How to setup a Wifi Access Point on Ubuntu 12.04 (or its derivatives).

install_wifi_access_point.sh

#!/bin/bash
### Setup a wifi Access Point on Ubuntu 12.04 (or its derivatives).

### make sure that this script is executed from root
if [ $(whoami) != 'root' ]
then
    echo "
This script should be executed as root or with sudo:
    sudo $0
"
    exit 1
fi

##############################################################
## Check whether the wireless card supports Access Point mode
##############################################################

### make sure that iw is installed
apt-get -y install iw

### check that AP is supported
supports_access_point=$(iw list | sed -n -e '/* AP$/p')
if [ "$supports_access_point" = '' ]
then
    echo "AP is not supported by the driver of the wireless card."
    echo "This script does not work for this driver."
    exit 1
fi

##############################################################
##  Setup and host a network
##############################################################

### install hostapd
apt-get -y install hostapd

### it should not start automatically on boot
update-rc.d hostapd disable

### get ssid and password
ssid=$(hostname --short)
read -p "The name of your hosted network (SSID) [$ssid]: " input
ssid=${input:-$ssid}
password='1234567890'
read -p "The password of your hosted network [$password]: " input
password=${input:-$password}

### get wifi interface
rfkill unblock wifi   # enable wifi in case it is somehow disabled (thanks to Darrin Wolf for this tip)
wifi_interface=$(lshw -quiet -c network | sed -n -e '/Wireless interface/,+12 p' | sed -n -e '/logical name:/p' | cut -d: -f2 | sed -e 's/ //g')

### create /etc/hostapd/hostapd.conf
cat <<EOF > /etc/hostapd/hostapd.conf
interface=$wifi_interface
driver=nl80211
ssid=$ssid
hw_mode=g
channel=1
macaddr_acl=0
auth_algs=1
ignore_broadcast_ssid=0
wpa=3
wpa_passphrase=$password
wpa_key_mgmt=WPA-PSK
wpa_pairwise=TKIP
rsn_pairwise=CCMP
EOF

### modify /etc/default/hostapd
cp -n /etc/default/hostapd{,.bak}
sed -i /etc/default/hostapd \
    -e '/DAEMON_CONF=/c DAEMON_CONF="/etc/hostapd/hostapd.conf"'

################################################
## Set up DHCP server for IP address management
################################################

### make sure that the DHCP server is installed
apt-get -y install isc-dhcp-server

### it should not start automatically on boot
update-rc.d isc-dhcp-server disable

### set the INTERFACES on /etc/default/isc-dhcp-server
cp -n /etc/default/isc-dhcp-server{,.bak}
sed -i /etc/default/isc-dhcp-server \
    -e "/INTERFACES=/c INTERFACES=\"$wifi_interface\""

### modify /etc/dhcp/dhcpd.conf
cp -n /etc/dhcp/dhcpd.conf{,.bak}
sed -i /etc/dhcp/dhcpd.conf \
    -e 's/^option domain-name/#option domain-name/' \
    -e 's/^option domain-name-servers/#option domain-name-servers/' \
    -e 's/^default-lease-time/#default-lease-time/' \
    -e 's/^max-lease-time/#max-lease-time/'

sed -i /etc/dhcp/dhcpd.conf \
    -e '/subnet 10.10.0.0 netmask 255.255.255.0/,+4 d'
cat <<EOF >> /etc/dhcp/dhcpd.conf
subnet 10.10.0.0 netmask 255.255.255.0 {
        range 10.10.0.2 10.10.0.16;
        option domain-name-servers 8.8.4.4, 208.67.222.222;
        option routers 10.10.0.1;
}
EOF

#################################################
## Create a startup script
#################################################

cat <<EOF > /etc/init.d/wifi_access_point
#!/bin/bash

ext_interface=\$(ip route | grep default | cut -d' ' -f5)

function stop_wifi_ap {
    ### stop services dhcpd and hostapd
    service isc-dhcp-server stop
    service hostapd stop

    ### disable IP forwarding
    echo 0 > /proc/sys/net/ipv4/ip_forward
    iptables -t nat -D POSTROUTING -s 10.10.0.0/16 -o \$ext_interface -j MASQUERADE 2>/dev/null
    
    ### remove the static IP from the wifi interface
    if grep -q 'auto $wifi_interface' /etc/network/interfaces
    then
        sed -i /etc/network/interfaces -e '/auto $wifi_interface/,\$ d'
        sed -i /etc/network/interfaces -e '\$ d'
    fi

    ### restart network manager to takeover wifi management
    service network-manager restart
}

function start_wifi_ap {
    stop_wifi_ap
    sleep 3

    ### see: https://bugs.launchpad.net/ubuntu/+source/wpa/+bug/1289047/comments/8
    nmcli nm wifi off
    rfkill unblock wlan

    ### give a static IP to the wifi interface
    ip link set dev $wifi_interface up
    ip address add 10.10.0.1/24 dev $wifi_interface

    ### protect the static IP from network-manger restart
    echo >> /etc/network/interfaces
    echo 'auto $wifi_interface' >> /etc/network/interfaces
    echo 'iface $wifi_interface' inet static >> /etc/network/interfaces
    echo 'address 10.10.0.1' >> /etc/network/interfaces
    echo 'netmask 255.255.255.0' >> /etc/network/interfaces

    ### enable IP forwarding
    echo 1 > /proc/sys/net/ipv4/ip_forward
    iptables -t nat -A POSTROUTING -s 10.10.0.0/16 -o \$ext_interface -j MASQUERADE

    ### start services dhcpd and hostapd
    service hostapd start
    service isc-dhcp-server start
}

### start/stop wifi access point
case "\$1" in
    start) start_wifi_ap ;;
    stop)  stop_wifi_ap  ;;
esac
EOF

chmod +x /etc/init.d/wifi_access_point

### make sure that it is stopped on boot
sed -i /etc/rc.local \
    -e '/service wifi_access_point stop/ d'
sed -i /etc/rc.local \
    -e '/^exit/ i service wifi_access_point stop'


### display usage message
echo "
======================================

Wifi Access Point installed.

You can start and stop it with:
    service wifi_access_point start
    service wifi_access_point stop

"

This procedure works fine for setting up the access point.. But the internet sharing is not working,, Could you please help in this regard and suggest some work around if any?

Thanks,
Dev

thanks , genius job it's solved my handheld wifi problem

how to restore the default after installing your script , can i undo the modifications?

Hey,

All worked good on Ubuntu 12.04. But on 14.04, I am getting this error. Please help.

:~$ sudo service wifi_access_point start
stop: Unknown instance: 
 * Stopping advanced IEEE 802.11 management hostapd                      [ OK ] 
network-manager stop/waiting
network-manager start/running, process 5917
RTNETLINK answers: Operation not possible due to RF-kill
 * Starting advanced IEEE 802.11 management hostapd                      [fail] 
isc-dhcp-server` start/running, process 6074

how to restore the default after installing your script , can i undo the modifications?

yeah i'd like to ask the similiar question, can guide pls?