IT Forensics · Linux

Forensic analysis of the kernel ring buffer (dmesg) – Reconstructing early system events

The kernel ring buffer logs messages from the operating system kernel, including hardware detection, driver events, file system mounts and security-related kernel warnings. It can be viewed using the dmesg command.

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As this is a cyclical buffer of limited size, older entries are overwritten whilst the system is running. For forensic analysis, it is therefore crucial to determine whether and how these messages were additionally logged in a persistent manner.

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Since its foundation, LanCologne has specialised in professional IT forensics. Our staff have decades of experience in the field of information technology and assist companies, solicitors, private individuals and, on a regular basis, the courts in the technical investigation of complex digital matters.

The examination is, as a matter of principle, carried out exclusively on a forensic copy, a forensic image or a data source captured in a technically equivalent manner that preserves the integrity of the evidence. The original evidence remains unchanged and is stored in a manner that preserves its integrity.

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We collect available dmesg output and persistent kernel logs, and analyse them for hardware events, device mounts and unmounts, and security-related kernel messages.

Typical areas of application

•Reconstruction of hardware and storage device events
•Investigation of USB and external device ports
•Investigating security-related kernel warnings
•Tracking system starts and crashes
•Incident Response on Linux Systems
•Judicial and non-judicial expert reports

How a dmesg analysis works

Provided the system is still running, the current ring buffer is backed up. In addition, persistent kernel logs – such as those in journald or traditional log files – are checked for supplementary kernel messages. Relevant hardware and system events are then chronologically ordered.

Why is dmesg analysis relevant in a forensic context?

Kernel messages can provide reliable indications of connected external storage devices, hardware changes or security-related system events that are not available in the same form in other log sources.

As the ring buffer is volatile and has limited capacity, the availability of relevant entries decreases as the system continues to run. Backing up data at an early stage whilst the system is running significantly increases the chances of success.

Frequently Asked Questions

Are dmesg messages retained after a reboot?+
The classic ring buffer is cleared upon a reboot. Continuous availability depends on whether kernel messages are also logged persistently.
What does `dmesg` typically display?+
These include, amongst other things, hardware detection, driver events, file system mounts and certain kernel security warnings.
Can `dmesg` detect USB ports?+
Yes, connected USB devices often generate characteristic kernel messages that can be timestamped.

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