Debian comes with a very handy utility called update-alternatives that helps to set default tools for various tasks.

It is possible for several programs fulfilling the same or similar functions to be installed on a single system at the same time. For example, many systems have several text editors installed at once. This gives choice to the users of a system, allowing each to use a different editor, if desired, but makes it difficult for a program to make a good choice for an editor to invoke if the user has not specified a particular preference.

On Linode, it seems that the default editor is nano, I prefer to use vim for editing git commits, visudo, and other things that use the default editor which is symbolically linked through /usr/bin/editor. The update-alternatives package basically changes the symbolic links for you. In order to change your default editor, you simply need to run the following command:

sudo update-alternatives --config editor

The output of this command is shown below. You will see a list of all of your editors that you currently have installed and will be asked to make a choice.

There are 3 choices for the alternative editor (providing /usr/bin/editor).

Selection Path Priority Status
------------------------------------------------------------
 0 /bin/nano 40 auto mode
 1 /bin/nano 40 manual mode
 2 /usr/bin/vim.basic 30 manual mode
* 3 /usr/bin/vim.tiny 10 manual mode

Press enter to keep the current choice[*], or type selection number:

Behind the scenes you can see that all this does it updates the symbolic links.

levlaz@dev:~$ ls -al /usr/bin/editor
lrwxrwxrwx 1 root root 24 Feb 10 20:49 /usr/bin/editor -> /etc/alternatives/editor
levlaz@dev:~$ ls -al /etc/alternatives/editor
lrwxrwxrwx 1 root root 17 Apr 28 18:56 /etc/alternatives/editor -> /usr/bin/vim.tiny

There are many other things that can be configured this way. For more information reading the man page for update-alternatives is worthwhile.