diff --git a/otautil/Android.bp b/otautil/Android.bp
index 73398c3..871dcae 100644
--- a/otautil/Android.bp
+++ b/otautil/Android.bp
@@ -24,12 +24,16 @@
 
     // Minimal set of files to support host build.
     srcs: [
+        "dirutil.cpp",
         "paths.cpp",
         "rangeset.cpp",
+        "sysutil.cpp",
     ],
 
     shared_libs: [
         "libbase",
+        "libcutils",
+        "libselinux",
     ],
 
     export_include_dirs: [
@@ -39,12 +43,10 @@
     target: {
         android: {
             srcs: [
-                "dirutil.cpp",
                 "logging.cpp",
                 "mounts.cpp",
                 "parse_install_logs.cpp",
                 "roots.cpp",
-                "sysutil.cpp",
                 "thermalutil.cpp",
             ],
 
@@ -57,10 +59,8 @@
             ],
 
             shared_libs: [
-                "libcutils",
                 "libext4_utils",
                 "libfs_mgr",
-                "libselinux",
             ],
 
             export_static_lib_headers: [
diff --git a/tests/Android.bp b/tests/Android.bp
index 67a65ae..4969c08 100644
--- a/tests/Android.bp
+++ b/tests/Android.bp
@@ -108,6 +108,7 @@
     defaults: [
         "recovery_test_defaults",
         "libupdater_defaults",
+        "libupdater_device_defaults",
     ],
 
     test_suites: ["device-tests"],
@@ -121,7 +122,8 @@
         "libfusesideload",
         "libminui",
         "libotautil",
-        "libupdater",
+        "libupdater_device",
+        "libupdater_core",
         "libupdate_verifier",
 
         "libgtest_prod",
diff --git a/updater/Android.bp b/updater/Android.bp
index 72f8bc9..a66155b 100644
--- a/updater/Android.bp
+++ b/updater/Android.bp
@@ -30,7 +30,6 @@
         "libfec",
         "libfec_rs",
         "libverity_tree",
-        "libfs_mgr",
         "libgtest_prod",
         "liblog",
         "liblp",
@@ -46,6 +45,14 @@
         "libcrypto_utils",
         "libcutils",
         "libutils",
+    ],
+}
+
+cc_defaults {
+    name: "libupdater_device_defaults",
+
+    static_libs: [
+        "libfs_mgr",
         "libtune2fs",
 
         "libext2_com_err",
@@ -54,11 +61,13 @@
         "libext2_uuid",
         "libext2_e2p",
         "libext2fs",
-    ],
+    ]
 }
 
 cc_library_static {
-    name: "libupdater",
+    name: "libupdater_core",
+
+    host_supported: true,
 
     defaults: [
         "recovery_defaults",
@@ -68,12 +77,33 @@
     srcs: [
         "blockimg.cpp",
         "commands.cpp",
-        "dynamic_partitions.cpp",
         "install.cpp",
         "updater.cpp",
+    ],
+
+    export_include_dirs: [
+        "include",
+    ],
+}
+
+cc_library_static {
+    name: "libupdater_device",
+
+    defaults: [
+        "recovery_defaults",
+        "libupdater_defaults",
+        "libupdater_device_defaults",
+    ],
+
+    srcs: [
+        "dynamic_partitions.cpp",
         "updater_runtime.cpp",
     ],
 
+    static_libs: [
+        "libupdater_core",
+    ],
+
     include_dirs: [
         "external/e2fsprogs/misc",
     ],
@@ -82,3 +112,26 @@
         "include",
     ],
 }
+
+cc_library_host_static {
+    name: "libupdater_host",
+
+    defaults: [
+        "recovery_defaults",
+        "libupdater_defaults",
+    ],
+
+    srcs: [
+        "simulator_runtime.cpp",
+        "target_files.cpp",
+    ],
+
+    static_libs: [
+        "libupdater_core",
+        "libfstab",
+    ],
+
+    export_include_dirs: [
+        "include",
+    ],
+}
diff --git a/updater/Android.mk b/updater/Android.mk
index 0178239..b8b5e5a 100644
--- a/updater/Android.mk
+++ b/updater/Android.mk
@@ -33,7 +33,6 @@
     libfec \
     libfec_rs \
     libverity_tree \
-    libfs_mgr \
     libgtest_prod \
     liblog \
     liblp \
@@ -48,9 +47,24 @@
     libcrypto \
     libcrypto_utils \
     libcutils \
-    libutils \
-    libtune2fs \
-    $(tune2fs_static_libraries)
+    libutils
+
+
+# Each library in TARGET_RECOVERY_UPDATER_LIBS should have a function
+# named "Register_<libname>()".  Here we emit a little C function that
+# gets #included by updater.cpp.  It calls all those registration
+# functions.
+# $(1): the path to the register.inc file
+# $(2): a list of TARGET_RECOVERY_UPDATER_LIBS
+define generate-register-inc
+    $(hide) mkdir -p $(dir $(1))
+    $(hide) echo "" > $(1)
+    $(hide) $(foreach lib,$(2),echo "extern void Register_$(lib)(void);" >> $(1);)
+    $(hide) echo "void RegisterDeviceExtensions() {" >> $(1)
+    $(hide) $(foreach lib,$(2),echo "  Register_$(lib)();" >> $(1);)
+    $(hide) echo "}" >> $(1)
+endef
+
 
