From Koha Wiki
This is the starting point on the journey of running Koha on Ubuntu. Decisions will need to be made and this will affect how you install or upgrade Koha. Let's begin!
The current recommendation for Ubuntu is 12.04 LTS. Only 12.04 and higher are recommended. Using anything less means that the support available may not be sufficient for your needs.
Ubuntu has various editions but for the purposes of running Koha, the recommendation is for the server edition. The desktop edition will also work, but is not recommended for a production environment.
If Ubuntu is already running, and it is prior to Ubuntu 12.04 LTS, please consider an upgrade to the latest LTS version. Running Koha on earlier versions is not supported due to dependency issues.
Not all computers support 64-bit. Some virtualization tools may only support 32-bit based on the host operating system. Determine which version is required and download it from the Ubuntu download website.
In a production system it is recommended that you use the packages install method. It will make administrator's life easier in terms of maintainability.
If you prefer to install from sources (because you maintain some personalizations or because you are developing a patch for Koha) you should stick to install from sources. Using either the official tarball packages or using git to pull the latest Koha source code.