Saturday 02 May 2015

Chromebook to Ubuntubook

Replace Chrome OS permanently with Ubuntu 15.04 Linux on the Acer C720 Chromebook.

Ubuntu 15.04 Vivid Vervet

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 experimenting with Ubuntu's latest and greatest and the Unity desktop.

Let's go!

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 [1].

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:

Source: Create a Chromebook recovery image

1. Prepare install media

Download the 64-bit 'Vivid Vervet' minimal installer and flash the image to a USB stick. An alternative (my choice) is adding the image to a USB stick with multiple Linux installers. Using the minimal console installer (requires network connection) vs. the graphical Ubuntu installer provides more options during setup [2] and downloads all the latest packages.

2. SeaBIOS

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.

No guarantees though... Hopefully you enjoy equal success!

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:

C720 annotated innards

[ Image: [3] The battery lock screw is #6 and the write-protect screw is #7 ].

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:

/usr/share/vboot/bin/set_gbb_flags.sh 0x489

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 [4].

Sources: Useful GBB flags for another new free software machine

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 [5]

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.

Source: Chromium OS developer information for the Acer C720 Chromebook

3. Install Ubuntu

My visual screenshot tour of installing Ubuntu 14.04 - a Long Term Support (LTS) release. Install steps remain the same for 15.04.

Alternative: At the tasksel stage select a different desktop: Lubuntu (LXDE), Xubuntu (XFCE), etc.

Chromebook's SSD will be divided into 3 partitions:

4. Touchpad

Ubuntu 15.04 installs Linux kernel 3.19 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

Problem: My 3-finger middle-click option required 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

Logout and back in. It works!

Sources: 50-c720-touchpad.conf, and pages for Touchpad Synaptics and the C720 Chromebook on ArchWiki

5. SSD

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>
/dev/mapper/sda3_crypt /               ext4    noatime,discard,errors=remount-ro 0       1
# /boot was on /dev/sda1 during installation
UUID=[some_long_random_string] /boot    ext4    noatime,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

Source: TRIM configuration on solid-state drives

6. Suspend

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 [6]:

#!/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.

Source: ehci-pci.sh

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:

$ sudo apt-get 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 $HOME/.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:

$ xbindkeys

Ubuntu auto-detects $HOME/.xbindkeysrc and will run xbindkeys on the next login.

Sources: xbindkeysrc, Xbindkeys, and another sample Chromebook-friendly xbindkeysrc

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.

8. Wireless

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

Sources: ath9k.conf, ath9k wireless driver and bluetooth coexistence

9. Helpful Resources

Happy hacking!

Notes

[1]Device information output of lshw, lspci, and lsusb.
[2]Specifically in this instance, the Ubuntu console installer provides a random key option for the encrypted swap partition.
[3]Image courtesy of Chromium.
[4]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.
[5]Switching between developer and normal (non-developer) modes will remove user accounts and their associated information from the Chromebook.
[6]Some HOWTOs talk about adding modprobe.blacklist=ehci_hcd,ehci_pci but in Ubuntu they are compiled into the kernel.