Warning message after doing backup in TWRP on Honor 8 (FRD-L09) When I do a backup in TWRP on my Honor 8 (FRD-L09), it invariably end with a message saying that it failed to unmount /system due to device or resource being busy. The header still says that the backup is complete, and that it was successful.

In case it makes a difference, I'm running FRD-L09C432B131, which is EMUI 4.1, Android 6.0. Kernel is 3.10.94 from 11 October 2016. This is what was installed on the phone when I got it. I got the bootloader unlock code from Huawei, by registering and applying for it. TWRP is 3.0.2-0 downloaded from here and flashed using fastboot on Windows 10.

Here's a photo of TWRP after finishing the backup:



Need I worry about this?
To isolate the problem, 1) reboot into Android and see if it does so properly, and 2) reboot back into recovery and do the same operations.

Judging from your response on the 2 points, it seems your recovery is at fault here. Not unmounting /system is usually not a problem: that step is done as a safety precaution to prevent accidental modification to /system when not flashing. As long as you don't do that yourself you should be fine.