[Galaxy S III General] schwarma:
After getting my GS3/i9300 I realized that I didn't have a Windows computer anymore to root it. So I was stuck finding an alternative to Odin. I had trouble finding one aggregated source of Mac info that was relatively recent (last post I see is from Feb 2012) and all in one place.

I'm on MacOS X 10.7.5 (Lion) which isn't the most current version. I'm also a noob so maybe I got lucky as I've seen many comments within the various threads where my steps didn't work for other people.

When you download Chainfire's Auto-Root zip file, you'll need to do things a bit differently than with Odin. After unzipping, you'll need to untar the .tar file as well. You'll want the recovery.img and cache.img files in a folder on your PC. You'll need to know the path to that directory.

Instead of using the Heimdall GUI (which I found confusing), I ended up finding Chainfire's comments about using the Linux/Terminal commands in one of his old posts. He said it was "hearsay" but I can confirm that it worked on my GS3. Credit goes to jzuijlek for posting it (his post).

You'll want to install Heimdall from here

Currently they're saying to install version 1.3.1 instead of 1.3.2.

After Heimdall installs, I suggest rebooting your Mac.

Now to the good stuff...

Boot your phone into download mode:

1) Unplug your phone from the computer.

2) Turn your phone off

3) Hold both the volume down + home button. Then press and hold power until download mode comes up. Then press the volume up key to continue.

3) Plug in your phone

4) Open up Terminal and then cd to your recovery/cache.img files directory

5) Then type in this command:

sudo heimdall flash --recovery recovery.img --cache cache.img

If all goes well then you'll see stuff being installed and your phone will reboot and you'll be DONE!

However, if you're like me, you got an error. The response from Heimdall said, "Claiming interface failed". It turns out that there may be conflicts with Kies kexts if you have it installed. If you don't have it installed and you're seeing this error, I'm not sure if I can help. I suggest uninstalling Kies as you won't need it after you root. I searched Google with my error and finally found this gem from March 2012!

http://blog.scott.wallace.sh/2012/03/getting-heimdall-to-work-on-your-mac.html

As such, if you've installed Kies on your Mac and you're having this error, I suggest using the following commands. It seems some kernel extensions that Kies installs conflict with Heimdall.

sudo kextunload -b com.devguru.driver.SamsungComposite

sudo kextunload -b com.devguru.driver.SamsungACMData

sudo kextunload -b com.devguru.driver.SamsungACMControl

After this, I tried to flash again and it worked like a charm!

Now you're rooted.

However, Chainfire doesn't support CWM in his CF-Autoroot anymore so you'll need to get CWM or some other recovery image (Philz, TWRP, etc.). You can search these forums but these links should be mostly correct :)

CWM (find the Samsung Galaxy S3 i9300 in the list: http://www.clockworkmod.com/rommanager

Philz (built on CWM): http://xdaforums.com/showthread.php?t=2002953

TWRP: http://xdaforums.com/showthread.php?t=1943592

You'll flash the same way as above with just the .img file

Boot into download mode using sequence above.

(Example with CWM)

Open up Terminal and cd to the directory with your .img file.

Then type:

sudo heimdall flash --recovery recovery-clockwork-6.0.2.7-i9300.img

For reference...to boot into recovery:

1. Unplug the USB cable.

2. Shut down the phone.

3. Hold down the 'HOME' + 'VOLUME UP' buttons and press the 'POWER' button for about 5 seconds to enter Recovery Mode.

I hope this helps! Let me know if you think I got anything wrong!