Step 1. Find the right input file, and record everything that comes across it. For example:

cat /dev/input/event5 | od -x

Step 2. Take the recording-file, and decode it with something like this:

• this.C program
• C program
• Perl
  • decent keylogger
  • unpack('L!L!S!S!i!', ...)
  • Linux::Input