title: Unable to start httpd service on Centos 7 "GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject"
body: <p>When trying to (re)start httpd service I get the following error:</p>
  <pre><code>** (pkttyagent:2574): WARNING **: 01:33:55.345: Unable to register authentication agent:
  GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject Error registering authentication agent:
  GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject (polkit-error-quark, 0) Job for httpd.service failed because the control process exited with error code. See &quot;systemctl status httpd.service&quot; and &quot;journalctl -xe&quot; for details.
  </code></pre>
  <p>Then</p>
  <pre><code>systemctl status httpd.service
  </code></pre>
  <p>sheds no light on the problem:</p>
  <pre><code>httpd.service - Web server Apache
     Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
     Active: failed (Result: exit-code) since Wed 2020-07-22 01:33:55 BST; 26min ago
    Process: 2578 ExecStart=/usr/local/apache/bin/apachectl start (code=exited, status=1/FAILURE)
  
  Jul 22 01:33:55 server... systemd[1]: Starting Web server Apache...
  Jul 22 01:33:55 server... systemd[1]: httpd.service: control process exited, code=exited status=1
  Jul 22 01:33:55 server... systemd[1]: Failed to start Web server Apache.
  Jul 22 01:33:55 server... systemd[1]: Unit httpd.service entered failed state.
  Jul 22 01:33:55 server... systemd[1]: httpd.service failed.
  </code></pre>
  <p>What might be causing this? Where should I look to debug?</p>