Shell Programming and Scripting

I have a box that has to start dhcpd when a certain connection is down and stop the dhcpd when the connection is up again. I would appriciate any help making this script:

From server A:

ping server B
if connection is ok then do nothing
if connection is not ok then start dhcpd
until connection to B is up again

Regards kim jensen

Welcome to the forum !

This is just a hint and am not very thorough with this.

Ping works using ICMP and a host might be still up and not accepting/responding to ICMP packets, in such cases ping might not help with. Instead, check if the destination ip is reachable. If that is so, start the process from the local host where request is initiated.

Let us know, how it goes

Hello there,
thank you for the reply! I guess I didn't make myself clear.
I only need to test if the connection is up the 'aliveness' of the B
server is uninteresting at this point.

I have tryed something like this:

#!/bin/bash
ping hostB -c3 -W3 > /dev/null
echo $? > A
if grep 0 /home/sipp/A > /dev/null
then exit;
elif
grep 1 /home/sipp/A
then
until grep 0 /home/sipp/A > /dev/null
do
[a command]
done
fi

my problem is that the loop keeps looping even if the connection is up again?

Regards KimJ

No need to redirect output of $? to a file "A" and then grep from that.
Instead use it directly in 'if' block

Code:

if [ $? -eq 0 ];
then
# stuff to do
fi

-thanks again
I do learn from this

My plan is to execute the script every minute by a cronjob that works fine. But the thing is that I made an infinite loop and I don't know how to get out of it again when the connection is up again ?

you miss a lot about how does work a daemon...
I do too: AFAIK
a daemon is still listening, ever, at what ever could come to it by its port...

daPeach thank you for the reply
my aim is this:
B is primary dhcp server
if A server have connectivity to the B server then nothing
If A server have no connectivity to the B server, it should start dhcpd -until connection to B server is up again..