MAC Address Spoofing

Change the MAC address to 00:01:02:03:04:05  in OSX:

sudo /System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airport -z
sudo ifconfig en1 ether 00:01:02:03:04:05

The first command disassociate from the current network, and the second changes the MAC address. 
Verification:

ifconfig en1 | grep ether

Change the MAC address to 00:01:02:03:04:05  in Linux:

 sudo ifconfig eth0 down
 sudo ifconfig eth0 hw ether 00:01:02:03:04:05
 sudo ifconfig eth0 up

Source: http://osxdaily.com/2008/01/17/how-to-spoof-your-mac-address-in-mac-os-x/