Linux – Raspberry Pi won’t bring up wlanX interface – multiple wireless interfaces

debianlinuxnetworkingraspberry piwireless-networking

Let me jump straight in.

I am using a raspberry pi 3 running latest version of raspbian (pixel) as a router/wifi hotspot

I have 3 wireless interfaces:

  1. built in wifi interface (brcmfmac)
  2. TP-Link WN722 for 2.4Ghz Wifi-AP (not working yet) (ath9k_htc)
  3. Comfast CF-912AC (rtl88112au)

purpose of each interface:

  • wlan0 => 5Ghz hostapd daemon
  • wlan1 => link to router (refer to wpa_supplicant in interfaces file)
  • wlan2 => 2.4Ghz hostapd daemon (not operational)

see bottom for more info

Problem:

This has been a frequent problem, I have had, with Raspberry Pi's

I simply cannot bring up an interface wlan0 and wlan2, and wlan2 won't budge to configuration set in /etc/network/interfaces.

I have tried various commands to bring up these interfaces, of which none work:

$ sudo ifdown wlan0
ifdown: interface wlan0 not configured

$ sudo ifup wlan0
RTNETLINK answers: File exists
Failed to bring up wlan0.

$ sudo ifdown wlan2
ifdown: interface wlan2 not configured

$ sudo ifup wlan2
Ignoring unknown interface wlan2=wlan2.

and with wlan0 and wlan2 being down seen from ip addr

`sudo ip link set wlan0 up`

`sudo ip link set wlan2 up`

which has no success in bringing up these interfaces (confirmed down state with ip tool).

How did this happen:

Note: all was working previously, although I could never bring up my tp-link wifi adapter, the ath9k_htc, so I left it down

  1. I was busy configuring my raspberry pi to run a second hostapd daemon on wlan2 (which I would have sorted out after – driver issue):

    • copied my working hostapd config and modified it for 2.4Ghz, saved into /etc/hostapd directory with a unique name.

  2. I used dnsmasq as the dhcp server, where dhcpcd was disabled and stopped:

    • I configured /etc/dnsmasq.conf to also listen on interface wlan2, adding ip to listen on 192.168.4.254 (not sure if needed)

  3. Lastly edited /etc/default/hostapd.conf and added the second hostapd config with a space separation mentioned here

  4. Finally, called a restart on these 2 services

    sudo service dnsmasq restart

    sudo service hostapd restart

This is where everything went to hell.

calling sudo service networking restart brought down wlan0 (existing 5ghz hostapd daemon) and I couldn't bring it up since, nor wlan0. However eth0 and wlan1 stayed up, i.e.

In conlusion:

I had a 5Ghz wifi hotspot, and attempted to create a 2.4Ghz hotspot, now I am in the hotseat with no hotspot

I removed all the settings (i.e. revert back to previous working state) but was unsuccessful.

Note aswel: several reboot did not solve anything

The question:

1. How do I bring up these interfaces

2. Why does this issue of not being able to bring up an interface occur when everything seems right

p.s. let me know if I missed anything

More info:

my interfaces file:

$ sudo cat /etc/network/interfaces

source-directory /etc/network/interfaces.d

auto lo
iface lo inet loopback

allow-hotplug wlan0
iface wlan0 inet static
    address 192.168.0.254
    subnet 255.255.255.0
    gateway 192.168.8.254
    network 192.168.0.0
    broadcast 192.168.0.255

allow-hotplug wlan2
iface wlan0 inet static
    address 192.168.4.254
    subnet 255.255.255.0
    gateway 192.168.8.254
    network 192.168.4.0
    broadcast 192.168.4.255

allow-hotplug eth0
iface eth0 inet static
    address 192.168.1.254
    subnet 255.255.255.0
    gateway 192.168.8.254
    network 192.168.1.0
    broadcast 192.168.1.255

allow-hotplug wlan1
iface wlan1 inet static
    address 192.168.8.254
    subnet 255.255.255.0
    gateway 192.168.8.1
    wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf

The logs:

running sudo ip link set wlan0 down

  • dmesg reports:

    n/a

  • but /var/log/syslog reports:

    Apr 24 20:47:09 gateway avahi-daemon[480]: Interface wlan0.IPv4 no longer relevant for mDNS.

    Apr 24 20:47:09 gateway avahi-daemon[480]: Leaving mDNS multicast group on interface wlan0.IPv4 with address 192.168.0.254.

