CopySync

CopySync / Ways to connect

Across networks with Tailscale

No public IP, and no wish to run a server? Install Tailscale on each computer and enter the other computer's Tailscale address when pairing. Syncs at home and at the office.

  1. Install Tailscale
  2. Find the address
  3. Pair
  4. Questions

As if on one LAN

Tailscale connects your devices into a private network: every device signed in to the same account gets a fixed address starting with 100, reachable from the others wherever they are. CopySync remembers the other computer's address when you pair, and connects as if both were on one network.

CopySync over Tailscale A Mac at the office and a Windows PC at home both run Tailscale and each has an address starting with 100 on the same private network. Copied content goes directly between them; there is no server. Tailscale network: every device has a 100.x address Mac At the office 100.88.20.5 Windows At home 100.92.41.17 Direct, encrypted twice Content stays between the two computers
  • No server, and no computer that has to stay on: two computers that are on and connected to Tailscale sync.
  • Enter the address once. A Tailscale address doesn't change; you enter it when pairing and the two computers find each other from then on.
  • Encrypted twice. Inside Tailscale's WireGuard tunnel runs CopySync's own end-to-end encrypted connection. Tailscale can't see the content.

Before you start

A Tailscale account
Free for personal use; sign in with Google, Microsoft, GitHub or Apple. Use the same account on every device.
Tailscale on every computer
There are clients for Windows, macOS and Linux. Every computer that runs CopySync needs it, connected.
CopySync installed
The app on each computer with background sync on; see the quick start. Leave the server address empty.
ZeroTier works too
So does any tool that gives each device a fixed virtual address: enter that address when pairing. This guide uses Tailscale.

Step 1

Install Tailscale on each computer

On every computer you sync, install it and sign in to the same account.

  1. Download the client for your system from the Tailscale website and install it.On Linux, run curl -fsSL https://tailscale.com/install.sh | sh, then sudo tailscale up, and open the link it prints to sign in.
  2. Open Tailscale and sign in, using the same account on every computer.
  3. The Tailscale admin console then lists all your devices, each with an address starting with 100.
Download Tailscale

Keep Tailscale connected

  • Windows: right-click the Tailscale icon in the notification area and check Run unattended under Preferences, so it stays connected after you sign out.
  • Mac: make sure Tailscale opens at login.
  • Disable key expiry: by default Tailscale asks devices to sign in again every 180 days. For a computer that rarely changes, open the menu at the end of its row on the Machines page and choose Disable key expiry.

Step 2

Find the other computer's Tailscale address

On the computer you'll pair with, click the Tailscale icon (in the menu bar on a Mac, in the notification area on Windows) to see its address, or run tailscale ip -4 in a terminal.

The steps below use 100.92.41.17, the Windows PC at home. Use your own address.

Step 3

Enter the address when pairing

Just like pairing on one network, with one extra address.

  1. On the Windows PC at home, open Devices, click Add device and note the 6-character code.
  2. On the Mac at the office, click Add device, switch to Enter a code and type it in; then click On a different subnet?, enter 100.92.41.17 and click Continue.
  3. Both screens show the same two fingerprint lines. Check them, then confirm. The two computers now sync wherever they are.
Enter a code: the code K7MP2X, with the Tailscale address 100.92.41.17 in the address field

When both computers are at home, CopySync also finds the other one on the LAN directly, so data takes no detour.

Questions

Devices show Direct, but it's slow

Direct in CopySync means the two computers connect directly on the Tailscale network. When Tailscale can't connect them peer to peer, it relays through its DERP servers, which can be far away.

Run tailscale ping other-address in a terminal: via DERP means Tailscale is relaying; via an IP and port means it's peer to peer. Office and campus networks relay more often; you can run your own DERP server or try another mesh VPN.

Pairing can't find the other computer

First make sure Tailscale is connected on both: run tailscale ping other-address and try again once it answers.

If ping works but pairing doesn't, the other computer's firewall is likely blocking it. On Windows, click Allow under Settings → Local network in CopySync; on a Mac, turn on CopySync Daemon under System Settings → Privacy & Security → Local Network.

Does every computer need Tailscale?

Yes, a computer without it can't reach the 100.x addresses. Computers on the same network don't need it; see the same network guide.

I set up a server at home with the old guide. Do I still need it?

No. Clear the server address in Settings on each computer and uninstall the server at home; paired devices stay paired. Keeping it doesn't hurt either: a server and Tailscale work together.

Can Tailscale see what I copy?

No. Tailscale connections are end-to-end encrypted with WireGuard, and inside runs CopySync's own DTLS-encrypted connection; only your two computers can open either layer. Tailscale's servers only exchange device keys and addresses, and its relays forward encrypted packets.

Will a Tailscale address change?

Usually not. The address belongs to the device and survives restarts and network changes; it only changes if you remove the device from Tailscale and add it again. If it does, enter it once more under Devices.

I have a public server. Do I need Tailscale?

No. Run the server on the machine with the public IP and enter that address on every computer; see the public server guide.

No server.
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Download CopySync

Version 1.6.4, free and open source. macOS 13 or later; Windows 10 and 11; Linux (x64 and ARM64).

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