How do I mute the startup chime on a modern Mac?

Question

How can I get my Macbook Pro Retina to not make that annoying 'bong' chime sound when booting up?

You can always hold "mute" during boot up, but that gets annoying fast if you always want the sound muted. Older systems (OS X 10.6 and below) can use StartupSound.prefPane, but that no longer works on modern Startup Ninja claims to do this, and it does, but it suffers from a bug where it will always unmute the system volume on login, even if the volume was muted when you last logged out.

Is there a way to accomplish this?

Answer 1

The solution I found was to use the nvram command to set the system's audio volume to a muted value. However, you have to re-run this command on every shutdown, since the firmwaresyncd daemon will overwrite whatever value you set regularly.

1. Create a script somewhere on your system (say called silence.sh) with the following content

   #!/usr/bin/env bash
   
   nvram SystemAudioVolume=%80
   

2. Run sudo chown root silence.sh; sudo chmod u+s silence.sh; sudo chmod o+x silence.sh (replacing silence.sh with the name/location of your script.)

3. Finally, run sudo defaults write com.apple.loginwindow LogoutHook /path/to/silence.sh(again replacing the file name/location with the full name and path to your own script.)