Server installer or pre-installed images?¶
The classic Ubuntu Server images for SBCs can be roughly divided into two types:
Pre-installed images which are written directly to their final target media
Installer images which are written to some installation media, booted on the target machine, and which then copy themselves to the final target media
Which you should choose depends on which board you have, and your particular needs for the eventual system. In some cases, the choice is limited. Notably, we currently only distribute pre-installed images for the Raspberry Pi series of boards (the general arm64 live server images do not boot on the Raspberry Pi).
Hardware requirements¶
The installer images necessarily require that you have two machines, one to generate the installation media (commonly a PC), and the target SBC to run the installer (assuming that the target SBC has no existing OS). It naturally follows that you need two drives: the installer drive (commonly a USB stick or SD card), and the final target media (often an SSD or NVMe drive).
The pre-installed images may require two machines. Certain boards, notably the later models of the Raspberry Pi, are capable of flashing pre-installed images to local media from their bootloader. Regardless, the pre-installed images typically only require one piece of target media (commonly an SD card), and thus have simpler initial requirements.
Storage flexibility¶
By their nature, the pre-installed images dictate the partition layout that the eventual system will have. Beyond selecting the type and size of your target media, you will have no option to customize the number or layout of partitions, and the selection of file-systems is essentially fixed.
Note
One notable exception here is that btrfs does include a tool to convert an ext4 partition in-place. If you would prefer a btrfs root file-system, it is usually possible to convert a pre-installed image to btrfs before booting it for the first time.
Installer images, via the subiquity installer, have the option to configure their storage including partition size, type, and file-system format selection.
Automated installation¶
The installer images provide an auto-install facility that can be used to automate the configuration of the new server, including user creation, package installation, and storage layout.
The pre-installed images also provide an automated setup facility via the cloud-init service. Barring storage layout, which is essentially fixed in pre-installed images, this provides as much flexibility in the configuration of users (Users and Groups module), package installation (Package Update Upgrade Install module), network configuration (Networking config Version 2), and more.
Note
Cloud-init does provide storage layout facilities via the Disk Setup module, but this is intended for specific cloud services where such things can be configured by the container or VM.
In short, both image types offer considerable flexibility for automated installation, so this shouldn’t be a limiting factor in your selection.