I have an NVIDIA graphics card (driver version 185.18.36), and wanted to use the proprietary drivers. However, every time I booted up, my resolution was set to a lower level than I wanted. I could re-set the resolution every session, using the NVIDIA control console, but I couldn't save the configuration with the control on the console, because I got the error message "Couldn't delete the file '/etc/X11/xorg.conf.backup'". I tried to delete this file manually, using Terminal and the "chown" command to obtain permissions for the delete, but the system would not allow me to delete the file.
Eventually, I found this advice on the webpage "http://www.cyberciti.biz/faq/howto-linux-unix-delete-remove-file/
"Usually, on most filesystems, deleting a file requires write permission on the parent directory (and execute permission, in order to enter the directory in the first place). (Note that, confusingly for beginners, permissions on the file itself are irrelevant
In order to allow the NVIDIA control program to re-set the display resolution permanently, I used this command on the Terminal program:
sudo chown username /etc/X11
You would use your own user name instead of "username". Problem solved.