Setting Path Environment Variable in Java

For the beginner one of the difficult and confusing task is to set path and classpath environment variables.

Path is nothing but setting up an environment for operating system. Path is a system variable used to tell to Operating System all locations of executable files. Operating System will look in this path variable for executable files.

Classpath is nothing but setting up an environment for java. Classpath is pure java variable, which is used to tell the Java Virtual Machine or the Java compiler where to look for user-defined classes and packages.

For example,assume that Java is installed in C:\Program Files\Java\jdk1.7.0_25\ and your code is in C:\Sample\example.java, then path and classpath should be set to like this:

classpath=C:\Sample

path= C:\Program Files\Java\jdk1.7.0_25\bin;

Or

path=%JAVA_HOME%\bin;

where JAVA_HOME is pointing to Home directory “C:\Program Files\Java\jdk1.7.0_25”, where jdk is installed

Let us see what exactly means by setting path variable

Whenever you try to compile a program using javac, JVM will search for javac in current directory where your program is residing, If it does not find javac and other executables in current directory then it will search in the directories where the path variable is set to. So setting path variable allows you to execute your program from any directory as location of executables java and javac is retrieved through path variable.

If you have not set path variable then it will show error like “javac is not a recognized command” . hence to remove this error set path environment variable as follows:

• Command to set path variable from command prompt

·         Set path=”C:\Program Files\Java\jdk1.7.0_25\bin”

·         Set path=%path%;”C:\Program Files\Java\jdk1.7.0_25\bin”

Here in second command we are just adding our path value to existing value of path variable.

• Command to remove value from path variable

·         Set path=

This will remove directory path from environment variable.

• Check whether environment variables are set correctly or not

·         If your environment variables are set correctly, then windows should recognize these commands.

C:\> java OR

C:\> javac

·         you can see current value of path variable by following command

C:\> echo %path%

Ubuntu: How to sort file contents using command ?

In this article, I will share my understanding of sort command with some examples. One important point to notice is that the file contents must be on separate line. If file contains only single line then we are not able to observe the effect of sort command. Before jumping directly to examples, here are some of its variations

To sort file contents                             : sort filename.txt

To sort according to column contents   : sort –k (column number) filename

To sort in reverse order                       : sort –r filename

To remove duplicates while sorting      : sort –u filename

•  Sorting numeric contents

           Suppose file contains only numeric data then file contents are sorted in ascending order of integer values as shown below.

$ cat file

015

004

016

009

003

018

002

020

$ sort file

002

003

004

009

016

018

020

•   Sorting alphabetic contents

            Suppose file contains only alphabetic data then file contents are sorted alphabetically as shown below.

$ cat file

Ashish Gaigole

Siyaram Vishwakarma

Deepak Jaiswal

Dashrath Sharma

$ sort file

Ashish Gaigole

Dashrath Sharma

Deepak Jaiswal

Siyaram Vishwakarma

•  Sorting alpha-numeric contents

           In case file has both numeric and alphabetic data then first all numeric data is sorted in ascending order followed by alphabetic data.

$ cat file

Ashish Gaigole

Siyaram Vishwakarma

Deepak Jaiswal

Dashrath Sharma

015

016

004

009

$ sort file

004

009

015

016

Ashish Gaigole

Dashrath Sharma

Deepak Jaiswal

Siyaram Vishwakarma

•  Sorting file contents according to particular column values

$ cat file

Ashish Gaigole 016 F-42

Siyaram Vishwakarma 015 F-43

Deepak Jaiswal 009 F-44

Dashrath Sharma 004 F-41

$ sort –k 3 file  : file is sorted according to third column in file.

Dashrath Sharma 004 F-44

Deepak Jaiswal 009 F-41

Siyaram Vishwakarma 015 F-43

Ashish Gaigole 016 F-42

$ sort –k 4 file  : file is sorted according to fourth column in file.

Deepak Jaiswal 009 F-41

Ashish Gaigole 016 F-42

Siyaram Vishwakarma 015 F-43

Dashrath Sharma 004 F-44                         

Ubuntu: ”How to recover root password ?”

Situation may arise that you want to login as root user and you don’t  know or you forgot the root password. In this case we need to boot in recovery mode. In some cases recovery mode option will not prompt automatically so need to press left shift key while booting. This will prompt option to boot in recovery mode. Once you boot in recovery mode, various options will be available. 

Selecting root option will login you as root in terminal without any password. Now you can create new root user, you can change the password of existing root user. 

After you have successfully changed the password, you need to reboot the system and now you can login with your new password.

For this just refer following commands.

You can get the list of current user                                 cat  /etc/passwd              

                                                  

You can add new user to the system                              useradd username  

 You can set the password of the user                             passwd username

A HAPPY LIFE or DESERTED ONE….!!

Green house gases absorb the infrared radiations, traps the heat for longer time and makes the atmosphere warmer. It is definitely true that one of the reasons that we are living on earth is because of these green house gases but if we are not careful about their atmospheric levels then they will kill us. According to the latest survey, the amount of greenhouse gases in the atmosphere is highest in last 2 million years. Carbon Dioxide (CO₂) is most harmful among all other green house gases.Before the industrial revolution, the problem was not that much serious. Now a days industrialization has become the benchmark for country’s development, almost every industry results in increasing the amount of green house gas in the atmosphere. The problem is much more serious as carbon levels are increasing exponentially. Previously it takes 7000 years to increase CO₂ level by some amount but now the carbon dioxide has gone up by the same amount in just 55 years.

                                                     What steps we can take as an individual to minimize the effect? As trees absorb CO₂ while photosynthesis we should plant more trees. We can use alternative eco-friendly fuels. We should save electricity, save water, walk whenever possible. If such things are added up by billions of people then definitely it will improve our climatic condition. Everything is in our hand and it’s up to us that what we want? We need to think about our next generation, what type of life you want to give to your generation?  
A HAPPY LIFE or DESERTED ONE….!!

Ubuntu: How to solve “Could not get lock on /var/lib/dpkg/lock“ problem ?

This one of the most frequent problems that arises while updating the installation packages. In order to solve this problem we need to remove the lock file from dpkg directory.as well as cache directory. After removing the lock we can update the packages without any error.

Remove Lock from dpkg    :     sudo rm /var/lib/dpkg/lock

Remove Lock from cache   :     sudo rm /var/cache/apt/archives/lock

Update packages                :     sudo apt-get update

Upgrade packages              :     sudo apt-get upgrade

Ubuntu:Waiting for jockey-backend to exit

After installation of Ubuntu the most common problem is updating or downloading softwares. When we try to update any package or tried to install any software, Ubuntu gives message Waiting for jockey-backend to exit in Update manager. Jockey is tool for installation of third party hardware drivers and need to be disabled safely.

In order to resolve this problem we need to kill this jockey-backend process. Here is solution to do that.

1.Get Administrative access             sudo -i
 
2.Get process id of jockey-backend process    ps -e | grep jockey

3.Kill this process                            kill -9  process_id

Lets Save Precious Water

Water is one of the most precious natural resource that the human beings got. The important thing is how serious we are about its usage?

The amount of water available on the earth is sufficient for human beings if we use it carefully. As population of the earth is increasing exponentially so is the demand of drinking water but we are wasting large amount of water just because currently we are having its sufficient supply. Currently we have to pay for 20 to 30 rupee for one water bottle. The most of the rural areas are still does not have sufficient water supply. They are supplied by water tankers that so not daily. The condition will become much more worsen in the future if we don’t save water. So let’s join our hands to save water as much as possible.

SAVE WATER, SAVE LIFE....!