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Safe to reboot? axon7toolkit boot.img remote: unknown command

Hey everyone,
I am in the process of rooting my axon7 (B10) and need some quick advice
I unlocked the bootloader using this method: https://forum.xda-developers.com/axon-7/how-to/guide-unlock-bootloader-easily-t3704595
Then went on to install twrp using the axon7toolkit. steps 1 and 2 reported to be working correctly but during the twrp install this came up. (see attached)
okay so recovery flashed successfully, but something went wrong with reboot? why, how, there is no indication that the tool wrote anything to boot.img so I should be fine? Can I just boot to recovery manually and continue normally? Or should I be worried that something went wrong?
the phone is currently still in fastboot mode and responding. however I am super cautious and don't want to brick the phone because I didn't ask so I am keeping it in this state for now.
any help is much appreciated
Checking ADB\Fastboot Connectivity...
ADB device connected!
Rebooting to bootloader...
Checking Fastboot Connectivity...
Fastboot device connected!
Flashing TWRP...
target reported max download size of 536870912 bytes
sending 'recovery' (14452 KB)...
OKAY [ 0.484s]
writing 'recovery'...
OKAY [ 0.113s]
finished. total time: 0.601s
Booting TWRP...
downloading 'boot.img'...
OKAY [ 0.475s]
booting...
FAILED (remote: unknown command)
finished. total time: 0.497s
Tap 'Keep read-only'" on startup!
Checking ADB Recovery Connectivity...
Checking ADB Recovery Connectivity...
Click to expand...
Click to collapse

fleity said:
Hey everyone,
I am in the process of rooting my axon7 (B10) and need some quick advice
I unlocked the bootloader using this method: https://forum.xda-developers.com/axon-7/how-to/guide-unlock-bootloader-easily-t3704595
Then went on to install twrp using the axon7toolkit. steps 1 and 2 reported to be working correctly but during the twrp install this came up. (see attached)
okay so recovery flashed successfully, but something went wrong with reboot? why, how, there is no indication that the tool wrote anything to boot.img so I should be fine? Can I just boot to recovery manually and continue normally? Or should I be worried that something went wrong?
the phone is currently still in fastboot mode and responding. however I am super cautious and don't want to brick the phone because I didn't ask so I am keeping it in this state for now.
any help is much appreciated
Click to expand...
Click to collapse
Why do you even use axon7toolkit? Use "fastboot flash recovery recovery.img" and you'll be able to avoid using the toolkit. It's finicky as hell.
Otherwise at least use EDL Tool...
Your boot image is untouched. Seemingly axon7toolkit does "fastboot boot recovery.img" which basically sends the recovery to RAM or something and makes the phone boot into that file instead of the actual boot.img.
If you are on Fastboot select "Recovery" from it and hit power. It will enter the recovery directly. This is important because if the phone boots, it will reinstall the stock one.
After you get into TWRP, FLASH MAGISK. This will let you retain TWRP.

Choose an username... said:
Why do you even use axon7toolkit? Use "fastboot flash recovery recovery.img" and you'll be able to avoid using the toolkit. It's finicky as hell.
Otherwise at least use EDL Tool...
Your boot image is untouched. Seemingly axon7toolkit does "fastboot boot recovery.img" which basically sends the recovery to RAM or something and makes the phone boot into that file instead of the actual boot.img.
If you are on Fastboot select "Recovery" from it and hit power. It will enter the recovery directly. This is important because if the phone boots, it will reinstall the stock one.
After you get into TWRP, FLASH MAGISK. This will let you retain TWRP.
Click to expand...
Click to collapse
yeah I don't know why it seemed like a good idea, it's a sticky post in the rom section... It's how I started and then wanted to stick to it somehow.
indeed booting into recovery works like a charm which is already pretty reassuring.
flashed magisk, twrp is not up to date (3.1.1.0), but system boots. thanks a bunch
I guess I'll update / flash the most current version of twrp via fastboot and then go on to flash lineage
again, thank you very much

