AngularJs interview question and answer for fresher and experienced

Question: What is AngularJS?
It is javasScript framework which is written in javascript. It is Best for Single Page Applications. It extend the html with new attributes which makes it more useful for UI Developer.


Question: In which language, AngularJS is written?
javaScript


Question: When First AngularJS was released?
2009


Question: When latest AngularJS was released?
November 19, 2015


Question: What is latest version of AngularJS?
1.4.8


Question: Who created AngularJS?
Misko Hevery started to work on AngularJS in 2009. He was employee of Google.

Question: Is it opensource?
Yes, It is free to use.



Question: Explain what are the key features of Angular.js?

1. Scope
2. Controller
3. Model
4. View
5. Services
6. Data Binding
7. Directives
8. Filters
9. Testable

Question: From where we can download the AngularJS File?

<script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.2.26/angular.min.js"></script>

Question: What is controller in AngularJS?
Controller is constructor function in Angular Controller.
When a Controller is attached to the DOM with use the ng-controller, Angular will instantiate a new Controller object using constructor function.



Question: Explain what are directives?
Directives are used to add new attributes of HTML.



Question: What are the different types of Directive?
Different types of directives are

1. Element directives
2. Attribute directives
3. CSS class directives
4. Comment directives

Question: Explain what is injector?
An injector is a service locator, used to retrieve object instances.



Question: Explain what are factory method in angularJs?
Factory method are used to create the directive. It is invoked only once, when compiler matches the directive for the first time.



Question: Does Angular use the jQuery library?
Ans. Yes, Angular can use jQuery if you have included the jQuery library.
IF Not, Angular falls back to its own implementation of the subset of jQuery that we call jQLite.



Question: What is ng-app, ng-init and ng-model?
ng-app - To initialize the Angular Application.
ng-init - To initialize the Angular Application data.
ng-model - To bind the html tags (input, select, textarea) to Angular Application Data.



Question: What is Data Binding in Angular JS?
It is synchronization of data between the model(Angular Application variable) and view components (display with {{}}).



Question: Give an Example of Data-Binding in AngularJS?

<div ng-app="" ng-init="quantity=10;cost=5">
<b>Total Cost: {{ quantity * cost }}</b>
</div>

Question: What is Looping in AngularJs and Give an Example?
It is used to display the data in loop same as foreach in PHP
Example:

<div data-ng-app="" data-ng-init="names=['Web','Technology','Experts','Notes']">
<b>Loop Example:</b>
  <br />
<ul>
<li data-ng-repeat="x in names">
      {{ x }}
    </li>
</ul>
</div>

Question: How to Write Expression in AngularJS?

<div ng-app="">
<b>Expression: {{ 15 + 55 }}</b>
</div>

Question: How to initiate variable in AngularJS?

<div ng-app="" ng-init="quantity=10;cost=5">
<b>Total Cost: {{ quantity * cost }}</b>
</div>

OR

<div ng-app="" ng-init="quantity=1;cost=5">
<b>Total Cost: <span ng-bind="quantity * cost"></span></b>
</div>

Question: Example of AngularJS Strings?

<div ng-app="" ng-init="Str1='Web';Str2='Technology'">
Full String is : <b>{{ Str1 + " " + Str2 }}</b>
</div>

Question: Example of AngularJS Object?

<div ng-app="" ng-init="myobj={Str1:'Web',Str2:'Technology'}">
String Display: <b>{{ myobj.Str2 }}</b></div>

Question: What is Angular Controllers & give an Example?
Controller is constructor function in Angular Controller.
When a Controller is attached to the DOM with use the ng-controller, Angular will instantiate a new Controller object using constructor function.
Example:

<div ng-app="" ng-controller="StrControllerExample">
String 1: <input ng-model="str1" type="text" /><br />
String 2: <input ng-model="str2" type="text" /><br />
Full String <b> {{fullString()}}</b>
</div>
<script>
function StrControllerExample($scope) {
    $scope.str1 = "Web",
    $scope.str2 = "Technology",
    $scope.fullString = function() {
        return $scope.str1+ " " + $scope.str2;
    }
}
</script>

1) What is Angular.js?
AngularJS is a javascript framework used for creating single web page applications.  It allows you to use HTML as your template language and enables you to extend HTML’s syntax to express your application’s components clearly
2) Explain what are the key features of Angular.js ?
The key features of angular.js are

• Scope
• Controller
• Model
• View
• Services
• Data Binding
• Directives
• Filters
• Testable

3) Explain what is scope in Angular.js ?
Scope refers to the application model, it acts like glue between application controller and the view.  Scopes are arranged in hierarchical structure and impersonate the DOM ( Document Object Model) structure of the application.  It can watch expressions and propagate events.
4) Explain what is services in Angular.js ?
In angular.js services are the singleton objects or functions that are used for carrying out specific tasks.  It holds some business logic and these function can be called as controllers, directive, filters and so on.
5) Explain what is Angular Expression? Explain what is key difference between angular expressions and JavaScript expressions?
Like JavaScript,  Angular expressions are code snippets that are usually placed in binding such as {{ expression }}
The key difference between the JavaScript expressions and Angular expressions

