Hypergrid
From OpenSimulator
Contents |
The OpenSim Hypergrid
What is the hypergrid?
The hypergrid is an extension to opensim that allows you to link your opensim to other opensims on the internet, and that supports seamless agent transfers among those opensims. It can be used both in standalone mode and in grid mode. The hypergrid is effectively supporting the emergence of a Web of virtual worlds.
The basic idea for the hypergrid is that region/grid administrations can place hyperlinks on their map to hypergrided regions run by others. Once those hyperlinks are established, users interact with those regions in exactly the same way as they interact with local regions. Specifically, users can choose to teleport there. Once the user reaches the region behind the hyperlink, she is automatically interacting with a different virtual world without having to logout from the world where she came from, and while still having access to her inventory.
The hypergrid started as a GForge project, but it is now included in the standard distribution of OpenSim. To run your OpenSim instance in hypergrid mode, please see Installing and Running.
Virtual World Hyperlinks
We're all familiar with hypertext links on the Web. But what is a virtual world hyperlink?
In the hypergrid model, we consider the 2D map of the virtual world as the equivalent of a web page. As such, a VW hyperlink is simply a region on that map.
The default model of opensim-based virtual worlds already supports this concept of hyperlink, to some extent. When you teleport from one region to another via the map, chances are you are migrating your agent into a different opensim server. This migration is a glorified "agent transfer" that also exists, in rudimentary form, on the web when hypertext links are followed. The default model, however, imposes two very strong constraints on these hyperlinks:
- The entire map of regions is controlled by a central service known as the grid service, whose job is to provide a uniform view of the world to all of its regions.
- The only agents that can be transferred are those pertaining to users known to another central service, the user service; if the incoming user is not on that service's database, the agent transfer doesn't go through.
The hypergrid simply removes these two constraints.
First, it allows individual opensim instances to add "neighbors" to their local map, shifting the control of the map down from the grid server to individual opensim instances (although hyperlinks can also be served by grid servers if grid admins so wish). In doing so, the world becomes a lot more interesting and varied. The map that you see in one opensim instance may be completely different from the map that you see after you teleport via an hyperlink. As an opensim administrator, you are free to define what other opensims you want to see on your map.
Second, it allows the transfer of agents pertaining to foreigner users, i.e. users who are registered elsewhere. Instead of assuming one central user service, the hypergrid assumes an arbitrarily large number of such services distributed all over the world. As such, when agents are transferred among hypergrided opensims, a lot more information is passed about the corresponding user. That information includes the collection of servers that the transferring user needs.
Usage Scenarios
The following are some usage scenarios. There isn't a clear separation between these scenarios, there's a large overlap between them. This is also not an exhaustive list. The purpose of these descriptions is to give you some starting ideas for how to use the hypergrid in practice. Please feel free to add other interesting scenarios to this list.
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Personal Worlds This first scenario pertains to standalone opensims. Normally, standalones are completely disconnected from the internet. However, when run in hypergrid mode, standalones become network-able. As such, you can run your own world in your own computer, and link your world to whoever you want. For example, you can link to your friends' hypergrided opensims and to hypergrid gateways in open grids such as OSGrid. The great thing about this scenario is that all of your assets are stored on your computer, and not on somebody else's server. You can back them up using ordinary backend tools. The not so great thing about this scenario is that all of your assets are stored on your computer! If your disk goes berserk, you loose them. (so make sure you make external backups regularly) |
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Communities This second scenario is about communities, broadly construed. The idea here is that a group of people come together to support a small community grid, i.e. a common world where shared activities take place. But at the same time, the members of the community maintain their own standalone worlds. The standalones link to the community grid, and the community grid may link back to the individual members' worlds and other places of interest. The members' identities are probably the identities they have on their standalones, and their assets are also probably stored there. The assets present in the community regions, however, are stored on the grid asset server. |
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Grid Public Regions Walled-gardens are here to stay, and they serve many useful purposes. There is a hybrid mode for the hypergrid that some walled-garden grid operators may be interested in supporting. In this hybrid mode, most opensim instances on the grid run in normal, wall-garden mode, so no foreign visitors are allowed there - technically it is impossible to reach them. However, a few opensim instances on that grid can run in hypergrid mode, so that foreign visitors are allowed. This way, there is a gateway for grid-local users and arbitrary visitors to meet. This is also a good strategy for attracting new users to the grid, since random users are able to visit those gateway regions without having to sign up for an account upfront. This hybrid mode is very similar to what happens on the web. For example, anyone can visit Facebook's public pages without having to sign up for a Facebook account. However, only Facebook users can go further inside. |
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Level Games The normal version of OpenSim enforces a common map for all the regions on a grid. The hypergrid removes that constraint. As such, it becomes easy to design VW games where the world looks different depending of where the player is. |
Security Concerns
There is a wide-spread assumption that open grids such as OSGrid and new forms of grids such as the hypergrid are inherently insecure, and that it will be impossible to develop a "goods-based" economy on top of them; only walled-gardens can be secured. This is both true and false. While it is true with the current state of things, open grids, whatever their form, can be made as secure as the web. The first step towards that is to define exactly what the security threats are, and how they affect (or not) open and closed grids. So, let's spell them out, and face them head-on. This will help put our feet on the ground so that we start developing appropriate solutions.
