How to set up WiFi hotspot and troubleshoot WiFi problems on Debian

There are a few decent tutorials on how to setup hotspot on Linux, which I will share below, but this tutorial will focus on adversities that you without doubt will face while setting up your AP.

For AP setup we will need:

Hostapd utility
Some dhcp utility
A bit of patience (that was for my case)

How do I know that my WiFi adapter supports AP mode?

In terminal type sudo iw list this command will show info about your wifi interfaces. Look for Supported interface entry, if AP is in it, that means your Wifi devices support hotspot mode.

Supported interface modes:
		 * IBSS
		 * managed
		 * AP
		 * AP/VLAN
		 * WDS
		 * monitor
		 * mesh point
		 * P2P-client
		 * P2P-GO

Okay, WiFi supports AP mode but not working!

Running sudo rfkill list usually the first thing I was running to troubleshoot WiFi. Command will output something like this:

0: phy0: Wireless LAN
    Soft blocked: no
    Hard blocked: yes
1: acer-wireless: Wireless LAN
    Soft blocked: yes
    Hard blocked: no

hard blocked

Usually means that ~~you are screwed~~ WiFi is disabled physically.

Try toggle WiFi button
Try enabling WiFi in BIOS

There is a chance that your Linux drivers can't handle WiFi button events properly, so try booting into Windows and enable WiFi from there.

soft blocked

Means that some software is blocking WiFi interface.

In most cases you can solve this by running

sudo rfkill unblock %blocked_device_name_as_listed_in_rfkill_list%

If solution above not working consider checking for a driver problem, see link for more details.
If the problem persists after every reboot consider removing your WiFi interface from Network Manager.

Dealing with Network Manager

Network Manager is a ~~super annoying~~ service that is aimed to automate network configuration, unfortunately it might also cause problems with networking. At the sight of any uneven issues perform the steps below to remove your interface from Network Manager.

Open /etc/NetworkManager/NetworkManager.conf and add lines
```
 [main]
 plugins=ifupdown,keyfile
 [ifupdown]
 managed=false
 [keyfile]
 unmanaged-devices=mac:ff:ff:ff:ff:ff:ff
```
instead of mac:ff:ff:ff:ff:ff:ff type in your real device mac
Restart Network Manager
```
 sudo service network-manager restart
```
Open Network Manager GUI and check that you can't manage device your device

Now we can continue with hotspot set up.

Setting up WiFi hotspot with hostapd

Install hostapd utility
```
sudo apt-get install hostapd
```
Create hostapd.conf in /etc/hostapd
```
touch /etc/hostapd/hostapd.conf
```
Add lines below to hostapd.conf. Meaning of most of them is obvious
```
interface=wlan0
channel=6
ieee80211n=1
hw_mode=g
ssid=TEST
wpa=2
wpa_passphrase=p@$$w0rd
wpa_key_mgmt=WPA-PSK
rsn_pairwise=CCMP
auth_algs=1
```
Be carefull with ieee80211n=1 parameter. In most tutorials you will see driver=nl80211 , but parameter diver didn't work for me, presumably because I have atheros driver, but it might work for you if you have nl.

Now you can check if your hotspot works properly run the command

sudo hostapd -d /etc/hostapd/hostapd.conf

-d enables full command output so if there are errors, you will see them.

The issues that you can run into at this point are:

Hostapd is already running.

nl80211: Could not configure driver mode
nl80211 driver initialization failed.
hostapd_free_hapd_data: Interface wlan0 wasn't started

Check that hostapd is already running in the system.

ps ax | grep hostapd

If command above returned anything stop the service.

sudo /etc/init.d/hostapd stop

sudo service hostapd stop

WiFi interface was soft blocked

Configuration file: /etc/hostapd/hostapd.conf
rfkill: WLAN soft blocked
wlan0: Could not connect to kernel driver
Using interface wlan0 with hwaddr ff:ff:ff:ff:ff:ff and ssid "TEST"
Failed to set beacon parameters
wlan0: Could not connect to kernel driver
Interface initialization failed
wlan0: interface state UNINITIALIZED->DISABLED
wlan0: AP-DISABLED 
wlan0: Unable to setup interface.
hostapd_free_hapd_data: Interface wlan0 wasn't started

This problem was described in the beginning of the article, so try running

sudo rfkill unblock wlan

Also you can try restarting WiFi

sudo nmcli radio wifi off
sudo nmcli radio wifi on

If hostapd started you will see that it is constanly writing log to terminal. You should be able to discover you AP with another device, but you won't be able to connect to it yet.

Now close the window with runnig service and check its status. There are few ways to do this:

sudo services hostapd status
sudo /etc/init.d/hostapd status

If service is stopped you can run it on background as a daemon with one of this commands:

sudo services hostapd start
sudo /etc/init.d/hostapd start

Decent article on hostpot setup with bash setup script

Setting up DHCP

Now you need to make your hotspot give all connected devices IP address for hotspot network. This can be achieved with DHCP service, I prefer isc-dhcp-server.

Install isc-dhcp-server sudo apt-get install isc-dhcp-server
Open dhcp config vim /etc/dhcp/dhcpd.conf. It contains a lot of entries with comments, but in most basic set up you will need to add lines specified below:

ddns-update-style none;
authoritative;

subnet 192.168.0.0 netmask 255.255.255.0 {
  interface wlan0; # your interface name here
  range 192.168.0.5 192.168.0.8; # desired ip range
  option routers 192.168.0.1;
  option subnet-mask 255.255.255.0;
  option broadcast-address 192.168.0.255;
}

Save config and check it with command dhcpd -t /etc/dhcp/dhcpd.conf
Start service service isc-dhcp-server start and check if devices that are connected to hostpot can obtain IP addresses.

Check this good article for more info about DHCP

Semant1ka/how_to_setup_hotspot.md

How do I know that my WiFi adapter supports AP mode?

Okay, WiFi supports AP mode but not working!

Dealing with Network Manager

Setting up WiFi hotspot with hostapd

Setting up DHCP

kimfom01 commented Jun 12, 2024