Video

Want to experience Android 5.1 on your Galaxy S3 today?  Even newer smartphones like Galaxy S6 and HTC One M9 don’t have Android 5.1 yet but you can already get it for your Galaxy S3 through CM12.1 ROM.

The CM12.1 ROM builds are available for all AT&T, T-Mobile, Sprint, Verizon, Canadian, and GT-i9300 Galaxy S3 models.  Although these are unofficial builds compiled from CyanogenMod sources, they are actually pretty stable, I haven’t found a single bug yet so far.

Since the update from Android 5.0.2 to 5.1 wasn’t a complete overhaul of the OS, we suspect that has a lot to do with its stability as developers don’t have to start from scratch to make everything integrated/stable.

Overall, Android 5.1 is going to give you the most performance improvement over previous Android OS versions along with much improved battery life.  If you can’t afford a new phone but you want to upgrade your phone for free, CM12.1 ROM may be the best way to do that so definitely give these builds a try and do let me know what you think!

(These unofficial builds are compiled from official Cyanogen sources, no bug found so far.)

You will find easy drop-down WiFi and bluetooth shortcuts, which is a new feature of Android 5.1.

With Android 5.1 CM12.1 ROM, you can specify exactly which apps can notify you and also set the priority for these notifications.

Have more than one user?  Take advantage of Android 5.1 Lollipop multi-user feature.

Camera and camcorder work flawless and CM12.1 comes with rotating launcher.

Download:

Download CM12.1 ROM for Galaxy S3 AT&T SGH-i747, T-Mobile SGH-T999, and Canadian SGH-i747M

Download CM12.1 ROM for Galaxy S3 Sprint SPH-L710

Download CM12.1 ROM for Galaxy S3 Verizon SCH-i535

Download CM12.1 ROM for Galaxy S3 GT-i9300

Download Android 5.1 Gapps for CM12.1 (DO NOT USE older Gapps, you will FC!!!)

To install, reboot into recovery, make backup ROM, format /system, wipe data/factory reset, install ROM, install Gapps, and reboot.

If you have AT&T or Verizon S3 with locked bootloader (Android 4.3 or up) and using SafeStrap, YOU CANNOT INSTALL THIS ROM, SORRY!

First time installing a custom ROM? See How to Install Custom ROM on Galaxy S3!

Can’t find root?  See How to Enable Root on CM12!

Credits – AT&T/T-Mobile/Canadian, Sprint, Verizon, GT-i9300 <— Please donate to the developers or hit the Thanks button on XDA if you like this ROM,thx!

* This Guide and the download pdf version will be maintained and updated at this location.

Preface for CyanogenMod ROM #11:
CM11 is a very good, dependable, and feature rich Kit Kat rom. A favorite of rommers everywhere with it's aggressive memory management and speed. Many other roms will use code from cm11 to build their own roms from. There is no "Official Handbook" for it, nor is any particular strategy "better than any other". This collection of tips has served me well and is one year in the making. My hope is that it serves you as well as it has served me.

Prerequisites for installing CM11:
Phone must be rooted and Safe Strap Recovery v3.75 installed from the stock slot and activated. Follow the instructions in the README.txt file. Thanks to @stargo!

Files:
CM11 FINAL SNAPSHOT 09/01/2015:
XT912 Device: Download: cm-11-20150901-SNAPSHOT-XNG3CAO3G1-spyder.zip (213.19 MB)
or, for the XT910: Download: cm-11-20150901-SNAPSHOT-XNG3CAO3G2-umts_spyder.zip (211.58 MB)

GAPPS:
Kit Kat 4.4.4
sd_shadow’s [Collection] of GApps

Install CM11 ROM:
Installing CyanogenMod ROM #11 is fairly straightforward and easy. Pick a known good build to install, download the latest gapps package and choose a smaller package like Mini-Modular or Micro-Modular. Have both the rom and gapps files on your phone, boot to Safe Strap recovery, and pick a rom slot, for this example, rom slot 1. At this time, you can choose the partition sizes for the rom slot you will use. If rom slot 1 has already been created, delete it, then go back to slot 1 to create it, and pick your partition sizes. These sizes are known to work well with cm11:

Slot1 - CM11
System: 700 Mb
Data: 2,000 Mb
Cache: 300 Mb

Once slot is created, go to the Install button in Safe Strap and flash the cm11 rom, Add more zips, and add the pa-gapps file. Swipe to flash the rom. You can now go to to the Wipe button, Advanced, and wipe ONLY dalvik and cache. Reboot to System. Finish the Startup Wizard.

