IMX8MP rootfs backup and recovery issue

[QiangF]

Hardware environment: imx8 development board (contain imx8mp core som ), HDMI monitor,、mouse、 keyboard
System environment: Ubuntu20.04  Linux imx8mpevk 5.4.70-2.3.0

Backup purpose: make a complete ubuntu desktop system, including all customer projects

Brief description of the problem:

1. We build and adapted the ubuntu desktop system on the development board based on the ubuntu-base-20.04.3-base-arm64.tar.gz version. After powering on the development board for the first time, enter the system and use the sudo unminimize command to install some necessary packages

2. Install QT, Opencv and other packages
The specific porting process is not written here. It is cross-compiled on the ubuntu18.04 host, and then the corresponding so package is copied to the development board rootfs

3. Install customer dev project
Simply put it under /home/user in the rootfs of the development board

4. At this point, verify that the customer's dev project functions normally, and connect the HDMI display at the same time, and the desktop system can be displayed normally. After restarting the development board, the verification function is still normal, and the HDMI monitor can display the desktop normally

6. Insert the USB disk to the board to backup rootfs, the command is as follows:

sudo tar cvpjf backup_20220721.tar.bz2 --exclude=/proc --exclude=/lost+found --exclude=/mnt --exclude=/sys /

7. Put the backup backup_20220721.tar.bz2 into the ok8mp-linux-sdk development package, and recompile the release version according to the process

tar xvfp backup_20220721.tar.bz2 -C prebuilt/rootfs/

8. flashing the firmware to emmc, after power on, the system can be normal boot, no errors are found in the background, but the HDMI display has picture output, and the desktop system cannot see it, if we use modetest  check the HDMI output, the colorbar is normal show

Pls give me some advice。