Replace Chrome OS permanently with Ubuntu 16.04 "Xenial Xerus" on the Acer C720 Chromebook.
Running a full-featured Linux on this little laptop is a delight: lightweight, several hours battery life, inexpensive, and snappy performance. I started with Debian, followed by Lubuntu 14.04 and Arch, and now running happy with Ubuntu + i3 tiling window manager.
This device is available in a few different configurations. Mine is the non-touchscreen model C720-2848 with (non-expandable) 2GB RAM and a (user-replaceable) 16GB SSD .
0. Recovery Image
Create a recovery image of Chrome OS (my C720 is model PEPPY C6A-N3C-A7O) to enable restoring the Chromebook to its default configuration. This will require a spare USB stick of 2GB or better:
- Log into the Chromebook and let it auto update, as there sometimes are firmware updates... check the updating status in the browser at chrome://help
- Insert the USB stick, enter chrome://imageburner and follow the directions to generate a recovery image
1. Prepare install media
Alternative: Add the image to a USB stick with multiple Linux installers.
SeaBIOS in combination with coreboot provides an open-source legacy BIOS that enables access to the MBR and the ability to install an alternative OS on the Chromebook. All this good stuff involves jumping through a few simple hoops and not trembling in fear at the "scary white screen" that pops up at power up stating that the boot loader detects something is very very wrong with the Chromebook and helpfully suggests pressing the spacebar to begin recovery. Do not press the spacebar or the Ubuntu installation will be wiped from disk!
There are 2 different methods for configuring SeaBIOS in preparation for installing Ubuntu. The first method uses a few simple commands in the Chrome OS shell to place the Chromebook into developer mode and allow booting the USB install media and replacing Chrome OS with Ubuntu. The drawback is that scary screen appears at every boot and you must press CTRL+L to boot to legacy-mode and onward to GRUB and Ubuntu (and ignore the helpful prompt to press spacebar and inadvertently begin the adventure of wiping clean the SSD).
The second method involves setting new flags for the write-protected Google Binary Block (GBB) in the device firmware. Delay at the boot screen can be reduced to a one second timeout and the legacy-mode BIOS set as the system default (no key combo required). Pressing the spacebar is disabled from doing any harm to Ubuntu (the Chromebook just beeps). The drawback is that it involves the (very simple) removal of the device's bottom cover and the temporary removal of the write-protect screw from the motherboard to permit flashing new flags to the GBB... and this may void the Chromebook's warranty (one of the case screws lies underneath a sticker declaring the warranty void if disturbed).
Experimenting with alternate OS installs on the Chromebook I first employed the developer mode method followed by the write-protect screw removal. I prefer configuring the device to default to legacy-mode BIOS but I have employed both methods successfully and describe their respective steps below.
2.1 Write-Protect Screw Method
Disconnect power. Turn the Chromebook over facing bottom up and remove the 13 screws (not missing the one hidden under the warranty sticker). Gently pry the case off starting with the seam where the display connects to device. It comes away pretty easy.
This is what you see ...
WARNING! This will wipe out whatever is installed on the SSD ...
- Remove the write-protect screw
- Close back cover using only the battery lock screw to hold in place
- Re-connect power, boot Chromebook and wait until it displays ...
Chrome OS is missing or damaged. Please insert a recovery USB stick or SD card.
- Insert USB recovery media prepared in Step 0 and it will proceed to restore Chrome OS and reboot
- At default Chrome OS "Welcome!" screen open a terminal CTRL+ALT+F2 (Right-arrow)
- Login as chronos (no password), then enter sudo su for superuser access
Set new GBB flags using the set_gbb_flags.sh script in Chrome OS. To enable short developer mode screen (1 second timeout) followed by default legacy mode boot use these flags ...
GBB_FLAG_DEV_SCREEN_SHORT_DELAY 0×00000001 GBB_FLAG_FORCE_DEV_SWITCH_ON 0×00000008 GBB_FLAG_FORCE_DEV_BOOT_LEGACY 0×00000080 GBB_FLAG_DEFAULT_DEV_BOOT_LEGACY 0×00000400
... which adds up to running in the shell ...
Shutdown with ...
# shutdown -h now
... and disconnect the power ...
- Remove the bottom cover again and reinstall the write-lock screw to protect the BIOS
- Close cover and reinstall all the case screws
Re-connect the power, insert the USB stick prepared in Step 1, and power up the Chromebook .
2.2 Developer Mode Method
The alternative to removing the write-protect screw above is to place the Chromebook into developer mode using the Chrome OS shell before booting the USB install media ...
- With the Chromebook off... Hold down ESC+F3 (Refresh) keys and power on the device
- Invoke Recovery, and at the Recovery screen press Ctrl+D
- Device will prompt for confirmation, press ENTER and the system reboots into developer mode
- Scary white boot screen appears and you need to press Ctrl+D to continue boot 
Enable the USB Boot and Legacy BIOS modes by opening the shell with Ctrl+Alt+T and enter shell. Set dev_boot_usb and dev_boot_legacy to active ...
