How to use TWRP to flash an Android device that refuses to boot to TWRP?

Last Christmas holiday I was tasked by older relatives to fix an Android tablet they had bought. One of those absolutely useless, 100€ devices that can't really run any apps, and struggle to even start. My first proposition was to return the device - but it was already past the return window.

Lenovo's bloated nightmare version of an Android was likely the biggest reason for slowness. My second course of action was to change the launcher and disable everything I could, but the device still couldn't run YouTube, Spotify, or YLE Areena.

I figured that I needed to change the device to run some other Android version, and there are multiple guides online on how to overwrite the operating system with an alternative. However, when you run into issues with tools like fastboot not working or TWRP (or similar custom bootloader) not working, the guides are no help. This article aims to fix that gap.

All that said, on to flashing the device!

Prerequisites

A couple of first steps were easy:

1. Enable Developer mode
2. Enable Debugging over USB
3. Install ADB and Fastboot drivers (you can get them from here: http://forum.xda-developers.com/showthread.php?p=48915118#post48915118)
4. Download the right TWRP image for your device (an example: https://unofficialtwrp.com/lenovo-tb-x103f-root-twrp/).
5. Upload your custom ROM of choice to the internal storage of the device
6. Upload custom Google Apps package to the internal storage of the device (https://opengapps.org/)

I won't go into details, as I suppose you're following a tutorial on XDA-developers or something, and only ended up on this article since you ran into the same issues I did. The tutorials do a good job detailing most of the steps but fall short when you run into issues.

Also, you won't need Magisk or similar if you're working with an otherwise useless device and don't need any backups (because nobody's been able to generate anything worth saving on the device so far). And if you're following tutorials on getdroidtips.com or something, be mindful of which links you're clicking and which files you download on MediaFire.

Anyway, back to the topic.

You should make sure your adb and fastboot installation path is included in your PATH variable - or, alternatively, just open your command line window (as an admin) to the installation directory directly.

Using TWRP to flash your android device:

Time needed: 5 minutes.

1. Unlock your bootloader

   You will need to make sure you can boot any media instead of the built-in one. To do this, connect the device with USB, debugging enabled, and run the following:

   fastboot oem unlock-go

   If that gives you an error, try this command instead:

   fastboot flashing unlock

   All good? Awesome! Onto the next step...

2. Install custom loader such as TWRP

   After this, it's supposed to be easy to flash TWRP to the device and boot to it using the commands below (the mentioned image needs to be in the folder you're running the commands from):

   adb reboot bootloader fastboot flash recovery TWRP-3.0.2_TB-X103F-beta.img fastboot reboot

   That was successful for me. But Lenovo had, unfortunately, made more annoying decisions. +Vol and power would take the Android tablet to recover mode - but even with TWRP successfully flashed to the recovery partition, you'd always be greeted with the useless, out-of-the-box recovery mode.

   Curiously, though, -Vol takes the user to a diagnostics mode that's in Chinese(?). I couldn't make anything out of it, so I decided to pursue another route.

   I spent a while reflashing, using different medias, and rebooting the device (which somehow takes multiple minutes), but to no avail. I couldn't find a way to force the device to start in TWRP instead of the out-of-the-box recovery mode.

   But luckily, there's another workaround available!

   Using fastboot you can actually flash the whole device if you have a suitable media at hand (I didn't), or force booting to TWRP from a media that's on your laptop. The latter ended up being my choice and worked nicely.

3. Load TWRP without replacing the built-in bootloader

   Should you want to do this, simply run this below (supposing you have the .img file in your working directory already):

   fastboot boot TWRP-3.0.2_TB-X103F-beta.img

   This should, after a while, boot your device into TWRP once. That should be all you need :)
   After this, it was trivial to install LineageOS to the machine using TWRP. And boy, was it faster than Lenovo's Android!

That's all for now. Hope it helps someone :)

References

• One of the tutorials I was following (this one had working links to downloads)
• How to root X103F (Lenovo Tab 10) (They had the hint for fastboot boot)
• How to install LineageOS on Lenovo Tab 10
• TWRP documentation
• TWRP instructions on XDA Developers
• TechRadar's useful tutorial with good pictures for rooting your phone
• Kinda same from GadgetHacks (just bear in mind their site is ultra annoying)