[SOLVED] `xset dpms force off' fails when called from a script

polytropos · 12-28-2018, 10:00 AM

Hi all

I am trying to run xset dpms force off when a keyboard button is pressed. The button generates video/switchmode ACPI event, and I have put the following code in /etc/acpi/default to trigger the command:

Code:

case "$group" in
	video)
		case "$action" in
			switchmode)
				DISPLAY=:0 xset dpms force off ;;
				 *)	log_unhandled $* ;;
		esac
		;;

	*)	log_unhandled $* ;;
esac

Here is what I know:
(i) The match works fine, for when I run `/etc/acpi/default.sh "video/switchmode"', my monitor switches off.
(ii) Acpid is working fine too, for if I replace

Code:

DISPLAY=:0 xset dpms force off ;;

with

Code:

touch /home/niku/test ;;

and restart acpid and then press the button, the file ~/test gets updated.
(iii) I tried prefixing `DISPLAY=:0' after the suggestion here but it didn't work!
(iv) Acpid runs as root. The command in (i) switches off the monitor both as normal user and root.
(v) Providing full path of xset (/usr/bin/xset) in the script doesn't help either.

What else should I try? The above link mentions checking other environment variables too, but I couldn't find any information about it xset's or acpid's manpage.

Edit: It is clearly a problem with getting xset to work. In the log files, in (ii), when using touch command, the script exits with 0. When using xset, the script exits with 1. I read somewhere (forgotten where), that 1 means that there is some "minor error".

Thanks!

smallpond · 12-29-2018, 07:21 PM

Try giving the full path to xset in the command. PATH may not be set the same when running the script.

polytropos · 12-29-2018, 08:29 PM

Thanks smallpond, but it doesn't help. (I tried it already, and had later updated my original post to mention it!)

polytropos · 12-30-2018, 08:30 PM

I got it working after allowing every user directly logged on the local machine (including the root) to access the display by running as the non-privileged user (the one who started the X server):

Code:

xhost +local:

For persistence, I added the command to my .xinitrc, but adding it to .bashrc should work fine too.
See this for a little more detail.

---

How I discovered the problem:
I got the xset error message into a file by changing the xset line to

Code:

xset -display :0 dpms force off > /home/niku/test 2>&1 ;;

The xset error messages said "No protocol specified", etc, for which I did a www search, which led to the above solution.

-

The curious question which remains is: why is xset able to access the display as root when run on the command line, but not when run by the acpid. (I verified that acpid runs as the root by adding logger "`whoami`" to the code at the top {logger sends the output to syslog}).