I have some files and folders on a USB drive connected to my iMac...I would like to sync them with a folder on my iMac...how do I do that?

Is there built-in functionality in Lion that allows me to do that, or do I have to use a 3rd party solution?

  • When you say "Sync", exactly what behavior do you want to see? How do you want discrepancies resolved?
    – Daniel
    Commented Jan 4, 2012 at 3:05
  • I want to make sure both folders contain the same files (no duplicates). So if one folder has newer files and then it replaces the old ones in the other folder. Basically, they just transfer files that are newer - or the diffs of existing files. Commented Jan 4, 2012 at 4:31
  • And older files clobbered without prompting
    – Daniel
    Commented Jan 4, 2012 at 5:26
  • Not necessarily, @Daniel. Chronosync, for example, allows you to archive X versions of the older files for Y days. Handy if you decide you want an older version back. Commented Jan 4, 2013 at 13:50
  • Use a launch deamon to automatically start rsync when your USB is connected. Commented May 21, 2015 at 7:20

10 Answers 10


arRsync is a free OS X GUI to the rsync command line utility. It will get you started on the path to rsync enlightenment. You can save common sync operations to recall them at a later time for easy rsync. And it supports the common rsync use case scenarios: push A to B but leave stuff that's in B but not A in place, push A to B and delete stuff that's in B but not in A, make A and B look the same (with a conflict report).

  • 1
    Some updates for Catalina or newer?
    – Zézouille
    Commented Mar 26, 2020 at 12:23
  • This is way too old, wont run on modern MacOS. Commented Sep 28, 2021 at 4:10
  • 2
    Meta discussion about whether to keep or delete this can be found here. It'll stay because the question specifically references Lion and the answer still applies if you're running Lion.
    – Ian C.
    Commented Oct 5, 2021 at 1:48
  • 1
    However, it’s a valid question whether there is a modern equivalent to this utility.
    – Calion
    Commented Oct 9, 2021 at 22:59
  • @Calion certainly, and an entirely new question should be posted to solicit those answers.
    – Ian C.
    Commented Nov 29, 2021 at 16:40

If you are comfortable with the terminal, rsync is a great utility that will sync folders easily. Take a look at a tutorial here (the tutorial is on an "Everything Linux" website, but the rsync utility comes with both Linux and Mac OS X).

Example commands:

Copy/merge everything newer from SOURCE into DEST, do not delete anything:

rsync -va   /path/to/folder/SOURCE/  /path/to/folder/DEST/

Copy everything newer into DEST, and delete any items from DEST that don't exist in SOURCE:

rsync -va --delete   /path/to/folder/SOURCE/  /path/to/folder/DEST/

Be sure to include the trailing forward-slash / at the end of your folder paths.

A useful hint here is that you can drag folders into the Terminal window to have it insert the full path to that folder (or file), saving you lots of typing and typos.

  • Here's a nice hint on using Mac OS X's built-in rsync and Automator to make a GUI for this: bananica.com/Geek-Stuff/…
    – Demis
    Commented Jan 29, 2016 at 20:37
  • 1
    If you're syncing in OSX, you probably want to add --exclude '.DS_Store' --exclude 'Thumbs.db' into your rsync command to avoid copying OSX metadata.
    – Hengjie
    Commented Mar 13, 2018 at 9:57

Another donationware is SyncTwoFolders:

This program synchronizes two folders. The oldest files will be replaced by the most recent, and in certain cases, some files will be removed. Use the help tags to familiarize yourself with the options. Be sure of what you are doing when you start a synchronization. If in doubt, do a Simulation. This will show you what will happen if you choose to synchronize, but no files will be replaced or removed.


SyncTwoFolders is a free great app that's very useful and handy for Mac users. I use this to sync my GoogleDrive and Dropbox folders. Here is the link to setup SyncTwoFolders.

Actually you can schedule a sync. You have to create as setting of your own for ex. "mysync' by clicking the '+' sign next to 'Last Settings' drop down and saving it. This 'mysync' will appear in your window to the right when you click the '*' button above the 'Synchronize' button.

At the bottom of that sliding schedule window you can set the time interval at which it can sync.

You need to keep the application running in the background for it do scheduled syncing.


I have had good luck with Chronosync for synching folders/Macs.


Install Xcode from the App Store and use File Merge.

Then you can open both directories, and compare individual differences and pick which one is "correct" (even down to lines of text within a file), merging the results to a new directory or over the top of one of the two you're comparing.

(it should be available in Spotlight after you've installed Xcode, if not open Xcode and from the Xcode Menu it's under "Other Developer Tool)

  • Useful utility! Although a little bit cumbersome, nice that it shows all the changes before you merge.
    – Demis
    Commented Jan 29, 2016 at 20:23

For a decent GUI based file synchronizer, check out File Synchronization (website found here) It is a low cost ($15) utility that has nice control over the sync process. GUI arrows give you a pretty good feel of what is going to happen, ensuring you use the tool properly and don't end up overwriting the wrong file. Nice tool.


I use Beyond Compare for Mac. I used it before on Windows and it is very good with maximum control.



Free Dropbox account is great if you need to sync small amount of files with other devices too, but if you have many devices, you should either upgrade Dropbox or get Chronosync. I personally use both of these solutions, so all my Macs are basically in sync. :)


Dropbox is the answer. Simple. Multi-platform. Free.

Give it a go!

  • 1
    Dropbox syncs between machines not a USN drive and a folder
    – mmmmmm
    Commented Sep 19, 2012 at 12:34

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