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1 Introduction
Recently, I accidentally typed sudo apt upgrade (not the same as update) on ubuntu, and then suddenly entered grub rescue after restarting. I was really afraid of this black screen problem. The online solutions did not work for me. I just reinstalled the system directly before putting it away! But after the system crashed too much, I knew what was going on. The reason for my situation was that the boot was missing. In this way, you can prepare a USB boot disk for ubuntu, reboot into (start with the USB disk) and try ubuntu, and then boot repair.
2. ubuntu18 downgrade
After repairing the boot and entering the ubuntu system, the biggest problem came. My interface was a bit abnormal. Checking with cat /etc/issue, I found that the ubuntu version was 18.04. I upgraded after I upgraded, but I didn’t feel that the upgrade was successful, there is no icon in the sidebar, and I don’t know if the environment I installed before is present. So decided to downgrade!
ubuntu18.04——>ubuntu16.04
insert the USB disk and enter the reinstallation interface. When selecting the partition, be careful not to format the /home partition. The other /, /boot, swap can be formatted, and you will find it after reinstalling. I originally installed everything in /home, as well as the software. Some of the configuration files in the root directory are no longer there, but if you install again with the original package, the configuration will be restored to its original appearance!