10.1 Named Roots
An installation root is a self-contained filesystem tree with its own package database. The default root is the system root — the anchor. A system may define others; the motivating case is an initramfs image, built and maintained alongside the main system through the same package graph.
A package names a root, never a filesystem location. Where a root lives is the installing system's business, which is what makes a tree relocatable and what stops a package dictating layout.
10.1.1 The grammar #
A root reference is one or more segments joined by ., each matching
[a-z0-9][a-z0-9_-]*. Any reference containing / is rejected as a
reference.
The grammar is implemented three times — in the manifest decoder, in the
command-line parser, and in the producer toolchain — and all three
agree, all three reject a /.
10.1.2 Nesting is structural #
There is no parent field anywhere. A root's registry lives in that
root's own database, so nesting falls out of where the registration is
recorded: initramfs.subroot is resolved by reading the anchor's
database for initramfs, then reading that root's database for
subroot.
Registered paths are stored relative to the owning root, which is the other half of relocatability.