what is the /etc/shadow for
What means * and ! at second field of /etc/shadow? As far as I know 2nd field of /etc/shadow is encrypted password of user. But some user e.g. daemon user have * in the field, in my environment(Ubuntu 12.04) root have ! in the field. I assume ! means like all password is invalid, you can not login with this user.. But I couldn't find document for it.