start-os/core/s9pk-structure.md

S9PK Package Format

S9PK is the package format for StartOS services. Version 2 uses a merkle archive structure for efficient downloading and cryptographic verification.

File Format

S9PK files begin with a 3-byte header: 0x3b 0x3b 0x02 (magic bytes + version 2).

The archive is cryptographically signed using Ed25519 with prehashed content (SHA-512 over blake3 merkle root hash).

Archive Structure

/
├── manifest.json           # Package metadata (required)
├── icon.<ext>              # Package icon - any image/* format (required)
├── LICENSE.md              # License text (required)
├── dependencies/           # Dependency metadata (optional)
│   └── <package-id>/
│       ├── metadata.json   # DependencyMetadata
│       └── icon.<ext>      # Dependency icon
├── javascript.squashfs     # Package JavaScript code (required)
├── assets.squashfs         # Static assets (optional, legacy: assets/ directory)
└── images/                 # Container images by architecture
    └── <arch>/             # e.g., x86_64, aarch64, riscv64
        ├── <image-id>.squashfs  # Container filesystem
        ├── <image-id>.json      # Image metadata
        └── <image-id>.env       # Environment variables

Components

manifest.json

The package manifest contains all metadata:

Field	Type	Description
id	string	Package identifier (e.g., bitcoind)
title	string	Display name
version	string	Extended version string
satisfies	string[]	Version ranges this version satisfies
releaseNotes	string/object	Release notes (localized)
canMigrateTo	string	Version range for forward migration
canMigrateFrom	string	Version range for backward migration
license	string	License type
wrapperRepo	string	StartOS wrapper repository URL
upstreamRepo	string	Upstream project URL
supportSite	string	Support site URL
marketingSite	string	Marketing site URL
donationUrl	string?	Optional donation URL
docsUrl	string?	Optional documentation URL
description	object	Short and long descriptions (localized)
images	object	Image configurations by image ID
volumes	string[]	Volume IDs for persistent data
alerts	object	User alerts for lifecycle events
dependencies	object	Package dependencies
hardwareRequirements	object	Hardware requirements (arch, RAM, devices)
hardwareAcceleration	boolean	Whether package uses hardware acceleration
gitHash	string?	Git commit hash
osVersion	string	Minimum StartOS version
sdkVersion	string?	SDK version used to build

javascript.squashfs

Contains the package JavaScript that implements the ABI interface from @start9labs/start-sdk-base. This code runs in the container runtime and manages the package lifecycle.

The squashfs is mounted at /usr/lib/startos/package/ and the runtime loads index.js.

images/

Container images organized by architecture:

• <image-id>.squashfs - Container root filesystem
• <image-id>.json - Image metadata (entrypoint, user, workdir, etc.)
• <image-id>.env - Environment variables for the container

Images are built from Docker/Podman and converted to squashfs. The ImageConfig in manifest specifies:

• arch - Supported architectures
• emulateMissingAs - Fallback architecture for emulation
• nvidiaContainer - Whether to enable NVIDIA container support

assets.squashfs

Static assets accessible to the package, mounted read-only at /media/startos/assets/ in the container.

dependencies/

Metadata for dependencies displayed in the UI:

• metadata.json - Just title for now
• icon.<ext> - Icon for the dependency

Merkle Archive

The S9PK uses a merkle tree structure where each file and directory has a blake3 hash. This enables:

1. Partial downloads - Download and verify individual files
2. Integrity verification - Verify any subset of the archive
3. Efficient updates - Only download changed portions
4. DOS protection - Size limits enforced before downloading content

Files are sorted by priority for streaming (manifest first, then icon, license, dependencies, javascript, assets, images).

Building S9PK

Use start-cli s9pk pack to build packages:

start-cli s9pk pack <manifest-path> -o <output.s9pk>

Images can be sourced from:

• Docker/Podman build (--docker-build)
• Existing Docker tag (--docker-tag)
• Pre-built squashfs files

Related Code

• core/src/s9pk/v2/mod.rs - S9pk struct and serialization
• core/src/s9pk/v2/manifest.rs - Manifest types
• core/src/s9pk/v2/pack.rs - Packing logic
• core/src/s9pk/merkle_archive/ - Merkle archive implementation