Udev

You can get the serial number of your FTDI usb/serial converter connected to your xbee via

udevadm info --query=all --attribute-walk --name=/dev/ttyUSB0

and looking for the lines

ATTRS{manufacturer}=="FTDI"
ATTRS{product}=="FT232R USB UART"
ATTRS{serial}=="A80081ej"

where the last one would be your serial you need to write into the rules file, e.g.

# your own XBee ground modem with FTDI USB adapter (adapt serial number)
SUBSYSTEM=="tty", ATTRS{product}=="FT232R USB UART", ATTRS{serial}=="A80081ej", SYMLINK+="paparazzi/xbee", GOTO="tty_FTDI232_end"

To see what udev rules would match (It may show incorrect results, because some values may be different, or not available at a simulation run.)

udevadm test --action=add $(udevadm info --query=path --name /dev/ttyUSB0)

To actually retrigger without having to re-plug it:

sudo udevadm trigger