Latest revision as of 18:13, 17 July 2017

Tutorial: How to install GalliumOS on a Chromebook

Objective of this Tutorial

This Tutorial is aimed at people with limited or zero computer programming experience who wish to install Linux GalliumOS on their Chromebook. It is a step-by-step recipe that requires no knowledge in computer programming. Its scope is limited in that it doesn't intend to show you how to install any Linux distribution but only GalliumOS. Furthermore, the user should not attempt to install GalliumOS on a Chromebook that IS NOT on the GalliumOS Hardware Compatibility List. (See below in "Things to check first"). 

GalliumOS is one of the numerous Linux "distributions". A Linux distribution is a set of software packages with an installation program that allows the user not only to access his or her computer with Linux Operating System (OS) but also to complete most of the tasks that an average user is expected to do with computers (word, presentation and spreadsheet processing, audio and video playing and editing, Internet browsing, e-mailing, etc.). In that respect, it differs from "commercial" operating systems that don't provide much besides access to the computer system. Linux is the most advanced operating system in the world: as of November 2015, 494 or 98.8% of the 500 world's fastest supercomputers use the Linux kernel. (See https://en.wikipedia.org/wiki/TOP500)

GalliumOS is different from other Linux distributions in that it is designed for Chromebooks. But then, why would you want Linux on your Chromebook?

Why Install Linux on a Chromebook

Chromebooks are lean and mean computing machines that are designed to work in conjunction with the Internet. A Chromebook "keeps" hardly any software on its internal drive; what the user needs to complete a task is downloaded from Internet - often for a price - and is not kept inside the computer when the task is done. This is why most Chromebooks are equipped with a very small solid-state drive (SSD), typically 16 or 32 gigabits (GB). Often, this SSD is not upgradable and most of the time, the random-acess memory (RAM) is not upgradable either: Chromebooks' SSD and RAM are frequently hard-wired to the motherboard. With Linux installed on a Chromebook, applications stay inside the computer and can be accessed any time, with or without Internet. 

The often talked about constraint about installing Linux on a Chromebook is the SSD size. This SHOULD NOT be a deterrent when installing Linux. 16 GB is plenty to install GalliumOS; all your music, photos, videos and other paraphernalia that don’t fit on the static drive can go to an external drive. On all Chromebooks, you have the luxury of at least three ports: two USB and one SD. Without spending much, you could have at any given time 768 GB of memory on your Chromebook with three 256 GB external drives! Even a Thunderbird mail profile, for instance, can sit on an external drive without any significant speed penalty. All your Linux OS and programs can sit nicely on the 16 GB internal drive with room to spare. 

Furthermore, quite a few Chromebooks now can be upgraded with a larger capacity static drive. For a little investment, you could end up with a powerful laptop for a fraction of the price that you would normally pay for something other than a Chromebook.

Things to check first

You probably don’t want to venture into uncharted territory, so you need to do a few checks before you start converting your Chromebook computer to a GalliumOS Linux machine. There are many benefits with using Linux, notably the ability to run thousands of excellent applications without ever accessing the Net, but you have to be reasonably certain that your Chromebook will allow you to do that. The first place to find out whether your Chromebook is supported for a GalliumOS install is: https://wiki.galliumos.org/Hardware_Compatibility

Here are a few explanations about this table:

Model: The basic idea is that it is not advisable to attempt a GalliumOS install unless your Chromebook Model is listed in this table.

Hardware ID: The Hardware ID is something that you will read in your Chromebook when you create a Recovery Media for your specific model (see below). This is valuable information; write it down!

Processor Name: The Processor name (Sandy/Ivy Bridge, Bay Trail, Haswell, Broadwell, etc.) is something else you will need when you select the GalliumOS version you have to download. See: https://galliumos.org/download.html

Supports GalliumOS: Better be safe than sorry! Make sure that your Chromebook is supported by GalliumOS.

Firmware: That is one of the crucial changes that may, or may not, be required to make your Chromebook a GalliumOS Linux machine. The firmware modification requirement is indicated in the column titled “…with custom firmware?”. Fortunately, this firmware change is a fairly straightforward operation thanks to the work of John Lewis. Basically, it boils down to opening a terminal page in Chrome on your Chromebook (we will get to that) and writing, or copying and pasting, a short script.

