This turns a Raspberry Pi into a WiFi hotspot that is not connected to the internet, hosting a single website.
When connecting to the Raspberry Pi it should redirect you to the website hosted on it.
This is done by mimicking a signin step, which opens a browser window on Windows, Android, and Apple devices when connecting to the WiFi.
This guide is an extension of the guide "Setting up a Raspberry Pi as a Wireless Access Point" from the RaspberryPi.org website.
Before proceeding, please ensure your Raspberry Pi is up to date and rebooted.
The Raspberry Pi can be used as a wireless access point, running a standalone network. This can be done using the inbuilt wireless features of the Raspberry Pi 3 or Raspberry Pi Zero W, or by using a suitable USB wireless dongle that supports access points.
Note that this documentation was tested on a Raspberry Pi Zero W, and it is possible that some USB dongles may need slight changes to their settings. If you are having trouble with a USB wireless dongle, please check the forums.
In order to work as an access point, the Raspberry Pi will need to have access point software installed, along with DHCP server software to provide connecting devices with a network address.
To create an access point, we'll need DNSMasq and HostAPD. Install all the required software in one go with this command:
sudo apt install dnsmasq hostapd
Since the configuration files are not ready yet, turn the new software off as follows:
sudo systemctl stop dnsmasq
sudo systemctl stop hostapd
We are configuring a standalone network to act as a server, so the Raspberry Pi needs to have a static IP address assigned to the wireless port. This documentation assumes that we are using the standard 192.168.x.x IP addresses for our wireless network, so we will assign the server the IP address 192.168.4.1. It is also assumed that the wireless device being used is wlan0.
To configure the static IP address, edit the dhcpcd configuration file with:
sudo nano /etc/dhcpcd.conf
Go to the end of the file and edit it so that it looks like the following:
interface wlan0
static ip_address=192.168.4.1/24
nohook wpa_supplicant
Now restart the dhcpcd daemon and set up the new wlan0 configuration:
sudo service dhcpcd restart
The DHCP service is provided by dnsmasq. By default, the configuration file contains a lot of information that is not needed, and it is easier to start from scratch. Rename this configuration file, and edit a new one:
sudo mv /etc/dnsmasq.conf /etc/dnsmasq.conf.orig
sudo nano /etc/dnsmasq.conf
Type or copy the following information into the dnsmasq configuration file and save it:
interface=wlan0 # Use the require wireless interface - usually wlan0
dhcp-range=192.168.4.2,192.168.4.255,255.255.255.0,15m
address=/#/192.168.4.1 # Redirect all domains (the #) to the address 192.168.4.1 (the server on the (Pi)
So for wlan0, we are going to provide IP addresses between 192.168.4.2 and 192.168.4.20, with a lease time of 15 minutes. If you are providing DHCP services for other network devices (e.g. eth0), you could add more sections with the appropriate interface header, with the range of addresses you intend to provide to that interface. We are also redirecting all domains to the ip address 192.168.4.1. Later on we're going to redirect all traffic destined for 192.168.4.1 to the IP and port where we're hosting the server - 192.168.4.1:3000.
There are many more options for dnsmasq; see the dnsmasq documentation for more details.
Reload dnsmasq to use the updated configuration:
sudo systemctl reload dnsmasq
You need to edit the hostapd configuration file, located at /etc/hostapd/hostapd.conf, to add the various parameters for your wireless network. After initial install, this will be a new/empty file.
sudo nano /etc/hostapd/hostapd.conf
Add the information below to the configuration file. This configuration assumes we are using channel 7, with a network name of Pi WiFi, and no password. This means anyone can connect to the network. The original Raspberry Pi guide has configuration options for a passworded WiFi.
