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  Create host only network on VirtualBox

Previously we showed how to install Ubuntu in VirtualBox. What if we want to communicate with the host OS from within the Guest OS on VirtualBox? There are a few ways to do this. For example, bridged network, Host only networks. Today we will show you how to enable network communication between host OS and guest OS using host only networks. A host only network will not need to access the physical network interface of the host OS. It will create a network between different virtual machines and th...

   VIRTUALBOX,NETWORK,VIRTUAL MACHINE,HOST-ONLY     2015-12-01 09:29:13

  Which program is using USB device?

Sometimes when we want to plug out our USB device, but the operating system tells us we cannot plug it out since some other processes are using the USB device. How do we know which process is using our USB device. Here is a simple solution.First, go to Start->All programs->Accessories->System Tools->Resource Monitor. (as in Windows 7, for other Windows systems, you may similar program called Resource Monitor but may not in the same location as in Windows 7).Then, open Resource Monito...

   Windows.ISB device,Plugout problem,Solut     2011-07-22 09:20:13

  Handle NXDomain error when resolving IP address in Ruby DNS resolver

In another post, we covered how to resolve SystemStackError when resolving IP address in Ruby. In this post, we would cover another common issue where a NXDomain error is returned when resolving an IP address. The NXDomain error means that the queried domain name does not exist in the DNS. In Ruby, DNS resolver library will use /etc/resolv.conf by default get the name servers to resolve the domain name. There are multiple DNS name servers can be specified in /etc/resolv.conf with below format. ...

   RUBY,RUBY ON RAILS,NETWORK,DNS,NXDOMAIN     2017-07-16 01:39:23

  Send email from Ubuntu command line

First install exim4 and exim4-config using the package manager then install mailx sudo apt-get install mailutils and follow the prompts once this is set up use the command “mail” to check your mail. if you would like to send mail type “mail” followed by the email address to mail it to eg mail me@examplecom enter the subject and press enter the body and keep pressing enter as many times as you need to, when your body is finished, press “Ctrl” and “D" toge...

   Ubuntu,Email,Command line,mailutils     2011-04-25 15:58:10

  4 asynchronous programming methods in JavaScript

You may know the execution environment of JavaScript is single threaded. The so called single thread means only one task can be running at any time, if there are many tasks, they need to be in a queue and wait for the previous task to be completed. The advantage of this mode is it's easy to implement and the execution environment is relative simple; the disadvantage is that if one task takes long time, the tasks following it must wait in the queue and this will delay other tasks consequently. Th...

   JAVASCRIPT,ASYNCHRONOUS PROGRAMMING, EVENT MODEL,PROMISE     2012-12-25 00:55:47

  Arrays.equals() vs MessageDigest.isEqual()

Both Arrays.equals() and MessageDigest.isEqual() are used to compare the equality of two arrays. They can be interchangeably in many cases. However, they do have some differences which lead to different use cases in real applications. One difference is that the arrays passed to MessageDigest.isEqual() cannot be null while it's ok for Arrays.equals(). The one major difference between these two methods is that Arrays.equals() is not time-constant while MessageDigest.isEqual() is time-constant. Thi...

   Arrays.equal(),MessageDigest.isEqual(),Java,Security     2015-05-14 22:03:29

  Resolve SystemStackError issue when resolving IP address in Ruby

In Ruby, Resolv is the default DNS resolution implementation. It can be used to resolve IP address of a hostname. To use it, one just needs to require 'resolv' in the code. But sometimes, a user would want to check /etc/hosts first or some other mechanisms to resolve an IP address. In this case, one can require 'resolv-replace' and then replace the default DNS resolvers with customized DNS resolvers. For example, using resolv-replace, one would write require 'resolv-replace' Resolv::DefaultResol...

   RUBY,RUBY ON RAILS,NETWORK     2017-07-08 09:54:35

  Add compiler argument to build Maven project

Maven is a software project to manage a project's build, reporting and documentation from a central piece of information. It's now widely used t build and deploy projects. It can help automatically maintain the dependencies of projects. There is a central project configuration file named pom.xml. Here you can configure the project you want to build.  In this post, we will show you how to add compiler argument when using javac to compile Java source code. Sometimes we need to pass compi...

   Maven,compiler argument, compiler option, Java 8     2015-04-10 21:59:00

  Generating CSR using Java

A CSR(Certificate Signing Request) is a kind of request generated by an application and is to be sent to a Certificate Authority to create a signed certificate which can be distributed. It usually contains certificate information such as subject name, public key info and signature info. In Java, keytool can be used to generate a certificate request with option -certreq.  But sometimes if an application wants to create a CSR programmatically, keytool will not do a favor, instead you should u...

   JAVA,SECURITY,CSR,CERTIFICATE REQUEST     2016-05-25 04:49:17

  NIO vs IO in Java

Java 1.4 provides a new API for handling IO -- NIO. This is a non-blocking and buffer oriented IO API. Below are main differences between the NIO and IO in Java. IO NIO Stream oriented Buffer oriented Blocking IO Non-blocking IO N/A Using selector Stream oriented vs Buffer oriented The main difference is that IO is stream oriented where the data is read byte by byte and the data will not be buffered normally.This means there is no pointer to move forward and backward in the stream. I...

   JAVA,IO,NIO     2016-01-10 01:40:02

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