The system can automatically install updates. If you want this, install unattended-upgrades package.vYou never miss a security update.

aptitude install unattended-upgrades

You must edit this file. Make a reconfiguration and select yes.

vi /etc/apt/apt.conf.d/50unattended-upgrades

....
Unattended-Upgrade::Allowed-Origins {
	"${distro_id}:${distro_codename}-security";
	"${distro_id}:${distro_codename}-updates";
	"${distro_id}:${distro_codename}-proposed";
	"${distro_id}:${distro_codename}-backports";
};
....

dpkg-reconfigure unattended-upgrades