The Linux Incident Response Lifecycle, Phase by Phase

What the Linux IR lifecycle is

Incident response follows a lifecycle: detect, triage, collect, analyze, contain and eradicate, recover, with documentation throughout. The framework is industry-standard and Linux does not change it. This sub fills the framework with the Linux specifics, the actual decisions and artifacts inside each phase, and maps the course modules onto the phases so you know where each skill fits.

It is the sub that connects everything before it into a single procedure. The earlier subs gave you the pieces, the evidence, the live system, the logs, the persistence locations; this one puts them in order.

A lifecycle, not a checklist

It helps to see the whole shape before the parts. A Linux investigation moves through six phases, and although they are drawn in order, real incidents loop: analysis in a late phase sends you back to collect something you missed, and a containment action can reveal a new lead. The order is the default path, not a rigid sequence.

The arrows are the default path, not a rule. The dashed return loop is the one that matters most: analysis routinely sends you back to collect something you missed, and the discipline is to let it, rather than forcing the investigation forward through a checklist.

Detection and triage

Every incident starts with a signal: a monitoring alert, an anomaly someone noticed, a report from another team, a connection to a known-bad address. Detection is simply that something has surfaced. Triage is the first real decision: is this a genuine incident, and if so, how urgent and how broad? You confirm the signal is not a false positive, establish a rough scope, and decide the response posture. The Linux-specific part of triage is fast and uses the skills from earlier sections: a quick read of the live process and network state from Section 0.4 to see if something malicious is running now, a glance at the authentication log from Section 0.5 for an obvious compromise, a check of the first-look persistence locations from Section 0.6. This rapid assessment, the subject of much of the early course work, tells you whether you are dealing with a contained nuisance or a serious breach, which governs everything that follows.

In practice triage has a rhythm, and building it is one of the first things the course trains. You arrive at the host and, in a few minutes, you read the live picture in a fixed order: who is logged in right now, what processes are running and which look wrong, what network connections are open and to where, and whether the obvious persistence locations show recent changes. None of this is deep analysis; it is a structured glance that answers one question, how bad is this, well enough to decide the response. A host with a cryptominer pinning the CPU and a single cron job is a different posture from a host with an active reverse shell, signs of lateral movement to other systems, and tampered logs. The triage glance sorts those two apart in minutes, and getting it right matters because over-reacting to a nuisance wastes the team while under-reacting to a breach lets it spread. Section 0.11 of this module is an interactive triage exercise built on exactly this sequence.

Collection

Once triage confirms an incident, you preserve evidence before it decays, in the order of volatility from Section 0.3. This is where the live-versus-cold decision is made and executed: capture memory if the situation warrants it, snapshot the volatile process and network state, collect the temporary filesystems, then image the disk or pull targeted artifacts. The output of this phase is a set of frozen evidence, files and images you can analyze without further touching the live host. The principle that governs the phase is collect first, analyze second, because everything you fail to preserve now may be gone by the time you want it. Modules 2, 3, and 12 build the collection techniques for the filesystem, the logs, and memory respectively.

Analysis

Analysis is the heart of the investigation and the largest part of the course. Working from the preserved evidence, you reconstruct what happened: the timeline from the independent sources, the entry point, the actions the attacker took, the persistence they planted, and the scope of what they reached. This is where the five-stage model from Section 0.2 becomes your map, where the correlation discipline from Section 0.5 assembles the timeline, and where the deep-dive modules earn their place. The compromise-scenario modules, 4 through 11, are each a worked analysis of a particular attack type, and the forensic modules, 2, 3, 12, and 13, are the techniques you apply. Analysis answers the questions the incident exists to answer: how, what, how far, and are they still here.

Two questions dominate the analysis phase and deserve naming now, because the whole course returns to them. The first is scope: which systems, accounts, and data did the attacker actually reach? Under-scoping is the most expensive analytical mistake, because an incident declared closed on one host while the attacker sits on three others is not closed at all. You scope by following the evidence outward, tracing every connection, credential, and lateral movement until the edges of the intrusion are mapped. The second is the root cause: not merely which account the attacker used, but how they got in originally, because a response that evicts the attacker without closing the door they came through invites them straight back. Analysis is not finished when you know what the attacker did; it is finished when you know how far they got and how they started.

Containment, eradication, and recovery

With the picture clear, you act. Containment limits ongoing damage, isolating the host from the network, killing a malicious process, blocking an attacker's address, while preserving evidence where you can. Eradication removes the attacker's access completely, and this is where the persistence discipline from Section 0.6 is decisive: you remove every foothold, not the first one, or the attacker returns. Recovery restores the system to trustworthy operation, which for a seriously compromised host often means rebuilding from a known-good state rather than cleaning in place, because you can never fully trust a system that has been root-compromised. The judgment of clean-versus-rebuild, and how to recover without reintroducing the compromise, is developed in the later modules.

Reporting runs throughout

One activity spans every phase rather than occupying its own box: documentation. From the first triage note to the final report, you record what you found, what you did, and when, building the timeline and preserving the chain of custody as you go rather than reconstructing it afterward. A Linux investigation that found everything but cannot prove it, because the evidence handling was not documented, fails when it matters. Module 14 is dedicated to turning an investigation into a defensible report, and the habit it builds, documenting continuously, starts at triage and never stops.

How the course maps onto the lifecycle

The arc of the seventeen modules follows this lifecycle. The foundations, Modules 0 and 1, give you the discipline and the underlying model. The forensic modules supply collection and analysis technique. The scenario modules walk complete investigations through detection, analysis, and response for specific attack types. The reporting module handles documentation, and the readiness and detection modules, 15 and 16, close the loop by preparing the environment so the next incident is detected sooner and investigated faster. You are not learning isolated tricks. You are learning a procedure, and every module is a part of it. The final section before lab setup asks the question that separates a response that felt busy from one that actually worked: how do you measure it?