In multiuser environments it is very important to use shadow passwords (provided by the shadow-utils package). Doing so enhances the security of system authentication files. For this reason, the installation program enables shadow passwords by default.
The following lists the advantages pf shadow passwords have over the traditional way of storing passwords on UNIX-based systems:
Improves system security by moving encrypted password hashes from the world-readable /etc/passwd file to /etc/shadow, which is readable only by the root user.
Stores information about password aging.
Allows the use the /etc/login.defs file to enforce security policies.
Most utilities provided by the shadow-utils package work properly whether or not shadow passwords are enabled. However, since password aging information is stored exclusively in the /etc/shadow file, any commands which create or modify password aging information do not work.
The following is a list of commands which do not work without first enabling shadow passwords:
/usr/sbin/usermod -e or -f options
/usr/sbin/useradd -e or -f options