On the Linux, Solaris, and BSD operating systems, wtmp is a file containing a history of all logins and logouts. On Linux systems, it is located at /var/log/wtmp.
Various commands access wtmp to report login statistics, including the who and lastb commands.
Computer abbreviations, Log, Operating system, Operating System terms
The “w” in “wtmp” stands for “who” — as it does in the w command, which displays what users are currently logged in to the system.
