Change hostname on Ubuntu 18.04 LTS

If you have Cloud cloud-ini installed you will have to edit

sudo nano /etc/cloud/cloud.cfg

to preserve your new hostname.

# This will cause the set+update hostname module to not operate (if true)
preserve_hostname: true

When that is done, run the rename command

sudo hostnamectl set-hostname new-hostname

Edit /etc/hosts so it corresponds with your new hostname

127.0.0.1   localhost
127.0.0.1   new-hostname

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters

You can verify your changes by running

hostnamectl

At last, reboot and it should show the correct hostname.