who — show WHO is logged on
who prints the info (login name, terminal line, login time, and remote hostname or X display) abt abt each user currently logged on.
who uses /var/run/utmp file to know abt the current users.
$ who — Show who are all logged on.
$ who -H — Show info with header.
$ who -m — only hostname and user associated with stdin.
$ who -q — Show currently logged username and count.
$ who -r — Show the current run level.
$ who -s — Short form.
$ who -T — Add user’s message status as +, – or ?
$ who -a — Show all info.
$ who am i — Your detail.
$ who mom likes — !!?? 🙂
$ who /var/log/wtmp — Who has previously logged on.
Read : man who