Malicious Clients
CopyBots
Everyone knows about the infamous CopyBot. Using libraries such as LibSL (now known as OpenMetaverse) it is possible to develop clients for opensim servers that do unorthodox things such as bypassing the permissions system to copy people's assets. Bots written by griefers can do lots of other nasty things.
Malicious bots are a problem for all opensim administrators, including walled-garden grids. They can be prevented, to a certain extent, by exo-technical solutions such as Terms of Service and real-world lawsuits. Technically speaking, the only way to keep intruders out is to run opensim inside a firewall, pretty much like all other pieces of client/server software out there. If that's an acceptable solution for your case, you should do it.
Unfortunately firewalls also keep the public out, and most opensim operators, even the ones running walled-garden grids, want to reach out to the public. In this case, opensim operators may develop additional technical obstacles for bots, similar to those we see on the Web. For example, make sure agents are being run by real people by giving them a human-challenge during the login/TP process, etc.
Every obstacle to malicious clients lowers the risk of an intruder attack. However keep this in mind: no matter how many obstacles one builds, a sufficiently skilled and motivated attacker will be able to overcome them to penetrate opensims connected to the public internet. This affects hypergrid nodes as much as walled-garden grids. In fact, it's more pervasive than that: it affects all servers (opensim, web, etc.) connected to the public internet. Fighting malicious intruders is a fact of a connected world. Fortunately, those attacks don't happen very often, or the Web would have been dead by now.
Web Clients
CopyBots are the most well-known bots for opensim-based virtual worlds, but these virtual worlds are also susceptible to attacks by regular web clients. With the current state of things, it is actually easier to copy assets with a web-based client than with a libsl-based one. The weakness is that asset servers are connected to the public internet, and the protocol for interacting with them is public.
OpenSim has some minimal guards in place to fence against these kinds of attacks. Specifically, when the inventory server receives a request for an item, it checks the session identifier of the requester. Web clients aren't logged in, so they are refused service. I don't want to expand much more on this, so not to make life easy for attackers, but let's just say that opensim has the necessary mechanisms in place to fence off web-based attackers.
Malicious Hosts
Actively Malicious Hosts
The new security threat introduced by openness, one that does not exist in closed grids, is the possibility of a user to visit a region that is running malicious code. In the current state of opensim, a malicious host can do serious damage to the user's assets. Let's see how.
Assume you have your assets in your hypergrided-standalone opensim, and you go visit another opensim that happens to be running malicious code. Here is a non-exhaustive list of vulnerabilities that you are exposed to:
- The host has your session id, so it can request your inventory items on your behalf and store copies in its local asset server. To add insult to injury, a malicious host could simply wipe out your inventory after having copied it.
- Even if the malicious host doesn't access your items by itself, every time you access items in your inventory while you are in that region, those items are cached in the region's local cache, and can be stored persistently by the malicious host.
Malicious hosts can do a lot more damage, but those two are enough to illustrate this new kind of vulnerability affecting open grids. Note that this affects all open grids, i.e. those where arbitrary people can plug-in their opensims, and not just the hypergrid.
Fortunately, there is a family of simple solutions to this problem that can be summarized as "protecting you from yourself." That proposal is described here.
