Preseed

Preseed is a mechanism used to automate the installation of Debian-based operating systems by providing answers to the questions asked by the installer in advance. A preseed file is a plain text configuration that populates debconf selections, enabling unattended or scripted installations across many machines.

During installation, the preseed file is read from a location specified by the boot process, such as a local medium, a URL, or a network share. The installer can be invoked with kernel boot parameters like auto=true and priority=critical to suppress prompts. Typical settings include locale, keyboard layout, time zone, user accounts, partitioning choices, and which software to install. The syntax uses lines beginning with d-i followed by the selection name and the desired value. For example: "d-i debian-installer/locale string en_US.UTF-8" and "d-i passwd/root-password password yourpassword". Additional directives such as "d-i preseed/early_command" or "d-i preseed/late_command" run commands before or after installation.

Usage and scope: Preseeding is common in automated deployments, image creation, and data center operations. It is supported by the Debian installer and by derivatives such as Ubuntu's server installer, and it can be integrated with network boot (PXE), ISO imaging, or cloud-based deployments. It allows fine-grained control over language, locale, disk layout, package selection, and post-install configuration.

Limitations and security: Preseed files may contain sensitive data such as root or user passwords. They must be protected and delivered over trusted networks. If the preseed is accessible, it compromises the installation. Also, preseeding requires compatibility with the installer's debconf questions; changes in newer installer versions may require updating the file. Some environments use alternative automation tools like kickstart or cloud-init depending on the platform.