The “who” reveals users who is currently logged in the system. It shows some information such as the username, the timestamp, and the IP address.
General syntax for who command:
$ who [OPTIONS...]
Show all users’ information
who -a
The -a option allows you to see all the details of each user logged into the current system.
Example: Entering the who -acommand and getting the output of all the information about the users on the system
Show system’s last boot time
who -b
Use the who command with the -b option to print the last boot time of the system.
Example: After using the command, the output will print the message “system boot,” next to which the date and time are displayed.
List all logged in users
who -q
The -q option displays a list of usernames and the number of users currently logged on to the system.
Example: Entering the command and see the users logged in and their current number
Check user’s write permission
who -T
Use the -T option to display the user’s post status. This will help you check the permissions to write messages to the terminal.
Example: Let’s type the who -T command to display user statuses in the terminal.
Show all dead processes
who -d
This command allows you to get a complete list of all dead processes.
Example: Typing the who command with the -d option to show details of all dead processes. Note: No dead processes in this case.
Show information about current user
who -m
The -m option displays the hostname and user associated with I/O devices such as keyboards.
Example: Let’s run the who -m command to see how this command works.
Show all active processes spawned by INIT process
who -p
Use the -p option to show a list of active processes spawned by init (background process which starts other processes).
Example: Entering the command with the -p option to get a list of processes. Note: No active processes in this case.
Show current runlevel
who -r
To display the current runlevel of the system, use the -r option.
Example: Executing the who -r command to get information about the system runlevel
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