We disable the local console when using x11vnc

Hello everyone,

there are many articles online about how to set up a remote connection to an existing Xorg session via x11vnc, but I couldn’t find anywhere how to disable the local monitor and input so that anyone sitting next to the remote computer cannot see what you are doing or press buttons in your session. Below is my method of making x11vnc behave more like connecting to Windows via RDP.

So, let's assume you already know how to use x11vnc; if not, you can Google it or read something like here.

Given: we launch x11vnc, connect to it with a client, everything works, but the local console of the computer is also available for viewing and input.

We want: disable the local console (monitor + keyboard + mouse) so that nothing can be seen or entered.

Turning off monitors

The first thing that came to mind was simply to turn off the monitor via xrandr like this:

$ xrandr --output CRT1 --off

but in doing so, the desktop environment (I have KDE) starts to think that the monitor is really disconnected and begins to move windows and panels, everything shifts and becomes sad.
There’s a more interesting way, which involves sending the monitor to sleep, you can do this like:

$ xset dpms force off

but it’s not completely smooth. The system wakes the monitor at the first event. A simple workaround is the following loop:

while :; do
    xset dpms force off
    sleep .5
done

I didn’t think any further — I was lazy, it serves its purpose — the monitors show nothing, even if buttons are pressed, the mouse is moved, etc.

UPD:

Thank you amarao for another method of turning brightness to zero:

$ xrandr --output CRT1 --brightness 0

Disabling input

To disable input, I used xinput. When run without parameters, it outputs a list of devices:

$ xinput
⎡ Virtual core pointer                          id=2    [master pointer  (3)]
⎜   ↳ Virtual core XTEST pointer                id=4    [slave  pointer  (2)]
⎜   ↳ Logitech USB Laser Mouse                  id=9    [slave  pointer  (2)]
⎣ Virtual core keyboard                         id=3    [master keyboard (2)]
    ↳ Virtual core XTEST keyboard               id=5    [slave  keyboard (3)]
    ↳ Power Button                              id=6    [slave  keyboard (3)]
    ↳ Power Button                              id=7    [slave  keyboard (3)]
    ↳ Sleep Button                              id=8    [slave  keyboard (3)]
    ↳ USB 2.0 Camera: HD 720P Webcam            id=10   [slave  keyboard (3)]
    ↳ HID 041e:30d3                             id=11   [slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard              id=12   [slave  keyboard (3)]

Devices Virtual core… disabling is not possible — an error is thrown, but the others can be turned on and off; for example, you can go a minute without a mouse like this:

xinput disable 9; sleep 60; xinput enable 9

Ready solution

For my case, I created a script that I run in the ssh session. It disables local input and starts the x11vnc server, and after the script completes, everything returns to normal. In total, I have three scripts, here they are (updated).

switch_local_console:

#!/bin/sh

case $1 in
    1|on)
    desired=1
    ;;
    0|off)
    desired=0
    ;;
    *)
    echo "USAGE: $0 0|1|on|off"
    exit 1
    ;;
esac

keyboards=`xinput | grep -v "XTEST" | grep "slave  keyboard" | sed -re 's/^.*sid=([0-9]+)s.*$/1/'`
mouses=`xinput | grep -v "XTEST" | grep "slave  pointer" | sed -re 's/^.*sid=([0-9]+)s.*$/1/'`
monitors=`xrandr | grep " connected" | sed -re 's/^(.+) connected.*$/1/'`

for device in $mouses
do
    xinput --set-prop $device "Device Enabled" $desired
done

for device in $keyboards
do
    xinput --set-prop $device "Device Enabled" $desired
done

for device in $monitors
do
    xrandr --output $device --brightness $desired
done

disable_local_console:

#!/bin/sh

trap "switch_local_console 1" EXIT

while :
do
    switch_local_console 0
    sleep 1
done

Actually, the main script (I have two monitors; I start one shared server and one for each monitor).

vnc_server:

#!/bin/bash

[[ ":0" == "$DISPLAY" ]] && echo "Should be run under ssh session" && exit 1

export DISPLAY=:0

killall x11vnc

rm -r /tmp/x11vnc
mkdir -p /tmp/x11vnc/{5900,5901,5902}

params="-fixscreen V=5 -forever -usepw -noxkb -noxdamage -repeat -nevershared"

echo "Starting VNC servers"

x11vnc -rfbport 5900 $params 2>&1 | tinylog -k 2 -r /tmp/x11vnc/5900 &
x11vnc -rfbport 5901 $params -clip 1920x1080+0+0 2>&1 | tinylog -k 2 -r /tmp/x11vnc/5901 &
x11vnc -rfbport 5902 $params -clip 1920x1080+1920+0 2>&1 | tinylog -k 2 -r /tmp/x11vnc/5902 &

echo "Waiting VNC servers"
while [ `ps afx | grep -c "x11vnc -rfbport"` -ne "4" ]
do
    sleep .5
done

echo "Disabling local console"
disable_local_console

echo "Killing VNC servers"
killall x11vnc

That's it. We SSH in, run vnc_server, while it's running, we have access via vnc and the local console is turned off.

Thank you for your attention; additions and improvements are welcome.

Source: habr.com