sudo apt install raspberrypi-kernel-headers得到错误E: Unable to locate package

在树莓派上尝试运行sudo apt install raspberrypi-kernel-headers得到以下错误提示

pi@raspberrypi:~ $ sudo apt install raspberrypi-kernel-headers
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package raspberrypi-kernel-headers

最终问题定位还是跟apt source有关，主要原因是之前把apt source更换为国内镜像时，按照某些网上的指引，把/etc/source/source.list.d/raspi.list这个文件重命名了，而这个文件里面有个很重要的源，正是跟raspberrypi-kernel-headers有关的，于是把/etc/source/source.list.d/raspi.list恢复回来，然后把里面的http链接改为https，内容如下：

deb https://archive.raspberrypi.org/debian/ stretch main ui
# Uncomment line below then 'apt-get update' to enable 'apt-get source'
deb-src https://archive.raspberrypi.org/debian/ stretch main ui

修改apt源后按照惯例运行sudo apt-get update，然后再次运行sudo apt install raspberrypi-kernel-headers就可以看到让人舒适的结果：

pi@raspberrypi:~ $ sudo apt-get install raspberrypi-kernel-headers
Reading pac