Flux multi-user server

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1 Definition

Flux multi-user server (alias Hydra) is Open Virtual Worlds Web Server made by Media Machines. Currently as on July 2007 in late alpha/early beta.

For the moment, this page is only of interest to technical folks. Hydra is not ready for the masses as on July 2007.

2 Installation

Daniel K. Schneider tried on his personal Linux Desktop (Ubuntu 6.10). Disclaimer: I am not a programmer nor a sysadmin. Also, I use root to do command-line installations (can't get myself to type sudo in repetition).

In progress so to speak ...


  1. Get the Hawk Network Library version 1.7 by Phil Frisbie (LGPL). You can find it in the downloads section.
  2. Get Hydra, Flux Multi-User.
  3. Get MySQL development libraries and MySQL is you don't have these (see below).
  4. Also install Flux Player 2.1 if you don't have it already.

2.2 Preparation of installation

  • Install MySQL and the development libraries!
  • Use Synaptic Package Manger or apt-get and install these

I took:


If don't want to type command-lines to mysql, you also may want to install a mysql administration client. I tried (but then only used it to change the root password of the mysql server).


This tool then will show up under Applications/Systems tools. First time you connect you can use 'root' without password.

Then, open a terminal and become root:

Hydras (files)

Currently (July 2007) you have to compile Hydras and HawkNL it yourself.

  • unzip into a folder, e.g. I used
Modify some source code
  • I suggest to make a change to scenemodel.c (else you will have to use database, user and password for MySQL... Change line 51 from:
(&hydra_db, "localhost", "user", "password", "database", 0, NULL, 0) != NULL);


(&hydra_db, "localhost", "hydrausr", "SECRET", "hydra", 0, NULL, 0) != NULL);
  • Edit hydras.c, i.e. replace
char *url = "http://worlds.webers.org/content/testbed/";

by something of your own

  • Put it in a folder named "HawkNL" at the same level as the folder containing the Hydra sources. E.g. I used
unzip HawkNL17b1src.zip [-d "flux directory"]
cd "flux directory"
ln -s HawkNL1.70 HawkNL
Result is something like this
lrwxrwxrwx 1 root root 10 2007-07-06 15:28 HawkNL -> HawkNL1.70
drwxr-xr-x 7 root root 4096 2007-07-06 15:27 HawkNL1.70
drwxr-xr-x 2 root root 4096 2007-07-06 15:40 hydra
drwxr-xr-x 2 root root 4096 2007-07-06 15:39 src

2.3 Compilation

cd HawkNL
make -f makefile.linux
make -f makefile.linux install

It will also copy the libraries in /usr/local/lib and header to /usr/local/include/nl.h

  • On Windows, load the hydras.sln or hydrac.sln solution files into MSVC 2003 or later (not tested).
  • On Linux (I used Ubuntu) run make on the Makefile with gcc installed.
cd hydra


gcc -I/usr/include/mysql -DUSE_MYSQL -c scenemodel.c
gcc -I/usr/include/mysql -DUSE_MYSQL -c netcontroller.c
gcc -c netview.c
gcc -c -ggdb swamp.c
gcc -o hydras -pthread hydras.o clients.o scenemodel.o netcontroller.o netview.o swamp.o ../HawkNL/src/libNL.a -I/usr/include/mysql -L/usr/lib/mysql -lmysqlclient
gcc -c -ggdb hydrac.c
gcc -o hydrac -pthread hydrac.o swamp.o ../HawkNL/src/libNL.a
hydrac.o: In function `printErrorExit':
/usr/local/flux/hydra/hydrac.c:76: warning: the `gets' function is dangerous and should not be used.
make: *** No rule to make target `hydrabot', needed by `all'. Stop.

This doesn't seem to be harmful (for the moment) since hydras (the server) is built.

2.4 MySQL database

I presuppose that both MySQL and your Hydra will run on the same machine.

Create a hydra database and a user (same as in scenemodel.c)

(I used the command line since I couldn't figure out how to use the GUI.)

mysql -p
  • You have to create a hydra_db databse called hydra
mysql> create database hydra;
  • Then create the user called hydrausr (change secret of course)
mysql> create user hydrausr identified by 'secret';
  • Then give it rights to the hydra database
mysql > GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP ON hydra.* TO 'hydrausr'@'localhost';
  • Then reload the privileges
mysql > flush privileges;
Create a User table

This is needed for avatars, else you get something like:

Client connected with yourid=1, mytoken=/MM-6-12345678, uid=6
SELECT login_name,avatar FROM users WHERE uid=6
wrote 61 bytes to 1
Segmentation fault (core dumped)

So you go:

mysql -p
use hydra

Copy/paste this:

CREATE TABLE `users` (
`login_name` varchar(32) default NULL,
`password_hash` varchar(128) default NULL,
`uid` int(10) unsigned NOT NULL auto_increment,
`avatar` varchar(128) default NULL,
`email` varchar(255) default NULL,
`iconurl` varchar(255) default '/users/media/defaulticon.jpg',
terms smallint unsigned default 0, /* signifies which terms user agreed to, should always be > 0 */
mailings smallint unsigned default 0, /* signifies the level of mailings user agreed to, 0 is only essential */

To check it:

mysqlshow hydra -p
Enter password: 
Database: hydra
| Tables |
| users  |
mysqlshow hydra users -p

2.5 Run it to test if it may work

Type: hypdras


You may see:

port is 13214
url is http://tecfa.unige.ch/guides/x3d/ex/hydra/testbed.html
connected to database
Listening on 13214

Note: if you didn't edit the *.c files as told above, you will get

url is http://worlds.webers.org/content/testbed/

From another terminal you also may launch a text client.

./hydrac -d

You may see:

read 4 bytes, messlen is 6
read 6 bytes, messlen is 6
hello yourid=0, mytoken=NA

... though I can't figure out how one could use this to test other things.

2.6 Run it with your own stuff

To test, get the Flux Multi-user test files from media machines and dezip on some webserver.

Then edit files localplane.x3d and testbed.x3d etc. and change from:


to the URL of your Hydra server (not the webserver !)

The try with a Flux Player. E.g. enter a URL like


Note: The hydra URL runs on my desktop and will be mostly down ... So don't bet on the files / server I installed.

If you correctly created the MySQL users table you'll see something like:

./hydras -d
port is 13214
url is http://tecfa.unige.ch/guides/x3d/ex/hydra/testbed.html
connected to database
Listening on 13214
Client connected from on socket 1
read 18 bytes from 1
wrote 6 bytes to 1
Client connected with yourid=1, mytoken=/MM-6-12345678, uid=6
SELECT login_name,avatar FROM users WHERE uid=6
wrote 61 bytes to 1
read 35 bytes from 1
read 35 bytes from 1
read 35 bytes from 1

2.7 Conclusion

I think I got it working somewhat. But the test scene has missing files and is sluggish (even on a good Dell XPS II laptop). I seem to wake up in the middle of an avatar etc. At some point I think I have seen 2 avatars, but it may have been a fatamorgana.

Maybe something to do with client stuff like avatars being identical from 2 different machines or so .... will look at it again at some point. Maybe something not correctly installed.

3 See also

4 Links

Help for installation