/etc/shadow password field
 

My shadow file contains * and ! in the password field. I know and have found documentation on the *. That disables an account. I can not find any written documentation on the ! in field two. Does anyone have a link to written documentation on ! being used?

I can't find documentation on this, but I am sure it means that no password has been set for that user.

I was assuming that an interactive login was not available. It is strange that documentation on that ! is so rare.