To change the hostname in CentOS 7, you have to do four things:
1. Modify /etc/sysconfig/network
HOSTNAME=hostname.domain.com
2. Modify /etc/hosts
Find:
127.0.0.1 localhost localhost.localdomain localhost4 localhost4.localdomain4 ::1 localhost localhost.localdomain localhost6 localhost6.localdomain6
Add below that your IP address (a.b.c.d) and the new hostname:
a.b.c.d hostname.domain.com hostname
3.
Run this command: hostname hostname.domain.com
4. Persist the change using /etc/init.d/network restart
Reference:
https://support.rackspace.com/how-to/centos-hostname-change/