Piracy
A second new security threat affecting open grids is one pertaining to commerce of virtual goods. Suppose you put something out for sale on your hypergrided opensim. A foreign user comes and buys it. What that really means is that that user will physically get a copy of the assets moved to his/her asset server, which is different from your asset server. The permissions will be whatever you define them to be, and using the regular VW client, that user can only do what you defined he/she should could do with the object, as usual. However, if the user has direct backend access to the asset and inventory servers, that person can simply modify the permissions on his/her copy. This is commonly known as piracy. (This is also a problem with programmers who have direct access to the cache that their client keeps; in this case, the only thing that needs to be done to enable piracy is for the user to actually see a texture/animation/in-world object. This does NOT allow scripts to be copied, though, since the script is only interpreted on the server and is never sent for interpretation by the client.)
This situation is the kernel of the belief that open grids are hopeless for a virtual-goods economy. DRM discussion aside, maybe they are hopeless. But then, everyone thought the web was hopeless for selling music, and look at the success of iTunes in spite of all the piracy that still exists out there. Who will be the equivalent of iTunes for virtual hair, skin and clothes?
Hypergrid Implementation
Hyperlinks and Agent Transfers
When you establish a link between your opensim and another, a message is sent out to that other opensim requesting information about it; the required information includes the network information of that opensim host, and the coordinates of its first region on its local grid in the form of a region handle. For example, suppose you are linking node X.com:9000, placing it in your local map at 900, 900. That opensim runs one or more regions that likely are not in 900, 900 on their own map; suppose the first region of that opensim is at 1100, 1100. From your point of view, it doesn't matter what those other coordinates are, and you don't need to know -- that's the key to being able to decentralize the "world" as given by a 2D map; you want to place it in your map at 900, 900. The "true" position of that simulator only matters for the LL viewer, when there are teleports between your world and that other opensim. This mapping between coordinate systems is the essence of hyperlinks for opensim; it's one simple but critical thing that the hypergrid implementation does. The mapping happens on the TeleportFinish event; instead of sending the local coordinates to the viewer, the hypergrid teleport wrapper sends the remote coordinates.
When an agent teleports through that hyperlink the following happens. First, before InformRegionOfChildAgent, the local opensim notifies the remote opensim of this foreign user via the "expect_hg_user" method. That message sends along the addresses of all the servers that this user uses, i.e. user, inventory and asset servers. The remote opensim places an entry for that user in its local user profile cache but not in its user database; the foreign user information is non-persistent. After that, the teleport process is exactly the same as the normal teleport process; the only difference is that the region handles are switched between the remote region's hyperlink position on the local grid and its actual position on its grid.
In summary, the two new concepts introduced by the hypergrid are the concept of an hyperlink and the concept of a "local user" vs. "foreign user".
Inventory Access
Inventory access from abroad is done by wrapping the existing scene-inventory interactions with additional code that gets or posts inventory assets from/to the user's asset server. When inventory is accessed, the hypergrid wrapper checks if the user is foreign and, if she is, the wrapper simply brings the necessary assets from the user's asset server to the local asset cache and server; from then on, the wrapper passes the control to the existing inventory access functions. When something is added to inventory, the hypergrid wrapper is notified via an event, and posts the assets to the user's asset server. A cache of the exchanged item identifiers is maintained so that they aren't brought back over and over again.
The result is that hypergrided opensim instances end up interacting with several asset servers, instead of just one. That interaction is implemented in a straightforward manner by instantiating several GridAssetClient objects, instead of just one.
The Hypergrid Classes
Currently, the hypergrid is implemented outside of the OpenSim namespace, so that there is complete separation between what already exists and this new behavior. It has its own namespace, HyperGrid. In it, there are 4 sub-namespaces that follow directly the software architecture of OpenSim, namely:
- OpenSim.Framework:
- ForeignUserProfileData extends UserProfileData by introducing information about the user's "home", namely the home address, port and remoting port. The user's home is not that user's user service; it's the opensim that the user has defined to be her home. This is necessary for supporting the home jump (Ctrl-Shift-H).
- HGNetworkServersInfo follows the spirit of NetworkServersInfo, although it neither extends it nor uses it. For now, it's a utility class whose two main functions are to convert domain names of servers to IP addresses, and to uniformly provide the answer to the question bool IsLocalUser(...).
- OpenSim.Region.Framework.Scenes.Hypergrid:
- HGSceneCommunicationService extends SceneCommunicationService, overriding RequestTeleportToLocation. There are two very small but critical changes to the base method: (a) on the TeleportFinish event, we switch the region handles when the destination region is an hyperlink; (b) the connections at the end are always closed for hyperlink TPs.
