Can't flash custom TWRP recovery image on Motorola Moto G7 Power phone I've got a brand new Motorola Moto G7 Power running Android 9. 

I also have Ubuntu 19.04 running on my desktop.

I want to root the phone.

I've managed to unlock the bootloader using Motorola's online instructions and the adb and fastboot utilities that come with Linux.

The next step is to flash a custom recovery application on the recovery partition.

I'm trying to flash twrp-3.3.0-0-river.img, a new image that I grabbed from here. 

When I tried to use fastboot to flash the image, I got this error: 

After this failed attempt, I attempted to put my phone into recovery just to see what would happen.

What I got was a screen displaying the Android mascot on its back with its chest plate opened and a black exclamation point inside a red triangle.

The words "No Command" were displayed underneath the graphic.

After waiting a few minutes, the phone, on its own, booted normally.

My phone's OS seems to operate perfectly fine.

I can only surmise that whatever was originally on my recovery partition from the manufacturer has been wiped and there is now nothing on the recovery partition at all.

So, I decided to see if I could boot into the TWRP image directly without flashing it. 

So, I ran this in the terminal window: fastboot boot twrp-3.3.0-0-river.img

I received this as a response: 

There didn't seem to be any errors.

The phone, however, switched from the bootloader screen to the Motorola splash screen, and then just shut off with no further response.

So, what am I missing?

How can I flash this image onto the recovery partition of my phone?
G7 Power, being a new device, has the new A/B partition layout, requiring new installation procedures that differ from standard A-only devices. This is clearly outlined in the thread where you got your image from:


  This device has 2 "slots" for ROMs / firmware. TWRP will detect whichever slot is currently active and use that slot for backup AND restore. There are buttons on the reboot page and under backup -> options to change slots. Changing the active slot will cause TWRP to switch which slot that TWRP is backing up or restoring. You can make a backup of slot A, switch to B, then restore the backup which will restore the backup of A to slot B. Changing the slot in TWRP also tells the bootloader to boot that slot.
  
  Decryption only works when TWRP is permanently installed.
  
  Installation
  
  To temporarily boot this recovery: 
  
  fastboot boot twrp-version-build-river.img
  
  To permanently install it:
  
  
  Temporarily boot TWRP
  Put the TWRP image in your external SD Card or, in case you don't have one, push it to /data with adb this way: adb push twrp-version-build-river.img /data/
  Tap Advanced -> Install Recovery Ramdisk -> Navigate to /data or /external_sd and select TWRP -> Swipe to Install
  If you previously installed Magisk: Select Fix Recovery Bootloop from Advanced to fix/avoid recovery bootloops
  Done! Optionally you can delete TWRP from /data or from your external SD Card now.
  


Read more carefully next time...