WHAT IS ROOTING AND WHY SHOULD YOU ROOT YOUR ANDROID

Rooting in android devices refers to the process post which the users gains superuser rights which otherwise remain hidden to the user.Once the user secures these rights,he/she can alter the basic functionalities of the phone as well as go for complete overhaul of the feel and interface.Procuring root access is the first step before you can start venturing into the territory of custom roms,kernels,mods etc and truly claim to have exploited your android to its core.

Rooting your Xperia U guide(universal)

I have already mentioned the purpose of rooting in my previous post,now let's go for the kill.
What you need:
1.A Sony Xperia U smartphone running any version of ICS(.10,.54,.89,.100)
2.Connectivity cable provided by Sony
3.A PC or a laptop running Windows XP or newer version of Windows.
4.The magical flashtool software from here: http://androxyde.github.io/
You are now good to go:
1.Install flashtool to your LOCAL DISC ONLY.
2.Now navigate to C:\Flashtool\drivers
3.Double click flashtool-drivers and install drivers available for all devices(that’s right,tick all devices).
4.Now take your phone and go to settings,about phone,build number.
FOR BUILD NUMBER ENDING WITH .10
Rooting your phone is a piece of cake.Just follow these steps.
1.Download the root packackage from here:http://forum.xda-developers.com/showthread.php?t=1886460
(you may thank the developer for his hardwork if you have XDA membership by pressing thanks button).
2.Extract the files from the archive to a convenient location,say the desktop.
3.Now turn USB debugging mode ON in your phone  Menu>>Settings>>Developer options>>USB debugging
4.Now connect your phone to your PC using the USB cable.
5. Double-click on the RunMe.bat file you extracted earlier to your Desktop.
6. When asked about mode, select Normal mode(for xperia u).
7. Select Root option in the tool and rooting will begin for your device.
8.After the process is over,just reboot your device.
VOILA your Xperia U is now rooted and should display superuser or superSU in your app drawer.
FOR BUILD NUMBER ENDING WITH .54,.89,.100
For some reason all versions of ICS that came after .10(yes,.10 is the oldest) are not directly rootable.By this i mean the kernel of these versions is not directly rootable,so we have to follow a turnaround procedure which involves replacint the kernel of these versions with the kernel of .10 version temporarily.rooting it and again flashing the kernel version that these versions come with,thus preserving the root access.The procedure is as follows:
First check the build number of your ics version before starting(if ending .54,.89,.100) and note it down.
1.Download 6.1.1.b.10 kernel from here: http://www.mediafire.com/download.php?s0l6400e86680rp
2.Now open flashtool on your pc installed earlier.
3.Now click the lightning icon on the top and select fastboot mode and click OK,
4.Now turn off your phone and after it is completely off,connect your phone to PC  while pressing VOLUME UP key(keep it firmly pressed until the led bar on xperia u lights up in blue colour).
5.Now come back to where you left in flashtool and click SELECT KERNEL TO FLASH on the right.
4.Now navigate to the kernel.elf file that you downloaded and select it and it will be flashed(After this step,you have flashed your phone with .10 kernel)
5.Now just follow the steps for rooting a phone running 6.1.1.b.1.10 as stated above.
6.After you have completed rooting(i.e. completed all 8 steps),
again flash the kernel your phone was running on earlier from following link:
6.1.1.b.1.54 kernel:http://www.mediafire.com/download.php?8eqdfx9kcupreir
6.1.1.b.1.89 kernel:http://www.4shared.com/file/1Fj-C3tc/Xperia_U__ST25i__611B189_ICS_4.html
6.1.1.b.1.100 kernel:http://www.4shared.com/file/1Fj-C3tc/Xperia_U__ST25i__611B189_ICS_4.html

Unlocking bootloader for your Xperia device

Warning:Unlocking bootloader may void your warranty or harm your phone for which i am not responsible.Further,BRAVIA ENGINE will not work for bootloader unlocked devices.However,the process is reversible.DO AT YOUR OWN RISK
Advantages:All the custom ROMs and kernels can be installed very easily on phones with unlocked bootloaders.

Procedure:

1.Input this code on your Xperia device:*#*#7378423#*#*
2. Goto Service info > Configuration > Rooting Status.If the Bootloader Unlock Allowed is yes, you can continue.
3.Note down your unique IMEI number obtained by dialing *#06#.
4.Now goto the following site:http://unlockbootloader.sonymobile.com/
5.Read through all the steps and risks involved and if ready,press continue and keep going.
6.Enter all the necessary info required such as your name,your phones’s unique IMEI,your correct e-mail address.
7.After submitting the form,you will receive a unique bootloader unlock ID in your mailbox.
8.Note it down very clearly and correctly.
9.Now install flashtool after downloading from here into your local drive:
http://androxyde.github.io/
10.Go here:C:\Flashtool\drivers and install all the drivers for all the devices(tick all the devices).
11.Open flashtool,connect your phone to your PC in USB debugging mode.
12.Click on Plugins > Bootloader Unlock > Run
13. Enter your unlock code sent by Sony and proceed as prompted.
14.Now,turn off your phone. Enter the fastboot mode (Press and hold the volume up button, and plug the cable. When the blue led appear, release the volume button)
14.Wait for it to complete.Your bootloader should now be unlocked.
You can check it by following step 2 and checking the rooting status.