A careful examination of the /etc/passwd and /etc/shadow files reveal that the passwords stored are hashed using some form of hashing function.A quick Google search reveals that by default, the passwords are encrypted using DES. If an entry begins with $, then it indicates that some other hashing function was used.For example, some entries on my Ubuntu machine begin with $6$...What do the various numbers represent?
What methods are used to encrypt passwords in /etc/passwd and /etc/shadow?
password;hashsum
The full list is in man 3 crypt (web version):          ID  | Method          -------------------------------------------------          1   | MD5          2a  | Blowfish (on some Linux distributions)          5   | SHA-256 (since glibc 2.7)          6   | SHA-512 (since glibc 2.7)(Blowfish can be either $2$ or $2a$ according to Wikipedia Crypt (Unix).)So $6$ means SHA-512.Which one your system uses is governed by any options passed to the pam_unix PAM module.The default on the latest version of Ubuntu is set in /etc/pam.d/common-password:password        [success=1 default=ignore]      pam_unix.so obscure sha512which means that next time you change your password, it will be hashed using SHA-512, assuming your account is local, rather than NIS/LDAP/Kerberos, etc.See also:FreeBSD cryptArchLinux Blowfish passwordsNetBSD crypt(3)PHP crypt function