• Context : In Angular, the expressions are evaluated against a scope object, while the Javascript expressions are evaluated against the global window
• Forgiving: In Angular expression evaluation is forgiving to null and undefined, while in Javascript undefined properties generates TypeError or ReferenceError
• No Control Flow Statements: Loops, conditionals or exceptions cannot be used in an angular expression
• Filters: To format data before displaying it you can use filters

6) With options on page load how you can initialize a select box ?
You can initialize a select box with options on page load by using ng-init directive

• <div ng-controller = “ apps/dashboard/account ” ng-switch
• On = “! ! accounts” ng-init = “ loadData ( ) ”>

7) Explain what are directives ? Mention some of the most commonly used directives in Angular.js application ? 
A directive is something that introduces new syntax, they are like markers on DOM element which attaches a special behavior to it. In any Angular.js application, directives are the most important components.
Some of the commonly used directives are ng-model, ng-App, ng-bind, ng-repeat , ng-show etc.
8) Mention what are the advantages of using Angular.js ?
Angular.js has several advantages in web development.

• Angular.js supports MVS pattern
• Can do two ways data binding using Angular.js
• It has per-defined form validations
• It supports both client server communication
• It supports animations

9) Explain what Angular JS routes does ?
Angular js routes enable you to create different URLs for different content in your application.  Different URLs for different content enables user to bookmark URLs to specific content.  Each such bookmarkable URL in Angular.js is called a route
A value in Angular JS is a simple object.  It can be a number, string or JavaScript object.  Values are typically used as configuration injected into factories, services or controllers. A value should be belong to an Angular.js module.
Injecting a value into an Angular.js controller function is done by adding a parameter with the same name as the value
10)  Explain what is data binding in Angular.js ?
Automatic synchronization of data between the model and view components is referred as data binding in Angular.js.  There are two ways for data binding

1. Data mining in classical template systems
2. Data binding in angular templates

11)  What makes angular.js better ?

• Registering Callbacks: There is no need to register callbacks . This makes your code simple and easy to debug.
• Control HTML DOM programmatically:  All the application that are created using Angular never have to manipulate the DOM although it can be done if it is required
• Transfer data to and from the UI: Angular.js helps to eliminate almost all of the boiler plate like validating the form, displaying validation errors, returning to an internal model and so on which occurs due to flow of marshalling data
• No initilization code: With angular.js you can bootstrap your app easily using services, which auto-injected into your application in Guice like dependency injection style

12)  Explain what is string interpolation in angular.js ?
In angular.js the compiler during the compilation process matches text and attributes using interpolate service to see if they contains embedded expressions.  As part of normal digest cycle these expressions are updated and registered as watches.

13)  Mention the steps for the compilation process of HTML happens?
Compilation of HTML process occurs in following ways

• Using the standard browser API, first the HTML is parsed into DOM
• By using the call to the $compile () method, compilation of the DOM is performed.  The method traverses the DOM and matches the directives.
• Link the template with scope by calling the linking function returned from the previous step

14)  Explain what is directive and Mention what are the different types of Directive?
During compilation process when specific HTML constructs are encountered a behaviour or function is triggered, this function is referred as directive.  It is executed when the compiler encounters it in the DOM.
Different types of directives are

• Element directives
• Attribute directives
• CSS class directives
• Comment directives

15)  Explain what is linking function and type of linking function?
Link combines the directives with a scope and produce a live view.  For registering DOM listeners as well as updating the DOM, link function is responsible. After the template is cloned it is executed.

• Pre-linking function: Pre-linking function is executed before the child elements are linked.  It is not considered as the safe way for DOM transformation.

• Post linking function: Post linking function is executed after the child elements are linked. It is safe to do DOM transformation by post-linking function

16)  Explain what is injector?
An injector is a service locator.  It is used to retrieve object instances as defined by provider, instantiate types, invoke methods and load modules.  There is a single injector per Angular application, it helps to look up an object instance by its name.
17)  Explain what is the difference between link and compile in angular.js?

• Compile function: It is used for template DOM Manipulation and collect all of the directives.
• Link function: It is used for registering DOM listeners as well as instance DOM manipulation. It is executed once the template has been cloned.

18)  Explain what is factory method in angular.js?
For creating the directive, factory method is used.  It is invoked only once, when compiler matches the directive for the first time.  By using $injector.invoke the factory method is invoked.
19)  Mention what are the styling form that ngModel adds to CSS classes ?
ngModel adds these CSS classes to allow styling of form as well as control

• ng- valid
• ng- invalid
• ng-pristine
• ng-dirty

20)  Mention what are the characteristics of “Scope”?

