If you run this:

/usr/lib/update-notifier/update-motd-updates-available

You will get the output regarding available updates in Ubuntu similar to the following

130 packages can be updated.
92 updates are security updates.

Ubuntu Version that I tried this on:

lsb_release -a

#output of lsb_release
Distributor ID: Ubuntu
Description: Ubuntu 14.04.5 LTS
Release: 14.04
Codename: trusty