Startings of booting linux on Samsung chromebook plus

0) Back up chromebook plus
1) This procedure will erase the entire hard drive, so you have been warned!
2) Go into recovery mode by turning off chromebook, hold the esc key and the refresh key at the same time (7/8 circle with an arrow)
3) A prompt will pop up, type ctrl-d at the prompt - it will boot into developer mode

Now enable booting from an external microsd card:

1. After booting into developer mode, hold Ctrl and Alt and poke the T key. This will open up the crosh shell.
2. Type shell to get into a bash shell.
3. Type sudo su to become root.
4. Then type this to enable USB booting:

   crossystem dev_boot_usb=1 dev_boot_signed_only=0

5. Reboot the system to allow the change to take effect

Your chromebook plus can now either boot into chrome by typing ctrl-d at the first prompt upon startup, or it can boot into linux (installed onto a microsd) by typing ctr-u.  You will not be able to boot into linux until you install linux onto the microsd.

Here are some instructions, that need modifications because chromebook plus is not like other chromebooks:

https://archlinuxarm.org/platforms/armv8/rockchip/samsung-chromebook-plus

First off, the microsd mount point in the shell within chrome browser is: /dev/mmcblk1p1

I found this by typing the following command into the chrome browser and waiting about 20 seconds: chrome://system/, then scroll down to disk usage, and then click expand - this should list the mount points for all the system drives