logkeys was having an issue on Arch Linux where it produced an empty log. The issue is now fixed in the repository (fix found by bytbox from the Arch Linux community), so if you're on Arch (or you seem to experience this issue), please checkout the source from git.
logkeys is a linux keylogger (GNU/Linux systems only). It is no more advanced than other available linux keyloggers, but is a bit more up to date, it doesn't unreliably repeat keys and it should never crash your X. All in all, it just seems to work. It relies on event interface of the Linux input subsystem. Once set, it logs all common character and function keys, while also being fully aware of Shift and AltGr key modifiers. It works with serial as well as USB keyboards.
Keylogger is a software that quietly monitors keyboard input so as to log any keypresses the user makes. Keyloggers can be used by malicious attackers to sniff out passwords and other sensitive textual information, but often times the user himself (or the corporate branch) wants to monitor his computer unattended (or the employees), reliably storing any unauthorized keyboard activity for later inspection. For example, when you leave your PC just to grab a quick bite from the vending machine, you might want to know if anybody was touching it while you were gone. Or you could use it to monitor your supposedly cheating wife, or young kids while they are surfing the web. You could also use it to obtain statistics of your most pressed keys in order to create your custom Dvorak-style keyboard (I've seen that done). Perhaps you want EVERYTHING you've typed or written in the past months archived for ANY purpose... Uses are limitless.
There is a plethora of keyloggers for Windows, but not so many for Linux. On GNU/Linux systems and other reasonable operating systems, keyloggers can be easily implemented with a few lines of shell code. Novice users, however, are usually limited to a narrow set of the following tools: lkl from 2005, uberkey, which appears dead, THC-vlogger, made by a renowned group of hackers, and PyKeylogger. All these tools have their pros and cons. Lkl, for example, sometimes abnormally repeats keys and its keymap configuration is rather awkward for a range of users. Uberkey, which is just over a hundred lines of code, also often repeats keys and what is worse, it makes your mouse move abruptly, loosing any sense of control. PyKeylogger, on the other hand, while very feature rich, only works in X environment. Finally, there is vlogger, ...umm..., about which I cannot say anything specifically, only that it is receiving low score all around the web and it only logs shell sessions. There may be other tools, but either way logkeys definitely makes a simple and competitive addition.
logkeys Linux keylogger works with serial as well as USB keyboards or similar "HID" devices. However, due to a certain bug, a workaround is necessary on some setups.
logkeys supports keyboards like on the image below (courtesy of SEOConsultants.com). These are standard 101 to 105-key PC keyboards with no Asian extensions.