[Samsung Galaxy Tab A series Guides, News, & Discus] TrinityTrip54:
Some more important steps I have found...

So, after much reading and several different sources I have come across the best method (for me) but with a few caveats. Some steps were not clear in other sources and others had incorrect sequencing, and others had tips that are important.

I got my fresh device OOTB and did initial setup to confirm it is working fully. Run some programs, try connectivity, volume etc. Then time to root...

1. Obtain the boot image - Find here: https://desktop.firmware.mobi/device:2029. I would have to assume you need to match the build number exactly. fyi I did the official update to 9.0 from 8.1 via the device first. Copy the file to the device. I used sdcard/Download.

2. Download and install Magisk Manager apk on the device. Run it. Make sure you are connected to the net. Make sure the ticks are green. Enable the "Keep AVB2.0/dm-verity" in the Magisk advanced settings. Tap on the 'Install' next to Magisk. Tap 'Install'. Tap 'Select and Patch a file'. Select the boot.img file you copied in step 1. Wait for completion. Copy this patched file back to the PC. I used USB MTP in windows explorer with no issues.

3. Use this tool to create the boot.tar.md5: https://xdaforums.com/showpost.php?p=42393470&postcount=2 . Pretty easy. Just follow the instructions. First create the .tar from the image. Then add the .md5 to the .tar.

4. Now unlock your OEM. There are various sources and all seem to have conflicting info but this is what I did:

Go to Settings-About Device-Software Information. Enable Developer mode i.e. tap build number 7 times.

Go to Developer Options. Find the OEM Unlock switch. Go through the motions until the device reboots and wipes. Re-initialize the setup and skip most steps. Don't allow the device to autoupdate the

firmware as this will nullify your boot image.

Go back to Developer Options and check if the OEM unlock is there. I could not see it the first few times at all. It only re-appeared after a few reboots. I believe this has something to do with

'Vaultkeeper'. More info here: https://topjohnwu.github.io/Magisk/install.html#samsung-system-as-root

Verify the unlock state by booting into download (Odin) mode. For some reason I cannot get directly into download mode from restart/reboot using the hard keys. I tried several times. The only way I could is

by getting to recovery and selecting 'reboot to bootloader': Hold Volume Up and Power until you get into recovery menu. Select the 'reboot to bootloader' option. The device will reboot to download mode.

Check the state of the locks. They should be 'Off'. I rebooted into the OS anyway to confirm good operation. At some point I could see the OEM Unlock switch again and it was on.

5. Get Odin 3.13.1. I had to get the latest Samsung USB drivers to let windows see the odin download mode. Ensure that the device is seen. Load up the boot.tar.md5 into the AP file slot. Deselect 'Auto reboot' option in settings. Click 'Start'. Make sure the operation succeeds.

6. Unplug your device and reboot. I had to hold Volume Down and Power until the device powers down.

7. You will likely get a yellow kernel warning message on the splash screen. Let the device start and wipe/reset when prompted. Reboot. You will likely get a double boot. I think this is normal. After final reboot do a quick setup (with internet) in case you might need to wipe again (if the rooting did not work), or not, your choice. There seemed to be some stuttering and lag on the setup screens, but this was only the first time. Install Magisk Manager again and confirm root.

This managed to work first time round.

I have to say that I quite like this device and the standard Pie update is perfectly usable. Display is awesome even if its IPS. Responsive UI. Battey is huge. Low price. I would reckon getting a custom ROM would not gain you much, since rooting lets you basically tweak almost anything. I have custom ROM'd all my SGS 2,4,6,8 devices and could not really see overwhelming benefits of custom over stock. And with the Magisk Modules you can do just that. And with LP things are even easier... you will know if you are in the know. ;)

I have not extensively used it yet, so I can't give full details on performance and stability. But for an occasional games, ebook and comic reader, and browser it will be more than sufficient. I mean, you really aren't solving quantum algorithms, so why would you need more than 8 processor cores! And 3Gb RAM! And more power than the space shuttle ever had! But that's my opinion, of course.

Have fun!

[Update] Ok, so after using the device for a while and successfully using apps, running tweaks, and general shenanigans, I was this morning presented with a continual boot loop. It went from showing the lockscreen for a second and then rebooting to the flashing samsung screen. After several loops, and no response to the power button, the device goes into a sort of recovery screen allowing you to retry, reset, power off and something else I can't remember. I attempted the reset and went through the steps to set-up the device from scratch. I still saw the yellow warranty kernel warning on the boot screen. After first entry into the OS I attempted to transfer data from my SGS8 (thinking I might save some time).

However after this initialised the bootloop came back. Then attempted to go into safe mode (which bootlooped as well) until finally the dreaded boot screen Security Error telling me the usual garbage about official binaries and secure fail: kernel yadda yadda. This was after a few reboots (when it was working) and no warning other than the android status bar message about system file problems and needing a restart.

Anyone else in this predicament? Best steps to follow now?

I am downloading the stock files and will attempt a full reinstall. Hopefully I don't need to go the PIT route...

Any help appreciated.

Thanks.