Check for internet connection cron?

[mac666]

Hey
I would like to add a cronjob to check for internet connection.
If the internet connection is down, i would like it to preform certain tasks.

Perhaps ping Google and if hostname isnt responding or resolved it will do this tasks,
how ever my bash skills is very low...
Anyone who has any idea how to do this?
Any input are welcome!
Thanks

[Ryan Dwyer]

My bash skills are pretty poor too, but this seems to work:



#!/bin/sh

result=`dig google.com +short | wc -l`

if [ "$result" -eq 0 ]; then
echo "The lookup failed"
fi

[Lars Noodén]

You can also use the special variable $?



#!/bin/sh

/usr/bin/host www.google.com 8.8.8.8 > /dev/null 2>&1;

if [ 0 -eq $? ]; then
/bin/echo OK;
else
/bin/echo NO;
fi


Unfortunately it does not work with dig (https://bugs.launchpad.net/ubuntu/+source/bind9/+bug/854705), since dig returns 0 regardless of the outcome of the query passed to it.

[SeijiSensei]

#!/bin/sh

/usr/bin/host www.google.com > /dev/null 2>&1;

if [ 0 -eq $? ]; then
echo OK;
else
echo NO;
fi


I haven't experimented to know if this is true, but might this fail to test properly if you use an internal nameserver that caches records? I suggest forcing the DNS query to use an external nameserver like Google's at 8.8.8.8. To do so, replace the host command above with:


/usr/bin/host www.google.com 8.8.8.8 > /dev/null 2>&1