$ sudo crossystem dev_boot_usb=1 $ sudo crossystem dev_boot_legacy=1
Insert the USB stick prepared in Step 1, reboot the Chromebook and press CTRL+L at the boot screen to enter legacy boot mode.
3. Install Ubuntu
My visual screenshot tour of installing Ubuntu 16.04 - a Long Term Support (LTS) release. Ubuntu's minimal install image makes it easy to create a console-only base configuration that can be later customized for various tasks and alternate desktops. I like the lightweight and delightful i3 window manager.
Chromebook's SSD will be divided into 3 partitions ...
- sda1 is a 300MB boot partition
- sda2 is a 1GB LUKS encrypted swap partition using a random key
- sda3 uses the remaining space as a LUKS encrypted root partition using a passphrase
Update: I replaced the factory-installed SSD with a 256GB device and a revised partition scheme ...
- sda1 is a 24GB root partition
- sda2 is a 2GB LUKS encrypted swap partition using a random key
- sda3 uses the remaining space as a LUKS encrypted home partition using a passphrase
Ubuntu installs a kernel with built-in support for the Chromebook's touchpad. Per-session modifications of touchpad settings can be made using synclient ...
$ synclient # display current settings $ synclient TapButton3=2 # 3-finger tap = middle-click
To make any desired touchpad settings permanent create a configuration file in /etc/X11/xorg.conf.d ...
$ sudo mkdir /etc/X11/xorg.conf.d $ sudo cp /usr/share/X11/xorg.conf.d/50-synaptics.conf /etc/X11/xorg.conf.d/50-c720-touchpad.conf
Modify this file to adjust timeouts, add tap-mouse actions (2-finger tap = right-click, 3-finger tap = middle-click), and 2-finger scrolling.
Sample config ...
Section "InputClass" Identifier "touchpad peppy cyapa" MatchIsTouchpad "on" MatchDevicePath "/dev/input/event*" MatchProduct "cyapa" Option "FingerLow" "5" Option "FingerHigh" "5" Option "VertEdgeScroll" "0" Option "VertTwoFingerScroll" "1" Option "HorizTwoFingerScroll" "1" Option "AreaRightEdge" "850" Option "AreaLeftEdge" "50" Option "TapButton1" "1" Option "TapButton2" "3" Option "TapButton3" "2" EndSection
Note: If using Ubuntu's default Unity desktop ... you may find the 3-finger middle-click option requires a manual reset each session.
Fix: Stop the Gnome Settings daemon from overiding 50-c720-touchpad.conf ...
$ gsettings set org.gnome.settings-daemon.plugins.mouse active false
The swappiness parameter controls the preference of the kernel to move processes out of physical memory to the swap partition. Range is 0-100, default is set to 60 and lower values cause the kernel to avoid swapping and higher values prompt more frequent swap use.
Check the current swappiness value ...
$ cat /proc/sys/vm/swappiness
To reduce writes on the SSD set a low value of 1 by setting vm.swappiness=1 in /etc/sysctl.conf.
TRIM optimizes SSD performance and is enabled by adding the discard option to /etc/crypttab and /etc/fstab. Ubuntu auto-magically configures crypttab but fstab needs to be set manually.
Sample fstab ...
# <file system> <mount point> <type> <options> <dump> <pass> # / was on /dev/sda1 during installation UUID=<______string___> / ext4 relatime,discard,errors=remount-ro 0 1 /dev/mapper/sda3_crypt /home ext4 relatime,discard 0 2 /dev/mapper/sda2_crypt none swap sw,discard 0 0
After modifying fstab update /boot/initrd.img-* by running ...
$ sudo update-initramfs -u -k all
Problem: Suspend-and-resume generates a stream of errors ...
ehci-pci 0000:00:1d.0: port 1 resume error -19 ehci-pci 0000:00:1d.0: port 2 resume error -19 usb usb3-port1: over-current condition usb usb3-port1: connect-debounce failed usb usb3-port2: over-current condition usb usb3-port2: connect-debounce failed
... and blocks the Chromebook from executing a proper restart/shutdown.
FIX: Create /lib/systemd/system-sleep/ehci-pci.sh ... 
#!/bin/bash case $1/$2 in pre/*) # Unbind ehci for preventing error echo -n "0000:00:1d.0" | tee /sys/bus/pci/drivers/ehci-pci/unbind ;; post/*) # Bind ehci for preventing error echo -n "0000:00:1d.0" | tee /sys/bus/pci/drivers/ehci-pci/bind ;; esac
... and make it executable ...
$ sudo chmod 755 /lib/systemd/system-sleep/ehci-pci.sh
Configure boot options in /etc/default/grub ...
