After a certain boot, the ubunut graphical interface can be displayed, but it cannot be logged in, and the startup session fails. Adjusted to the tty interface can not log in.
First boot into ubuntu advanced option mode
Repair the file
Reboot into tty mode to log in
sudo apt-get install ubuntu-session
reboot
reboot
Sidebar disappears after reboot
Reset compiz: dconf reset -f /org/compiz
Restart unity: setsid unity
Note: If it prompts that setsid cannot execute unity in this step, you need to reinstall unity: sudo apt install unity
Then restart unity
reboot
After restarting the computer, the sidebar is restored