[Honor 5X Questions & Answers] Et tu Brute?:
Good evening XDA Developers Forum,

I am trying to figure out how to install LineageOS 14.1 on a Huawei Honor 5X without getting into too much hassle. (If you are not interested in my chit-chat, I recommend reading only the bold text.)

Why do I need help? I tried to install LineageOS 14.1 right after buying a fresh new Honor 5X following the instructions at the LineageOS-Wiki*, but things didn't went as expected. After 5 days of macgyvering the (suspectedly) bricked phone I managed to get it running again, but not yet with LinageOS. So I wanted to share my experiences to help others having similar problems and I want to avoid too much stress with the next steps. (* I wanted to link to the Wiki, but due to being a new user, I am not allowed to. You may follow the kiwi-Install-Instructions in the LineageOS-Wiki.)

Kind of disclaimer: I've modified my mobile devices a few times in the past years. I rooted and installed CyanogenMod 12.1 and later an XDA-Dev-built Android 7.1.2 on a Nexus 7 3G 2012. I rooted and installed CyanogenMod 12.1 and later 13.0 on a Nexus 5. I stumbled over some problems, but after some trial and error everything worked. Therefore I thought I was a bit experienced and could easily do that stuff with a phone that is listed as "supported"... I didn't ignore mandatory steps of the LineageOS Wiki. I did RTFM and read this forum. I often found questions being close to my problems, but sometimes I didn't understand the answer or often the answers didn't work for me. I hated to see how this forum tried to help new users that didn't reply on questions and how some new users neither followed the instructions nor posted their solution. I promise not to let the thread die before I summarize a solution. As soon as I'm allowed to, I'll link all the files I used to their source, I kept track of them all.

You may skip the history passage if you're not interested in the pre-story or if you don't want to profit of my trial and error experience. So here comes what I did until today:

Update Google USB drivers, already have adb and fastboot installed

Buy a new Huawei Honor 5X

Check its attributes: It's a KIW-L21 with a Huawei version of Android installed, version 5.1.1 and EMUI 3.1. This device is called "kiwi".

Successfully receive unlock code via Huawei

Root the phone via fastboot, until the fastboot & rescue mode screen says "OEM Unlocked, FRP Unlocked"

Flash TWRP 3.1.1.0 (kiwi) to recovery

Push lineage-14.1-20170809-nightly-kiwi-signed.zip to /sdcard on the phone

Wipe cache, system and data

Start install of the above LineageOS .zip file in TWRP

Installation getting aborted with "assert failed: kiwi.verify_trustzone(...) ==1" and ending with an "Error 7"

Learn from the forums that I should have installed "stock MM" first. "MM" seems to be Marshmallow, also known as Android 6.0

Search for images of "stock MM", end with a complete mess of gigabytes of dozens of images, differing by region (Arab/Europe/Americas/etc.), build numbers, firmware stuff, model numbers... oh crap, I don't understand a word

Extract different "stock recoverys" from multiple firmware packages, try to combine them with all kinds of firmwares

Flash stock recovery "recovery_l21_b130.img" to recovery, put SD card with /dload/UPDATE.APP (KIW-L21C432B130CUSTC432D005.dload.modaco.zip) into phone, reboot with Volume-up + power button, start factory reset, end with "data and cache format failed"

Flash stock recovery "recovery_l21_b130.img" to recovery, put SD card with /dload/UPDATE.APP (08_Huawei_KIW-L21_Firmware_C432B130CUSTC432D005_Android 5.1_EMUI 3.1_Finland.zip) into phone, reboot with Volume-up + power button, start factory reset, end with "data and cache format failed"

Flash stock recovery "RECOVERY.img" (from Extracted_L21_B130.zip) to recovery, put SD card with /dload/UPDATE.APP (08_Huawei_KIW-L21_Firmware_C432B130CUSTC432D005_Android 5.1_EMUI 3.1_Finland.zip) into phone, reboot with Volume-up + power button, start factory reset, end with "data and cache format failed"

All of the issues resulted in a boot loop

Wife getting mad because I bricked her new phone and wasted nights for it :)

Finally find this nice file depot of the Honor 5X in this forum but do not understand all the different headers or the structure of the list

Find out that the used firmware versions may have been too old (although I thought I should have used "stock" and therefore the oldest ones)

Try my luck with flashing L21_B130\RECOVERY.img (from Extracted_L21_B130.zip) to recovery, used "KIW-L21 C432B350 - D003" from the file depot to copy its UPDATE.APP to /dload/ at the external SD card, held both volume buttons and the power button until reboot

The Honor reboots into an autorecovery mode, installing the file from UPDATE.APP automatically and for the first time not cancelling the process

Great success!

I feel myself like I "unbricked" the phone

I am now holding a running Huawei-crippled Android 6.0.1 in my hands

My current situation is a running Huawei Honor 5X with a Huawei-branded Android 6.0.1, EMUI 4.0, build KIW-L21C432B350, custom version CUSTC432D003, fastboot & rescue mode screen saying "PHONE Unlocked". Unfortunately – you may have noticed – that is not LineageOS 14.1, which I actually wanted to install. How do I do that? Should I just follow the wiki instructions? Do I now have a "stock MM installed"? Doesn't it become uninstalled when I wipe system in TWRP before I install LineageOS?

When I try to read information of the phone via "fastboot getvar all", I just get an empty value after "all:". Why is that?

Rather than struggling over anything else when I try to follow the LineageOS wiki install guide again: What should I do or check first? I do not want to get a "kiwi.verify_trustzone" error again. How do I avoid that?

Thanks for your patience in advance!