How to chang the rubygems and apt source list
Change the rubygems source list
$ gem source --add https://mirrors.ustc.edu.cn/rubygems
$ gem source
*** CURRENT SOURCES ***
http://rubygems.org
https://mirrors.ustc.edu.cn/rubygems/
$ gem source -r http://rubygems.org/
$ gem source
*** CURRENT SOURCES ***
https://mirrors.ustc.edu.cn/rubygems
$ gem source -a http://rubygems.org/
$ gem source
*** CURRENT SOURCES ***
https://mirrors.ustc.edu.cn/rubygems
http://rubygems.org/
Change the apt source list
$ apt edit-sources