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 
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/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

Sun Happy Meal Card???

So we all know that Sun is a cool company with a great sense of humor, but they really outdid themselves when they named this combination SCSI / Ethernet card Happy Meal!

It’s a pretty old card, and honestly I had forgotten that I had installed it in my test system until I setup REL 3 on it last week. For some reason, the Red Hat installer wanted to remove the device before adding it back in. Luckily I had my camera with me when I saw the hardware detection message pop up.