Ubuntu Server 设置Emacs为默认编辑器方法很简单，用update-alternatives命令。
update-alternatives --config editor
There are 5 choices for the alternative editor (providing /usr/bin/editor).
Selection Path Priority Status
------------------------------------------------------------
* 0 /bin/nano 40 auto mode
1 /bin/ed -100 manual mode
2 /bin/nano 40 manual mode
3 /usr/bin/emacs23 0 manual mode
4 /usr/bin/vim.basic 30 manual mode
5 /usr/bin/vim.tiny 10 manual mode
Press enter to keep the current choice[*], or type selection number: 3
update-alternatives: using /usr/bin/emacs23 to provide /usr/bin/editor (editor) in manual mode.