 # updater (static executable)
 # ===============================
@@ -69,33 +83,26 @@
     -Werror
 
 LOCAL_STATIC_LIBRARIES := \
-    libupdater \
+    libupdater_device \
+    libupdater_core \
     $(TARGET_RECOVERY_UPDATER_LIBS) \
     $(TARGET_RECOVERY_UPDATER_EXTRA_LIBS) \
-    $(updater_common_static_libraries)
+    $(updater_common_static_libraries) \
+    libfs_mgr \
+    libtune2fs \
+    $(tune2fs_static_libraries)
 
-# Each library in TARGET_RECOVERY_UPDATER_LIBS should have a function
-# named "Register_<libname>()".  Here we emit a little C function that
-# gets #included by updater.c.  It calls all those registration
-# functions.
+LOCAL_MODULE_CLASS := EXECUTABLES
+inc := $(call local-generated-sources-dir)/register.inc
 
 # Devices can also add libraries to TARGET_RECOVERY_UPDATER_EXTRA_LIBS.
 # These libs are also linked in with updater, but we don't try to call
 # any sort of registration function for these.  Use this variable for
 # any subsidiary static libraries required for your registered
 # extension libs.
-
-LOCAL_MODULE_CLASS := EXECUTABLES
-inc := $(call local-generated-sources-dir)/register.inc
-
 $(inc) : libs := $(TARGET_RECOVERY_UPDATER_LIBS)
 $(inc) :
-	$(hide) mkdir -p $(dir $@)
-	$(hide) echo "" > $@
-	$(hide) $(foreach lib,$(libs),echo "extern void Register_$(lib)(void);" >> $@;)
-	$(hide) echo "void RegisterDeviceExtensions() {" >> $@
-	$(hide) $(foreach lib,$(libs),echo "  Register_$(lib)();" >> $@;)
-	$(hide) echo "}" >> $@
+	$(call generate-register-inc,$@,$(libs))
 
 LOCAL_GENERATED_SOURCES := $(inc)
 
