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qBittorrent: migrating seeding torrents from Windows to Linux

qBittorrent: migrating seeding torrents from Windows to Linux (Docker)

A guide for moving a large set of seeding torrents from a qBittorrent client on Windows to qBittorrent in Docker on Linux — without breaking the seeding (which matters for private trackers like TorrentLeech and their Hit-and-Run rules).

Done 2026-06-29: 193 torrents (movies, anime, TV, PC games, OS ISOs) migrated from a Windows server to Docker qBittorrent on the arr-server. All 193 are seeding, verified to survive a reboot.

Prerequisites

  • The source files already live on the NAS (the same physical files the Linux client will seed).
  • Both the Windows and Linux qBittorrent run a standard release (not a beta or fork) — otherwise the tracker may ban the client. qBittorrent 5.2.2 is fine for TorrentLeech.
  • The torrents have already met the tracker's minimum seed time (if not: migrate anyway, but be aware of the Hit-and-Run risk).

NAS layout (NFS on the arr-server)

NAS Export Mount point
NAS01 /volume1/Movies /mnt/media/movies
NAS01 /volume1/Apps /mnt/media/apps
NAS02 /volume1/TV /mnt/media/tv
NAS02 /volume1/Anime /mnt/media/anime
NAS02 /volume1/Games-PC /mnt/media/games-pc

Each share is in /etc/fstab with _netdev and bind-mounted into the qBittorrent container (/mnt/media/x:/mnt/media/x).

Step 1 — Export from Windows

The .torrent and .fastresume files live in:

C:\Users\<user>\AppData\Local\qBittorrent\BT_backup\

Copy the entire folder (both the .torrent AND the .fastresume files) to somewhere Linux can reach, e.g. a temp folder on the NAS.

Note: always keep an untouched copy as a "pristine source" — never touch it, always recreate from it.

Step 2 — Docker volumes

The qBittorrent container must see the files at the same path the .fastresume points to. Add the NAS mounts to docker-compose.yml:

  qbittorrent:
    volumes:
      - ./config/qbittorrent:/config
      - /mnt/media/movies:/mnt/media/movies
      - /mnt/media/tv:/mnt/media/tv
      # ...and so on for each share

Step 3 — Rewrite the paths in .fastresume

.fastresume is bencode-encoded (binary, with length prefixes). A plain sed will NOT work — you have to decode, swap the fields, and re-encode. Two fields hold paths:

  • save_path (libtorrent's — the one that actually counts)
  • qBt-savePath (qBittorrent's own)

Mapping rule (Windows → Linux), prefix-preserving:

Windows save_path Linux
//nas01/Movies (movie in a subfolder) /mnt/media/movies
//nas01/Movies/<movie> (file directly) /mnt/media/movies/<movie>
//nas02/Anime/<x> /mnt/media/anime/<x>
//nas02/TV/<x> /mnt/media/tv/<x>

Important: don't blanket-swap everything to the same folder. If the save_path includes the movie name, that means the content is the file directly — in which case the subfolder has to be preserved.

The Python script uses its own bencode decode/encode with a safety check: encode(decode(file)) == file must be byte-identical before anything is written (otherwise the encoder isn't canonical → abort). Stop qBittorrent before editing the files (it overwrites .fastresume on shutdown).

Step 4 — Load them in and recheck

  1. Copy the .torrent files + the rewritten .fastresume files into the Linux qBittorrent's BT_backup.
  2. docker compose up -d qbittorrent (recreate if volumes changed).
  3. qBittorrent rechecks and starts seeding. Torrents that find their files go to stalledUP/uploading.

Common errors:

  • missingFiles = qBittorrent can't find the files → wrong path, a missing docker volume, or a folder name that doesn't match (e.g. a dedup that renamed it).
  • Trailing space in a folder name: Windows allows/strips trailing spaces differently from Linux. Fix it qBittorrent-native with the torrents/renameFolder API (do NOT rename the folder on disk — Radarr/Jellyfin expect it without the space).

Step 5 — Turn off the seeding queue

For a seedbox that should seed everything forever: turn off queueing so all torrents announce at once.

POST /api/v2/app/setPreferences   json={"queueing_enabled":false}

Otherwise max_active_uploads/max_active_torrents limit how many actually seed.

Step 6 — Make it reboot-safe (critical!)

An fstab entry with _netdev survives a reboot — but Docker doesn't wait for the NFS mounts by default. If Docker starts qBittorrent before NFS is ready, empty folders get bind-mounted → every torrent becomes missingFiles.

Fix — a systemd drop-in at /etc/systemd/system/docker.service.d/wait-for-nfs.conf:

[Unit]
After=remote-fs.target
Wants=remote-fs.target

Then systemctl daemon-reload. This orders Docker after all _netdev mounts are ready.

Verify with an actual reboot: after restarting, all mounts should be active, qBittorrent up, and every torrent seeding (0 missingFiles).

Verification commands

# Mounts active?
findmnt -t nfs4 -o TARGET,SOURCE

# fstab valid?
sudo findmnt --verify

# Can qBittorrent see the files?
docker exec qbittorrent ls /mnt/media/movies

# Torrent states (via the API, after getting a login cookie)
curl -s -b cookie 'http://localhost:8080/api/v2/torrents/info' \
  | grep -o '"state":"[^"]*"' | sort | uniq -c

# Tracker announcing? (status 2 = working)
curl -s -b cookie 'http://localhost:8080/api/v2/torrents/trackers?hash=<HASH>'
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