how to change hostname in Oracle Linux 7.2

[root@localhost ~]# hostname

oracle12cdb1

[root@localhost ~]# hostnamectl

   Static hostname: oracle12cdb1

         Icon name: computer-vm

           Chassis: vm

        Machine ID: 8ced32e2f6ce7e4182560e468ff0fb52

           Boot ID: 07e076fe742343a68c9c022c10b0911b

    Virtualization: kvm

  Operating System: Oracle Linux Server 7.2

       CPE OS Name: cpe:/o:oracle:linux:7:2:server

            Kernel: Linux 3.8.13-98.7.1.el7uek.x86_64

      Architecture: x86-64

[root@localhost ~]# hostnamectl set-hostname oracle12cdb1.testlab.com

[root@localhost ~]# hostname

oracle12cdb1.testlab.com