I thought I would share some of my commonly used commands for finding out user information:
Shows a listing of currently logged-in users. This command reads /var/log/utmp.
Shows who is logged on and what they are doing.
Shows a list of last logged-in users, including login time, logout time etc. This command reads /var/log/wtmp.
Same as last, except that by default it shows a log of the file /var/log/btmp, which contains all the bad login attempts.
This command reports data maintained in /var/log/lastlog, which is a record of the last time a user logged in.
Prints out the connect time in hours on a per-user basis or daily basis etc. This command reads /var/log/wtmp.
Converts the raw data from /var/run/utmp or /var/log/wtmp into ASCII-parsable format.
The ftpwho program utility displays all active ftp users, and their current process information on the system.
The output of the command is in the format of the "/bin/ps" command.
The ftpcount program utility, a simplified version of ftpwho, shows only the current number of users logged in to
the system, and the maximum number of users allowed.
Please add more.