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How to sync folders across Mac, Windows and Linux

Setting up Copy Shelter Sync between computers, and what happens when two of them change the same file. Updated October 2026.

Short answer: install Copy Shelter on each computer, sign in with the same email address, create a Sync on one, and approve the others when they ask to join. Sync is part of Pro.

What Sync does

Sync keeps the folders you choose the same on your Macs, Windows PCs and Linux machines. A change on one shows up on the others, and every change keeps earlier versions you can go back to. Each computer also keeps its own backup of the Sync, so a mistake on one machine can be undone everywhere.

Set it up

  1. Install Copy Shelter on each computer from copyshelter.com/download.
  2. Sign in on each one with the same email address.
  3. On the first computer, open Sync, choose New Sync, and pick the folders.
  4. On each other computer, choose Join a Sync. The same six-character code shows on both screens. Check it matches, then approve on the first computer.

Two ways the computers connect

When two computers change the same file

Copy Shelter shows the conflict and lets you keep yours, keep theirs, or keep both. Nothing is thrown away while you decide.

Phones and tablets

Phones and tablets back up to a computer or a cloud folder of their own. Sync is for computers.

Questions

How many computers can join a Sync?

Ten devices come with Pro, counting phones, tablets and computers together.

Does Sync need the internet?

No. Computers on the same network sync directly. A shared folder or bucket covers computers that are apart.

Is a Sync encrypted?

Yes. Files are encrypted before they leave each computer, and a new computer joins only after you approve it on one you already use.