codeaft@codeaft:~$ who
codeaft :0           2020-05-31 10:48 (:0)

codeaft@codeaft:~$ whoami
codeaft

codeaft@codeaft:~$ who -a
           system boot  2020-05-31 16:15
           run-level 5  2020-05-31 10:46
codeaft ? :0           2020-05-31 10:48   ?          1859 (:0)

codeaft@codeaft:~$ who -b
         system boot  2020-05-31 16:15

codeaft@codeaft:~$ who -Hu
NAME     LINE         TIME             IDLE          PID COMMENT
codeaft :0           2020-05-31 10:48   ?          1859 (:0)

codeaft@codeaft:~$ who -q
codeaft
# users=1

codeaft@codeaft:~$ who -T
codeaft ? :0           2020-05-31 10:48 (:0)

codeaft@codeaft:~$ who --help
Usage: 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
      --ips         print ips instead of hostnames. with --lookup,
                    canonicalizes based on stored IP, if available,
                    rather than stored hostname
  -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.

GNU coreutils online help: https://www.gnu.org/software/coreutils/
Full documentation at: https://www.gnu.org/software/coreutils/who
or available locally via: info '(coreutils) who invocation'
codeaft@codeaft:~$