fleity said:
yeah I don't know why it seemed like a good idea, it's a sticky post in the rom section... It's how I started and then wanted to stick to it somehow.
indeed booting into recovery works like a charm which is already pretty reassuring.
flashed magisk, twrp is not up to date (3.1.1.0), but system boots. thanks a bunch
I guess I'll update / flash the most current version of twrp via fastboot and then go on to flash lineage
again, thank you very much
Click to expand...
Click to collapse
Is your twrp installed as "Keep Read Only" or did you select "Swipe to Allow Modifications"?
After giving flash in the Magisk you gave wipe?
Thanks if you can respond.
Enviado de meu ZTE A2017 usando o Tapatalk

EwertonR19 said:
Is your twrp installed as "Keep Read Only" or did you select "Swipe to Allow Modifications"?
After giving flash in the Magisk you gave wipe?
Thanks if you can respond.
Enviado de meu ZTE A2017 usando o Tapatalk
Click to expand...
Click to collapse
If you're asking because you want to know:
-swipe to allow modifications is okay
-If you want to get rid of encryption, you have to FORMAT data (not wipe). You'll lose the internal storage. After that, flash magisk.
You can just flash it without formatting , but your storage will be encrypted, and you'll lose the internal storage if you ever change ROMs.

I swiped to allow modifications
I backed up everything I needed from the phone. I actually planned for removing everything to get a fresh setup.

Choose an username... said:
If you're asking because you want to know:
-swipe to allow modifications is okay
-If you want to get rid of encryption, you have to FORMAT data (not wipe). You'll lose the internal storage. After that, flash magisk.
You can just flash it without formatting , but your storage will be encrypted, and you'll lose the internal storage if you ever change ROMs.
Click to expand...
Click to collapse
So after installing twrp I format the Data partition and give flash in Magisk, correct?
I am afraid to enter bootloop because I have already done several procedures and in all the same thing happened. I hope everything will work out this time.

EwertonR19 said:
So after installing twrp I format the Data partition and give flash in Magisk, correct?
I am afraid to enter bootloop because I have already done several procedures and in all the same thing happened. I hope everything will work out this time.
Click to expand...
Click to collapse
yes

fastboot boot twrp.img FAILED (remote: unknown command)

So as I woke up I had just seen that omg Android 10 is finally being released, the stable version. I just downloaded the OTA and flashed it and wow am i impressed. The first thing I did was do an antutu benchmark and I got 354802 which I thought was pretty impressive. Then I saw that it said that my device was rooted, which was odd, because I just updated the rom. I checked magisk manager and it showed that magisk was not installed. I tried the usual way to get into recovery by using fastboot boot twrp.img but it just didnt work.
Is this a bug or something else?

AmonRatMC said:
So as I woke up I had just seen that omg Android 10 is finally being released, the stable version. I just downloaded the OTA and flashed it and wow am i impressed. The first thing I did was do an antutu benchmark and I got 354802 which I thought was pretty impressive. Then I saw that it said that my device was rooted, which was odd, because I just updated the rom. I checked magisk manager and it showed that magisk was not installed. I tried the usual way to get into recovery by using fastboot boot twrp.img but it just didnt work.
Is this a bug or something else?
Click to expand...
Click to collapse
Well, it's expected behaviour for A10. fastboot boot is currently disabled by OnePlus devs.

Try Fastboot flash boot magisk_patched.img(or whatever you named the file)

I did this and it was flashing the TWRP as boot.img. After that my OP6T didn't get out of the locked screen or showed the Qualcomm CrashDumb.
After several times pressing the power button, finally the bootloader showed up again and I was able to flash the original boot.img again

Twrp can't flash anything to system in A10 right now, so unless that is fixed there is no point at this moment anyway. A10 uses a virtualized system partition which doesn't allow R/W access to system....

boot img
tom1807 said:
I did this and it was flashing the TWRP as boot.img. After that my OP6T didn't get out of the locked screen or showed the Qualcomm CrashDumb.
After several times pressing the power button, finally the bootloader showed up again and I was able to flash the original boot.img again
Click to expand...
Click to collapse
hey man,
can I ask you where I can find the original boot.img, I have your same problem but I can't find the recovery image and then I can't restart the phone with android 10.
Thanks

dbarrett480 said:
Twrp can't flash anything to system in A10 right now, so unless that is fixed there is no point at this moment anyway. A10 uses a virtualized system partition which doesn't allow R/W access to system....
Click to expand...
Click to collapse
Is it still true?

