# 2.4 peipkg-compose

_Peios / Advanced Peios / peipkg / The Tools_

> Assembling an image without installing anything onto the building machine, sharing peipkg's resolver and archive reader.

`peipkg-compose` builds a filesystem tree from packages, without
installing anything onto the machine doing the building. It is how an
image is assembled.

It shares peipkg's resolver, its archive reader, its claim logic, and
its package database schema. What it does not share is the runtime: it
has no transaction journal to recover, no lock to hold against a running
system, and no operator sitting in front of it.

Composition runs in two phases, and they can be run separately.

**Resolve** performs the full repository trust ceremony, resolves the
requested package set against the configured repositories' indexes, and
writes a **lock**: the pinned closure, with each package's URL and hash.

**Build** reads the lock, fetches each package, checks its bytes against
the hash the lock recorded, and assembles the tree — extracting payload,
materialising claim links, and seeding a package database so that the
resulting image knows what it contains.

Chapter 10 describes composition in detail, including what it does not
do that an installed system's peipkg would.