How to use the who command:

The main syntax of the who command is as follows:

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

When called without any options or arguments, the output is something like this:

root     pts/0        2020-11-17 20:10 (10.10.0.2)  shetaban    pts/1        2020-11-17 20:11 (10.10.0.8)

The who command produces a formatted list of all users currently logged into the system.

Each line consists of four fields separated by one or more spaces:

Registered user name
User terminal
When the user is logged in.
The hostname or IP address from where the user logged in. To force Ips, use the –ips option.

If you want to print column headings, add the -H (–heading) option:

who -h

Output:

NAME      LINE         TIME             COMMENT  root      pts/0        2020-11-17 20:10 (10.10.0.2)  linuxize  pts/1        2020-11-17 20:11 (10.10.0.8)

This command captures information about the system and people logged in from the /var/run/utmp file. If you want to use another file, pass the file path to the command.

The who command accepts two non-optional arguments. When invoked with two arguments, the command prints only information about the terminal associated with the current user. The same output is displayed when using the -m option.

You can use either argument:

who am i  who mom love  who foo bar  who -m

Each of the above commands prints the same information:

shetaban pts/1        2020-11-17 20:11 (10.10.0.8)

who command options:

The who command accepts several rarely used options.

The -b, –boot option tells you who last printed the system boot:

         system boot  2020-07-20 19:02

To get a list of all dead processes, use the -d, –dead option:

who -d

The -r, –runlevel option tells who to show the current level:

who -r

Output:

         run-level 5  2020-07-20 19:02

To get just the username and the number of currently logged in users, use the -q, –count option:

who -q

Output:

root shetaban  # users=2

The -a option forces everyone to print all information:

who -a

Output:

system boot  2020-07-20 19:02  LOGIN      tty1         2020-07-20 19:02               673 id=tty1             run-level

who command in Linux