If the /etc/cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the /etc/cron.allow file does not
exist but the /etc/cron.deny file does exist, then you must not be listed in the /etc/cron.deny file in order to use this command. If neither of
these files exists, then depending on site-dependent configuration parameters, only the super user will be allowed to use this command, or all users
will be able to use this command. For standard Debian systems, all users may use this command.
Although cron requires that each entry in a crontab end in a newline character, neither the crontab command nor the cron daemon will detect this
error. Instead, the crontab will appear to load normally. However, the command will never run. The best choice is to ensure that your crontab has a
blank line at the end.