Changed Default Page For Nagios Version 4.4.x

Search for a file named index.php. The file located in your nagios installation folder /..../nagios/share/index.php

and then search for $url = 'main.php';
This is the default page for Nagios. Change only main.php to your desired default page, either Type 1 or Type 2. It's your call.

Type 1;
$url='map.php?host=all';

Type 2;
$url='cgi-bin/tac.cgi';

Actually, it's just changing the URL for the default page.
After editing the file, don't forget to restart your Apache.