@n.webtec please make separate topics for different issues. (Forum Guidelines: Please read before posting!)
Since we’re talking about chroot jails, I’ll continue in that vein, and encourage you to open new topics for your other questions.
Another option for preventing users from seeing the rest of the filesystem is to force use of FTP and the File Manager (or Upload and Download module), which “chroots” the user without actually using chroot, which is where all the complexity comes from. You do this by not giving them an interactive shell.
That obviously limits users quite a bit…they can’t run any commands, and can only upload/delete/edit files. But, if you really want to lock things down, giving users a shell makes things complicated.