So the wireless driver for TP-Link TL-WN725N I wrote about earlier is a bit prone to dropping the connection every now and then. To mitigate this problem and keep the wireless connection up I wrote a bash script which is run by root’s cron every 5 minutes.

Cron

Use crontab -e to add a cron job

[shell]pi@raspberrypi ~ $ sudo crontab -e[/shell]

Then just place the entry at the bottom, save and exit. (Nano: ctrl + x, then y. Vi(m): :w)

[shell]*/5 * * * * /home/pi/src/netmon.sh[/shell]

If you want to see the output it’s recommended to pipe it to a file.

[shell]*/5 * * * * bash /home/pi/src/netmon.sh >/home/pi/src/netmon.log 2>&1[/shell]

netmon.sh

You can change the interface to check by editing the INTERFACE variable, see highlighted row below. Requires root privileges as it resets the interface.

[shell highlight=”5″]
#!/bin/bash
#netmon.sh

#Config
INTERFACE="wlan0"

#Commands
ROUTE=`which route`
AWK=`which awk`
HEAD=`which head`
TAIL=`which tail`
IFCONFIG=`which ifconfig`
IP=`which ip`
PING=`which ping`
SLEEP=`which sleep`

#ifup and ifdown are not normally in the cron’s environment so we specify the paths here
IFUP="/sbin/ifup"
IFDOWN="/sbin/ifdown"

#Config (auto)
GATEWAY=`$ROUTE | $AWK {‘print $2’} | $HEAD -n 3 | $TAIL -n 1`
INTERFACEIP=$($IP addr show $INTERFACE | $AWK ‘/inet / {print $2}’ | cut -d/ -f 1)

function valid_ip() {
local ip=$1
local stat=1

if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
OIFS=$IFS
IFS=’.’
ip=($ip)
IFS=$OIFS
[[ ${ip[0]} -le 255 && ${ip[1]} -le 255 \
&& ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
stat=$?
fi
return $stat
}

function ping_ip() {
$PING $1 -c 4

return $?
}

function toggle_network_connection() {
#Always set network down first
`$IFDOWN $1`

#Sleep 5 seconds before bringing it up
$SLEEP 5

#Bring network up
`$IFUP $1`

return $?
}

if [[ ! -z "$INTERFACEIP" ]]; then
if valid_ip $INTERFACEIP; then
echo "Interface up with IP $INTERFACEIP"
else
if ping_ip $GATEWAY; then
echo "Network is having issues, gateway $GATEWAY reachable on at least one interface"
toggle_network_connection $INTERFACE
RESET=$?
else
echo "Network connection is down! Gateway unreachable. Attempting reconnection."
toggle_network_connection $INTERFACE
RESET=$?
fi
fi
else
echo "Interface has no ip address. Toggling interface."
toggle_network_connection $INTERFACE
RESET=$?
fi

if [[ ! -z "$RESET" ]]; then
if [[ $RESET -eq 0 ]]; then
echo "Interface was reset successfully"
else
echo "Network connection could not be reset. Reboot recommended."
fi
else
echo "No problems with interface $INTERFACE was detected."
fi
[/shell]

Sample output

Interface up:
[shell]pi@raspberrypi ~ $ sudo bash netmon.sh
Network up with IP 192.168.10.17
No problems with interface wlan0 was detected.
[/shell]

Interface down:
[shell]pi@raspberrypi ~ $ sudo bash netmon.sh
Network has no ip address. Toggling interface.
/sbin/ifdown: interface wlan0 not configured
Network connection was reset successfully
[/shell]