Friday, November 30, 2012

How to redirect incoming TCP connections to other ports (Example : 80 to 8080)

 Hello Everybody,

Today, I will show you how I solved a problem which occurred when I started setting a java web application in a production server.
We all now that Apache Tomcat Server uses the 8080 port by default. So we have to add ":8080" every time to reach the application.

The solution is to replace the 8080 port by 80. There are two ways: 

  1. Configuring Apache Tomcat
  2. Redirect incoming TCP connections from 80 port to the 8080 one.
Below the command to redirect the incoming tcp connections :

iptables -A PREROUTING -t nat -i eth0 -p tcp --dport 80 -j REDIRECT --to-port 8080

I have no idea which is the best way to resolve such problem ( I think the first option is the cleanest). However, this method is the quickest because it saves you some minutes.

Good bye :-)

Friday, November 23, 2012

Check opened ports in Linux with nmap & netstat

Several times, I would know which are the opened ports in my Linux servers (yes I have many Linux servers :p ).

There are two good methods to check what ports are open in Linux :
  1. nmap : a port scanner
  2. netstat

nmap can be used to scan your machine to check opened ports.
Enter the following command to scan your computers machine:

nmap -sS -O

Once the scan has finished you will get the following ouput:

Starting nmap 3.70 ( ) at 2005-01-16 05:48 GMT
Interesting ports on localhost.localdomain (
(The 1656 ports scanned but not shown below are in state: closed)
PORT     STATE SERVICE22/tcp   open  ssh80/tcp   open  http443/tcp  open  https1241/tcp open  nessusDevice type: general purposeRunning: Linux 2.4.X|2.5.X|2.6.X
OS details: Linux 2.5.25 - 2.6.3 or Gentoo 1.2 Linux 2.4.19 rc1-rc7)
Uptime 1.985 days (since Fri Jan 14 06:10:41 2005)
Nmap run completed -- 1 IP address (1 host up) scanned in 2.341 seconds

The second method consist in using netstat. netstat can show hidden ports and what programs using them. 

Type following command as root:

netstat -nap

It will show you the output of something similar to:

Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address               Foreign Address             State       PID/Program name
tcp        0      0   *                   LISTEN      5277/wish
tcp        0      0    *                   LISTEN      3920/mDNSResponder
tcp        0      0      *                   LISTEN      31438/nessusd: wait
tcp        0      0           ESTABLISHED 5062/xchat
tcp        0      0            ESTABLISHED 5277/wish
tcp        0      0                ESTABLISHED 5062/xchat
tcp        0      0 :::80                       :::*                        LISTEN      4355/httpd
tcp        0      0 :::22                       :::*                        LISTEN      32372/sshd
tcp        0      0 :::443                      :::*                        LISTEN      4355/httpd
udp        0      0    *                           3614/dhclient
udp        0      0  *                           3920/mDNSResponder

A quick post certainly, but I hope it would be useful for you.

PS: for more details try google :p

Good Bye ;-)

Tuesday, January 17, 2012

Error Booting CentOs in VirtualBox - FATAL: INT18: BOOT FAILURE

Tonight, I tried to install CentOs in VirtualBox VM. I didn't find any problem with installation until the first reboot on which the system told me:


If this happens to you, be sure to check if the installation media (the cd-rom or the dvd-rom) is still present in the CD/DVD player device. You have to remove it.
It appears to be a known issue with VirtualBox, since a bug #2680 opened 4 years ago and still unresolved.

Finally, have nice time with the GREAT CentOS 6

Good Bye :-) 

NB: this solution can be applied for the CentOs' brothers , Fedora, Redhat, Enterprise Linux, ... ;)

EDIT: An additional solution 

Hans de Raad

3 weeks ago  -  Shared publicly
You could also press F12 on booting and select booting directly from the virtual harddrive. Also works.

Friday, January 6, 2012

How To Install Tomcat 6 and AXIS2 on linux Mint in 3 steps

Today, I will share with you a good experience with linux Mint. Last Night, I tried to prepare Tomcat and Axis2 to create and test web services.
The implementation was easy and it only took some minutes.

Follow  the 3 steps below to install Tomcat 6 and Axis2 on linux Mint:
  1. Installation of Tomcat6 packages:
    With Linux Mint, you will find  
    java version 1.6.* installed. You have only to install tomcat6 packages with this command 

    sudo apt-get install tomcat6 tomcat6-admin tomcat6-docs tomcat6-examples

    Now, you can try accessing localhost:8080/ in your browser

  2. Tomcat's Configuration
    Tomcat6 default install hasn’t the admin user parameters in config file, you’ll have to edit tomcat-users.xml file

    sudo gedit /etc/tomcat6/tomcat-users.xml  

    you’ll have to add next lines:

    <?xml version='1.0' encoding='utf-8'?>

          <role rolename="manager"/>
          <role rolename="tomcat"/>
          <role rolename="admin"/>
          <user username="admin" password="password" roles="manager,tomcat,admin"/>

    Don't forget to change 
     “password” with your own  :-).Finally, you will need to restart tomcat6 with this command
    sudo service tomcat6 restart
  3. AXIS2 Deployment
    In this step, we will try to deploy axis2 on our installed tomcat6. First, download  the WAR archive from this link:
    Open Tomcat Web Application Manager with this URL: http://localhost:8080/manager/html and deploy the WAR archive on tomcat from the "WAR file to deploy" menu.If all works fine, you can access it through this link : http://localhost:8080/axis2/

Good Bye :-)

NB: May be you will have some permissions and access problems, try this  : 
sudo chmod -R 777  /var/lib/tomcat6/webapps/axis2/WEB-INF/