debootstrap

debootstrap is a tool used to install a Debian-based base system into a subdirectory of an existing system or into a disk image, without requiring a full installation. It downloads packages from a Debian (or Ubuntu) mirror and unpacks them to create a minimal, working root filesystem that can be used for chroot environments, containers, or image provisioning.

The program builds the target system by fetching the packages that constitute the chosen release and architecture, setting up the appropriate package sources, and performing basic post-installation configuration. It supports multiple architectures and can perform a two-stage bootstrap: a first stage that runs on the host and a second stage that runs inside the target system (using options such as --foreign and --second-stage) for non-native architectures or more complex setups.

Typical uses include creating isolated test environments for package building or testing, provisioning container or virtual machine roots, and assembling disk images for installers or embedded systems. debootstrap can be used directly for simple setups or in combination with other tools such as schroot, systemd-nspawn, LXD, or QEMU to run or manage the resulting root filesystem.

Limitations and considerations: debootstrap does not install a kernel or bootloader by default, so a kernel and boot configuration must be added separately for a bootable system. The resulting environment is a base system that users typically customize on first boot. While it targets Debian-based systems and can bootstrap Ubuntu, some distribution-specific features may require additional steps after bootstrap.