I've had this problem before on an old machine and managed to fix it quite quickly, but the things I tried before don't seem to be working on this machine.
Basically, when I go in to Terminal and try running something with sudo, it just echoes:
sudo: can't open /private/etc/sudoers: Permission denied
sudo: no valid sudoers sources found, quitting
I also get the same message when booted in to Single user mode, thinking it might just have been an issue with my users id. I have already tried changing the file permissions, editing the sudoers file to add in my local users record etc...... but then it just gives me a different error message (eventually coming back to the above when I try changing something else to fix it).
I've run Applejack and Diskutility, but as expected they don't work either........
Any help would be much appreciated!- my new MacBook Pro won't even install anything requiring root permissions any longer, giving the same error message in the /var/log/install.log! :-(
As you can understand, I'm very upset because it is a new machine, and I have no idea what would have caused this to happen. The usual cause is editing the sudoers file without using visudo, but I can never recall doing that.
I need my root access back!
Back up all data, if not already done. Boot from your recovery partition (command-R at startup) and reinstall Lion. If you upgraded from 10.6, you'll need the Apple ID and password you used to buy Lion from the App Store. Don't erase the boot volume; just reinstall in place. You won't need your backup unless something goes wrong.