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CompTIA Linux+ XK0-005 - 2.1 - Linux Hardening: Enforcing Password Strength

Ensuring strong and secure passwords is a fundamental aspect of Linux hardening. Passwords serve as a primary line of defense against unauthorized access and play a crucial role in protecting sensitive data. This guide provides an overview of the purpose and use of enforcing password strength in a Linux environment, along with the relevant files and concepts involved.

Password Strength Requirements

Enforcing password strength involves setting specific requirements for the complexity and length of passwords. By establishing strong password policies, organizations can reduce the risk of password guessing or brute-force attacks. Typical password strength requirements include:

  1. Length: Passwords should meet a minimum length requirement, often ranging from 8 to 12 characters or more. Longer passwords are generally more secure.

  2. Character Complexity: Passwords should include a combination of uppercase and lowercase letters, numbers, and special characters. This complexity makes passwords harder to guess.

  3. Password Expiration: Passwords should expire after a certain period, typically every 30, 60, or 90 days. Regular password changes minimize the chances of compromised passwords being used over an extended period.

  4. Password History: Prevent users from reusing previously used passwords. By maintaining a password history, users are encouraged to create new and unique passwords.

Configuration Files

To enforce password strength, Linux systems utilize specific configuration files. Here are some commonly used files and settings:

  1. PAM Configuration Files: The Pluggable Authentication Modules (PAM) framework controls the authentication process on Linux systems. PAM configuration files, such as /etc/pam.d/system-auth or /etc/pam.d/common-password, define the rules and settings for password strength requirements.

  2. PAM Modules: PAM modules are responsible for implementing various authentication policies. The pam_pwquality module is commonly used to enforce password complexity requirements, including length, character types, and password history.

  3. Password Aging: Linux systems use the /etc/shadow file to store password-related information, including password expiration dates and password history. Tools like chage or passwd allow administrators to set password expiration dates and manage password aging policies.

Enforcing Password Strength

To enforce password strength on a Linux system, follow these general steps:

  1. Identify the appropriate PAM configuration file for password strength settings (e.g., /etc/pam.d/system-auth).

  2. Open the PAM configuration file using a text editor.

  3. Locate the line(s) or section responsible for password authentication (password section).

  4. Add or modify the relevant parameters to enforce password strength requirements. These parameters may include minlen for minimum length, dcredit, ucredit, ocredit, and lcredit for character complexity, remember for password history, and maxage for password expiration.

  5. Save the changes and exit the text editor.

  6. Optionally, use tools like chage or passwd to set password expiration dates and manage password aging policies.


Enforcing password strength is a vital component of Linux hardening practices. By setting password complexity requirements and regularly expiring passwords, organizations can significantly enhance the security of their Linux systems.

Password strength enforcement involves modifying the PAM configuration files to specify parameters like minimum length, character complexity, password history, and expiration dates. Administrators can use tools like pam_pwquality and chage to implement and manage these requirements effectively.

By educating users about the importance of strong passwords and enforcing password strength policies, organizations can mitigate the risk of unauthorized access, data breaches, and other security incidents.

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