Chapter 16. Security Event Auditing

Written by Tom Rhodes and Robert Watson.

16.1. Synopsis

The FreeBSD operating system includes support for security event auditing. Event auditing supports reliable, fine-grained, and configurable logging of a variety of security-relevant system events, including logins, configuration changes, and file and network access. These log records can be invaluable for live system monitoring, intrusion detection, and postmortem analysis. FreeBSD implements Sun™'s published Basic Security Module (BSM) Application Programming Interface (API) and file format, and is interoperable with the Solaris™ and Mac OS(R) X audit implementations.

This chapter focuses on the installation and configuration of event auditing. It explains audit policies and provides an example audit configuration.

After reading this chapter, you will know:

  • What event auditing is and how it works.

  • How to configure event auditing on FreeBSD for users and processes.

  • How to review the audit trail using the audit reduction and review tools.

Before reading this chapter, you should:


The audit facility has some known limitations. Not all security-relevant system events are auditable and some login mechanisms, such as Xorg-based display managers and third-party daemons, do not properly configure auditing for user login sessions.

The security event auditing facility is able to generate very detailed logs of system activity. On a busy system, trail file data can be very large when configured for high detail, exceeding gigabytes a week in some configurations. Administrators should take into account the disk space requirements associated with high volume audit configurations. For example, it may be desirable to dedicate a file system to /var/audit so that other file systems are not affected if the audit file system becomes full.