“No input file specified” is one of the most frequently encountered issues in Nginx. People on serverfault and in the #nginx IRC channel asks for help with this so often that this post is mostly to allow me to be lazy and not have to type up the same answer every time.

This is actually an error from PHP and due to display_errors being 0 people will often just get a blank page with no output. In a typical setup PHP will then send the error to stderr or stdout and Nginx will pick up on it and log it in the Nginx error log file. Thus people spend a ton of time trying to figure out why Nginx isn’t working.

The root cause of the error is that PHP cannot find the file Nginx is telling it to look for, and there are two common cases that causes this. Either you’re not giving PHP the right path to the file or your file permissions are incorrect.

Wrong Path Sent to PHP

The most common reason at the time of writing happens because a user uses a horrible tutorial found via google instead of actually understanding Nginx. Reading my primer will equip you to actually solve this on your own but since this post is actually dedicated to the error I’ll cheat this once and allow you to be lazy by just giving you the full solution.

Nginx tells PHP about the file to execute via the SCRIPT_FILENAME fastcgi_param value. Most examples in the wiki should define this as $document_root$fastcgi_script_name. The horrible tutorials will often hardcode the path value but this is not desirable as we don’t want to duplicate information and invite future screw ups. So you’ve gone with the $document_root$fastcgi_script_name option and suddenly it’s no longer working.

This happens because Nginx has 3 levels of inheritance commonly referred to as blocks, these being http, server and location, each being a sub-block of the parent. Directives in nginx inherit downwards but never up or across, so if you define something in one location block it will never be applied in any other location block under any circumstance.

Typically users define their index and root directive in location / because a tutorial told them to. So when they then define SCRIPT_FILENAME using $document_root the root directive is not actually defined and thus the SCRIPT_FILENAME value becomes just the URI making PHP look at the root server dir.

The simple solution here is to just define the directive in your server block. (or http block even!) Generally the higher up your can define a directive the less duplicate directives you’ll need.

Incorrect File Permissions

Most people don’t really believe me when I tell them their file permissions are incorrect. They’re looking at the damn permissions and the PHP user can read the file just fine! Sadly, this shows a lack of understanding of Unix user permissions. Being able to read a file is not enough, a user must also be able to traverse to the file.

This effectively means that not only should the file have read permission, but the entire directory structure should have execute permission so that the PHP user can traverse the path. An example of this:

Say you have an index.php file in /var/www. /var/www/index.php must have read permission and both /var and /var/www must have execute permissions!

If you’ve corrected both things and still have this issue then please put a comment so I can look into it, as far as I know there should be no other reasons  for this error.

Related posts:

  1. File Uploading With PHP & Nginx
  2. 12,000 Requests per second with Nginx, PHP and Memcached
  3. Implementing Full-Page caching with Nginx and PHP
  4. Nginx Primer
  5. Optimizing Nginx for High Traffic Loads

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