(NOTE: Although there is still the possibility to dual-boot (GalliumOS and ChromeOS), this is not discussed here as it is assumed that the user has a limited, small static drive on which space doesn’t really allow two Operating Systems. In this tutorial, we will dedicate the entire drive space to Linux.)

I strongly suggest that you note all the data regarding the Model name, Hardware ID, Processor Name and Firmware modification requirement specific to your Chromebook. You will need it later.

Now that you have determined that you can give yourself the go-ahead for a GalliumOS installation on your Chromebook, let’s do first a little bit of house-cleaning and preparation.

Backup

You may have a few files on your Chromebook drive that you wish to keep. You should transfer all those files onto an USB flash drive or an SD drive. Remember that everything on your drive is going to be wiped out when you install GalliumOS Linux.

Chromebook Recovery Media

You need to create a Chromebook Recovery Media in case, further down the road, you wish to return your Chromebook to its original state. (See at the end of this Tutorial "Back to ChromeOS".) To do that, you need to download the Chromebook Recovery Utility from the Google Web Store (it is in your ChromeOS Menu). Once downloaded, the Recovery icon will also be in your ChromeOS Menu.

This software allows you to create a recovery media for your Chromebook. You need a 4GB USB flash drive or SD card that does not contain data that you want to keep because this drive too is going to be totally erased to receive the recovery data. 

Once the Recovery icon is in your Chromebook Launcher, click on it to start the Recovery Media creation process. Go past the first page by clicking on "Get started" to access the next page titled “Identify your Chromebook”. This page contains important information regarding your specific Chromebook model number. 

Your Chromebook Identity

There is a line that states: “For this Chromebook, enter XYZ XXX-XXX-XXX-XXX”.

Write down the MODEL NUMBER for YOUR Chromebook. It could be something like:

GNAWTY C2C-E3N-A2M

YUNA D21-A3B-L4A-A35

YUNA D25-B3B-B4A-A4M, etc.

Everything is important in this number, so keep it in a safe place; add it to the other info you already wrote down (Model, Hardware ID, Processor, firmware required, etc.). The first word could be something like: BANJO, CANDY, FALCO, GNAWTY, MONROE, PARROT, YUNA, etc. You notice that this first word is the Hardware ID that you have seen on the “GalliumOS Support by Model” table, that we have already talked about and is displayed at:

https://wiki.galliumos.org/Hardware_Compatibility

You need the whole number, not just the first word, to create a recovery utility; you also need the name if you ever need a “shellball” to bring your Chromebook back to its original state. We’ll get back to that, but for now, make sure you have this whole number kept somewhere.

In the "Identify your Chromebook" page of the Recovery Utility, the number we just talked about extensively is already written in blue in the Recovery window; just click on it and it will print automagically in the window below. But if you were to create a recovery utility for ANOTHER Chromebook, this is the window where you would enter the specific model number as outlined above. Since Google is nice to you, you could also select the Chromebook from a list that you call up by clicking on “Select a model from a list”. It is safer however to use the model number.

Click on Continue to proceed with the actual Media creation. Just follow the instructions.

Create your GalliumOS USB or SD installation drive

The Operating System you want to install, GalliumOS, must be available to you on a “bootable” USB or SD drive that you need to create. You therefore proceed to https://galliumos.org/download where you download the GalliumOS version appropriate to your Chromebook architecture (Haswell, Broadwell, Bay Trail, etc.). These are the Processor names that are displayed in the Hardware Compatibility List; you should have the name specific to your Chromebook available, if you wrote it down as was suggested earlier.