XT912 Devices with GSM for Overseas Use:
It has come to our attention that the XT912 phone is a US based phone for use primarily in the United States. It does support CDMA, LTE, and GSM, but the GSM in the XT912 phone is only for use in the US. Members in other countries using the XT912 device have reported a variety of problems on GSM such as:

• SIM Card NOT detected
• No signal
• Low signal
• No Data
• No Text Messaging
• And other various issues that are related to the radio and GSM connection in foreign countries

Great News for you guys outside the US with XT912 devices on GSM. @Mentor.37 has created a new version of his famous GSM Patch for XT912 phones! There is a free patch available that is easy to flash and it will clear up any communication errors that arise with GSM on an XT912 outside of the US. Download, read the instructions, and flash the GSM zip file patch:
[PATCH] Patch CDMA to GSM for Android Global Phones

CM11 Setup and Maintenance:
Once CM11 and pa-gapps are installed and you finish the Startup Wizard, you are on your way to enjoying this fantastic rom for yourself. And right now is when you get the opportunity to prune and shape it into the rom you want to have and use. If you take several steps right here and now, you can always depend on this rom to serve you well.

Hardware Notes:
The Droid Razr phones are close to 3 years old and that, is more than one lifetime for modern, digital equipment. At the time of their release, the Droid Razr was a top of the line, $600 Smartphone. As the phones become more sophisticated, got faster multi-core CPUs, and more dynamic system RAM, the Android Operating system and all of the apps take advantage of all this new "Power" available and can easily "choke" an older device like a Droid Razr rather quickly. Here is where the setup and maintenance become very important issues.

If you do not take measures quickly, Google will quickly reinstall 200-300 apps back to your device and all of these apps and services will quickly "take over your phone" and slow it to a crawl. Manually take control over your phone now!

Required Apps:

• Titanium Backup Pro $6.58
• Greenify Donation Pack $2.99

You can use these paid apps on every Android device that you own. Both of these apps are available as "Free" versions, but to seriously take control over your phone, you will need the pay versions. If you love Android, then this will be the best ten bucks you ever spent. Get ready to purchase and install them very soon.

How to install and maintain CM11 for a good running phone:

