How to root Nexus S with Ice Cream Sandwich (ICS)

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How to root Nexus S with Ice Cream Sandwich (ICS) manually

First get a backup of your existing boot image

You can download ClockWorkMod from here:
- ROM Manager and Clockwork Recovery Image
Power the Nexus S down, and hold Volume Up & the Power button until booted into the bootloader
Verify your phone is connected with yout PC:
>fastboot.exe devices
Boot your phone with fastboot and the ClockworkMod image on a PC.
>fastboot.exe boot recovery-clockwork-5.0.2.0-crespo.img
Make a backup to the of the phone with ClockworkMod
- backup and restore

- backup
Boot your phone to Android again, and copy the ClockworkMod backup to your PC.
It is loccated in \clockworkmod\backup...
Locate boot.img in the backup and put it in an empty folder on an Ubunto system

On Ubunto

Download split_bootimg.pl
Download The superuser app from here: androisu.com
copy split_bootimg.pl and mkbootimg to the same folder
$ chmod +x split_bootimg.pl
$ chmod +x mkbootimg
$ ./split_bootimg.pl boot.img
Page size: 4096 (0x00001000)

Kernel size: 2858444 (0x002b9dcc)

Ramdisk size: 143086 (0x00022eee)

Second size: 0 (0x00000000)

Board name:

Command line: console=ttyFIQ0 no_console_suspend

Writing boot.img-kernel ... complete.

Writing boot.img-ramdisk.gz ... complete
Now you have
boot.img-kernel

boot.img-ramdisk.gz
$ gzip -d boot.img-ramdisk.gz (extract the ramdisk)
$ mkdir tmp
$ cd tmp
$ cpio -i -F ../boot.img-ramdisk (extract the ramdisk in the tmp folder to have a clean environment)
Edit the file init.rc and find the line ## Daemon processes to be run by init.
After the second ##

Insert the folowing four lines:

service superboot /system/bin/sh /superboot/superboot.sh
class main

user root

group root

oneshot
Save the file and quit
$ mkdir superboot
Create the files:
superboot/superboot/su

superboot/su

superboot/superboot.sh

superboot/Superuser.apk
$ find . | cpio -o -H newc | gzip > ../newramdisk.gz
$ cd ..
$ ./mkbootimg --kernel boot.img-kernel --ramdisk newramdisk.gz --cmdline 'console=ttyFIQ0 no_console_suspend' --base 0x30000000 --pagesize 4096 --output newboot.img

Content of superboot.sh should be:

mount -o rw,remount -t ext4 /dev/block/platform/s3c-sdhci.0/by-name/system /system
rm /system/bin/su
rm /system/xbin/su
mkdir /system/xbin
cat /superboot/su>/system/xbin/su
chmod 6755 /system/xbin/su
cat /superboot/Superuser.apk>/system/app/Superuser.apk
mount -o ro,remount -t ext4 /dev/block/platform/s3c-sdhci.0/by-name/system /system

To verify that ext4 /dev/block/platform/s3c-sdhci.0/by-name/system is the right filesystem on future versions of Android you can type:

> adb shell
shell@android:/ $ mount

This will show a list of al all filesystems on your phone.

Flash the new image to your phone

On Windows:

Verify it works before flashing

>fastboot.exe boot newboot.img

Flash image

>fastboot.exe flash boot newboot.img

>fastboot.exe reboot

Additional information

How to compile mkbootimg

Get Android source code: http://source.android.com/source/downloading.html
$ cd /path/to/android-src
$ cd system/core/libmincrypt/
$ gcc -c *.c -I../include
$ ar rcs libmincrypt.a *.o
$ cd ../mkbootimg
$ gcc mkbootimg.c -o mkbootimg -I../include ../libmincrypt/libmincrypt.a
$ cd ../cpio
$ gcc mkbootfs.c -o mkbootfs -I../include

copy system/core/mkbootimg/mkbootimg, system/core/cpio/mkbootfs to a directory in your path. location: tools/mkbootimg/mkbootimg.c

Guide - How to create your own superboot.img Or how to root your phone :)

Additional links

Fastboot

Commandline parameters

cpio command line parameters

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How to root Nexus S with Ice Cream Sandwich (ICS)

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