This GalliumOS installation file you download is an .iso file. The beauty of a file of this type is that you have on a single file all the bits and pieces required to install a Linux operating system with everything you need on a computer. Once this file has been downloaded, however, it needs to be decompressed and put on an USB flash or SD drive. To do that, it is recommended you use an application called Etcher that is available for Linux, Windows and Mac.  It can be downloaded at:

http://www.etcher.io/

Once Etcher is installed on your computer, you plug in an USB or SD drive and follow the instructions to create the install media. More detail can be found at Installing/Creating_Bootable_USB

Now, you should have two drives (USB or SB) to keep: one with your Chromebook Recovery Media; one with GalliumOS. Make sure you label them properly and don’t misplace or erase them.

Prepare the Chromebook

Select the procedure according to your Chromebook architecture

For this step, please see https://wiki.galliumos.org/Installing/Preparing This Wiki page explains how a Chromebook has to be prepared for installation according to the architecture of its processor (CPU). You notice that the architecture names (Sandy Bridge, Haswell, Broadwell, etc.) for which a specific installation is described are the same as the Processor names we already saw at https://wiki.galliumos.org/Hardware_Compatibility

If you followed our indications so far, your Chromebook architecture should have be noted somewhere.

For every architecture, the GalliumOS Installing/Preparing tutorial refers to SeaBIOS firmware. BIOS stands for Basic Input/Output System. It is a tiny – but very important – program (firmware) that tells your computer, among other things, where to look to find an operating system that will make it go. A special type of BIOS called SeaBIOS is required to install Linux on a Chromebook. Chromebooks with Haswell CPU architecture come with SeaBIOS already installed and you normally shouldn't have to worry about it. However, some bugs are reported in the SeaBIOS preinstalled on Haswell Chromebooks. (See https://wiki.galliumos.org/Firmware) It may therefore be advisable to install another version of the SeaBIOS on these machines. If you need to “flash” (replace) the BIOS firmware on your machine, you follow the procedure indicated in the Installing/Preparing tutorial. This is a delicate operation that you don't want to botch up as you may "brick" your Chromebook. ("Bricking" means that you make your computer worth no more than a brick of the same weight!) Luckily, John Lewis’ scripts to flash Chromebook BIOS makes it very easy. Before we get there, however, you need to put your Chromebook in developer mode.

Get into Developer Mode

The process to put the device in developer mode is very well described in the GalliumOS Installing/Preparing Tutorial. Just in case you are looking for the Refresh key, it is the 4th one from the top left; it shows a clockwise arrow. As indicated in the Tutorial, you need to hold the "esc" (escape) and Refresh key and start your Chromebook to begin the process of getting into Developer mode. The first page you see is the "scary one": "Chrome OS is missing or damaged. Please insert a recovery USB stick or SD card."

Scary, but informative!

Once your heartbeat is back to normal after having read this ominous warning, you can quietly read what else is written on this page. You notice on the last line, at the bottom of the page, the Chromeboook Model number. If you haven't written it down yet, as you should have, you get another chance to do it. (Got the message?). Now press "ctrl+D" (the letter "D" for "developer"). You get to another (less) scary white page which, again, shows the Model number. (Did I tell you this number is important?). But it also states that "To turn OS verification OFF, press ENTER." As it's written, "Your system will reboot and local data will be cleared". Go ahead, but it's your last chance to save your birthday photos on your Chromebook SSD! If you are not sure, press ESC.

Last chance to change your mind!

From now on, you let your computer do its thing. It first reboots and shows a big red exclamation mark.

Let your computer do its thing!

After 30 seconds, the Chromebook beeps twice and reboots, then you have another chance to change your mind and, after 30 seconds, it restarts again and prepares the system for Developer Mode.

Once you are in Developer Mode, your Chromebook is “rooted”; it means that you have access to the “root” of the computer system. It also means you have to tread carefully… Note that some older Chromebooks have a physical switch that you'll have to flip in order to turn on Developer Mode. If you aren't sure, look up instructions for your specific device on enabling Developer Mode.

It takes about 15 minutes to put your Chromebook into Developer Mode. When it's done, it reboots and you get the scary message again. Since you don't want to stare at it for 30 seconds, just press "ctrl+D" to get to your familiar ChromeOS Welcome screen.

