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Calling all teens: join the latest round of Google Code-in

Yesterday marked the start of the 7th year of Google Code-in (GCI), our pre-university contest introducing students to open source development. GCI takes place entirely online and is open to students between the ages of 13 and 17 around the globe.

Open source software makes up the backbone of the internet, from servers and routers to the phone in your pocket, but it’s a community-driven effort. Google Code-in serves a dual purpose of encouraging young developers and ensuring that open source communities continue to grow.

The concept is simple: students complete bite-sized tasks created by 17 participating …Read More

Source:: Calling all teens: join the latest round of Google Code-in

How to Create a Bootable USB for Ubuntu Server

If you’re reading this blog post then you’re probably in the realms of playing with hardware and building a mini server, media server, web server or something along those lines. Great! So now you’ve got your hardware pieced together, it’s now time to start installing software on it. For the purposes of this blog post, I’m not going to go into the details of what/why/when/who/how for the vast array of choices and options available for configuring software on your server. Instead, I’m just going to look specifically about how to create a bootable USB for installing Ubuntu Server. Simple and straight to the point.  

 

Step 1: Install Universal USB Installer 

Download here, https://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/ 

This software will turn a .iso file into a bootable partition on a USB drive.  

 

Step 2: Download Ubuntu Server 

Download the relevant version here, https://www.ubuntu.com/download/alternative-downloads#alternate-ubuntu-server-installer 

Note, make sure you’re downloading the correct version for what you require, there are quite a few different versions! 

This step will download the .iso file to your computer. You’ll need this file in the next step.  

 

Step 3: Create the Bootable USB 

Follow the instructions here, https://www.pendrivelinux.com/universal-usb-installer-easy-as-1-2-3/ 

In essence, you’re installing the .iso file you downloaded in the previous step onto your USB Pen Drive. Note, make sure you install on the correct drive on your computer or you can really really really mess things up! 

When you are creating the bootable USB for Ubuntu Server, make sure you actually select Ubuntu Server from the dropdown list, as there is also an option for installing Ubuntu (desktop) version too, which you don’t want.  

 

Complete! 

That’s it! You’re done. You’ve just created yourself a bootable USB that can be used for installing Ubuntu Server. Simply plug this device into your server, make sure that it has priority boot settings so your installer can then run and you’re on your way! 

 

Note for Ubuntu Server 18.04

The above software doesn’t seem to like Ubuntu Server 18.04, so you’ll probably need to use the Rufus software instead – https://rufus.akeo.ie/

 

How to Loop Through a Map in Java Using JSTL on a JSP

Quick info for reference.
Loop through a Map and output the Key and Value data using;

<c:forEach items="${map}" var="entry">
  Key: <c:out value="${entry.key}"/>
  Value: <c:out value="${entry.value}"/>
</c:forEach>

If you have an object within the Key:Value pair, such as within an object Map(), you can get this data as follows;

${map.key}

Then you can iterate over the above list using the code to get the Attribute data within the CustomerInformation object a follows;

<c:forEach items="${map.value}" var="customerInformation"> 
  <tr>
    <td>${customerInformation.firstName}</td>
  </tr>
</c:forEach>

How to Increase the Maximum Connections on Apache Tomcat

The maximum number of connections that Apache Tomcat can handle is defined within the Tomcat settings. In essence, this setting determines the number of concurrent connections that can be handled by Apache Tomcat.

Out of the box, Apache Tomcat is configured to handle around 200 simultaneous connections (kind of…), which for most web servers and projects is more than adequate. But when you get into the realms of millions of monthly active users and concurrent connections, you’ll soon need to optimise Tomcat to suit your needs accordingly.

Ultimately though, the number of simultaneous connections that the Apache Tomcat software on your web server is capable is handling is determined by the physical limitations of your web server. The bigger your hardware, the bigger the number of connections that Apache Tomcat is capable of handling. This being said, the 200 maximum connections as a default is merely an arbitrary number, so you’ll need to assess this in relation to the hardware you are running on. The bigger the server hardware you’re running on, the higher the number of maximum connections on Apache Tomcat your server will be able to handle. As always, this can change depending on what you are doing. For example, if you have a process on your really fast server that is calling a third party dog slow server, then this soon becomes the limiting factor in the chain.

Max connections from an Apache Tomcat perspective is calculated based on a number of factors such as the number of simultaneous connections multiplied by the maximum execution time that each thread is capable of handling. Under normal circumstances this can appear to be behaving correctly, so keep in mind exceptional circumstances when things don’t quite perform as you wish. What you’ll soon spot (via the Tomcat Manager) is that the Max Connections soon starts to creep up and eat up all the resources on your server. This can be caused by many factors, from long running processes on your own server, or code on that is calling third party servers which may be running slow and causing problems.

With all this in mind, let’s take a look at how to increase the maximum connections on Apache Tomcat. It’s actually quite simple to do.

Run the command;

 


sudo nano /usr/share/tomcat8/conf/server.xml

 

This command will open the editor to edit the file Server.xml which controls many of the settings required for configuring Apache Tomcat. You’ll note that it is Apache Tomcat 8 that is being used in this example, so edit this accordingly for the version of Apache Tomcat that you are using. Again, depending on your individual configuration of your server, this file may live in a different file path. So to easily find the file if the above command doesn’t work, then run the command below;

 


find / -type f -name server.xml

 

The above command will search for a File (f) called “server.xml”

What you’re looking for within this file is the setting for “maxConnections” which will have a value set. You may not have this variable set so look out for the core settings for the port that your Tomcat instance is listening on, for example;

 


<Connector port=”8080” protocol=”HTTP/1.1” maxConnections=”200”/>

 

The maximum number of connections that the server will accept and process at any given time. When this number has been reached, the server will accept, but not process, one further connection. This additional connection be blocked until the number of connections being processed falls below maxConnections at which point the server will start accepting and processing new connections again.

Depending on your specific requirements, you may also need to increase the maxThreads setting too. Hope that helps getting you started with tuning Apache Tomcat for your specific needs.

How to Make Apache HTTPD Service Start Automatically on Server Reboot and Startup

If you’re looking for a quick answer and you’re running a common version of Linux, just type this when you are SSH’d into your server;

 


sudo chkconfig httpd on

 

Now for a bit more technical details about what this all does.

 

What is chkconfig?

The Chkconfig command in Linux is used to setup, view, or change services that are configured to start automatically during the system startup which abstracts some of the underlying settings that are stored within the /etc/rc.d/init.d/ directory. Chkconfig basically helps you to easily make service start or not when your system reboots.

Some handy chkconfig commands that you’ll find handy;

  • chkconfig –list (dash dash)
    • This will list the details of all services that are running on startup
  • chkconfig –list httpd (dash dash)
    • This allows you to list specifically the details of the service you care about, to avoid you having to trawl through the entire list. Simply change ‘httpd’ to whatever service name you are interested in looking at.

When you start to look through the outputs from the above commands, it may be a little confusing seeing 7 levels, some with a status of on and some with a status of off, but what do they all mean? The different levels are what is known as Linux Runlevels. Generally speaking, you probably don’t need to worry about those at all. But if you do need some fine grain control over what happens and when, when that may be covered in a future blog post.