OpenSim Archives

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Technical Reference -> Terms -> OAR Format -> How do I use the OAR Function?


How do I use the OpenSim Archive Function?


The OpenSim Archive (OAR) function has existed since OpenSim 0.5.9. Basically, it does a similar job to load-xml2/save-xml2 in that it saves prims so that they can be later reloaded. However, OpenSim archives (OAR) go a step further in that they can save all the necessary asset data so that you may fully restore the terrain, the textures of objects and their inventories when loaded onto a completely different system using a different asset database.


From the region console, one can type

save oar [<filename>]

to save an OpenSim archive. If no filename is given, then the name region.oar is used in the current directory


save oar
save oar my.oar
save oar c:/mybackups/filename.oar
save oar oars/11nov.oar

To load an archive, type

load oar [--merge] [<location>]

at the console. The location can be a filesystem path (as for "save oar") or an HTTP address to load an oar directly over the web. If no location is given, then the server looks for a file called region.oar in the current directory.


load oar
load oar my.oar
load oar --merge oars/3rd-party.oar
load oar

By default, loading an archive will delete all the existing objects in the regions and replace them with the archive contents. It's like being in the Matrix (when they swap environments), except much slower (all the scene objects are slowly deleted before the new environment is loaded :-)

If the --merge option is specified, then the oar will be merged with the existing region objects rather than replace them. The existing terrain, region settings and parcels will be left in place.

When an archive is loaded, owners will be restored if the relevant uuids can be found in the OpenSim installation's user database. Otherwise, prim ownership will default to the master avatar for the region.

I recommend that you use filenames with the extension .oar. The filename extension of the download links on this page is .tar.gz which illustrates that the .oar format is actually a zipped tar file.

Example OARs

cyberlandia.tar.gz - cyberlandia landscape designed by the architect Simone Riccardi aka turboy. Contemporary architecture surrounded with a natural/synthetic context image_1 image_2 (work under Creative Commons by attribution).

OpenVCE 3D Assets OAR

The virtual worlds assets described at provided by Clever Zebra and the team at AIAI in the University of Edinburgh are available as an OAR (Opensim Archive) file.

Get file "opensim-openvce.oar" from there (right click on the file in the above directory in your browser, and select download is the easiest way to obtain the materials). A "full" set of the buildings with a large 400 seat amphitheatre intended to be placed on the corner of 4 sims is also available via "opensim-openvce-full.oar". Images of the buildings in place in Opensim are at: Image 1, Image 2


Please feel free to place links to other environments here, though unfortunately you'll have to host them on some other site.

Do not forget to also check out this page

Further Information

Use cases

Possible current uses are

1. To migrate data from an SQLite region database to one based on MySQL

2. To distribute entire regions to other people.

Current limitations

  • Performance is not very good, especially with large archives. This will be addressed in the future

File Formats

OAR File Formats


1. What is this .tar.gz format you are using for the internal OAR format? Why not zip?

.tar.gz is a standard unix way of zipping up files into a single larger compressed file for distribution. Windows users should be able to open these files using freeware programs such as 7-zip.

I'm using .tar.gz because all the zip (and tar) libraries for .net are licensed either under the GPL (with exception) or under the MSPL. Unfortunately, not all members of the OpenSim development team are comfortable with the MSPL, so these libaries are not currently an option. It is also significantly easier to write code to create and read tar archives than zip archives.

Also, if you're only ever loading and saving oars (rather than pulling them apart and putting them back together), then you don't need to worry about the internal format at all :)

2. Can you load and save multiple regions to an archive?

Not yet.

3. Can you load and save parts of a region to an archive?

Not yet.


  • Due to a possible bug in the Mono 1.2.4 libraries, this feature may cause a debug dump when used (the problem appears to be in writing out a compressed stream). Mono 1.2.6 is okay. Since Mono 1.2.4 is fairly old now, this bug will not be addressed.

Current Status

Operational. Bug reports are appreciated Justincc 14:53, 14 September 2009 (UTC)

Though we will strive to maintain compatibilty for old archives with newer OpenSimulator versions, please don't rely on these archives as the only backup for regions.

See Also

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