[Sony Xperia S, Acro S, Ion] thecrazyguy:
If you are reading this most probably you are new to xda, Welcome :D, and facing storm of questions what is root, bootloader etc and how to do that. But Before answering to your question Introduce yourself with forum RULES, Now Guide and explanation of every term is given below for FAQ's please check end of the post.

Rooting

Rooting means getting full control on your phone.

Why ?

1. Rooting allows to move app from internal memory to SD card.

2. You can use your phone as wifi spot without paying.

3. You can install custom ROM'S

OhhGreat But How!!!

1.Flash Tool by - Bin4ry & Androxyde

2. Eroot by eroot

I recommend eroot (simple and quick)

Note - click on name (tool) to download

Note for both method or anything - Make sue Correct drivers are installed on PC (Use your mobile with PC companion tool to do so) & USB-Debugging is on (settings --> Developers option --> Check USB-Debugging )

Eroot

1. Download and run it

2. Connect your Device to the Computer

3. just click the “一键root ” then wait a moment

4. when it says “恭喜您，获取root 权限成功”，Done :D

Flash Tool

1. Download and Install

2. Install drivers from " C:\Flashtool\drivers "

3. Connect your device

4. Start flashtool, press root button, select superuser and press OK.

5. When prompted click the restore button on your phone, be sure you select the 'RootME' recovery!

6. Device will reboot almost 3 times.

7. After flast tool log says "Finished", your phone is now rooted :) .

Unrooting

1. Open eroot

2. Click on button shown in pic

Recovery

Custom recovery for Android phones and tablets that allows you to perform several advanced recovery, restoration, installation and maintenance operations on your Android device that aren’t possible with the stock recovery

Recoverx by LEDelete

"You just have to launch RecoverX, enter “install” and select your device, the recovery you want to install and RecoverX does the rest, it’s that simple." - LEDelete

Instruction

1. Download tool (Click on name to do so) & unzip

2. Run RecoverX

3. Select your brand phone model & recovery type

4. Click Next then Next (After it complete downloading)

5. Read instruction and then next

6. Done :D :)

Alternative Method (Fastboot Kernel) - for unlocked bootloader (unlock your bootloader...scroll down for instructions)

1. Download Kernel for you android version as .elf (eg. advanced ICS kernel for ICS (4.0.4))

2. Open flashtool

3. Switch off your phone and hold volume up button and plug usb cable along with holding

4. Click on flash icon in flashtool

5. Select fastboot mode

6. Select kernel to flash

7. Flash

Bootloader unlocking

Bootloader unlocking allows you to install different custom ROM'S and Kernels.

Disadvantage - No bravia Engine

- No music info

Dont worry after relocking bravia engine will work :) but you cant install many custom ROM's on Phone after relocking.

Instruction

1. Get your keys through Sony bootloader unlocking official , Read the instruction there, just get the keys & preserve it for future use. (Dont follow the full instruction just get the key's )

2. Make sure that USB debugging is on

3. Turn off your device

4. Run flashtool --> Plugins --> Bootloader unlock & follow the instruction there.

Hint - For devices like xperia S, back button is volume down and home button is volume up.

Backup & restore

Before you start flashing Create a n android backup so if anything bad happens and you are not in position to find a solution RESTORE ()

To create back up

1. Boot into recovery

2. Restore & backup -> Backup (ROM + Kernel , data, apps, settings...everything)

Restore

1. Boot into recovery

2. Restore & backup -> Restore (for complete restore, ROM + Kernel , data, apps, settings...everything)

Custom Restore

1. Boot into recovery

2. Restore & backup -> Advance (choose your desired option)

Flashing

1. Download Rom + Latest Gapps(If required )

2. Copy them to SDCard

3. boot into Recovery

4. Factory Reset/Wipe data

5. Wipe Cache

6. Advanced -> Wipe Dalvik Cache

7. Advanced -> Fix permissions

8. Mounts and Storage -> Format /system

9. Install zip from SDCard -> Choose zip from SDCard -> Choose the Rom and install

10. Reboot (Its important for PAC ROM not with CM or slimbean you can flash gapps with ROM, but everytime befor flashing gapps i generally reboot my device and use it for a while)

11. Let the Rom settle a bit, then reboot into Recovery again

12. Install zip from SDCard -> Choose zip from SDCard -> Now choose the Gapps and install

13. Reboot

Hint - To go down & up, press volume down & up button resp. and to select press camera key.

To get back from where you started

Flash ICS Then -> [GUIDE] Get Bravia and Music Info working again on ICS with ReLock bootloader by revan17

Big

THANKS

to Original tool Developer's [MENTION=2807379]Androxyde[/MENTION], [MENTION=1346722]Bin4ry[/MENTION], [MENTION=4617223]LEDelete[/MENTION] ,eroot and [MENTION=3371022]revan17[/MENTION]

FAQ's

Q.Can i go back

A. Yes, how ? check guide again

Q. Is unlocking bootloader is important?

A. yes it is to install custom ROM's and kernels.

Q. Can i update my phone after unlocking bootloader

A. No

Q.Is unrooting is necessary to get official update

A. No, but bootloader relocking is!

Q. Is there is any way to get back bravia engine after unlocking bootloader?

A. No

Q. What are gapps

A. gapps is collection of google apps which cannot be included with ROM as it is illegal to do so.

Q. What is a kernel

A. In short kernel is intermediate b/w system software and hardware, for full explanation Visit THIS

Q. what is Bootloop ?

A. It happens when you flash a different android version kernel with different android version system, phone will stuck at logo and will restart again and again.

Q. How to get rid of bootloop ?

A, Extract boot.img from ROM zip file you are using and fastboot it with flashtool (instruction - check alternative method for installing recovery)

Q. Can i use Xperia S ROM's for SL, any special instruction ?

A. Yes you can use S ROM's for SL and no special instruction but for PAC ROM it is given there to remove

the first 2 lines of the updater script found in the zip. META INF / com / google / android

Q. Recoverx eroors or downloading link not working

A. Recoverx is used by many all around the world so sometime due to high traffic it show error or download link dosent work, the only solution is to wait and try again.