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NOTE: This is a full rewrite of my previous question. They are related but not duplicates.

I am looking for a Mac (or Linux) equivalent for the Windows Offline Files feature. I'm looking to keep some local copies of files that are in a network storage, because I cannot connect to the NAS all the time. However, I would like to ensure that the files get synced as soon as I am connected to the drive again (and would like them to be synced after than).

Please note that the feature permits you to copy (cache) few folders out of the external harddrive, not the entire harddrive.

Is there such a thing?

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up vote 2 down vote accepted

Try Unison.

Unison is a file-synchronization tool for Unix and Windows. It allows
two replicas of a collection of files and directories to be stored on
different hosts (or different disks on the same host), modified
separately, and then brought up to date by propagating the changes in
each replica to the other.

It lets you specify directories to sync - these will be the folders you want to cache. You can also finely control the direction of sync. It will not auto-run when you connect to the drive. You'll need to trigger that yourself, depending on the Linux distro you run and how you/it connects to the remote drive. e.g if you use the mount command, wrap it in a script that calls unison after the mount. There's a brief write-up of how to use it on the Ubuntu community documentation site.

Unison is a command-line tool that also has a GUI of the same name. If you're on Ubuntu, both packages are included in the universe but not installed by default.

$sudo apt-get install unison unison-gtk

It is also available for the Mac via ports (Fink, Macports etc).


 * Unison runs on both Windows (95, 98, NT, 2k, and XP) and Unix
   (OSX, Solaris, Linux, etc.) systems. Moreover, Unison works across
   platforms, allowing you to synchronize a Windows laptop with a
   Unix server, for example.
 * Unlike a distributed filesystem, Unison is a user-level program:
   there is no need to modify the kernel or to have superuser
   privileges on either host.
 * Unlike simple mirroring or backup utilities, Unison can deal with
   updates to both replicas of a distributed directory structure.
   Updates that do not conflict are propagated automatically.
   Conflicting updates are detected and displayed.
 * Unison works between any pair of machines connected to the
   internet, communicating over either a direct socket link or
   tunneling over an encrypted ssh connection. It is careful with
   network bandwidth, and runs well over slow links such as PPP
   connections. Transfers of small updates to large files are
   optimized using a compression protocol similar to rsync.
 * Unison has a clear and precise specification, described below.
 * Unison is resilient to failure. It is careful to leave the
   replicas and its own private structures in a sensible state at all
   times, even in case of abnormal termination or communication
 * Unison is free; full source code is available under the GNU Public
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FileSync will do what you want on the Macintosh.

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I have had good success with ifolder, which is cross platform solution for bi-directional file sharing. It appears to be stable. Its a client-server solution.

Also, you could look at, I haven't tried this, but it looks interesting.

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This is not entirely what you asked for, but depending on what specifically you want to achieve you might want to consider using a version control system such as subversion). Your files won't be synchronized automatically, but you will get a version history and some other neat features in return.

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