I am running a single board computer (Intel Atom based) off a battery, with Ubuntu 18.04 as the OS, to do some remote monitoring and processing.
Aim is to get the system to run for 72 hours which I have done.
However, I have noted that though there is no monitor connected, with monitor output enabled an extra 0.1A is drawn.
Disabling monitor output using a
xset dpms force off command or
xrandr --output HDMI-I --off saves me my 0.1A.
However, whilst both commands work fine when issued from an application running in a terminal, they don't work when the application autostarts on boot up (I am using cron to fire up the application on boot using
@reboot python3 /bin/bootapp.py &).
Application is Python and the commands to switch are issued using os.system(
xset dpms force off) or os.system(
xrandr --output HDMI-I --off).
I note that the application is up and running well before Ubuntu finishes booting so thinking that Ubuntu might be overriding the command I also issue it 5 minutes after boot up.
But still, the monitor output is enabled.
How do you disable the monitor output? I could usefully do with the extra 0.1A.