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Base Packages

Base packages are a fixed set of packages that FlatRoot always includes to ensure a functional rootfs. They are added as seed packages before dependency resolution starts.

Per-distribution base packages

Distribution Base packages Mechanism
Debian (dynamic from index) Packages with Essential: yes are scanned from the index and included automatically
Ubuntu (dynamic from index) Same as Debian — uses Essential: yes
Arch Linux filesystem, glibc, bash, coreutils Hardcoded list
CachyOS filesystem, glibc, bash, coreutils Hardcoded list
Alpine Linux musl, busybox, alpine-baselayout, busybox-binsh Hardcoded list
CentOS filesystem, basesystem, bash, coreutils, glibc, glibc-common Hardcoded list
Fedora filesystem, basesystem, bash, coreutils, glibc, glibc-common Hardcoded list
AlmaLinux filesystem, basesystem, bash, coreutils, glibc, glibc-common Hardcoded list
Rocky Linux filesystem, basesystem, bash, coreutils, glibc, glibc-common Hardcoded list
openSUSE filesystem, bash, coreutils, glibc Hardcoded list

Debian Essential packages

Debian and Ubuntu don't use a hardcoded base package list. Instead, certain packages in the repository are marked with Essential: yes in their index entry:

Package: dash
Essential: yes

FlatRoot scans the entire index for this field and adds all Essential packages to the seed list. This typically includes:

  • dash — the default /bin/sh
  • coreutils — basic file/text utilities
  • grep, sed, findutils — text processing
  • base-passwd — /etc/passwd and /etc/group
  • base-files — filesystem structure
  • dpkg — package manager (needed by postinst scripts)
  • libc-bin — dynamic linker configuration

The advantage of this approach is that the base set evolves with the distribution — when Debian adds or removes an Essential package, FlatRoot picks up the change automatically without a code update.

Why base packages matter

Without base packages, the rootfs would contain only the requested package and its hard dependencies. This typically works for the binaries themselves, but the rootfs would be missing:

  • /bin/sh — required by postinst scripts and many applications
  • /etc/passwd, /etc/group — required by applications that look up user/group names
  • The C library (glibc or musl) — implicitly needed by every binary but often not declared as a dependency because it's assumed to be present
  • Basic filesystem structure (/tmp, /var, /etc) — created by filesystem packages
  • Appendix / Packages / Virtual Packages — A virtual package is a name that doesn't correspond to a real package in the repository but is "provided" by one or more real packages. When a package depends on a virtual...
    appendix dependencies
  • Appendix / Dependencies / Alternative Dependencies — An alternative dependency can be satisfied by any one of several packages. The resolver tries each option in order and picks the first that exists and satisfies any version...
    appendix dependencies resolver
  • Appendix / Dependencies / BFS Traversal — Depth-first search (DFS) would also visit every reachable package, but BFS has two properties flatroot relies on:
    appendix dependencies resolver