Information
The pam_pwquality.so module checks the strength of passwords. It performs checks such as making sure a password is not a dictionary word, it is a certain length, contains a mix of characters (e.g. alphabet, numeric, other) and more. The following are definitions of the pam_pwquality.so options.
The following options are set in the /etc/security/pwquality.conf file:
Password Length:
minlen = 14 - password must be 14 characters or more
Password complexity:
minclass = 4 - The minimum number of required classes of characters for the new password (digits, uppercase, lowercase, others)
OR
dcredit = -1 - provide at least one digit
ucredit = -1 - provide at least one uppercase character
ocredit = -1 - provide at least one special character
lcredit = -1 - provide at least one lowercase character
The following is st in the /etc/pam.d/common-password file:
retry=3 - Allow 3 tries before sending back a failure. The settings shown above are one possible policy. Alter these values to conform to your own organization's password policies.
Rationale:
Strong passwords protect systems from being hacked through brute force methods.
Solution
Run the following command to install the pam_pwquality module:
apt install libpam-pwquality
Edit the file /etc/security/pwquality.conf and add or modify the following line for password length to conform to site policy
minlen = 14
Edit the file /etc/security/pwquality.conf and add or modify the following line for password complexity to conform to site policy
minclass = 4
OR
dcredit = -1
ucredit = -1
ocredit = -1
lcredit = -1
Edit the /etc/pam.d/common-password file to include the appropriate options for pam_pwquality.so and to conform to site policy:
password requisite pam_pwquality.so retry=3
Additional Information:
Additional module options may be set, recommendation requirements only cover including try_first_pass and minlen set to 14 or more.
Settings in /etc/security/pwquality.conf must use spaces around the = symbol.