script using tmutil command not working in cron job

I have a simple shell script that gives me status information about my disks, backups, etc.. It uses the

"tmutil listlocalsnapshots mountpoint" command. When I run this script at the terminal prompt it works as desired, but when I run it via a crob job all I get from the "tmutil listlocalsnapshots mountpoint" is the command's single header line "Snapshots for disk mountpoint:". The rest of the script works fine.

Any idea why this might be?