对apt-get进行任何操作都会报错：
pi@raspberrypi:~ $ sudo apt-get upgrade
Reading package lists... Done
E: The value ‘\stable‘ is invalid for APT::Default-Release as such a release is not available in the sources
解决方法：把/etc/apt/apt.conf.d/10defaultRelease这个文件删了。
树莓派apt-get The value '\stable' is invalid for APT 错误
原文：https://www.cnblogs.com/shawn-meng/p/9218444.html