Do manual man 1 crontab
:
If the /etc/cron.allow file exists, then you must be listed (one user per line)
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.
If both files exist then /etc/cron.allow takes precedence. Which means that
/etc/cron.deny is not considered and your user must be listed in /etc/cron.allow in
order to be able to use the crontab.
Regardless of the existance of any of these files, the root administrative user is
always allowed to setup a crontab. For standard Debian systems, all users may use
this command.
Eu dei um try no Debian 7, e ele está funcionando exatamente desse jeito.