1. Start with a clean install of CM11.
2. Immediately go to the play store and shut off Automatic Updates!
3. Greenify requires the Xposed Framework to run. Install it now.
4. Install Titanium Backup Pro and Greenify Donation Pack.
5. Xposed Framework and the Greenify Xposed Module ALL require a reboot to get them running. Reboot your phone now.
6. Immediately backup your working cm11 rom in Safe Strap so that if something goes wrong, you can restore your backup. Do NOT backup cache or webtop. Check the "Enable compression" box to save almost 1Gb per backup of sdcard space.
7. Make your own meaningful Backup Names such as: ROM Date, Comment, Backup date. Examples: 01-01-15_LAG_01-03-14 or 01-05-15_GOOD_01-09-15.
8. Reboot to System.
9. AT this point, "Thin Out" the apps and services that you have installed on your phone, well before you allow Google Play Store to restore your optional apps. The CM11 rom comes complete with many features, some of which you will never use or want. With Titanium Backup, you can uninstall or freeze apps and services that come with the rom. Choose Freeze over Uninstall because any apps that are frozen will not come back on next update of your cm11 rom.
10. Things you can Freeze in Titanium Backup: Any apps and services NOT critical for the phone itself that you do not want or will never use. Examples: Apollo, Exchange Mail and Exchanges Services, Default SMS app if you use a different one, Google Play *anything* such as Books, Movies, News, Music, anything you will never use. I do use Play Music so that one I leave alone. Do not get too aggressive at this point as you can come back later to Freeze more apps. If you froze something you shouldn't have and the rom will not boot, restore the backup that you made.
11. Go to /Settings/Google/Accounts/Your email address/ and uncheck Sync for anything you do not need. Remember that you can sync this data at any time manually so do not be afraid to turn sync off.
12. Manually restore the apps you want from the Play Store or Titanium Backup. Restore apps only and avoid restoring app data. * "Avoid" means do not restore apps & data in general. But some apps like Games where you have made progress and will lose it without restoring data is fine, restore app & data. I have all of my cloud logins in ES File Explorer as well as my WiFi logins so I did restore data for that app. The closer to identical the roms are, the better restoring data works. NEVER restore data on wildly different rom versions such as CM11 from CM10. Credit to @sherri for this valuable nugget of information.
13. If you find that there are apps you never use for more than a month, skip these apps and only install the ones you need and use almost every day.
14. Test out your phone for performance and issues. You should have a pretty good working rom by now but we are not done yet!
15. Open the Greenify app and tap the menu to reach the Experimental Features menu. Set Working Mode to Boost. I check every box in this Experimental menu, you can read them and check the features you want enabled.
16. Tap the Back button to see the Greenify Interface. Tap each app you wish to put to sleep. With the experimental features enabled in the Donation Pack, you can also hibernate system services. For now, tap all the running apps that are NOT ESSENTIAL for the phone to run and then tap the Zzz button to put them all to sleep. Include ALL social media apps such as Facebook, Hangouts, our any others as these are the worst offenders. They have a large impact on system performance and battery life. These apps never go to sleep and act as if they are the most important apps on the system. Anything you put to sleep in Greenify will work normally if you tap the app itself. The Experimental Features will allow them to gather messages and sync in bulk, rather than constantly waking your phone to sync themselves. You will get warnings about putting system apps to sleep, avoid putting them to sleep right now.
17. Your phone should be working pretty darned good by now. If so, make another backup in Safe Strap, use the same naming format as suggested above.
18. Test your phone for a day or so to make sure everything is working properly.
19. Time to tackle those System Apps that also contribute to slowing down the phone. Open Greenify again and pick system apps that are not necessary to run the phone such as Google Search, CM Updater, Mail, Music, Browsers, Cloud Drives, anything not required to run the phone. When you get warned about putting system apps to sleep, check the "Do not show me this again" box and put them to sleep. You can tap the + button in Greenify to show more running apps that you can now hibernate. Do not "Go Crazy" and put everything to sleep, do a few at a time and check that the phone still runs well.
20. Learning what you can put to sleep in Greenify is a process you learn as you go. Make frequent backups so you can restore your rom in the event you put something to sleep that you shouldn't have. You will be surprised to learn that there are a LOT of system apps you can put to sleep that will not adversely affect the operation of the phone.
21. That is essentially it, follow these steps and you should have a good running install of cm11 that will not only run, but will be fast and responsive and will make you happy.
22. Enjoy!

Tips:

