When you try to edit your cronjobs (e.g. crontab -e) on headnodes, you'll get an error. This is on purpose because the access to new login nodes (login-d and login-s) are dynamically routed to servers depending on their load. This means, you may not be able to find the cron you have installed the next time you login to one of these nodes.
Currently only PACE admins can install the cronjobs on behalf of users to ensure consistency. If you need to add (or edit existing) cronjobs, please send firstname.lastname@example.org a request and we'll be happy to help you.