How to prevent ssh user to login if same user is still logged in?

For security reasons, I want to restrict users to have more than one ssh connection. In terminal, if I check $ last user , I'll find the user is still logged in. Is any solution to check if user is still logged in don't allow to login again?

You can't directly limit the ssh connections. But you can limit the logins of this user. Edit /etc/security/limits.conf and add line:

specificuser  hard    maxlogins   1

This will limit the logins to 1 for specificuser (independently if we talk about ssh, telnet or console logins)

Configure the option "MaxStartups " in the "/etc/ssh/sshd_config file":

MaxStartups 1

Then restart the ssh service. This setting allows a maximum of one connection for each user

https://man7.org/linux/man-pages/man5/sshd_config.5.html

If you are using the same user for all users on your company (aka root), you can add the next code on the begging of the /etc/profile file to filter one user by IP address:

# Limit logins to one user by IP
NEW_LOGIN=$(last -n 1 | head -n 1 | awk '{print $3}')
CURRENT_LOGINS=$(w -hs | awk '{print $3}' | grep "$NEW_LOGIN" | wc -l)
if [ "$CURRENT_LOGINS" -ge "2" ]; then
  echo "Only one login per user/IP is allowed, closing this connection to $NEW_LOGIN"
  exit 1
fi