1. Install the very few Xposed Modules that you really need. AVOID system tuner apps and heavy system use modules. Use extreme caution in modules like Trickster or GravityBox not to make system changes like CPU speed, governor, I/O rates, read ahead values, and minfree. CM11 is a good system, allow the rom to do it's job and make changes like CPU Governor to INTERACTIVE from the rom /Settings/ menu instead of various modules and apps scattered all over the place.Keep System Settings in one place like the CM11 Settings Menu!
2. Avoid using custom kernels and other system changes until you gain the experience to use them effectively. CM11 does not require any external kernels or addons to work perfectly. I do not use JBX or any other custom kernel.
3. Make a Safe Strap backup before updating your cm11 rom to a new build! You can always restore this backup if the new rom you install gives you problems that you never had before.
4. Check the CM11 Developer Thread for new Build Reports and advice for a good build to install. We frequently test and report on new builds available and tell you which ones are good and which ones to avoid. If you cannot find a build report, search for it in the search box at bottom of page or make a new post and ask for which new builds are good to install.
5. Only install the Xposed Modules you need and that have a light footprint on the system. The fancy system monitor apps are often so heavy that they slow the entire phone down. I found one module that does not slow down the system, CPUFreq in Statusbar. If you care to use it, set Update Interval to no less than 250 Ms. This will update the CPU Frequency in the Statusbar to 4 times per second and does not slow down the system. The big, graphical system monitor modules like Cool Tool and Android Tuner will slow your phone to a crawl!
6. Remember, all of the apps and services that you put into hibernation in Greenify will still work and they will still get mail, messages, and sync as they should. But they will not be active and running at all times, substantially slowing down your phone.
7. Remember to keep your app count light. 300 Apps is really pushing it. I confess that I do have over 200 Apps installed, but since they are not running or active unless opened, they do not consume system memory (RAM) and have no impact on the system when they are not running.
8. Memory is not the same as sdcard space! Many people confuse these two terms. Genuine memory, RAM (Random Access Memory) is what the system uses to run the operating system and apps themselves. If the app is not running, it does not consume RAM. We only have a Gig of system memory (RAM) while all of the new phones have 2Gb or more of active system memory. Therefor it is very necessary for us to trim what apps and services that run at any given time as not to exceed the available amount of RAM in the system. Here are some system specifications for a Droid Razr Maxx and is typical of all OMAP4 devices. Motorola DROID RAZR MAXX Specifications
9. installed apps will be installed to the sdcard system partition and the settings and data for them go into your Data partition. These apps ONLY use RAM when they are up and running! RAM is in short supply so it is necessary to restrict what we allow to run at any given time.

Updating your CM11 ROM:
Although cm11 is now at the end of it's development cycle, is now considered Final, CyanogenMod is still releasing weekly builds to address such issues as bug fixes, improve stability and performance, and to incorporate all of the latest changes to the CM11 rom itself. Although any build you install since November is considered Final, the latest build is always the most desirable one to have. When installing a CM11 Update, be sure that the new build meets the required criteria.

Criteria for a new Build:
The new rom build must be equal to or better than the rom that it will be replacing

So if the new rom has lag, issues, or is in anyway worse than the rom before it, restore your previous rom backup!

OTA (Over The Air) rom updating is now obsolete as it was at one time. CM11 downloads are no longer available to use the OTA update method directly, but it still remains, to this day, the fastest, easiest, and most hassle free way to update your CM11 rom! NO need for gapps or wipes. You can also use this very same method to downgrade to a previous rom and keep your updates and settings this way!

Simple Update Procedure for CM11 ROMS:

1. Backup your currently running, perfectly adjusted rom with Safe Strap before EVER performing a rom update!
2. Download the CM11 rom of your choice for updating and place it on the phone's sdcard. It must be placed in a very specific location; /sdcard/cmupdater/.
3. Update your rom from /Settings/About Phone/CyanogenMod Updates/ and tap the updated rom "Door Icon" for the rom you put there there yourself to install it.
4. Reboot, allow to settle for 2 minutes, and then update AdAway if installed, BetterBatteryStats to System App, and Xposed Frameworks install/update.
5. Reboot to System.
6. Test this rom for a day or 2 and if it is positive, backup the new rom in Safe Strap.

If the rom develops issues such as lag after a day of use, reboot the device to clear it. If you find that you must reboot every day to keep the rom running well without lag, then it is a bad rom. Restore your backup of the previous good running rom.
How to Update CM11 or Downgrade CM11 to an earlier Build w/out losing your current updates or settings:
This is now the preferred update method for CM11 as OTA updates are no longer available. This very same, versatile procedure can also be used to downgrade to an earlier version of CM11.
There are times when it may become necessary to downgrade your cm11 rom to a previous build because you forgot to make a backup first before upgrading (Shame on you!), or you your upgraded rom stinks and you wish to go back down to a previous or earlier rom build without losing your updates. Thanks to to @Dwillian for what I affectionately call "The Dwillian Dump".

This procedure calls for a WIPE of the system partition on your phone. It is imperative that you have the necessary two files on your phone before you begin this procedure or you will have no way to boot your phone unless you have a previous Safe Strap backup to restore! Make a CM11 folder on your internal sdcard. Put the zip file build of cm11 you wish to change to along with the most current version of pa-gapps zip file you can get into this folder so they will be available to flash once you wipe the system partition in Safe Strap.

