Which one of the following statements concerning Linux passwords is true?

Passwords are stored as irreversible hashes, not encrypted values; no master password or key can reverse a cryptographic hash.

Linux places no restriction on the first character of a password; digits, symbols, and any printable character are all valid starting characters.

Users can change their own password at any time by running the passwd command; no administrative lock prevents self-service password changes.

Linux uses one-way hashing algorithms such as SHA-512 or bcrypt to transform passwords before storage in /etc/shadow. Because hashing is irreversible, the plaintext password cannot be reconstructed from the hash, meaning even the system administrator cannot read or decrypt a user's password.

Modern Linux systems support passwords far longer than six characters; PAM-based policies typically allow 72 or more characters depending on the hashing algorithm used.