[Fire HD 8 and HD 10 General] NerdFire:
tl;dr: I managed to soft-brick my Fire HD 10 (7th Gen) by trying to use the KingoRoot APK. I've managed to mostly recover, but it was a pain in the neck.

THE SITUATION: There's a popular thread at the moment showing how to get root access on your Kindle Fire HD 10 (7th Gen). This sounded pretty exciting to me because I had a 5th gen HD 10 that I rooted soon after I got it, and one of the few things I felt was missing from the new toy I bought myself for Christmas was root access.

There was one hitch, though. The root process Bibikalka describes in his tutorial requires you to download, install and run a Windows version of the KingoRoot rooting app. All well and good for the many people out there who have Windows machines, but I am a dedicated Linux and Mac user and don't have access to a Windows computer. Kingo doesn't have a version for those platforms.

It does, however, have a version for Android itself, so I decided what the heck, I can give that a try. Odds are good that if they have a rooting solution for Windows, it's present in the Android version, right?

Right??

THE SETUP: So I removed my SD card for safekeeping (nothing on it but tunes, books and videos) and plugged in my USB cable. I'd done a fair amount of ADB work before so the tablet was already set up for USB debugging and to accept APKs from unknown sources. I successfully installed the KingoRoot APK after downloading it from their site, launched it and sat back to watch what happened.

KingoRoot seemed to progress about like I would have expected, except that it stalled three times, once at 40%, once at 70% and once at 90%. When it hit 90% I waited for a few minutes to see if it would give me any kind of yea-or-nay as to whether the tablet was rooted (it never did), and then went back to the ADB window and opened up an ADB shell session to see if I could figure out what was going on.

adb shell
shell@suez:/ $ su
root@suez:/ #

Success! I had a root prompt! I immediately started following some of the steps in the tutorial and contemplating how I was going to accomplish some of the other steps I'd done on other Fires, like replacing Amazon's launcher with my beloved Nova.

After about fifteen minutes, though, I began to wonder why KingoRoot was still showing 90%. Surely it should have finished by now? so I used ADB to reboot the tablet. That's where the fun started, and by "fun" I mean "pain."

THE SINKING FEELING: I rebooted the tablet, watched the Amazon logo come up, followed by the Fire logo. And I watched the Fire logo. And I watched it cycle through its animation for at least five minutes. At the same time I opened another ADB session, and I could still get a root prompt by running the "su" command, and some other onboard commands like "ps" and "du" worked fine, but once I returned to ADB I found that I couldn't install or uninstall APKs, just to use an example. The command would launch but then hang, and I would have to control-C out of it to get back to my Mac shell prompt.

After about fifteen minutes I started getting this sinking feeling that I had just reduced my nice, big, shiny toy to a thin plastic box that did the visual equivalent of screaming its name over and over again.

THE RECOVERY: By this time I was pretty sure I had hosed my tablet, so nothing ventured, nothing gained. I downloaded the latest Fire HD 10 firmware update from Amazon, watching all the while as it continued to cycle through the Fire logo. When the update was downloaded I booted into the recovery menu, sideloaded the update, and watched nervously as the tablet updated, restarted and . . . went right back to cycling through the Fire logo animation. Head, meet desk.

Then, suddenly, the message that my tablet was optimizing its programs! I have never been so happy to see that particular piece of annoying information. About ten minutes later after re-registering the tablet and completing setup I was right back where I had started when I first bought the device. No Google Play Store, no Nova Launcher, no Ticket to Ride or other favorite games, but it was working.

That sudden gust of wind you heard was my exhaling a sigh of relief.

LATHER, RINSE, REPEAT: Now that I had a blank slate, as it were, and knew that I could recover when I needed to, I decided to try the process once again just to make sure I hadn't missed any steps or done something out of sequence. Long story short, I ended up with an unusable tablet again and had to reload the Fire firmware update.

THE TAKEAWAY: I am posting this as a cautionary tale. I was lucky in that all of my music files, videos and downloaded books live on my SD card so all I lost in this process was some time and customization. It could have been much, much worse.

Until someone can document success with it and explain how they did it, please don't try to root your Kindle Fire HD 10 (7th Edition 2017) using the APK version of KingoRoot. Use the desktop version of the software documented elsewhere in the forums. You'll be happier and more likely to succeed.

Best of luck to you!