. How does the /etc/hosts file play a role in hostname lookups

On most systems, user can override hostname lookups with the /etc/hosts file, usually the file contains the IP addresses of localhost in it. The other entries illustrate a simple way to add hosts on a local subnet. Here's an example of the entries in this file:-

127.0.0.1   localhost localhost.localdomain localhost4 localhost4.localdomai    n4
  2 ::1         localhost localhost.localdomain localhost6 localhost6.localdomai    n6