errorlog

An errorlog, or error log, is a log file that records error messages, warnings, and critical faults generated by software applications, services, or operating systems. It serves as a primary source of information for diagnosing problems, assessing system health, and auditing failures. Entries usually include a timestamp, a severity level, an error code or type, a short description, and the component or module that produced the message; many entries also carry contextual data such as request identifiers, user IDs, or a stack trace.

Error logs appear in various forms and locations. Some programs write to a dedicated file named errorlog or error_log, while others use centralized logging services or the system log. Web servers commonly maintain an error log that records startup issues, runtime errors, and configuration problems; in Unix-like systems these are often managed by syslog, rsyslog, or journald, whereas Windows systems may write to the Windows Event Log. Formats range from plain text lines to structured JSON or key=value pairs.

Management practices include setting appropriate log levels, rotating and archiving old logs to prevent disk use, and ensuring proper permissions. Privacy and security considerations advise avoiding logging sensitive data, minimizing personal data, and masking or removing secrets. Logs can be analyzed with manual search, scripting, or centralized platforms such as ELK stacks or Splunk to detect anomalies and trigger alerts.