Before attempting to install Replicant, you need to backup everything you can from the device as most of the data will be erased during the installation.
You can skip this step if you have no data you want to keep.
To install the Replicant recovery, follow the instructions on the Recovery installation with Heimdall wiki page.
Once this is done, you then need to wipe the existing system partition. This is to ensure that the system partition is formatted correctly.
To do that, once you are in the recovery:
1. Select Advanced
2. Select Wipe system partition
3. It will ask you to confirm the wipe, so you will need to select Yes to confirm it.
4. Press the back key to get back to the general menu
Once this is done, you will need to do a factory reset.
To do a Factory reset, you need to be in the recovery.
1. Select Factory reset
2. Select Wipe data (keep media)
3. It will ask you to confirm the wipe, so you will need to select Yes to confirm it.
4. Press the back key to get back to the general menu
Once the factory reset is done, you can then reboot the device.
In the recovery:
1. Select Reboot system now to reboot the device
2. Your device now has Replicant installed!
Now that Replicant is installed, it's a good idea to do a backup of the EFS partition which has the modem data.
Only the following devices that are supported by Replicant have an EFS:First make sure that you have adb setup correctly and that it gives you a root shell on the device by following the wiki page that explains how to install adb and get a root shell on your device.
Once this is done you can then backup the EFS.
For the Galaxy SIII (I9300), run the following commands to do that:
mkdir backup_efs cd backup_efs adb pull /efs/ efs adb shell "cat /dev/block/platform/*/by-name/EFS" > EFS.img
This will create a copy of the contents of /efs in the backup_efs directory. It will also backup the full partition.
Keep these files around as a backup in case anything goes wrong.