Here's what I did on Debian Jessie:install cron via apt-get install cronput a backup_crontab file in /etc/cron.d/However the task is never running.Here are some outputs:/# crontab -lno crontab for root/# cd /etc/cron.d && lsbackup_crontab/etc/cron.d# cat backup_crontab0,15,30,45 * * * * /backup.sh >/dev/null 2>&1Is there something to do to activate a particular crontab, or to activate the cron service in itself?
Crontab never running while in /etc/cron.d
debian;cron
Files in /etc/cron.d need to also list the user that the job is to be run under.i.e.0,15,30,45 * * * * root /backup.sh >/dev/null 2>&1You should also ensure the permissions and owner:group are set correctly (-rw-r--r-- and owned by root:root)