Sometimes you need to write a debug log when developing flex. The best way to do that in linux is first configure your ~/mm.cfg file with the following:

ErrorReportingEnable=1 TraceOutputFileEnable=1

Then either use the flash player debug plugin or use the standalone debug player. I prefer the standalone because I can launch it from the command line right after a successful mxmlc compile. Both are in the tar file here

The log will by default be written at ~/.macromedia/Flash_Player/Logs/flashlog.txt And no this is current as of 2008-9-11, well after the macromedia/adobe merge. Adobe just hasnt bothered changing the path yet.