Virtual Machine Requirements

There must NOT be a graphical interface
You must NOT be able to connect to a root user via ssh
UFW and Sudo must be installed and properly configured
The root user must be your login + 42 [login42] and the normal user must be your login.
The normal user should remain in the sudo and user42 groups.

Intro

Password directives

/etc/login.defs:

[....]
PASS_MAX_DAYS   30
PASS_MIN_DAYS   2
PASS_WARN_AGE   7
[....]

/etc/pam-d/common-password:

[....]
password requisite pam_pwquality.so retry=3 minlen=10 maxrepeat=3 ucredit=-1 lcredit=-1 dcredit=-1 reject_username enforce_for_root difok=7
[....]

return: Number of attempts before the system returns an error.
minlen: Minimum password length.
maxrepeat: the maximum number of times a single character may be repeated.
ucredit: Capitalized characters that must be present.
lcredit: Capitalized characters that must be present.
lowercase characters it must have.
dcredit: The number of digits the new password must have.