# systemd/casync

Content-Addressable Data Synchronization Tool

Repository: https://github.com/systemd/casync
Canonical: https://ross.abutalabs.com/products/casync
Language: C
License Family: other
Topics: archive, tar, file-system, http, chunking, synchronization, download, upload, delivery
Last push: 2025-09-22T12:02:05+00:00

## Health v2 (maintenance only)
Score: 42/100 (v2, computed 2026-09-02T17:46:02.011165+00:00)
- activity 43, release rhythm 8, longevity 100
- inputs: {"age_days": 3519, "days_push": 345, "days_rel": null, "gap_med": null, "n_releases_24m": 0}
- flags: no_license
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 1608, forks 117 (observed 2026-08-28T04:05:10.712645+00:00)

## What it is
casync is a content-addressable data synchronization tool that combines the rsync algorithm with content-addressable storage. It splits data streams into variable-sized, content-defined chunks to efficiently store, deliver, and update large file system trees, OS/VM/container images, and backups over HTTP.

## Use cases
- distribute OS or container images over HTTP with minimal bandwidth
- store many related versions of large directory trees efficiently
- create deduplicated backups of file systems
- update VM or IoT images via CDN-friendly chunk indexes
- synchronize directory trees similar to rsync but with content-addressable chunking
- serialize directory trees in a reproducible modern tar-like format

## When to choose
- you need to deliver or update large images over HTTP/CDN with minimal transfer
- you store many similar versions of file system trees and want deduplication
- you want a backup system based on content-addressable chunks
- file boundaries get in the way of rsync-style delta transfer

## When to avoid
- you need simple one-off file sync between two machines (rsync is simpler)
- you require per-file granularity or file metadata fidelity like OSTree
- you need a tool with active feature development or a clearly licensed release
- you work on non-Linux platforms

## Facets
- artifact type: cli-tool
- maturity: maintenance
- function: compression, file-system, backup, serialization, http-client
- domain: developer-tools, files, self-hosted, infrastructure-as-code
- platform: cli, c
- tags: content-addressable-storage, chunking, rsync-alternative, image-delivery, deduplication, os-images, container-images, cdn-friendly, linux

## Member repositories
- systemd/casync (main) score 42

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:05:10.712645+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-30T03:51:35.168471+00:00, confidence not recorded.
  - readme: https://github.com/systemd/casync (fetched 2026-08-28T04:05:10.712645+00:00, sha bbb38b917656)
- Data as of 2026-08-30T08:39:29.467469+00:00.