Logs
De whats Wiki
UTMP/UTMPX
utmp/utmpx file is used to store info about currently logged in users. This info can be viewed with commands like "w" and "who". This file is usually cleared at the startup of the machine.
WTMP/WTMPX
wtmp/wtmpx file is used to store info about all the users that ever logged into the system
LASTLOG
lastlog file is used to store last login info of all users on the system
