diff --git a/metropolis/node/build/genosrelease/BUILD.bazel b/metropolis/node/build/genosrelease/BUILD.bazel
index bd66e56..bae7f1d 100644
--- a/metropolis/node/build/genosrelease/BUILD.bazel
+++ b/metropolis/node/build/genosrelease/BUILD.bazel
@@ -11,5 +11,5 @@
 go_binary(
     name = "genosrelease",
     embed = [":go_default_library"],
-    visibility = ["//metropolis/node:__pkg__"],
+    visibility = ["//metropolis/node:__subpackages__"],
 )
diff --git a/metropolis/node/installer/BUILD.bazel b/metropolis/node/installer/BUILD.bazel
new file mode 100644
index 0000000..f69ecbe
--- /dev/null
+++ b/metropolis/node/installer/BUILD.bazel
@@ -0,0 +1,47 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+load("//metropolis/node/build:def.bzl", "node_initramfs")
+load("//metropolis/node/build/genosrelease:defs.bzl", "os_release")
+load("//metropolis/node/build:efi.bzl", "efi_unified_kernel_image")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["main.go"],
+    importpath = "source.monogon.dev/metropolis/node/installer",
+    visibility = ["//visibility:private"],
+    deps = [
+        "//metropolis/node/build/mkimage/osimage:go_default_library",
+        "//metropolis/pkg/efivarfs:go_default_library",
+        "//metropolis/pkg/sysfs:go_default_library",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
+
+go_binary(
+    name = "installer",
+    embed = [":go_default_library"],
+    visibility = ["//visibility:private"],
+)
+
+node_initramfs(
+    name = "initramfs",
+    files = {
+        "//metropolis/node/installer": "/init",
+    },
+    visibility = ["//visibility:private"],
+)
+
+os_release(
+    name = "installer-release-info",
+    os_id = "metropolis-installer",
+    os_name = "Metropolis Installer",
+    stamp_var = "STABLE_METROPOLIS_version",
+)
+
+efi_unified_kernel_image(
+    name = "kernel",
+    cmdline = "console=ttyS0",
+    initramfs = ":initramfs",
+    kernel = "//third_party/linux",
+    os_release = ":installer-release-info",
+    visibility = ["//visibility:public"],
+)
diff --git a/metropolis/node/installer/main.go b/metropolis/node/installer/main.go
new file mode 100644
index 0000000..356247a
--- /dev/null
+++ b/metropolis/node/installer/main.go
@@ -0,0 +1,281 @@
+// 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.
+
+// Installer creates a Metropolis image at a suitable block device based on the
+// installer bundle present in the installation medium's ESP, after which it
+// reboots. It's meant to be used as an init process.
+package main
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"path/filepath"
+	"strings"
+	"syscall"
+
+	"golang.org/x/sys/unix"
+	"source.monogon.dev/metropolis/node/build/mkimage/osimage"
+	"source.monogon.dev/metropolis/pkg/efivarfs"
+	"source.monogon.dev/metropolis/pkg/sysfs"
+)
+
+const mib = 1024 * 1024
+
+// mountPseudoFS mounts efivarfs, devtmpfs and sysfs, used by the installer in
+// the block device discovery stage.
+func mountPseudoFS() error {
+	for _, m := range []struct {
+		dir   string
+		fs    string
+		flags uintptr
+	}{
+		{"/sys", "sysfs", unix.MS_NOEXEC | unix.MS_NOSUID | unix.MS_NODEV},
+		{efivarfs.Path, "efivarfs", unix.MS_NOEXEC | unix.MS_NOSUID | unix.MS_NODEV},
+		{"/dev", "devtmpfs", unix.MS_NOEXEC | unix.MS_NOSUID},
+	} {
+		if err := unix.Mkdir(m.dir, 0700); err != nil && !os.IsExist(err) {
+			return fmt.Errorf("couldn't create the mountpoint at %q: %w", m.dir, err)
+		}
+		if err := unix.Mount(m.fs, m.dir, m.fs, m.flags, ""); err != nil {
+			return fmt.Errorf("couldn't mount %q at %q: %w", m.fs, m.dir, err)
+		}
+	}
+	return nil
+}
+
+// mountInstallerESP mounts the filesystem the installer was loaded from based
+// on espPath, which must point to the appropriate partition block device. The
+// filesystem is mounted at /installer.
+func mountInstallerESP(espPath string) error {
+	// Create the mountpoint.
+	if err := unix.Mkdir("/installer", 0700); err != nil {
+		return fmt.Errorf("couldn't create the installer mountpoint: %w", err)
+	}
+	// Mount the filesystem.
