Here is the message being faced on our x3-8 Exadata (Note that this can happen on any linux system):
[root@ex01db01 etc]# su – oracle
[oracle@ex01db01 ~]$ crontab -l
You (oracle) are not allowed to use this program (crontab)
See crontab(1) for more information
Some MOS note that describe NON-ROOT users having difficulty using crontab:
Non Root Users Are Unable To Create Crontab Entries [ID 1268765.1] Cron Scripts Might Not Be Executed After A Fresh Install On Exadata [ID 1323999.1]
You can execute crontab if your name appears in the file /etc/cron.allow.
If that file does not exist, you can use crontab if your name does not appear in the file /etc/cron.deny.
If only cron.deny exists and is empty, all users can use crontab.
If neither file exists, only the root user can use crontab.
You’ll need to contact your systems administrator unless you have SUDO capabilities to make the file adjustments/modifications.