I recently setup Arch on my laptop, but after 10 minutes of looking at the screen my eyes start to hurt. I looked up how to turn this down, and xbacklight seemed like a commonly used choice. However, trying to use a command like "xbacklight -set 60" resulted in "No outputs have backlight property". After some searching I found this thread: "https://bbs.archlinux.org/viewtopic.php?id=102060". It would seem the solution that was taken there was to use "setpci". Taking a look at the wiki, I also found this solution under the "Backlight" article. Yet, here it is posted that this solution is "risky and generally is not a good idea". So I was wondering if anyone might know of a way to fix the problem with xbacklight? Or is there another equivalent solution like xbacklight that might work? Also, how risky/generally not a good idea is using "setpci" to directly manipulate the hardware?
Thank you for your time!
Last edited by golmschenk (2012-02-03 20:43:10)
It is a Toshiba Satellite L305D-S5934. The graphics card is an ATI Radeon 3100HD RS780MC. Thanks.
Do you have any entries under /sys/class/backlight?
Indeed I do. Know I had seen something about this folder when I was looking the rest up, but when I checked from my Ubuntu install I thought I didn't see anything.
I have a acpi_video0 directory as well as a toshiba directory. I'll start looking up again what I can do with this, but if you happen to know please let me know. Thanks!
I've found that "cat /sys/class/backlight/acpi_video0/max_brightness" returns 7. So I tried "echo 5 > /sys/class/backlight/acpi_video0/brightness", however, permission was denied whether I was using sudo or not. Any suggestions?
This is totally problem avoidance, but I get the same message when I run xbacklight. So instead, I just use xrandr's --brightness to set my screen's backlight.
Oh, of course. I just had to change the permissions of the file to edit it.
And no worries. Changing the brightness file rather than using xbacklight is also problem avoidance.
Sorry for reopening, but I'm loosing hope here. I have the same problem with not being able to adjust the backlight on my Acer One aspire D257 (intel atom n570 processor with GMA3150 chipset). I've also tried everything on the "backlight wiki" page apart from "xcalib" (as it's not the best solution) without any luck. Changing the "brightness" file doesn't change the backlight at all. Is the backlight supposed to change instantly when executing the "echo x > /sys/.../brightness" command?
Just to clarify, "xbacklight -dec 40" gives me the same output: "No outputs have backlight property"
Adjusting my kernel parameters in grub also did not work.
I had Xubuntu installed on this netbook before Arch and the backlight adjustment worked out of the box (so it is possible)...
Any help would be greatly appreciated. Please let me know if you need any more system information. Thanks!
I got the same problem and I got tired of fiddling with my kernel line with ever changing parameters, so I wrote this script called by a key shortcut (the now deceased brightness control keys).
Increase brightness by 2%
$ brightness.sh +2
Decrease brightness by 2%
$ brightness.sh +2
#!/bin/bash # base dir for backlight class basedir="/sys/class/backlight/" # get the backlight handler handler=$basedir$(ls $basedir)"/" # get current brightness old_brightness=$(cat $handler"brightness") # get max brightness max_brightness=$(cat $handler"max_brightness") # get current brightness % old_brightness_p=$(( 100 * $old_brightness / $max_brightness )) # calculate new brightness % new_brightness_p=$(($old_brightness_p $1)) # calculate new brightness value new_brightness=$(( $max_brightness * $new_brightness_p / 100 )) # set the new brightness value sudo chmod 666 $handler"brightness" echo $new_brightness > $handler"brightness"
Last edited by marcelof (2014-08-20 13:37:15)
When you depress the backlight keys (up/down), do they generate ACPI event codes? First, confirm that you have acpi and acpid installed
$ pacman -Qs acpi
and that acpid.service is started/enabled through systemd
$ sudo systemctl enable acpid $ systemctl status acpid
Once enabled/started, type this in your terminal and then depress the keys you use to raise/lower the brightness. If you get an output similar to this, then depressing the brightness keys generates an ACPI event that you can take advantage of to raise and lower the brightness.
$ acpi_listen video/brightnessup BRTUP 00000086 00000000 K video/brightnessdown BRTDN 00000087 00000000 K
If you get event codes like this, you can create two scripts in your /etc/acpi/actions folder and two corresponding files in the /etc/acpi/events folder to control the backlight. Here are mine so that you can use them as a starting point. Put these scripts into the /etc/acpi/actions folder.
#!/bin/sh bl_device=/sys/class/backlight/samsung/brightness echo $(($(cat $bl_device)-1)) | sudo tee $bl_device
#!/bin/sh bl_device=/sys/class/backlight/samsung/brightness echo $(($(cat $bl_device)+1)) | sudo tee $bl_device
The bl_device path should point to the brightness file in /sys/class/backlight/some_manufacturer/. You should test out whether you can manually control the backlight by changing the file permissions and using
$ echo x > /sys/class/backlight/some_manufacturer/brightness
to manually adjust the brightness where "x" is some value that corresponds to the brightness level.
It's also worth checking the value in max_brightness to see how bright you can make your screen and what kind of system of numbers you need to use to control the backlight. On my system, the max_brightness is 8, so I use +/-1 in the scripts. Your values may be different, so check them out and modify the files as appropriate.
Don't forget to run
$ chmod +x bl_down.sh $ chmod +x bl_up.sh
to make the scripts executable.
Next, create the corresponding files in /etc/acpi/events.
event=video/brightnessdown BRTDN 00000087 00000000 K action=/etc/acpi/actions/bl_down.sh
event=video/brightnessup BRTUP 00000086 00000000 K action=/etc/acpi/actions/bl_up.sh
For the event value, paste in the output you got from above using
and depressing the corresponding brightness keys.
If all goes well, you should be able to use your brightness keys to control the backlight once all these pieces are in place. Good luck!
Last edited by cmorgenstern (2014-08-21 22:30:51)
"Never ascribe to malice that which is adequately explained by incompetence."
~ Napoleon I