macOS

A Mach port is a kernel-managed message queue that tasks reach through capabilities called rights. Exactly one task holds the receive right; any number may hold send rights. Like a file descriptor, a port name is task-local, but it names a capability to communicate rather than an open object.

launchd creates and binds the listening socket itself at load time and watches it. The job's process is started only when a connection arrives, and it receives the already-bound file descriptors from launchd by checking in with launch_activate_socket, keyed by the name used in the plist.

The key is created inside a separate coprocessor and never leaves it in usable form. Software can ask the enclave to sign or perform key agreement, but cannot read, copy or back up the key material, and the enclave enforces a per-use policy such as requiring a biometric match.

softwareupdate lists, downloads and installs updates from the command line and can fetch a full macOS installer. On Apple Silicon, installing a macOS update requires credentials of a volume owner, supplied with --user and --stdinpass or authorised centrally by an MDM-escrowed bootstrap token, so a plain root script is not enough.

Homebrew is rolling-release with no lockfile, so a Brewfile pins which packages are installed but not their versions. Reproducibility comes from versioned formulae, per-project version managers, an internal tap or bottle mirror, and moving builds into Linux containers.