外部存储权限被拒绝

Question

我要从服务器下载一个apk并以编程方式安装它。我有两种类型的设备：一种使用Android 6.0.1，另一种使用Android 4.2.2，两者均已扎根。在Android 6.0.1上它可以正常工作，但是在Android 4.2.2上，“ su”命令不起作用，因此我认为我应该使用系统认证（从以下位置收到的platform.pk8和platform.x509.pem）对apk进行签名制造商），我已经完成了。因此，问题是在Android 4.2.2上发现的，当未使用系统证书对apk进行签名时，会下载apk，但是当我对其进行签名并在清单中添加android:sharedUserId="android.uid.system时，会收到下一个错误：

/mnt/sdcard/Download/aaa.apk: open failed: EACCESS(Permission denied). 

我不知道该怎么办...如果apk未签名，则“ su”命令不起作用，如果已签名，我将收到权限被拒绝的错误：

/mnt/sdcard/Download/aaa.apk: open failed: EACCESS(Permission denied)

---

private void downloadApkFromURl(String url) {
            Log.d("TAG", "" + "Started: " + Thread.currentThread().getName());
            try {
                URL url1 = new URL(url);
                final HttpURLConnection c = (HttpURLConnection) url1.openConnection();
                c.connect();

                File sdcard = Environment.getExternalStorageDirectory();
                File myDir = new File(sdcard, "/Download/");
                myDir.mkdirs();
                File outputFile = new File(myDir, "aaa.apk");


                FileOutputStream fos = new FileOutputStream(outputFile);

                final InputStream is = c.getInputStream();

                byte[] buffer = new byte[4096];
                int len1 = 0;
                while ((len1 = is.read(buffer)) != -1) {


                    fos.write(buffer, 0, len1);
                }

                fos.flush();
                fos.close();
                is.close();

                final String command = "pm install -r " + outputFile.getAbsolutePath();

                Process proc = Runtime.getRuntime().exec(new String[]{"su", "-c", command});
                try {
                    proc.waitFor();
                } catch (final InterruptedException e) {
                    sendErrorEvent(e.getMessage());
                    e.printStackTrace();
                }
                PackageManager pm = mContext.getPackageManager();
                boolean isInstalled = isPackageInstalled("com.myPackage.app", pm);
                if (isInstalled) {
                    deleteFileAfterInstall();
                    if (mListener != null) {
                        mListener.onSuccess();
                    }

                    Intent intent = mContext.getPackageManager().getLaunchIntentForPackage("com.myPackage.app");
                    mContext.startActivity(intent);
                } else {
                    sendErrorEvent("App not installed");
                }
            } catch (final ProtocolException e) {
                sendErrorEvent(e.getMessage());
                e.printStackTrace();
            } catch (final IOException e) {
                sendErrorEvent(e.getMessage());
            }

        }

App Manifest文件：

 manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.myPackage.app"
    **android:sharedUserId="android.uid.system**">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />



    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <provider
            android:name="com.myPackage.app.MultiprocessPreferences"
            android:authorities="@string/multiprocess_preferences_authority"
            android:exported="true"
            />

        <service android:name=".ApkDownloaderService"
            android:exported="true"
            />

    </application>