BesoC said:
Is it still true?
Click to expand...
Click to collapse
Fastboot flash boot twrp.img woks for me.
After that manualy reboot to recovery and flash twrp.zip.

fress said:
Fastboot flash boot twrp.img woks for me.
After that manualy reboot to recovery and flash twrp.zip.
Click to expand...
Click to collapse
Now it's booting only to TWRP lol

paolo.pise said:
hey man,
can I ask you where I can find the original boot.img, I have your same problem but I can't find the recovery image and then I can't restart the phone with android 10.
Thanks
Click to expand...
Click to collapse
Sorry, I didn't get notification. I downloaded the complete zip file and extracted from payload.bin all images with payload_dumper-win64.
Cheers
Tom

I'm having the same problem. Did anybody manage to get the fastboot boot twrp.img command working?

Darshan A S said:
I'm having the same problem. Did anybody manage to get the fastboot boot twrp.img command working?
Click to expand...
Click to collapse
It depends upon the context. If you are already in A10 and If you are using Twrp which is for Android Q, it should.

If you're on OOS 10.3.0 it should work as is
In other cases try 'fastboot flash boot twrp img'
Numerous posts about that

Is it possible to root OOS 10.0.1?

lately I did a clean install of OOS 10.0.1 on my International 6t. Installed OOS and magisk from TWRP.
After booting there was a Magisk Manager in applications claiming that Magisk itself was not installed. I tried to install Magisk from Manager, but failed. Then I reboot the phone into the recovery and TWRP was gone!! There was only a stock recovery. Well, I tried to run TWRP from computer with 'fastboot boot .\twrp-3.3.1-28-fajita-Q-mauronofrio.img'. Error - "remote: unknown command".
I searched forum and found a thread fastboot boot twrp.img FAILED (remote: unknown command). @dbarrett480 wrote: 'Twrp can't flash anything to system in A10 right now, so unless that is fixed there is no point at this moment anyway. A10 uses a virtualized system partition which doesn't allow R/W access to system....'. Does it mean that rooting is not possible with stock OOS and only possible solution is to use custom ROM?

It is. Look for the patched boot.img and flash that through fastboot. Make sure to install magisk manager first.

BesoC said:
Well, I tried to run TWRP from computer with 'fastboot boot .\twrp-3.3.1-28-fajita-Q-mauronofrio.img'. Error - "remote: unknown command".
I searched forum and found a thread fastboot boot twrp.img FAILED (remote: unknown command). @dbarrett480 wrote: 'Twrp can't flash anything to system in A10 right now, so unless that is fixed there is no point at this moment anyway. A10 uses a virtualized system partition which doesn't allow R/W access to system....'. Does it mean that rooting is not possible with stock OOS and only possible solution is to use custom ROM?
Click to expand...
Click to collapse
The information you found is outdated. I'm surprised you didn't properly read through the official TWRP thread here, more specifically this post clarifies the error in your use of fastboot (or better said: the use of fastboot according to the mistakes made by OnePlus). Which is also mentioned several times in the page you linked to.
As a senior member, please don't create new threads inquiring information you could easily find. Even though the methods to obtain it have been challenging for a short while, being able to achieve root has never been interrupted for this device. Even without being able to modify system files. Systemless rules!
Wrapped with delicious Fajita [emoji896]

bokkoman said:
It is. Look for the patched boot.img and flash that through fastboot. Make sure to install magisk manager first.
Click to expand...
Click to collapse
So, should do following:
Install Magisk Manager
Flash patched boot.img through fastboot
Install TWRP
Install Magisk
Is it correct?

