Simple Mender Update Tool (SMUT)

A lightweight daemon for managing Mender updates on embedded Linux systems via Redis.

Archived. Proof-of-concept update tooling, kept for reference. Production OTA handling lives in update-service.

Part of the Librescoot open-source platform.

Overview

SMUT runs on embedded Linux systems (MDB and DBC) and triggers Mender updates via Redis. It handles resumable downloads, checksum verification, and interacts with Mender.

Features

• Redis BLPOP for update requests
• Resumable downloads with retry
• Checksum verification (SHA256)
• Support for file:// URLs for local file installation
• Automatic Mender update install and commit
• Error reporting via Redis
• Cross-compilation for armv7l
• No CGO

Requirements

• Go 1.16+ (for building)
• Redis server
• Mender update client (mender-update in PATH)
• Linux (armv7l target)

Building

For Local Development

make

For ARM Target (armv7l)

make build-arm

Clean Build

make clean build

Installation

The project includes an installer script that handles deployment to both MDB and DBC systems.

1. Build the ARM binary:

make build-arm

2. Run the installer:

./install.sh <target-host> <target>

Where:

• target-host: The hostname/IP of the MDB system
• target: One of:
  • mdb: Install only on MDB
  • dbc: Install only on DBC
  • both: Install on both MDB and DBC

The installer handles:

• Copying files to target systems
• Service installation and configuration
• GPIO management for DBC communication
• Service startup and verification

Usage

Command-Line Arguments

• --redis-addr: Redis server address (default: "localhost:6379")
• --update-key: Redis key for update URLs (default: "mender/update/url")
• --checksum-key: Redis key for checksums (default: "mender/update/checksum")
• --failure-key: Redis key to set on failure (default: "mender/update/last-failure")
• --download-dir: Directory to store downloaded update files (default: "/tmp")
• --update-type: Type of update ('blocking' for DBC, 'non-blocking' for MDB) (default: "non-blocking")

Redis Usage

SMUT uses the ota Redis hash to report status and update type. The status field indicates the current state, and the update-type field indicates if the update is blocking or non-blocking.

To trigger an update, push the URL to the update key using LPUSH:

# For MDB system with remote file
redis-cli LPUSH mender/update/mdb/url "http://example.com/path/to/update.mender"

# For DBC system with remote file
redis-cli LPUSH mender/update/dbc/url "http://example.com/path/to/update.mender"

# For MDB system with local file
redis-cli LPUSH mender/update/mdb/url "file:///path/to/local/update.mender"

# For DBC system with local file
redis-cli LPUSH mender/update/dbc/url "file:///path/to/local/update.mender"

When using file:// URLs, SMUT will skip the download step and directly use the specified local file for installation. The file path must be absolute and accessible to the SMUT process.

To set a checksum (optional):

# For MDB system
redis-cli SET mender/update/mdb/checksum "sha256:abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890"

# For DBC system
redis-cli SET mender/update/dbc/checksum "sha256:abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890"

The checksum is optional. If provided, it should be in the format algorithm:hash. Currently, only SHA256 is supported.

Error Reporting

Errors are reported by setting the configured failure key in Redis with the error message as a string. The status field in the ota hash will also be updated to reflect the error state.

Monitoring

Logs

When running as a systemd service, logs can be viewed with:

journalctl -u smut@<system> -f

Replace <system> with mdb or dbc.

Status

Check the service status with:

systemctl status smut@<system>

Replace <system> with mdb or dbc.

License

Affero GPL 3.0