Fortunately for everyone, Android 4.2 Jelly Bean CM 10.1 update is now available for the Samsung Galaxy S3 i9300 and you can flash it right away. I will let you know how to do it later in this article, but first I have to tell you some things about it.
The current CM 10.1 version is unofficial and very unstable, which means it’s mostly built for development and testing purposes. You shouldn’t rely on it as a daily driver, because it does have a lot of bugs and lacks many features. The UI is pretty laggy, the Phone app doesn’t work, which means you can’t do phone calls, camera recording effects aren’t working, touch two focus is buggy, bluetooth streaming is laggy, FM Radio and TV Out aren’t working at all. And these are only some of the bugs, but it might have other undiscovered ones.
Also please note that flashing this update requires you to have the Galaxy S3 rooted, which voids the warranty. There is a way of recovering the warranty, but it can be a dangerous process if you aren’t careful.
This guide is only for the international Samsung Galaxy S3 i9300 and it shouldn’t be installed on any other variant, because it will simply brick it.
You also need to know that installing the CM 10.1 update requires you to factory reset your Galaxy S3, so I will tell you how to perform a backup before starting the flashing update.
Backup your device
There are many ways to backup your device and I will try to list them all.
You should also backup your EFS partition by using this guide.
How to update Galaxy S3 i9300 to CM 10.1 Android 4.2 Jelly Bean
Performing the update is pretty simple, once you have a rooted device with ClockworkMod ( CWM ) recovery installed. You also have to be very careful and follow all the steps accordingly, because doing something wrong might get your Galaxy S3 bricked and you definitely don’t want this.
Once you’ve downloaded the ROM and gapps, you are ready to go. Copy both files to your Galaxy S3 SD card and boot in recovery mode.
Now you should perform the backup we have been talking before. This backup will help you restore your device in case you’re not satisfied with this ROM. If you perform a nandroid backup, everything will be restored exactly the way it was, so you don’t have to worry about losing anything.
Once the backup is done, you will have to wipe data / factory reset. So go to “wipe data” and then select yes. This will delete everything on the internal memory, except the SD card, so you will lose apps, contacts, call logs and so on, except your files and photos.
Now head to “install zip from sd card”, choose the location where you copied the ROM and select yes. Wait until it finishes flashing the CM 10.1 ROM and then do the same with gapps.
After it finishes installing, reboot the device and wait until it boots up. It might take up to 10 minutes to boot, but if it takes longer, then pull the battery and try to boot again. If it still doesn’t work, then wipe data once again, then flash the ROM and gapps.
If you are unsatisfied with the ROM, then read the guide about ClockworkMod recovery backup in order to restore your Galaxy S3 to the previous state. Everything will be exactly as before and you won’t lost anything.
If you encounter any issues, please let us know and we will do our best to help.