Several tutorials exist for becoming root on a Galaxy S3 ; unluckily for me they did not work on my international model available in France (GT-I9300). I must admit that only one minor but key extra step was required to be able to activate the super-user mode. Still I needed quite some time to figure it out. There is always a risk to block your device, although it is very small if you are careful enough to fully charge your battery and follow the steps closely.
I did it under a GNU/Linux operating system, but the unluckiest among you could likely find their way under trickier circumstances.
1. Install a Odin compatible software on your computer
Odin is the protocol used by Samsung to flash the Galaxy S3. Under Linux you can use a piece of software called heimdall. If you are lucky enough you can find on the Heimdall website a package working for your distro, or you can do as I did, download the sources and build your own. Just in case, here is the package I used on my debian wheezy amd64:
2. Download the new recovery mode
www.clockworkmod.com is creating a recovery system to install packages from zip archives while booting. This is needed to add the superuser command switch.
I used the version 18.104.22.168 from the web site, you can also download it from here:
3. Get the software to become root
SuperSU is one of several available applications to become superuser ; in my case, I used this version:
4. Flash the new recovery mode
First you need to copy the CWM-SuperSU file on you sd card (with the MTP protocol, or PTP, or send it via email, a webdav server, FTP, whatever mean you are used to). Then, to flash the new recovery mode, connect your S3 to your computer with the micro-USB cable. You need to switch the phone into “download mode”. Check first that the “USB debugging” option is activated in the developer section of you settings. Once everything is set, you can switch in download mode with two methods:
- Simultaneously press the Volume down, Power and Home buttons
- If you happen to have the android SDK installed, use the command adb reboot download
Once in the download mode, use heimdall to install the new recovery mode:
sudo heimdall flash –recovery recovery-clockwork-22.214.171.124-i9300.img –no-reboot
When the download is finished, remove the battery. Count up to ten and put it back. This is the crucial step I needed to add in the tutorials I saw for my Galaxy S3. If you let heimdall reboot your device (removing the –no-reboot option) the phone will automatically reinstall the default recovery mode, preventing any further step from working, and giving you the impression that something went wrong in the download of the new recovery mode.
5. Start your phone with the new recovery mode
Simultaneously press Volume Up, Home and Power, you should boot in the new ClockWorkMod recovery mode and select the menu entry install zip from sdcard.
Use the zip of SuperSU you copied before and it will be installed, then reboot your phone normally.
Once booted, use the terminal emulator to check if the installation was successful. Type the su command, a popup should ask you if you want to grant the superuser permission to this operation, grant it.
You can then check that the superuser mode is working with the command id.