Installation of Wireguard server. Tested on Ubuntu 20.04. Should work on 18.04 as well.

install-wireguard-server.sh

#!/usr/bin/env bash
set -e

echo
if ! [[ $(id -u) = 0 ]]; then
  echo "Please run 'sudo ./install-wireguard.sh'" >&2
  exit 1
fi

read -e -p "Use VPN for *all* internet traffic? [y/n] " -i n ROUTE_ALL
if [[ $ROUTE_ALL = y* ]]; then
  SUBNET=0.0.0.0/0
elif [[ $ROUTE_ALL = n* ]]; then
  SUBNET=10.42.42.0/24
else
  echo Unknown response
  exit 1
fi

read -e -p "# of clients? [Betwen 1 and 253] " -i 5 NUM
read -e -p "Server hostname/IP? " -i $(curl -s ifconfig.me) SERVER

apt-get install -y wireguard
if [ `sysctl net.ipv4.ip_forward -b` == 0 ]; then
  echo "running this"
  cat "net.ipv4.ip_forward=1" >> /etc/sysctl.d/99-sysctl.conf
  sysctl -w net.ipv4.ip_forward=1
fi
wg genkey | tee server.key | wg pubkey > server.pub

cat > /etc/wireguard/wg0.conf << EOF
[Interface]
Address = 10.42.42.1/24
PostUp = iptables -A FORWARD -i wg0 -j ACCEPT; iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE; ip6tables -A FORWARD -i wg0 -j ACCEPT; ip6tables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
PostDown = iptables -D FORWARD -i wg0 -j ACCEPT; iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE; ip6tables -D FORWARD -i wg0 -j ACCEPT; ip6tables -t nat -D POSTROUTING -o eth0 -j MASQUERADE
ListenPort = 51820
PrivateKey = $(cat server.key)
EOF

mkdir -p clients
# IP 1 is reserved for server
NUM=$(($NUM + 1))

for i in $(seq 2 $NUM)
do
wg genkey | tee $i.key | wg pubkey > $i.pub
echo "[Interface]
PrivateKey = $(cat $i.key)
Address = 10.42.42.$i/24
[Peer]
PublicKey = $(cat server.pub)
Endpoint = $SERVER:51820
AllowedIPs = $SUBNET
PersistentKeepalive = 15
" > clients/$i.conf

echo "
# $i
[Peer]
PublicKey = $(cat $i.pub)
AllowedIPs = 10.42.42.$i/32" >> /etc/wireguard/wg0.conf
done

ufw allow 51820/udp
systemctl enable wg-quick@wg0
systemctl start wg-quick@wg0

if [ $SUDO_USER ]; then user=$SUDO_USER
else user=$(whoami); fi
tar -czf clients.tgz clients
chown -R $user clients*

rm *.{key,pub}
ip -4 a show wg0
echo 
echo Done. clients.tgz contains your client configuration files.