tar -zxvf <tar filename> <file you want to extract>
-x: instructs tar to extract files.
-f: specifies filename / tarball name.
-v: Verbose (show progress while extracting files).
-z: filter archive through gzip, use to decompress .gz files.

tar -zxvf <tar filename> -C /path/to/existent/folder ?? 

PRÜFEN

source: http://unix.stackexchange.com/questions/113754/allow-user1-to-su-user2-without-password add following to /etc/pam.d/su below pam_roottok.so line:

auth       [success=ignore default=1] pam_succeed_if.so user = user2
auth       sufficient   pam_succeed_if.so use_uid user = user1

or for user in group GROUP:

auth       [success=ignore default=1] pam_succeed_if.so user = user2
auth       sufficient pam_succeed_if.so user ingroup GROUP 

hmm funktioniert noch nicht.. muss man das noch neustarten?