I know about netstat, ncat,tcpdump and some others tools that show all connections, but what tool should I use if I want to see a specific connection established with a specific server?

For example: I am connecting to www.google.com port 80 from a simple web client; I need a command which only shows my connection with "www.google.com port 80".


You need to parse the output of netstat. On my system, netstat doesn't display the string "Google" when listing hosts. So, instead of simply using netstat -t | grep -i Google, you would need to lookup the name of the host. Something like:

$ sudo netstat -tn | awk '/EST/{print $5}' | sed 's/:.*//' | 
    while read ip; do 
        whois $ip | grep -qi google && echo "$ip"; 


  • sudo netstat -tn : run netstat showing only tcp connections (-t) and numerical IPs (-n);
  • awk '/EST/{print $5}' : print the 5th field (the IP) if this line matches EST (show only established connections);
  • sed 's/:.*//' : remove the port, leaving only the IP;
  • while read ip; do ...; done : iterate over each IP found;
  • whois $ip | grep -qi google : lookup the IP and search the output for google. The -i means case insensitive searching and the -q suppresses output.
  • && echo "$ip" : if the grep was successful, print this IP.

Running the command netstat with the flags -tanp on Ubuntu will list all the PIDs (Process Identification Numbers) and ports of each connection.

NOTE: to see all PIDs you should run the command with sudo permissions so sudo netstat -tanp


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  • thanks. its correct, but is there a way to only see one specific connection not all. like filtering with grep or so? if i use " netstat -tanp | grep tcp" , there it again shows lots of connections which is bothering.
    – Maria
    Jun 7 '15 at 8:42
  • Sure you can. Run sudo netstat -tanp | grep xxx and the command will show only the lines that have `xxx' in it.
    – user404182
    Jun 7 '15 at 9:38

I wrote a c++ program titled addressid, that employs the netstat command with the whois utility. On 14.04 the whois utility doesnt come 'stock out of the box', so you will have to install via command line as well as build-essential to compile the class file into binary.

:~$ sudo apt-get install build-essential -y

:~$ sudo apt-get install whois -y  

The program also expects two other directories to be in existence, /usr/local/addressId and /var/log/addressid so you will have to create these:

:~$ sudo mkdir -p -m0755 /usr/local/addressId

:~$ sudo mkdir -p -m0755 /var/log/adressid

Copy the program into gedit text editor, then compile the program as shown below:

:~$ g++ -o adressid addressId.cpp

Next move the program to /usr/bin (which is already in your $PATH) and use the new utility from command line as shown below

:~$ sudo mv addressid /usr/bin/

:~$ sudo addressid

You have to run the program as root, because the netstat utility requires root privileges to display all of the systems tcp information.

// This addressId.cpp class is created to input the output from   
// the netstat -tanp command and create a shell script that will be         
// executed performing the ip address (a dotted quad) look up on the   
// whois server (with whois utility).  
// author:GeoWade

#include <iostream>
#include <fstream>
#include <string>
#include <list>
#include <cstdlib>
#include <cstring>
#include <locale>

using namespace std;

const int MAX_INDY = 300;

int main()

    // create string variables
    string line;
    string holdWord = "";

    // create a string array to hold the ip addresses
    string holdArry[MAX_INDY];

    // create string variables to be used as test vars in regexs
    string theTcp = "tcp";
    string firstLn = "";
    string theSix = "tcp6"; 

    // create list<string> container object to hold input strings
    list<string> addressList;

    // create integer variables
    int index;
    int cardex;
    int count = 0;

    // use the system function to execute the netstat command and the data
    system("sudo netstat -tanp > /usr/local/addressId/Ntstat.txt");

    // create an ifstream object 
    ifstream inFile("/usr/local/addressId/Ntstat.txt");

    while ( getline( inFile, line ) ) {

        if ( !line.compare(44,7,firstLn) == 0 ) {

            if ( line.compare(0,3,theTcp) == 0 ) {

                if ( !line.compare(0,4,theSix) == 0 ) {

                    // find the index position of the line at which point it ends 
                    cardex = line.find('\0');

                    // store the substring of the line based on index positions
                    string intermStr = line.substr(44,cardex);

                    // locate the index position of the substring at which a colon
                    // resides
                    index = intermStr.find(":");

                    // create a second substr out of the first substring.
                    holdWord = intermStr.substr(0,index);

                // null the holdWord var and increment the count integer
                holdWord = "";              




    cout << "The data has been inputted to the program!" << endl;

    for (int i = 0; i < count; i++) {

        string outStack = addressList.front();

        holdWord = outStack;

        holdArry[i] = holdWord;
        holdWord = "";      


    // create an ofstream object
    ofstream outOne;    
    outOne << "#! /bin/bash\n\nMYWH=\"whois\"\nUPD=\"updatedb\"\n"
           << "TDTD=\"date\"\n\n$TDTD >> "
           << "/var/log/addressid/addressid.log\n" << endl;

    for (int j = count-1; j >= 0; j--) {

        string outHold = holdArry[j];
        holdArry[j] = "";
        holdWord = outHold;

        outOne << "$MYWH " << holdWord << " >> "
               << "/var/log/addressid/addressid.log" 
               << "\n" << endl;
        holdWord = "";      


    outOne << "$UPD\n\nexit\n" << endl;


    system("chmod +x /usr/local/addressId/myWhois.sh");


    // delete the previously created and executed my
    system("rm -rf /usr/local/addressId/myWhois.sh");

    count = 0;

    // output a statement to the user of the binary
    cout << "The operation has completed successfully!" << endl;
    return 0;


I wrote this program about 3 years ago, back on 12.04 as part of a security and logging suite I created. None the less it will log every address and those addresses information when it is ran, it also adds the date to the log each time it is ran. You can view the log by using the cat command or make a back-up as shown below

:~$ cat /var/log/addressid/addressid.log


:~$ cat /var/log/addressid/addressid.log >> $HOME/addressid.log.bak

The Program is legit, I just deleted my /usr/bin/addressid, copied the program (to verify there was no errors) from this web-page, compiled it, and perform the necessary sudo mv addressid /usr/bin/ and ran it as sudo addressid.

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