Robert G. Brown rgb at
Sat Mar 8 15:38:56 PST 2003

On Sat, 8 Mar 2003, Donald Becker wrote:

> On Thu, 6 Mar 2003 john152 at wrote:
> > I'd like to do a code  that monitors the link status (link active and
> > connected to net or not...) and gives me an error if this status
> > changes. Is there any software today that does so? 
> You can easily write a script that monitors the exit status of
>    mii-diag --status eth0
> or the output of
>    mii-diag --watch eth0

There is one other trick that mii-diag makes possible that is so lovely
that I've seriously considered posting it back to e.g. RH for permanent
inclusion in their boot cycle.  See the following modified
/etc/sysconfig/ifcfg-eth0 (or really, ethX as the same trick can be used
for each eth device).  Pretty crude, but adequate.

I use a laptop that I move around a lot, booting it with/without
ethernet wire attached, with/without a wireless card.  Waiting for all
its ethernet initialization to time out is a real PITA.  So I used
mii-diag to check for link beat.  If there is none, chance are you're
not plugged in (yet) so I set ONBOOT=no instead of yes.  I can still
bring up a network manually at any time (after plugging in the wire or
whatever) but I don't have to wait.


Robert G. Brown	             
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at

# We are rather tired of having to wait for the interface to time out
# on boots when the system isn't on a network.  We therefore check for
# the existence of a link BEFORE trying to initialize it, much as we
# check for the insertion of a PCMCIA card for the wireless interface
# on eth1.
# If variable NE is not empty after this call, there is no link
if [ -x /sbin/mii-diag ]
  NE=`/sbin/mii-diag eth0 | grep "not established"`
# So if it IS empty, we have a link and start up the interface, trusting
# that there is a dhcp server out there somewhere.
if [ -z "$NE" ]
  # This cleans up the device and sets it so it DOES initialize
  # at boot.
  echo "Link beat found on interface eth0, initializing..."
  # This cleans up the device and sets it so it does NOT initialize
  # at boot.
  echo "Warning: No link beat found, NOT initializing interface eth0!"
  echo " Solution: First connect to a network, then bring up network

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