CyanogenMod is Dead as of 31/12/2016 but the code of CyanogenMod has gave birth to Lineage OS and its just a branding change with few tweaks and not to worry as soon there will be lot of Official ROM builds for many devices and it work pretty much the same as CyanogenMod if not better.
So CyanogenMod dead ha! So when will we get the Lineage OS for our devices?
Well we are not sure but there are developments happening to the source code of the phones and soon after that we expect them to build and announce the Official ROMS. But if you cant wait until then no problem! Developers are working round the clock to bring the experience to these devices and many devices have already gotten these. But the catch here is that it may not be complete or even stable,and maybe an half baked version plus these are Unofficial Versions.
Disclaimer:-This is an early build and may not be stable heck! it may not even boot. Have a complete backup before Flashing this. Try this at your own risk you could even brick your phone
Note:- All the required Links are at the end of this post.
Install Lineage OS on Samsung Galaxy S2
1) You Need to have a Unlocked bootloader and have a custom recovery like TWRP flashed.
2) Take a Complete Backup of your Device. This is the most important step as if you screw up something you'll have a complete backup so you can restore to the previous state. Here is a video on How to Backup your android.
4) Download Gapps for google apps from here.
5) Copy the downloaded files to the internal storage of your Samsung Galaxy S2.
6) Shut down your Android device and then hold Volume Down and Power button simultaneously to boot into recovery.
8) Go back to the home page of the TWRP then tap on -->"Install", then navigate to the folder where you have copied the Lineage OS rom and the Gapps file which you downloaded before.
9) Select the -->"Lineage OS rom zip file" and then click on -->"Add More Zip Files", then select the -->"Open Gapps Zip File", then swipe to confirm the flash and wait until it gets completed. Have patience as it may take 5-20 minutes for installation.
11) Now select your Language and configure your device like you would do when you have brought an new Android.
12) While configuring your google account if you are redirected back to the first stage of configuration then disconnect from the wifi and turn of your Mobile data and skip google account configuration for now and you will be good to go!
Download TWRP for Samsung Galaxy S2 (i9100) :- https://dl.twrp.me/i9100/
Download Lineage OS for Samsung Galaxy S2 :- http://bit.ly/2iSJnYL
Download Gapps for Samsung Galaxy S2 :- http://opengapps.org/
Devolper's GitHub Profile :- https://github.com/rINanDO
I didn't Install this as I don't have an Samsung Galaxy S2 device and the Images may be different for you but the procedure will be 99% same below is the video where i install lineage OS on OnePlus 2 its just for reference. if you have any problem watch the video.