Fixing xbacklight

I recently decided to upgrade from Ubuntu 16.04 LTS to 16.10. This was unfortunate for a couple reasons: 1. The upgrade broke some dependencies leading to apt no longer working and 2. I made the decision at midnight on a worknight.

I ended up reinstalling 16.04 and trying to restore a backup of my home folder. In this process, I ended up breaking plenty of my configuration. The most frustrating of which was the breaking of xbacklight for backlight control. Before the reinstall, xbacklight worked perfectly. Now, it returned a frustrating error: “No outputs have backlight property”

I knew this wasn’t true because it worked before, but I didn’t know what exactly was wrong, so I explored several options.

1. Modifying kernel parameters – Adding parameters like acpi_backlight=vendor to grub to somehow change ACPI behavior on boot. This never changed anything as far as I could tell, and was annoying to test because it required restarting.
2. Adding a line to xorg.conf – Adding “EnableBrightnessControl=1” to a device section of an xorg config file. This also never seemed to do anything at all.
3. Writing to /sys/class – One can change their brightness by writing to the brightness file in /sys/class/backlight/intel_backlight, but this requires root permissions, and doesn’t fixxbacklight, the basis of my backlight control config.

Ultimately I found a debian bug page that led to my result. The problem exists in an updated x/video package. What I needed was xserver-xorg-video-intel, but what I had was xserver-xorg-core.

According to this bug report, someone was able to force rollback to xserver-xorg-video-intel by creating the following file:

/usr/share/X11/xorg.conf.d/10-backlight.conf

Section "Device"
	Identifier "Intel"
	Driver "intel"
EndSection

And indeed it worked for me too. I created this file and rebooted, and xbacklight worked again!

Lenovo Thinkpad Carbon X1, 4th gen
Ubuntu 16.04 LTS
Kernel 4.8.0-41-generic
xbacklight 1.2.1