If your network uses local files to authenticate users, the password information is kept in the system's /etc/passwd and /etc/shadow files. The user name and other information are kept in the password file /etc/passwd. The encrypted password itself is kept in a separate shadow file, /etc/shadow. This security measure prevents a user from gaining access to the encrypted passwords. While the /etc/passwd file is available to anyone who can log in to a system, only superuser or an equivalent role can read the /etc/shadow file. You can use the passwd command to change a user's password on a local system.