What is LOG?

LOG (.log) files contain timestamped records of events, errors, warnings, and informational messages from software applications, operating systems, web servers, and network devices. Each line typically includes a timestamp, severity level, source component, and message describing what happened.

Log files are crucial for troubleshooting issues, monitoring system health, security auditing, and analyzing performance. Formats vary from simple text to structured formats like JSON. Common examples include access.log (web servers), error.log (applications), and syslog (Unix/Linux systems).

Did you know? The term "log" comes from ship logbooks where captains recorded daily events!

History

Logging has been fundamental to computing since early mainframe systems. The practice of recording system events in files evolved from paper logs used in early computing facilities.

Key Milestones

  • 1960s-70s: Mainframe systems record events to printouts
  • 1980: Unix syslog standardizes logging
  • 1990s: Web server logs (Apache, IIS)
  • 2000s: Log aggregation tools emerge
  • 2010s: Structured logging (JSON, ELK stack)
  • Present: Cloud logging and observability platforms

Key Features

Core Capabilities

  • Timestamps: When events occurred
  • Severity Levels: INFO, WARNING, ERROR, DEBUG
  • Source Identification: Which component logged
  • Message Details: What happened
  • Stack Traces: Error debugging information
  • Rotation: Automatic archival of old logs

Common Use Cases

Debugging

Troubleshoot application errors

Monitoring

System health tracking

Security Audits

Access and security events

Performance

Response time analysis

Advantages

  • Essential for debugging
  • Audit trail for security
  • Performance analysis
  • Human-readable format
  • Universal support
  • Historical record of events

Disadvantages

  • Can grow very large
  • Unstructured format (often)
  • Difficult to parse without tools
  • Storage management needed
  • Performance impact if excessive

Technical Information

Format Specifications

Specification Details
File Extension .log
MIME Type text/plain
Format Type Text or structured (JSON)
Encoding UTF-8, ASCII
Common Levels DEBUG, INFO, WARN, ERROR
Rotation Daily, size-based, or manual

Common Tools

  • Viewers: less, tail, Notepad++
  • Analysis: grep, awk, ELK Stack
  • Aggregation: Splunk, Datadog, Graylog