Ubuntu – 15.10 Dell XPS 15 (9550) External Monitor not waking

15.10monitormultiple-monitorsunity

I'm in Ubuntu 15.10, with Kernel 4.3. Things are working better than I could ever imagine. Other than ONE bug…

When my laptop turns off it's screen and my external monitor's screen (I have it set for 5 minutes, in case I forget to lock the laptop), The external monitor never wakes up.

I have it hooked up with an HDMI to DVI cable. It works perfect other then it not waking up.

If I reboot with the cable plugged in, it still doesn't wake up.

If I unplug it and reboot, it wakes up.

The strange thing is that, I think Ubuntu thinks it did wake up. The reason I say that is because it doesn't gather my windows into the main screen until I unplug the HDMI cable. I even see the screen flicker as if the driver noticed a cable has been unplugged and it needs to do something.

So my questions are: Anyone know how to fix this? Or, if anything, know a command line command to wake the 2nd monitor?

Thanks!

EDIT: This might be fixed in kernel 4.7 per this article.

EDIT: This still happens with a standard HDMI cable.

Best Answer

Resources?

About resources you don't have to worry, the script checks once per ten seconds if the idle time is exceeded. Even if I make it 10 times per second, the load is practically none.

#!/usr/bin/env python3
import subprocess
import time

t = 300

scr = True
while True:
    time.sleep(10)
    idle = int(subprocess.check_output("xprintidle").decode("utf-8").strip())/1000
    if idle > t and scr == True:
        subprocess.Popen(["xset", "dpms", "force", "off"])
        scr = False
    elif idle < t and scr == False:
        subprocess.Popen(["xset", "dpms", "force", "on"])
        scr = True

How to use

The script needs xprintidle:
```
sudo apt-get install xprintidle
```
Copy the script into an empty file, save it as switchoff.py
In the head of the script, set the idle time (in seconds) in the line:
```
t = 300
```
Switch off your "normal" switch-off-screen-after-x idletime -settings
Run the script with the command:
```
python3 /path/to/switchoff.py
```
If all works fine, add it to Startup Applications: Dash > Startup Applications > Add.

Add the command:
```
/bin/bash -c "sleep 15 &&  python3 /path/to/switchoff.py"
```

EDIT

As requested in a comment, below the bash version of the same script. You'd still need to install xprintidle though.

#!/bin/bash

# --- set the idle time in seconds below
let "t = 300"
# ---

let "div = 1000"
t=$(($t * $div))
scr=true

while true
do
  sleep 10
  let "idle = "$(xprintidle)""
  if  [ "$idle" -gt "$t" ] && [ "$scr" = true ] 
  then
    scr=false
    xset dpms force off
  elif [ "$idle" -lt "$t" ] && [ "$scr" = false ] 
  then
    xset dpms force on
    scr=true
  fi
done

Note

Since we don't know what causes the behaviour on your system, we still need to find out if it is necessary to specifically switch off your screens per screen by xrandr. You'd have to try.

Ubuntu – HDMI monitor not detected by laptop after unplugging and plugging back in

The closest I could find to your problem is this thread (ubuntuforums.org - Nvidia GTX 950 and TV not seeing signal after input change or power off/on) which references solutions for nVidia 970/980. It would seem your 960 is in between.

The solution proposed there is to reset the monitor to a bad mode and then a good mode using this code:

#!/bin/sh
#Fix TV state when HDMI link is lost.
#By Mario Limonciello <email address hidden>
sleep 10
OUTPUT="HDMI-0"
BAD_MODE="1280x720"
GOOD_MODE="1920x1080"

for MODE in $BAD_MODE $GOOD_MODE; do
DISPLAY=:0 xrandr --output $OUTPUT --mode $MODE
sleep 2
done

I think this script can be improved but wanted to post it in it's original incarnation.

One of the authors in the link wanted to setup udev to automatically call the script on hot-plug event. I've done this for HDMI with this code (hotplugtv) in the past to fix Ubuntu 16.04 pulseaudio 8 bug:

#!/bin/bash

if [[ $(cat /sys/class/drm/card*-HDMI-A-1/status | grep -Ec "^connected") -eq 1 ]]; then
        /bin/sleep 2;
        export PULSE_RUNTIME_PATH="/run/user/1000/pulse/";
        sudo -u rick -E pacmd set-card-profile 0 output:hdmi-stereo;
else
        export PULSE_RUNTIME_PATH="/run/user/1000/pulse/";
        sudo -u rick -E pacmd set-card-profile 0 output:analog-stereo;
fi

exit 0

You will need to modify the if test with your /sys/class/drm/... directory. Then modify the true side of the if test with your script file that resets hdmi screen. On the false side of the if test simply replace the code with a : (noop) if there is nothing to do when the hdmi device is unplugged.

In order to call this scrip from udev during hot-plug events create the file /etc/udev/rules.d/99-hotplugtv.rules containing:

ACTION=="change", SUBSYSTEM=="drm", ENV{HOTPLUG}=="1", RUN+="/path/to/hotplugtv"

Change /path/to/ to the path where you placed hotplugtv script.