The patched boot.img already contains magisk.
But you don't need twrp to be rooted, unless you really want to use it for something else... But i don't use it anymore. So I'm fully stock, except that I'm unlocked and rooted.
So it should be:
1. Install magisk manager.
2. Flash boot.img
3. Enjoy. But check magisk manager if it was successful.

bokkoman said:
The patched boot.img already contains magisk.
But you don't need twrp to be rooted, unless you really want to use it for something else... But i don't use it anymore. So I'm fully stock, except that I'm unlocked and rooted.
So it should be:
1. Install magisk manager.
2. Flash boot.img
3. Enjoy. But check magisk manager if it was successful.
Click to expand...
Click to collapse
Regarding all that was said here, is rooting possible by following these steps?
Reboot
Fastboot TWRP img
Use volume up to recovery and power button to boot to recovery
Flash 10.0.1 stock boot img from TWRP
Flash TWRP zip
Reboot to recovery
Flash Magisk 20.1
Flash kernel if want
Reboot system
Click to expand...
Click to collapse

BesoC said:
Regarding all that was said here, is rooting possible by following these steps?
Click to expand...
Click to collapse
Yes, this tutorial with the twrp should work ...

BesoC said:
Regarding all that was said here, is rooting possible by following these steps?
Click to expand...
Click to collapse
That's only if you need TWRP.
But for what I've been reading, you don't need TWRP and then i suggest to not install it.
Just flash everything stock and keep it that way. Only thing to flash is the patched boot.img with root in it.
You can always update Android from the settings and patch/install boot with magisk manager on inactive slot. This will keep your device rooted without the need of TWRP.

Here what I found:
https://forum.xda-developers.com/showpost.php?p=81111389&postcount=145
Today I installed the new update, 10.0.1 for OP 6T and then I discovered that there is no magisk patched boot.img yet. I extracted it with payload dumper, patched with the installed magisk and flashed successfully.
I uploaded it to my drive for others. https://drive.google.com/open?id=1kb...VgWNaWgLN6j17b
The commands for flashing are:
fastboot flash boot_a magisk_patched.img
fastboot flash boot_b magisk_patched.img
Maybe someone can add it to the first post.
original 10.0.1 boot.img https://drive.google.com/open?id=1HP...Du8zCOFMXInjXq
Click to expand...
Click to collapse

I used this method to root 10.0.01
https://forum.xda-developers.com/oneplus-6t/how-to/ultimateguide-t4004367
I went from rooted 9.0.17 to 10 to 10.0.01
Never had an issue and everything works fine for me.

Today I installed the new update, 10.0.1 for OP 6T and then I discovered that there is no magisk patched boot.img yet. I extracted it with payload dumper, patched with the installed magisk and flashed successfully.
I uploaded it to my drive for others. https://drive.google.com/open?id=1kb...VgWNaWgLN6j17b
The commands for flashing are:
fastboot flash boot_a magisk_patched.img
fastboot flash boot_b magisk_patched.img
Maybe someone can add it to the first post.
original 10.0.1 boot.img https://drive.google.com/open?id=1HP...Du8zCOFMXInjXq
Click to expand...
Click to collapse
My phone get stuck on the boot animation by following this guide. I have not factory reset my phone.

DrXperience said:
My phone get stuck on the boot animation by following this guide. I have not factory reset my phone.
Click to expand...
Click to collapse
I still don't get why people don't use the good old way:
fastboot flash boot twrp.img (latest version)
If you just need root use twrp to flash Magisk zip
If you need twrp flash twrp installer also
Reboot
All the mess before was because we didn't have a working TWRP! Now that we have it don't need to use patched boot img made by others.