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash tpm_tis.force=1"
... save the changes and run ...
$ sudo update-grub
Suspend now works reliably when triggered from Ubuntu's shutdown menu or closing the lid and will resume the system with the desktop locked and a password prompt.
7. Keyboard Shortcuts
Top row on the keyboard with the shortcut icons (brightness, volume, etc.) identify in Linux as the F1-F10 keys and the Search key (in the CapsLk position) acts as the Super (Windows) modifier key.
Create keyboard shortcuts by first installing ...
- xbindkeys - associate keys to shell commands
- xbacklight - set backlight level using RandR
- pulseaudio-utils - manage sound with pactl
- xvkbd - send characters to another client
$ sudo apt install xbindkeys xbacklight pulseaudio-utils xvkbd
7.1 Direction, Brightness, Volume, Page Keys
$ xbindkeys -k
Enable the function keys to modify the sound and brightness settings by creating ~/.xbindkeysrc ...
# ~/.xbindkeysrc # backward/forward "xvkbd -xsendevent -text "\A\[Left]"" F1 "xvkbd -xsendevent -text "\A\[Right]"" F2 # backlight decrease/increase "xbacklight -dec 10" F6 "xbacklight -inc 10" F7 # volume mute/decrease/increase # pactl - control a running pulseaudio server # pactl list sinks - retrieve info # on my c770 chromebook... single audio sink is 'Sink #0' # named 'alsa_output.pci-0000_00_1b.0.analog-stereo' "pactl set-sink-mute alsa_output.pci-0000_00_1b.0.analog-stereo toggle" F8 "pactl set-sink-volume alsa_output.pci-0000_00_1b.0.analog-stereo -10%" F9 "pactl set-sink-volume alsa_output.pci-0000_00_1b.0.analog-stereo +10%" F10 # page up/down, home, end "xvkbd -xsendevent -text '\[Page_Up]'" Alt + Up "xvkbd -xsendevent -text '\[Page_Down]'" Alt + Down "xvkbd -xsendevent -text '\[Home]'" Alt + Left "xvkbd -xsendevent -text '\[End]'" Alt + Right
Enable the new key shortcuts by running ...
Ubuntu auto-detects ~/.xbindkeysrc and will run xbindkeys on the next login.
7.2 Power Key
Power key in upper-right corner ignores any configuration in the window manager and triggers poweroff without delay when pressed (easy to do by accident as its positioned next to backspace).
If you want to disable the power key edit /etc/systemd/logind.conf and set HandlePowerKey=ignore.
Update: With the >= 4.2 kernels I have not been required to make any modifications. Works OK.
There are a few settings to modify to improve performance of Chromebook's wireless chipset. Identify the card and parameters ...
$ lspci | grep -i net 01:00.0 Network controller: Qualcomm Atheros AR9462 Wireless Network Adapter (rev 01) $ modinfo ath9k | grep parm parm: debug:Debugging mask (uint) parm: nohwcrypt:Disable hardware encryption (int) parm: blink:Enable LED blink on activity (int) parm: btcoex_enable:Enable wifi-BT coexistence (int) parm: bt_ant_diversity:Enable WLAN/BT RX antenna diversity (int) parm: ps_enable:Enable WLAN PowerSave (int) parm: use_chanctx:Enable channel context for concurrency (int)
Create /etc/modprobe.d/ath9k.conf with the following options ...
options ath9k bt_ant_diversity=1 ps_enable=0
Confirm the microphone is un-muted in alsamixer. Create /etc/modprobe.d/snd-hda-intel.conf ...
options snd_hda_intel model=,alc283-dac-wcaps
... and restart. Give it a try ...
$ arecord -d 5 chr-mic.wav $ aplay chr-mic.wav
10. Good stuff
- My former Lubuntu 14.04 LTS install on the Chromebook and configuration (under upstart init vs systemd in the current 15.10)
- Arch Linux C720 installation with useful post-install details
- Turn Chromebooks into Ubuntu-based code learning machines for kids
- Lightweight i3 tiling window manager is snappy on the Chromebook's modest hardware
|||Device information output of lshw, lspci, and lsusb.|
|||Specifically in this instance, the Ubuntu console installer provides a random key option for the encrypted swap partition.|
|||Image courtesy of Chromium.|
|||Whenever you remove battery power to the Chromebook (like opening up the case) the hardware clock on the motherboard resets to a future year (mine travelled to 2040). Providing a network connection is up during the Ubuntu installation the system should fetch a correct time from a NTP server. Otherwise fix the fallout from an incorrect clock by re-mounting partitions read-only and correct filesystem timestamps using fsck.|
|||Switching between developer and normal (non-developer) modes will remove user accounts and their associated information from the Chromebook.|
|||Some HOWTOs talk about adding modprobe.blacklist=ehci_hcd,ehci_pci but in Ubuntu they are compiled into the kernel.|