Log file - definition & overview

Log files are the primary data source for network observability. A log file is a computer-generated data file that contains information about usage patterns, activities and operations within an operating system, application, server or another device. Log files show whether resources are performing properly and optimally.

Log files are crucial for monitoring and troubleshooting system issues and tracking events, security incidents and user activities. They provide valuable insights into the performance and health of a system, enabling administrators to identify problems, analyze trends and ensure the efficient operation of servers and applications. Diagnosing and resolving issues promptly would be challenging without log files, leading to potential downtime, security breaches and performance degradation.

Examples of different types of logs include:

1. System log: Capture system-level events and activities, such as startup/shutdown messages, hardware failures, kernel messages and system resource utilization.

2. Application log: Record events specific to an application, including errors, warnings, user actions and performance metrics.

3. Security log: Document security-related events like login attempts, access control changes, authentication successes or failures and intrusion detection alerts.

4. Audit log: Track activities within a system or application for auditing purposes, ensuring compliance with regulatory requirements and monitoring user actions.

5. Event log: Provide a chronological record of notable events, notifications and administrative actions within a system or software application.

6. Access logs: Capture details of user access to resources, such as login/logout timestamps, accessed files, permission changes and network connections.

7. Error log: Record errors, exceptions, warnings and debug information to help diagnose and troubleshoot issues in software, systems or applications.

8. Performance log: Monitor system or application performance metrics, such as response times, CPU usage, memory usage and network traffic, to optimize performance and identify bottlenecks.

9. Transaction log: Record details of database transactions, including data modifications, queries and commit/rollback operations, to ensure data integrity and facilitate recovery.

10. Change logs: Document changes made to configurations, settings, files, or databases to track modifications, identify discrepancies and maintain version control.

Each log type serves a specific purpose in monitoring, troubleshooting, auditing and analyzing activities within systems, applications and networks to maintain operational efficiency, security and compliance.

Log file examples for common operating systems

Each of the leading operating systems is uniquely configured to generate and categorize event logs in response to specific types of events. Log management systems centralize all log files to gather, sort and analyze log data and make it easy to understand, trace and address key issues related to application performance.

Windows event logs

Windows is pre-configured to classify events into six categories:

• Application log - when an event takes place inside an application, these logs help code developers understand and measure how applications are behaving during development and before release.
• Directory service logs - a computer configured to respond to security authentication requests within a Windows Server domain—known as a domain controller—may generate directory service logs. These logs record user privilege changes, authentication operations, requests and other operations in Windows Active Directory.
• DNS server log - a Domain Name System (DNS) server contains the databases that match hostnames of websites on the internet with their appropriate IP addresses. Each time you navigate to a new web page, DNS servers are involved in processing requests and helping your browser get to the right page. A DNS server log is a special log file for recording activity on a DNS server.
• File replication service log - another type of log file that is only available for domain controllers. They record information about file replications that take place on the computer.
• Security log - security logs are created in response to security events on the computer. These can include various events such as failed log-ins, password changes, failed authentication requests, file deletion and more. Network administrators can configure which events are application events and which should be entered into the security log.
• System log - system logs, not to be confused with Syslog, record events that occur within the operating system itself, such as driver errors during start-up, sign-in and sign-out events and other activities.

Linux event logs

The Linux operating system creates a continuous timeline of events on the system, including every event related to the server, kernel and running applications. Linux places events in four distinct categories:

• App logs
• Event logs
• Service logs
• System logs

These categories are analogous to those used by Windows O/S.

iOS event logs

iOS takes a unique approach to event log generation compared to other operating systems. iOS does not log every event in the system, but it generates documentation for application crashes. Later versions of iOS (10.0 and beyond) offer an API that can be used to log application events on the system. The iOS logging API allows network administrators to access log file data from:

• Integration security
• Apple pay
• Data encryption
• Device controls
• Internet services
• Network security
• Privacy controls
• User password management

Large IT organizations depend on an extensive network of IT infrastructure and applications to power key business services. Log file monitoring and analysis increase the observability of this network, creating transparency and allowing visibility into the cloud computing environment. While observability should not be treated as an ultimate goal, it should always be seen as a mechanism for achieving real business objectives:

• Improving the reliability of systems for the end-user

Log files include information about system performance that can be used to determine when additional capacity is needed to optimize the user experience. Log files can help analysts identify slow queries, errors that are causing transactions to take too long or bugs that impact website or application performance.

• Maintain the security posture of cloud computing environments and prevent data breaches

Log files capture things like unsuccessful log-in attempts, failed user authentication, or unexpected server overloads, which can signal to an analyst that a cyberattack might be in progress. The best security monitoring tools can send alerts and automate responses when these events are detected on the network.

• Improve business decision-making.

Log files capture the behavior of users within an application, giving rise to an area of inquiry known as user entity behavior analytics (UEBA). By analyzing the actions of users within an application, developers can optimize the application to get users to their goals more quickly, improving customer satisfaction and driving revenue in the process.

Sumo Logic is the industry-leading cloud-native platform that makes it easy for IT organizations to aggregate and analyze every log file generated within private, public or hybrid cloud environments. With Sumo Logic's log file analysis capabilities, your IT organization can identify new business risks and opportunities while responding efficiently to security threats and operational issues before they negatively impact users.

Learn more in our ultimate guide to log analytics.

What are examples of common log file formats used in logging systems?

• Common log format (CLF)

• Extended log format (ELF)

• Structured Data (JSON, XML)

• Apache log

• Syslog

• W3C extended log file format

• CSV (Comma-Separated Values)

How can log file security and data integrity be ensured to prevent unauthorized access?

• Limit who can view, modify or delete log files

• Encrypt log files both at rest and in transit

• Conduct regular audits of log files

• Regularly back up log files and store them securely

• Verify the integrity of log files

• Log access to log files

• Centralize log management to a secure server or platform

• Set up monitoring systems with alerts

How can I use log files for audit trails and compliance requirements?

• Comprehensive record-keeping

• Monitor user actions

• Generate compliance reports

• Maintaining data integrity

• Auditing and documentation