I have wrote a service with c++ which is always run and now I want to get with it the exact time in that the user log in or log out and then run a script. but the problem is that how could i find that the user logged in or logged out with out checking something frequently?
thanks

you can use wtmp & utmp / implementation of who.

thanks, but i think this can't be useful.i think i did not describe the problem correctly. the service should do an action when user logged in and another when user logged out.

the service has to send a message to a server and one part of the message is that if any body logged in or out.

Running the moral equivalent of tail -f on wtmp will block until the file is written to with a new record, so it might fit your needs after all.

See also http://groups.google.com/group/comp....3d5311b1fec584

sorry! but I think the program again has to always wait for a change

The read() blocks when no data is available. The sleep(1) happens when no data is available; you can adjust for how long it sleeps before it tries again, obviously. But this is admittedly a workaround. I don't think there is a platform-independent way to trigger on log-in or log-out events. If you have dbus or similar, maybe that has the facility you are looking for.