Unable to start Apache: Duplicated Listen entries in Apache configuration file

Symptoms

• Unable to start the Apache service on a Plesk server with the error:

  httpd[18332]: (98)Address already in use: AH00072: make_sock: could not bind to address 0.0.0.0:80
  httpd[18332]: no listening sockets available, shutting down

• The websites show the "Web Server's Default" page.

Cause

Duplicated Listen entries in the Apache configuration file.

Resolution

1. Log into the server via SSH.

2. Find Apache configuration file which contains the duplicated Listen entries:

   # grep -r Listen /etc/httpd/*
   /etc/httpd/conf/httpd.conf:Listen 80
   /etc/httpd/conf/httpd.conf:Listen 80

3. Using the vi text editor open the found /etc/httpd/conf/httpd.conf file in step №2 and remove the second line with "Listen 80" directive. 
4. Restart the Apache service to apply the changes:

   # service httpd restart

5. Execute the command below to rebuild Apache configuration for domains:

   # /usr/local/psa/admin/bin/httpdmng --reconfigure-all

   Note: execution of the command above may lead to the websites downtime, perform the execution in the maintenance window.