There are other options for installing the additional features on a ChromeBook, I chose the approach that allows me to operate the Ubuntu utilities that I use/need in a Chrome Tab.

Step 1: Enable Developer Mode.

Generally Chromebooks are LOCKED DOWN and so installing additional features is limited. Here we specifically need to by-pass this.

Press and hold the <esc> and <refresh>; keys and then tap the power button.

This will enable 'recovery mode'. The recovery screen will guide you through setting Developer Mode. NOTE: if you proceed this will erase any data that you may have stored on your ChromeBook.

Pressing the <Ctrl-D> as instructed will enable Developer Mode. This will take some time, for me it was less than five minutes, but the system warns that it may be longer.

On ALL subsequent 'boots' of your ChromeBook you will be warned that you are operating in Developer Mode and requested to press <Ctrl-D> to proceed, or wait 30 seconds. Otherwise you can 'scrub' the changes and any data and revert to s standard, more secure ChromeOs.

Step 2: Get Crouton

Crouton can be collected from http://goo.gl/fd3zc. Just use the chrome browser to download this file which will collect the most recent version.

Step 3: Get to Shell

At the chrome browser press <Ctrl-T>. This will initiate the chosh shell, a very limited Linux shell, provided by ChromeOs.

At the chrosh shell enter the word 'shell' and press <enter>. This will invoke the more traditional Linux shell. (Note: this works only if Developer Mode is enabled.)

Step 4: Install

At the shell enter:
sudo install -Dt /usr/local/bin -m 755 ~/Downloads/crouton
sudo cp ~/Downloads/crouton /usr/local/bin
sudo sh -e /usr/local/bin/crouton -e -r focal -t xiwi,lxde
This will execute the file that you just downloaded and tell crouton that you wish to use the lxde desktop (-t) and an encrypted system (-e). Other desktops are available, but I like xfce. (The xiwi is required to allow for integration and operation in a tab.) .

The process will start and will take an extended period as crouton collects and installs all it needs. For me it took about ten minutes but it may be significantly longer, depending on the speed of your internet connection.

Step 5: Create 'Start A Session' Script

Create the batch file that will be used to start sessions by entering:
echo sudo startlxde >~/linux

Step 6: Execute the File

You may wish to test the script at this time by entering:
. ~/linux
The session that has just been started can be switched to and from using the <Ctrl-Alt-Shift-Forward> and the <Ctrl-Alt-Shift-Backward> keys. Note the Forward and Backward are the second and third function keys.

Step 7: Integrate Into Chrome

In the web browser visit the Crouton Integration page and install the extension.

Note: once this extension is installed the switching between ChromeOs and your linux session is no longer accomplished with the <Ctrl-Alt-Shift-Forward> and <Ctrl-Alt-Shift-Backward> keys, linux runs in a tab.

You Are Ready! On future boots of the system:

1. The system will require that you press <Ctrl-D> to remain in Developer Mode
2. When the system is up - in the browser enter <Ctrl-Alt-T> to get to the chosh shell
3. At the crosh shell enter
   shell
   to start the linux shell
4. At the linux shell enter:
   . ~/linux
   The system will start your linux session for you.
5. Enter your passphrase and the encryption passphrase that you set up when you created your partition when requested
6. To switch press <Alt-Tab> or the Crouton Icon that appears at the bottom of the screen.

NOTE: You can 'undo' this integration any time and 'scrub' the your machine by re-booting and instead of entering <Ctrl-D> press <enter>.

Backing up your chroot area is also a good idea, this is also performed at the chromeOs shell by:
sudo edit-chroot -b trusty

This backup CAN NOT be performed while crouton is running.