Bash/sh: How to detect that there is no internet connection anymore?

frenchn00b · 09-12-2009, 02:15 AM

Hello,

I would like to restart my modules of my networking kernel (bugy) for my machine, when it is gone, ie no internet.

I was thinking to detect if I have internet, to ping, but well.

I would be glad to check out a code of a specialist, whiling or having aleready eventually some code to propose.

thanks

catkin · 09-12-2009, 03:32 AM

If your objective s to test networking in the kernel then best to start by specifying what you want to test. ping is OK to test IP connectivity (it's "pass" if a reply comes and "not known" if it doesn't) but I guess there's more to test than that in networking in the kernel.

jlinkels · 09-13-2009, 07:39 AM

I use this Bash script to log and reset my VPN connection. It can be easliy adapted, if you set OPEN_VPN_CMD to the script you want to have executed when the network is gone. I call this script from cron every 2 minutes. If you set debug_out to /dev/null, relevant messages are appended to /var/log/messages.

Code:

! /bin/sh

debug_out=/dev/null
#debug_out=/dev/stdout
NEXTHOP=star_pc.mydomain.com
OPEN_VPN_CMD="/etc/init.d/openvpn restart"
PING=/bin/ping

logger_opts="-t $0"
if [ "$debug_out" = "/dev/stdout" ]
then
        logger_opts="$logger_opts -s"
fi

pckts_rcvd=`$PING -c 8 -q -W 2 $NEXTHOP | grep transm | awk '{print $4}'`
echo "host: $NEXTHOP, pckts_rcvd: $pckts_rcvd" >$debug_out
if [ $pckts_rcvd -eq 0 ]
then
        echo "Connection with $NEXTHOP lost, resetting" | logger $logopts
        $OPEN_VPN_CMD > $debug_out
else
        echo "Connection with $NEXTHOP up, no action" | logger $logopts
fi