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I am unable to setup remote debugging for my Tomcat 6 web app on Ubuntu 12.04.

I have tried the solutions offered in the following related question: Remote debugging Tomcat with Eclipse

The highest ranked solution says I should open catalina.sh and change the JPDA_OPTS variable to: JPDA_OPTS="-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n"

Then start tomcat using jpda: catalina.sh jpda start

I checked my app at localhost, port 8000 and got an 'Unable to connect error'.

The next best solution was:

In catalina.bat file please modify the below.

Step 1: CATALINA_OPTS="-Xdebug -Xrunjdwp:transport=dt_socket,address=8000,server=y,suspend=n"

Step 2: JPDA_OPTS="-agentlib:jdwp=transport=dt_socket,address=8000,server=y,suspend=n"

Step 3: Run Tomcat from command prompt like below: catalina.sh jpda start

When I checked localhost, port 8000 I got the same 'Unable to connect error'. Attempting to connect to the tomcat debugger through Eclipse after both of these attempts gave me an error: 

Failed to connect to remote VM. Connection refused.
Connection refused

This made me think that port 8000 might be closed so I ran an nmap command to show which ports on my 'localhost' were open. It returned the following:

ryan@ryan-K53E:~$ nmap -v localhost

Starting Nmap 5.21 ( http://nmap.org ) at 2013-04-15 22:12 BST
Initiating Ping Scan at 22:12
Scanning localhost (127.0.0.1) [2 ports]
Completed Ping Scan at 22:12, 0.00s elapsed (1 total hosts)
Initiating Connect Scan at 22:12
Scanning localhost (127.0.0.1) [1000 ports]
Discovered open port 80/tcp on 127.0.0.1
Discovered open port 3306/tcp on 127.0.0.1
Discovered open port 53/tcp on 127.0.0.1
Discovered open port 22/tcp on 127.0.0.1
Discovered open port 8080/tcp on 127.0.0.1
Discovered open port 631/tcp on 127.0.0.1
Completed Connect Scan at 22:12, 0.02s elapsed (1000 total ports)
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00028s latency).
Not shown: 994 closed ports
PORT     STATE SERVICE
22/tcp   open  ssh
53/tcp   open  domain
80/tcp   open  http
631/tcp  open  ipp
3306/tcp open  mysql
8080/tcp open  http-proxy

Read data files from: /usr/share/nmap
Nmap done: 1 IP address (1 host up) scanned in 0.07 seconds

This looks to confirm that port 8000 is closed so I defined 'tomcat-debug' as a service in the '/etc/services' file like so:

tomcat-debug        8000/tcp        # Remote tomcat debugging

Then tried to open port 8000 with iptables using the following command:

sudo iptables -A INPUT -p tcp --dport tomcat-debug -j ACCEPT

This doesn't seem to have made a difference as nmap is still showing the same list of open ports as before. Any help here would be greatly appreciated.

Community
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Ryan Deery
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  • Just wanted to point out that JDWP is a dangerous thing to expose. http://nmap.org/nsedoc/scripts/jdwp-exec.html and http://stackoverflow.com/a/9200263/1183387 – bonsaiviking Apr 16 '13 at 00:33
  • Thanks for pointing that out. I don't think the port is open according to my nmap output, do you think it is? – Ryan Deery Apr 16 '13 at 08:13
  • No, it does not look open, but you intend to open it. Just make sure there are other controls in place (like a source IP restriction in your iptables rule) to prevent others from accessing it. I think the debugger can be opened in client mode, too (meaning you have a debugger listening for the incoming connection). To avoid the complete Nmap scan every time, use -p 8000 – bonsaiviking Apr 16 '13 at 11:49

1 Answers1

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Before checking if port 8000 is reachable form outside (your test with nmap) , have you tried to check if tomcat is listening on port 8000 ?

I'd use sudo netstat -pnl | grep 8000 to get a list of all process listening on port and filter this list for lines containing 8000. you should receive something like this :

tcp 0 0 127.0.0.1:8000 0.0.0.0:* LISTEN 14236/java

This line tell that the process java (pid 14236) is listening for tcp on localhost(127.0.0.1) port 8000.

You should check that you tomcat process is listening on an external address if you want to connect to from external.

fred
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  • I'm having the same problem as the OP. In my case there is nothing listening on port 8000, and I have no idea why. – Jeremy List Apr 25 '14 at 03:23