What is in the ETC shadow file?

/etc/shadow is a text file that contains information about the system’s users’ passwords. It is owned by user root and group shadow, and has 640 permissions .

What is ETC shadow used for?

/etc/shadow is used to increase the security level of passwords by restricting all but highly privileged users’ access to hashed password data. Typically, that data is kept in files owned by and accessible only by the super user.