I just got my backup to exceed the 500MB by running the tar command as root. Try adding su root -c to your tar command. It should look like this: su root -c "tar -zcvf $local_backup_dir/01/$backup_full_file_name -C /opt/backup/tmp zimbra >> $log_file_name_local_path" Let me know if it worked for you. Make sure you use the quotes. After testing it again, it only created a 500MB file.