Kill a Frozen or Crashed UNIX / Linux X Desktop

Posted on in Categories Gnome, Kde, Linux, Linux desktop, UNIX, X server last updated November 23, 2008

Here is a quick tip to kill a crashed Linux / UNIX X desktop system. Many new user do not know this simple tip and end up hitting computer reboot button. Press CTRL + ALT + Backspace to kill GUI and get back to login screen. There are more ways to kill a crashed desktop without restarting your computer.

Linux Iptables block remote X Window server connection

Posted on in Categories Iptables, Linux, Security, X server last updated October 29, 2007

It is true that connections to remote X Window servers should be always made over SSH. SSH supports X windows connections. So my task was allow X over ssh but block unprivileged X windows mangers TCP ports.

The first running server (or display) use TCP port 6000. Next server will use 6001 and so on upto 6063 (max 64 X managers are allowed from 6000-6063).

So assuming that you are going to force user to use ssh for remote connections, here are rules for IPTABLES (add to your firewall script):

iptables -A OUTPUT -o eth0 -p tcp --syn --destination-port 6000:6063 -j REJECT
iptables -A INPUT -i eth0 -p tcp --syn --destination-port 6000:6063 -j DROP

a) The first rules blocks outgoing connection attempt to remove X windows manger.

b) The second rule block incoming request for X windows manger. By using –syn flag you are blocking only connection establishments to the server port.

This is the good way to disallow unprivileged X windows mangers – TCP 6000:6063 ports :)

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