Disable automatic update checks if booting from a removable device.

main.cc

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <string>
 #include <tr1/memory>
 #include <vector>
 
 #include <gflags/gflags.h>
 #include <glib.h>
@@ skipping 31 matching lines @@
 }
 
 gboolean UpdatePeriodically(void* arg) {
   UpdateAttempter* update_attempter = reinterpret_cast<UpdateAttempter*>(arg);
   update_attempter->Update("", "");
   return TRUE;
 }
 
 void SchedulePeriodicUpdateChecks(UpdateAttempter* update_attempter) {
   if (!utils::IsOfficialBuild()) {
-    LOG(WARNING) << "No periodic update checks on non-official builds.";
+    LOG(WARNING) << "Non-official build: periodic update checks disabled.";
     return;
   }
 
+  if (utils::IsRemovableDevice(utils::RootDevice(utils::BootDevice()))) {
+    LOG(WARNING) << "Removable device boot: periodic update checks disabled.";
+    return;
+  }
+
   // Kick off periodic updating. First, update after 2 minutes. Also, update
   // every 30 minutes.
   g_timeout_add(2 * 60 * 1000, &UpdateOnce, update_attempter);
   g_timeout_add(30 * 60 * 1000, &UpdatePeriodically, update_attempter);
 }
 
 void SetupDbusService(UpdateEngineService* service) {
   DBusGConnection *bus;
   DBusGProxy *proxy;
   GError *error = NULL;
@@ skipping 80 matching lines @@
   g_main_loop_run(loop);
 
   // Cleanup:
   g_main_loop_unref(loop);
   update_attempter.set_dbus_service(NULL);
   g_object_unref(G_OBJECT(service));
 
   LOG(INFO) << "Chrome OS Update Engine terminating";
   return 0;
 }