title: ifup eth0 already configured
body: <p>I'm building an operating system for my device with <code>buildroot-2017.08</code>. The operating system that I got started successfully on my device except one big problem:I have no ipv4 address for eth0.</p>
  
  <p>I have an initial script that configures all interfaces that I have. When started it runs the code: 
      <code>ifup -a</code>.
  I've checked that the script really runs at the start of the system and checked the output of <code>ifup</code>. And I get the message:"Interface eth0 already configured". Just after the boot... Who might have configured this interface? I'm stuck. So it doesn't assign the ip address cause it's already configured...</p>
  
  <p>This is my <code>/etc/network/interfaces file</code></p>
  
  <pre><code>    # /etc/network/interfaces -- configuration file for ifup(8), ifdown(8)
  
      # The loopback interface
      auto lo
      iface lo inet loopback
  
      # Wired or wireless interfaces
      auto eth0
      # iface eth0 inet dhcp
      iface eth0 inet static
          address 192.168.0.136
          netmask 255.255.255.0
          gateway 192.168.0.2
  
      auto can0
      iface can0 inet manual
      #pre-up ip link set $IFACE type can bitrate 125000 listen-only off
          pre-up ip link set $IFACE type can bitrate 125000 triple-sampling on
          up ifconfig $IFACE up
          down ifconfig $IFACE down
  </code></pre>
  
  <p>Can somebody give me a clue of what is going on? Maybe I missed some important settings in <code>make-menuconfig</code> or anywhere else. Thank you in advance!</p>