Setup your Raspberry Pi as a Wi-Fi access point

setup-ap.sh

#!/bin/bash

# Helper log function
log () {
  local COLOR='\033[0;32m'   # Blue color code
  case "${2}" in
      error) COLOR='\033[0;31m';;
      warning) COLOR='\033[1;33m';;
  esac
  local NC='\033[0m'        # No color code
  echo -e "${COLOR}[$(date +'%Y-%m-%d %H:%M:%S')] $1${NC}"
}

if ! [ $(cat /etc/os-release 2>/dev/null | grep "Raspbian") ]; then
  log "Your device is not running Raspbian :(" error
  exit 1
fi


if ! [ $(iw list 2>/dev/null | grep "Supported interface modes" -A 8 | grep AP) ]; then
  log "Your device does not support being used as an access point :(" error
  exit 1
fi

# Check if the script is being run as root
if [ $(id -u) -ne 0 ]; then
  echo "This script must be run as root. Use sudo."
  exit 1
fi

if [ "$1" = "" ]; then
  echo "Invalid arguments."
  echo "Give SSID as 1st parameter"
  exit 1
fi

if [ "$2" = "" ]; then
  echo "Invalid arguments."
  echo "Give password as 2nd parameter"
  exit 1
fi
# Install required apt packages
installRequiredPackages() {
  log "Installing required packages..."
  # Allow non interactive installation of iptables-persistent
  echo iptables-persistent iptables-persistent/autosave_v4 boolean true | sudo debconf-set-selections
  echo iptables-persistent iptables-persistent/autosave_v6 boolean true | sudo debconf-set-selections 
  # Install required packages
  apt install -y dnsmasq hostapd netfilter-persistent iptables-persistent
  
  log "Installed!"
}

uninstallRequiredPackages() {
  log "Uninstalling required packages..."
  # Install required packages
  apt purge -y dnsmasq hostapd netfilter-persistent iptables-persistent
  
  log "Uninstalled!"
}

# hostapd configuration
configureHostapd() {
  log "Configuring hostapd..."
  test -f /etc/hostapd/hostapd.conf || (touch /etc/hostapd/hostapd.conf && log "Touched /etc/hostapd/hostapd.conf")
  # tee /etc/hostapd/hostapd.conf > /etc/hostapd/hostapd.conf <<\EOF
  echo "ctrl_interface=/var/run/hostapd" | tee /etc/hostapd/hostapd.conf > /dev/null
  echo "driver=nl80211" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "country_code=IT # Use your country code" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "ssid=$1" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "hw_mode=g" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "channel=7" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "auth_algs=1" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "wpa=2" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "wpa_passphrase=$2" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "wpa_key_mgmt=WPA-PSK" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "wpa_pairwise=TKIP" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "rsn_pairwise=CCMP" | tee -a /etc/hostapd/hostapd.conf > /dev/null
  echo "ignore_broadcast_ssid=1" | tee -a /etc/hostapd/hostapd.conf > /dev/null

  # Change conf file permissions
  chmod 600 /etc/hostapd/hostapd.conf
  log "Configured hostapd!"
}

deconfigureHostapd() {
  log "Deleting conf file /etc/hostapd/hostapd.conf..."
  test -f /etc/hostapd/hostapd.conf && rm /etc/hostapd/hostapd.conf
  log "Configured hostapd!"
}

# Creates the uap service required to host the access point
createUAPService() {
  log "Creating uap service..."
  test -f /etc/systemd/system/uap@.service || (touch /etc/systemd/system/uap@.service &&  log "Touched /etc/systemd/system/uap@.service file")
  # tee /etc/systemd/system/uap@.service > /dev/null <<\EOF
  echo "[Unit]" | tee /etc/systemd/system/uap@.service > /dev/null
  echo "Description=IEEE 802.11 %p%i AP on wlan%i with hostapd" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "After=network.target" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo $'\n' | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "[Service]" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "Type=forking" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "PIDFile=/run/hostapd.pid" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "Restart=on-failure" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "RestartSec=2" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "Environment=DAEMON_CONF=/etc/hostapd/hostapd.conf" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "EnvironmentFile=-/etc/default/hostapd" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "ExecStartPre=/sbin/iw dev wlan%i interface add %p%i type __ap" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "ExecStart=/usr/sbin/hostapd -i %p%i -P /run/hostapd.pid -B \$DAEMON_OPTS \${DAEMON_CONF}" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "ExecStopPost=-/sbin/iw dev %p0 del" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo $'\n' | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "[Install]" | tee -a /etc/systemd/system/uap@.service > /dev/null
  echo "WantedBy=multi-user.target" | tee -a /etc/systemd/system/uap@.service > /dev/null

  log "Stopping hostapd..."
  systemctl stop hostapd # if the default hostapd service was active before
  log "Disabling hostapd..."
  systemctl disable hostapd # if the default hostapd service was enabled before
  log "Enabling uap@0.service..."
  systemctl enable uap@0.service
  log "Unblocking wlan..."
  rfkill unblock wlan
  log "Created!"
}

