The default command line text editor in shell on Linux BSD determines what is used when you run commands such as "crontab -e" and this is often not what you want to use. Typically vi/vim is the default text editor.
First make sure Nano is installed by running this command:
yum install nano
While you are there, you might want to download these common tools for CentOS as well:
yum install nano wget curl net-tools lsof bash-completion
We prefer to use Nano which can be enabled with one simple code.