为什么gradle会抱怨Android SDK是只读的？

Question

通过gradle包装器(不涉及Android Studio)在CLI中构建apk,Gradle似乎抱怨SDK是只读的.

我的问题是2倍,真的:

1. 为什么要对SDK进行写访问？
2. 如果它肯定需要写权限,那么SDK的哪个部分？

我不想让SDK世界可写(实际上甚至用户也不可写)

Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-15/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-16/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-17/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-18/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-19/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-21/package.xml. Probably the SDK is read-only
Exception while marshalling /opt/android-dev/android-sdk-linux/add-ons/addon-google_apis-google-22/package.xml. Probably the SDK is read-only