with a user name like that, I thought you might already know the admin stuff..."permissions"
a simple search offers plenty of pages to follow... permissions linux group
Near everything including drive space...
http://www.yolinux.com/TUTORIALS/Lin...ingGroups.html
how to check the permissions of a file...
http://linuxcommand.org/lts0070.php
archlinux have some of the best tutorials on the web...
https://wiki.archlinux.org/index.php/Users_and_groups
<edit>
ok, after all that, for a proxy server you would setup the proxy to be transparent,
and to be used system wide (globally).
I used to use squid and iptables to do just that.
http://www.brennan.id.au/11-Squid_We...ml#transparent
Again, a quick search will uncover what needs to be done.
</edit>
hope this helps
regards Glenn