Getting unknown command error when trying to run script via cron
cron uses /usr/bin:/bin as the default PATH and diskutil is in /usr/sbin.

Specify the full path to diskutil or add a line like PATH=/usr/bin:/bin:/usr/sbin:/sbin to the start of your crontab.

Enter which diskutil to find its path, or enter echo $PATH to find the path where your commands are working.