$ sudo apt-get update
$ sudo apt-get install gpsd gpsd-client python-gps
Enable the serial interface and disable serial login shell with raspi-config
then reboot.
Confirm /dev/ttyS0 exists
$ ls -l /dev/serial*
lrwxrwxrwx 1 root root 5 May 9 10:38 /dev/serial0 -> ttyS0