How to get rid of 'FastCGI sent in stderr: Primary script unknown' in nginx logs

I've tried countless methods to get rid of annoying messages in my nginx log, like [error] 358#0: *44 open() and [error] 10643#0: *2262 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream.

These are errors, sent to STDERR by the FastCGI upstream, in this case, PHP-FPM, and they happen when either index.php is not present in the folder or when a nonexistent file gets redirected to index.php and in can't handle it.

Apparently, I was missing a single line:

location ~ ^(?<script_name>.+?\.php)(?<path_info>.*)$ {
    try_files $uri $script_name =404;
    ...
}

That try_files $uri $script_name =404; needs to go into the PHP handling block of nginx, and the error vanishes from the logs.

This entry was written by Peter Molnar, and originally posted on petermolnar dot net.