Ytdyklly

I'm using this method...

if [[ "$(ping -c 1 8.8.8.8 | grep '100% packet loss' )" != "" ]]; then

    echo "Internet isn't present"

    exit 1

else

    echo "Internet is present"

    wget www.site.com

fi

I just used

nm-online

which pauses until a network connection is present by network manager. Worked well. You can do other stuff with it too.

Checking to see if a site is up is usually done with a monitoring tool like nagios. This will continuously monitor the site, and can notify you of outages.

When checking if the Internet is up from the command line I run through a number of steps:

• Check Internet is up ping google.com (checks DNS and known reachable site).


• Check web site is up use wget or w3m to fetch page.

If Internet is not up diagnose outward.

• Check gateway is pingable. (Check ifconfig for gateway address.)


• Check DNS servers are pingable. (Check /etc/resolv.conf for addresses.)


• Check to see if firewall is blocking. (Check /var/log/syslog as I log blocks.)

If Internet is up but site is down check with w3m http://isup.me/example.com replacing example.com with the site that appears down. Use wget, lynx, or which ever command line browser you have available if you don't have the w3m browser installed.

This is the shell srcript I'm using to test for internet connectivity:

alarm.sh

#! /bin/bash



if curl --silent --head http://www.google.com/ |

    egrep "20[0-9] Found|30[0-9] Found" >/dev/null

then

    echo Internet status: OK

else

    echo Internet status: ERROR

    mpg321 alarm.mp3 &> /dev/null

fi

sleep 60

clear



./alarm.sh

You will need to install curl and mpg321

sudo apt-get install curl mpg321

You will need a .mp3 sound file renamed to alarm.mp3 in the same folder if you want audible alarm functionality. Finally configure website URL and egrep to your needs.

Checking whether internet is working

sudo nm-tool | grep "State: connected" | wc -l

From output (excerpt):

1 #System is connected to internet

However, as mentioned by others, this is not telling whether you really have connectivity or not. Eg. You could be connected to the router and router is not necessarily connected to internet.

I am using this method:

if curl -s --head  --request GET www.google.com | grep "200 OK" > /dev/null ; then

    echo "Internet is present"

else

    echo "Internet isn't present"

fi

It will try to connect to a well-known website and if it can connect to it then we will assume there is the internet.

I needed help with the same question, and I got my answer this way:

echo $(nm-online) $? connection problems

Checking whether Internet is working is not so trivial. ping is ICMP, so it might work even if the web proxy is down. Something similar occurs with DNS if you test with an IP.

Since my Internet connection is unstable I created this script (based on this one) that makes a gentle chord sound to call me, and also uses Ubuntu notify when the Internet connection comes back:

#!/bin/bash



hash play 2>&- || { echo >&2 "I require «play» but it's not installed. Try apt-get install sox. Aborting."; exit 1; }



WGET="`which wget`"

URL="http://www.google.com"

delay=3;

noConnectionMessage="No connection, trying again in $delay seconds...";

connectionMessage="WE HAVE INTERNET! :) Trying again in $delay seconds...";



echo "INTERNET TESTER: Type Ctrl+C to quit";

rm --force /tmp/index.site



function playSound {

    time=1;    # Time played

    if [ `sox --version| grep -oP "v[0-9.]+" | sed "s/[v.]//g"` -lt 1431 ]; then    #analize sox version, if greater than v14.3.1 can use pluck

        play -q -n synth $time sine;

    else

        play -q -n synth $time pluck $1;

        #for i in G4 G4 G4 E4;do play -n synth 0.1 pluck $i repeat 2;done    # You can play with something like this also :) (first three notes from Beethoven 5th symphony)

    fi

}



while [ 1 -eq 1 ]; do

    $WGET -q --tries=10 --timeout=2 $URL -O /tmp/index.site &> /dev/null

    if [ ! -s /tmp/index.site ];then

        echo $noConnectionMessage;

        #playSound E2

        sleep 1;

    else

        #~ zenity --warning --text "ADDRESS is back"

        notify-send -i "notification-network-wireless-full" "Connection state:" "$connectionMessage";

        echo $connectionMessage;

        playSound E3

    fi

    sleep $delay;

done



exit 0;

I was looking for a script that would continuously test my internet connection, that would be started whenever my server was up and I made this:

1. 
   

