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I'm working on a lab for a cyber-security class and need to find out when certain users are communicating with each other (through named pipes).

The users use:

python gameProgram.py

And then that process takes input and writes it to the named pipes.

I know of the /dev/random file which is modified when someone types, but that can't tell me WHO it typing, right?

I'm thinking of using something like:

grep "voluntary_switches" /proc/####/sched

I'm honestly pretty stuck. The above just returns an integer. Plus I need to get the process number somehow. I'm now struggling with coming up with a script that will let me go from (A) a list of running processes to (B) outputting a username when that user is typing. And unfortunately no sudo privileges.

I need to do something along the lines of:

echo 'ps | grep "python" |    ???    |  grep "voluntary_switches"'

Sort of ...?

Any help would be greatly appreciated!

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closed as not constructive by Keltari, Brad Patton, Dave Rook, Dave M, 8088 Apr 23 '13 at 16:46

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1 Answer

The goal of the exercise is to train you in a different way of thinking so an answer with a 20 line bash script to just solve your problem won't really help. To put the question in some other words

How can user Alice, using off-the-mill Unix commands only, determine whether user Bob is active/typing?

One way to solve that is to look at all the information Bob (or the processes run by Bob) are "leaking" via standard Unix functionality, in this case primarily the process table (which is accessed by ps, top and a bunch of other tools). To find out what information is available, it's best to experiment:

  • Log in once and run python gameProgram.py with a friend of yours (don't type anything let, just let it idle)
  • Log in with a second session and use ps to look at the python process. Does any information change while nobody is typing or is everything staying the same between different calls to ps?
  • Start typing/chatting with your friend
  • Use ps again to see whether anything changes in the output now (something at least will). Can you use this to your advantage?

Once you have the basics together (i.e. know which information from ps is relevant to determine user activity), combine everything together in a shell script.

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