who - show who is logged on

who [OPTION]... [ FILE | ARG1 ARG2 ]

Print information about users who are currently logged in.

-a, --all

same as -b -d --login -p -r -t -T -u

-b, --boot

time of last system boot

-d, --dead

print dead processes

-H, --heading

print line of column headings

-l, --login

print system login processes

--lookup

attempt to canonicalize hostnames via DNS

-m

only hostname and user associated with stdin

-p, --process

print active processes spawned by init

-q, --count

all login names and number of users logged on

-r, --runlevel

print current runlevel

-s, --short

print only name, line, and time (default)

-t, --time

print last system clock change

-T, -w, --mesg

add user's message status as +, - or ?

-u, --users

list users logged in

--message

same as -T

--writable

same as -T

--help

display this help and exit

--version

output version information and exit

If FILE is not specified, use /var/run/utmp. /var/log/wtmp as FILE is common. If ARG1 ARG2 given, -m presumed: 'am i' or 'mom likes' are usual.

Full documentation <https://www.gnu.org/software/coreutils/who>
or available locally via: info '(coreutils) who invocation'