Log Analysis

Log analysis (or system and network log analysis) is an art and science seeking to make sense out of computer-generated records (also called log or audit trail records). The process of creating such records is called data logging.

Typical reasons why people perform log analysis are:

• Compliance with security policies
• Compliance with audit or regulation
• System troubleshooting
• Forensics (during investigations or in response to subpoena)
• Security incident response

Logs are emitted by network devices, operating systems, applications and all manner of intelligent or programmable device. A stream of messages in time-sequence often comprise a log. Logs may be directed to files and stored on disk, or directed as a network stream to a log collector.

Log messages must usually be interpreted with respect to the internal state of its source (e.g., application) and announce security-relevant or operations-relevant events (e.g., a user login, or a systems error).

Logs are often created by software developers to aid in the debugging of the operation of an application. The syntax and semantics of data within log messages are usually application or vendor-specific. Terminology may also vary; for example, the authentication of a user to an application may be described as a login, a logon, a user connection or authentication event. Hence, log analysis must interpret messages within the context of an application, vendor, system or configuration in order to make useful comparisons to messages from different log sources.

Log message format or content may not always be fully documented. A task of the log analyst is to induce the system to emit the full range of messages in order to understand the complete domain from which the messages must be interpreted.

A log analyst may map varying terminology from different log sources into a uniform, normalized terminology so that reports and statistics can be derived from a heterogeneous environment. For example log messages from Windows, Unix, network firewalls, databases may be aggregated into a "normalized" report for the auditor. Different systems may signal different message priorities with a different vocabulary, such as "error" and "warning" vs. "err", "warn", and "critical".

Hence, log analysis practices exist on the continuum from text retrieval to reverse engineering of software.