I'm sorry but Hippomormor's suggestion did not work for me... this, however, did.
1. Launch Terminal (from Applications > Utilities > Terminal);
2. Wait for the Terminal UI to display your computer’s name (root directory) and punch in:
sudo nvram SystemAudioVolume=%80
3. Hit Return/Enter;
4. Now you’ll be prompted to type in your administrator password. Do that, hit OK, and you’re done.
When you restart your Mac, the OS X boot chime should no longer play. If you somehow decide you want the boot sound back, simply fire up Terminal again and, instead of the aforementioned command, use sudo nvram -d SystemAudioVolume.
And yes, I'm on Mavericks. Hope this helps, cheers.
Why use third party stuff for something you can do yourself in terminal?
1. Login as administrator and open a terminal window
2. Create scriptfile for muting
sudo nano /path/to/mute-on.sh
3. Enter this as content, when done press control+O to save and control+X to exit:
osascript -e ‘set volume with output muted’
4. Create scriptfile for unmuting
sudo nano /path/to/mute-off.sh
5. Enter this as content, when done press control+O to save and control+X to exit:
osascript -e ‘set volume without output muted’
6. Make both files executable:
sudo chmod u+x /path/to/mute-on.sh
sudo chmod u+x /path/to/mute-off.sh
7. Check if any hooks already exist (these will be overwritten, so make sure it is OK for you)
sudo defaults read com.apple.loginwindow LoginHook
sudo defaults read com.apple.loginwindow LogoutHook
8. Add hooks for muting
sudo defaults write com.apple.loginwindow LogoutHook /path/to/mute-on.sh
sudo defaults write com.apple.loginwindow LoginHook /path/to/mute-off.sh
- /path/to/ is the location of the scripts, I used /Library/Scripts/
- you can skip the unmuting loginhook (i.e. each logout will silence your machine), but I like it this way because I always have sound available exactly at the volume level I set last time
- root has to be the owner of the script files – running an editor from command line with sudo is the easiest way to achieve that (otherwise you need to chown)
- to delete the hooks, use the following:
sudo defaults delete com.apple.loginwindow LoginHook
sudo defaults delete com.apple.loginwindow LogoutHook
hold down the mute key when turning it on