I have changed the permission of The root folder, where /tmp and /usr are to:
sudo chown - R root *
Now I cannot login, only black screen is showing and everything is a mess. Is there anyway to reverse it to normal. Should I do a fresh install?
You have accidentaly changed the owner of every folder to be root , thus you are unable to login anymore.
Most probably you havent set the root password , if you have just skip this section:
Part 1
(recovery) at the end of it.Drop to root shell promtroot@ubuntu:~#mount -rw -o remount / to get rid of the read only thingpasswd , which will prompt you the enter a new password for the rootHere you have successfully set up a new root password , if you are having problems then refer to this question.
Part 2 Here you are going to change the permissions for your home directory.
Ctrl + Alt + F1chown -R root:username /home/usernamechown -R <username>:<username> /home/<username>. Change the username to your username.Hope it helps , thank you.