removeUAPService() {
  log "Stopping uap@0.service..."
  systemctl stop uap@0.service
  log "Disabling uap@0.service..."
  systemctl disable uap@0.service
  log "Removing files..."
  test -f /etc/systemd/system/uap@.service && rm /etc/systemd/system/uap@.service && log $'\t/etc/systemd/system/uap@.service'
  test -f /usr/lib/systemd/system/uap@.service && rm /usr/lib/systemd/system/uap@.service && log $'\t/usr/lib/systemd/system/uap@.service'
  log "Daemon-reloading..."
  systemctl daemon-reload
}

setupDhcpcd() {
  log "Setting up DHCPCD..."
  # tee -a /etc/dhcpcd.conf > /dev/null <<\EOF
  # these two lines are not strictly needed, as wlan0 uses the default configuration
  echo "interface wlan0" | tee -a /etc/dhcpcd.conf > /dev/null
  echo "    dhcp" | tee -a /etc/dhcpcd.conf > /dev/null
  echo $'\n' | tee -a /etc/dhcpcd.conf > /dev/null
  # this defines static addressing to uap0 and disables wpa_supplicant for this interface
  echo "interface uap0 " | tee -a /etc/dhcpcd.conf > /dev/null
  echo "    static ip_address=192.168.50.1/24" | tee -a /etc/dhcpcd.conf > /dev/null
  echo "    ipv4only" | tee -a /etc/dhcpcd.conf > /dev/null
  echo "    nohook wpa_supplicant" | tee -a /etc/dhcpcd.conf > /dev/null

  log "Set up DHCPCD successful!"
}

removeDhcpcd() {
  log "Removing conf lines from /etc/dhcpcd.conf..."
  test -f /etc/dhcpcd.conf && sed -i '/interface wlan0/,+2d; /interface uap0/,+4d' /etc/dhcpcd.conf
  log "Removed DHCPCD!"
}

setupRouting() {
  log "Setting up routing..."
  test -f /etc/sysctl.d/routed-ap.conf || (touch /etc/sysctl.d/routed-ap.conf && log "Touched /etc/sysctl.d/routed-ap.conf")
  # tee /etc/sysctl.d/routed-ap.conf > /dev/null <<\EOF
  echo "# https://www.raspberrypi.org/documentation/configuration/wireless/access-point-routed.md" | tee /etc/sysctl.d/routed-ap.conf > /dev/null
  echo "# Enable IPv4 routing" | tee -a /etc/sysctl.d/routed-ap.conf > /dev/null
  echo "net.ipv4.ip_forward=1" | tee -a /etc/sysctl.d/routed-ap.conf > /dev/null

  log "Updating firewall rules..."
  sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
  sudo iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
  sudo iptables -A FORWARD -i wlan0 -o uap0 -m state --state RELATED,ESTABLISHED -j ACCEPT
  sudo iptables -A FORWARD -i uap0 -o wlan0 -j ACCEPT
  sudo netfilter-persistent save
  log "Updated and persisted!"

  log "Appending to dnsmasq configuration..."

  # tee -a /etc/dnsmasq.conf >/dev/null <<\EOF
  echo "# disables dnsmasq reading any other files like /etc/resolv.conf for nameservers" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "no-resolv" | tee -a /etc/dnsmasq.conf > /dev/null
  echo $'\n' | tee -a /etc/dnsmasq.conf > /dev/null
  echo "interface=uap0" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "no-dhcp-interface=lo,wlan0" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "domain-needed" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "bogus-priv" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "server=8.8.8.8" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "dhcp-range=192.168.50.50,192.168.50.199,12h" | tee -a /etc/dnsmasq.conf > /dev/null
  echo "dhcp-option=3,192.168.50.1" | tee -a /etc/dnsmasq.conf > /dev/null

  log "Set up routing successful!"
}

removeRouting() {
  log "Deleting /etc/sysctl.d/routed-ap.conf..."
  test -f /etc/sysctl.d/routed-ap.conf || rm /etc/sysctl.d/routed-ap.conf

  log "Deleting forwarding rules..."
  sudo iptables -D FORWARD -i wlan0 -o uap0 -m state --state RELATED,ESTABLISHED -j ACCEPT || log "Rule 1 non-existent"
  sudo iptables -D FORWARD -i uap0 -o wlan0 -j ACCEPT || log "Rule 2 non-existent"
  sudo iptables -t nat -D POSTROUTING -o wlan0 -j MASQUERADE || log "Rule 3 non-existent"
  sudo iptables -t nat -D POSTROUTING -o eth0 -j MASQUERADE || log "Rule 4 non-existent"

  log "Removing lines added on /etc/dnsmasq.conf..."
  sed -i '/no-resolv\|interface=uap0\|no-dhcp-interface=lo,wlan0\|domain-needed\|bogus-priv\|server=8.8.8.8\|dhcp-range=192.168.50.50,192.168.50.199,12h\|dhcp-option=3,192.168.50.1/d' /etc/dnsmasq.conf
  log "Removed routing!"
}

set -e # Exit if an error occurs
while getopts u flag
do
    case "${flag}" in
        u) uninstall=1;;
    esac
done

if [ -z $uninstall ]; then
  installRequiredPackages
  configureHostapd
  createUAPService
  setupDhcpcd
  setupRouting
else 
  removeRouting
  removeDhcpcd
  removeUAPService
  deconfigureHostapd
  uninstallRequiredPackages
fi

log "WARNING:: YOU HAVE TO REBOOT TO SEE THESE ACTIONS TAKE EFFECT" warning