Crontab Permissions
There are two files that control the permissions for crontab: /etc/cron.allow and /etc/cron.deny. If there is a cron.allow file, then the user or users that need to use cron will need to be listed in the file. You can use cron.deny to explicitly disallow certain users from using cron.
If neither files exist, then only the super user is allowed to run cron.
Well, that depends on the system specific configuration to be exact. Most configuration do not allow any users to run jobs, while some systems allow all users to run jobs by default.