Multiple architectures on Ubuntu

List current main architecture:

> dpkg --print-architecture
amd64

List other architectures that are allowed on this system:

> dpkg --print-foreign-architectures
i386

Modify non-main architectures:

sudo dpkg --add-architecture test
sudo dpkg --remove-architecture test

Specifying the architecture when installing packages:

sudo apt-get install libsdl-image1.2:i386

Foreign architectures will be installed in separate directories. E.g.: /usr/lib/i386-linux-gnu/.

Show all packages with a foreign architecture:

dpkg -l | grep :i386

More info: https://wiki.debian.org/Multiarch/HOWTO