Today, after installing a desktop extension, the system crashed and back to the login interface. After entering the password, the screen splash and back to the login interface again. Restarting the computer does not fix the problem. I found many tutorials on the Internet, including modifying the permissions of Xauthority, which is not suitable for my situation. Later, I found an effective solution and take this as a note.
Recently I uninstalled the built-in thunderbird client in Ubuntu(not easy to update/maintenance), instead, I use the Linux version from their official site. It is quite annoying every time to open it through the terminal or file system, so I decide to make a launch icon for it.
Recently I was trying to free the system disk and moving the user directories to a portable disk. But Ubuntu system will automatically re-make a new one in the former path to store files e.g., the screenshots in image folder. Or if you switch the system language, these user dirs name may still follow your former language.
If you have similar problems, here is a solution.
Due to the recent need to log in to the laboratory server, I learned how to log in to SSH using RSA. Take a note.