Today I got sufficiently annoyed with the stock version of Lollipop on my phone and decided to try (again) CyanogenMod (no longer alive). I've tried to follow the steps in the wiki, but got into problems, so here's my alternative experience.
Make sure you install TWRP or CWM so you can enter recovery mode. The "Installing a custom recovery on G2" section worked just fine for me with AutoRec (play store link).
Do some backups. I cannot emphasize this enough. You can do a backup in TWRP or use a third party tool like Titanium. Once you did that, make sure you either back it up or avoid deleting (backing up TWRP backups via adb can be a bit of a pain IMO).
My personal preference is Titanium PRO because it allows me to automate backing up things and has Dropbox support.
You need a ROM image for CyanogenMod and you're also likely to need a Google Apps image (since CyanogenMod developers don't support it implicitly). For ROM images, at the time of writing this, D802 has stable (12) and nightlies (12.1) images. CM 12 flavour corresponds to Lollipop 5.1 and CM 12.1 to 5.1.1.
If you install CM 12, the wiki page will suffice. However, CM 12.1 has some hiccups IMO:
- Google Apps and
- Putting images on the device
None of the gapps alternatives provided in the page has the 5.1.1 variant. There is however a thread on XDA with the proper version for 12.1. You can get away with installing the pico version and then adding things as you need them.
This is important because installing the wrong version won't fail, but it will render your phone unusable (e.g. the AOSP keyboard stopped working error).
The images will end up on the device sooner or later (except if you use the side-load method). Therefore, I prefer to download them directly on the phone instead of downloading them on a PC/Mac and using ADB to move them across.
Given that the whole download can be around 1G, you'll need to clean up your phone beforehand. This is much easier if you're not in recovery mode (you can sync media files to your PC/Mac and then delete them from the phone).
I've got into some errors while going through the process.
First, I couldn't get my phone connection recognised by ADB in recovery mode. Installing the drivers from LG doesn't help. You need the Android ADB interface. I've ended up installing the adb driver (original thread).
I've installed the wrong version of Google Apps. To wipe it you need to practically reinstall everything again:
- Manually wipe (format) your System partition (this is important!)
- Flash your ROM
- Flash the proper Google Apps package
- Wipe the Dalvik & Cache