+	if err := unix.Mount(espPath, "/installer", "vfat", unix.MS_NOEXEC|unix.MS_RDONLY, ""); err != nil {
+		return fmt.Errorf("couldn't mount the installer ESP (%q -> %q): %w", espPath, "/installer", err)
+	}
+	return nil
+}
+
+// findInstallableBlockDevices returns names of all the block devices suitable
+// for hosting a Metropolis installation, limited by the size expressed in
+// bytes minSize. The install medium espDev will be excluded from the result.
+func findInstallableBlockDevices(espDev string, minSize uint64) ([]string, error) {
+	// Use the partition's name to find and return the name of its parent
+	// device. It will be excluded from the list of suitable target devices.
+	srcDev, err := sysfs.ParentBlockDevice(espDev)
+	// Build the exclusion list containing forbidden handle prefixes.
+	exclude := []string{"dm-", "zram", "ram", "loop", srcDev}
+
+	// Get the block device handles by looking up directory contents.
+	const blkDirPath = "/sys/class/block"
+	blkDevs, err := os.ReadDir(blkDirPath)
+	if err != nil {
+		return nil, fmt.Errorf("couldn't read %q: %w", blkDirPath, err)
+	}
+	// Iterate over the handles, skipping any block device that either points to
+	// a partition, matches the exclusion list, or is smaller than minSize.
+	var suitable []string
+probeLoop:
+	for _, devInfo := range blkDevs {
+		// Skip devices according to the exclusion list.
+		for _, prefix := range exclude {
+			if strings.HasPrefix(devInfo.Name(), prefix) {
+				continue probeLoop
+			}
+		}
+
+		// Skip partition symlinks.
+		if _, err := os.Stat(filepath.Join(blkDirPath, devInfo.Name(), "partition")); err == nil {
+			continue
+		} else if !os.IsNotExist(err) {
+			return nil, fmt.Errorf("while probing sysfs: %w", err)
+		}
+
+		// Skip devices of insufficient size.
+		devPath := filepath.Join("/dev", devInfo.Name())
+		dev, err := os.Open(devPath)
+		if err != nil {
+			return nil, fmt.Errorf("couldn't open a block device at %q: %w", devPath, err)
+		}
+		size, err := unix.IoctlGetInt(int(dev.Fd()), unix.BLKGETSIZE64)
+		dev.Close()
+		if err != nil {
+			return nil, fmt.Errorf("couldn't probe the size of %q: %w", devPath, err)
+		}
+		if uint64(size) < minSize {
+			continue
+		}
+
+		suitable = append(suitable, devInfo.Name())
+	}
+	return suitable, nil
+}
+
+// rereadPartitionTable causes the kernel to read the partition table present
+// in the block device at blkdevPath. It may return an error.
+func rereadPartitionTable(blkdevPath string) error {
+	dev, err := os.Open(blkdevPath)
+	if err != nil {
+		return fmt.Errorf("couldn't open the block device at %q: %w", blkdevPath, err)
+	}
+	defer dev.Close()
+	ret, err := unix.IoctlRetInt(int(dev.Fd()), unix.BLKRRPART)
+	if err != nil {
+		return fmt.Errorf("while doing an ioctl: %w", err)
+	}
+	if syscall.Errno(ret) == unix.EINVAL {
+		return fmt.Errorf("got an EINVAL from BLKRRPART ioctl")
+	}
+	return nil
+}
+
+// initializeSystemPartition writes image contents to the node's system
+// partition using the block device abstraction layer as opposed to slower
+// go-diskfs. tgtBlkdev must contain a path pointing to the block device
+// associated with the system partition. It may return an error.
+func initializeSystemPartition(image io.Reader, tgtBlkdev string) error {
+	// Check that tgtBlkdev points at an actual block device.
+	info, err := os.Stat(tgtBlkdev)
+	if err != nil {
+		return fmt.Errorf("couldn't stat the system partition at %q: %w", tgtBlkdev, err)
+	}
+	if info.Mode()&os.ModeDevice == 0 {
+		return fmt.Errorf("system partition path %q doesn't point to a block device", tgtBlkdev)
+	}
+
+	// Get the system partition's file descriptor.
+	sys, err := os.OpenFile(tgtBlkdev, os.O_WRONLY, 0600)
+	if err != nil {
+		return fmt.Errorf("couldn't open the system partition at %q: %w", tgtBlkdev, err)
+	}
+	defer sys.Close()
+	// Copy the system partition contents. Use a bigger buffer to optimize disk
+	// writes.
+	buf := make([]byte, mib)
+	if _, err := io.CopyBuffer(sys, image, buf); err != nil {
+		return fmt.Errorf("couldn't copy partition contents: %w", err)
+	}
+	return nil
+}
+
+func main() {
+	// Mount sysfs, devtmpfs and efivarfs.
