How to Root Samsung Galaxy S2 I9100G

There are many ways to root I9100G, but the simplest way is using "S2 Root" tool developed by a developer on xdaforums. For this to work, first you must flash an insecure kernel or any custom kernel using odin.

Follow the below steps exactly as mentioned by its developer.

Step 1: Download Odin3 v1.85

Step 2: Download Insecure/Original Kernels from HERE or Download Superatmos Kernel(2.1) here(Better)

Step 3: Goto Settings > Applications > Development and Enable USB Debugging on your device.

Step 4: Reboot your device into Download Mode. (With Device OFF, Hold Vol Down + Home + Power) If done correctly your device should have a big Yellow Triangle in the middle of the screen with the words 'Downloading... Do not turn off target' underneath. (Or Press 'Jump To Download Mode' Button in S2 Root).

Step 5: Connect your device to your PC and start Odin3 v1.83. If you installed Samsung Kies correctly, you should see the box in the top left corner of Odin underneath where it says ID:COM should be Yellow and displaying the name of a Com Port your device is connected to.

Step 6: Check Odin's settings, Only the Auto Reboot and F. Reset Time checkboxes should be selected.

Step 7: Now press the PDA button and select the Insecure Kernel you downloaded earlier. (Note: This should be in *.tar, *.md5 or *.smd format.)

Step 8: Now press the Start button and wait for your device to reboot.

Step 9: If you have done everything correctly, you will notice a Yellow Triangle with an exclamation mark on the boot screen when the device is starting up. This indicates you are running an Insecure Kernel with Temp Root priviledges.

Step 10: When the device has finished booting, start S2 Root then press the Root Device button. Wait for the device to reboot depending on which Reboot option you selected then you are done Rooting.

Credits to Xda developer