So, (1) total n00b here (2) I've been Googling for about an hour on how to achieve this without success.
All I am looking for is a step-by-step tutorial on how to prevent someone with account SFTP credentials from accessing anything beyond the directory they are supposed to have access to. In brief, if user xyz has access to /opt/application/folder/, they should not be able to access /opt/ or /etc/ or /opt/application/ but /opt/application/folder/filexyz.txt or /opt/application/folder/folder2/filestu.html. You would think this is simple enough, but I just can't seem to do it.
I have followed instructions to install Webmin, which was super simple. I also got to add a user here, which is able to login via SFTP and is redirected to a specific directory once connected - however, they can still navigate to anywhere else on the server. Next, I was able to activate the ProFTPD server after some trying. I also got ProFTPD switched to "Limit users to directories: Home directory", but it appears to be ignored. I know there are a few posts on Chroot here, but they were to no avail to me.
If you would be willing to help, I'd appreciate it. Don't expect any technical knowledge. I know how to ssh into the server and I know how to use Cyberduck to sftp onto the server. That's about it.