[SOLVED] Execute disper second time doesn't take effect

shogun1234 · 02-20-2018, 10:36 AM

I use disper to auto detect the event when my external monitor is plugged again.

The problem is if the command gets executed once it won't take effect at the second time (I believe it's because I don't understand its or its backend xrandr behavior).

For instance,

1. Unplug the external monitor.
2. Plug the external monitor again.
3. Execute `disper -d auto -e` takes effect because the external monitor is back displaying window manager's workspace.
4. Do 1.
5. Do 2.
6. Do 3 again (execute `disper -d auto -e` again), but this time the external monitor stays black without displaying workspace.

If executing command that basically swaps the position of monitors (e.g. first time inner monitor is at left, external monitor is at right; then swap to inner monitor is at right, external monitor is at left) like `disper -e -t left`. Then the monitor would display window manager's workspace without a problem.

My questions - why the command being executed the second doesn't take effect? And more importantly what steps should I follow so that monitors plug/unplug events auto detection can be done without a problem?

AwesomeMachine · 02-20-2018, 09:10 PM

I think disper parses a command line for xrandr. After xrandr is run and the monitor is working, and then you unplug it, disper might not undo the xrandr command. So, when you run the program again it's trying to add a mode that's already been added.

OK, usually laptops have a button along the top to toggle between video devices, or ports. gnome-control-center will allow you to configure your displays persistently, so they won't change. When you unplug the ext. monitor, it will shut off the port.

When you plug it back in, use the key on your keyboard to toggle it back on.

shogun1234 · 02-22-2018, 05:34 PM

Quote:

Originally Posted by AwesomeMachine

I think disper parses a command line for xrandr. After xrandr is run and the monitor is working, and then you unplug it, disper might not undo the xrandr command. So, when you run the program again it's trying to add a mode that's already been added.

OK, usually laptops have a button along the top to toggle between video devices, or ports. gnome-control-center will allow you to configure your displays persistently, so they won't change. When you unplug the ext. monitor, it will shut off the port.

When you plug it back in, use the key on your keyboard to toggle it back on.

Thanks for the explanation. That helps me a lot! I then switch to run `disper -e` when unplug. Then `disper -e` again once the external monitor is plugged. This solves my problem. The procedure is:
1. write udev rule to detect plug/ unplug event.

Code:

KERNEL=="card?", SUBSYSTEM=="drm", ACTION=="change", ENV{DISPLAY}=":0", ENV{XAUTHORITY}="/home/user/.Xauthority", RUN+="/path/to/disper-script"

2. export X env variable
3. execute disper command with sudo -u <user> <disper command>

Code:

USER=<user-id>
XPID=`pgrep X | head -n 1`
XCOMMANDLINE="ps --no-header -o command $XPID"
export DISPLAY=`$XCOMMANDLINE | sed 's/.\+:/:/;s/ \+.*//'`
export XAUTHORITY=`$XCOMMANDLINE | sed 's/.*-auth *//;s/ \+-.*//'`
sudo -u $USER disper -e