Disabling MacBook Startup Sound in Linux

There is an easy way to disable the MacBook startup sound (boot chime) even after wiping out OS X and installing Linux.

This sound can be easily disabled if you mute the volume in OS X and shutdown the computer. The value is stored in NVRAM.

Reboot the computer and hold Cmd+Alt(Option)+R. This will start OS X Internet recovery mode;
Open the terminal and issue the following command
```
nvram SystemAudioVolume=%00
```
Reboot.

Voila. In Linux try this:

# efivar -l | grep SystemAudioVolume
 7c436110-ab2a-4bbb-a880-fe41995c9f82-SystemAudioVolume
 7c436110-ab2a-4bbb-a880-fe41995c9f82-SystemAudioVolumeDB

# efivar -n 7c436110-ab2a-4bbb-a880-fe41995c9f82-SystemAudioVolume -p
GUID: 7c436110-ab2a-4bbb-a880-fe41995c9f82
Name: "SystemAudioVolume"
Attributes:
    Non-Volatile
    Boot Service Access
    Runtime Service Access
Value:
00000000  00                                                |.               |

# efivar -n 7c436110-ab2a-4bbb-a880-fe41995c9f82-SystemAudioVolumeDB -p
GUID: 7c436110-ab2a-4bbb-a880-fe41995c9f82
Name: "SystemAudioVolumeDB"
Attributes:
    Non-Volatile
    Boot Service Access
    Runtime Service Access
Value:
00000000  00 
#

Note 1: Before disabling both variables had non zero values. Also SystemAudioVolumeDB doesn't seem to have any effect.

Note 2: RHEL or CentOS users need to rebuild efivar from the Fedora src.rpm.

Note 3: several Internet sources suggest that writing EFI variables from Linux may sometimes corrupt your Apple firmware. I didn't research this any further. If you happen to figure out how to successfully write to these variables under Linux please let everyone know in the comments (in case OS X recovery mode goes missing, you know).

Thanks to my reader Alexander, who gave me the hint in a previous blog post.

Comments !