diff --git a/src/cmd/moby/build.go b/src/cmd/moby/build.go
new file mode 100644
index 000000000..d8778e6d1
--- /dev/null
+++ b/src/cmd/moby/build.go
@@ -0,0 +1,133 @@
+package main
+
+import (
+	"archive/tar"
+	"bytes"
+	"errors"
+	"io"
+	"log"
+
+	"github.com/docker/moby/src/initrd"
+)
+
+const (
+	docker2tar = "mobylinux/docker2tar:82a3f11f70b2959c7100dd6e184b511ebfc65908@sha256:e4fd36febc108477a2e5316d263ac257527779409891c7ac10d455a162df05c1"
+)
+
+func untarKernel(buf *bytes.Buffer, bzimageName, ktarName string) (*bytes.Buffer, *bytes.Buffer, error) {
+	tr := tar.NewReader(buf)
+
+	var bzimage, ktar *bytes.Buffer
+
+	for {
+		hdr, err := tr.Next()
+		if err == io.EOF {
+			break
+		}
+		if err != nil {
+			log.Fatalln(err)
+		}
+		switch hdr.Name {
+		case bzimageName:
+			bzimage = new(bytes.Buffer)
+			_, err := io.Copy(bzimage, tr)
+			if err != nil {
+				return nil, nil, err
+			}
+		case ktarName:
+			ktar = new(bytes.Buffer)
+			_, err := io.Copy(bzimage, tr)
+			if err != nil {
+				return nil, nil, err
+			}
+		default:
+			continue
+		}
+	}
+
+	if ktar == nil || bzimage == nil {
+		return nil, nil, errors.New("did not find bzImage and kernel.tar in tarball")
+	}
+
+	return bzimage, ktar, nil
+}
+
+func containersInitrd(containers []*bytes.Buffer) (*bytes.Buffer, error) {
+	w := new(bytes.Buffer)
+	iw := initrd.NewWriter(w)
+	defer iw.Close()
+	for _, file := range containers {
+		_, err := initrd.Copy(iw, file)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return w, nil
+}
+
+func build(m *Moby, name string) {
+	containers := []*bytes.Buffer{}
+
+	// get kernel bzImage and initrd tarball from container
+	// TODO examine contents to see what names they might have
+	const (
+		bzimageName = "bzImage"
+		ktarName    = "kernel.tar"
+	)
+	out, err := dockerRun(m.Kernel.Image, "tar", "cf", "-", bzimageName, ktarName)
+	if err != nil {
+		log.Fatalf("Failed to extract kernel image and tarball: %v", err)
+	}
+	buf := bytes.NewBuffer(out)
+	bzimage, ktar, err := untarKernel(buf, bzimageName, ktarName)
+	if err != nil {
+		log.Fatalf("Could not extract bzImage and kernel filesystem from tarball")
+	}
+	containers = append(containers, ktar)
+
+	// convert init image to tarball
+	init, err := dockerRun("-v", "/var/run/docker.sock:/var/run/docker.sock", docker2tar, m.Init)
+	if err != nil {
+		log.Fatalf("Failed to build init tarball: %v", err)
+	}
+	buffer := bytes.NewBuffer(init)
+	containers = append(containers, buffer)
+
+	for i, image := range m.System {
+		args := ConfigToRun(i, "system", &image)
+		out, err := dockerRun(args...)
+		if err != nil {
+			log.Fatalf("Failed to build container tarball: %v", err)
+		}
+		buffer := bytes.NewBuffer(out)
+		containers = append(containers, buffer)
+	}
+
+	for i, image := range m.Daemon {
+		args := ConfigToRun(i, "daemon", &image)
+		out, err := dockerRun(args...)
+		if err != nil {
+			log.Fatalf("Failed to build container tarball: %v", err)
+		}
+		buffer := bytes.NewBuffer(out)
+		containers = append(containers, buffer)
+	}
+
+	// add files
+	buffer, err = filesystem(m)
+	if err != nil {
+		log.Fatalf("failed to add filesystem parts: %v", err)
+	}
+	containers = append(containers, buffer)
+
+	initrd, err := containersInitrd(containers)
+	if err != nil {
+		log.Fatalf("Failed to make initrd %v", err)
+	}
+
+	err = outputs(m, name, bzimage.Bytes(), initrd.Bytes())
+	if err != nil {
+		log.Fatalf("Error writing outputs: %v", err)
+	}
+}
diff --git a/src/cmd/moby/main.go b/src/cmd/moby/main.go
index ff6c4319a..bcada2d9a 100644
--- a/src/cmd/moby/main.go
+++ b/src/cmd/moby/main.go
@@ -1,8 +1,6 @@
 package main
 