- HGScene extends Scene, overriding TeleportClientHome(...). The only change to the base method is to stay away from the user server, for now, because the user service is still not completely wrapped up for foreign users. Once the user service is properly wrapped up, this class will become unnecessary.
- HGScene.Inventory is a partial class of HGScene, just like what happens in the OpenSim framework. This part of HGScene overrides some inventory-scene interaction methods, so that assets are fetched/posted from/to the user's asset server. Once that extra fetching/posting is done, these methods simply pass the ball to the base methods.
- HGAssetMapper: this is a new class specific to the hypergrid that manages the fetching and posting of assets between foreign regions where the user is and the user's asset server.
- OpenSim.Region.Communications.HyperGrid is a mashup of OpenSim.Region.Communications.*. This is the place where most of the hypergrid extension lies. One of the reasons for this is that the hypergrid communications part is doing one additional thing: it is making standalones network-able.
- HGCommunicationsStandalone extends CommuniationsLocal. Just as its base, it is a hub for the several network services available in standalone mode. The main difference is that those services are extensions of what's in OpenSim.
- HGCommunicationsGridMode extends CommunicationsManager directly. Again, it's a hub for the network services available in grid mode, those services being extensions of OpenSim.
- The cluster HGGridServices (superclass), HGGridServicesStandalone and HGGridServicesGridMode (subclasses) implements the OpenSim interfaces IGridServices and IInterRegionCommunications. The 2 subclasses are wrappers for LocalBackEndServices and OGS1GridServices, respectively. There is one common pattern throughout these classes: check if the region to talk to is an hyperlink; if it's not, simply delegate the work to LocalBackEndServices/OGS1GridServices; if it is, push the work to the base class HGGridServices. HGGridServices, in turn, does the management of hyperlink regions, and defines two additional pieces of inter-region protocol:
- region_uuid: for linking regions
- expect_hg_user: similar to the existing expect_user interface, but with a lot more information about the user being passed around, namely all the user's servers (inventory, asset, user, home, etc.)
- HGInventoryService extends LocalInventoryService and implements ISecureInventoryService. This class is the most obvious mashup of the pack, mixing local service access for standalone users and remote inventory access for when users are out and about. Right now, there is a fair amount of selective copy-and-paste, to stay away from the ugliness coming from OGS1InventoryService and OGS1SecureInventoryService. HGInventoryService is always a ISecureInventoryService. Its methods all follow the same pattern: check if the user is a local standalone user; if it is, pass the work to the base method (in LocalInventoryService); if it's not perform secure remote access.
- HGUserServices wraps OSG1UserServices, but it's not functional yet.
- OpenSim.Region.CoreModules.HyperGrid is a collection of 3 region modules:
- HGWorldMapModule extends WorldMapModule. It reuses almost everything from the base class. The only small change is in RequestMapBlocks, where it tries to send Offline mapblocks to the client.
- HGStandaloneInventoryService and HGStandaloneAssetService do what their names say. They are region modules that allow access to inventory and assets for standalones, when the standalone user is out and about. In spirit, there is a lot in common between these modules and the REST inventory/asset plugin. Unfortunately, that plugin could not be used because it defines a completely different interface than that used by existing inventory and asset servers, and the access for the hypergrid must use a consistent interface.
Installing and Running Hypergrid
Installing
- Checkout OpenSim, prebuild and build as normal.
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- If you're running your opensim in grid mode with the UGAIM servers on other machines, you're done. If you're running in standalone and you want it to be network-able, or if you have your grid on loopback (127.0.0.1) change all the [Network] server addresses to "http://<external_host_name>:<http_port>". See below.
- Run opensim like this: [mono] OpenSim.exe -hypergrid=true. To make sure the hypergrid is running type this on your console: link-region. If you don't hear anything back, the hypergrid is not properly installed.
