Ubuntu – How to bring up a network interface only if it is physically present in Ubuntu 14.04

12.0414.04bootnetworkingwireless

This is a follow-up on my old question:

What would be the best way to make kernel bring a network interface up
only if it is physically plugged in? So, if it doesn't exist, just
move on with initializing other interfaces (if any) and continue to
the login screen, without "waiting for network configuration" delay.

The solution then came up with then was the following in etc/network/interfaces, it used to work in 12.04:

auto wlan9
iface wlan9 inet manual
        wpa-ssid MYSSD
        wpa-psk MYKEY
        wpa-proto RSN
        wpa-pairwise CCMP
        wpa-group CCMP
        wireless-power off
        pre-up if [ -f /sys/class/net/wlan9/operstate ]; then ifconfig wlan9 up; fi
        up if [ -f /sys/class/net/wlan9/operstate ]; then dhclient wlan9; fi

Unfortunately, it stopped working once I upgraded to 14.04 Trusty Tahr. If the interface is physically absent (i.e. the USB WiFi card unplugged), I again experience the 2 minutes "waiting for network configuration" delay.

How can I get the same logic working in 14.04?

Best Answer

You can use an upstart job for this. Rip out the pre-up and up sections then make a file /etc/init/network-interface_wlan9.conf :

start on net-device-added INTERFACE=wlan9
task
exec ifup wlan9

Related Solutions

Ubuntu – The correct syntax for /etc/network/interfaces

Wireless will require the addition of the network you intend to connect to and any encryption details. Also, your interfaces file is a bit busy; may I suggest:

auto lo
iface lo inet loopback

auto wlan0
iface wlan0 inet static
address 192.168.1.xxx
netmask 255.255.255.0
gateway 192.168.1.1
wpa-ssid mynetwork
wpa-psk 0123456789

dns-nameservers 208.67.222.222 8.8.8.8
dns-search lan
dns-domain lan

I also suggested a backup DNS nameserver. If you are not using WPA or WPA2, the wording will be slightly different.

Ubuntu – How to bring up a network interface only if it is physically present

Also for server: use NetworkManager

Install it:
```
sudo apt-get install network-manager
```
Unfortunately, this will pull in a lot of dependencies.
Bring down the interface currently configured the traditional way.
```
ifdown wlan9
```
Disable any manual settings in /etc/network/interfaces by removing all lines concerning that interface.
Add a connection setting for your wireless connection in /etc/NetworkManager/system-connections/ (make up a name):
```
[connection]
id=Some name of my connection
uuid=0d791425-87c5-45e6-948e-01b1863901f7
type=802-11-wireless

[802-11-wireless]
ssid=mySSID
mode=infrastructure
mac-address=24:77:00:01:02:03
security=802-11-wireless-security

[802-11-wireless-security]
key-mgmt=wpa-psk
psk=mypassword

[ipv4]
method=auto

[ipv6]
method=ignore
```
- For uuid use the command uuidgen to generate a random one.
- For mac-address use the MAC address of your wireless adapter (use ifconfig -a wlan9 to find out). This binds this configuration file to only this adapter - if it's not present it would not use it for another adapter, nor would it wait for the adapter to be present.
- Other fields speak for themselves I hope. :)
Restart NetworkManager or reboot.
```
restart network-manager
```

Best Answer

Related Solutions

Ubuntu – The correct syntax for /etc/network/interfaces

Ubuntu – How to bring up a network interface only if it is physically present

Also for server: use NetworkManager

Related Question