1. Get the cm11 rom file that you wish to upgrade or downgrade to along with the most recent pa-gapps file and put them on your sdcard. Once you Wipe in Safe Strap, you will be in a LOT of trouble if you do not have these two files available!
2. Reboot to Safe Strap recovery and go to the Wipe button, then Advanced Wipe.
3. Put checks in the following boxes ONLY! /cache, /dalvick, and /system. Slide to wipe these partitions.
4. Tap the Install button and choose the newer or older version cm11 rom you wish to install.
5. Tap Add more zips and browse for the most recent pa-gapps file you have. Slide to perform the operation.
6. Now go back to Wipe, Advanced, and wipe ONLY cache and dalvik.
7. Reboot to your now upgraded or downgraded system. All updates performed to Play Store apps will remain as well as any system settings that you have made.

Conclusion:
This set of instructions for cleaning up the phone and maintaining performance is what I have gathered over a period of one year by interviewing the very few Senior Members that no matter what, "Always have good running and fast phones" when the rest of us have nothing but problems and poor performance. I was one very frustrated cm11 user because I had not changed my habits to become rather conservative as to what I allow to run on my phone. I was never happy. I complained a lot. But once I got the gist of what it takes to get this phone in top performance and begin to apply these methods religiously, I finally had the phone and rom that I always dreamed of.

Once you get your phone in tip top running condition, it takes very little additional maintenance to keep the phone running this way. What works for me may not always work for someone else. Many Senior Members have "their own way" of running their phones and keeping them running well, but the common issues have been condensed into this Guide to CM11 Performance and Maintenance that I have published for you. This set of instructions and rules applies to CM11 and if you are experimenting with CM12, you will need a different version of Safe Strap and it is suggested you visit the Official CM12 Thread for advice on CM12.

CM11 is now and has always been my "Daily Driver" for almost a full year. CyanogenMod intended for the M12 SNAPSHOT to be the "End of the line" for CM11. But real life testing revealed that more testing and builds be produced to works out several bugs such as the dreaded "Process com.android.phone has stopped unexpectedly" FC where you could tap OK and it would come right back, rendering the rom unusable. Our beloved developer @stargo did troubleshoot this down to the WhisperPush in the cm11 rom and the patch for it has been merged into the cm11 build tree as of January 1, 2015. The cm11 rom itself has been labeled as Final as of the beginning of November 2014 because development and new features has stopped and the rom is considered Final. Subsequent builds are only for the purpose of cleaning up bugs and including any Android additions for consistency with Android Kit Kat.

The build labeling system has been changed by CyanogenMod since CM9 and CM10. They will not longer use the term "stable". More information about the current rom labeling can be found here:
CM ROM Release Versioning

This explains why you will not see the word "Stable" on this particular rom. When the final M13 SNAPSHOT is released, it "should be" the best, most stable and final release of cm11 there will be. If this last snapshot does not perform as well for you as an earlier build did, then pick the rom that works best for you.

Installing CM11 as your Stock ROM:
UPDATE: I can now lay claim to having hands on experience with installing cm11 to my stock slot. I was giving you what I was told, not what I had experienced. Our good friend, Mr. Chen, @ChungHung.Chenhas posted the procedure that works and since this is a group effort, I will post his instructions in combination with my own observations to make this as painless as possible.

Yes, CM11 can be installed as your Stock ROM. I have finally done this myself and although you must start over again, from scratch, if you are well prepared in advance, the procedure was not as bad as I thought. I actually had a complete duplicate of my best cm11 installation on slot1 on stock in less than 24 hours!

If you have a good, working, already setup cm11 system installed on a rom slot in Safe Strap 3.75, make a fresh backup of it first. Make a backup of your current Stock system as well. These two items are "Must Do" things before you proceed!

NOTE: Some members of the development thread reported success in restoring their cm11 backup in Safe Strap from another slot to the Stock Partition and reporting that it works. I have not had success with this nor can I report it as working. If you dare try this, backup both systems first so at least you have "something to go back to" in the event it fails.

