A log file can be used to track a range of data such as visitors to a website or a history of file modifications. Log files have multiple use cases for fields ranging from programming to SEO. For example, they can help understand how visitors or search engine bots access a website. They can also be useful for debugging, as they can track the events that happened before an error occurred, etc.
Data loss protection with log files
Log files can be extremely useful in the case of data loss. Whether by accident or by malicious activity, data may become corrupt or get lost. Log files help to trace activity on a computer, such as when a file was opened or moved. This can help to either locate lost data or understand when or how it became corrupt.
Software ranging from operating systems to websites and apps typically keeps data logs for all sorts of activities. These can range from tracking system updates and monitoring when new programs are installed, executed, or deleted, to Windows event and error logs, that help debug computer crashes.
Data analysis using log files
Log files are also very commonly used for data analysis. Web servers will run multiple log files, categorized by their different uses which enable different types of analyses. The file types below are common for most servers, but certain systems may use different names or categorization methods.
An access log is a log of every file request made to a system. Every time a user accesses a page of a website, it will trigger a number of different access requests. It will access required files, such as any HTML, CSS, images, or other necessary file to display the page. They will also contain the type of request a user made - whether that is GET or POST to receive or send data respectively.
Access logs are useful for a variety of purposes. They can identify when a user tried to access a file that does not exist, which suggests a file is missing or a link somewhere is wrong. They can also identify attempts to access sensitive areas of a website or provide evidence of when and where a website was compromised.
An error log contains a list of errors generated by a website. These are useful for web developers, as they help to indicate when and where errors occur on a website. This can provide valuable information to aid in debugging websites and fixing problems.
Depending on how a system is set up, some may include a warning log file. These can be considered as a less severe version of an error log file, so much so that some systems do not split the two into separate files.
Whereas an error log contains errors that prevent a page from working, a warning log contains warnings that do not prevent users from accessing pages. Examples of warnings may include websites receiving unexpected input that is ignored or interpreted in a way that does not generate an error.
.log and .txt for Windows and Mac
The two most common file types for log files are .log and .txt.
.log is often simply used to make them easier to identify - the format is most often plain text, making them functionally equivalent to .txt files.
Both Windows and Mac operating systems generate log files. These files can be opened using software to read plain text files, such as Notepad on Windows or TextEdit on Mac. Mac also supports viewing log files directly through the console.
Log files are particularly useful in trying to debug system issues, such as crashes and unexpected shutdown events.
Importance for SEO
Log files can provide valuable information for SEO. Both regular users and search engine crawl bots can be identified in access log files. Browsing these files can thus help to understand user activity and provide insight into how search engines crawl a website. Tracking the frequency of search engine visits can give an indication of how relevant the website is considered, and over time can be used to analyze if changes to that site have any impact on crawl bots' activity.
In addition, log file analyses are often applied in the context of crawl budget optimization in order to identify web pages that do not get crawled by search engine bots. The 'crawl budget' is the number of URLs a search engine crawler will crawl on your site on a particular visit. Crawl budget optimization is not only about maximizing this number but also about using it more efficiently, i.e. making sure that all important content on a website gets crawled.