IMP: This is for unlocked bootloader only and only for Xperia S LT26i. I have not tested it on any other device.

Things you will need:

1. Nazomi Recovery Image – you can get it from here -> http://forum.xda-developers.com/showthread.php?t=1596285

2. Super User App – You can get it from here -> http://forum.xda-developers.com/showthread.php?t=1538053

3. Kernel file of the firmware you are trying to root. For version 6.1.A.2.45 you can get it from here -> http://www.bhootnath.in/sxs/kernel.Stock6.1.A.2.45_IN_en.sin

4. Fastboot binaries and Fastboot usb drivers which can be downloaded from http://www.bhootnath.in/sxs/fastboot.zip and http://www.bhootnath.in/sxs/usb_driver.zip

5. Not required but good to have Android SDK. http://developer.android.com/sdk/index.html

Prepping Up:

1. Follow the path  Enter “Settings” and select  “Applications” from where your will see a option “Development “just tick  USB debugging there and USB debugging would be enabled on your mobile device.

2. Disable all and any Antivirus on the phone.

3. If you have download the Android SDK, install it.

4. Extract the Fastboot.zip to a folder on your computer.

5. Extract the USB drivers to a folder on your computer.

6. Connect your phone using the USB cable to your PC.

7. Copy the recovery image file “recovery-nozomi.img” and the kernel file “kernel.Stock6.1.A.2.45_IN_en.sin” to the folder on your PC where you have extracted the Fastboot binaries.

8. Copy the SU app zip file “CWM-SuperSU-v0.96.zip” to a folder on your phone (some folder on your SD Card).

 

Fire it up:

1. Lets reboot the device in Fastboot mode. There are two ways to do that

1.1. If you have Android SDK installed, browse to platform-tools directory and with SHIFT key do a RIGHT click of the mouse and then select “Open Command Prompt here”. In the command windows run

adb reboot bootloader

1.2. If you do not have Android SDK installed, power off device and with VOL UP button pressed, connect the phone using USB cable to the PC.

BLUE LED should come up.

 

2. Browse to the directory where you extracted fastboot binaries and with SHIFT key do a RIGHT click of the mouse and then select “Open Command Prompt here”. In the command windows first to check if we are connected in the right mode run

fastboot devices

3. You should see sometghing like

PSDN:DW925S3BFT&POI     fastboot

4. This verfies that the devices is connected in the right mode. Now run
fastboot flash boot recovery-nozomi.img

5. It should show something like
sending 'boot' (5414 KB)...
(bootloader) USB download speed was 9847kB/s
OKAY [ 0.579s]
writing 'boot'...
(bootloader) Flash of partition 'boot' requested
(bootloader) S1 partID 0x00000003, block 0x00002000-0x0000bfff
(bootloader) Erase operation complete, 0 bad blocks encountered
(bootloader) Flashing...
(bootloader) Flash operation complete
OKAY [ 1.851s]
finished. total time: 2.432s

6. Wait till it shows “OKAY” and “finished”

7. So far so good, our recovery image has been flashed to the phone. Now time to reboot. In the same command windows, type in
fastboot reboot

8. Now the phone will boot into recovery mode and select the option “Install zip from SDCard”. Browse to the folder where you had copied the SU zip file (CWM-SuperSU-v0.96.zip), select it and install it.

9. Now select the “Reboot System” option and while it is booting press the VOL UP button to boot back into the fastboot mode. Now run
fastboot flash boot kernel.LT26i_6.1.A.2.45_IN_en.sin

10. Again you should see something like this
sending 'boot' (5590 KB)...
(bootloader) USB download speed was 9588kB/s
OKAY [ 0.612s]
writing 'boot'...
(bootloader) Flash of partition 'boot' requested
(bootloader) S1 partID 0x00000003, block 0x00002000-0x0000bfff
(bootloader) Erase operation complete, 0 bad blocks encountered
(bootloader) Flashing...
(bootloader) Flash operation complete
OKAY [ 2.976s]
finished. total time: 3.589s

11. Once you see “OKAY” and “finished” and cursor is back to the shell, run
fastboot reboot

All done:

The phone will reboot into normal mode and it is rooted now :-D

 

Special thanks to this guide by Doomlord on XDA

http://forum.xda-developers.com/showpost.php?p=23181182&postcount=7

and plenty of other threads from there…

 

Potential Issues:

You are not able to boot into Fastboot mode.

It may happen that you run into problem trying to boot into the Fastboot mode or phone is not detected properly. Make sure that the drivers we downloaded above are installed for the device. Sometimes, drivers wont get installed, windows 7 may not even prompt you for proper drivers. Go to device manager, right click on the yellow device, select update driver, browse to the directory where drivers are extracted and install them.

 

This method is to root your official firmware. Ofcourse easier is to flash any of the custom kernels from XDA forums like Advanced ICS or SSpeed which provide auto rooting but then again if you are one of those people like me who want to stick with the stock and still have root :-)