    Apr 24 20:47:09 gateway avahi-daemon[480]: Withdrawing address record for 192.168.0.254 on wlan0.

followed by running sudo ip link set wlan0 up

  • dmesg reports:

    IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready

  • but /var/log/syslog reports:

    Apr 24 20:50:06 gateway avahi-daemon[480]: Joining mDNS multicast group on interface wlan0.IPv4 with address 192.168.0.254.

    Apr 24 20:50:06 gateway avahi-daemon[480]: New relevant interface wlan0.IPv4 for mDNS.

    Apr 24 20:50:06 gateway avahi-daemon[480]: Registering new address record for 192.168.0.254 on wlan0.IPv4.

    Apr 24 20:50:06 gateway kernel: [ 2964.213013] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready

NIC status

 $ ip addr

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:e5:67:fb brd ff:ff:ff:ff:ff:ff
    inet 192.168.1.254/24 brd 192.168.1.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::ba27:ebff:fee5:67fb/64 scope link 
       valid_lft forever preferred_lft forever
3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 40:a5:ef:d9:9c:4f brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.254/24 brd 192.168.0.255 scope global wlan0
       valid_lft forever preferred_lft forever
4: wlan1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether b8:27:eb:b0:32:ae brd ff:ff:ff:ff:ff:ff
    inet 192.168.8.254/24 brd 192.168.8.255 scope global wlan1
       valid_lft forever preferred_lft forever
    inet6 fe80::ba27:ebff:feb0:32ae/64 scope link 
       valid_lft forever preferred_lft forever
5: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    link/none 
    inet 192.168.10.1 peer 192.168.10.2/32 scope global tun0
       valid_lft forever preferred_lft forever
6: tun1: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    link/none 
    inet 192.168.11.1 peer 192.168.11.2/32 scope global tun1
       valid_lft forever preferred_lft forever
7: wlan2: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc mq state DOWN group default qlen 1000
    link/ether 90:f6:52:13:aa:82 brd ff:ff:ff:ff:ff:ff

NIC Info

$ sudo lshw -C net

  *-usb:1                 
       description: Wireless interface
       product: USB2.0 WLAN
       vendor: ATHEROS
       physical id: 2
       bus info: usb@1:1.2
       logical name: wlan2
       version: 1.08
       serial: 12345
       capabilities: usb-2.00 ethernet physical wireless
       configuration: broadcast=yes driver=ath9k_htc driverversion=4.4.50-v7+ firmware=1.3 link=no maxpower=500mA multicast=yes speed=480Mbit/s wireless=IEEE 802.11bgn
  *-usb:2
       description: Wireless interface
       product: 802.11n NIC
       vendor: Realtek
       physical id: 5
       bus info: usb@1:1.5
       logical name: wlan0
       version: 0.00
       serial: 123456
       capabilities: usb-2.00 ethernet physical wireless
       configuration: broadcast=yes driver=rtl8812au ip=192.168.0.254 maxpower=500mA multicast=yes speed=480Mbit/s wireless=unassociated
  *-network:0
       description: Ethernet interface
       physical id: 2
       logical name: eth0
       serial: b8:27:eb:e5:67:fb
       size: 100Mbit/s
       capacity: 100Mbit/s
       capabilities: ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=smsc95xx driverversion=22-Aug-2005 duplex=full firmware=smsc95xx USB 2.0 Ethernet ip=192.168.1.254 link=yes multicast=yes port=MII speed=100Mbit/s
  *-network:1
       description: Wireless interface
       physical id: 3
       logical name: wlan1
       serial: b8:27:eb:b0:32:ae
       capabilities: ethernet physical wireless
       configuration: broadcast=yes driver=brcmfmac driverversion=7.45.41.26 firmware=01-df77e4a7 ip=192.168.8.254 multicast=yes wireless=IEEE 802.11bgn

Best Answer

So I after some time, I found out that Raspbian uses the ifupdown package which you can manually download from here.

So the reason for your interface not coming up can vary, thus I cannot tell you what is the cause, but the logs CAN definitely help you if Googled.

Get the Logs

TO find these logs, use either this for a quick status update:

systemctl status networking.service

or this for detailed logs:

journalctl -u networking.service

About networking.service

You can find the service file here /lib/systemd/system/networking.service

Open it using nano/vim (I prefer nano) to view

The service runs /sbin/ifup -a --read-environment, but you can add additional verbosity -v to get more information about your network interfaces

Thus, running /sbin/ifup -a --read-environment -v will give you insight into why the interfaces cannot be brought up.

You can find an example output of the above command here, from this AskUbuntu post

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