[Gllug] Network synchronisation tool

[Xander D Harkness]

Dave Cridland wrote:

>On Tue, 2002-08-27 at 15:56, Garry Heaton wrote:
>  
>
>>I've been using a utility called Robocopy on Win2000/XP for some time to 
>>synchronise/backup folders between 2 machines at home. It enables me to 
>>write a batch file specifying folders to be synchronised via a mapped 
>>drive. Since moving most of my work to Linux I now need a similar tool 
>>to do the same job between 2 Linux machines but there are probably many 
>>alternatives I'm not aware of. What is the right tool for the job? Perl 
>>script? DrakSync (Mandrake)? ssh/scp with appropriate flags? This is 
>>only for the network backup. I'll be using the CD burner for external 
>>backups.
>>    
>>
>
>rsync is your friend.
>
>It'll do some very strange things, such as only copying parts of files
>which have changed. Very network efficient. It operates over rsh or ssh,
>or it'll use its own protocol.
>
>It's also useful, I found, as a simple replacement for scp, or even cp,
>because of it's network efficiency, and ability to "resume" broken
>copies. I tend to use it when copying to/from mounted windows shares
>instead of cp, for instance.
>
>Dave.
>
>
>  
>
And for variety : http://www.cis.upenn.edu/~bcpierce/unison/

Unison is a file-synchronization tool for Unix and Windows. (It also 
works on OSX to some extent, but it does not yet deal with 'resource 
forks' correctly; more information on OSX usage can be found on the 
unison-users mailing list archives.) 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.

Unison shares a number of features with tools such as configuration 
management packages (CVS <http://www.cyclic.com/>,PRCS 
<http://www.XCF.Berkeley.EDU/%7Ejmacd/prcs.html>, etc.), distributed 
filesystems (Coda <http://www.coda.cs.cmu.edu/>, etc.), uni-directional 
mirroring utilities (rsync <http://samba.anu.edu.au/rsync/>, etc.), and 
other synchronizers (Intellisync <http://www.pumatech.com>, Reconcile 
<http://www.merl.com/reports/TR99-14/>, etc). However, there are several 
points where it differs:

    * Unison runs on both Windows (95, 98, NT, and 2k) and Unix
      (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 hack (or own!) 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 rsh or 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.
    * 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
      failures.
    * Unison is free; full source code is available under the GNU Public
      License.





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