Magisk W/ Android 11 on OnePlus 8 Pro

Hello all...
Just a quick question as I am reading and seeing so many different answers. I have the UNLOCKED US version OnePlus 8 Pro (IN2025) Which is currently running Oxygen OS 11.IN11AA (Android 11 Official). I have successfully unlocked the bootloader and am ready to root with Magisk. I am at a loss because I dont know which Magisk to use or how to properly flash it. I have Magisk Manager 8.0.2 and have Magisk version 21.0
I have also downloaded the patched boot image from here... https://forum.xda-developers.com/oneplus-8-pro/how-to/root-patched-boot-img-android-11-op8-t4174919
What am I doing wrong? Can someone please just give me a quick rundown... I am not new to rooting just haven't done in in over a year. Thank you!

Don't think your doing anything wrong, just need to get that image on your pc, and fastboot flash it to both a/b slots then reboot your phone and you should have root available
adb reboot bootloader
fastboot boot (name of image).img - Try this one first as it just allows you to see if the phone boots up fine, if it does reboot back into the bootloader and then do the following...
fastboot flash boot_a (name of image).img
fastboot flash boot_b (name of image).img
fastboot reboot

How do I get Magisk 21.0 to install through Magisk Manager?

You don't, that's why you've downloaded a patched img, that has been patched with magisk already, just need to flash it accordingly

CraigHardy said:
You don't, that's why you've downloaded a patched img, that has been patched with magisk already, just need to flash it accordingly
Click to expand...
Click to collapse
This is what I am getting after following your directions to a T!
I also flashed to both partitions. Please see attachments. I sent 2 screenshots.

You don't do the install from magisk, have to copy the patched img to a pc where you have adb/fastboot installed then install from command prompt

CraigHardy said:
You don't do the install from magisk, have to copy the patched img to a pc where you have adb/fastboot installed then install from command prompt
Click to expand...
Click to collapse
I did not do the install through Magisk Manager I did the install via adb and fastboot in fastboot mode. It Said flash successful. But when I go into Magisk Manager after rebooting, nothing changes.

Doesn't work. Download the patched image, put it on the phone, use magisk canary manager to patch it again, transfer it off your phone, then boot into Fastboot and flash it.
It has to be patched in the phone it will be installed to otherwise it will not work.

akinkoff85 said:
I did not do the install through Magisk Manager I did the install via adb and fastboot in fastboot mode. It Said flash successful. But when I go into Magisk Manager after rebooting, nothing changes.
Click to expand...
Click to collapse
Use the beta magisk.
Re-patch it in your newly updated magisk manager then flash to both slots..
Also verify the size of the file prior to flashing.. Mine was 96MB

Here is the exact size.

Problem uploading image

I am a little confused now... I uninstalled root for a few days and now have the second release of android 11... I am in fastboot mode doing fastboot flash boot... then the file name and all it says is waiting for device?? Any help??

dladz said:
Use the beta magisk.
Re-patch it in your newly updated magisk manager then flash to both slots..
Also verify the size of the file prior to flashing.. Mine was 96MB
Click to expand...
Click to collapse
Indeed, using the beta version worked for me! Thanks for the tip!

imval said:
Indeed, using the beta version worked for me! Thanks for the tip!
Click to expand...
Click to collapse
No worries man, glad you're sorted

CraigHardy said:
Don't think your doing anything wrong, just need to get that image on your pc, and fastboot flash it to both a/b slots then reboot your phone and you should have root available
adb reboot bootloader
fastboot boot (name of image).img - Try this one first as it just allows you to see if the phone boots up fine, if it does reboot back into the bootloader and then do the following...
fastboot flash boot_a (name of image).img
fastboot flash boot_b (name of image).img
fastboot reboot
Click to expand...
Click to collapse
What is the explanation as to why one needs to fastboot flash Magisk to both slots instead of using the following command:
adb reboot bootloader
fastboot getvar current-slot
*in my case Slot B*
fastboot flash boot_b magisk_patched.img
fastboot reboot

rodken said:
What is the explanation as to why one needs to fastboot flash Magisk to both slots instead of using the following command:
adb reboot bootloader
fastboot getvar current-slot
*in my case Slot B*
fastboot flash boot_b magisk_patched.img
fastboot reboot
Click to expand...
Click to collapse
You can, however flashing to both slots is seemingly easier.
Personally I wouldn't flash at all.
Just boot to avoid the possibility of a bad boot.

