How to troubleshoot "No input file specified" errors

Introduction

Visiting a domain results in the message "No input file specified"

[root@the ~]$ curl -sL http://domain.tld
No input file specified.

This problem can have multiple causes, however, most commonly is a PHP related error. Knowing where to look and what logs to review will help you in determining what the root of the problem is and how you can attempt to solve it.

Procedure

You will want to start by reviewing the Apache error logs:

The following command will tail Apache's logs and update your terminal with any output reported by Apache. Once you execute this command, you will need to visit your domain to trigger the failure.

tail -fn0 /etc/apache2/logs/error_log

If the Apache logs are not enough, you will want to review the PHP error logs:

By default, most applications will write the PHP error logs to a file called "error_log" within the working directory or document root.

tail -fn0 /home/$USER/public_html/error_log

For subdomains or addon domains, you will want to use the appropriate document root.

If you are using PHP-FPM, the logs will be consolidated in the "logs" directory within the user's root directory.

tail -fn0 /home/$USER/logs/$DOMAIN_TLD.php.error.log

For similar errors, you may want to review PHP configurations such as handlers in use, or any custom directives that may not be supported within the .user.ini files as these could lead to the reported failure.