To use the 5 GHz band, you can change the operations mode from hw_mode=g to hw_mode=a. Possible values for hw_mode are:
- a = IEEE 802.11a (5 GHz)
- b = IEEE 802.11b (2.4 GHz)
- g = IEEE 802.11g (2.4 GHz)
- ad = IEEE 802.11ad (60 GHz) (Not available on the Raspberry Pi)
interface=wlan0
driver=nl80211
ssid=Pi WiFi
channel=7
hw_mode=g
We now need to tell the system where to find this configuration file.
sudo nano /etc/default/hostapd
Find the line with #DAEMON_CONF, and replace it with this:
DAEMON_CONF="/etc/hostapd/hostapd.conf"
Now enable and start hostapd:
sudo systemctl unmask hostapd
sudo systemctl enable hostapd
sudo systemctl start hostapd
Do a quick check of their status to ensure they are active and running:
sudo systemctl status hostapd
sudo systemctl status dnsmasq
Edit /etc/sysctl.conf and uncomment this line:
net.ipv4.ip_forward=1
Add a masquerade for outbound traffic on eth0:
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
(more information about masquerade in iptables https://askubuntu.com/a/466451)
Add redirect for all inbound http traffic for 192.168.4.1 (which we defined earlier in dnsmasq.conf) to our Node.js server on port 3000 (192.168.4.1:3000).
sudo iptables -t nat -I PREROUTING -d 192.168.4.1 -p tcp --dport 80 -j DNAT --to-destination 192.168.4.1:3000
Save the iptables rules.
sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"
Edit /etc/rc.local
sudo nano /etc/rc.local
and add this just above "exit 0" to install the iptables rules on boot.
iptables-restore < /etc/iptables.ipv4.nat
Reboot and ensure it still functions.
Using a wireless device, search for networks. The network SSID you specified in the hostapd configuration should now be present, and it should be accessible with the specified password.
If SSH is enabled on the Raspberry Pi access point, it should be possible to connect to it from another Linux box (or a system with SSH connectivity present) as follows, assuming the pi account is present:
ssh pi@192.168.4.1
By this point, the Raspberry Pi is acting as an access point, and other devices can associate with it. Associated devices can access the Raspberry Pi access point via its IP address for operations such as rsync, scp, or ssh.
Create service that starts the Node.js server automatically whenever the Pi boots up.
Create a directory for the Node.js files:
sudo mkdir -p /Node/PiWiFi
Change to the directory:
cd Node/PiWiFi
Create a package.json file for our Node.js server and accept all the default options:
npm init
Install express as a dependency:
npm install express
Create the Node.js file:
sudo nano app.js
And write / paste the code:
const express = require('express');
const app = express();
const port = 3000;
var hostName = 'pi.wifi';
app.use((req, res, next) => {
if (req.get('host') != hostName) {
return res.redirect(`http://${hostName}`);
}
next();
})
app.get('/', (req, res, next) => {
res.send('Pi WiFi - Captive Portal');
})
app.listen(port, () => {
console.log(`Server listening on port ${port}`)
})
The key part here is the redirection of any requests that were not from the hostname "pi.wifi".
The redirection command returns a 302 status code. It's this 302 code that triggers the "Sign in to network" functionality, the kind you see when connecting to an open WiFi network at an airport etc.
Create the service file:
sudo nano piwifi.service
And write / paste the code:
[Unit]
Description=Pi WiFi Hotspot Service
After=network.target
[Service]
WorkingDirectory=/home/pi/Node/PiWiFi
ExecStart=/usr/bin/nodejs /home/pi/Node/PiWiFi/app.js
Restart=on-failure
User=root
Environment=PORT=3000
[Install]
WantedBy=multi-user.target
Copy the file across:
sudo cp piwifi.service /etc/systemd/system
and set it up with:
sudo systemctl enable piwifi.service
It will start automatically on boot, but you can start it now with:
sudo systemctl start piwifi
When you connect to the WiFi you should be prompted to signin to the network (tested on Windows, Android, and iPhone). Otherwise, any time you try to connect to a http site, you should be redirected to the web server at the domain pi.wifi, a domain that doesn't exist on the "real" internet.
If you are redirected to the site successfully, you should see the text "Pi WiFi - Captive Portal".