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Many Logitech input peripherals - mostly mouse and keyboards, but also numpads, presenters, trackballs and touchpads - come with a unique USB receiver. If your peripherals and receiver are not paired from fabric, but support the Logitech Unifying technology, you can still pair them using the app-misc/ltunify package.
The package is available for ~amd64 and ~x86 only.
emerge --ask app-misc/ltunify
The usage is trivial.
shows the devices actually paired.
ltunify unpair idx
removes a listed paired devices that doesn't exist anymore.
adds a device simply asking to switch it off and on.
shows a complete help.