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Cryptographic integrity checks can verify that system files match an expected state, but they are not a natural fit for every Linux update model. In his September 14, 2026 account of RoamSwitch OS, Tetsuharu Fujiki says he left out whole-root-filesystem protection because dm-verity’s immutable-image model conflicted with the project’s rolling, package-managed Arch base, while IMA appraisal was unavailable in the Arch kernel configurations he inspected without maintaining a custom kernel. The decision reflects that project’s constraints—not a general limit of Linux integrity tools.
What the project was trying to protect—and what it chose not to build
RoamSwitch OS was Fujiki’s early-stage personal hardening project: an Arch-based installer and live ISO intended to assemble established tools rather than create a new distribution stack. He says the project was not ready for general use and was a research and showcase effort, not a production-hardened release.
Within that scope, Fujiki decided against cryptographically verifying the entire root filesystem. His governing constraint was to retain Arch’s rolling package ecosystem and existing driver support without taking on image-distribution or kernel-maintenance work. As he put it, “The governing principle stayed simple: don’t reinvent tools that already work, build on Arch’s rolling package ecosystem and existing driver support rather than around them.”
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Why encryption did not answer the integrity question
Disk encryption and integrity verification address different threats. Encryption protects data at rest when a device or drive is unavailable to an attacker. It does not prove that the operating system files are unmodified, and Arch Linux’s security guidance notes that mounted data is as vulnerable as data on an unencrypted drive.
Integrity mechanisms instead compare system content with an expected state, or enforce policies about which content may be used. They do not, by themselves, establish that firmware, the bootloader, kernel, initramfs, and root filesystem form a trusted boot chain. Secure Boot, encryption, integrity checking, and runtime monitoring therefore need to be evaluated as separate parts of a threat model, not treated as interchangeable labels for “security.”
Why dm-verity conflicted with a rolling root filesystem
dm-verity verifies blocks against a cryptographic hash tree and is structurally suited to an immutable block device. Fujiki’s objection was that RoamSwitch OS was intended to use a mutable, package-managed root filesystem: routine package updates change installed files, whereas an immutable verified image is normally rebuilt and deployed as a unit.
That mismatch would have required more than switching on a kernel feature. The project would need an image-generation and boot-update process that keeps the root image and its verification data synchronized, along with a reliable way to install and recover updates. Fujiki judged that a larger change in operating-system design inconsistent with the project’s goal of building around Arch’s rolling package system.
This is a project-specific architectural assessment. It does not mean dm-verity cannot protect a Linux root filesystem; it means the author did not consider an immutable-image workflow a fit for this particular system.
Why IMA appraisal was not a drop-in alternative
IMA, the Linux Integrity Measurement Architecture, can measure files and support appraisal policies that check integrity. Unlike a whole immutable root image, this approach can be considered in systems where files change, but its practical availability depends on kernel configuration and policy setup.
Fujiki reports that he inspected the configurations for Arch’s standard linux kernel and linux-hardened kernel and found CONFIG_IMA unset in both. This is his September 2026 finding about the configurations he checked, not a statement that IMA is unsupported by Linux or disabled in every Arch kernel build.
As he understood the choices, enabling IMA would mean replacing the official kernel packages with a build he would have to maintain. That added a continuing distribution-maintenance responsibility the project was designed to avoid. A kernel option’s presence alone would not settle the question, either: a usable appraisal setup also depends on policies, keys, update handling, and recovery procedures.
What the project used instead
Rather than claim comprehensive cryptographic protection, Fujiki describes narrower checks and monitoring for different kinds of change. These are reported project design choices, not independently verified defenses or evidence of production readiness.
Selected system paths with AIDE
The project used AIDE, a file-integrity checking tool, on selected system paths rather than scanning and protecting the whole filesystem. Fujiki reports that scans of a narrow set of paths took 1 to 15 seconds, while a broader scan took 2 minutes 33 seconds. Those are measurements from his project, not a general performance benchmark; the result depends on the paths, files, storage, and configuration involved.
AIDE can report that monitored files differ from a saved baseline. That is useful for discovering unexpected changes, but a report is not the same as preventing a modified file from being used. Baseline creation and updates also matter: if an attacker can alter both the files and the trusted baseline, the comparison loses its value.
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Tamper evidence for one incident log
Fujiki also describes using a TPM2-based sealing and signing arrangement for a specific incident log. This is a scoped tamper-evidence measure for that log, not a claim that the TPM continuously validates the entire operating system.
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Monitoring and rollback for changing user data
For user files that change regularly, the author describes watcher-style behavioral monitoring and rollback. This addresses a different problem from static rootfs verification: monitoring can react to suspicious patterns in data activity and may trigger recovery, while an integrity check identifies a difference from an expected state. The account does not establish independently measured ransomware protection or guarantee that a rollback will succeed.
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Arch’s documentation describes full-system dm-crypt arrangements that can combine LUKS encryption with Secure Boot and TPM integration. These components can contribute to a boot and unlock design, but TPM-backed unlocking is conditional, not a blanket check that a computer is uncompromised.
In systemd’s systemd-cryptenroll(1) documentation, TPM2 key release can be bound to selected Platform Configuration Register (PCR) measurements. A secret is made available only when the configured measured state satisfies the binding. Which PCRs are selected affects behavior during boot changes and updates: tighter bindings may require deliberate reenrollment or recovery steps when legitimate components change. Administrators need to plan for key recovery and test update paths rather than assume automatic unlocking will remain reliable.
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How to choose an integrity approach for a personal Linux system
Start with the threat and operating model, not the name of a tool. A useful design review asks what must be protected and what ongoing work the chosen control creates.
- Identify the threat: distinguish theft of powered-off media, unauthorized modification of system files, untrusted boot components, and malicious activity after login. They call for different controls.
- Choose a mutation model: decide whether the system will boot an immutable image, update a rolling package-managed root, or combine a managed base with selected protected areas. An integrity mechanism should fit the update method.
- Map the trust chain: determine what authenticates or measures firmware, bootloader, kernel, initramfs, root filesystem, and any secret released by a TPM. Do not infer whole-chain trust from one successful check.
- Count the operational burden: include image generation and signing, kernel configuration and maintenance, update reliability, key recovery, and restore testing—not just initial setup.
- Separate prevention from detection: ask whether a mechanism blocks changed content before use, reports a difference afterward, or detects suspicious behavior and attempts recovery.
- Test recovery deliberately: verify how the system handles a legitimate update, a changed measurement, a failed boot, a lost recovery key, and restoration from a known-good state.
For a rolling Arch installation, a whole-root immutable verification design may require changing the image and update workflow. A scoped integrity check can be easier to fit, but it has limited coverage and needs a trustworthy baseline. TPM binding can strengthen a specific unlock policy, but it brings configuration and recovery trade-offs. There is no universal combination: the right balance is the one whose guarantees and maintenance costs match the system’s actual use.
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