 import (
-	"archive/tar"
-	"bytes"
 	"errors"
 	"flag"
 	"fmt"
@@ -11,12 +9,6 @@ import (
 	"log"
 	"os/exec"
 	"path/filepath"
-
-	"github.com/docker/moby/src/initrd"
-)
-
-const (
-	docker2tar = "mobylinux/docker2tar:82a3f11f70b2959c7100dd6e184b511ebfc65908@sha256:e4fd36febc108477a2e5316d263ac257527779409891c7ac10d455a162df05c1"
 )
 
 func dockerRun(args ...string) ([]byte, error) {
@@ -104,124 +96,6 @@ func dockerRunInput(input io.Reader, args ...string) ([]byte, error) {
 	return stdout, nil
 }
 
-func untarKernel(buf *bytes.Buffer, bzimageName, ktarName string) (*bytes.Buffer, *bytes.Buffer, error) {
-	tr := tar.NewReader(buf)
-
-	var bzimage, ktar *bytes.Buffer
-
-	for {
-		hdr, err := tr.Next()
-		if err == io.EOF {
-			break
-		}
-		if err != nil {
-			log.Fatalln(err)
-		}
-		switch hdr.Name {
-		case bzimageName:
-			bzimage = new(bytes.Buffer)
-			_, err := io.Copy(bzimage, tr)
-			if err != nil {
-				return nil, nil, err
-			}
-		case ktarName:
-			ktar = new(bytes.Buffer)
-			_, err := io.Copy(bzimage, tr)
-			if err != nil {
-				return nil, nil, err
-			}
-		default:
-			continue
-		}
-	}
-
-	if ktar == nil || bzimage == nil {
-		return nil, nil, errors.New("did not find bzImage and kernel.tar in tarball")
-	}
-
-	return bzimage, ktar, nil
-}
-
-func containersInitrd(containers []*bytes.Buffer) (*bytes.Buffer, error) {
-	w := new(bytes.Buffer)
-	iw := initrd.NewWriter(w)
-	defer iw.Close()
-	for _, file := range containers {
-		_, err := initrd.Copy(iw, file)
-		if err != nil {
-			return nil, err
-		}
-	}
-
-	return w, nil
-}
-
-func build(m *Moby, name string) {
-	containers := []*bytes.Buffer{}
-
-	// get kernel bzImage and initrd tarball from container
-	// TODO examine contents to see what names they might have
-	const (
-		bzimageName = "bzImage"
-		ktarName    = "kernel.tar"
-	)
-	out, err := dockerRun(m.Kernel.Image, "tar", "cf", "-", bzimageName, ktarName)
-	if err != nil {
-		log.Fatalf("Failed to extract kernel image and tarball: %v", err)
-	}
-	buf := bytes.NewBuffer(out)
-	bzimage, ktar, err := untarKernel(buf, bzimageName, ktarName)
-	if err != nil {
-		log.Fatalf("Could not extract bzImage and kernel filesystem from tarball")
-	}
-	containers = append(containers, ktar)
-
-	// convert init image to tarball
-	init, err := dockerRun("-v", "/var/run/docker.sock:/var/run/docker.sock", docker2tar, m.Init)
-	if err != nil {
-		log.Fatalf("Failed to build init tarball: %v", err)
-	}
-	buffer := bytes.NewBuffer(init)
-	containers = append(containers, buffer)
-
-	for i, image := range m.System {
-		args := ConfigToRun(i, "system", &image)
-		out, err := dockerRun(args...)
-		if err != nil {
-			log.Fatalf("Failed to build container tarball: %v", err)
-		}
-		buffer := bytes.NewBuffer(out)
-		containers = append(containers, buffer)
-	}
-
-	for i, image := range m.Daemon {
-		args := ConfigToRun(i, "daemon", &image)
-		out, err := dockerRun(args...)
-		if err != nil {
-			log.Fatalf("Failed to build container tarball: %v", err)
-		}
-		buffer := bytes.NewBuffer(out)
-		containers = append(containers, buffer)
-	}
-
-	// add files
-	buffer, err = filesystem(m)
-	if err != nil {
-		log.Fatalf("failed to add filesystem parts: %v", err)
-	}
-	containers = append(containers, buffer)
-
-	initrd, err := containersInitrd(containers)
-	if err != nil {
-		log.Fatalf("Failed to make initrd %v", err)
-	}
-
-	err = outputs(m, name, bzimage.Bytes(), initrd.Bytes())
-	if err != nil {
-		log.Fatalf("Error writing outputs: %v", err)
-	}
-}
-
 var (
 	conf string
 	name string