Fix Borked Sudoers File on Ubuntu – How to Guide

The absolute last thing I would want to do, is create a separate sudoers file, like Dave suggests. If you have a lot of machines, and only subtle differences apply (as is often the case), you really do not want this. It will generate a lot of overhead.

What you really want to do, is create one sudoers file. In that sudoers file, you can then define Host_Aliases for groups of systems for which you want a certain policy to apply. You can also make User_Aliases and whatnot. Done right, this gives you a huge benefit by having one file to edit, so it is easy to see what applies where and you don't have to worry about different versions of the sudoers file being deployed on different machines by accident.

New versions of sudo even support the sudoers.d directory in /etc, which might be of help too, but I haven't tried that yet.

If you have the root password then you can use su to gain root permissions and change the perms on the sudoers file.

$ su -
Password:
# 

Another option is to boot into single user mode. To do this restart your system and at the grub screen press Esc. Select the kernel you want to boot and press e selct the kernel line and press e again. Append S to the end of the line and press Enter then press b. This will take you to single user mode and allow you to change the perms on /etc/sudoers.

Note that Ubuntu systems may have a (recovery mode) option which boots to single user mode already configured in grub.