Fresh Install of Ubuntu Server 19.04 Has No Internet?

Solution 1:

To obtain IP address from DHCP server manually you can run

sudo dhclient enp0s25 

To make this solution permanent you should use the corresponding configuration file inside 19.04 for Netplan (see server guide, p. 43) - /etc/netplan/01-netcfg.yaml with the following contents:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      dhcp4: yes

then apply the configuration with sudo netplan apply.

The file contents of /etc/netplan/01-netcfg.yaml above is modified variant of /usr/share/doc/netplan/examples/dhcp.yaml configuration file.
More examples of Netplan configuration are shown in /usr/share/doc/netplan/examples/.