Let's pretend it's some sort of auditing ;-)
Actually, I use my keylogger (advertised above) more for "situation reconstruction" rather than spying. When you happen to have a multi-root
environment and people "forget what they did", stuff like ttyrpld can really be a gift compared to .bash_history (if it exists, after all).
If one needs it a bit less intrusive, she can also patch bash. A possible solution can be found here:
http://www.drugphish.ch/patches/ratz/bash/bash-3.0-fix_1439-3.diff
But http://ttyrpld.sourceforge.net/ looks indeed interesting, however no 2.4.x support from what I can see.
Regards,
Roberto Nibali, ratz