April 2009

On unix based systems permissions work differently then on Microsoft windows based systems. You need to execute your program with "root" privilege in order to see it.

Secondly, also make sure to print out the error message return in the "errbuf" parameter you passed into Pcap.findAllDevs method. It should contain information about the cause of your problem.

I'm doing some preliminary testing with tcpdump so that I can get a better understanding of how to use libpcap (through jNetPcap) before actually running a real test with jNetPcap. I'm sending four pings from one PC to another and capturing them on the receive side using "tcpdump 'icmp' ". This works but there's a delay of perhaps 15 seconds before tcpdump even shows the traffic. I suppose I can expect to see this same delay in jNetPcap ...right?

Why is there such a long delay ?

edited:
RESOLVED: Without the "-n" argument, tcpdump does a DNS lookup on incoming traffic. With the "-n" argument, tcpdump is fast !

Thank you!

I'm trying to run the ClassicPcapExample.java, but I can't seem to get it to run inside of Eclipse or from the command-line. I'm hoping it's something simple, but I can't figure it out yet

Eclipse has been updated to the latest version, and I'm using Java 6 update 13.

I added the jnetpcap-1.2.rc5.jar file to the referenced libraries for my project, so it seems to build fine.

I also added the -Djava.library.path=C:\jnetpcap-1.2.rc5 to the VM arguments, and that fixed the link error. But, now when I try to run it I keep getting the following error.


java.lang.NoClassDefFoundError: examples/ClassicPcapExample
Caused by: java.lang.ClassNotFoundException: examples.ClassicPcapExample
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
Exception in thread "main"


Here is the source file that I'm currently using


package example;

import java.nio.ByteBuffer;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;

import org.jnetpcap.Pcap;
import org.jnetpcap.PcapHandler;
import org.jnetpcap.PcapIf;

@SuppressWarnings("deprecation")
public class ClassicPcapExample {
public static void main(String[] args) {
List alldevs = new ArrayList(); // Will be filled with NICs
StringBuilder errbuf = new StringBuilder(); // For any error msgs

/********************************************
* First get a list of devices on this system
********************************************/
int r = Pcap.findAllDevs(alldevs, errbuf);
if (r == Pcap.NOT_OK || alldevs.isEmpty()) {

I have just installed jNetPcap and am trying to get the "ClassicPcapExample.java" to run (RHEL Linux). I am new to Java; I have many years experience as a C/C++ Developer.

Here's what I did for the install:
1. Downloaded the RPM and installed it.
2. Verified that libpcap is installed; version 0.9.4 of libpcap.so is in /usr/lib/ (with usual softlinks).
3. > LD_LIBRARY_PATH=/usr/lib

Here's what I do to compile and run:

javac -classpath /usr/share/java/jnetpcap-1.2.rc5.jar:./  -Xlint:deprecation ClassicPcapExample.java

   ...this gives some warnings for PcapHandler but it does compile a .class file.


java -classpath /usr/share/java/jnetpcap-1.2.rc5.jar:./  ClassicPcapExample

    ...this gives java.lang.NoClassDefFoundError for ClassicPcapExample

What's going on ??