Syncthing: Self-Hosted Peer-to-Peer File Synchronization without Cloud

Why Syncthing?

Cloud sync services own your data. Syncthing syncs directly between your devices:

Peer-to-peer — No cloud server, no storage limits.
End-to-end encryption — Data encrypted in transit (TLS).
File versioning — Keep old versions of changed files.
Selective sync — Choose folders and devices.
Conflict resolution — .sync-conflict files preserve both versions.
Multi-platform — Linux, macOS, Windows, Android.
No subscription — Completely free, forever.

Prerequisites

Two or more devices.
Network connectivity between them (LAN or internet).

Step 1: Install and Pair

# Docker
docker run -d \
  --name syncthing \
  --restart=always \
  -p 8384:8384 \
  -p 22000:22000/tcp \
  -p 22000:22000/udp \
  -v /path/to/sync:/var/syncthing \
  syncthing/syncthing:latest

Web UI at http://device:8384.

Step 2: Sync Patterns

Pattern	Setup	Use Case
Laptop ↔ Desktop	Share device IDs, select folders	Same files on both machines
Phone → NAS	Android app syncs camera folder	Automatic photo backup
Multi-device mesh	All devices paired, shared folders	Team document sharing
One-way send	Send-only on source, receive-only on target	Backup archive
Selective folders	Different folders per device	Work on laptop, media on NAS

File Versioning Options

Type	Behavior	Best For
Trash can	Deleted/replaced files go to .stversions	Simple recovery
Simple	Keep N old versions	Predictable cleanup
Staggered	Keep versions at increasing intervals	Long-term history
External	Run custom script on version	Advanced workflows

Syncthing vs Cloud Sync Services

Feature	Syncthing	Dropbox	Google Drive	Nextcloud
Architecture	P2P (no server)	Cloud	Cloud	Self-hosted server
Privacy	E2E, no third party	Their servers	Their servers	Your server
Storage limit	Your disk	2 GB free	15 GB free	Your disk
Cost	Free	$12/mo (2 TB)	$3/mo (100 GB)	Free (self-hosted)
File versioning	Built-in	30 days	30 days	Built-in
Mobile	Android	iOS + Android	iOS + Android	iOS + Android
Offline	Full offline	Selective	Selective	Selective

Troubleshooting

Problem	Solution
Devices not discovering each other	Ensure both are on same network or enable global discovery; check firewall ports 22000/TCP+UDP
Sync slow over internet	Enable relaying as fallback; check if UPnP is disabled on router
Conflict files appearing	Normal — review .sync-conflict files and keep the correct version
High CPU/disk during initial sync	Expected for large folders; will settle after initial sync completes

Summary

P2P sync — your files, your devices, no cloud.
File versioning with four strategies for different needs.
Zero cost, zero limits — sync as much as your disks hold.
Works on every platform including Android for photo backup.

Frequently Asked Questions

What is Syncthing and how is it different from Dropbox?

Syncthing is a peer-to-peer file synchronization tool — files sync directly between your devices without any cloud server. Dropbox/Google Drive store your files on their servers. With Syncthing, your data never touches a third-party server, and there are no storage limits or subscription costs.

Does Syncthing work without a central server?

Yes. Syncthing syncs directly between devices (peer-to-peer). It uses relay servers only for discovery and NAT traversal — actual file data is transferred directly between your devices with E2E encryption.

Can I sync specific folders?

Yes. You choose exactly which folders to sync and with which devices. Each folder can have different sharing rules — one folder shared with your laptop, another with your NAS, another with a family member.

What about file conflicts?

If the same file is modified on two devices before syncing, Syncthing renames the conflicting file with a .sync-conflict suffix so you don't lose either version.