Synopsis

Simple hotspot script allowing to make a wifi hotspot from the computer. If you have an Ethernet/LAN connection on your computer that you wish to share via Wifi to other equipment (e.g mobile phone)

Requirement

This is an init.d script, you need to be root to install it and/or launch it It requires the following packages/programs:

• hostapd
• dnsmasq
• iptables (normally natively present in most Linux distro)

How

It uses hostapd for the control of the access point and authentication You can set the password (WPA2) in the script (yes in clear for now):

wpa=2
#wpa_psk=0123456789abcdef0123456789abcdef0123456789abcdef0123456789abcdef
wpa_passphrase=my_password_right_here
wpa_key_mgmt=WPA-PSK
wpa_pairwise=CCMP
rsn_pairwise=CCMP

Then uses dnsmasq as for DHCP :

dnsmasq_args="--interface=wlan0 --except-interface=lo --bind-interfaces --bogus-priv --dhcp-range=10.0.0.101,10.0.0.200,6h --pid-file=${save_place}/dnsmasq_hotspot.pid"
[...]
dnsmasq $dnsmasq_args

And finally iptables for nat redirection:

iptables -t nat -A POSTROUTING -o $iftarget -s 10.0.0.0/24 -j MASQUERADE
iptables -A FORWARD -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i wlan0 -m conntrack --ctstate NEW -j ACCEPT

Beforehand, the script saves the original configuration of hostapd and iptables When turning off the script reverse all it did by applying back these configs :

#configure save place
eni="/etc/network/interfaces"
hostapd_conf="/etc/hostapd/hostapd.conf"
save_place="/tmp/.hotspot"

[...]

#saving/copying original confs
cp $eni $save_place/interfaces.save
cp $hostapd_conf $save_place/hostapd.conf.save
iptables-save -c -t filter > $save_place/filter.iptables-save
iptables-save -c -t nat > $save_place/nat.iptables-save

[...]

#do stuff

[...]

#restoring back when turning off
kill -9 $(cat $save_place/dnsmasq_hotspot.pid)
iptables-restore -c < $save_place/filter.iptables-save
iptables-restore -c < $save_place/nat.iptables-save
rm $save_place/filter.iptables-save
rm $save_place/nat.iptables-save
mv $save_place/interfaces.save $eni
rm $save_place/dnsmasq_hotspot.pid
mv $save_place/hostapd.conf.save $hostapd_conf

Note:

There is intentionnaly a "sleep 60" at the beginning of the script to be sure that everything is in place before the script actually start (even if in LSB header Required-Start is set as $all, this leave enough time to the user to login and, perhaps, activate wifi hardware)

Tested on:

Debian Jessie 8.8
Debian Stretch