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Hello i have been using Linux for two years so im still new to the whole community. please forgive me in advanced if this question is stupid and/or in the wrong forum.

I have a laptop this particular laptop is an optimus with dual graphics. i have correctly set up bumblebee which enables me to use the discrete graphics card correctly (are at least i hope) however this has caused an issue in xbacklight not being able to adjust brightness. I have looked around and found a program on github that can adjust brightness (brightlight v7). however it requires root to run. I would like to run this program without root. The author has given a statement about how to do this but i wish to ask for clarification and/or how to achieve this before i mess anything up.

In case anyone wants to know im using Arch with i3-gaps

Author Quote:

"This program is intended to be installed setuid root, as the files in sysfs are owned by user and group root by default; however it is also possible to change the permissions on the sysfs files at boot time to a different user and group using the 'anacron' functionality found in some cron implementations, using systemd-tmpfiles or even in "/etc/rc.local" (where appropriate functionality is available). This would allow for regular users (possibly members of a special group) to change the backlight brightness without the requirement of suid binaries."

https://github.com/multiplexd/brightlight

~Thanks you for your time i try not to ask for help but im just worried about messing something up.

EDIT: I was able to fix the issue my laptop uses intel_backlight however you can write a systemd service to allow this program to modify the system files by allowing write and append access.

just change intel_backlight to whatever you use.

This file as i named it is brightlight.service and is located /etc/systemd/system/

[Unit]
Description Hopefully will be a solution for you reading.
Before nodered.service

[Service]
Type oneshot
User root
ExecStart=/bin/bash -c "/bin/chmod a+w /sys/class/backlight/intel_backlight/*"

[Install]
WantedBy=multi-user.target
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I am not sure, but I think that program has created a group in your laptop called like the program. In this case you need to add your user to this group and open a new shell. Try this: with root privileges:

# gpasswd -a <your_user> <program_name>

or with sudo:

$ sudo gpasswd -a <your_user> <program_name>

I hope you find it useful!

  • Thank you but unfortunately the program did not create any groups. However i was able to get it to work as stated above with a systemd service. This service if im correct just allows access to the intel_backlight/ directory to regular users instead of just sudo. This is a fix to my problem however are there any repercussions to allow read write access to a directory that is supposed to only be used by sudoers in this way? – mr Stap Oct 16 '19 at 10:14
  • I have found the answer to your question in the ArchWiki. wiki.archlinux.org/index.php/Backlight . Read the section Hardware Interfaces > APCI . They explain there how to change privileges of this folder. – Jamil KR Oct 16 '19 at 10:31
  • Thanks it means a lot – mr Stap Oct 17 '19 at 11:12

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