In Developer Mode, your Chromebook still works normally. The only difference is a white window that is displayed for 30 seconds upon restart and that you can bypass by entering ctrl+D. After you are in Developer mode, it is suggested you configure your Internet access normally and enter your Gmail name and password, just to reassure you that your Chromebook is still alive and well. Also, for the continuation of the operation, you will need Internet access.

Remove the Write Protection, if required

The BIOS is write-protected through physical and software means. If you have a Sandy Bridge / Ivy Bridge or a Bay Trail Chromebook, you will have to remove the physical write protection. To do that, you have to open the computer and, generally, remove a screw. You will find the information on how to do that through a quick search in Google. 

Write-protection screw (circled in red) on an Acer Chromebook 15.

Access the “shell” and flash the firmware

Let’s assume now that you have restarted your Chromebook in Developer mode, entered your password and accessed the Chrome browser in your Chromebook. The next step is to open a Terminal window. This will take you to the heart of your computer. The Terminal is the screen that allows you to talk to the innards of your machine through commands and scripts. (Just like you see in the movies when the hacker is about to steal government secrets!) You can do all that in a Chromebook. (Not steal government secrets, but access a terminal window!) You just have to press CTRL+ALT+T. (Kind of an anticlimax, isn’t it?)

In this black terminal screen, at the prompt, you type: “shell” (without quotation marks) and hit Enter. From now on, follow the Preparing/Installing tutorial for your appropriate CPU architecture from the line where it is stated:

“and hit enter. Now you should be in bash. You’ll have a prompt that looks something like this.”

(NOTE: If your Chromebook has a Haswell architecture but you prefer to flash the BIOS, follow the procedure outlined for the Broadwell architecture.)

Follow John Lewis’ script carefully. I recommend that you cut and paste it into the terminal. Remember that the Terminal is just another tab in the Chrome browser; you can access any other Internet site in other tabs and flip through tabs to Cut and Paste whatever you want from one page to another page.

After John Lewis’ script has been run, you continue with the GalliumOS Installing/Preparing Tutorial with a little caveat. Where it states: “Reboot your computer, plug in your GalliumOS USB and start installing!”, it should be the other way round. You must first plug in your GalliumOS USB drive, then reboot your computer.

Install GalliumOS

When the Chromebook starts, a blue Unetbootin page comes up. It shows three options and states that you edit options with the Tab key. Actually, you don’t want to edit options at this stage; you only want to select one of them. You change selections with the Arrow keys and press Enter to select. I suggest you select the second one, “Gallium Live Image and Installer”. (Selecting "Default" is also fine; it does the same thing as the second option but it doesn't say so.)

Use the Arrow down key to select GalliumOS Live

In a few seconds, you get a beautiful display of a glass skyscraper shot from below. You also have a fully functional Operating System at your disposal but your SSD is untouched because this is a “Live USB” (or "Live SD"): you totally bypass your SDD drive to talk to your computer. You can configure your WiFi and browse the Net. You can open AbiWord text processor and write your biography. But this is not what you want right now: you want to install GalliumOS. Fortunately, at the top right of the screen, there is an icon that states – Would you believe? – Install GalliumOS. Just double-click on it and follow the instructions.

Just double-click on Install GalliumOS icon!

When it comes to the page titled “Preparing to install GalliumOS, a Warning pop-up windows may come up to inform you of an error. You can safely ignore. You then come up to the Installation type window. The choice here is easy: select the first option, “Erase disk and install GalliumOS”. The installation may take 15-20 minutes. Relax and let GalliumOS do its thing. 

An easy choice at last: Erase the disk!

GalliumOS is installed!

Now you have removed your GalliumOS installation USB drive and restarted your computer. The first thing you see is “Press ESC for boot menu.” You press ESC and the screen shows “Select boot device:” and a choice of devices. If there is no USB flash or SD drive plugged into your computer, you have only choice # 1, that is the computer SSD. If more than one device is displayed, select the one you know is your SSD. The type and the size should help you determine which the right one is. And if you make a mistake, no big deal: you just won’t start GalliumOS.

Once GalliumOS is opened, you will want to test the applications that come with it. You can also add other applications: you have tens of thousands applications to choose from! If you want to add applications, open Synaptic Package Manager that you will find in the Menu under System.

