在AndroidManifest.xml中聲明
android:sharedUserId="android.uid.system"
后，該應用程序將沒有權限讀寫SD卡。
Processes that continue holding open fds on the sdcard a little after it is
requested to be unmounted will be killed so that it can unmount.
We don't want the system process to? be able to access the sdcard to avoid
these kinds of issues (and just general security cleanliness), so that it
does not have permission to access it.
http://groups.google.com/group/android-porting/browse_thread/thread/c6af65d7ddd5eff3http://stackoverflow.com/questions/5617797/android-shared-user-id-and-reading-writing-a-filehttp://stackoverflow.com/questions/6679011/it-cant-access-the-sdcard-after-setting-android-uid-system-in-my-applicationhttp://www.eoeandroid.com/forum.php?mod=viewthread&tid=63314&page=1#pid636737