1. Open Arduino IDE. Open File | Examples | ArduinoISP.
The version that comes with the IDE does not always work on Linux / Mac computers (the /Applications/Arduino.app directory is a good indication that @Drc3p0 has a Mac).
avrdude: Recv: . 
avrdude: stk500_getsync(): not in sync: resp=0x15
Huh. That's a symptom I've never seen. @Drc3p0, you sure have a knack for getting entangled with strange problems.
I suspect the Uno bootloader is responding instead of the ArduinoISP sketch. Make certain...
• The disable-auto-reset capacitor is put in place after uploading the modified ArduinoISP sketch
• The disable-auto-reset capacitor is making good electrical contact if, like me, you connect it directly to your Uno