Can I force screen blank and ignore input?

Question

I would like to force my screen to blank, and leave it stay blank regardless of what I do with my keyboard and mouse until it receives a command to unblank (kind of like a lock).

The commands I know are:

xset dpms force off
sleep 2
xset dpms force on

I only want it to blank for two seconds then unblank, but I want it to absolutely stay blank for these two seconds no matter what. Can this be done?

Answer 1

You could just disable your keyboard and mouse for the duration. First, get your keyboard and mouse IDs:

$ xinput --list
⎡ Virtual core pointer                      id=2    [master pointer  (3)]
⎜   ↳ Logitech M325                             id=14   [slave  pointer  (2)]
⎣ Virtual core keyboard                     id=3    [master keyboard (2)]
    ↳ SIGMACHIP USB Keyboard                    id=11   [slave  keyboard (3)]

I have various things connected to my machine and am running a laptop so the output of xinput --list is very long. I have redacted it here for clarity. You need to figure out what the IDs of the devices you need to disable are. In my case, they were 14 and 11.

Now, switch off your screen, disable your keyboard and mouse, wait 2 seconds and switch everything back on again:

xinput set-prop 'Logitech M325' 'Device Enabled'  0 &&
xinput set-prop 'SIGMACHIP USB Keyboard' 'Device Enabled' 0 &&
xset dpms force off &&
sleep 2 &&
xinput set-prop 'Logitech M325' 'Device Enabled' 1 &&
xinput set-prop 'SIGMACHIP USB Keyboard' 'Device Enabled' 1 &&
xset dpms force on

On my system, SIGMACHIP USB matches more than one device. For some reason it is also identified as a mouse. To be 100% sure of getting the right devices, you can prepend their class to their name:

xinput set-prop 'pointer:Logitech M325' 'Device Enabled'  0 &&
xinput set-prop 'keyboard:SIGMACHIP USB Keyboard' 'Device Enabled' 0 &&
xset dpms force off &&
sleep 2 &&
xinput set-prop 'pointer:Logitech M325' 'Device Enabled' 1 &&
xinput set-prop 'keyboard:SIGMACHIP USB Keyboard' 'Device Enabled' 1 &&
xset dpms force on

Answer 2

You can use xrandr. For example if your display is HDMI1 you can do

xrandr --output HDMI1 --off
sleep 2
xrandr --output HDMI1 --auto

You can find the name with

xrandr|grep ' connected'

Answer 3

I finally figured out an answer that at least works on my systems (a Lenovo ThinkPad X201 and a ThinkPad X201 Tablet, which both use LVDS panels). It actually disables the backlight, but unless you have a transflective or reflective LCD (which is pretty unusual), it should effectively be the same as having the LCD switched off.

First, I installed Intel GPU Tools (README here for more information). In debian, this was done with:

# apt-get install intel-gpu-tools

This package contains a program called intel_backlight, which directly interacts with Intel GPUs' registers and thus is not limited to the 'safe range' in modern Linux kernels' sysfs filesystem, where brightness level 0 is always supposed to be 'on at a low level of brightness.'

Unfortunately, this program needs to be run as root, and it doesn't really sanitize its inputs very well (it just blindly atoi()'s the first argument to the script and assumes it's actually a number). I'm still working on a proper solution to this, but for now your options are to either:

1. Run this as root
2. Write a script and acpid configuration to trigger it upon a specific ACPI event.

I chose the latter option. I picked a key combination which acpi_listen detected as firing an ACPI event, but which was not mapped to do anything already on my laptop. I chose fn+f1. Theoretically, one could also have it fire on the brightness-down key, check if the brightness was already at the minimum, and if so turn off the backlight.

I wrote the following files:

/etc/acpi/events/fnf1-toggle-lcd:

event=button/fnf1
action=/etc/acpi/toggle-thinklight-or-tablet-lcd.sh "%e"

/etc/acpi/toggle-thinklight-or-tablet-lcd.sh:

#! /bin/bash
# intel_backlight appears to require root privs.

# is the light on or off?
export INTEL_BACKLIGHT="/usr/bin/intel_backlight"
export light_state=$("$INTEL_BACKLIGHT" | sed 's/current backlight value: //g'|sed 's/%//g')
if [ "$light_state" -eq 0 ]; then # if the backlight is currently off
  # restore brightness level
  cat /root/brightness > /sys/class/backlight/acpi_video0/brightness
else # the backlight is currently on
  # back up current brightness level
  cat /sys/class/backlight/acpi_video0/brightness > /root/brightness
  # turn off backlight
  "$INTEL_BACKLIGHT" 0
fi

Be sure the shell script is marked as executable.

Maybe not exactly what was wanted, and I know I'm late to the party, but it's working here.

Alternatively, on eDP panels, doing echo 0 > /sys/class/backlight/acpi_video0/bl_power might work. This absolutely will not work on LVDS panels, because apparently some kernel developers thought that was a good idea.