Check Users Login Activity
Do you know that you can get a lot of information about users connect time to your Linux server using “ac” command.
Can be very useful in checking the authorized and non-authorized activity on your Linux server.
As per man pages of ac:
ac prints out a report of connect time (in hours) based on the logins/logouts in the current wtmp file. A total is also printed out.
Here is a small screenshot from my machine.