Automatically rebooting for kernel updates

I use reboot-notifier on most of my servers to let me know when I need to reboot them for kernel updates since I want to decide exactly when those machines go down. On the other hand, my home backup server has very predictable usage patterns and so I decided to go one step further there and automate these necessary reboots.

To do that, I first installed reboot-notifier which puts the following script in /etc/kernel/postinst.d/reboot-notifier to detect when a new kernel was installed:

#!/bin/sh

if [ "$0" = "/etc/kernel/postinst.d/reboot-notifier" ]; then
    DPKG_MAINTSCRIPT_PACKAGE=linux-base
fi

echo "*** System restart required ***" > /var/run/reboot-required
echo "$DPKG_MAINTSCRIPT_PACKAGE" >> /var/run/reboot-required.pkgs

Note that unattended-upgrades puts a similar script in /etc/kernel/postinst.d/unattended-upgrades:

#!/bin/sh

case "$DPKG_MAINTSCRIPT_PACKAGE::$DPKG_MAINTSCRIPT_NAME" in
   linux-image-extra*::postrm)
      exit 0;;
esac

if [ -d /var/run ]; then
    touch /var/run/reboot-required
    if ! grep -q "^$DPKG_MAINTSCRIPT_PACKAGE$" /var/run/reboot-required.pkgs 2> /dev/null ; then
        echo "$DPKG_MAINTSCRIPT_PACKAGE" >> /var/run/reboot-required.pkgs
    fi
fi

and so you only need one of them to be installed since they both write to /var/run/reboot-required. It doesn't hurt to have both of them though.

Then I created the following cron job (/etc/cron.daily/reboot-local) to actually reboot the server:

#!/bin/bash

REBOOT_REQUIRED=/var/run/reboot-required

if [ -s $REBOOT_REQUIRED ] ; then
    cat "$REBOOT_REQUIRED" | /usr/bin/mail -s "Rebooting $HOSTNAME" root
    /bin/systemctl reboot
fi

With that in place, my server will send me an email and then automatically reboot itself.

This is a work in progress because I'd like to add some checks later on to make sure that no backup is in progress during that time (maybe by looking for active ssh connections?), but it works well enough for now. Feel free to leave a comment if you've got a smarter script you'd like to share.