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What Is an Error Log?

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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 05 November 2014
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An error log is a log of errors encountered by a system. There are a number of different ways in which error logs can be used, and they can be extremely useful tools for people who need to diagnose and manage systems such as web servers, office networks, and so forth. Accessing the error log may require special administrative permissions which are designed as a security measure to prevent unauthorized people from seeing documentation of errors.

Some error logs list every single error which occurs. Others may be programmed to selectively save information about errors, listing only certain error codes. However the system work, each entry in the error log includes an error code, a time, and may add other information such as an action someone was trying to complete, someone's location, and whether or not the error was resolved. Error logs can be searched to identify specific patterns or errors encountered by a particular user.

For webmasters, checking error logs can provide useful information about problems people are encountering. People do not always report errors, and if a webmaster has a bad link, a form which can't submit, or a similar problem, it may show up on the error log before someone brings the webmaster's attention to the problem. Error logs can also provide information about hacking attempts, as hackers may cause errors on the server while they attempt to compromise the system.

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For systems like office networks, error logs are used to keep track of problems encountered by users and to try and determine what causes these errors. An error log on an individual system or piece of equipment can also be useful, especially if someone reports problems. By viewing the error log, a technician can get more information about the problems encountered and what, exactly, happened. The technician can resolve the error or provide the user with information about where he or she went wrong.

Some systems will maintain an error log up to a certain number of entries, while others archive error logs so that they can be consulted at any time. It may also be possible to adjust these settings inside the control panel of the system. Someone launching a new website, for example, might want a large error log archive, anticipating potential problems when the site goes live, while a site which is stable and well established might not need to have such an extensive archive.

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miriam98
Post 4

@NathanG - I do database administration at work and so use the MSSQL error log to see where processes didn’t go as I expected. For example if a script didn’t run or a backup failed, I need to know where it happened and the error log will give the module, time and date where it happened. I can’t live without these tools; they save me a lot of time and trouble in pinpointing problems.

NathanG
Post 3

@everetra - I’ve used both event logs and error logs in my software development. An event log and an error log are similar in concept but two different things. An error log, as the name would suggest, is used to track down errors.

An event log tracks events—anything that you want to monitor, whether it’s an error or not.

For example, in one application I developed at work, I was communicating with a serial device. I needed to track down all of the commands sent to the serial device. Instead of outputting all the information to the console, I output everything to an event log and presto—every second, even every millisecond, I knew the exact command being sent to the serial device.

That beats stepping through the code like I used to do before and of course it’s much faster too.

David09
Post 2

@everetra - I use the event viewer in Windows whenever I want to track down system level events where something went wrong. With this viewer, for example, I can see what the possible issues are when a program crashes; it doesn’t give me all the detail that I need but sometimes it points me in the right direction.

The event viewer also helps me to track down security level events as well, with date and time of the type of event that occurred.

everetra
Post 1

Sometimes it’s the simple things that make all the difference. As a programmer I can tell you that error logs are one of those simple things that are simply awesome. In the old days when I wanted to track errors I would put popup message boxes all over the place in my code to show me where an error took place.

However, this proved to be time consuming. A friend suggested creating an application event log instead, and it was just the thing I needed. With the log I was able to trace every place in the program where the code was executing before it tripped up the error. I saved a lot of time and improved my debugging a hundred fold.

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