growisofs and cron

Hi. In /etc/cron.weekly i have a script for a weekly backup to DVD. The line to write the DVD is: growisofs -Z /dev/scd0 -r -J $datum where $datum is the directory to write. This line produces an error: FATAL: /dev/scd0 already carries isofs! Actually this is correct, but if I execute the script from the command line, growisofs waits for 5 seconds and overwrites the DVD. This is what I want, but cron stops and does not overwrite. Any help? TIA, Ralf -- Ralf Haueisen ralf.haueisen@pi.uka.de df1iaz@darc.de http://www.qsl.net/df1iaz