Last Christmas I got a present for my parents, an awesome Kindle 4 non-touch (NT). It happened to be more useful than I thought, I bring with me a tone of books in a device that weights 170g and its battery lasts almost one month. BTW, the picture I currently have on the right side of the blog it's me using it.Since I have a strong interest in GNU/Linux and its kernel, and taking advantage of the fact that Amazon released the code of all kindles, I have been digging into its code and I think I will be spending some of my free time trying not bricking it while testing my costume kernels/apps. Paradoxically, one of the books I am reading with my kindle is about the kernel development.
By default you do not have root privileges in the normal course of reading in your Kindle. Hence, the first step you have to carry out if you want rock & roll is to get root access. There is a lot of information you can find on google regarding this process. In my case, I used this and this links to do it.
Firstly, you have to create a blank file, called ENABLE_DIAGS in the root of the kindle filesystem. To do so, you need to plug the USB cable and mount the filesystem.
After it, you need to reboot your Kindle (press the Menu key, select Settings, press the Menu key again, select Restart). The Kindle will reboot in diagnostics mode.
Then, enable USBnet in the menu Misc individual diagnostics -> Utilities -> Enable USBnet. This will enable network access to your Kindle via USB.
You can also check there its network configuration.
Setup the IP for the new connection: IP 192.168.15.1 Subnet 255.255.255.0, all the other options are empty. Open an ssh client like putty and connect to 192.168.15.244.
To get SSH access you have to use the root username and mario password. If it doesn't work you should go to http://members.ping.de/~sven/kindle.html and generate the password for your kindle, by giving it the serial number of it.
When you done with Kindle press Right a few times and go to 'Exit, Reboot or Disable Diags' -> 'Disable Diagnostics'

