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I have encountered a series of errors after my Ubuntu server was restarted. It seems to have forgotten how to connect to my router as it cannot ping local or other IPs.

When I start it up it says

Waiting for network configuration
Waiting 60 more seconds for network configuration

If I enter ping http://google.com it returns:

ping: Unknown host http://google.com

If I enter ping 192.168.1.1 it returns:

connect: Network is unreachable

If I enter /etc/init.d/networking restart it returns:

Reconfiguring network interfaces...

then hangs until it says

Failed to bring up eth0

Currently the networking/interfaces file looks like this

auto eth0
iface eth0 inet dhcp

The router reports that the server is: Inactive..

Any advice?

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What is the output of ip addr, and ip route. –  Zoredache Apr 10 '12 at 21:31
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2 Answers 2

up vote 1 down vote accepted

3 things to check:

  1. what eth device do you see? dmesg | grep eth will show you. was it renamed?

  2. if eth0 is available, sudo ethtool eth0 to see if it is really up.

  3. is the nic light on (most nics should have indicator lights)

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Alright. 1. When I typed that in is filled the entire screen with entries and since I have lost SSH to the server I can only summarize. I see Numbers in brackets on the left then on each entry it says 'eth' in red, some sort of timestamp or something (all set to 0000:00:07.0) eth0: link up/down. It says up/down/up/down/up/down in sequence. 2. ethtool command not found. 3. Network indicator light is on both the router and the server. –  Michael Apr 10 '12 at 21:17
    
looks like it may be a link problem, if it keeps going up and down. try dmesg | grep eth0 | tail -10 just to make sure it is indeed eth0. try to reseat your nic connectors to see if it does anything. –  johnshen64 Apr 10 '12 at 21:21
    
forcedeath eth0 link up/down/up/down I'll try reseating. –  Michael Apr 10 '12 at 21:23
    
Alright just checked the nic connectors.. it is part of my motherboard so it could not be moved really. –  Michael Apr 10 '12 at 21:25
    
just unplug nic cable and replug. also, you can replace the nic cable with a known good one to rule out that it is the cable. if this still does not fix it, then i would say your nic port is kaput. do you have another nic on the server or can insert a nic card to replace this nic? looks like it is a nic hw issue most likely (after ruling out cable issue that is). –  johnshen64 Apr 10 '12 at 21:27
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probably to late, but take out auto eth0. It will auto config anyways when it boots. I had this problem for some time before reading about the fix.

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Not too late for me, thanks! Any idea why the 'auto eth0' balls things up? –  Dan Oct 22 '12 at 20:23
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