catalina full disk access

[macports at parvis.nl]

from cron i run a bash job that runs a bash job that runs rsnapshot from an external usb disk to another external usb disk. 
gcp -al (called from rsnapshot) fails with operation not permitted.
it runs fine from ssh from iterm on another mac.

/usr/sbin/cron
/opt/local/bin/bash
/opt/local/bin/rsnapshot
/opt/local/bin/rsync
/opt/local/bin/gcp 
all have full disk access in system preferences.

what can i do?

thanks,
paul.