The Nikon D600 does not offer the mass storage option that previous Nikons had any more - thus you have to mount the camera via the PTP protocol. First, install gphotofs and set up the surroundings:
sudo aptitude install gphotofs sudo adduser YOUR_USERNAME plugdev sudo mkdir /media/YOUR_USERNAME/d600 sudo chmod a+rwx /media/YOUR_USERNAME/d600
Then to mount your camera, enter
and to unmount
fusermount -u /media/YOUR_USERNAME/d600
You might want to create more appropriately named scripts that do the mount and unmount for you.