Create Access Point on Debian/Ubuntu

access_point.sh

#!/bin/bash

### CONFIG ###

ETH=enp4s0    # interface connected to the Internet
WLAN=wlp5s0   # interface serving as an Access Point
ACCESS_POINT_SSID=thinkpad
ACCESS_POINT_PASS=password
SERVER_IP=192.168.42.1
SERVER_SUBNET=192.168.42.0
CLIENT_IP_MIN=192.168.42.2
CLIENT_IP_MAX=192.168.42.3

##############

# install packages
sudo apt install hostapd isc-dhcp-server iptables

# stop services
sudo service networking stop
sudo service hostapd stop
sudo service isc-dhcp-server stop

# stop interfaces
sudo ifconfig ${ETH} down
sudo ifconfig ${WLAN} down

# setup interfaces
sudo ifconfig ${ETH} up
sudo dhclient ${ETH}
sudo ifconfig ${WLAN} up
sudo ifconfig ${WLAN} ${SERVER_IP}

# create hostapd config file
(
  echo "interface=${WLAN}"
  echo "driver=nl80211"
  echo "ssid=${ACCESS_POINT_SSID}"
  echo "hw_mode=g"
  echo "channel=1"
  echo "macaddr_acl=0"
  echo "auth_algs=1"
  echo "ignore_broadcast_ssid=0"
  echo "wpa=2"
  echo "wpa_passphrase=${ACCESS_POINT_PASS}"
  echo "wpa_key_mgmt=WPA-PSK"
  echo "wpa_pairwise=TKIP"
  echo "rsn_pairwise=CCMP"
) | sudo tee /etc/default/hostapd

# register hostapd config file
(
  echo 'DAEMON_CONF="/etc/hostapd/hostapd.conf"'
) | sudo tee /etc/default/hostapd

# create dhcpd config file
(
  echo "default-lease-time 600;"
  echo "max-lease-time 7200;"
  echo ""
  echo "authoritative;"
  echo ""
  echo "subnet ${SERVER_SUBNET} netmask 255.255.255.0 {"
  echo "  range ${CLIENT_IP_MIN} ${CLIENT_IP_MAX};"
  echo "  option routers ${SERVER_IP};"
  echo "  option domain-name-servers 8.8.8.8, 8.8.4.4;"
  echo "}"
) | sudo tee /etc/dhcp/dhcpd.conf

# update routing rules
sudo iptables -t nat -A POSTROUTING -o ${ETH} -j MASQUERADE
sudo iptables -A FORWARD -i ${ETH} -o ${WLAN} -m state --state RELATED,ESTABLISHED -j ACCEPT
sudo iptables -A FORWARD -i ${WLAN} -o ${ETH} -j ACCEPT

# apply routing rules
sudo sh -c "echo 1 > /proc/sys/net/ipv4/ip_forward"

# start dhcp daemon
sudo service isc-dhcp-server start

# start Access Point daemon
sudo service hostapd start