The sudoers file is a way on Unix systems to administer various levels of permissions to different users. It is important to make sure you "know what you're doing" when editing this file. Especially so because if you mangle the syntax of the file, you could lock out yourself and even the root user from doing all kinds of things. Even from being able to update and fix this file.
Fortunately, there is a command—visudo—that opens the sudoers file in an
editor that will perform pre-save checks to ensure the file is valid syntax.
$ visudoThis command has vi in the name because it used to be that it would default
to vi as the editor. On Ubuntu, at the very least, this has changed and the
default is now nano.
If you'd like to still have visudo open to vi (or vim), you can specify
that with the SUDO_EDITOR env var.
$ SUDO_EDITOR=vim visudo