Here’s a no-frills and fool proof guide to rooting the Samsung Galaxy S2. The SGS2 is a great smartphone and it’s even better with root access. Let’s rock.
1) Download Odin3-v1.85.zip from the xda-developers forum and extract it on your computer to the folder of your choice.
2) Now you need to grab the correct rooted kernel from the xda-developers from either this post or this one. The various kernels are named CF-Root-xxx-vX.X.zip and to figure out which one to download, go to Settings > About phone on your Samsung Galaxy S2 and check the “Kernel version” label. This is what it looked like on my phone.
It says “184.108.40.206-I19100XWKF3-CL276555”. I have made the essential part of the kernel version bold – look for that key among the available kernels on the XDA and you will have no trouble downloading the correct one. In my case, I downloaded CF-Root-SGS2_XW_CLK_KF3-v4.0-CWM4.zip. Extract the ZIP-file so you get a file with the .TAR extension.
3) Make sure your Galaxy SII isn’t connected to your computer and launch Odin3 v1.85.exe. This is what the interface looks like – the important parts are highlighted. Click on the image to see the full size version.
4) Click the PDA button and select the .TAR file you extracted earlier.
5) Turn off your Galaxy SII. Start it by pressing and holding the Home button, the Volume down button and the Power button at the same time. A warning message will be displayed – just press Volume up to continue. This will boot the device into Download Mode.
6) Connect your Galaxy S2 to your computer using a USB cable. Your operating system might install new drivers. Let it finish. Make sure the “Re-Partition” option in Odin 3 v1.85 is NOT selected. Both the “Auto Reboot” and “F. Reset Time” options should be selected, however. Click the Start button.
7) Let Odin do its thing and the device will soon reboot. Now you have a rooted Samsung Galaxy S2, congratulations! Please note that a yellow triangle with an exclamation mark will be displayed when you boot your Galaxy S2 from now on – this is normal.
Another thing worth mentioning is that this rooting method, CF-Root, includes ClockworkMod Recovery, but it isn’t compatible with the ROM Manager app. Because of this, the developer has included an app called CWM Manager that will be automatically installed on your device when using the guide above. It’s listed as CWM on your phone.
Visit the source for this guide at xda-developers for even more info, and if you have any questions – feel free to leave a comment and I’ll do my best to help!