Volume control will often stop working, if your sound server (normally pulseaudio) dies or restarts whether by itself or by you. The reason pulseaudio may need to be restarted is due to some sort of crash or other issue that prevents sound from working (normally restarting or doing a killall pulseaudio fixes things).
However, you will normally find at least in OS's like Ubuntu/Mint 16/18+ that you cannot control the volume whether adjusting the level, changing input/outputs and........
This assumes your system is a fresh and normally working install.
What often happens is that many new devices have multiple audio outputs which are generally analog and HDMI/Digital out. Sometimes the OS defaults to the wrong one that you didn't want.
For example if your sound is supposed to play over the HDMI, perhaps the output is set to analog or vice versa.........
This just simply outputs what you need a username and password that can be used to authenticate from .htaccess
htpasswd -nb user password
If you want to write it straight to a file
htpasswd -cb /tmp/somefile.pw user password
How To Use This In .htaccess