Warning: require(/wp-admin/wp-blog-header.php): failed to open stream: No such file or directory in /wp-admin/index.php on line 17

Solution:

You need to modify the index.php file as below to resolve this issue, only if you are running WordPress installation from the root directory. You just need to change the following lines:

Require (‘. /wp-blog-header.php’);

To this:

Require (‘wp-blog-header.php’);