The last command is a handy way to find out who has been connecting to a
machine and when.
Last will list the sessions of specified users, ttys, and hosts, in reverse time order. Each line of output contains the user name, the tty from which the session was conducted, any hostname, the start and stop times for the session, and the duration of the session. If the session is still continuing or was cut short by a crash or shutdown, last will so indicate.
In particular, this can be useful for finding an IP address that you want to connect to.
See man last for more details.