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File sharing between Mac OS X and the Raspberry Pi is easier than I thought.
FIrst make sure you have a working internet connection on your RaPi, then start a terminal screen, enter "sudo su -" and follow the procedure below:
apt-get update apt-get install netatalk
Answer Y when prompted and wait for a few minutes.
The installation has finished when you are returned to the command prompt.
On your Mac, open Finder and you will see the Raspberry Pi in the list of shared devices on the left hand side of the Finder window. Click on "Connect" and enter your Rapi username and password which is most likely "pi" and "raspberry" unless you have changed it.
You will now have access to your home directory.
To start and stop the file server use the following commands:
service netatalk stop
service netatlak start
To share other directories:
service netatalk stop
nano /etc/natatalk/AppleVolumes.default
Scroll to the end of the file (ctrl-v) where you can see the line
"~/ "Home Directory"
That's where you can add an extra path. ~/ is the home directory of the current user, you can add /media to to share all plugged in USB drives.
Finally you need to start the file service:
service netatalk start
Wait for a little while (30s) and your newly configured Pi file service will show up on your Mac