title: How to enable firewall on Centos 7?
body: <p>My firewall is currently inactive. </p>
  
  <pre><code># systemctl status firewalld
  firewalld.service
      Loaded: masked (/dev/null)
      Active: inactive (dead)
  </code></pre>
  
  <p>I used the following command to enable the firewall</p>
  
  <pre><code>$systemctl unmask firewalld
  </code></pre>
  
  <p>but I got this error</p>
  
  <pre><code># systemctl unmask firewalld
  Failed to issue method call: Access denied
  </code></pre>
  
  <p>Please advise. </p>
  
  <p>Thanks in advance!</p>