Starting a Script When a Volume Mounts

February 14, 2006 - 12:42am

Question

Is there a way to react to hardware events on Mac OS X (something along the lines of udev rules on linux)? Specifically, I have most of my music on an external hard drive and some on my notebook, with music in each of those two locations stored in a different iTunes Library. I’d like to write a script that will switch between the two libraries (something alont the lines of Libra?) that gets triggered when my external hard drive is mounted. So when I connect the external hard drive it should automatically switch to the one library, when it gets unmounted it should automatically switch to the other library. Is there a way to automatically react to events such as mounting and unmounting of a specific volume?

Answer

Yes and no. Yes I can do what you ask, no I can’t do it the way you want.

We’ve done something like this before with Azureus and a drive dedicated to downloading and can do something similar here. Simply create a launchd item that watches /Volumes and starts your script, which looks for the proper drive to exist and then quits iTunes, soft-links the iTunes Library with the one on the external disk, and then starts iTunes. Removing the disk would then trigger, perhaps, linking to a local iTunes Library for local music or whatnot.

I could draw it out into a complete answer, but it seems trivial enough given the other article as a starting point.

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February 14, 2006 - 6:34am

bynkii said

You don’t have to use launchd for this. you can also attach a folder action to /Volumes/ that will be started when a new mountpoint shows up. It has the advantages of not running as root

February 14, 2006 - 7:00am

Adam Knight said

launchd items do not always run as root. Read one of the many launchd articles on this site for more about them.

Finder Actions will start only AppleScripts. You can start a shell script from that AppleScript, or start either a shell or AppleScript with a launchd item.

February 19, 2006 - 4:47am

michelr said

I think the “Peripheral Vision” tool can help you:
http://www.grantedsw.com/p-vision/index.shtml

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