Excel Emitter error in UNIX box

Hello Community,

Since integration of BIRT 2.6, it has been fairly easy to generate large excel reports. By mentioning large I mean to say such reports which has more than 64k rows.
I tried this in a Windows box and it was working all well.

But, the same code when ported to a UNIX box, it fails because of some permission issue. The stack trace is as follows:

Dec 29, 2010 9:25:16 AM org.eclipse.birt.report.engine.emitter.excel.ExcelEmitter outputSheet

SEVERE: /tmp_BIRTEMITTER_EXCEL_TEMP_FILE27 (Permission denied)

java.io.FileNotFoundException: /tmp_BIRTEMITTER_EXCEL_TEMP_FILE27 (Permission denied)

        at java.io.FileOutputStream.open(Native Method)

        at java.io.FileOutputStream.<init>(FileOutputStream.java:179)

        at java.io.FileOutputStream.<init>(FileOutputStream.java:70)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelWriter.initializeWriterAsTempWriter(ExcelWriter.java:166)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelWriter.startSheet(ExcelWriter.java:151)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelEmitter.outputCacheData(ExcelEmitter.java:543)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelEmitter.outputSheet(ExcelEmitter.java:502)

        at org.eclipse.birt.report.engine.emitter.excel.layout.ExcelLayoutEngine.outputDataIfBufferIsFull(ExcelLayoutEngine.java:1050)

        at org.eclipse.birt.report.engine.emitter.excel.layout.ExcelLayoutEngine.addData(ExcelLayoutEngine.java:933)

        at org.eclipse.birt.report.engine.emitter.excel.layout.ExcelLayoutEngine.addData(ExcelLayoutEngine.java:665)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelEmitter.addDataContent(ExcelEmitter.java:433)

        at org.eclipse.birt.report.engine.emitter.excel.ExcelEmitter.startData(ExcelEmitter.java:390)

        at org.eclipse.birt.report.engine.emitter.CompositeContentEmitter.startData(CompositeContentEmitter.java:258)

        at org.eclipse.birt.report.engine.emitter.ContentEmitterUtil.startContent(ContentEmitterUtil.java:71)

        at org.eclipse.birt.report.engine.layout.html.HTMLTableLayoutEmitter.startContent(HTMLTableLayoutEmitter.java:146)

        at org.eclipse.birt.report.engine.emitter.ContentEmitterAdapter.startText(ContentEmitterAdapter.java:147)

        at org.eclipse.birt.report.engine.emitter.ContentEmitterAdapter.startData(ContentEmitterAdapter.java:163)

        at org.eclipse.birt.report.engine.emitter.ContentEmitterUtil.startContent(ContentEmitterUtil.java:71)

        at org.eclipse.birt.report.engine.layout.html.buffer.DummyPageBuffer.startContent(DummyPageBuffer.java:125)

        at org.eclipse.birt.report.engine.layout.html.HTMLLeafItemLM.start(HTMLLeafItemLM.java:67)

        at org.eclipse.birt.report.engine.layout.html.HTMLAbstractLM.layout(HTMLAbstractLM.java:139)

        at org.eclipse.birt.report.engine.layout.html.HTMLBlockStackingLM.layoutNodes(HTMLBlockStackingLM.java:70)

        at org.eclipse.birt.report.engine.layout.html.HTMLStackingLM.layoutChildren(HTMLStackingLM.java:26)

        at org.eclipse.birt.report.engine.layout.html.HTMLAbstractLM.layout(HTMLAbstractLM.java:140)

        at org.eclipse.birt.report.engine.layout.html.HTMLInlineStackingLM.resumeLayout(HTMLInlineStackingLM.java:111)

        at org.eclipse.birt.report.engine.layout.html.HTMLInlineStackingLM.layoutNodes(HTMLInlineStackingLM.java:160)

        at org.eclipse.birt.report.engine.layout.html.HTMLStackingLM.layoutChildren(HTMLStackingLM.java:26)

        at org.eclipse.birt.report.engine.layout.html.HTMLAbstractLM.layout(HTMLAbstractLM.java:140)

        at org.eclipse.birt.report.engine.layout.html.HTMLBlockStackingLM.layoutNodes(HTMLBlockStackingLM.java:70)

        at org.eclipse.birt.report.engine.layout.html.HTMLStackingLM.layoutChildren(HTMLStackingLM.java:26)

        at org.eclipse.birt.report.engine.layout.html.HTMLTableBandLM.layoutChildren(HTMLTableBandLM.java:67)