akinkoff85 said:
Hello all...
Just a quick question as I am reading and seeing so many different answers. I have the UNLOCKED US version OnePlus 8 Pro (IN2025) Which is currently running Oxygen OS 11.IN11AA (Android 11 Official). I have successfully unlocked the bootloader and am ready to root with Magisk. I am at a loss because I dont know which Magisk to use or how to properly flash it. I have Magisk Manager 8.0.2 and have Magisk version 21.0
I have also downloaded the patched boot image from here... https://forum.xda-developers.com/oneplus-8-pro/how-to/root-patched-boot-img-android-11-op8-t4174919
What am I doing wrong? Can someone please just give me a quick rundown... I am not new to rooting just haven't done in in over a year. Thank you!
Click to expand...
Click to collapse
Watch this video it helped me out allot

dladz said:
You can, however flashing to both slots is seemingly easier.
Personally I wouldn't flash at all.
Just boot to avoid the possibility of a bad boot.
Click to expand...
Click to collapse
I did not know that one can just boot a magisk_patched.img instead of flashing.

rodken said:
I did not know that one can just boot a magisk_patched.img instead of flashing.
Click to expand...
Click to collapse
It's preferable.
There are some things to note.
1st. You are only booting it, meaning if you reboot; you will start using the installed / flashed image and the booted image will be lost.
2nd. For the above reason. If you want to make root permanent you have to open magisk after opening and then click install - install directly.
As magisk will already have root access, it will be able to accomplish patching, if you tried this whilst unrooted it would fail, or not be an option.
3rd. By booting you avoid the potential bootloop problems you can and almost will have at some point if you always flash, bad images are pretty rife for a number of reasons.
I've got a large guide for rooting in the guides section which covers all the bases and their shortcomings /benefits.

flashing twrp into recovery

Hi, I'm trying to follow the instructions here to install Lineage OS on my OnePlus6T device: https://www.howtogeek.com/348545/how-to-install-lineageos-on-android/ but I've run into the following issue. It used to show "recovery_a" before but after a bunch of experiments where I switched the partition, I've finally managed to factory reset the device and re-trying the procedure from the start. "fastboot devices" is able to recognize the device fine. Can someone please help?
(base) ➜ fastboot flash recovery twrp-3.5.0_9-0-fajita.img
Sending 'recovery' (30980 KB) OKAY [ 0.667s]
Writing 'recovery' FAILED (remote: '(recovery_b) No such partition')
fastboot: error: Command failed

Flow the instructions on the twrp site, works flawless, read carefully and follow them.
OnePlus 6T (fajita)
Disclaimer:Team Win strives to provide a quality product. However, it is your decision to install our software on your device. Team Win takes no ...
twrp.me

Thanks @saint6822, I was able to install the TWRP zip file after
fastboot boot twrp*.img
I then rebooted the device, however now I'm unable to get back into TWRP in order to continue the process of installing Lineage OS. Can someone point to the procedure to install Lineage OS once the TWRP zip file has been installed. I'm able to get into fastboot mode easily but can't boot into TWRP. Thanks!

vv_777 said:
Hi, I'm trying to follow the instructions here to install Lineage OS on my OnePlus6T device: https://www.howtogeek.com/348545/how-to-install-lineageos-on-android/ but I've run into the following issue. It used to show "recovery_a" before but after a bunch of experiments where I switched the partition, I've finally managed to factory reset the device and re-trying the procedure from the start. "fastboot devices" is able to recognize the device fine. Can someone please help?
(base) ➜ fastboot flash recovery twrp-3.5.0_9-0-fajita.img
Sending 'recovery' (30980 KB) OKAY [ 0.667s]
Writing 'recovery' FAILED (remote: '(recovery_b) No such partition')
fastboot: error: Command failed
Click to expand...
Click to collapse
That doesn't work, because there is no recovery partition, you never flash the the .img on these devices.... Only boot it. That is why there is an installer, it installs the recovery.
Don't use that guide, and back up your data if your phone still boots.
I have a guide here, for the 6T.
I will update it soon, as the latest version of TWRP does work fine with LOS 17.1 and 18.1, doesn't matter. So use the latest version of TWRP.

