Since version 20.04, the server installer supports automated installation mode (autoinstallation for short). You might also know this feature as *unattended*, *hands-off*, or *preseeded* installation.
Autoinstallation lets you answer all those configuration questions ahead of time with an *autoinstall config*, and lets the installation process run without any interaction.
* The format is completely different (cloud-init config, usually YAML, vs. `debconf-set-selections` format).
* When the answer to a question is not present in a preseed, d-i stops and asks the user for input. Autoinstalls are not like this: by default, if there is any autoinstall config at all, the installer takes the default for any unanswered question (and fails if there is no default).
* You can designate particular sections in the config as "interactive", which means the installer will still stop and ask about those.
The autoinstall config is provided via cloud-init configuration, which is almost endlessly flexible. In most scenarios, the easiest way will be to provide user data [via the NoCloud datasource](https://cloudinit.readthedocs.io/en/latest/reference/datasources/nocloud.html).
Even if a fully non-interactive autoinstall config is found, the server installer will ask for confirmation before writing to the disks unless `autoinstall` is present on the kernel command line. This is to make it harder to accidentally create a USB stick that will reformat the machine it is plugged into at boot. Many autoinstalls will be done via netboot, where the kernel command line is controlled by the netboot config -- just remember to put `autoinstall` in there!
When any system is installed using the server installer, an autoinstall file for repeating the install is created at `/var/log/installer/autoinstall-user-data`.
If you have a preseed file already, the [autoinstall-generator snap](https://snapcraft.io/autoinstall-generator) can help translate that preseed data to an autoinstall file. See this discussion on the [autoinstall generator tool](https://discourse.ubuntu.com/t/autoinstall-generator-tool-to-help-with-creation-of-autoinstall-files-based-on-preseed/21334) for more details on how to set this up.
Technically speaking, the config is not defined as a textual format, but cloud-init config is usually provided as YAML so that is the syntax the documentation uses. A minimal config consists of:
Many keys and values correspond straightforwardly to questions the installer asks (e.g. keyboard selection). See the reference for details of those that do not.
Progress through the installer is reported via [the `reporting` system](/t/automated-server-install-reference/16613#reporting), including errors. In addition, when a fatal error occurs, the [`error-commands`](/t/automated-server-install-reference/16613#error-commands) are executed and the traceback printed to the console. The server then just waits.
Cloud-config can be used to deliver the autoinstall data to the installation environment. The [autoinstall quickstart](/t/automated-server-install-quickstart/16614) has an example of [writing the autoinstall config](/t/automated-server-install-quickstart/16614#write-your-autoinstall-config).
Note that autoinstall is processed by Subiquity (not cloud-init), so please direct defects in autoinstall behavior and [bug reports to Subiquity](https://bugs.launchpad.net/subiquity/+filebug).
At install time, the live-server environment is just that: a live but ephemeral copy of Ubuntu Server. This means that cloud-init is present and running in that environment, and existing methods of interacting with cloud-init can be used to configure the live-server ephemeral environment. For example, any #cloud-config user data keys are presented to the live-server containing [`ssh_import_id`]( https://cloudinit.readthedocs.io/en/latest/reference/modules.html#ssh-import-id), then SSH keys will be added to the `authorized_keys` list for the ephemeral environment.
Autoinstall data may optionally contain a [user data sub-section](/t/automated-server-install-reference/16613#user-data), which is cloud-config data that is used to configure the target system on first boot.
Starting with Ubuntu 22.10, once cloud-init has performed this first boot configuration, it will disable itself as cloud-init completes configuration in the target system on first boot.