Add an ethX:X interface definition to /etc/network/interfaces like so:

auto eth0
iface eth0 inet static
        address 10.0.1.5
        netmask 255.255.255.0
        network 10.0.1.0
        broadcast 10.0.1.255
        dns-nameservers 10.0.1.10 10.0.2.10
        post-up route add -host 172.16.31.31 gw 10.0.1.252

auto eth0:1
iface eth0:1 inet static
        address 10.0.1.6
        netmask 255.255.255.128

The example also includes a specific host-route in the 'post-up' line.

Now bring both interface online separately:

sudo ifdown eth0
sudo ifup eth0
sudo ifdown eth0:1
sudo ifup eth0:1

See:
Debian - Networkconfiguration - Multiple IP addresses on one Interface
Ask Ubuntu - Add static route in Ubuntu 14.04 [duplicate]

Updates for older releases are found on <countrycode>.archive.ubuntu.com and security.ubuntu.com but will be removed from there when newer releases are made.

To update an Ubuntu release that has been removed from archive.ubuntu.com and security.ubuntu.com open your /etc/apt/sources.list and replace occurences of archive.ubuntu.com and security.ubuntu.com with:

old-releases.ubuntu.com

Source: Ask Ubuntu: apt-get update for ubuntu 10.04 [on hold]