Tripwire is an Open Source program created to monitor changes in a key subset of files identified by you, and report on any changes in any of those files. When changes are detected, you, as the sysadmin, can determine whether those changes occurred due to normal, permitted activity, or whether they where caused by a breakin. If the former, you can update the system baseline to the new files. If the latter, you can shut down and begin repair and forensic activities.

Tripwire's principle is simple enough. The sysadmin identifies key files and causes Tripwire to record checksums for those files. He also puts in place a cron job to scan those files at intervals (daily or more frequently), comparing to the original checksum. Any changes, additions or deletions are reported, so the proper action can be taken.

This issue of Linux Productivity Magazine is devoted to Tripwire, which can alert you quickly when there's an intrusion. So kick back, relax, enjoy, and remember that if you're an Open Source user, this is your magazine.

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