Instructions written against Ubuntu 18.04.3 LTS (bionic) Change the hostname:

Instructions written against Ubuntu 18.04.3 LTS (bionic)

Change the hostname:

sudo hostnamectl set-hostname server1

Check result by running hostnamectl:

root@www:/# hostnamectl
   Static hostname: server1       <-- Check this value
         Icon name: computer-vm
           Chassis: vm
        Machine ID: 202c4264b06d49e48cfe72599781a798
           Boot ID: 43654fe8bdbf4387a0013ab30a155872
    Virtualization: xen
  Operating System: Ubuntu 18.04.3 LTS
            Kernel: Linux 4.15.0-65-generic
      Architecture: x86-64

Change the domain via new network manager, Netplan, by editing /etc/netplan/01-netcfg.yaml and changing the search parameter:

sudoedit /etc/netplan/01-netcfg.yaml

Sample configuration:

# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      dhcp4: yes
      nameservers:
          search: [ domain.org ]

Test changes by logging in a second time, and running sudo netplan try in one of the sessions and checking settings in the other:

# netplan try
Do you want to keep these settings?


Press ENTER before the timeout to accept the new configuration


Changes will revert in  97 seconds
Configuration accepted.

# systemd-resolve --status
...
Link 2 (eth0)
      Current Scopes: DNS
       LLMNR setting: yes
MulticastDNS setting: no
      DNSSEC setting: no
    DNSSEC supported: no
         DNS Servers: 8.8.8.8
                      8.8.4.4
          DNS Domain: domain.org      <-- Check this value

# cat /etc/resolv.conf
...
nameserver 127.0.0.53
options edns0
search domain.org    <-- Check this value

# hostname -f
server1.domain.org

It all is well, press ENTER at the sudo netplan try prompt to make things permanent.