Secure Shell (SSH) is a widely used protocol for accessing remote servers securely. However, like any other authentication system, SSH is also vulnerable to brute force attacks where malicious actors attempt to gain unauthorized access by trying multiple login attempts with different passwords.

To protect your SSH server from such attacks, you can use the pam_faillock module to lock out users after a certain number of failed login attempts. This can help prevent unauthorized access and improve the overall security of your server.

Here’s how you can set up pam_faillock to lock out users after a certain number of failed login attempts:

1. Install pam_faillock:
   First, ensure that the pam_faillock module is installed on your system. You can install it using your package manager. For example, on Ubuntu, you can install it using the following command:

   sudo apt-get install libpam_faillock

2. Configure pam_faillock:
   Next, you need to configure pam_faillock in the SSH PAM configuration file. Open the file /etc/pam.d/sshd using a text editor (sudo privileges may be required) and add the following lines at the end of the file:

   auth required pam_faillock.so preauth
   auth required pam_unix.so
   auth required pam_faillock.so authfail
   account required pam_faillock.so

3. Set up faillock options:
   You can configure the number of allowed failed login attempts and the lockout period for users. By default, pam_faillock locks out a user after 3 failed attempts and unlocks the account after 600 seconds. You can customize these options by editing the file /etc/security/faillock.conf:

   
   # Number of failed attempts before locking out the user
   fail_interval = 3

Duration of lockout in seconds

unlock_time = 600

4. Testing:
After configuring pam_faillock, restart the SSH service to apply the changes. You can test the setup by intentionally entering incorrect passwords multiple times. You should see a message indicating that the account has been temporarily locked out after the configured number of failed attempts.

By implementing pam_faillock in your SSH configuration, you can effectively mitigate brute force attacks and enhance the security of your server. Remember to regularly monitor login attempts and review logs for any suspicious activity to ensure the continued security of your system.