etc/runonce.d/01-generate-hostname

#!/bin/bash

random_word()
{
    local wordlist=$1; shift
    local max=$(wc -l $wordlist |awk '{ print $1 }')
    local line=$(($RANDOM % $max + 1))

    head -n $line $wordlist |tail -n 1
}

generate_hostname()
{
    local adj=$(random_word /tmp/adjectives.txt)
    local noun=$(random_word /tmp/nouns.txt)

    echo "${adj}-${noun}"
}

hostname=$(generate_hostname)
echo $hostname >/etc/hostname
/usr/bin/hostnamectl set-hostname $hostname