###################
# netstat - Basic #
###################

See: https://www.cyberciti.biz/faq/what-process-has-open-linux-port/

Type the following command:
--------------------------

    netstat -tulpn

Sample outputs:
--------------

    Active Internet connections (only servers)
    Proto Recv-Q Send-Q Local Address        Foreign Address    State      PID/Program name
    tcp        0      0 127.0.0.1:3306       0.0.0.0:*          LISTEN     1138/mysqld
    tcp        0      0 0.0.0.0:111          0.0.0.0:*          LISTEN     850/portmap
    tcp        0      0 0.0.0.0:80           0.0.0.0:*          LISTEN     1607/apache2
    tcp        0      0 0.0.0.0:55091        0.0.0.0:*          LISTEN     910/rpc.statd
    tcp        0      0 192.168.122.1:53     0.0.0.0:*          LISTEN     1467/dnsmasq
    tcp        0      0 0.0.0.0:22           0.0.0.0:*          LISTEN     992/sshd
    tcp        0      0 127.0.0.1:631        0.0.0.0:*          LISTEN     1565/cupsd
    tcp        0      0 0.0.0.0:7000         0.0.0.0:*          LISTEN     3813/transmission
    tcp6       0      0 :::22                :::*               LISTEN     992/sshd
    tcp6       0      0 ::1:631              :::*               LISTEN     1565/cupsd
    tcp6       0      0 :::7000              :::*               LISTEN     3813/transmission
    udp        0      0 0.0.0.0:111          0.0.0.0:*                     850/portmap
    udp        0      0 0.0.0.0:662          0.0.0.0:*                     910/rpc.statd
    udp        0      0 192.168.122.1:53     0.0.0.0:*                     1467/dnsmasq
    udp        0      0 0.0.0.0:67           0.0.0.0:*                     1467/dnsmasq
    udp        0      0 0.0.0.0:68           0.0.0.0:*                     3697/dhclient
    udp        0      0 0.0.0.0:7000         0.0.0.0:*                     3813/transmission
    udp        0      0 0.0.0.0:54746        0.0.0.0:*                     910/rpc.statd

TCP port 3306 was opened by mysqld process having PID # 1138. You can 
verify this using /proc, enter:

    ls -l /proc/1138/exe

Sample outputs:
--------------

    lrwxrwxrwx 1 root root 0 2010-10-29 10:20 /proc/1138/exe -> /usr/sbin/mysqld

You can use grep command to filter out information:
--------------------------------------------------

    netstat -tulpn | grep :80

Sample outputs:
--------------

tcp        0      0 0.0.0.0:80              0.0.0.0:*               LISTEN      1607/apache2


 1.  List all ports listening and non-listening:
    ------------------------------------------

     netstat -a | more
    
 2. List all TCP ports:
    ------------------

     netstat -at | more
    
 3.  List all UDP ports:
    ------------------
   
     netstat -au | more
    
 4.  List sockets which are in listening state:
    -----------------------------------------
   
     netstat -l | more
    
     netstat -lt | more #TCP ports
    
     netstat -lu | more #UDP ports
    
 5. Show the statistics for each protocol:
    -------------------------------------
   
     netstat -s
    
     netstat -st #TCP ports
    
     netstat -su #UDP ports
    
 6.  Display PID and program names in netstat output:
    -----------------------------------------------
   
     netstat -lp | more
    
     netstat -ltp | more #TCP ports
    
     netstat -lup | more #UDP ports
    
 7.  Print netstat information continuously:
    --------------------------------------
   
     netstat -c
   
     netstat -ct #TCP ports
   
     netstat -cu #UDP ports
   
 8. Find non supportive address families in your system:
    ---------------------------------------------------
   
     netstat --verbose
    
 9. Display kernel routing information:
    ----------------------------------
   
     netstat -r
    
10. Find out on which port a program is running:
    -------------------------------------------
    
     netstat -ap | grep SSH
    
     netstat -an | grep ":80"
    
11. Show the list of network interfaces:
    -----------------------------------
    
     netstat -i
     
     netstat -ie
     
12. Listing all UNIX listening ports:
    --------------------------------
    
     netstat -lx
     
13. Displaying promiscuous mode:
    ---------------------------
    
     netstat -ac 5 | grep tcp
     
14. Displaying IPv4 and IPv6 information:
    ------------------------------------
    
     netstat -g
     
15. Displaying RAW network statistics:
    ---------------------------------
    
     netstat --statistics --raw