Our example commands are for Ubuntu 14.04. You need to have access to install hostapd and dnsmasq Dnsmasq is a small DNS/DHCP server which we’ll use in this setup. To start simply run:

sudo apt-get install hostapd dnsmasq

After that you need to create and edit the configuration file:

zcat /usr/share/doc/hostapd/examples/hostapd.conf.gz | sudo tee -a /etc/hostapd/hostapd.conf

The configuration file /etc/hostapd/hostapd.conf is filled with configuration examples and documentation in comments. The relevant parts for a simple WPA2 protected 802.11g network with the SSID ‘Example-WLAN‘ and password ‘PASS‘ are:

interface=wlan0
ssid=Example-WLAN
hw_mode=g
wpa=2
wpa_passphrase=PASS
wpa_key_mgmt=WPA-PSK WPA-EAP WPA-PSK-SHA256 WPA-EAP-SHA256

Next you need to edit the network interfaces configuration to force the WLAN card to only run in the access point mode. Assuming that the access point network will use the address space 192.168.8.* the file /etc/network/interfaces should look something like this:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

auto wlan0
iface wlan0 inet static
hostapd /etc/hostapd/hostapd.conf
address 192.168.8.1
netmask 255.255.255.0

Then we need to have a DNS relay and DHCP server on our wlan0 interface so the clients actually get a working Internet connection, and this can be accomplished by configuring dnsmasq. Like hostapd it also has a very verbose configuration file /etc/dnsmasq.conf, but the relevant parts look like this:

interface=lo,wlan0
no-dhcp-interface=lo
dhcp-range=192.168.8.20,192.168.8.254,255.255.255.0,12h

Next we need to make sure that the Linux kernel forwards traffic from our wireless network onto other destination networks. For that you need to edit the file /etc/sysctl.conf and make sure it has lines like this:

net.ipv4.ip_forward=1

We need to activate NAT in the built-in firewall of Linux to make sure the traffic going out uses the external address as its source address and thus can be routed back. It can be done for example by appending the following line to the file /etc/rc.local:

iptables -t nat -A POSTROUTING -s 192.168.8.0/24 ! -d 192.168.8.0/24 -j MASQUERADE

Some WLAN card hardware might have a virtual on/off switch. If you have such hardware you might need to also run rfkill to enable the hardware using a command like rfkill unblock 0.

The same computer also runs Network Manager (as for example Ubuntu does by default) you need to edit it’s settings so that if won’t interfere with the new wifi access point. Make sure file /etc/NetworkManager/NetworkManager.conf looks like this:

[main]
plugins=ifupdown,keyfile,ofono
dns=dnsmasq

[ifupdown]
managed=false

Now all configuration should be done. To be sure all changes take effect, finish by rebooting the computer.

If everything is working, a new WLAN network should be detected by other devices.
On the WLAN-server you’ll see similar output from these commands:

$ iw wlan0 info
Interface wlan0
ifindex 3
type AP
wiphy 0

$ iwconfig
wlan0 IEEE 802.11bgn Mode:Master Tx-Power=20 dBm
Retry long limit:7 RTS thr:off Fragment thr:off
Power Management:off

$ ifconfig
wlan0 Link encap:Ethernet HWaddr f4:ec:38c8:d2
inet addr:192.168.8.1 Bcast:192.168.8.255 Mask:255.255.255.0
inet6 addr: fe80::f6ec:38ff:fede:c8d2/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5463040 errors:0 dropped:0 overruns:0 frame:0
TX packets:8166528 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:861148382 (861.1 MB) TX bytes:9489973056 (9.4 GB)