Server Log Files in a Nutshell

Servers take a lot of requests daily, we know that…We also know that the server responds instantly. But who makes the request? What do they want, and what exactly are they looking for? Where do these visitors come from? How often they are making a request: once a month, once a day, almost every minute?

Well, answers to these, and potentially a lot more questions, can be found in a single place - the server log file.

What is a server log file?

A server log file is a simple text document that contains all activities of a specific server in a given period of time (for example, one day). It is automatically created and maintained by the server, and it can provide you with a detailed insight into how, when, and by whom your website or the application was accessed.

Most servers generate CLF (Common Log Format) files, or raw log files, which are rather crude and difficult to understand for the most part. They also tend to become rather complex and comprehensive in a very short amount of time, which is why the server automatically erases them after a period of time.

CLF files are files in which each line represents one request. Therefore, if the visitor clicks the link and gets a HTML file with three additional images on it, four lines of text will appear in the log file.

Each line contains an abundance of information, which may include:

  • IP address and identity of the device making a request
  • Name, location, and size of the requested file
  • Time and date of the request, and the request method
  • The referred webpage
  • HTTP status code (if a file was not found, for example)

The log files are available only to administrative personnel, disabling general users from accessing them. Because these files provide an abundance of information, they are excellent tools to help you improve website administration efficiency, increase overall traffic to your site, or even fine-tune your SEO efforts.

Why Should You Centralize your Server Logs?

Having all your server logs in one single place is of the utmost importance if you are required to have two or more servers active at all times. Some of the advantages to utilizing centralize server logs include:

  • Saving time:  Accessing all data in one place is much more time-effective than accessing all of your servers locally.
  • Troubleshooting: Regular insight into centralized logs gives you a “before and after” picture of the status of your servers. Determining what went wrong and correcting the mistake quickly and easily is at the heart of optimum network administration.
  • Reducing the possibility of losing data: If an individual server is down, there is no way to access its data locally. With a centralized hub, you can still access the data.
  • Improving your network security: Reviewing server logs in a centralized place lets you easily and effectively pinpoint any unusual behavior (for example, an excessive number of login attempts in a short period of time) and adjust your network security accordingly.

Types of Log Files

Even though most websites rely on the CLF for their server log files, there are other formats as well.

Access Log

What are access log files? Access logs record information about which HTML files and graphic images are being requested from your server. Access logs tell you the number of visitors as well as their origins (did they come from the .com, .edu, or the .gov site, for example). Also, you can get usage patterns and information about which page visitors requested the most.

Agent Log

What are agent log files? Agent logs record and can provide you with information about which web clients made requests on your server.

Referrer Log

What are referrer log files? Referrer logs record information about the URL the visitor was on immediately before moving onto your web page and making a request on your server. This type of log is extremely useful when you want to pinpoint the origin of the requests on your web server as well as which web pages are referring traffic to your server.

Error Log

What are error log files? Error logs record and provide you with information about a server’s failed requests. Essentially, it automatically generates an error message as soon as someone tries to access a nonexistent file on your server.


Centralized log solutions give you a better overall understanding of log files through better readability and understandability. More significantly, they prevent information from slipping through your fingers due to data scattered across your environment. And the knowledge that your data is safe and secure is what’s most important of all.

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