Finding Device Names in Ubuntu 16.04.x
In this latest LTS release, Ubuntu no longer uses the traditional interface device names like "eth0" or "wlan0" for some reason. I'm sure there is some explanation for this, but it does mean that the new names must be discovered. This information can be found by searching the output of the "dmesg" command for the old names:
dmesg | grep wlan0
In both cases there will be a line that states (in part) for example: ".. renamed from eth0 ..". Those lines will reveal the current names of the devices. Just to keep things interesting, one system I upgraded in-place from Mint 17.3 to Mint 18 (based on Ubuntu 16.04.x) kept the traditional device names. Go figure.
Configuring Network Interfaces, Old School
The first thing is to take care of the /etc/network/interfaces file, which defines the network interfaces. My interfaces file looks like this:
=======================================================================
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
source /etc/network/interfaces.d/*
# The loopback network interface
auto lo
iface lo inet loopback
# Ethernet NIC is the "leaf" sub-net, needs static address -jrl
auto enp9s0
iface enp9s0 inet static
address 10.10.1.1
netmask 255.255.255.0
broadcast 10.10.1.255
# Just define the wifi interface, don't bring it up prematurely -jrl
# auto wlp12s0
iface wlp12s0 inet dhcp
=======================================================================
The ethernet interface (enp9s0 formerly known as eth0) will be my "leaf" subnet and needs a static IP address because it will become the default router address for the sub-net clients, as well as the DHCP server for those clients.
The wifi interface (wlp12s0 formerly known as wlan0) is merely defined here, and not initialized. Initializing this interface requires several additional steps. In this example the wifi NIC will be a DHCP client of the main network, but static assignment is another option. This NIC receives a static dhcp address assignment from the DHCP server on the main network (eventually). This is important, since this router does not implement NAT it's address must be known to the default router on the main network as the gateway to the leaf subnet. Notice in particular that the line "auto wlp12s0" is commented out, this is because otherwise the system boot sequence will "block" for 5 min. and 10 sec. while it tries (and fails) to initialize the wifi interface. The "auto" line doesn't have to be there, I left it commented as a reminder.
The next step is to prepare what is needed to configure and initialize the wifi interface. This will require the generation of a configuration file for the "wpasupplicant" utility that will be used to establish an association between the local wifi NIC and the wifi access point on the main network. The first step is to generate the skeleton of wpasupplicant configuration file. This is done with the "wpa_passphrase" utility. This utility takes two arguments: the SSID of the network you wish to join, and the WPA passphrase that is needed for that network. In this example, the SSID is "CoreNet" and the WPA passphrase is "SuperSecretPassword":
wpa_passphrase CoreNet SuperSecretPassword >/etc/wpa_supplicant/wpa_supplicant.conf
The command line above is performed as root or with sudo. After the file is created, restrict the permissions, you don't want the passphrase (or the generated key) to be world readable. When first generated, the skeleton file looks like this:
network={
ssid="CoreNet"
#psk="SuperSecretPassword"
psk=e098eb13f5467b23b186f013a211f6399aebc6e462758898d71d23e0949cf370
}
I added a couple of directives and took out the clear-text of the key so the final file looks like this:
network={
ssid="CoreNet"
scan_ssid=1
key_mgmt=WPA-PSK
psk=e098eb13f5467b23b186f013a211f6399aebc6e462758898d71d23e0949cf370
}
Once this file is finalized, we are ready to begin initializing the NIC. First step, bring the interface "up"
ifconfig wlp12s0 up
Next we invoke wpasupplicant with the configuration file we generated:
wpa_supplicant -Dwext -i wlp12s0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B
We are almost there. At this point the interface is associated with the access point for "CoreNet", but we have no IP address. We obtain our IP parameters from the DHCP server on the main network through the use of the "dhclient" utility:
dhclient wlp12s0
Now we should be in business.
Once the "interfaces" and "wpa_supplicant.conf" files are properly set up, we can automate the initialization at boot time by placing the needed commands in the /etc/rc.local file, which on my system looks like this:
=======================================================================
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Make sure that the script will "exit 0" on success or any other
# value on error.
#
# In order to enable or disable this script just change the execution
# bits.
#
# By default this script does nothing.
#
# wait until things settle down -jrl
sleep 10
# initialize wifi interface the hard way -jrl
#
ifconfig wlp12s0 up
wpa_supplicant -Dwext -i wlp12s0 -c /etc/wpa_supplicant/wpa_supplicant.conf -B
dhclient wlp12s0
exit 0
=======================================================================
There may be slicker ways of bringing up a WPA protected wifi interface on Ubuntu server, but this worked for me.
The most useful documentation I found were the manual pages for "wpa_passphrase", "wpa_supplicant.conf" and "wpa_supplicant". Here are some online links for those pages:
http://linux.die.net/man/8/wpa_passphrase
http://linux.die.net/man/5/wpa_supplicant.conf
http://linux.die.net/man/8/wpa_supplicant
