Instructions for write-protection screw access:
http://ausdroid.net/2015/03/12/chromebook-engineer-shows-of-the-pixel-2-innards-and-speaks-about-the-internals/

Part 1:  https://gist.github.com/bendavis78/827089ff8f2a8d8975ee
At Grub boot selection screen, TAB and append video=800x600 to get legible text size.
ChromeOS
From off:  ESC + F3 + Power.  CTRL+D then ENTER to get Dev mode.
Browser CTRL+T, "shell":
    sudo crossystem dev_boot_usb=1 dev_boot_legacy=1
DON'T DO THIS.  For dual-boot only (does not support btrfs):
[Reboot to Dev (CTRL+D)
    CTRL+ALT+F2
    chronos /
    sudo stop ui
    chronos /
    cd /
    curl -L -O http://goo.gl/9sgchs  # Verify downloaded. Unreliable site.
    sudo bash 9sgchs
]
Reboot on USB.  At dev-mode splash, CTRL+L to get SeaBIOS.

Install samus4 Kernel AS NON-ROOT:  yaourt* -S linux-samus4
 docs https://github.com/raphael/linux-samus

+X:
xf86-input-synaptics  Then write "/etc/X11/xorg.conf.d/25-touchpad.conf"
j from contents on web page.