But before you do this, it is strongly recommended that you get your feet wet, Follow the instructions in this guide to get the experience you need to install and run cm11 effectively and keep it that way. Use Titanium Backup to backup all the apps that you have and want to restore. Then wait for CM11 to end and pick the best running rom for your phone, test it, and make sure you are happy with it. Then you can install it to your stock slot. When you are satisfied that you can install and run cm11 smoothly, efficiently, and have picked the Final rom that you will use, you are ready to install cm11 to your Stock Slot.

If you already have a wonderful, working, already setup CM11 system on another rom slot, you can save a LOT of time and work if you take some steps in advance. Titanium Backup is your best friend here. @sShadowSs has given us some wonderful advice here on how to almost completely restore your CM11 system on stock with Titanium Backup with a simple procedure. It requires that you make a fresh backup of your current CM11 system of all installed apps and data.

The Stock Slot in Safe Strap is a very large partition and the sizes of the partitions cannot be changed. So, it would make a very good place to install a Final and Stable version of CM11. Installing CM11 to stock requires that you do the install from scratch all over again. You cannot restore your backup to the Stock Slot.

Before you dare install CM11 on your Stock Slot, be sure to have the following two files on your sdcard.The cm11 rom you wish to install, AND the pa-gapps you must install with them. Once you get into Safe Strap and wipe your entire Stock System, you are in trouble if you do not have the necessary files to continue and get CM11 installed to stock!

The procedure to install CM11 to Stock Slot is:

1. Flash stock JB rom and boot into stock to install SuperSU / SafeStrap 3.75.
2. Install custom recovery from SafeStrap.
3. Reboot to recovery, make a backup of your stock rom for fast recovery.
4. Do a factory reset to wipe your /data. (Internal SD will keep.) Factory reset will erase whole /data(including dalvik-cache) and /cache.
5. Wipe /system and Go to Install, now you should be able to install without error.
6. Install CM11 zip, Add More Zips, and find your Gapps.
7. Reboot and configure your new CM system, reinstall and launch SafeStrap to make sure Recovery status is "Installed" (no need to re-install).
8. [Optional] Restore apps from TiBu.
9. TRIM is a new speed up utility that is available ONLY to the Stock Slot for Kit Kat and you can now use this to keep your sdcard clean and up to speed. Trimmer (fstrim) is a nice, free front end for you to use the built in fstrim command to speed up your sdcard and keep it that way. Install Trimmer and use it on your Stock Partition. Do this often and schedule your Trim operations once a day or every week.
10. Enjoy your CM system.

That's it, guys. Follow these instructions and you should have no problems with installing and running CM11 as a dependable Daily Driver for your phone! Suggestions, praise, and questions are always welcome.

* A fully clickable pdf file of this procedure is attached as an Adobe Acrobat pdf file zipped up for you to have and to keep.

Happy Romming, guys! 

CREDITS:
This is especially difficult for me as there were just so many contributing members over the past year that I will no way remember every one of you. Please send me a PM if you did help me with this and wish to be included in the credits.
@sherri, @stargo, @Mr-Glass, @DumbleCore, @JakeDHS07, @Bobcus Leper, @brkahughes, @Dwillian, @ChungHung.Chen, @welder73, @hakarune, @mattlgroff, @tydiamond11, @my2cents @ef141, @Doublecrosser, @sd_shadow, @Mentor.37, @TStarGermany
For those that did not make the list, please send me a PM to be included. Thank all of you, very, very much!

Update:
If you go and look at the Edits for this post, you see that I have updated this post several times today from anything as minor as spelling to important stuff as additional procedures and tips. Each time I update the post, I have to perform that totally PITA process of recreating the downloadable pdf file so if you did save the pdf early on, go back and download the latest version. Thanks you everyone for your support for this Guide and I am very pleased to provide something important to the thread that may reduce the frustration and questions that are sent to the Help Desk every day. This should provide you with everything you need! 

Credit: Xda Developer 

Livesuit Flashing Tool support and work with Allwinner A10,A13,A20,A31 Chipset based Tablets . Its great tool to restore your tablet on stock firmware or upgrade tablet pc. However there are more tools available for flashing Allwinner tablet but Livesuit is best available flashing tool for Allwinner Tablets.