Apache/NCSA Common Log Format:

A "common" log file format is like this:
216.67.1.91 - leon [01/Jul/2002:12:11:52 +0000] "GET /index.html HTTP/1.1" 200 431

The following are the fields in Common log format:

host rfc931 username date:time request statuscode bytes

The following is a description of the fields in the fields in the Common log format:

host (216.67.1.91 in the example)
     The IP address or host/subdomain name of the HTTP client that made the HTTP resource request.

rfc931 ("-" in the example)
    The identifier used to identify the client making the HTTP request. If no value is present, a "-" is substituted.

username (leon in the example)
    The username, (or user ID) used by the client for authentication. If no value is present, a "-" is substituted.

date:time ([01/Jul/2002:12:11:52 +0000] in the example)

     The date and time stamp of the HTTP request.  The fields in the date/time field are:
     [dd/MMM/yyyy/:hh/:mm/:ss/ +-hhmm] where the fields are defined as follow:

dd	day of the month
MMM	the month
yyy	the year
:hh	the hour
:mm	the minute
:ss	the seconds
+-hhmm	the time zone

In practice, the day is typically logged in two-digit format even for single-digit days. For example, the second day of the month would be represented as 02. However, some HTTP servers do log a single digit day as a single digit. When parsing log records, you should be aware of both possible day representations.

	request ("GET /index.html HTTP/1.1" in the example)
	The HTTP request. The request field contains three pieces of information. The main piece is the requested resource (index.html). The request field also contains the HTTP method (GET) and the HTTP protocol version (1.1).
	statuscode (200 in the example)
	The status is the numeric code indicating the success or failure of the HTTP request.
	bytes (431 in the example)
	The bytes field is a numeric field containing the number of bytes of data transferred as part of the HTTP request, not including the HTTP header.

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Nihuo Web Log Analyzer also supports other log formats; See the list containing Apache/NCSA Common Log Format and all other supported formats.