/lib/udev/rules.d/40-libgnuradio-fcd3.7.2.1.rules is in libgnuradio-fcd3.7.2.1 3.7.2.1-5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | # Funcube Dongle
ACTION=="add", BUS=="usb", SYSFS{idVendor}=="04d8", SYSFS{idProduct}=="fb56", GROUP:="usrp", MODE:="0660", SYMLINK+="FCD"
# Funcube Dongle
SUBSYSTEMS=="usb", ATTRS{idVendor}=="04d8", ATTRS{idProduct}=="fb56",GROUP:="usrp", MODE:="0660", SYMLINK+="FCD"
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