NOTE: Many Chromebooks have small screens. In Linux, it may happen that you are not able to see the bottom of a displayed window. This is particularly embarrassing if you have something to click on in that area. There is an easy trick: keep a finger on Left Alt and click on the window. As long as you keep the Left Alt key and the left mouse button pressed in, you can bring the window up or down, and move it around wherever you please.

Keyboard

GalliumOS is a fantastic Linux distribution tailored to Chromebooks. So, of course, the first thing to check is the keyboard because, as you know, the Chromebook keyboard is not standard.

Capital Lock Key

You may be from the "old school" like me and prefer to use the Chromebook Search key as a "Normal" Capital Lock key.

To get your Capital Lock back, you have to modify a file and create another one.

Besides being useful, this procedure will show you how easy it is to change things in Linux.

• Open Thunar File Manager. Under View, select "Show Hidden Files". Files that you were not aware of now show up in your Home folder.
• One of the file is ".bashrc". Notice the dot (.) before the file name. This dot is what causes this file to be hidden. Simple, isn't it?
• Right click on .bashrc and select "Open with Mousepad".
• When .bashrc is open in Mousepad, cut and paste the following lines at the bottom of the file.

if [-s ~/.Xmodmap]; then

xmodmap ~/.Xmodmap 

fi

• Save the file.
• Still in Mousepad, go to File and click on New.
• In this new document, just enter:

keycode 133 = Caps_Lock

• Save this file in your Home folder as .Xmodmap (Don't forget the "dot" before the file name!).
• Close Mousepad and Log out of your session and back in. Your Capital Lock key should now work "normally".

Note that an external keyboard plugged into your Chromebook through whatever connection (USB, Bluetooth, etc.) will work as it is supposed to do according to the particular model, even if you modify/create the configuration files as indicated above. (See below in "Chromebook Special Keys".)

Chromebook Special Keys

Once you have confirmed that your Capital Lock is working, go the GalliumOS Menu (Icon in the left hand corner of the Taskbar) and go to Settings, then to Settings Manager. In the Settings window, click on Keyboard (under Hardware). Select the tab Layout. Under "Keyboard model", select: "Chromebook | No overlay | F keys mapped to media keys". You now have a standard Chromebook keyboard with the exception of the Search key that is now a normal Caps Lock. You can use the special function keys normally (Full Screen, Brightness, Volume, etc.).

You can also use the Keyboard Model window to select an external keyboard you wish to use if you plug one in. If you don't find the exact keyboard model in the list, you may use one close enough (same manufacturer, similar performance, etc.). You can try and see until you find a model that fits your needs. You can always use your mouse to change your selection if your external keyboard has a strange behavior.

Mouse and Touchpad

You may also prefer to use a mouse because the touchpad may feel awkward to use for you and interferes with your typing. Many people prefer having the touchpad deactivated when they type. There is a simple solution called: Touchpad Indicator. To install this application, go to:

http://tipsonubuntu.com/2014/05/26/install-touchpad-indicator-ubuntu-14-04/

Follow the instructions, except that at the beginning, you won't access the terminal by entering Ctrl+Alt+T. But it's even simpler in GalliumOS: just click in the taskbar on the icon that shows an arrow head and a minus sign.

Once Touchpad Indicator is installed, you need to reboot the computer for the Touchpad-indicator to work. In the Menu, the application is under Accessories; click on it to start. It will put an icon in the right of the taskbar, in an area generally called the "tray". However, the icon may not be visible, depending on the Desktop theme you have selected. If you see what looks like an empty spot in the tray, it may well be the Touchpad indicator icon. Click on it and select Preferences. First go to Theme and select the icon on the right; the Touchpad-indicator icon should now be visible in the tray. While you are in Touchpad indicator Preferences, go to the Actions tab, and select "Disable touchpad when a mouse plugged" and "Enable touuchpad on exit". In General options, select "Autostart". With this configuration, the touchpad will be ON when you start the computer without a mouse and OFF when a mouse is plugged in.

