I have not executed commands with OpenHAB. There is a hint here.
In your rule you could try executeCommandLine("/volume1/homes/openhab/conf/scripts/openhablogs.sh", 10000) Apparently you need to specify how long the script may run.
executeCommandLine("/volume1/homes/openhab/conf/scripts/openhablogs.sh", 10000)
EDIT: More troubleshooting hints. How to solve Exec binding problems