One of the packages that got lost in the transition from Debian wheezy to jessie was the update-notifier-common package which could be used to receive notifications when a reboot is needed (for example, after installing a kernel update).

I decided to wrap this piece of functionality along with a simple cron job and create a new package: reboot-notifier.

Because it uses the same file (/var/run/reboot-required) to indicate that a reboot is needed, it should work fine with any custom scripts that admins might have written prior to jessie.

If you're running sid or strech, all you need to do is:

apt install reboot-notifier

On jessie, you'll need to add the backports repository to /etc/apt/sources.list:

deb jessie-backports main