Printers

Your printers may have been detected by Linux and configured. In the GalliumOS Menu, under System, select Printers. Click on Add. If you have one or more Network printers - that is the most probable scenario - just click on Network Printer and Find Network Printer. It may take a while (15-20 seconds), but the printers on your local network should be detected. If the system proposes a "generic printer" or if you cannot find the exact printer model in the list under the manufacturer's name, it means that the driver is not available in the present Linux kernel; however, it is most probably available on the manufacturer’s site. Just go to their site, enter your computer model and follow the instructions. Actually, as a rule, it always safer to check if there is a Linux driver on the manufacturer's site.

If you have downloaded a printer driver, or any other software for that matter, as a .deb file (the application file format in GalliumOS), you install it using GDebi. To do so, open your Thunar file manager (the icon on the taskbar that looks like a folder), go to the Downloads folder and find in there the file with the ".deb" suffix you just downloaded. Right click on the file icon and select "Open with GDebi package manager". Follow the instructions.

New Applications and Updates

You have thousands of applications at your disposal in Linux. You also have in GalliumOS a very easy and efficient tool to install applications: Synaptic Package Manager. In GalliumOS Menu, the Synaptic Package Manager is found under System. Just click on it, enter your password, search the application you need and, when it is listed in the window, right click on the window and select "Mark for Installation". You may have to Mark additional required changes (the system will ask you if you accept to do that), and you then click Apply. That's all.

If you want to install all updates that may have cropped up since your GalliumOS version first came out, you also use the Synaptic Package Manager. First, you click on All, in the left window, then on Reload, in the Icon bar, then on Mark All Upgrades, also in the Icon bar. You just have to click Apply, still in the Icon bar, and all your software will be updated.

File Transfer on Private Network

If you want to transfer files between computers on your own private network, through your own router, the easiest way is to install Nautilus file manager. Use Synaptic Package Manager to select and install the Nautilus application.

In Nautilus, you just right click on the folder you want to share and select Share on local network.

Office Suite

AbiWord is a simple and efficient application for word-processing. In AbiWord, you can open and save Microsoft^TM Office Word documents.

If you need a full Office Suite, look no further than LibreOffice, a free and open-source software. All the praise you may read on Internet about this Office Suite is well deserved.

In case you absolutely need the actual Microsoft^TM Office Suite, your option is to use Wine, an application that makes Windows applications "believe" they are in Windows OS. Wine per se is a bit tricky to configure; the user without a thorough knowledge of Wine may not obtain satisfactory results when attempting to use it. However, you will find in Synaptic Package Manager a front-end for Wine called PlayOnLinux that will make installing Windows application a breeze. Once installed in GalliumOS, PlayOnLinux comes in the Menu under Games (?!!). Installing Microsoft Office with PlayOnLinux is fairly straightforward. However, installing the updates or "Service Packs (SP)" may be a bit trickier, so here is how it goes.

Let's assume that you have installed MS Office 2007 with PlayOnLinux. You also downloaded the appropriate update from the MS site (SP3, in the case of Office 2007); it goes into your Downloads folder. You now open PlayOnLinux (in Games, remember?) and you click on the Configure icon. In the PlayOnLinux configuration window, you click on Office2007 (or whichever MS Office Suite you installed). You now click on the Miscellaneous tab and click on "Run a .exe file in this virtual drive". You select in Downloads the MS Office Service Pack .exe file and follow the instructions. Your MS Office 2007 will be updated as required.

If you really want to make it very simple, you may wish to install CrossOver Office by Codeweavers. (See https://www.codeweavers.com) This application is not free but it simplifies greatly the installation of Windows applications in Linux.

Back to ChromeOS

At some point, you may wish to return your Chromebook to its original factory state. This is a fairly simple operation as long as you read, understand, and follow the procedure below.

Restore the stock firmware

If you flashed your ChromeOS device's firmware to install GalliumOS, you may have to restore the stock firmware before resetting ChromeOS.

NOTE: if you used chrx to install GalliumOS, or only updated your device's RW_LEGACY firmware, then skip ahead to the next section as your device is still running the stock/factory firmware.

