Wall execution problems from cron

So I've been tasked with creating a shell script to run in a cron every few minutes to check duplex settings on my eth0 nic card. I would like for the server to send a wall message to whoever is on the console or in a terminal session. Below is what I have so far.

0,10,20,30,40,50 * * * *  /home/acc4000d/test10

I have it in my root's cron so that wall will run. Can someone tell me what I'm missing for the wall to actually happen?

Script looks like this;

#!/bin/bash
DUPLEX=$(ethtool eth0 | sed -n 's/Duplex:\(.*\)/\1/p')
if [ $DUPLEX = Half ]
then /usr/bin/wall duplex_error 
fi

annnnd the wall message file is called "duplex_error"

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