After upgrading my wife’s 2010 13” MacBook Pro to OS X Lion I got bit by a nasty bug that affects the volume control buttons on the keyboard. Whenever she tried to adjust the volume the on-screen display would come up as usual, but instead of increasing/decreasing/muting the volume it would display a little no symbol under the speaker and do nothing. I did some digging and found that the problem would correct itself if she plugged her headphones into the 3.5mm jack, but it only lasted until she rebooted. A bit annoying having to do that every reboot.
The good news is that I found a minor tweak in coreaudiod that enables the controls to resume functioning and persists across reboots:
Open Terminal.appRun sudo vi /System/Library/LaunchDaemons/com.apple.audio.coreaudiod.plistLook for the line: <key>KeepAlive</key>Change the next line from <false/> to <true/>Reboot et voila!
Let me know in the comments if this works for you. Seemed to clear things up on my wife’s laptop where other recommendations (resetting PRAM, writing a script to restart coreaudiod at system startup, etc.) didn’t.