Run sh ~/Downloads/crouton -r list to list the recognized releases and which distros they belong to.

I don't always use Linux, but when I do, I use CLI

1. You can save a chunk of space by ditching X and just installing command-line tools using -t core or -t cli-extra
2. Enter the chroot in as many crosh shells as you want simultaneously using sudo enter-chroot
3. Use the Crosh Window extension to keep Chromium OS from eating standard keyboard shortcuts.

A new version of crouton came out; my chroot is therefore obsolete and sad

1. Check for updates, download the latest version, and see what's new by running croutonversion -u -d -c from the chroot (run croutonversion -h to see what those parameters actually do).
2. Exit the chroot and run sudo sh ~/Downloads/crouton -u -n chrootname. It will update all installed targets.
3. You can use this with -e to encrypt a non-encrypted chroot, but make sure you don't interrupt the operation.

A backup a day keeps the price-gouging data restoration services away

1. sudo edit-chroot -b chrootname backs up your chroot to a timestamped tarball in the current directory. Chroots are named either via the -n parameter when created or by the release name if -n was not specified.
2. sudo edit-chroot -r chrootname restores the chroot from the most recent timestamped tarball. You can explicitly specify the tarball with -f
3. If your machine is new, powerwashed, or held upside-down and shaken, you can use the crouton installer to restore a chroot and relevant scripts: sudo sh ~/Downloads/crouton -f mybackup.tar.gz

Unlike with Chromium OS, the data in your chroot isn't synced to the cloud.

This chroot's name/location/password/existence sucks. How to fix?

1. Check out the edit-chroot command; it likely does what you need it to do.
2. If you set a Chromium OS root password, you can change it with sudo chromeos-setdevpasswd
3. You can change the password inside your chroot with passwd

I want to install the chroot to another location

1. Use -p to specify the directory in which to install the chroot and scripts. Be sure to quote or escape spaces.
2. When entering the chroot, either specify the full path of the enter-chroot or start* scripts (i.e. sudo sh /path/to/enter-chroot), or use the -c parameter to explicitly specify the chroots directory.

Downloading bootstrap files over and over again is a waste of time

1. Download crouton
2. Open a shell (Ctrl+Alt+T, type shell and hit enter) and run sudo sh ~/Downloads/crouton -d -f ~/Downloads/mybootstrap.tar.bz2
3. Include the -r parameter if you want to specify for which release to prepare a bootstrap.
4. You can then create chroots using the tarball by running sudo sh ~/Downloads/crouton -f ~/Downloads/mybootstrap.tar.bz2

This is the quickest way to create multiple chroots at once, since you won't have to determine and download the bootstrap files every time.

Targets are cool. Abusing them for fun and profit is even cooler

1. You can make your own target files (start by copying one of the existing ones) and then use them with any version of crouton via the -T parameter.

This is great for automating common tasks when creating chroots.

Help! I've created a monster that must be slain!

1. The delete-chroot command is your sword, shield, and only true friend. sudo delete-chroot evilchroot
2. It's actually just a shortcut to sudo edit-chroot -d evilchroot, which I suppose makes it a bit of a deceptive swis-army-knife friend...still good?

Tips

• Chroots are cheap! Create multiple ones using -n, break them, then make new, better ones!
• You can change the distro mirror from the default by using -m
• Behind a proxy? -P lets you specify one.
• A script is installed in your chroot called brightness. You can assign this to keyboard shortcuts to adjust the brightness of the screen (e.g. brightness up) or keyboard (e.g. brightness k down).
• Multiple monitors will work fine in the chroot, but you may have to switch to Chromium OS and back to enable them.
• You can make commands run in the background so that you can close the terminal. This is particularly useful for desktop environments: try running sudo startxfce4 -b
• Want to disable Chromium OS's power management? Run croutonpowerd -i
• Only want power management disabled for the duration of a command? croutonpowerd -i command and arguments will automatically stop inhibiting power management when the command exits.
• Have a Pixel or two or 4.352 million? -t touch improves touch support.
• Want more tips? Check the wiki.

Issues?

Running another OS in a chroot is a pretty messy technique (although it's hidden behind very pretty scripts), and these scripts are relatively new, so problems are not surprising. Check the issue tracker and file a bug if your issue isn't there. When filing a new bug, include the output of croutonversion run from inside the chroot (if possible).

I want to be a Contributor!

That's great! But before your code can be merged, you'll need to have signed the Individual Contributor License Agreement. Don't worry, it only takes a minute and you'll definitely get to keep your firstborn, probably. If you've already signed it for contributing to Chromium or Chromium OS, you're already done.

If you don't know what to do with your time as an official Contributor, here's some suggestions:

• Really like a certain desktop environment? Fork crouton, add the target, and create a pull request.
• Feel like hacking around with Chromium OS integration? Fork crouton, improve integration, and create a pull request.
• Is your distro underrepresented? Want to contribute to the elusive and mythical beast known as "croagh"? Fork crouton, add the distro, and create a pull request.
• Discovered a bug lurking within the scripts, or a papercut that bothers you just enough to make you want to actually do something about it? You guessed it: fork crouton, fix everything, and create a pull request.

Are there other, non-Contributory ways I can help?

Yes!

But how?

There's a way For Everyone to help!

• Something broken? File a bug! Bonus points if you try to fix it. It helps if you provide the output of croutonversion when you submit the bug.
• Want to try and break something? Look through requests for testing and then do your best to brutally rip the author's work to shreds.
• Look through open issues and see if there's a topic or application you happen to have experience with. And then, preferably, share that experience with others.
• Find issues that need wiki entries and add the relevant info to the wiki. Or just add things to/improve things in the wiki in general, but do try to keep it relevant and organized.
• Really like a certain desktop environment, but not up for coding? Open or comment on a bug with steps to get things working well.
• Hang out in the #crouton IRC channel on freenode.net!

License

crouton (including this eloquently-written README) is copyright © 2014 The crouton Authors. All rights reserved. Use of the source code included here is governed by a BSD-style license that can be found in the LICENSE file in the source tree.