@@ -104,3 +111,41 @@
 LOCAL_FORCE_STATIC_EXECUTABLE := true
 
 include $(BUILD_EXECUTABLE)
+
+
+# update_host_simulator (static executable)
+# ===============================
+include $(CLEAR_VARS)
+
+LOCAL_MODULE := update_host_simulator
+
+LOCAL_SRC_FILES := \
+    update_simulator_main.cpp
+
+LOCAL_C_INCLUDES := \
+    $(LOCAL_PATH)/include
+
+LOCAL_CFLAGS := \
+    -Wall \
+    -Werror
+
+LOCAL_STATIC_LIBRARIES := \
+    libupdater_host \
+    libupdater_core \
+    $(TARGET_RECOVERY_UPDATER_HOST_LIBS) \
+    $(TARGET_RECOVERY_UPDATER_HOST_EXTRA_LIBS) \
+    $(updater_common_static_libraries) \
+    libfstab
+
+LOCAL_MODULE_CLASS := EXECUTABLES
+inc := $(call local-generated-sources-dir)/register.inc
+
+$(inc) : libs := $(TARGET_RECOVERY_UPDATER_HOST_LIBS)
+$(inc) :
+	$(call generate-register-inc,$@,$(libs))
+
+LOCAL_GENERATED_SOURCES := $(inc)
+
+inc :=
+
+include $(BUILD_HOST_EXECUTABLE)
diff --git a/updater/include/updater/simulator_runtime.h b/updater/include/updater/simulator_runtime.h
new file mode 100644
index 0000000..93fa2a4
--- /dev/null
+++ b/updater/include/updater/simulator_runtime.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <map>
+#include <memory>
+#include <string>
+#include <string_view>
+#include <utility>
+#include <vector>
+
+#include "edify/updater_runtime_interface.h"
+#include "updater/target_files.h"
+
+class SimulatorRuntime : public UpdaterRuntimeInterface {
+ public:
+  explicit SimulatorRuntime(TargetFiles* source) : source_(source) {}
+
+  bool IsSimulator() const override {
+    return true;
+  }
+
+  std::string GetProperty(const std::string_view key,
+                          const std::string_view default_value) const override;
+
+  int Mount(const std::string_view location, const std::string_view mount_point,
+            const std::string_view fs_type, const std::string_view mount_options) override;
+  bool IsMounted(const std::string_view mount_point) const override;
+  std::pair<bool, int> Unmount(const std::string_view mount_point) override;
+
+  bool ReadFileToString(const std::string_view filename, std::string* content) const override;
+  bool WriteStringToFile(const std::string_view content,
+                         const std::string_view filename) const override;
+
+  int WipeBlockDevice(const std::string_view filename, size_t len) const override;
+  int RunProgram(const std::vector<std::string>& args, bool is_vfork) const override;
+  int Tune2Fs(const std::vector<std::string>& args) const override;
+
+ private:
+  std::string FindBlockDeviceName(const std::string_view name) const override;
+
+  TargetFiles* source_;
+  std::map<std::string, std::string, std::less<>> mounted_partitions_;
+};
diff --git a/updater/include/updater/target_files.h b/updater/include/updater/target_files.h
new file mode 100644
index 0000000..9ef1a5b
--- /dev/null
+++ b/updater/include/updater/target_files.h
@@ -0,0 +1,36 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#pragma once
+
+#include <string>
+
+// This class parses a given target file for the build properties and image files. Then it creates
+// and maintains the temporary files to simulate the block devices on host.
+class TargetFiles {
+ public:
+  TargetFiles(std::string path, std::string work_dir)
+      : path_(std::move(path)), work_dir_(std::move(work_dir)) {}
+
+  std::string GetProperty(const std::string_view key, const std::string_view default_value) const;
+
+  std::string FindBlockDeviceName(const std::string_view name) const;
+
+ private:
+  std::string path_;  // Path to the target file.
+
+  std::string work_dir_;  // A temporary directory to store the extracted image files
+};
diff --git a/updater/simulator_runtime.cpp b/updater/simulator_runtime.cpp
new file mode 100644
index 0000000..c3b3d95
--- /dev/null
+++ b/updater/simulator_runtime.cpp
@@ -0,0 +1,97 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "updater/simulator_runtime.h"
+
+#include <string.h>
+#include <sys/mount.h>
+#include <sys/stat.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+#include <android-base/properties.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+#include <ext4_utils/wipe.h>
+#include <selinux/label.h>
+
+#include "otautil/mounts.h"
+#include "otautil/sysutil.h"
+
+std::string SimulatorRuntime::GetProperty(const std::string_view key,
+                                          const std::string_view default_value) const {
+  return source_->GetProperty(key, default_value);
+}
+
+int SimulatorRuntime::Mount(const std::string_view location, const std::string_view mount_point,
+                            const std::string_view /* fs_type */,
+                            const std::string_view /* mount_options */) {
+  if (auto mounted_location = mounted_partitions_.find(mount_point);
+      mounted_location != mounted_partitions_.end() && mounted_location->second != location) {
+    LOG(ERROR) << mount_point << " has been mounted at " << mounted_location->second;
