If a network card is to be configured, a user has to decide on the IP-address, FQDN and possible aliases for use in the /etc/hosts file. An example is:
<my-IP> myhost.mydomain.org aliases
It should made sure that the IP-address is in the private network IP-address range. Valid ranges are:
Class Networks
A 10.0.0.0
B 172.16.0.0 through 172.31.0.0
C 192.168.0.0 through 192.168.255.0
A valid IP address could be 192.168.1.1. A valid FQDN for this IP could be www.linuxfromscratch.org
If a user is not going to use a network card, he still needs to come up with a FQDN. This is necessary for programs like Sendmail to operate correctly (in fact; Sendmail won't run when it can't determine the FQDN).
If a network card is not going to be configured, a new file /etc/hosts is created by running:
cat > /etc/hosts << "EOF"
# Begin /etc/hosts (no network card version)
127.0.0.1 www.mydomain.com <value of HOSTNAME> localhost
# End /etc/hosts (no network card version)
EOF
If a network card is to be configured, a new file /etc/hosts is created containing:
cat > /etc/hosts << "EOF"
# Begin /etc/hosts (network card version)
127.0.0.1 localhost.localdomain localhost
192.168.1.1 www.mydomain.org <value of HOSTNAME>
# End /etc/hosts (network card version)
EOF
Of course, the 192.168.1.1 and www.mydomain.org have to be changed to the users liking (or requirements if assigned an IP-address by a network/system administrator and this machine is planned to be connected to that network).