LKL is a user space keylogger that runs under linux--x86/arch. LKL sniffs and logs everything passes trought the hardware keyboard port (0x60).

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(2)Log Key:-
logkeys is a linux keylogger. It is no more advanced than other available linux
keyloggers, notably lkl and uberkey, but is a bit newer, more up to date, it doesn't unreliably repeat keys and it shouldn't crash your X. All in all, it just seems to work. It relies on event interface of the Linux input subsystem.

Once completely set, it logs all common character and function keys, while also
being fully aware of Shift and Altr key modifiers.

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ttyrpld is a kit to log any traffic and actions which go through any of your Kernel's tty
devices. In common-term language, this is a Keylogger

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(4)uber key :-
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(6)Simple keylogger Python script:-
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If you are free & want to learn how keyboard driver works in linux kernal , I would recommended you to read from following link .

Also read this article which is quite interesting.