Lenovo ThinkPad T420

This article covers the installation and configuration of Arch Linux on a Lenovo T420 laptop.

Installation

This laptop supports UEFI as well as the traditional BIOS.

There are no issues with installing Arch Linux with the latest Archiso.

The rest of the installation process can be followed with the Installation guide.

Hardware

All hardware works out of the box except the following:

Fingerprint reader

Fingerprint reader works great with fprint and PAM (installation of fingerprint-gui recommended).

See Fingerprint-gui for more information.

Some Media keys

• See Media Keys

Untested

• Firewire

Laptop Settings

ACPI

ACPI is well supported here. No obvious troubleshoots.

Tp_smapi

Unfortunately, tp_smapi is only partially supported on the Thinkpad T420. A number of features work since version 0.41. For example, the hard drive protection mechanism HDAPS now works well. See the linked wiki entry.

Some features like setting the starting threshold for charging the battery do not yet work. To control the battery charging thresholds, install the Perl script tpacpi-bat from the AUR.

Insert the acpi_call kernel module by running

modprobe acpi_call

Manually set the thresholds by calling

/usr/bin/perl /usr/bin/tpacpi-bat -v -s SP 0 80 
/usr/bin/perl /usr/bin/tpacpi-bat -v -s ST 0 40

The example values 40 and 80 given here represent the percentage of full battery capacity remaining. Adjust them to your own needs. You may also want to write a simple set-battery.service and enable it to set them at startup. While these values should be permanent, they will be reset any time the battery is removed.

[Unit]
Description=Set battery capacity

[Service]
Type=oneshot
ExecStart=/usr/bin/perl /usr/bin/tpacpi-bat -v -s SP 0 80
ExecStart=/usr/bin/perl /usr/bin/tpacpi-bat -v -s ST 0 40

[Install]
WantedBy=multi-user.target

Also, if you are dual booting with Windows, you can still control the battery charging thresholds with Lenovo's Power Manager which communicates directly to the battery controller.

When using systemd, you may want to blacklist the tp_smapi module if your systemd-modules-load.service fails, as new ThinkPads handle everything over acpi.

CPU frequency scaling

CPU frequency scaling is fully supported with all of the available processor models with this laptop.

Fans

Install the package thinkfan^AUR. It will automatically create the necessary acpi configuration file in /usr/lib/modprobe.d/thinkpad_acpi.conf.

Copy the example sensor settings file from "/usr/share/doc/thinkfan/examples/thinkfan.conf.simple" to "/etc/thinkfan.conf".

# cp /usr/share/doc/thinkfan/examples/thinkfan.conf.simple /etc/thinkfan.conf

Aftwards replace the default hwmon in the settings file /etc/thinkfan.conf with the following:

/etc/thinkfan.conf

hwmon /sys/devices/virtual/thermal/thermal_zone0/temp

Alternatively, sensors can be generated using following command. Add hwmon before the sensor lines.

find /sys/devices -type f -name "temp*_input"

In the same configuration file replace the default fan level settings with your needs (the last lines of the file). Useful values are

(0,	0,	42)
(1,	40,	47)
(2,	45,	52)
(3,	50,	57)
(4,	55,	62)
(5,	60,	67)
(6,	65,	72)
(7,	70,	77)
(127,	75,	32767)

Finally enable the thinkfan service.

# systemctl enable thinkfan

Laptop Mode Tools

No significant issues were found using Laptop Mode Tools.

Possible bug with #Shutdown on battery.

The package tlp is an alternative tool that can replace laptop-mode-tools^AUR.

NVIDIA Optimus

Bumblebee works as intended on models with NVIDIA Optimus

Optional kernel boot arguments

Using the following kernel boot parameters reduces battery drain:

i915.i915_enable_rc6=1
i915.i915_enable_fbc=1
i915.lvds_downclock=1 
i915.semaphores=1

Troubleshooting

Media Keys

Media keys that (should) work out of the box:

• Wireless On/Off
• Backlight Brightness settings
• Thinklight
• Mute
• Microphone mute

Media Keys that Do Not work out of the box:

• Volume keys (Works out-of-the-box in GNOME)

You must find a workaround and bind the keys yourself for the rest of them.

xbindkeys and xbindkeys_config-gtk2^AUR can be a solution for media keys that are not working. This solution also allows you to rebind the ThinkVantage button and certain FN layer shortcuts (the blue logos on the keyboard).

Rebind Forward and Back keys

Keys forward and back (next to cursor keys) can be easily remapped to PageDown/PageUp.

Install xmodmap with the package xorg-xmodmap

Create a ~/.Xmodmap file with content:

keysym XF86Back = Page_Up
keysym XF86Forward = Page_Down

Add this line to your ~/.xinitrc to make it work:

xmodmap ~/.Xmodmap

You can also re-map AudioPrev (Fn+Left) and AudioNext (Fn+Right) to Home/End:

keysym XF86AudioNext = End
keysym XF86AudioPrev = Home

Note:

• You have to log out for the changes to take effect.
• The keys should work out of the box, at least on KDE.

Turn touchpad on and off

For some, the (Fn+F8) key does not switch the touchpad on and off. See Touchpad Synaptics#Software toggle for a workaround.

Volume up/down not changing volume

See Xbindkeys.

Shutdown on battery

Some users have reported that the T420 was rebooting on shutdown on battery power. There have been quite a few attempts to fix this. Three are detailed here.

One way is to disable the module ehci_hcd. See Kernel modules#Blacklisting for more information.

Or try disable Laptop-mode. Add !laptop-mode to the DAEMONS array in /etc/rc.conf:

DAEMONS=(...!laptop-mode...)

This forum post details another way to have your computer not reboot on shutdown. Turning off the laptop-mode daemon causes battery life to suffer, so when on the move and in need of a simple way to shutdown, this seems to work better.

Hang on reboot

This is a problem on many laptops and can be fixed by blacklisting the e1000e kernel module.

See also

• Lenovo ThinkPad T420s
• Arch Linux on ThinkPad T420i