"cannot open display" from /etc/acpi/ script

[timrichardson]

I want to modify /etc/acpi/video_brightnessdown.sh to call xbacklight
I have used
xbacklight -display 0:0 -set 50
but in /var/log/acpid I see an error message

No protocol specified.
Cannot open display "0:0"




I know the syntax is correct. Why can acpid not run this?

[timrichardson]

By copying lid.sh I solved this.

The call to xbacklight needs to be su the logged in user (I tried to solve this with setuid but lid.sh has a much simpler solution)

Secondly, working out the display name is not so trivial, but once again, it is already done in existing scripts such as lid.sh