This post about making your own fastboot ROMs maybe helpful too. Just so you have the latest one. Just in case.

In the guide I I gave you it explains to install the zip file once in twrp after booting with the image to make it permanent. That's why I said follow it carefully. It does work. I am typing this on a 6t that I installed twrp on with that guide.
vv_777 said:
Thanks @saint6822, I was able to install the TWRP zip file after
fastboot boot twrp*.img
I then rebooted the device, however now I'm unable to get back into TWRP in order to continue the process of installing Lineage OS. Can someone point to the procedure to install Lineage OS once the TWRP zip file has been installed. I'm able to get into fastboot mode easily but can't boot into TWRP. Thanks!
Click to expand...
Click to collapse

I beg to differ the guide does work, he didn't follow it, it clearly says once in after booting with the image to flash the zip, thus making it permanent.
OhioYJ said:
That doesn't work, because there is no recovery partition, you never flash the the .img on these devices.... Only boot it. That is why there is an installer, it installs the recovery.
Don't use that guide, and back up your data if your phone still boots.
I have a guide here, for the 6T.
I will update it soon, as the latest version of TWRP does work fine with LOS 17.1 and 18.1, doesn't matter. So use the latest version of TWRP.
Click to expand...
Click to collapse

saint6822 said:
I beg to differ the guide does work, he didn't follow it, it clearly says once in after booting with the image to flash the zip, thus making it permanent.
Click to expand...
Click to collapse
I'm guessing you don't own a 6T? You can't do that on this device. That's immediately how I knew that guide was not right. *** Edit *** I'm just skimming that guide, it appears to say flash the .img file, which is what the OP tried to do. Does it actually say to flash a .zip file? Either way that generic guide is misleading to new users and leads to issues like this.
Another source then, the official maintainer of TWRP for the 6T,
6T TWRP Thread.
I use the old install instructions, and what I recommend, still: (from that thread)
1. Install fastboot tools from google's sdk on your PC
2. Enter fastboot mode
3. Unlock your bootloader
4. Run "fastboot boot recoveryimgfilename.img" in command line (if you want to have it permanently you should flash the installer)
5. If you will flash the installer and you are stock you need also to flash magisk or your phone will not boot again
6. Enjoy it
Click to expand...
Click to collapse
Do NOT run fastboot flash, you can not flash the .img file. The OP is lucky it did not work. This used to result in the boot partition needing to be reflashed, and a phone that would not boot.

Edit: in fairness OhioYJ, you are clicking on the link I gave him TWRP's 6t specific site, not the one he was using? If you are and still can't read then see below.
I'm on a 6t typing this that I followed those instructions for. Fastbooted the image and then flashed the zip. So your lack of understanding and knowledge doesn't translate to something not working just your inept abilities to follow instructions. He didn't flash the zip simple as that. Feel free to hold his hand through what ever method you choose just understand blind leading the blind will be fun for you.
Edit: directly from page I gave,
"First download the TWRP zip file directly on your device. If you don't download the zip file to your device first for any reason, you will need to adb push the zip to the device because MTP is not currently working on the OnePlus 6T in TWRP. If you are unable to use adb, you can also use a USB stick with an OTG cable, if you have those handy. Power off the device. Hold volume up to get into fastboot mode. Run this command on your computer: fastboot boot twrp-3.2.1-0-fajita.img
In TWRP, tap on Install and browse to the zip and install it (the zip will probably be in /sdcard/Downloads). TWRP will now be installed to both slots. TWRP is now installed and you can reboot and use your device as normal."
OhioYJ said:
I'm guessing you don't own a 6T? You can't do that on this device. That's immediately how I knew that guide was not right. *** Edit *** I'm just skimming that guide, it appears to say flash the .img file, which is what the OP tried to do. Does it actually say to flash a .zip file? Either way that generic guide is misleading to new users and leads to issues like this.
Another source then, the official maintainer of TWRP for the 6T,
6T TWRP Thread.
I use the old install instructions, and what I recommend, still: (from that thread)
Do NOT run fastboot flash, you can not flash the .img file. The OP is lucky it did not work. This used to result in the boot partition needing to be reflashed, and a phone that would not boot.
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saint6822 said:
Edit: in fairness OhioYJ, you are clicking on the link I gave him TWRP's 6t specific site, not the one he was using? If you are and still can't read then see below
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Haha, I see where the confusion came in. I was referring to the OP link, not yours. I wasn't replying to you. I guess I should have quoted that post. That generic howtogeek article won't work on many devices, any of the ones I use on a regular basis actually.

