BitTorrent Sync is free software, available for all major platforms, that keeps folders in sync across your devices and enables you to share them securely with other people. That may sound suspiciously like Dropbox, iCloud Drive, and dozens of other cloud storage services—and indeed, the end result is much the same. The big difference is that BitTorrent Sync uses peer-to-peer networking rather than relying on cloud servers.
This approach has several significant advantages. You can have as much storage as you like (limited only by your local disk space) without paying a penny, and because your files are never stored in the cloud, no one else can access them without your explicit permission.
There are downsides too, though. At least one of the computers where your files are synced must be turned on and accessible to the Internet for you to access your files, and you’ll be subject to your ISP’s bandwidth and data caps. Although BitTorrent Sync encrypts your data as it travels between your devices over the Internet, it doesn’t encrypt files on disk—if you want to do that, you’re on your own. And you’re unlikely to find many third-party iOS apps with built-in support for BitTorrent Sync, whereas support for Dropbox, iCloud Drive, and other cloud services is common.
For these reasons, I suggest thinking of BitTorrent Sync as a supplement to cloud storage, not a replacement. Now at version 2.0 (and without the “beta” designation), the app has made tremendous strides in both feature set and usability. Even so, some aspects of its user interface are still obscure or confusing, and setup requires a somewhat odd series of steps. I’ll walk you through some of the basics.
Linking identities
In previous versions of BitTorrent Sync, each folder you wanted to sync had to be linked individually on each device–a somewhat tedious process. As of version 2.0, you can instead create a private identity that you share across your devices; once every device uses the same identity, any individual folders you share on one become available on the others automatically (with a qualification I’ll explain). This feature requires a paid Pro account, but since every 2.0 user gets 30 days of Pro service free, setting up your devices this way is the default.
When you launch BitTorrent Sync 2.0 for the first time, it walks you through a brief setup procedure. On your first Mac, when you get to the screen that says Link Devices, click This Is My First Sync 2.0 Device. Then, on the Create Identity screen, type the name you want to use for your identity and click Create Identity. At this point, you can begin adding folders. (To do so, click the Add Folder icon in the upper-left corner, navigate to the folder you want to sync, and click Open.) But you may want to postpone adding folders until you’ve set up another Mac and read about the extra steps needed to sync folders to their expected locations.
On this screen you can set up a new identity or link to another Mac already running BitTorrent Sync 2.0.
To configure your second Mac, install and run BitTorrent Sync 2.0, but when you get to the Link Devices screen, instead click Link a Device Already Running Sync 2.0. When you see the large QR code, click Link a Desktop Device Manually. You’ll be prompted to enter a key.
To find that key, go back to your first Mac, click the gear icon, and choose My Devices from the pop-up menu. Click Link Device followed by Link a Desktop Device Manually. You’ll see a 35-character key; type it on the second Mac and click Link. From the New Folders from Other Devices Will Be pop-up menu, choose Synced. Then choose a default location for folders synced from other devices (such as /Users/you/BitTorrent Sync–more on this in a moment) and click Link. Once you’ve done all this, you can close the key’s window on the first Mac.
Make sure you choose Synced from the pop-up menu, and take note of the default location for storing new folders.
At this point, your two Macs are linked, so any folder you share on either of them will appear on the other–but probably not where you expect it to, at least if that folder already existed on your other Mac.
For example, say I go to Mac A and share my Desktop folder (/Users/you/Desktop). I might assume that since I have a folder with the same name and location on Mac B, whatever I put on the Desktop of one will now appear on the other. But no, on Mac B, a new folder called Desktop will appear inside my default BitTorrent Sync folder (the location I chose during setup), and that’s where synced files from Mac A’s Desktop folder will go.
Here’s how you can sync existing folders without duplicating them. On the second Mac, open BitTorrent Sync, hover over the folder name, and click the icon on the right (with three vertical dots). From the pop-up menu, choose Disconnect, select Delete Synced Files, and click OK. Now hover over the folder name again and click Connect. Enter the exact path of the existing folder, or click Change and navigate to it. (For example, you might change /Users/you/BitTorrent Sync/Desktop to /Users/you/Desktop). Make sure Sync All is turned On. Then click Connect. When you see the confirmation alert (“Destination folder is not empty. Add anyway?”), click OK.
If you add a folder on Mac A that doesn’t already exist on Mac B, it’ll still go inside your default BitTorrent Sync folder, but you can simply drag it to a new location in the Finder and BitTorrent Sync will keep track of it and continue syncing it automatically.
