Ubuntu 20 udev rules not working

[ITler]

I did sudo apt install brightnessctl, but it seems for Ubuntu 20 LTS that although udev rules get copied to /lib/udev/rules.d/ as desired in the debian install routine, it is not possible to use brigthnessctl without sudo.

[Hummer12007]

Can you show me the installed rules and the output of your id command?

[ITler]

sure .. and I am very confident that my user is the default user created during OS installation, so no special tweaks in regards of group membership.

$ id
uid=1000(itler) gid=1000(itler) groups=1000(itler),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),120(lpadmin),131(lxd),132(sambashare),998(docker)

$ cat /lib/udev/rules.d/90-brightnessctl.rules 
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="leds", RUN+="/bin/chgrp input /sys/class/leds/%k/brightness"
ACTION=="add", SUBSYSTEM=="leds", RUN+="/bin/chmod g+w /sys/class/leds/%k/brightness"

$ brightnessctl s 20%+
Can't modify brightness: Permission denied

You should run this program with root privileges.
Alternatively, get write permissions for device files.

$ ls -la /sys/class/backlight/intel_backlight/brightness
-rw-rw-r-- 1 root video 4096 Mar  2 08:11 /sys/class/backlight/intel_backlight/brightness

[ITler]

Ah, I am blind. Yes that could be the reason. Maybe GIDs changed in Ubuntu20

[Hummer12007]

The easiest way to fix it would be to add yourself to the video group via usermod -aG video ${USER} or something similar.

[ITler]

Sure no worries. Just wondering if this is a generic problem on Ubuntu 20 to be dealt with or some specifics to my machine.
Anyways, thanks for supporting. Feel free to close this issue if not needed anymore.

[nelson-ricardo]

I am running with that same problem but I am unable to use the program without using sudo. My user is nelson and it is the only user on the system. I am using Elementary which follows the Ubuntu 18.04LTS

$ cat /etc/group | grep video
video:x:44:nelson
 $ cat /etc/group | grep input
input:x:104:nelson
 $ cat /lib/udev/rules.d/90-brightnessctl.rules
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chgrp video /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="backlight", RUN+="/bin/chmod g+w /sys/class/backlight/%k/brightness"
ACTION=="add", SUBSYSTEM=="leds", RUN+="/bin/chgrp input /sys/class/leds/%k/brightness"
ACTION=="add", SUBSYSTEM=="leds", RUN+="/bin/chmod g+w /sys/class/leds/%k/brightness"

[nickcat325]

sudo usermod -aG video ${USER} and rebooting fixed my issue. For a temporary solution you can change permissions of /sys/class/backlight/%k/brightness from other=read to other=read+write. Just remember the permissions will be reverted after a reboot.

[Eliot-Roxbergh]

sudo usermod -aG video ${USER}

This indeed fixed it for me, could it be made clearer in the readme or error message? (that you may need to add current user to video and input)