Common Log Format
Template:Short description Template:Refimprove For computer log management, the Common Log Format,[1] also known as the NCSA Common log format,[2] (after NCSA HTTPd) is a historically standardized text file format from 2004 that was used by web servers when generating server log files.[3] Because the format was standardized, the files had been readily analyzed by a variety of web analysis programs, for example Webalizer and Analog.
Each line in a file stored in the Common Log Format has the following
The format is extended by the Combined Log Format with referer and user-agent fields.[4][5]
Example
127.0.0.1 ident alice [01/May/2025:07:20:10 +0000] "GET /index.html HTTP/1.1" 200 9481
A field set to dash (-) indicates missing data.
127.0.0.1is the IP address of the client (remote host) which made the request to the server.identis the RFC 1413 identity of the client, if supplied.aliceis the userid of the person requesting the document. Missing unless HTTP authentication is used.[01/May/2025:07:20:10 +0000]is the request timestamp. Here in strftime format%d/%b/%Y:%H:%M:%S %z."GET /index.html HTTP/1.1"is the request line from the client. The methodGET,/index.htmlthe resource requested, andHTTP/1.1the HTTP protocol version.200is the HTTP status code returned to the client.9481is the response size, in bytes.
Usage
Log files are a standard tool for computer systems developers and administrators. They record the "what happened, when, by whom" of the system. This information can record faults and help their diagnosis. It can identify security breaches and other computer misuse. It can be used for auditing. It can be used for accounting purposes.[citation needed]
The information stored is only available for later analysis if it is stored in a form that can be analysed. This data can be structured in many ways for analysis. For example, storing it in a relational database would force the data into a query-able format. However, it would also make it more difficult to retrieve if the computer crashed, and logging would not be available unless the database was available. A plain text format minimises dependencies on other system processes, and assists logging at all phases of computer operation, including start-up and shut-down, where such processes might be unavailable.[citation needed]
See also
- Extended Log Format
- Log management and intelligence
- Web log analysis software
- Web counter
- Data logging
- Syslog
References
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- ^ Page Module:Citation/CS1/styles.css has no content."Logging in W3C httpd". World Wide Web Consortium. 1995-10-12. Retrieved 2015-04-16.
- ^ Page Module:Citation/CS1/styles.css has no content."Log File Formats: NCSA Common". IBM. 2004-05-19. Archived from the original on 2021-02-24. Retrieved 2013-05-07.
- ^ Page Module:Citation/CS1/styles.css has no content.stevewhims. "NCSA Logging - Win32 apps". learn.microsoft.com. Retrieved 2023-02-17.
- ^ Page Module:Citation/CS1/styles.css has no content."Module ngx_http_log_module". nginx.org. Retrieved 1 May 2025.
- ^ Page Module:Citation/CS1/styles.css has no content."Log Files - Apache HTTP Server Version 2.4". httpd.apache.org. Apache Software Foundation. Retrieved 1 May 2025.
