Identify and enable second NIC card on a Ubuntu machine

Mike Caldwell
Mike Caldwell used Ask the Experts™
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I have a machine with Ubuntu 14.04 that my son set up for me to be a Plex server.  It has stopped connecting to the internet or even just the LAN. I verified the switch and cable by swapping in a CAT5 cable from another machine that sits right next to it and is working; no change.

I can see that this machine has a second NIC card port.  I have no documentation about the mother board.  I need an Ubuntu command to identify the MAC address of the second NIC card; I think when I have that I can set it up with the Network dialog box.
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From the terminal, try this command:

ifconfig -a

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This will list the NICs and reveal their MAC addresses.

The below commands should show an "operstate" field.  This should give a hint if a cable is physically connected:

grep "" eth0/*

grep "" eth1/*  

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You might see what you can see in /sys/class/net/

You might want to try these commands:

sudo ethtool eth0 | grep Link

sudo ethtool eth1 | grep Link

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The above was largely taken from this link.

If you look at both NICs that are physically connected to the server, are they flashing green, amber or solid red?  Those could help give clues.
Mike CaldwellConsultant to IP industry

Author

Commented:
Thanks for pointing me in the right direction.  ifconfig showed only one ETH channel.  So I did open up the cabinet, get the MB model, and find the manual on line.  The "Integrated Peripherals" selection in the BIOS offered how to turn on the other ETH channel.  Did so, and Ubuntu really tried to get something out of it; it showed "Connecting" but never actually connected.  From the system diagram I have concluded that the PCI Experss bus must be shot, but to give this machine one more chance I'm going to pick up an outboard NIC card in the morning and see if that works.  If not, time to say goodbye to this MB.  Stay tuned for more!
Top Expert 2016

Commented:
the BIOS offered how to turn on the other ETH channel.

it is not very likely that both internal MB ethernet ports were defective. are they flashing red? you didn't answer to Phil's question.

you better check the connectivity again and try to Exchange the cable, plug the cable into another port of your switch or router and check the connectors. also unplug the router or switch from power, wait some time, and replug.

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Mike CaldwellConsultant to IP industry

Author

Commented:
There were flashing yellow lights.  I swapped in the same CAT5 cable to the same switch that another unit nearby uses; no change.  I then plugged in the CAT5 coming from the router to the switch directly to this unit; no change.  Ubuntu would show that ETH2 was "connecting" but then timed out.  That would imply an external problem, but with the swapping that seems to not be the case.  So my theory is that there must be a common point from the CPU to the serial channels is bad; both are on the PCIe bus.  So for $15 I can get a NIC card and give it a try.  

If the NIC card does not work, and the externals are OK, I don't see what else I can do.
Some motherboards have utilities that you can run on them.  Dell's hardware has such programs that test them without booting to an OS.  This can tell you if the motherboard is defective.
Mike CaldwellConsultant to IP industry

Author

Commented:
Finally got ETH1 configured and ETH0 disabled.  Now reaching the internet.  Thanks to all.
Mike CaldwellConsultant to IP industry

Author

Commented:
Thanks Phil.  Didn't use all of this; the ifconfig got me going down the right path, plus I found the manual on line.

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