Root, TWRP and factory ROMs

[wooky69]

Hi all. After reading a few posts I'm still a little unclear on an aspect of rooting and different phones. I've rooted my S5 and use CM but I've never rooted a phone and kept the factiry ROM with TWRP. I'm soon going to buy a Moto X Force, so I'm reading up on rooting it but I have a couple of questions that i can quite get a straight answer to.

If I root a phone and install TWRP can you still keep the factory ROM or do you have to go with a custom ROM and if you install TWRP can you do full backups of the factory ROM etc?

Also can you then receive OTA updates from the Manufacturer or will that remove TWRP?

Thanks all

 

[Hadron]

Installing a custom recovery is needed before installing custom ROMs, but it's entirely separate. So you can install TWRP and carry on using the stock ROM. You can also use TWRP to back up the stock ROM same as you could with a custom ROM.

On devices I'm familiar with having a custom recovery installed will prevent stock updates installing at all. You should reflash the stock recovery for that. I'd be wary of stock updates on a rooted phone anyway - they aren't intended to be installed over modified software.

 

[scary alien]

On the vast majority of my rooted devices, I would run stock but install root.

Also, most of the time, I would not actually install (flash) a custom recovery, but would keep the stock recovery installed. When I wanted to use a custom recovery, I would use fastboot to softboot (and not actually flash) the custom recovery.

I could use fastboot since my bootloaders were unlocked.

As @Hadron indicated, OTAs on rooted device will either typically not install (the cross-checks will fail) or the device won't boot (i.e., you'll go into a boot loop). See this thread for some background regarding this.

An OTA may very well install / update the recovery partition (removing your custom recovery)--that depends on what is being done in that particular OTA, of course--and it's certainly very likely to check that the currently installed recovery is/matches the stock SHA1 that it expects to find during it's cross-checks.

There is a caveat nowadays with the newer root package from Chainfire where systemless root is available for your device where you can use something like Chainfire's FlashFire app to install an OTA on a device rooted with Chainfire's Update-SuperSU-v##.zip--i.e., if you use something like King Root or KingoRoot, etc. to root your device, then do NOT attempt to install an over-the-air (OTA) update. BTW, systemless root installs the root bits in it's own partition and not on the /system partition--but it takes modifying the boot.img to to do this--yet another component that the OTA might (likely will) check and need/want to replace.

So, the TL;DR version: to be safe, only accept and install an OTA on a completely stock system unless you have a way (and the knowledge and tools) to recover/restore your device with something like fastboot or factory flashing tools.

Cheers!

 

[wooky69]

Ok thanks for the replys. Can I ask why you would keep the stock recovery if you had rooted the phone so couldn't receive OTA updates anyway?

Also can you link a tutorial for softbooting TWRP as you suggested? I have a spare old phone to play with

Cheers

 

[scary alien]

Ok thanks for the replys. Can I ask why you would keep the stock recovery if you had rooted the phone so couldn't receive OTA updates anyway?

Well, I only really needed the custom recovery to flash Chainfire's root .zip package and to take a Nandroid backup. I do most of my messing-around when I'm home and on my desktop, so I'm always able to soft-boot a custom recovery when I need to and it's not too much more inconvenient than having a custom recovery already installed.

Soft-booting also reduces the write cycles to my device--I've done a LOT of flashing of custom recoveries in the past on certain devices .

Also can you link a tutorial for softbooting TWRP as you suggested? I have a spare old phone to play with

Cheers

If your device supports (responds to) fastboot and you've got an unlocked bootloader, then the fastboot boot command will (should) boot-up any bootable .img file appropriate for your device:

fastboot boot <bootable .img file>​

(note that the bootable image file can be a custom recovery (CWM, TWRP, etc.) or a boot.img such, etc.)

This is in contrast to the flashing operation where you would use this syntax:

fastboot flash <partition name> <file to be flashed>​

The above command is the dangerous one since you need to be very careful about what you are flashing to where .

Caveat emptor .

Not all devices use fastboot for flashing, so your mileage may vary .

Also, use "fastboot help" for full syntax and options.