[mono] OpenSim.exe -hypergrid=true
Here is an example of the Network settings for a standalone:
[Network] http_listener_port = 9300 remoting_listener_port = 9895 grid_server_url = http://example.com:9300 grid_send_key = null grid_recv_key = null user_server_url = http://example.com:9300 user_send_key = null user_recv_key = null asset_server_url = http://example.com:9300 inventory_server_url = http://example.com:9300 messaging_server_url = http://example.com:9300
Here is an example of the Network settings for a grided opensim:
[Network] http_listener_port = 9300 remoting_listener_port = 9895 grid_server_url = http://example.com:8001 grid_send_key = null grid_recv_key = null user_server_url = http://example.com:8002 user_send_key = null user_recv_key = null asset_server_url = http://example.com:8003 inventory_server_url = http://example.com:8004 ; Port 8005 reserved messaging_server_url = http://example.com:8006
Important Note
Make sure you have a 'home' set. If your home region doesn't exist, the hyperlink TPs may not work. To set your home, go to one of your local regions and "Set Home" from the viewer.
Linking regions
Method 1
On the console, type for example:
link-region <Xloc> <Yloc> osl2.nac.uci.edu:9006
- Use Xloc and Yloc that make sense to your world, i.e. close to your regions, but not adjacent.
- replace osl2.nac.uci.edu and 9006 with the domain name / ip address and the http_listener_port of the simulator where the region is running you want to link to
You can link to a specific region within an instance, by using the name of the region at the end, for example:
link-region 997 997 osl2.nac.uci.edu:9006:UCI Welcome
Method 2
There is also some initial support for reading the links from a xml file.
Use the console command: link-region <URI> [<excludeList>]
The uri can be either the path of a local xml file or a xml document on a http server.
The format of the xml file is:
<Nini> <Section Name="Region1"> <Key Name="xloc" Value="1002"/> <Key Name="yloc" Value="1006" /> <Key Name="externalPort" Value="9006" /> <Key Name="externalHostName" Value="osl2.nac.uci.edu" /> <Key Name="localName" Value="OSGrid-Gateway" /> <Key Name="real-xloc" Value="10222"/> //optional field that gives the region's real location on its home grid <Key Name="real-yloc" Value="10265" /> //optional field that gives the region's real location on its home grid </Section> <Section Name="Region2"> ... </Section> ... </Nini>
[Note] The section names can be anything you want, but they all should be different and have no spaces in the name.
ExcludeList:
The exclude list is a single string paramater with the format: excludeList:<SectionName>[;<SectionName>]
This means that while reading from the xml file any sections that are listed in the excludeList will be ignored and no HyperGrid link created for them.
This could allow, link lists to be created on a webserver that everyone could add their own regions to, and then they just make sure they add their own section name(s) to the exclude list on their own region(s).
So for example, someone might create a editable online list for the up coming OpenSimulator's 2nd birthday. Which might look something like:
<Nini> <Section Name="OSGrid-Party"> <Key Name="xloc" Value="1002"/> <Key Name="yloc" Value="1006" /> <Key Name="externalPort" Value="9006" /> <Key Name="externalHostName" Value="osl2.nac.uci.edu" /> <Key Name="localName" Value="OSGrid-Gateway" /> </Section> <Section Name="UCIGrid-Party"> ... </Section> </Nini>
I could then add my own region to the list with the section name "MW-Party". Then when I startup that region that I want to be part of this hypergrid, I use the command: "link-region <URI of xml file> excludeList:MW-Party"
This is so that my region doesn't try to create a hyper link to itself.
Method 3 (dynamic)
Starting in r8193, if you're in an HG-enabled region, you'll be able to dynamically link sims, and TP there, in any one of these ways (and probably more). All you need to know is the target addresse, e.g. from the list below.
1) Type for example secondlife://ucigrid04.nacs.uci.edu:9007/ in the chat box, pull up the chat history and click on that link
2) Pull up the map and search for things like ucigrid04.nacs.uci.edu:9007
3) Using the embedded browser visit pages that have links like secondlife://ucigrid04.nacs.uci.edu:9007/ (there's one up at http://www.ics.uci.edu/~lopes/hypergrid/test.html)
Again, you can link to a specific region within an instance by adding the name of that region at the end, like this: secondlife://ucigrid04.nacs.uci.edu:9007:Gateway 7000/
Important Note
Due to a viewer bug, you can only TP between regions that are no more than 4096 cells apart in any dimension. What this means in practice is that if you want to link to OSGrid, you must have your own regions reachable from the (10,000; 10,000) point on the map, which is where OSGrid is centered. Place your regions somewhere in the 8,000s or the 12,000s.