        at org.eclipse.birt.report.engine.layout.html.HTMLAbstractLM.layout(HTMLAbstractLM.java:140)

        at org.eclipse.birt.report.engine.layout.html.HTMLBlockStackingLM.layoutNodes(HTMLBlockStackingLM.java:70)

        at org.eclipse.birt.report.engine.layout.html.HTMLStackingLM.layoutChildren(HTMLStackingLM.java:26)

        at org.eclipse.birt.report.engine.layout.html.HTMLTableLM.layoutChildren(HTMLTableLM.java:132)

        at org.eclipse.birt.report.engine.layout.html.HTMLAbstractLM.layout(HTMLAbstractLM.java:140)

        at org.eclipse.birt.report.engine.layout.html.HTMLBlockStackingLM.layoutNodes(HTMLBlockStackingLM.java:70)

        at org.eclipse.birt.report.engine.layout.html.HTMLPageLM.layout(HTMLPageLM.java:90)

        at org.eclipse.birt.report.engine.layout.html.HTMLReportLayoutEngine.layout(HTMLReportLayoutEngine.java:99)

        at org.eclipse.birt.report.engine.api.impl.RunAndRenderTask.doRun(RunAndRenderTask.java:172)

        at org.eclipse.birt.report.engine.api.impl.RunAndRenderTask.run(RunAndRenderTask.java:75)

By pondering on the exception I have figured out the possible reason to be the lacking permission in '/' directory.

Now a few things that I don't have any idea are:
1) Why is the '/' considered as temp, it could have been '/tmp'
2) Is there any way that I can override this feature and assign a different temp directory
3) The code snippet to start the engine follows, is there anything else that can be done here

URL url = RunBillTask.class.getResource( taskParameters.getDesignFileName() );
        if ( url == null )
            throw new RunBillTaskException( "Cannot find file " + taskParameters.getDesignFileName() );

        // Get the complete file name
        String strRptDesign = url.getFile();

        IReportEngine engine = null;
        String strOutputFileName = "";
        try
        {
            EngineConfig config = new EngineConfig();

            String birtHome;

            birtHome = System.getenv( "BIRT_HOME" );

            if ( birtHome == null )
                throw new BillException( "BIRT_HOME not set in system properties" );

            config.setEngineHome( birtHome );
            config.setLogConfig( FileHelper.sparkTempPath, Level.FINE );

            Platform.startup( config );
            IReportEngineFactory factory = (IReportEngineFactory)Platform.createFactoryObject( IReportEngineFactory.EXTENSION_REPORT_ENGINE_FACTORY );
            engine = factory.createReportEngine( config );
            engine.changeLogLevel( Level.SEVERE );

            // Open a report design
            IReportRunnable design;

            design = engine.openReportDesign( strRptDesign );

            // Create task to run the report - use the task to execute the
            // report and save to disk.
            IRunAndRenderTask task = engine.createRunAndRenderTask( design );
          
            RenderOption options = null;
            if(taskParameters.getExtension().equals(PDF_EXTENSION))
            {
        	options = new PDFRenderOption();
            }
            else if(taskParameters.getExtension().equals(EXCEL_EXTENSION))
            {
        	options = new EXCELRenderOption(); 
        	((EXCELRenderOption)options).setWrappingText(true);
            }

            strOutputFileName = FileHelper.sparkTempPathFile + "/" + taskParameters.getOutputFileName() + "." + taskParameters.getExtension();

            options.setOutputFileName( strOutputFileName );
            options.setOutputFormat( taskParameters.getExtension() );
            task.setRenderOption( options );

            // Supply the input parameters
            for ( ParameterMap< Integer > parameter : taskParameters.getIntParameterList() )
            {
                task.setParameterValue( parameter.key, parameter.value );
            }

            for ( ParameterMap< String > parameter : taskParameters.getStrParameterList() )
            {
                task.setParameterValue( parameter.key, parameter.value );
            }

            for ( ParameterMap< Boolean > parameter : taskParameters.getBoolParameterList() )
            {
                task.setParameterValue( parameter.key, parameter.value );
            }
            
            for ( ParameterMap< Double > parameter : taskParameters.getDecimalParameterList() )
            {
                task.setParameterValue( parameter.key, parameter.value );
            }
            
            for ( ParameterMap< Float > parameter : taskParameters.getFloatParameterList() )
            {
                task.setParameterValue( parameter.key, parameter.value );
            }

            // run the report and destroy the engine
            task.run();

            task.close();

Need help ASAP!!!

regards
Arpan