Easy Way:
Download: https://docs.google.com/open?id=0B3l…EhYM3pZV2JrNDg (https://docs.google.com/open?id=0B3l36qXIC0HdeEhYM3pZV2JrNDg)
This is the prerooted system.img of Generic CH Rom!

Then flash this systemimage with fastboot, to flash it type:

fastboot flash system XperiaS_prerooted_ICS_452.img
reboot & done

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Fast boot download
https://docs.google.com/folder/d/0B4MFR0Z7cidONTFvYXV0dnhHalE/edit?docId=0B4MFR0Z7cidOOHVwUng4cHBxcVU

Credit file : http://hatsunumike.exteen.com/
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How to easily flash the prerooted ICS image with FlashTool:

  1. You must have ICS already installed. Be sure your bootloader is unlocked. Unlocking it is very easy, just go on http://unlockbootloader.sonymobile.com/ and follow the steps.
  2. Download the prerooted image you can find in the first page of this discussion.
  3. Download and install the latest version of FlashTools if you haven’t already. Install the drivers for Xperia S and FastBoot if you haven’t already. You can find them in the driver floder inside of where FlashTool is installed.
  4. Rename the prerooted image you downloaded earlier to “system.img“.
  5. Launch FlashTool. Click on the flash symbol (the first one you see) and choose FastBoot mode.
  6. On the left, click on “Reboot into FastBoot mode (via ADB)“. Wait until the notification LED on your device turns blue.
  7. Then, in the middle of the FastBoot Toolbox, click on “Select system to Flash” and choose the “system.img” (the prerooted image you renamed earlier).
  8. Wait until it finishes. You will know it’s finished when the event window of FlashTool will display “Before reboot check for the log status” or something similar.
  9. On the FastBoot Toolbox click on “Reboot device into system“, in the middle column.
  10. Wait for the reboot and you’re done! You should see the SU icon between your apps now.
    How to easily flash the prerooted ICS image with FlashTool:

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