vi /path/to/some/file.conf
[make some edits]
:w
VIM Message: E45: 'readonly' option is set (add ! to override)
:q!
$ sudo vi /path/to/some/file.conf
[make all my edits AGAIN]
:w

I have gone through this process so many times that I knew there must be an easy fix for it. (I know about sudo !! for running the previous command, but I only recently started developing the habit of using it.) After forgetting to use sudo while editing a configuration file yet again this morning, I finally decided to search Google and find a solution. Here it is:

vi /path/to/some/file.conf
[make some edits]
:w
VIM Message: E45: 'readonly' option is set (add ! to override)
:w !sudo tee %

The :w !sudo tee % command tells VIM to write the file (w) but run the sudo command first (!sudo) and read the writing of the file from standard input to standard output (tee) using the same filename as the one we’re editing (%).

After saving the file as root, you’ll get this message: “W12: Warning: File “/private/etc/smb.conf” has changed and the buffer was changed in Vim as well”. You’ll be given the option to reload it, but since you were already looking at the new version it doesn’t much matter which option you choose (OK or Reload).

And last but not least, if you don’t want to remember the syntax for this command, you can map the command in your ~/.vimrc file:

cmap w!! w !sudo tee % >/dev/null

Now, if you forget to edit a file with sudo, you can simply type :w!! to fix the problem!