Definition: What Is an Error Log?
An error log is a file that keeps track of any or all errors that occur while running an application, operating system, or server. It contains information about what happened, when it happened, how critical it was, and maybe even what was the cause. That is why checking the error log and error messages is the easiest way to determine the reason for an application outage or performance issue.
Why Is an Error Log Useful?
Let’s look at the benefits of using error logs in more detail.
Error logs are the starting point for most of the support engineers to pinpoint the root cause of a problem. For example, it can identify performance-related issues, such as when your application freezes, memory problems, slow throughput, etc. This information can later be used to update your infrastructure for better performance.
Faster troubleshooting leads to faster resolution time, reducing the chances of having long downtimes in your systems. By correlating error logs with metrics you can identify potential performance issues, low throughput and bottlenecks and get ahead of the problem before it starts causing your systems to crash or having downtimes.
Before you make any decision in any situation you need to have some data input regarding what is causing the problem, how it will affect your systems, who is affected by this issue and so on. Visualizing error logs, creating trends, and dashboards can help you answer these questions. That analysis enables you to prioritize and address the critical issues first – identify which part of your system is causing you the most trouble, organize your team and fix it as a high priority.
By analyzing error logs, you can determine the cause for software freezes, slow performance, or memory bottleneck.
For example, when you are experiencing slowness in your APIs and websites, you can check the error logs of the systems hosting these APIs and websites to pinpoint the issue. The root cause might differ depending on your system setup. For instance, if your APIs are connecting to a database it might be a slow query issue or wrong usage of indexes, which you can identify with error logging. Or it can be because of insufficient memory, CPU, I/O disk resources. Once you identify the reason you can apply a fix and improve your website or APIs performance.
Security-related error logs can be examined for patterns over time to assist in identifying suspicious activities such as past hacking attempts or failed login attempts, or a compromised system. In addition, this information can be used to alert the user and strengthen account security by changing the password or suggesting two-factor authentication.
What Do Error Logs Contain?
The value of an error log depends on how many details it provides for each error. Though the structure of the error logs can vary, here are some of the most common components of any error log:
- Error ID: Unique ID to identify each error.
- IP Addresses: Sometimes, the IP addresses of the sending and receiving devices are included in error messages.
- Device or Server: The name or IP address of the device from which the application received an error.
- Timestamp: Shows the time and date of the error, ideally including time zone. With an ISO 8601 format and is used for distributed systems.
- Log Level: Most log entries have a criticality level indicating if immediate action is needed.Commonly used levels include TRACE, DEBUG, INFO, WARN, ERROR, and FATAL where TRACE is the least crucial level, and FATAL is the most critical.
- Username: This column reveals the network username linked with the issue; the system user’s action usually causes it. Usernames help with troubleshooting and historical analysis.
- Message / Description: This is the error message precisely describing the type and cause of error. For example, “Access Denied: Insufficient Privileges”.
How to Get the Most Out of Your Error Logs
Here are some of the best practices when using error logs to get the most of it:
Know Which Log to Monitor
Large volumes of error log data can make it difficult to identify important information, complicating log storage and administration. Instead, monitoring the right data provides better results. For instance, data related to production, user experience, or security breaches, are extremely useful when troubleshooting. On the other hand you don’t usually collect TRACE logs or DEBUG logs in production. It will create noise and make it difficult to focus on what matters the most. These logs are usually enabled in test environments when you are troubleshooting a specific service.
Use Right Log Level
Each error log entry should include the proper log level, differentiating severe and important events from irregular or routine ones. For example, use TRACE to annotate algorithm steps and query parameters in your code; use DEBUG to test applications in a test environment or use ERROR in case of login failures.
Read the article on logging levels to learn more about how to choose the right severity level.
Use Structured Log Formats
Use a consistent format for error logging and data storage. For example, timestamp, severity, message, and other relevant data fields like process ID, transaction ID, etc., should all be included in a structured log format (e.g., JSON or key/value format).
Analyze Error Trends
Examining past error trends over time can benefit you in spotting anomalies in them. Which can be used for benchmarking and standardizing those trends. For example, when performance-related errors start to show up under intense CPU usage of more than 80%, you know those are the baseline numbers and can use them as a benchmark when updating your infrastructure.
Create Meaningful Alerts
Alerts created from errors must be clear and concise and sent to relevant teams. For example, send security-related errors to the security team. At the same time, make sure you use log levels when defining alert rules for your error logs to help the team decide which events need immediate action and prioritize accordingly.
Use Log Management and Monitoring Tools
With log management tools, analyzing application error logs is as simple as connecting suitable data sources to destinations. As a result, you no longer need to devote resources into building a logging infrastructure to monitor and log activity in your applications.
For more recommendations on how to use logs efficiently read the article on log management best practices.
Error Log Management with Sematext
Sematext Logs is a hassle-free log aggregation and analysis tool that helps you correlate logs with events and metrics across your infrastructure in a central location. This enables you to get a comprehensive view of your entire system, detect anomalies, and set threshold-based alerts so you get notified when the number of logs hits the threshold. As an all-in-one platform, when there is a spike in your error logs, you can correlate with metrics on a single page and find the root cause of issues in real-time.
Sematext integrates with various notification platforms and allows you to receive alerts from team chat applications and pick channels to ensure notifications are delivered to relevant people in your team. Or integrate with third party applications which provide Incident Management solutions. Rich visualization dashboards are available to facilitate alert analysis. You can detect what kind of anomaly in your error logs are causing the alert to trigger, and compare them with the logs and metrics when your system was running normally.
Sematext also provides pipelines, which lets you structure logs based on your needs, extract information into new fields, mask sensitive data or drop unwanted logs to reduce your costs.
With its auto-discovery capabilities, Sematext allows you to ship discovered log sources automatically without any additional configuration. You can ship logs from different environments such as containers, AWS, operating systems, APIs, Syslog protocols, and many more with the help of various integrations.
Watch the video below to learn more about what Sematext Logs can do for you. Or, better yet, start the 14-day free trial and try Sematext yourself!