Some of you may have heard of Heimdall, and wondered 'wtf is it?' 

Well, simply put; it's a better, cross-platform alternative to ODIN. What's more, it's totally open source and runs on Qt for its GUI and uses libusb to communicate over USB. In summary, it means you're not limited to ODIN+Windows any more. 

This guide will explain the basics of flashing with Heimdall. 

Flashing with Heimdall is a little bit different than with Odin. With Odin you usually select a PIT, if necessary, add the PDA.tar.md5, Modem.tar.md5 and CSC.tar.md5 to the locations, put the phone in download mode and hit go. Heimdall takes a different approach. In the Heimdall GUI you need to select all components you want to flash. This means extracting the TAR-archives and pointing Heimdall to their respective files. This allow relative fine-grained control over what you flash and doesn't depend on files being named correctly.

Installing Heimdall

Simply head to this website: http://www.glassechidna.com.au/products/heimdall/ and download it. 

Manually flashing with Heimdall

I'm not going to explain how to use the GUI, as it's straightforward in every sense. Instead, I'll explain how to MANUALLY flash with heimdall via command line. 

This really couldn't be simpler. Assuming you have heimdall in your path (if not, just cd to the heimdall directory and place files there), and place the extracted contents of the tar.md5 in a folder and cd to it. 

Let's say you want to flash system, and system only. First of all, you'll have to boot into download mode. Depending on the Samsung device, there will be a button combination to do so. The simplest way however, is 'adb reboot download' from your computer with the device on and usb debugging enabled. 

With the phone now in download mode, you're ready to flash. So... as mentioned previously, in this example we're flashing System, and system only. I'm going to use the Galaxy SII as an example. Connect your phone to the computer and type:

heimdall flash --factoryfs factoryfs.img

Then press ENTER. Heimdall will flash the system image and reboot the device. 

Now, let's say you want to flash system, and kernel. Simply type:

heimdall flash --kernel zImage --factoryfs factoryfs.img

Really, it couldn't be simpler! For a guide on how to use Heimdall's GUI, visit : http://forum.xda-developers.com/showthread.php?t=878686

A huge thanks to the creator: Benjamin Dobell, and the source for this guide : daenney (XDA)