+	if err := mountPseudoFS(); err != nil {
+		log.Fatalf("while mounting pseudo-filesystems: %s", err.Error())
+	}
+	// Read the installer ESP UUID from efivarfs.
+	espUuid, err := efivarfs.ReadLoaderDevicePartUUID()
+	if err != nil {
+		log.Fatalf("while reading the installer ESP UUID: %s", err.Error())
+	}
+	// Look up the installer partition based on espUuid.
+	espDev, err := sysfs.DeviceByPartUUID(espUuid)
+	espPath := filepath.Join("/dev", espDev)
+	if err != nil {
+		log.Fatalf("while resolving the installer device handle: %s", err.Error())
+	}
+	// Mount the installer partition. The installer bundle will be read from it.
+	if err := mountInstallerESP(espPath); err != nil {
+		log.Fatalf("while mounting the installer ESP: %s", err.Error())
+	}
+
+	// Build the osimage parameters.
+	installParams := osimage.Params{
+		PartitionSize: osimage.PartitionSizeInfo{
+			// ESP is the size of the node ESP partition, expressed in mebibytes.
+			ESP: 128,
+			// System is the size of the node system partition, expressed in
+			// mebibytes.
+			System: 4096,
+			// Data must be nonzero in order for the data partition to be created.
+			// osimage will extend the data partition to fill all the available space
+			// whenever it's writing to block devices, such as now.
+			Data: 128,
+		},
+		// Due to a bug in go-diskfs causing slow writes, SystemImage is explicitly
+		// marked unused here, as system partition contents will be written using
+		// a workaround below instead.
+		// TODO(mateusz@monogon.tech): Address that bug either by patching go-diskfs
+		// or rewriting osimage.
+		SystemImage: nil,
+		// TODO(mateusz@monogon.tech): Plug in.
+		EFIPayload:     strings.NewReader("TODO"),
+		NodeParameters: strings.NewReader("TODO"),
+	}
+	// Calculate the minimum target size based on the installation parameters.
+	minSize := uint64((installParams.PartitionSize.ESP +
+		installParams.PartitionSize.System +
+		installParams.PartitionSize.Data + 1) * mib)
+
+	// Look for suitable block devices, given the minimum size.
+	blkDevs, err := findInstallableBlockDevices(espDev, minSize)
+	if err != nil {
+		log.Fatal(err.Error())
+	}
+	if len(blkDevs) == 0 {
+		log.Fatal("couldn't find a suitable block device.")
+	}
+	// Set the first suitable block device found as the installation target.
+	tgtBlkdevName := blkDevs[0]
+	// Update the osimage parameters with a path pointing at the target device.
+	tgtBlkdevPath := filepath.Join("/dev", tgtBlkdevName)
+	installParams.OutputPath = tgtBlkdevPath
+
+	// Use osimage to partition the target block device and set up its ESP.
+	// Create will return an EFI boot entry on success.
+	log.Printf("Installing to %s\n", tgtBlkdevPath)
+	be, err := osimage.Create(&installParams)
+	if err != nil {
+		log.Fatalf("while installing: %s", err.Error())
+	}
+	// The target device's partition table has just been updated. Re-read it to
+	// make the node system partition reachable through /dev.
+	if err := rereadPartitionTable(tgtBlkdevPath); err != nil {
+		log.Fatalf("while re-reading the partition table of %q: %s", tgtBlkdevPath, err.Error())
+	}
+	// Look up the node's system partition path to be later used in the
+	// initialization step. It's always the second partition, right after
+	// the ESP.
+	sysBlkdevName, err := sysfs.PartitionBlockDevice(tgtBlkdevName, 2)
+	if err != nil {
+		log.Fatalf("while looking up the system partition: %s", err.Error())
+	}
+	sysBlkdevPath := filepath.Join("/dev", sysBlkdevName)
+	// Copy the system partition contents.
+	contents := strings.NewReader("TODO") // TODO(mz): plug in
+	if err := initializeSystemPartition(contents, sysBlkdevPath); err != nil {
+		log.Fatalf("while initializing the system partition at %q: %s", sysBlkdevPath, err.Error())
+	}
+
+	// Create an EFI boot entry for Metropolis.
+	en, err := efivarfs.CreateBootEntry(be)
+	if err != nil {
+		log.Fatalf("while creating a boot entry: %s", err.Error())
+	}
+	// Erase the preexisting boot order, leaving Metropolis as the only option.
+	if err := efivarfs.SetBootOrder(&efivarfs.BootOrder{uint16(en)}); err != nil {
+		log.Fatalf("while adjusting the boot order: %s", err.Error())
+	}
+
+	// Reboot.
+	unix.Sync()
+	log.Print("Installation completed. Rebooting.")
+	unix.Reboot(unix.LINUX_REBOOT_CMD_RESTART)
+}