When developing an embedded Linux system, there are a large number of choices available, not just in terms of hardware components, but also software. A Linux system is not just about the kernel, but also the user-space software layer that sits above it. Some of the most commonly chosen options are:

• Custom/Hand-built - in some ways this is probably the most common. It allows the most flexibility, and generally results in the tightest integration. It does however require the most developer effort, and the most on-going maintenance.
• OpenEmbedded - this is a source-based Linux distribution system. In some ways it is a meta-distribution, allowing for your own customised distribution to be made. It requires a reasonable amount of initial setup effort, but once configured additional packages can be trivially added. As its named implies, this system is targeted towards embedded systems, and a lot of effort has been made to ensure it is easy to make small installations using it.
• T2 - this is another meta-distribution, although it is not solely targeted towards the embedded market, or even only Linux. As with OpenEmbedded, it allows for a large amount of flexibility
• EmbeddedUbuntu/ Embedded Fedora/EmDebian - Several of the larger Linux distributions have started to target the embedded market. They have the advantage of a huge existing installation and package base, but also have the disadvantage of a large amount of desktop/server baggage that generally isn't required on an embedded system.

Each of these systems has their own merits, and there is definitely no correct answer for all situations. At Bluewater, we have made the decision to go with a mixture of a custom & OpenEmbedded solution. We start with the BusyBox minimal suite of tools. This provides almost all of the standard Linux command line utilities. Using just BusyBox, and the libraries from the GCC compiler tool chain, we are able to get what we call our minimal root filesystem into around 3MB. This can be shrunk even further by using a smaller C library, and a cut-down selection of BusyBox's utilities. From this base, we then add packages using the OpenEmbedded distribution. These are easily added, and once we have built up our core repository of packages we can easily make custom filesystems for different projects. As with any development system, care must be taken not only to the suitablity of the solution with respect to the product, but also with respect to the developers using it. The wrong choice can result in a nightmarish mix of package versions and build environments, where only the most grand Linux guru can find their way out. The correct choice however results in a system as easy to manage as a desktop PC, where packages can be added and removed trivially, meaning developers are free to choose the packages that best solve their problems, rather than those that are the easiest to install.