在 ubuntu 服务器中安装 docker 时出现的问题

Question

sudo apt-get install linux-image-extra-$(uname -r) 
   linux-image-extra-virtual

收到错误

demo@demo:~$ sudo apt-get install linux-image-extra-$(uname -r) linux-image-extra-virtual
Reading package lists... Done
Building dependency tree       
Reading state information... Done
E: Unable to locate package linux-image-extra-4.15.0-29-generic
E: Couldn't find any package by glob 'linux-image-extra-4.15.0-29-generic'
E: Couldn't find any package by regex 'linux-image-extra-4.15.0-29-generic'

为什么我会收到此错误以及如何解决它？