All good, sorry for getting short with you. I'm old and crusty by nature.
OhioYJ said:
Haha, I see where the confusion came in. I was referring to the OP link, not yours. I wasn't replying to you. I guess I should have quoted that post. That generic howtogeek article won't work on many devices, any of the ones I use on a regular basis actually.
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Just to be clear, I am able to install the TWRP zip file using the instructions from @saint6822 and @OhioYJ that have been
> adb reboot bootloader
> fastboot devices // To confirm device can be viewed
> fastboot boot twrp-3.5.0_9-0-fajita.img
Then I navigate the "Install" and locate the TWRP zip file, namely twrp-installer-fajita-3.2.3-2.zip and that installs fine. My problem arises after that, specifically after selecting Reboot and then Recovery the device reboots into the fastboot menu (i.e. the same menu I saw in the first step with "adb reboot bootloader").
I have no doubt TWRP has been installed on the device (per the installation messages appearing on the screen) but it does *not* boot back into it

Have you tried powering off and holding volume don't when you power it back on to enter recovery?
vv_777 said:
Just to be clear, I am able to install the TWRP zip file using the instructions from @saint6822 and @OhioYJ that have been
> adb reboot bootloader
> fastboot devices // To confirm device can be viewed
> fastboot boot twrp-3.5.0_9-0-fajita.img
Then I navigate the "Install" and locate the TWRP zip file, namely twrp-installer-fajita-3.2.3-2.zip and that installs fine. My problem arises after that, specifically after selecting Reboot and then Recovery the device reboots into the fastboot menu (i.e. the same menu I saw in the first step with "adb reboot bootloader").
I have no doubt TWRP has been installed on the device (per the installation messages appearing on the screen) but it does *not* boot back into it
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I did, and it does go back to the same bootloader menu (as with "adb reboot bootloader")

The current slot is "B", hopefully that does not make a difference here. I'm also wondering if I should try different TWRP img and zip than above.

Those files worked for me, the latest LineageOs for Microg has it's own recovery (not twrp) you could try going fastboot the twrp.IMG, and from twrp and flash the OS zip before rebooting and call it done and give up on TWRP.
vv_777 said:
The current slot is "B", hopefully that does not make a difference here. I'm also wondering if I should try different TWRP img and zip than above.
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vv_777 said:
Then I navigate the "Install" and locate the TWRP zip file, namely twrp-installer-fajita-3.2.3-2.zip and that installs fine.
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Why are you installing such an old version? Is that a typo? That could be your problem. Have you tried the installer for 3.5.0_9-0?
Slot and name don't make a difference. I've never changed the name.

The TWRP site lists the old version at the top and you have to scroll down to the newer version I bet he's not the first to make this mistake.
OhioYJ said:
Why are you installing such an old version? Is that a typo? That could be your problem. Have you tried the installer for 3.5.0_9-0?
Slot and name don't make a difference. I've never changed the name.
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saint6822 said:
The TWRP site lists the old version at the top and you have to scroll down to the newer version I bet he's not the first to make this mistake.
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He's not. It took me a while to see it too.