Linux Kernel Stuff
Ubuntu Hardy 64bit kernels
Our Hardy based Brightboxes are 32bit but the kernels are 64bit. The 64bit kernel is faster and more stable when virtualized, and the 32bit userland lets us be more efficient with RAM. This does limit each process' ram to 4gig, but this is usually fine for most web applications. (our MySQL systems are 64bit userland to allow higher ram addressing).
Some 3rd party programs, such as the Fiveruns client, may incorrectly detect the box as 64bit. You need to force these programs to install as 32bit.
Extra kernel modules
We load most common kernel modules on boot, but if you need to load extra kernel modules (for example, the ipsec vpn modules) you need to install the 64bit kernel package. Installing a 64bit kernel package in a 32bit userland can't be done via apt:
wget http://launchpadlibrarian.net/21747344/linux-image-2.6.24-23-xen_2.6.24-23.48_amd64.deb sudo dpkg --force-architecture -i linux-image-2.6.24-23-xen_2.6.24-23.48_amd64.deb