WEBMATHEMATICA TUTORIAL

Configuring for the X Window System (Linux only)

There are special problems associated with running the Mathematica front end under X from within a web server. This is because, typically, the web server is run as a special account, such as tomcat. This means that when webMathematica runs the front end, it is running as this account. For the front end to operate, it must connect to an X server; this could be achieved by logging into the console of the web server machine with this special account running an X server. There are a few problems with this approach: first, you may not want to leave the machine with an open login on the console; secondly, every time the front end does something, a window will appear on the screen, which may be distracting for someone using the machine.

If a different user logs into the console and runs an X server, the front end (which is run by the special webMathematica account) will not be able to connect to this server at all under the standard authentication system of X. While it is possible to configure the server to allow these connections, it is not satisfactory because webMathematica will be displaying windows on the screen every time it does something with the front end. This topic is discussed in greater length in a later section.

These problems are solved by running a virtual X server, such as Xvnc, as described in the following section. Running a virtual server prevents the windows created by the Mathematica front end from displaying on the screen console of the computer running Mathematica.

Configuring Xvnc and webMathematica

Xvnc is the Linux VNC server. It provides a virtual X server that can be used by applications, such as the Mathematica front end, when it is running for webMathematica. It also provides a VNC server so that a VNC viewer can connect to view and control any applications running in the server. This can be useful since it can help track down problems in running the front end.

Xvnc comes with a number of Linux distributions. It can also be ovtained from RealVNC, http://www.realvnc.com/, and TightVNC, http://www.tightvnc.com.

Install Xvnc

Installation of Xvnc is quite straightforward; you unpack the archive and then copy the relevant files into some local bin directory, for example, /usr/local/bin. (Note that some modern Linux distributions already have Xvnc installed.) Copying of the Xvnc binaries is shown below.

Launch Xvnc

Launching Xvnc is also quite straightforward; this should be done as the user that will be running webMathematica, for example, the user tomcat. The first time Xvnc is launched, it asks for a password. In the example below, the server is launched as display :1.

Test Xvnc

Once it is launched, it is a good idea to test the server by running an application to use it, for example, the Mathematica front end. This is shown below.

Of course, when this is done, you do not see an actual window on your screen; this is because it is a virtual server. To see the window from the Mathematica front end, you can run the vncviewer. This can be done as shown below.

This should show you a screen with the front end window visible. You should be able to type into the front end and see it working. At any time webMathematica is running, you can view the desktop with vncviewer.

Configure webMathematica

The final step is to modify your MSPConfiguration.xml file to instruct the front end to use this server. The setting of FrontEndLaunchFlags is described in the Appendix: Site Configuration. Here is a sample setting that connects to the X server on display :1.

<FrontEndLaunchFlags>
-display :1 -nogui -geometry 1000x500+10+10
</FrontEndLaunchFlags>

Now your Linux server should be ready to run webMathematica.

If you find that the front end does not launch correctly, it may help to add the name of the server in the configuration file. An example is shown below; here, myserver is the name of the machine on which webMathematica and Xvnc are running.

<FrontEndLaunchFlags>
-display myserver:1 -nogui -geometry 1000x500+10+10
</FrontEndLaunchFlags>

Other X Related Issues

The following section describes a number of further issues that relate to using webMathematica in conjunction with an X server. If you have set up an Xvnc server as described above it should not be necessary to study these.

Connecting to the X Server

When the Mathematica front end runs, it must connect to an X server. If the X server is being run by a different user than the user running the front end, the X server will reject the connection, as shown below.

One way to avoid this problem is to allow all connections from the local machine.

This is not a good technique since there is a potential for security problems. These are probably limited since it is only connections from the same machine that are allowed. Another problem is that every time the front end is used, a window will be drawn on the screen, which may be annoying to a user of the system.

A more satisfactory alternative is to run a virtual X server, such as Xvnc.

Xvfb

Xvfb is a virtual frame buffer server described at http://www.xfree86.org/4.3.0/Xvfb.1.html. It can be used as an alternative to Xvnc, but typically we have found Xvnc to be easier to use and provide more functionality.

For Linux, you can download an RPM archive from http://www.redhat.com. After installation, you can launch it as follows (you will probably run this as root).

This command launches Xvfb referencing a font server on port 7100 and adding directories that contain the Mathematica fonts. Note that if you install Mathematica in some alternative location, you should modify these directories. Under some Mathematica installations the location of Mathematica fonts is added to the font server configuration; in this case the Mathematica fonts do not need to be referenced when Xvfb is launched. Xvfb could then be launched as shown here.

In these examples, Xvfb expects to use port 7100 on the local machine for the font server. The actual setting may need to be modified if some alternative configuration of font server is used. For example, under Redhat 6 the font server uses a local Unix socket and Xvfb should be launched as follows.

If you are not running a font server, you may need to launch Xvfb with no font server reference. In this case, it may be necessary to copy the Mathematica fonts into the X distribution layout as described in the section below on manual font installation.

Once you have launched the virtual frame buffer server, you can test that it is running. You will probably run this as root.

Of course, one problem with confirming that the front end is running correctly with this server is that you cannot see it on the screen! This makes it hard to see a dialog box indicating an error. One way to see what the front end is displaying is to inspect a dump of the server with xwd and xwud, which you can do with the following.

This will show what the front end is displaying. For example, if you see a message about not finding the password, you may need to add a pwfile command-line option.

When you are running the virtual frame buffer X server, you will need to modify your MSPConfiguration.xml file to instruct the front end to use this server. The setting of FrontEndLaunchFlags is described in Appendix: Configuration. Here is a sample setting.

<FrontEndLaunchFlags>
-display :1 -nogui -geometry 1000x500+10+10
</FrontEndLaunchFlags>

Manual Font Installation

The front end cannot run without access to the Mathematica fonts. If you notice from the output of the X server with vncviewer or xwd that the front end is displaying a dialog box indicating that it cannot find its fonts, you will have to take some further steps to locate the fonts. One solution that is simple but drastic is to copy the Mathematica fonts into your X distribution.

This is really a poor solution to be avoided if possible. One deficiency is that if you update your copy of Mathematica, you will have to remember to copy the new fonts. The proper solution is to launch Xvfb so it either uses a font server or a font path setting, as described above. Remember that this is not a problem when working under Windows.

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