+    return -1;
+  }
+
+  mounted_partitions_.emplace(mount_point, location);
+  return 0;
+}
+
+bool SimulatorRuntime::IsMounted(const std::string_view mount_point) const {
+  return mounted_partitions_.find(mount_point) != mounted_partitions_.end();
+}
+
+std::pair<bool, int> SimulatorRuntime::Unmount(const std::string_view mount_point) {
+  if (!IsMounted(mount_point)) {
+    return { false, -1 };
+  }
+
+  mounted_partitions_.erase(std::string(mount_point));
+  return { true, 0 };
+}
+
+std::string SimulatorRuntime::FindBlockDeviceName(const std::string_view name) const {
+  return source_->FindBlockDeviceName(name);
+}
+
+// TODO(xunchang) implement the utility functions in simulator.
+int SimulatorRuntime::RunProgram(const std::vector<std::string>& args, bool /* is_vfork */) const {
+  LOG(INFO) << "Running program with args " << android::base::Join(args, " ");
+  return 0;
+}
+
+int SimulatorRuntime::Tune2Fs(const std::vector<std::string>& args) const {
+  LOG(INFO) << "Running Tune2Fs with args " << android::base::Join(args, " ");
+  return 0;
+}
+
+int SimulatorRuntime::WipeBlockDevice(const std::string_view filename, size_t /* len */) const {
+  LOG(INFO) << "SKip wiping block device " << filename;
+  return 0;
+}
+
+bool SimulatorRuntime::ReadFileToString(const std::string_view filename,
+                                        std::string* /* content */) const {
+  LOG(INFO) << "SKip reading filename " << filename;
+  return true;
+}
+
+bool SimulatorRuntime::WriteStringToFile(const std::string_view content,
+                                         const std::string_view filename) const {
+  LOG(INFO) << "SKip writing " << content.size() << " bytes to file " << filename;
+  return true;
+}
diff --git a/updater/target_files.cpp b/updater/target_files.cpp
new file mode 100644
index 0000000..53671dd
--- /dev/null
+++ b/updater/target_files.cpp
@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include "updater/target_files.h"
+
+std::string TargetFiles::GetProperty(const std::string_view /*key*/,
+                                     const std::string_view default_value) const {
+  return std::string(default_value);
+}
+
+std::string TargetFiles::FindBlockDeviceName(const std::string_view name) const {
+  return std::string(name);
+}
diff --git a/updater/update_simulator_main.cpp b/updater/update_simulator_main.cpp
new file mode 100644
index 0000000..d10453c
--- /dev/null
+++ b/updater/update_simulator_main.cpp
@@ -0,0 +1,76 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * 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.
+ */
+
+#include <string>
+
+#include <android-base/file.h>
+#include <android-base/logging.h>
+
+#include "otautil/error_code.h"
+#include "otautil/paths.h"
+#include "updater/blockimg.h"
+#include "updater/install.h"
+#include "updater/simulator_runtime.h"
+#include "updater/target_files.h"
+#include "updater/updater.h"
+
+int main(int argc, char** argv) {
+  // Write the logs to stdout.
+  android::base::InitLogging(argv, &android::base::StderrLogger);
+
+  if (argc != 3 && argc != 4) {
+    LOG(ERROR) << "unexpected number of arguments: " << argc << std::endl
+               << "Usage: " << argv[0] << " <source_target-file> <ota_package>";
+    return 1;
+  }
+
+  // TODO(xunchang) implement a commandline parser, e.g. it can take an oem property so that the
+  // file_getprop() will return correct value.
+
+  std::string source_target_file = argv[1];
+  std::string package_name = argv[2];
+
+  // Configure edify's functions.
+  RegisterBuiltins();
+  RegisterInstallFunctions();
+  RegisterBlockImageFunctions();
+
+  TemporaryFile temp_saved_source;
+  TemporaryFile temp_last_command;
+  TemporaryDir temp_stash_base;
+
+  Paths::Get().set_cache_temp_source(temp_saved_source.path);
+  Paths::Get().set_last_command_file(temp_last_command.path);
+  Paths::Get().set_stash_directory_base(temp_stash_base.path);
+
+  TemporaryFile cmd_pipe;
+
+  TemporaryDir source_temp_dir;
+  TargetFiles source(source_target_file, source_temp_dir.path);
+
+  Updater updater(std::make_unique<SimulatorRuntime>(&source));
+  if (!updater.Init(cmd_pipe.release(), package_name, false)) {
+    return 1;
+  }
+
+  if (!updater.RunUpdate()) {
+    return 1;
+  }
+
+  LOG(INFO) << "\nscript succeeded, result: " << updater.GetResult();
+
+  return 0;
+}
diff --git a/updater/updater.cpp b/updater/updater.cpp
index 426c6dc..8f4a6ed 100644
--- a/updater/updater.cpp
+++ b/updater/updater.cpp
@@ -175,7 +175,8 @@
   int extract_err = ExtractToMemory(za, &entry, reinterpret_cast<uint8_t*>(&content->at(0)),
                                     entry.uncompressed_length);
   if (extract_err != 0) {
-    LOG(ERROR) << "failed to read script from package: " << ErrorCodeString(extract_err);
+    LOG(ERROR) << "failed to read " << entry_name
+               << " from package: " << ErrorCodeString(extract_err);
     return false;
   }