What Is the Combined Log Format?
The Combined Log Format (CLF+) is the most widely used access log format for Apache and Nginx web servers. It extends the Common Log Format by appending two additional fields: the HTTP Referer header and the User-Agent header. A typical line looks like: 192.168.1.1 - - [10/Oct/2025:13:55:36 +0000] "GET /page HTTP/1.1" 200 2326 "https://google.com" "Mozilla/5.0 ..."
Why It Matters for SEO
The Combined Log Format is the gold standard for SEO log analysis because it includes the user-agent string (essential for identifying crawlers) and the referrer (essential for understanding traffic sources). Without the user-agent field, you cannot distinguish Googlebot from regular users. Without the referrer, you cannot track which pages link to which resources.
How to Configure It
In Nginx, set access_log /var/log/nginx/access.log combined; in your server block. In Apache, use LogFormat "%h %l %u %t "%r" %>s %b "%{Referer}i" "%{User-Agent}i"" combined. Most servers use this format by default. LogBeast natively supports Combined Log Format with auto-detection.
📖 Related Article: Understanding Server Log Formats — Read our in-depth guide for practical examples and advanced techniques.
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