When setting up DAViCal with Nginx and PHP-FPM, many developers encounter the frustrating "File not found" error with the accompanying FastCGI error message: "Primary script unknown". This typically occurs when using alias directives in Nginx configuration while trying to serve PHP applications.

The core issue lies in how Nginx handles the SCRIPT_FILENAME parameter when using alias directives with PHP-FPM. The standard configuration using $request_filename doesn't properly resolve the correct file path when aliases are involved.

# Problematic default setting in fastcgi_params
fastcgi_param SCRIPT_FILENAME $request_filename;

Here are two working approaches to solve this issue:

Solution 1: Modify the PHP location block

Update your PHP location block to properly handle aliased paths:

location ~ \\.php$ {
    include /etc/nginx/fastcgi_params;
    fastcgi_split_path_info ^(.+\\.php)(/.+)$;
    
    # Critical fix: Use $document_root$fastcgi_script_name instead of $request_filename
    fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
    
    fastcgi_pass unix:/var/run/php5-fpm.sock;
    fastcgi_index index.php;
}

Solution 2: Specific configuration for the aliased directory

For the DAViCal specific location, add a dedicated PHP handler:

location /kalender {
    alias /usr/share/davical/htdocs;
    
    location ~ \\.php$ {
        include /etc/nginx/fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $request_filename;
        fastcgi_pass unix:/var/run/php5-fpm.sock;
    }
    
    try_files $uri $uri/ /kalendar/index.php;
}

When implementing these solutions, ensure:

• Your PHP-FPM pool has proper permissions to access the files
• The alias path points to the correct directory
• Files in the target directory have appropriate permissions (typically www-data:www-data)
• You restart both Nginx and PHP-FPM after configuration changes

Create a simple test PHP file in your aliased directory:

echo "<?php phpinfo(); ?>" | sudo tee /usr/share/davical/htdocs/info.php
sudo chown www-data:www-data /usr/share/davical/htdocs/info.php

Then access it through your browser at http://your-server/kalendar/info.php to verify everything works correctly.

When setting up DAViCal with Nginx, I encountered the frustrating "File not found" error with the following message in the logs:

FastCGI sent in stderr: "Primary script unknown"

Here's the relevant part of my Nginx configuration that was causing issues:

location /kalender {
    alias  /usr/share/davical/htdocs;
}

location ~ \.php$ {
    include /etc/nginx/fastcgi_params;
    fastcgi_split_path_info ^(.+\.php)(/.+)$;
    fastcgi_pass unix:/var/run/php5-fpm.sock;
    fastcgi_index index.php;
}

The issue occurs because when using alias with PHP-FPM, Nginx passes the wrong SCRIPT_FILENAME to PHP-FPM. The default fastcgi_param SCRIPT_FILENAME $request_filename doesn't work correctly with alias directives.

Here's the corrected configuration that worked for me:

location /kalender {
    alias /usr/share/davical/htdocs;
    
    location ~ \.php$ {
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_index index.php;
    }
}

• Nested the PHP location block inside the alias location
• Modified SCRIPT_FILENAME to use $document_root$fastcgi_script_name
• Removed fastcgi_split_path_info as it wasn't needed in this case

Here's the full server block that worked successfully:

server {
    listen 80;
    listen [::]:80 default_server ipv6only=on;
    
    root /var/www-data;
    index index.html index.htm index.shtml index.php;
    
    server_name just.a.server;
    
    location / {
        try_files $uri $uri/ /index.html;
        ssi on;
    }
    
    location /kalender {
        alias /usr/share/davical/htdocs;
        
        location ~ \.php$ {
            include fastcgi_params;
            fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
            fastcgi_pass unix:/var/run/php5-fpm.sock;
            fastcgi_index index.php;
        }
    }
}

Make sure:

• PHP-FPM is running and listening on the correct socket
• File permissions are set correctly for the DAViCal files
• Nginx worker process has read access to the files