Regardless if you flashed your device with BOOT_STUB firmware, or a Legacy boot or UEFI Full ROM firmware, the easiest way to restore the stock firmware is with MrChromebox's ChromeOS Firmware Utility Script. Open a terminal window, then copy the URL to download/run the Firmware Utility Script and paste into the terminal window, then hit enter:

cd; curl -LO https://mrchromebox.tech/firmware-util.sh && sudo bash firmware-util.sh

On the main menu of the ChromeOS Firmware Utility Script, options will be available to restore either the stock BOOT_STUB firmware or the full stock firmware, depending on your device and type of firmware it is currently running. Select the option available for your device and follow the script's prompts/instructions. If you're restoring the full stock firmware, you will be prompted to supply your stock firmware backup on USB; if you don't have one, the script will supply a backup for you.

Once the stock firmware has been restored, chose the 'poweroff' (p) option from the script to shut down your ChromeOS device.

Use ChromeOS Recovery Media

Recovery Mode is a built-in boot mode of the stock ChromeOS firmware which allows for your ChromeOS device to be quickly and easily reset to factory-fresh state. You will need to create Recovery Media from another device using Google's ChromeOS Recovery Tool. The instructions for doing so can be found here.

Once the recovery media has been prepared, you need to boot your ChromeOS device into Recovery Mode. On Chromebooks, this is done by pressing ESC + Refresh + Power simultaneously. On Chromeboxes, normally there is a recovery button when must be depressed via paperclip (eg) at power on.

When booted into Recovery Mode, you will see a screen with an exclamation point and the text 'ChromeOS is missing or damaged.' At this point, simply insert the recovery media and your device will begin the recovery process. All data on the internal storage will be wiped, the normal ChromeOS partition layout will be restored, and any updated RW_LEGACY firmware will be reset.

NOTE: If you set the firmware boot flags (GBB Flags) using MrChromebox's Firmware Utility Script, those are *not* reset by the recovery process, and will need to be reset separately afterwards.

Resetting the Firmware Boot Flags (GBB Flags)

If you removed the firmware write-protect screw and set the Firmware boot flags / GBB flags (using MrChromebox's script or otherwise), they will likely need to be reset. This is easily done from a ChromeOS shell, but if your flags are set to boot in Legacy Boot mode by default, you may need to use CTRL+D to boot ChromeOS.

Once ChromeOS is booted to the login screen, open up a terminal via CTRL+ALT+F2 (forward arrow --> on a ChromeOS keyboard), then login as 'chronos'; no password is required. To reset the Firmware boot flags, simply type the command below, then press enter:

sudo /usr/share/vboot/bin/set_gbb_flags.sh 0x0

then reboot: sudo reboot

Exiting Developer Mode

Upon boot, simply press the space bar on the Developer Mode splash screen (OS Verification is Off). You will be prompted to confirm, and upon doing so the system will revert back to standard / verified boot mode, completing your transition back to stock. If pressing the space bar produces an angry beep, it means that your Firmware Boot flags are set to prevent exiting Developer Mode, and must be reset per the instructions above.

Conclusion: How much space left?

The major concern for a Chromebook user after installing GalliumOS is the amount of space left on the SDD. As initially mentioned, unless you have a large SSD because either you bought a top-of-the line Chromebook or you upgraded to a larger SSD, the usual SSD size on a Chromebook is 16GB. Normally, however, the data files (text, image, video, etc.) should preferably be stored on external drives when using a Chromebook. Still, as a matter of interest, I checked with GParted (available in Settings) the space used on my 16GB Acer CB3-111 after a GalliumOS installation; several applications were added and a complete OS update was performed. I have 5.74GB of free space left, that is more than 1/3 of the drive. But I have to mention that I installed more applications than I'll ever need! For instance, I installed the complete LibreOffice Suite AS WELL AS the complete Microsoft Office 2007 suite, with three grammar and spell-checkers (English, Spanish, French). I also installed Firefox AND Chrome on top of Chromium. So it may be safe to say that for about 90% of the average computer users, space should not be an issue on a Chromebook, provided external USB flash or SD drives are used to keep non-executable files.