diff --git a/osbase/build/mkimage/main.go b/osbase/build/mkimage/main.go
new file mode 100644
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+++ b/osbase/build/mkimage/main.go
@@ -0,0 +1,106 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+// mkimage is a tool to generate node disk images.
+// It can be used both to initialize block devices and to create image
+// files.
+//
+// The tool takes a path to an EFI payload (--efi), and a path to a
+// system image (--system) as its only required inputs. In
+// addition, an output path must be supplied (--out).
+// Node parameters file path (--node_parameters) may also be supplied, in
+// which case the file will be copied to the EFI system partition.
+// Partition sizes are fixed and may be overridden by command line flags.
+package main
+
+import (
+	"bytes"
+	_ "embed"
+	"flag"
+	"log"
+	"os"
+
+	"source.monogon.dev/osbase/blkio"
+	"source.monogon.dev/osbase/blockdev"
+	"source.monogon.dev/osbase/build/mkimage/osimage"
+)
+
+//go:embed metropolis/node/core/abloader/abloader_bin.efi
+var abloader []byte
+
+func main() {
+	// Fill in the image parameters based on flags.
+	var (
+		efiPayload  string
+		systemImage string
+		nodeParams  string
+		outputPath  string
+		diskUUID    string
+		cfg         osimage.Params
+	)
+	flag.StringVar(&efiPayload, "efi", "", "Path to the UEFI payload used")
+	flag.StringVar(&systemImage, "system", "", "Path to the system partition image used")
+	flag.StringVar(&nodeParams, "node_parameters", "", "Path to Node Parameters to be written to the ESP (default: don't write Node Parameters)")
+	flag.StringVar(&outputPath, "out", "", "Path to the resulting disk image or block device")
+	flag.Int64Var(&cfg.PartitionSize.Data, "data_partition_size", 2048, "Override the data partition size (default 2048 MiB). Used only when generating image files.")
+	flag.Int64Var(&cfg.PartitionSize.ESP, "esp_partition_size", 128, "Override the ESP partition size (default: 128MiB)")
+	flag.Int64Var(&cfg.PartitionSize.System, "system_partition_size", 1024, "Override the System partition size (default: 1024MiB)")
+	flag.StringVar(&diskUUID, "GUID", "", "Disk GUID marked in the resulting image's partition table (default: randomly generated)")
+	flag.Parse()
+
+	// Open the input files for osimage.Create, fill in reader objects and
+	// metadata in osimage.Params.
+	// Start with the EFI Payload the OS will boot from.
+	p, err := blkio.NewFileReader(efiPayload)
+	if err != nil {
+		log.Fatalf("while opening the EFI payload at %q: %v", efiPayload, err)
+	}
+	cfg.EFIPayload = p
+
+	// Attempt to open the system image if its path is set. In case the path
+	// isn't set, the system partition will still be created, but no
+	// contents will be written into it.
+	if systemImage != "" {
+		img, err := os.Open(systemImage)
+		if err != nil {
+			log.Fatalf("while opening the system image at %q: %v", systemImage, err)
+		}
+		defer img.Close()
+		cfg.SystemImage = img
+	}
+
+	// Attempt to open the node parameters file if its path is set.
+	if nodeParams != "" {
+		np, err := blkio.NewFileReader(nodeParams)
+		if err != nil {
+			log.Fatalf("while opening node parameters at %q: %v", nodeParams, err)
+		}
+		cfg.NodeParameters = np
+	}
+
+	// TODO(#254): Build and use dynamically-grown block devices
+	cfg.Output, err = blockdev.CreateFile(outputPath, 512, 10*1024*1024)
+	if err != nil {
+		panic(err)
+	}
+
+	cfg.ABLoader = bytes.NewReader(abloader)
+
+	// Write the parametrized OS image.
+	if _, err := osimage.Write(&cfg); err != nil {
+		log.Fatalf("while creating a Metropolis OS image: %v", err)
+	}
+}