How to install postgresql on Ubuntu 16.04 VM despite "unmet dependencies" to set up Ruby on Rails project - postgresql

Question

Ubuntu 16.04 on VirtualBox VM using Vagrant.
Windows 10 host.
Git Bash terminal.
Connected to vagrant up, vagrant ssh.
I have a fresh VM and have installed ruby and rails. I am trying to install postgresql to use for a Ruby on Rails project, but I get the following error:
vagrant#vagrant-ubuntu-trusty-64:~$ sudo apt-get install postgresql postgresql-contrib
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
postgresql : Depends: postgresql-9.6 but it is not going to be installed
postgresql-contrib : Depends: postgresql-contrib-9.6 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
I've tried various things, and nothing seems to let me install postgres

Answer 1

I was facing same problem in my ubuntu 16.04
but i fixed that problem and it's very simple just follow these step and you will be able to install postgresql 10 in your system :
Add this to your sources.list:
sudo vim /etc/apt/sources.list
deb http://ftp.de.debian.org/debian/ wheezy main non-free contrib
deb-src http://ftp.de.debian.org/debian/ wheezy main non-free contrib
after that add these link to your pgdg.list file if it's not there you have to create and add link and save it.
sudo vim /etc/apt/sources.list.d/pgdg.list
deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main
deb http://apt.postgresql.org/pub/repos/apt/ precise-pgdg main
then update your system
sudo apt-get update
sudo apt-get upgrade
and install that unmet dependencies :
apt-get install ssl-cert
that's it. now Install postgresql using these command
sudo apt-get install postgresql-10

Answer 2

#JosMac pointed out that I am running Ubuntu 14.04 instead of 16.04 as I had thought.
I was still running into similar errors, but I just ended up installing the rails-dev-box (https://github.com/rails/rails-dev-box) way which uses yakkety64, and seems to work.