   First, install fping

   
   
   

   apt-get install fping
   
   

   
   


2. 
   

   Create an init script in the /etc/init.d folder with the following content (I called it testcon)

   
   
   

   #!/bin/bash
   
   
   
   PIDFILE=/var/run/testcon.pid
   
   
   
   . /lib/lsb/init-functions
   
   
   
   case "$1" in
   
     start)
   
           log_daemon_msg "Starting internet connection tester"
   
           /etc/init.d/testcond &
   
           echo $! > $PIDFILE
   
           log_end_msg $?
   
       ;;
   
     stop)
   
           log_daemon_msg "Stopping internet connection tester"
   
           PID=$(cat $PIDFILE)
   
           kill -9 "$PID"
   
           log_end_msg $?
   
       ;;
   
     *)
   
       echo "Usage: /etc/init.d/testcon {start|stop}"
   
       exit 1
   
       ;;
   
   esac
   
   
   
   exit 0
   
   

   
   


3. 
   

   Create a script in the /etc/init.d folder with the following content (I called it testcond)

   
   
   

   #echo Computer starting or testing daemon init
   
   while [ "$itest" == "" ] 
   
   do
   
       #wait 5 seconds 
   
       sleep 5
   
       itest=$(fping 8.8.8.8 | grep alive)
   
   done
   
   date | mail -s "Server is up and Internet is online" your_email@gmail.com
   
   
   
   #loop forever
   
   while [ "1" == "1" ] 
   
   do
   
       itest=$(fping 8.8.8.8 | grep alive)
   
       #if internet is down
   
       if [ "$itest" == "" ] 
   
       then
   
           #echo Internet is down
   
           #log time it was found down
   
           current_time=$(date)
   
           echo "Internet was found down @ $current_time" >> /mnt/data/Server/internet_log.txt
   
           #loop until it is back
   
           while [ "$itest" == "" ] 
   
           do
   
               #wait 60 seconds 
   
               sleep 60
   
               itest=$(fping 8.8.8.8 | grep alive) # test the internet
   
           done
   
           #when it is back
   
           current_time=$(date)
   
           echo "Internet is back        @ $current_time" >> /mnt/data/Server/internet_log.txt
   
           body=$(tail -2 /mnt/data/Server/internet_log.txt)
   
           echo "$body" | mail -s "Internet is back online" your_email@gmail.com
   
       fi
   
       #echo Internet is online
   
       #wait 60 seconds
   
       sleep 60
   
           done
   
   

   
   


4. 
   

   Then I run the commands below to add to the start-up:

   
   
   

   sudo update-rc.d testcon defaults
   
   sudo update-rc.d testcon enable
   
   

   
   



5. Reboot

I was faced with random droppings of Wi-Fi connections by my Broadcom BCM94331CD chip. I devised the following bash script (infinite loop) checking each second if the Internet Wi-Fi connection is up and running. Other command line proposed here will wait for at least 5 to 10 seconds before closing with a status i.e. ping. In the mean time I am looking for a definitive solution as well.

From results on askubuntu, I will have to purge the bcmwl-kernel-source package as I use firmware-b43-installer and b43-fwcutter.

Thanks everyone for their suggestions (above).

This script needs to be added in the Start-Up Programs and don't need super user privilege to run as well.

#!/bin/bash

#



# Check if Wi-Fi is disabled e.g. 'out of range'

# If so quickly re-enable Wi-Fi

# Due to a problem with Broadcom proprietary driver in package firmware-b43-installer



# Script is part of Start-Up programs

# Stored in /usr/local/bin/

# Infinite loop checking every second if Wi-Fi is up and running



while true; do

  # https://askubuntu.com/questions/27954/how-can-i-check-internet-connectivity-in-a-console

  if [[ $(nmcli -f STATE -t g) != 'connected' ]]; then

    # Disable and Re-Enable Wi-Fi as the Wi-Fi is now 'out of range' (disconnected)

    nmcli radio wifi off

    nmcli radio wifi on

  fi

  sleep 1

done