EnismanY / linux_wifi.md
This provides details including, frequency of WiFi, BSSID, SSID, encryption (for WPA2-PSK, should see pairwise_cipher and group_cipher are CCMP ) MAC address and IP address.
There are several options for turning off WiFi, what works will be dependent on how the system is configured. Assuming the WiFi interface is wlan0 , options are:
sudo ip link set wlan0 down - First list all devices using:
0: phy0: Wireless LAN Soft blocked: no Hard blocked: no 1: hci0: Bluetooth Soft blocked: no Hard blocked: no Again, there are multiple options:
sudo ip link set wlan0 up Alternatively, assuming the number of the device has been ascertained using rfkill list ( 0 in the example below) execute:
Display information about the WiFi interface
Assuming WiFi interface is wlan0 :
Finding WiFi link quality & signal level
iwconfig wlan0 | grep -i --color "Quality\|Signal" The numbers reported for quality will be WiFi driver dependent.
Continous update of link quality
The file /proc/net/wireless contains information about the WiFi signal. This can be viewed continually using a combination of the cat and watch commands.
watch -n 1 cat /proc/net/wireless Alternatively, the ncurses-based monitoring application wavemon can be used. This will likely need installing, which in Debian based distributions can be achieved using:
To use the application simply run:
Setting a prefered WiFi band
It is possible to set a preferred WiFi band, ie 2.5 or 5 GHz. This may be desirable to avoid interference from other devices or to improve range/speed. Remember, 2.5 GHz has the better range and 5 GHz the better speed.
First check the network interface is capable of using both bands. There are at least two methods to determine this.
sudo iwlist wlan0 scan | grep -i "Frequency\|Address\|ESSID" THe output will be similar to:
Cell 01 - Address: ab:12:cd:34:ef:56 Frequency:2.412 GHz ESSID:"DESIRED SSID" Cell 02 - Address: gh:78:ij:90:kl:12 Frequency:5.70 GHz ESSID:"DESIRED SSID" . iw list | grep -i "Frequencies\|MHz\|GHz" In the output look for the section(s) entitles Frequencies, which will be similar to:
Frequencies: * 5180 MHz [36] (22.0 dBm) (no IR) * 5200 MHz [40] (22.0 dBm) (no IR) * 5220 MHz [44] (22.0 dBm) (no IR) * 5240 MHz [48] (22.0 dBm) (no IR) . The frequencies are the centre of the band.
Both the SSID and BSSID are required, the BSSID is the MAC address for a particular band of the access point. To obtain this information, enter the wpa command line interface by running the following, where wlan0 is the name of the wireless network interface:
Once in the iteractive mode, indicated by:
run the following two commands, letting the first command complete execution (indicated by a return of the > prompt) before running the second.
The output will be similar to:
bssid / frequency / signal level / flags / ssid ab:12:cd:34:ef:56 2412 -79 [WPA2-PSK-CCMP][WPA2-PSK-CCMP][ESS] DESIRED SSID gh:78:ij:90:kl:12 5700 -84 [WPA2-PSK-CCMP][WPA2-PSK-CCMP][ESS] DESIRED SSID . This shows the desired SSID and the frequencies, 2.5 and 5 GHz, along with their respective BSSIDs.
Quit the interactive mode by entering q .
To modify the settings
Kill network-manager and wpa_supplicant:
sudo service network-manager stop && sudo killall wpa_supplicant On the Raspberry Pi (August 2020) networking this can be achieved using:
sudo service networking stop && sudo killall wpa_supplicant If /etc/wpa_supplicant.conf does not exist, create the file using:
sudo wpa_passphrase > /etc/wpa_supplicant must be replaced with the SSID of the WiFi network. A blank prompt will be received awaiting the user to enter the password for the WiFi. Once this has been done edit the file using:
sudo nano /etc/wpa_supplicant.conf Add the following to the file.
ctrl_interface=/var/run/wpa_supplicant #settings for an AP using preshared keys, PSK network= < ssid=ssid scan_ssid=1 key_mgmt=WPA-PSK #psk==Password psk="Passkey generated by wpa_passphrase" bssid=gh:78:ij:90:kl:12 #the important part >#settings for an open AP. if you use this then don't use the above settings network=
ssid and psk will be those entered when using the wpa_passphrase command.
Delete the commented line containing the password, and ensure the bssid matches that of the access point and the desired band you wish to connect to, ie 2.5 or 5 GHz.
Now start the daemon in the background by running:
sudo wpa_supplicant -B -c /etc/wpa_supplicant/wpa_supplicant.conf -i wlan0 If this fails, debug problems by running:
sudo wpa_supplicant -c /etc/wpa_supplicant/wpa_supplicant.conf -i wlan0 -d Unsure about the dhclient section (next two commands)
After authentication, tell dhclient to release the current lease ie IP address, it has from the server:
Request a dynamic IPv4 address (DHCP):
Finally, reconfigure the interface with:
wpa_cli -i wlan0 reconfigure Verify whether WiFi has successfully connected and the correct band is being used by executing:
sudo wpa_cli -i wlan0 status If the ip_address is not populated, the device has not connected to the network, check that thr password and ESSID are correct.
Configure WiFi Connections
This section explains how to establish a WiFi connection. It covers creating and modifying connections as well as directly connecting.
Establish a Wireless Connection
This section will show how to establish a wifi connection to the wireless network. Note that directly connecting will implicitly create a connection (that can be seen with “nmcli c”). The naming of such will follow “SSID N” pattern, where N is a number.
First, determine the name of the WiFi interface:
$ nmcli d DEVICE TYPE STATE CONNECTION . wlan0 wifi disconnected -- Make sure the WiFi radio is on (which is its default state):
Then, list the available WiFi networks:
$ nmcli d wifi list * SSID MODE CHAN RATE SIGNAL BARS SECURITY . my_wifi Infra 5 54 Mbit/s 89 ▂▄▆█ WPA2 As an example, to connect to the access point ‘my_wifi’, you would use the following command:
$ nmcli d wifi connect my_wifi password
is the password for the connection which needs to have 8-63 characters or 64 hexadecimal characters to specify a full 256-bit key.
Connect to a Hidden Network
A hidden network is a normal wireless network that simply does not broadcast it’s SSID unless solicited. This means that its name cannot be searched and must be known from some other source.
Issue the following command to create a connection associated with a hidden network :
$ nmcli c add type wifi con-name ifname wlan0 ssid $ nmcli c modify wifi-sec.key-mgmt wpa-psk wifi-sec.psk
Now you can establish a connection by typing:
is an arbitrary name given to the connection and is the password to the network. It needs to have between 8-63 characters or 64 hexadecimal characters in order to specify a full 256-bit key.
Further Information
You will find further information and more detailed examples on following pages: