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 oldest supported Ubuntu version is 16.04 LTS. Ubuntu 16.04 includes MySQL 5.7 which defaults to strict mode. And while it can be turned off, this only masks problems that may exist.
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 16.04 LTS, please upgrade to Ubuntu 16.04 LTS. 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.