Kalpik, help me understand the rooting process,
1. Download the ROM you want and flash it using ODIN. You can use Heimdall too.
So, here I've flashed my SGS with the stock ROM or unrooted ROM, right?
2. Download the kernel — zImage-root.tar — for ODIN from here. [For Heimdall, download kernel -- zImage-root -- from here]
3. Disconnect your phone if it's connected and Switch it Off. Wait for vibration to confirm complete switch off. Press and hold VolumeDown+Home+Power keys to get it in Download Mode.
4. Connect your phone to PC now.
5. Open ODIN (or Heimdall) and select the zImage-root.tar (or zImage-root in case of Heimdall) as PDA.
6. Keep Re-partition box unchecked. Keep the 'Auto Reboot' and 'F. Reset Time' checked.
7. Hit 'Start' button to flash the kernel 'zImage'.
8. After the zImage is flashed, phone will restart and crash/shutdown. Root will be installed and you're a SuperUser now.
So, here I've installed the "fugroot" kernel, right?
9. Now you need to flash the original kernel back (that of your ROM that you downloaded and flashed in step 1)
What does this mean? Again flash with original ROM? Won't it delete all the previous changes?
10. You'll need a free — but great– software for PC, 7-zip. Get it from here.
11. Now, you need to get the zImage file from your stock ROM. For that, extract the PDA tar or tar.md5 of your original ROM and copy the zImage file to other folder.
12. Create and save the .tar file of your extracted zImage file. This tar will contain only one file, and that's the zImage you just extracted. Rename this tar as zImage-new.tar
13. Now flash the zImage-new.tar with Odin/Heimdall by going to Download Mode and selecting it as PDA. Keep Re-partition unchecked while 'Auto Reboot' and 'F. Reset Time' checked.
14. Let the phone restart. That's it.
Well, I've already flashed my mobile with original ROM in step 9, so what I'm doing here again with the zImage of the original ROM?
Root ref