Rkhunter — Old but Handy Rootkit Scanner
Why It Matters
Rootkits dig deep into Linux, hiding files, tweaking binaries, and loading shady kernel modules. Standard monitoring often misses them. Rkhunter has been around for years as a simple check-up tool. It doesn’t pretend to be a full-blown EDR — just a script that goes through the system looking for common traces of tampering. Admins still keep it in their bag of tricks for audits, quick sanity checks, or incident response when something feels off.
How It Works
Rkhunter is essentially a bash script with a collection of tests. Run it, and it compares system binaries with known hashes, looks for files that shouldn’t be there, scans modules loaded into the kernel, and flags oddities in startup scripts. Before scanning, updating signatures with `rkhunter –update` is a must, otherwise results can be stale. The tool spits out logs and console warnings. It won’t tell you “infected” or “clean” with certainty — it points at suspicious bits, and the admin has to decide what’s noise and what’s real.
Technical Notes
Area | Notes |
OS support | Linux and other Unix-like platforms |
What it does | Rootkit detection, integrity checks on binaries |
Looks at | File hashes, hidden files, kernel modules, init/startup scripts |
Output | Console messages + /var/log/rkhunter.log |
Updates | Uses online database (`rkhunter –update`) |
License | GPL, open source |
Deployment Notes
– Install from your distro repo or compile from source.
– Run `rkhunter –update` first to grab latest data.
– Then `rkhunter –check` for the actual scan.
– Review /var/log/rkhunter.log carefully — most results need context.
– Often tied into cron so it runs daily or weekly in the background.
Where It Fits
– Audits: quick host integrity check before compliance reviews.
– Incident response: first-pass tool when a box looks suspicious.
– Daily hygiene: routine scans on Linux servers, even if noisy.
Caveats
– Signature-driven, so stealthy or custom rootkits may slip through.
– High rate of false positives — human review is unavoidable.
– Only detects, never cleans.
– Can be slow on big filesystems with lots of binaries.