To limit the number of concurrent SSH connections on an Ubuntu Linux system using ufw, you can use the ufw limit command to create a rate limit for incoming SSH connections.
For example, to allow a maximum of 10 connections per minute, you can run the following command:
sudo ufw limit ssh/tcp
This will create a rate limit of 10 connections per minute for incoming SSH connections.
To allow a different number of connections, you can use the --limit option followed by the number of connections and the time period, like this:
sudo ufw limit ssh/tcp --limit 20/minute
This will allow a maximum of 20 connections per minute. You can specify the time period as minute, hour, or day.
To remove the rate limit for incoming SSH connections, you can run the following command:
sudo ufw delete limit ssh/tcp