RDMALink

A macOS utility that prepares Thunderbolt 5 ports for RDMA over Thunderbolt on the Mac it runs on. It shows you a 3D model of your machine with every receptacle where it really is, walks you through a three-step assistant — choose a port, read exactly what will change, watch it happen — and leaves the port out of the Thunderbolt Bridge with an IPv6 link-local service of its own, ready to carry RDMA to another Mac. It keeps an undo note for every port it touches, so it can put everything back the way it found it. It configures only the Mac it is running on; run it on each Mac of a pair or cluster and pick the ports.

RDMALink is a network-configuration tool. Before you run it, know this much:

• It changes your network settings. It removes a Thunderbolt port from every bridge it is in and creates a network service for that port with IPv4 off and IPv6 link-local only. It never creates or deletes a bridge, and it never touches a port you did not pick.
• It uses a private macOS interface. Bridge membership has no public API, so RDMALink resolves the undocumented SCBridgeInterface* symbols with dlsym before it uses them. If one is missing on your system, the change stops and is rolled back, and the app explains the manual route through System Settings instead of guessing.
• It asks for an administrator password, once per change. That is macOS's own prompt for the right to change network settings (system.services.systemconfiguration.network). RDMALink holds that right for one burst of writes and then drops it. Putting a port back asks again.
• It keeps undo notes on your disk, one small JSON file per port, in ~/Library/Application Support/RDMALink. Those notes are what makes "put it back" possible. They are safe to back up and safe to leave alone.
• It is not sandboxed. Neither the Authorization API nor the bridge SPI is available to a sandboxed app, so RDMALink ships outside the App Store as a notarized download.
• It talks to nothing. There is no network request, no telemetry, no update check and no background agent. It is a tool you open, not a thing that lives on your Mac.

If RDMALink cannot recognize your Mac, or the Mac has Thunderbolt 4 rather than 5, it puts itself in read-only mode: you can look at everything, and it changes nothing.

• Apple silicon, macOS 27.
• Thunderbolt 5 ports. Thunderbolt 4 Macs open read-only — RDMA over Thunderbolt needs Thunderbolt 5.
• RDMA over Thunderbolt switched on, in System Settings › Privacy & Security › Developer Tools, followed by a restart. This is not RDMALink's to flip: the switch lives in NVRAM and only System Settings sets it. The app detects it, deep-links you to the right pane, and notices the moment it is on (see docs/ARCHITECTURE.md under Decisions, "RDMA switch").
• A second Mac at the other end of one Thunderbolt cable, set up the same way. Keep it to one cable between any pair: a bridge forwards like a hub, and a second cable between the same two Macs makes a loop.

Download RDMALink-<version>.dmg from the releases page, open it and drag RDMALink to Applications. The app is signed with a Developer ID and notarized, so macOS opens it without any override.

Or with Homebrew, from the dev7a tap:

brew install --cask dev7a/tap/rdmalink

The cask downloads the same release image, checks its pinned SHA-256 and puts RDMALink in Applications. brew upgrade --cask dev7a/tap/rdmalink follows new releases; uninstalling the cask removes the app and keeps the undo notes.

Every release carries SHA256SUMS and release.json beside the image. Put the image next to SHA256SUMS and run both of these:

shasum -a 256 -c SHA256SUMS
spctl --assess --type open --context context:primary-signature -vv RDMALink-<version>.dmg

The first must print OK. The second must print source=Notarized Developer ID — anything else means the image is not the one Apple notarized. There is more on this in script/release/README.md.

release.json is the build's receipt: the tag, the commit and the tag object the image was built from, the version and build number, the architecture and minimum macOS, the team and bundle identifier, Apple's notarization result for both the app and the image, and the Xcode version that built it.

Bugs, port layouts RDMALink does not recognize, and anything it got wrong about your Mac: GitHub Issues. The app's Help menu has Save a Diagnostics File…, which writes a plain text file with what RDMALink can see on this Mac and what it changed — that file is the single most useful thing to attach.

For a security vulnerability, do not open an issue. See SECURITY.md.

Xcode 27 on macOS 27. The gate is:

script/test.sh

It builds and tests the Core package and the command-line tool, runs the presentation and stage-math suites and the three release-script tests, and builds the app Debug with an ad-hoc signature — so it needs no signing identity and no network.

script/package_dmg.sh builds the signed, notarized disk image. It is maintainer-only: it requires the project's Developer ID Application identity in your Keychain, and a release is cut by pushing a signed v<version> tag, which builds and notarizes on GitHub. See script/release/README.md.

There is also rdmalink, a read-only command-line companion built by the Core package: inventory, status, refusals, changes, and a preview of what each operation would do. It never writes anything.

• Every string in the app, screen by screen, and the reasoning behind them: docs/UX_SPEC.md
• Module layout, the verified macOS constraints behind each decision, packaging and the release pipeline: docs/ARCHITECTURE.md

MIT. See LICENSE.