How to automatically mute on headphones disconnect? Or how to tap bash script to system event listener?

My life would be easier if Ubuntu was muting the sound each time I disconnect the headphones, since every time surrounding is different (example day / night), but the same output volume.

I may figure out the script for that but not without interaction with Ubuntu event listener. I know nothing about it so far.

I will appreciate solution or tip for either subject, but rather not installation of any package for so simple thing, bunch of these is making update way too long + I like my system to be possibly clean or reasoned.

Actually I would write a lot more solutions I'm missing with the knowledge of reaction to events, like auto-adjusting USB mouse settings on connect (the hell they reset for?) or auto enabling GSM modem on connect.

First of, open alsamixer program in terminal (Ctrl+Alt+T).

Check if automute is Enabled. You can navigate to it by using left-right keys, and up down to toggle the value. Esc to exit.

Now, if you mute sound without headphones , plug the headphones, and unplug them again, sound through speakers should stay muted. At least on my machine, with Auto-Mute enabled, I can keep speakers muted, while headphones can output sound upon plugging in.

Short answer

1. To see notifications you have to install notify-osd sudo apt install notify-osd
2. Create a text file <my_name>.sh in your /home/<user_name>/ directory. And add execute permission to the file chmod +x /home/<user_name>/<my_name>.sh

3. Paste the text below to the <my_name>.sh file

   #!/bin/bash
   acpi_listen | while IFS= read -r line;
   do
       if [ "$line" = "jack/headphone HEADPHONE plug" ]
       then
          amixer -D pulse set Master mute
          notify-send "headphones connected. Sound is muted"
       elif [ "$line" = "jack/headphone HEADPHONE unplug" ]
       then
          amixer -D pulse set Master mute
          notify-send "headphones disconnected.  Sound is muted"
       fi
   done
   

4. Go to Startup Configurations menu of your linux system (ubuntu, kubuntu, xubuntu etc). Set /home/<user_name>/<my_name>.sh file to autostart with you desktop environment (xfce, KDE, Gnome etc).

Warning! If you use KDE then DON NOT add the file for "Start script before KDE" or "Application" with bash /home/<user_name>/<my_name>.sh.
Use as script (scenario) and "Start WITH KDE".
IF you did that already then press ctrl + alt + F2, login as user and delete rm /home/<user_name>/<my_name>.sh. If you don't have permissions to delete then remount your disk before deleting mount -o remount, rw /.

How to edit the script

Some linux based systems cache autostart scripts. That means even if you edit /home/<user_name>/<my_name>.sh and logout / login or restart the system then the script will stay the same.
In KDE you can find the cached script symbolic link in /home/<user_name>/.config/autostart-scripts/<my_name>.sh. Delete the <my_name>.sh file manually, logout / login system, add the script to autostart again and logout / login again.
It seems to me it's KDE bug. I don't know about other DE (xfce, Gnome etc)

What you need to know

You can see text as "jack/headphone HEADPHONE plug" in the code above. It's the headphones event name.

To see events:
1. Type in the console acpi_listen
2. Plug and unplug headphones (or another devices)
3. You will see event names in the console. It'll be something like a text below

    user@user-PC:~$ acpi_listen
    jack/headphone HEADPHONE unplug
    jack/microphone MICROPHONE unplug
    jack/headphone HEADPHONE plug
    jack/microphone MICROPHONE plug

If event names in the script above are different then replace them by your event names from the console output.

ACPI and events

To see and test ACPI events you can use evtest sudo apt install evtest

    user@user-PC:~$ sudo evtest
    No device specified, trying to scan all of /dev/input/event*
    Available devices:
    /dev/input/event0:      Lid Switch
    /dev/input/event1:      Power Button
    /dev/input/event2:      Power Button
    /dev/input/event3:      AT Translated Set 2 keyboard
    /dev/input/event4:      Video Bus
    /dev/input/event5:      SynPS/2 Synaptics TouchPad
    /dev/input/event6:      COMPANY USB Device
    /dev/input/event7:      COMPANY USB Device
    /dev/input/event8:      COMPANY USB Device
    /dev/input/event9:      HP Wireless hotkeys
    /dev/input/event10:     HDA Intel HDMI HDMI/DP,pcm=3
    /dev/input/event11:     HDA Intel HDMI HDMI/DP,pcm=7
    /dev/input/event12:     HDA Intel HDMI HDMI/DP,pcm=8
    /dev/input/event13:     HDA Intel HDMI HDMI/DP,pcm=9
    /dev/input/event14:     HDA Intel HDMI HDMI/DP,pcm=10
    /dev/input/event15:     HDA Intel PCH Mic
    /dev/input/event16:     HDA Intel PCH Headphone
    /dev/input/event17:     HP WMI hotkeys
    /dev/input/event18:     HP Webcam: HP Webcam
    Select the device event number [0-18]: 16
    Input driver version is 1.0.1
    Input device ID: bus 0x0 vendor 0x0 product 0x0 version 0x0
    Input device name: "HDA Intel PCH Headphone"
    Supported events:
    Event type 0 (EV_SYN)
    Event type 5 (EV_SW)
        Event code 2 (SW_HEADPHONE_INSERT) state 1
    Properties:
    Testing ... (interrupt to exit)
    Event: time 1522588668.319567, type 5 (EV_SW), code 2 (SW_HEADPHONE_INSERT), value 0
    Event: time 1522588668.319567, -------------- SYN_REPORT ------------                      
    Event: time 1522588670.035275, type 5 (EV_SW), code 2 (SW_HEADPHONE_INSERT), value 1       
    Event: time 1522588670.035275, -------------- SYN_REPORT ------------

For some reasons /etc/acpi/events/jack does not work for me. Possibly I have wrong CONFIG_SND_HDA_INPUT_JACK option. To test that use

    sudo grep CONFIG_SND_HDA_INPUT_JACK /boot/config-$(uname -r)

My answer is based on this answer.