Permanently disable startup chime on macOS

Permanently disable startup chime on macOS.md

How to do it

Complete the following steps (with sudo permissions):

1. Add sound-off.sh and sound-on.sh to /Library/Scripts/
2. Run the following commands:

sudo chmod u+x /Library/Scripts/sound-off.sh /Library/Scripts/sound-on.sh
sudo defaults write com.apple.loginwindow LogoutHook /Library/Scripts/sound-off.sh
sudo defaults write com.apple.loginwindow LoginHook /Library/Scripts/sound-on.sh

How it works

The shell scripts are added as hooks for the logout and login procedures. Both these hooks execute an osascript command, muting all output sound during login/shutdown, and subsequently unmuting during login/startup.

The osascript command is used for executing AppleScripts and other Open Scripting Architecture (OSA) language scripts, and executes the given script files (or stdin if no file is provided).

Why use hooks?

Most search results for this issue all seem to provide the same solution, which is:

sudo nvram SystemAudioVolume=%80   # turn off chime
sudo nvram -d SystemAudioVolume    # turn on chime

This, however, doesn't seem to provide a permanent solution, and doesn't even seem to work at all with the last couple of updates to macOS. Using the login/logout hooks provided here seem to do the trick though, and is permanent.

Reverse procedure

To reverse this procedure, do the following:

1. Delete the sound-off.sh file and run:
   • sudo defaults delete com.apple.loginwindow LogoutHook
2. Reboot and log back in
3. Delete the sound-on.sh file and run:
   • sudo defaults delete com.apple.loginwindow LoginHook
4. You're done!

Source

JacksAdvice - How To Turn Off The Mac Startup Sound (Alex Krenshaw, November 6, 2018)

sound-off.sh

#!/bin/bash

osascript -e ‘set volume output muted 1’

sound-on.sh

#!/bin/bash

osascript -e ‘set volume 4’