Here is some additional information about Informix@Ubuntu that I received from Andreas Breitfeld and Alexander Koerner from IBM Munich regarding the Informix Ubuntu packages:

The packages have been build for Ubuntu 8.04 LTS (Long Term Support) and are availabe on the Canoncial Partner repository. The installation could be performed from the command line or through the Synaptic GUI interface.

Command Line:
Activate the Canoncial repository by uncommenting the following to lines in /etc/apt/sources.list:

• deb http://archive.canonical.com/ubuntu hardy partner
• deb-src http://archive.canonical.com/ubuntu hardy partner

Search and Install the Informix packages:

• apt-get update
• apt-cache search informix
• apt-get install

Synaptic GUI:
Activate the Canoncial repository:

• Settings->Repository

Search and Install the Informix packages:

• Reload
• Search informix
• Mark packages for installation
• Apply

Hint for installing on Ubuntu 9.10 (Karmic Koala):

Download and install libstd++5 from:

• http://packages.ubuntu.com/jaunty/i386/libstdc++5/download