ubuntu18.04 modify the hostname

1, modify the file /etc/cloud/cloud.cfg

1 sed -i "s/^preserve_hostname: false/preserve_hostname: true/g" /etc/cloud/cloud.cfg

2, modify the hostname

1 sed -i "s/$HOSTNAME/new-hostname/g" /etc/hostname

3, modify the localhost

1 sed -i "s/$HOSTNAME/new-hostname/g" /etc/hosts