diff --git a/common/subprocess.h b/common/subprocess.h
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--- /dev/null
+++ b/common/subprocess.h
@@ -0,0 +1,141 @@
+//
+// Copyright (C) 2011 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.
+//
+
+#ifndef UPDATE_ENGINE_COMMON_SUBPROCESS_H_
+#define UPDATE_ENGINE_COMMON_SUBPROCESS_H_
+
+#include <unistd.h>
+
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+#include <base/callback.h>
+#include <base/logging.h>
+#include <base/macros.h>
+#include <brillo/asynchronous_signal_handler_interface.h>
+#include <brillo/message_loops/message_loop.h>
+#include <brillo/process.h>
+#include <brillo/process_reaper.h>
+#include <gtest/gtest_prod.h>  // for FRIEND_TEST
+
+// The Subprocess class is a singleton. It's used to spawn off a subprocess
+// and get notified when the subprocess exits. The result of Exec() can
+// be saved and used to cancel the callback request and kill your process. If
+// you know you won't call KillExec(), you may safely lose the return value
+// from Exec().
+
+// To create the Subprocess singleton just instantiate it with and call Init().
+// You can't have two Subprocess instances initialized at the same time.
+
+namespace chromeos_update_engine {
+
+class Subprocess {
+ public:
+  enum Flags {
+    kSearchPath = 1 << 0,
+    kRedirectStderrToStdout = 1 << 1,
+  };
+
+  // Callback type used when an async process terminates. It receives the exit
+  // code and the stdout output (and stderr if redirected).
+  using ExecCallback = base::Callback<void(int, const std::string&)>;
+
+  Subprocess() = default;
+
+  // Destroy and unregister the Subprocess singleton.
+  ~Subprocess();
+
+  // Initialize and register the Subprocess singleton.
+  void Init(brillo::AsynchronousSignalHandlerInterface* async_signal_handler);
+
+  // Launches a process in the background and calls the passed |callback| when
+  // the process exits.
+  // Returns the process id of the new launched process or 0 in case of failure.
+  pid_t Exec(const std::vector<std::string>& cmd, const ExecCallback& callback);
+  pid_t ExecFlags(const std::vector<std::string>& cmd,
+                  uint32_t flags,
+                  const ExecCallback& callback);
+
+  // Kills the running process with SIGTERM and ignores the callback.
+  void KillExec(pid_t tag);
+
+  // Executes a command synchronously. Returns true on success. If |stdout| is
+  // non-null, the process output is stored in it, otherwise the output is
+  // logged. Note that stderr is redirected to stdout.
+  static bool SynchronousExec(const std::vector<std::string>& cmd,
+                              int* return_code,
+                              std::string* stdout);
+  static bool SynchronousExecFlags(const std::vector<std::string>& cmd,
+                                   uint32_t flags,
+                                   int* return_code,
+                                   std::string* stdout);
+
+  // Gets the one instance.
+  static Subprocess& Get() {
+    return *subprocess_singleton_;
+  }
+
+  // Returns true iff there is at least one subprocess we're waiting on.
+  bool SubprocessInFlight();
+
+ private:
+  FRIEND_TEST(SubprocessTest, CancelTest);
+
+  struct SubprocessRecord {
+    explicit SubprocessRecord(const ExecCallback& callback)
+      : callback(callback) {}
+
+    // The callback supplied by the caller.
+    ExecCallback callback;
+
+    // The ProcessImpl instance managing the child process. Destroying this
+    // will close our end of the pipes we have open.
+    brillo::ProcessImpl proc;
+
+    // These are used to monitor the stdout of the running process, including
+    // the stderr if it was redirected.
+    brillo::MessageLoop::TaskId stdout_task_id{
+        brillo::MessageLoop::kTaskIdNull};
+    int stdout_fd{-1};
+    std::string stdout;
+  };
+
+  // Callback which runs whenever there is input available on the subprocess
+  // stdout pipe.
+  static void OnStdoutReady(SubprocessRecord* record);
+
+  // Callback for when any subprocess terminates. This calls the user
+  // requested callback.
+  void ChildExitedCallback(const siginfo_t& info);
+
+  // The global instance.
+  static Subprocess* subprocess_singleton_;
+
+  // A map from the asynchronous subprocess tag (see Exec) to the subprocess
+  // record structure for all active asynchronous subprocesses.
+  std::map<pid_t, std::unique_ptr<SubprocessRecord>> subprocess_records_;
+
+  // Used to watch for child processes.
+  brillo::ProcessReaper process_reaper_;
+
+  DISALLOW_COPY_AND_ASSIGN(Subprocess);
+};
+
+}  // namespace chromeos_update_engine
+
+#endif  // UPDATE_ENGINE_COMMON_SUBPROCESS_H_