How do I find the computer name who connected to ssh

Question

I have an ubuntu20 server and a bash script located in /etc/profile.d sends a message to telegram if anyone connect using ssh. The purpose of this script is to find out if there is a hack and to take actions.

I want to know the name of the computer that connected to ssh to include in a telegram message to see if the connecter is someone from my team or a hacker. I tried storing the whoami result in a variable but it shows the linux username, not the computer username of whoever connected. Can I execute the whoami command on the device of the connecter? Or any other way to meet what I'm thinking of. the bash code:

#!/usr/bin/env bash
# Import credentials form config file
. /home/roots/credentials.config
URL="https://api.telegram.org/bot${KEY}/sendMessage"
DATE="$(date "+%d %b %Y %H:%M")"
if [ -n "$SSH_CLIENT" ]; then
ip="$(echo $SSH_CONNECTION | cut -d " " -f 1)"
TEXT=" New login via ssh, username ${USER} IP (*${ip}*)
Date: ${DATE}"
curl -s -d "chat_id=${USERID}&text=${TEXT}&disable_web_page_preview=true&parse_mode=markdown" $URL > /dev/null
fi

Answer 1

Based on the post Determining the name of the host currently connected via SSH :

ssh sets the environment variable $SSH_CONNECTION to contain client IP address, client port number, server IP address, and server port number seperated by spaces.

You can use

echo ${SSH_CONNECTION%% *}

to get the client's IP address. To get the DNS name use something like host or dig -x:

host ${SSH_CONNECTION%% *}

Try then the command host ${SSH_CONNECTION%% *}.

Another answer noted that SSH_CONNECTION is lost when starting a sub-process such as by calling su.

Other answers in the post might also be useful.