An online server implementation of pcb2gcode, requires pcb2gcode.  This was made so you could host a pcb2gcode server and have clients use it instead of installing pcb2gcode on several machines.  LinuxCNC is based on Ubuntu 10.04 or earlier, which doesn't have pcb2gcode on their repositories.  Ubuntu 11.10+ does.  It's a pain to install pcb2gcode from source...or at least it was for me...  So this just makes life easier...  Although right when I was about done with this, I found this site:  http://fablabamersfoort.nl/pcb2gcode/