playlink

Deduplicate music libraries with hardlinks. playlink finds songs that exist in both a master library (e.g. your full Albums) and a slave library (e.g. a curated Singles library) and replaces the slave copy with a hardlink to the master copy. Each song then takes up disk space only once, while both libraries keep looking exactly the same to Plex, Navidrome, Jellyfin and other media servers.

It ships as a single Go binary with an embedded React web UI and SQLite state, packaged as a small Docker image, in the style of qui.

What it does

Files are matched by their path relative to each library root. Any folder layout works (Artist/Album/Title.ext, Genre/Artist/Title.ext, flat, …) as long as both libraries use the same one, so that a song sits at the same relative path on both sides. The fallbacks below catch small differences, and a scan warns when the two layouts don't line up.

Situation	What playlink does
Same relative path, byte-identical	Status identical. Link with one click, in bulk, or automatically after each scan.
Same path, different bytes (re-encode, different tags)	Status different. Manual review with a codec/bitrate/bit-depth/duration comparison.
Same title, different format (Song.mp3 vs Song.flac)	Status similar (other format). Manual review.
Same title after ignoring track numbers/punctuation (01 - Song!.flac vs Song.mp3)	Status similar (similar title). Manual review.
Same top-level folder and title, but a different subfolder	Status similar (same top folder, other subfolder). Manual review.
(opt-in) Approximately the same title, disc folders ignored (Cats/Disc 02/07 Memory.flac vs Cats/07 Memory.mp3)	Status similar (approximate match), with the reason shown. Manual review.
Only exists in the slave library	Status unmatched. Never touched.
Already the same inode	Status linked.

Approximate matching is an opt-in setting on each pair. For slave files the strict rules could not place, it searches the same album with disc folders (Disc 02, CD2, …) ignored, then the whole top-level folder, and compares titles by similarity against a threshold you choose (85% by default; a matching track number adds a small bonus). Several guards keep it from linking the wrong song: version words such as Live, Remix, Reprise or Instrumental must agree on both sides, a file is left unmatched when two candidates are nearly tied, and approximate matches never auto-link.

Manual review shows both files side by side and ranks their quality: lossless beats lossy, then bit depth and sample rate, then codec-weighted bitrate (Opus and AAC count for more per kbps than MP3). You then have three choices:

• Upgrade / link to master copy. The default. When the master copy is better, the match is flagged as an upgrade and listed under the Upgrades filter. The master is kept because it belongs to a complete album. If the master is lower quality, playlink warns you and asks for explicit confirmation.
• Use slave copy as master. The override. The slave's better file replaces the master file, the old master file is quarantined, and both libraries share the better file.
• Ignore. The pair is hidden from review until you un-ignore it.

Build mode covers the "start fresh" workflow. Point the slave at an empty folder, browse the master library, tick the folders or songs you want, and playlink hardlinks them in at the same relative path. Remove deletes slave files, but only ones that are hardlinks of the master file.

Safety model

playlink is built so that no user data is ever lost, even if it crashes or loses power mid-operation:

• Dry run is on by default. Every action is recorded in Activity as planned until you switch to live mode.
• Files are re-verified before any change. Both files must still be plain regular files with the same inode, size and mtime that the scan recorded, or the action is refused ("changed since scan").
• Identical files are compared again right before linking. The check is a full byte-for-byte compare, like cmp, and it also detects files that change while being read.
• Replacements are atomic. The new link is staged next to the target (.playlink-tmp-*), checked by inode, and then rename(2)d over the target. The path always points at a complete file.
• Nothing non-identical is ever deleted directly. Before a non-identical file is replaced, a hardlink to it is created in the quarantine (<slave>/.playlink-trash/<op-id>/…). It can be restored with one click until the retention period (default 30 days) expires, or until you purge it.
• Every operation can be undone. An identical link is undone by writing an independent, verified copy back. A quarantined file is undone by restoring the original.
• Removal is limited to hardlinks. Build/Remove only deletes a slave file that shares an inode with the master file, so the last copy of any data is never deleted.
• Paths are confined. Libraries and the quarantine must be inside PLAYLINK_ALLOWED_ROOTS. Symlinks are never followed or replaced, .. is rejected, and master and slave may not overlap.
• Mutations are serialized. Only one filesystem mutation runs at a time, and only one job runs per pair.
• Auto-link is conservative. It only acts on files with the exact same path, and it skips files modified within the settle time (default 10 minutes) so it never touches a download in progress.
• Interrupted operations are cleaned up. Operations cut short by a crash are marked interrupted on startup, and their staging files are removed.
• The web UI requires login. Passwords are hashed with bcrypt, sessions use SameSite=Strict HttpOnly cookies, and state-changing requests need a custom request header and a same-origin check. Logins are rate-limited, and a strict CSP is sent.

Quick start (Docker / Unraid)

services:
  playlink:
    build: .            # or your published image
    container_name: playlink
    user: "99:100"      # owner of your music files (Unraid nobody:users)
    ports: ["7480:7480"]
    environment:
      - PLAYLINK_ALLOWED_ROOTS=/data
    volumes:
      - /mnt/user/appdata/playlink:/config
      - /mnt/user/Sapphire/Media/Music:/data/Music   # ONE mount containing both libraries
    restart: unless-stopped

Then open http://<server>:7480, create your account, and add a pair:

• Master: /data/Music/Albums
• Slave: /data/Music/Instances/cdnutter/Singles

Run a scan, check the Review tab, and turn off dry run once the planned actions in Activity look right.

Hardlink requirements

• Both libraries must be visible through one bind mount. Docker bind mounts are separate mount points, and link(2) fails across them (EXDEV) even when they are on the same disk. Mount a common parent folder, as shown above.
• Both libraries must be on the same filesystem. playlink checks this when you save a pair and before every operation.
• Unraid: hardlinks through /mnt/user require Settings → Global Share Settings → Tunable (support Hard Links) to be Yes (the default). If the share uses a cache pool, make sure your mover preserves hardlinks. Every link is verified by inode, and a failed link aborts safely with the original untouched.

Configuration

Variable	Default	Description
PLAYLINK_ADDR	:7480	Listen address.
PLAYLINK_DATA_DIR	/config (Docker) or ./config	Where the SQLite database lives.
PLAYLINK_ALLOWED_ROOTS	/data	Comma-separated folders that libraries and the quarantine must live in. / is refused.
PLAYLINK_SECURE_COOKIES	false	Set to true when served over HTTPS.
PLAYLINK_FFPROBE	ffprobe	Path to ffprobe. Without it, quality comparison is disabled but everything else works.
PLAYLINK_LOG_LEVEL	info	debug for verbose logs.

Per-pair settings (in the UI) are file extensions, auto-link, approximate matching and its threshold, scan interval, quarantine folder, retention and settle time.

Development

Requires Go 1.27+ and Node 22+.

make test          # go vet, go test -race, tsc
make build         # builds web/dist and the ./playlink binary (UI embedded)
cd web && npm run dev   # Vite dev server on :5173, proxies /api to :7480

Layout:

cmd/playlink        entrypoint, config, scheduler
internal/fsops      safety-critical primitives (confined paths, cmp, atomic link/replace)
internal/engine     scanning, matching, link/promote/build/remove/undo, jobs
internal/probe      ffprobe wrapper and quality ranking
internal/store      SQLite schema and queries
internal/api        HTTP API, auth, embedded UI serving
web/                React + TypeScript + Tailwind UI