Banning Foreign Users
Even though the current viewers are incapable of dealing with foreign users, it is possible to ban specific foreign users from your estates. For now, you have to do it on the backend, i.e. directly editing the database and reviewing the log. Not easy for the faint of heart, but any sys admin should be able to do this with their eyes shut. What follows are instructions for adding a foreign user to the estate's ban list.
The first thing you need to do is to find out the UUID and IP address of the user you want to ban. For that you need to look at OpenSim.log. Search for log messages like this:
2009-01-23 03:45:11,995 INFO - OpenSim.Region.Communications.Hypergrid.HGGridServicesGridMode [HGrid]: Incoming HGrid Agent Annoying.Person http://problematic.domain.org:9002 2009-01-23 03:45:11,995 DEBUG - OpenSim.Region.Environment.Scenes.Scene [CONNECTION BEGIN]: Region Gateway 3000 told of incoming client Annoying.Person http://problematic.domain.org:9002 c3c9ecbf-bfb3-43eb-8dce-140afad7995f (circuit code 1896255323)
In this case, the information you need is: UUID = c3c9ecbf-bfb3-43eb-8dce-140afad7995f and IPAddress = problematic.domain.org
Next, let's add this foreign user to the ban list. Note that the estate information and ban lists are kept at the region server, not in the UGAIM. If you are using local storage for your regions, this information is stored in bin/OpenSim.db. So, open that DB with whatever tool you use to access your DBs. The instructions here assume a local sqlite database; if you're using MySql or other DB technologies for the regions' storage, the instructions are almost identical, but may need adjustments.
SqlLite usually comes with a common Linux installation. In Linux, just type:
$ sqlite3 OpenSim.db
In Windows, you need to get it from here. Once installed, run it on your OpenSim.db, like this, for example (on a command shell):
$ C:/Opt/SQLite3/sqlite3.exe OpenSim.db
Once you are connected to the database, you can explore as much as you want. What follows are the concrete interactions you need for adding that foreign user into an estate ban list. Change the data for your situation.
[opensim@ucigrid04 bin]$ sqlite3 OpenSim.db
SQLite version 3.3.6
Enter ".help" for instructions
sqlite> .tables
estate_groups estate_users migrations regionban
estate_managers estateban primitems regionsettings
estate_map land prims terrain
estate_settings landaccesslist primshapes
sqlite> .schema estateban
CREATE TABLE estateban (
EstateID int(10) NOT NULL,
bannedUUID varchar(36) NOT NULL,
bannedIp varchar(16) NOT NULL,
bannedIpHostMask varchar(16) NOT NULL,
bannedNameMask varchar(64) default NULL
);
CREATE INDEX estate_ban_estate_id on estateban(EstateID);
sqlite> select EstateID, EstateName from estate_settings;
100|My Estate
101|My Estate
102|My Estate
103|My Estate
sqlite> insert into estateban values (100, 'c3c9ecbf-bfb3-43eb-8dce-140afad7995f', 'problematic.domain.org', ' ', ' ');
sqlite> insert into estateban values (101, 'c3c9ecbf-bfb3-43eb-8dce-140afad7995f', 'problematic.domain.org', ' ', ' ');
sqlite> insert into estateban values (102, 'c3c9ecbf-bfb3-43eb-8dce-140afad7995f', 'problematic.domain.org', ' ', ' ');
sqlite> insert into estateban values (103, 'c3c9ecbf-bfb3-43eb-8dce-140afad7995f', 'problematic.domain.org', ' ', ' ');
sqlite> select * from estateban;
100|c3c9ecbf-bfb3-43eb-8dce-140afad7995f|mecatreco.game-host.org||
101|c3c9ecbf-bfb3-43eb-8dce-140afad7995f|mecatreco.game-host.org||
102|c3c9ecbf-bfb3-43eb-8dce-140afad7995f|mecatreco.game-host.org||
103|c3c9ecbf-bfb3-43eb-8dce-140afad7995f|mecatreco.game-host.org||
sqlite> .quit
Once this data is entered you need to restart OpenSim, so that it gets loaded.
Public Hypergrid Nodes
Please see Public Hypergrid Nodes.
Hypergrid Lists
Please see Hypergrid Lists.
Manuals and Tutorials
- Unofficial Hypernauta's Basic Manual: If you are a real beginner it can be for you. Talking about "personal" worlds created using domestic computers. LINK
