Article 1

1: Edit /etc/sysconfig/network

change the parameter value for "hostname"
example:
# cat /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=instance-ol6 <--------- change here

2: In the file /etc/oci-hostname.conf change the value of PRESERVE_HOSTINFO to 2.

/etc/oci-hostname.conf
PRESERVE_HOSTINFO=2

This change will be persistent across reboots

1: Update the /etc/hostname file with below command.

    hostnamectl set-hostname <new name>

2: Edit the oci configuration file for hostnames as given below to update the needed value to 2.
    vi /etc/oci-hostname.conf
    PRESERVE_HOSTINFO=2
    save the changes.

3: Edit the FQDN from OCI console GUI
go to compute instances
--> select the instance
--> scroll down
--> at the left bottom corner select attached VNIC under resources
--> edit appropriate VNIC
--> change hostname to update FQDN
--> update VNIC

4: Reboot the instance

5: Check the hostname with hostname command.