Download the Joomscan from here:
Copy/Move the downloaded files in directory
Now you have to set permission for the Joomscan file. In order to this, Type the following command in Terminal(if you don’t know how to open terminal at all, please stop reading this and start it from basics of Linux).
Update the scanner to latest version. To do this, enter the following command in Terminal:
Now everything ok, we have to scan our joomla site for vulnerability. To do this, enter the following command in Terminal:
Wait for a while, and it will list of the vulnerability found.