When you first invoke the crontab command in Ubuntu you are prompted for the default editor. If someone has already set this to nano and you are a vim-person this can be very annoying.

To change it to vim use the select-editor command

root@ns1:/etc# select-editor

 
Select an editor.  To change later, run 'select-editor'.
  1. /bin/nano        <---- easiest
  2. /usr/bin/vim.basic
  3. /usr/bin/vim.tiny
 
Choose 1-3 [1]: 2