You might have run into this error when updating packages. The error is probably because you don’t have the public key corresponding to whatever private key the package was signed with. Hopefully, you can just download the public key from keyserver.ubuntu.com and get on with your day. In my case, it was a Google SDK key
8B57C5C2836F4BEB that was missing. Just use the following command, replacing the key ID with the key you need.
sudo apt-key adv –keyserver keyserver.ubuntu.com –recv-keys 8B57C5C2836F4BEB
sudo apt-get update should just work. If it doesn’t, feel free to leave a comment.
At least for me, the GUI brightness controls only allow the brightness to be dimmed so far.
$ cat /sys/class/backlight/intel_backlight/brightness
By editing that file, you can bring it down further.
echo "1" | sudo tee /sys/class/backlight/intel_backlight/brightness
For me, the value
0 works fine as well, but it doesn’t appear to be any different than
1, and I get this weird feeling that some XFCE is going decide to black out the screen on
0 someday so I just play it safe with