IFCONFIG Does Not give You Link Status; ETHTOOL Does

For some reason that is a complete mystery to me, RHEL does not give you the link status when you run # ifconfig -a. This makes it incredibly hard to debug link integrity issues! Buried amongst all of Red Hat’s proprietary commands, however, is a utility called ethtool, which does give you the status of your link.

Since ethtool is used for querying settings of an ethernet device and changing them, it does a lot more than just give link status. Amongst other things, you can use it to turn on or off autonegotiation on your network card. Run # /sbin/ethtool -h for full usage.

Here’s how you use it to see if your server has link:

# /sbin/ethtool eth0

You should see something like this:

Settings for eth0:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full
                                100baseT/Half 100baseT/Full
                                1000baseT/Full
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 1
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: g
        Wake-on: d
        Link detected: yes

This entry was posted on Friday, February 16th, 2007 at 12:17 pm and is filed under Data and Technology. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

fabioamd87

Sep 1st

can you explain me what you mean with link status?
Thanks
cliff

Sep 4th

All the output is important because it indicates the type and health of the link, but the main thing you are often looking for is this:

Link detected: yes
fabioamd87

Sep 6th

link detected means cable connected?

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