On my Ubuntu Server, 14.04.1 LTS, I have not specified any devices in /etc/network/interfaces, yet they (multiple ethernets) work completely as intended with static IP.

I have heard from multiple sources that that file is the only place where the network configuration is taken from, but clearly this can't be the case as mine only contains the bare minimum for loopback and local interfaces.

Network Manager is not installed on this machine.

How does Ubuntu Server manage devices not declared in /etc/network/interfaces?

  • Where and how did you specify the static IP addresses? – chili555 Dec 2 '14 at 2:05
  • @chili555 That's part of the problem, I'm not the one who specified the static IPs. I looked in common places, yet I need to figure out how to do so. Worth editing my question? – Robobenklein Dec 2 '14 at 2:08
  • Is this running a desktop environment or command-line only? If desktop, then probably Network Manager. Check: nm-tool – chili555 Dec 2 '14 at 2:10
  • @chili555 Complete Server install fresh 14.04. – Robobenklein Dec 2 '14 at 2:13
  • 1
    My guess would be that whoever set the machine up wrote their own custom rc script to manually run ifconfig to set the address. – psusi Dec 2 '14 at 14:32

I don't know if your setup is anything like mine but if so it could clarify.

I am behind a NAT router with port 80 open and forwarded to internal IP 192.168..

I have a static external IP and I have not configured my network interfaces file.

Upon install Ubuntu configures the network interfaces file to display a static IP on eth0

I then have nginx so when the traffic comes to my external IP my router sends it to my server and then nginx takes care of the rest.

Hope this helps :)

  • You're really close, but the problem was that the device was a static IP when the /etc/network/interfaces file was completely empty. (Apart from local and loop back) When I set a device in the interfaces file, it does exactly as it should. So how does it know to be static IP when that file is empty? – Robobenklein Dec 2 '14 at 12:19

Check if there is any command in rc.local file cat /etc/rc.local

It should be empty by default

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