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Cerin
Asked: 2012-04-18 09:52:30 +0800 CST

How to allow key functions while desktop locked

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Is it possible to allow a keyboard's volume keys to continue working when your desktop is locked? Currently, the default behavior disables all special-function keys until the desktop's unlocked. I like to use my PC as a music player and leave it locked when I'm not directly at the console, but I still want to let people to control the volume if a song's too loud.

shortcut-keys music lock-screen

2 Answers

  1. Somewhat of a shameful plug, but since there didn't seem to be any existing solution, and since the task seemed relatively straight-forward, I wrote a simple Python daemon to fix the problem. It uses the python-xlib API to capture system-wide key presses and then runs custom shell commands. It assumes a basic Debian/Ubuntu setup, but would probably work on most Linux systems with a few tweaks.

    For my case, the volume up/down keys map to the code 122/123, so the corresponding commands to lower or raise volume only when the desktop is locked are:

    gnome-screensaver-command -q | grep "is active" && bash -c '/usr/bin/pactl -- set-sink-volume `pacmd list-sinks | grep -P -o "(?<=\* index: )[0-9]+"` -10%'
gnome-screensaver-command -q | grep "is active" && bash -c '/usr/bin/pactl -- set-sink-volume `pacmd list-sinks | grep -P -o "(?<=\* index: )[0-9]+"` +10%'

    Admittedly, that's a bit verbose. The second grep is to find the active sound interface on systems that might have several (e.g. my laptop has a Master and Headphone interface, allowing these commands to control either).

    Edit: This no longer works as of Ubuntu 16. All X functions seem to become disabled, even from the terminal, once the screen locks.

    • 9

  2. I wrote this script which works for me on Ubuntu 18.04:

    #!/bin/bash

EVFILE=/dev/input/event3
USR=flurl


evtest $EVFILE \
    | grep --line-buffered -E "KEY_MUTE|KEY_VOLUMEDOWN|KEY_VOLUMEUP" \
    | grep --line-buffered "value 1" \
    | stdbuf -oL awk -F '[()]' '{print $4}' \
    | while read KEY; do
        if [ "$KEY" = "KEY_MUTE" ]; then
            su - $USR -c "amixer -D pulse sset Master +1 toggle"
        elif [ "$KEY" = "KEY_VOLUMEUP" ]; then
            su - $USR -c "amixer -D pulse sset Master 5%+"
        elif [ "$KEY" = "KEY_VOLUMEDOWN" ]; then
            su - $USR -c "amixer -D pulse sset Master 5%-"
        fi  
      done

    You have to run it as root and adapt the variables EVFILE and USR

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