Add X hacks post.

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+While writing up my [[mxcons]] post, I ran across the *ease of
+(ab)using X11" articles ([1][] and [2][]) Brian Hatch posted in 2004.
+In the first part, he walks you through `DISPLAY` and `xauth`, which
+I'd seen before, but the second part contained more nice tricks.  The
+difficulty here is remembering all the useful little utilities for
+manipulating X.  Here's a quick list:
+
+* `xmessage` for popping up dialog windows
+* `xlsclients -l` for listing all connected clients (this is how you
+  get those window ids!)
+* `xwininfo -id windowid` to get more info on a given window
+* `xwd` for taking screenshots
+* `xev`, the classic X event monitor
+* `xkey`, non-standard keysniffer
+* `x2x` to connect your mouse and keyboard to another display
+* `xdpyinfo` to get information about an X display.
+
+Here are some examples:
+
+Grab whole desktop as a png:
+
+    $ xwd -root -silent - | convert - root.png
+
+Grab single window as a png:
+
+    $ xwd -id windowid -silent - | convert - win.png
+
+Determine which window has the focus:
+
+    $ xdpyinfo | grep focus
+
+Brian's [subsequent article][3] discusses malicious sysadmins abusing
+X to log keystrokes on your home computer.
+
+Everyone should read these before they start using X, which would help
+avoid exposure to [simple attacks][].
+
+[1]: http://www.hackinglinuxexposed.com/articles/20040513.html
+[2]: http://www.hackinglinuxexposed.com/articles/20040608.html
+[3]: http://www.hackinglinuxexposed.com/articles/20040705.html
+[simple attacks]: http://seclists.org/educause/2007/q1/138
+
+[[!tag tags/linux]]
+[[!tag tags/tools]]