can't edit permissions of directory after changing them using "sudo chmod 444 etc"

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http://stackoverflow.com – I'm using Ubuntu 12.04.1 LTS (GNU/Linux 3.2.0-31-virtual x86_64) and changed the permissions of the "etc" directory to 444 (sudo chmod 444 etc). I now cant change the permissions to anything else and am receiving the following message: $ sudo chmod 777 etc sudo: unable to open /etc/sudoers: Permission denied sudo: no valid sudoers sources found, quitting I've tried to change to root user and change the permissions but I am prompted for a password which I was never asked to set, and am presented with this message: $ su Password: su: Authentication failure (HowTos)