Set up folder sync
If your trial Pro account expires and you don’t want to pay to continue it–or if you want to sync folders with a computer that has a different identity–you’ll follow a different procedure to sync folders.
In the BitTorrent Sync app on your first Mac, click the Add Folder icon, navigate to the folder you want to sync, select it, and click Open. Then hover over the folder name and click Share. In the dialog that appears, select Read & Write under Permission (to let yourself modify the folder on any of your own devices). Click Email to create a new message in your default email client, address it to yourself, and click Send.
You can choose Read Only or Read & Write, among other options, when syncing a folder, either with your own devices or with other people.
So far, you’ve merely made a folder available for syncing. The next step is to set up a peer–another device that will sync this folder.
On another Mac, open the email message you just sent yourself on that Mac and click the link. A web page opens with two buttons. If the Mac already has BitTorrent Sync 2.0 installed, click “I already have Sync 2.0.” If not, click “Install Sync 2.0” to download and install the software, and then return to the page and click Get the Folder.
In the dialog that appears, make sure the path shows where you want the synced folder to be stored–it should have the same name (not necessarily the same location) as the one on the first Mac. Be careful here–if you’re syncing a folder named Example and you choose, say, /Users/you/Example in this dialog, BitTorrent Sync will add a folder at /Users/you/Example/Example. If you want to sync with an existing folder called Example, choose its parent folder (as in /Users/you) or edit the path manually to eliminate the duplicated folder name. (If the folder you select doesn’t already exist, BitTorrent Sync creates it. If it does exist and you click OK at the “Add anyway?” prompt, the software merges the contents of the folder on the second Mac with the contents of the folder on the first one.) Click Connect.
Now go back to the first Mac, where BitTorrent Sync shows an alert asking you to approve access from the new client. Click the green check mark to approve.
BitTorrent Sync’s unassuming, customizable main window shows all the folders you’re syncing and how many peers each one has.
And that’s it–from now on, the folder you selected on each end should stay in sync across your Macs as long as they’re both online. (For files over 4MB, BitTorrent Sync copies only the changed portions of files, in 4MB chunks, which speeds syncing considerably.) You can open the same email message on additional computers and click the link to add more peers, or repeat the entire process to sync additional folders.
You can also use the BitTorrent Sync iOS app (or comparable apps for other mobile devices) to view or download any of your files. The mobile apps don’t sync entire folders by default since that could overwhelm your device’s storage, but you can enable syncing for any folder, and can also prevent the app from using cellular data.
Share a folder
You can also share any of your folders with other people, either read-only or read-write. To do this, open BitTorrent Sync, hover over a folder, and click Share. Choose the options you want, which are identical to those you saw when you set up the folder for syncing, and click Email to send someone an invitation.
To share a folder, click this button, which appears only when you hover over the folder name.
As is the case when syncing your own folders, each person you share with must have BitTorrent Sync installed on at least one of their devices. Unlike cloud storage services, there’s no website someone can connect to to see your files in a browser.
Feeling left out
The least intuitive aspect of BitTorrent Sync is how to exclude a file or folder from syncing when you’re syncing its parent folder. For example, if I have an app that already syncs its data across Macs in some other way ( DEVONthink Pro Office is one such app I use every day), letting BitTorrent Sync copy the same files would lead to conflicts and inconsistencies. So I want to tell BitTorrent Sync, “Sync everything in this folder except the following subfolders.”
It would be nice if the BitTorrent Sync client had a user-friendly interface for excluding files, but adding them to this IgnoredList file isn’t too difficult.
Doing this requires editing an file in an invisible folder–not exactly user-friendly! (A BitTorrent representative told me that a more convenient user interface for excluding items is in the works.) Here’s how to do it. In the Finder, choose Go > Go to Folder, enter the full path of the folder you’re syncing followed by /.sync (such as /Users/joe/Documents/.sync) and click Go. In the Finder window that opens, double-click the file IgnoreList to open it in TextEdit (or your default app for text files). Add the file(s) or folder(s) you want to exclude at the end of the list, one item per line. (You can use the wildcards * and ? to indicate patterns, such as IMG_*.jpeg.) Save the file. From now on, the designated items will no longer sync, but BitTorrent Sync doesn’t remove any copies that had already synced to your other devices–you’ll have to do that manually.