Test internet connection existence

[Mlehliw]

I'm looking for a standard way to test the existance of an internet connection under Linux. Is anyone aware of any standard methods?

[t3hi3x]

You could always ping a website like google.

[LaRoza]

Usually, I just ping a site. Actually, I use google because it is always there.

[Mlehliw]

Yea, I guess that's an option. I was wondering because I want to pop up a dialog if an internet connection isn't detected.

[LaRoza]

Yea, I guess that's an option. I was wondering because I want to pop up a dialog if an internet connection isn't detected.

I wrote a program that did exactly that. I'll go look for it.

[LaRoza]

Better solution in Bash (the old program was for Windows)

#! /bin/bash

main()
{
    ping -c 64.233.169.103 > /dev/null
    if [ "$?" -eq 0 ] 
    then
        zenity --info --text "Internet Lost";
    else
        sleep 30
        main
    fi
}

main

You can tweak this to your liking. It pings google, and if it fails, it will give a popup notifying you, if it suceeds, it waits 30 seconds and does it again.

[alex_o]

Better solution in Bash (the old program was for Windows)

#! /bin/bash

main()
{
    ping -c 64.233.169.103 > /dev/null
    if [ "$?" -eq 0 ] 
    then
        zenity --info --text "Internet Lost";
    else
        sleep 30
        main
    fi
}

main

You can tweak this to your liking. It pings google, and if it fails, it will give a popup notifying you, if it suceeds, it waits 30 seconds and does it again.

actually the line ping -c 64.233.169.103

gives you the usage because you need to specify the limit of pings to the -c flag ie:
ping -c 1 64.233.169.103

so in total it should look like:

#! /bin/bash

main()
{
    if ping -c 1 64.233.169.103 > /dev/null;then
        zenity --info --text "Internet Lost";
    else
        sleep 30
        main
    fi
}

main

[fax8]

@alex_o actually your code above does alert the user when the connection is working! The instructions in the if and else statements should be switched.

Fabio Varesano

[rnerwein]

hi
you have to use: netstat -punt | grep -i VERBUNDEN ( in english i think it is CONNECTED ) in a selfmade script.
and then, if $? is zero --> do your stuff ( 0 == VERBUNDEN || CONNECTED - depends on your language)
--> -punt will give you the name and the process-id of the process.
ciao

[Zugzwang]

you have to use: netstat -punt | grep -i

Uuuh, I don't think that this is a good idea. First of all, even if there is a connection, if there is no process at the point of time of checking this, you will receive a false negative. Then, intranet connections are also taken into account. Finally, there are pay-per-use internet connection providers which simply reroute all port-80 traffic through the connection to their payment site and block all other connections until you have bought some connectivity. Here, you get a false positive with your approach.

Finally, for getting rid of the language problem, you can always set "LANG=C" before calling the tool to make sure that the result is in english: "LANG=C netstat -punt"