• To observer model mutations scopes provide APIs ($watch)
• To propagate any model changes through the system into the view from outside of the Angular realm
• A scope inherits properties from its parent scope,  while providing access to shared model properties, scopes can be nested to isolate application components
• Scope provides context against which expressions are evaluated

21)  Explain what is DI (Dependency Injection ) and how an object or function can get a hold of its dependencies ?
DI or Dependency Injection is a software design pattern that deals with how code gets hold of its dependencies.  In order to retrieve elements of the application which is required to be configured when module gets loaded , the operation “config” uses dependency injection.
These are the ways that object uses to hold of its dependencies

• Typically using the new operator, dependency can be created
• By referring to a global variable, dependency can be looked up
• Dependency can be passed into where it is required

22)  Mention what are the advantages of using Angular.js framework ?
Advantages of using Angular.js as framework are

• Supports two way data-binding
• Supports MVC pattern
• Support static template and angular template
• Can add custom directive
• Supports REST full services
• Supports form validations
• Support both client and server communication
• Support dependency injection
• Applying Animations
• Event Handlers

23)  Explain the concept of scope hierarchy?  How many scope can an application have?
Each angular application consist of one root scope but may have several child scopes. As child controllers and some directives create new child scopes, application can have multiple scopes. When new scopes are formed or created they are added as a children of their parent scope. Similar to DOM, they also creates a hierarchical structure.
24)  Explain what is the difference between angular.js and backbone.js?
Angular.js combines the functionalities of most of the 3^rd party libraries, it supports individual functionalities required to develop HTML5 Apps.  While Backbone.js do their jobs individually.
25)  Who created Angular JS ?
Intially it was developed by Misko Hevery and Adam Abrons. Currently it is being developed by Google.

how to retrive data from mysql using nodejs?

Step 1-> create simple your project folde "testapp" under below directory "www"

C:\Bikash\codetest\wamp\www\testapp

create app.js

var mysql = require("mysql");

// First you need to create a connection to the db
var con = mysql.createConnection({
  host: "localhost",
  user: "root",
  password: "",
  database : 'test',
});

con.connect(function(err){
  if(err){
    console.log('Error connecting to Db');
    return;
  }


  console.log('Connection established');
});


function getColour(uid, roomCount, callback)
{

    con.query('SELECT u_name FROM user WHERE u_id = ?', [roomCount], function(err, result)
    {


        if (err)
            callback(err,null);
        else
            callback(null,result[0].u_name);

    });

}

//call Fn for db query with callback
getColour("2",1, function(err,data){
        if (err) {
            // error handling code goes here
            console.log("ERROR : ",err);          
        } else {          
            // code to execute on data retrieval
            console.log("result from db is : ",data);  
        }  

});

con.end(function(err) {
 console.log('Connection has been closed');
});

Step2->open cmd
Step4->C:\Bikash\codetest\wamp\www\testapp>npm install mysql
step5->run like : C:\Bikash\codetest\wamp\www\test>node app.js

AngularJS using java example

AngularJS Example Using a Java RESTful Web Service

AngularJS is the current MVV-Whatever JavaScript framework by Google. Among other things, it provides bidirectional data binding.
Although I’m neither a Java nor a JavaScript expert, I choose the following scenario for my ‘Hello-World’ example:

1. Java backend provides a RESTful web service.
2. AngularJS consumes the web service.

That’s it.

Project structure

I intentionally put the backend and frontend code in the same project to simplify the example. In a real project you probably want to have seperate projects for front- and backend.

1 2 3 4 5 6 7 8

+---------------------------------------------------+ | demo project | | | | +----------------+ +---------------+ | | | backend (Java) | < -(REST)- > | frontend (JS) | | | +----------------+ +---------------+ | | | +---------------------------------------------------+

Since the backend is Java based, I used a Maven default structure (maven-archetype-site-simple):

project structure

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

├── _documentation │   └── readme.txt ├── ngdemo.iml ├── pom.xml └── src └── main ├── java │   └── ngdemo │   ├── domain │   │   └── User.java │   ├── rest │   │   └── UserRestService.java │   └── service │   └── UserService.java └── webapp ├── css │   └── app.css ├── img ├── index-async.html ├── index.html ├── index.jsp ├── js │   ├── app.js │   ├── controllers.js │   ├── directives.js │   ├── filters.js │   └── services.js ├── lib │   └── angular │   ├── angular-cookies.js │   ├── angular-cookies.min.js │   ├── angular.js │   ├── angular-loader.js │   ├── angular-loader.min.js │   ├── angular.min.js │   ├── angular-resource.js │   ├── angular-resource.min.js │   ├── angular-sanitize.js │   ├── angular-sanitize.min.js │   └── version.txt ├── partials │   └── partial1.html └── WEB-INF └── web.xml

src/main/java is the backend.
src/main/webapp/js is the frontend.
src/main/webapp/ also includes a copy of angular-seed.

RESTful web service (backend)

Jersey is the Java reference implementation for providing REST.
Install the following dependencies in your pom.xml:

pom.xml

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

<!-- .. --> <!-- RESTful web service: Jersey --> <dependency> <groupId>com.sun.jersey</groupId> <artifactId>jersey-server</artifactId> <version>1.17.1</version> </dependency> <dependency> <groupId>com.sun.jersey</groupId> <artifactId>jersey-servlet</artifactId> <version>1.17.1</version> </dependency> <dependency> <groupId>com.sun.jersey</groupId> <artifactId>jersey-json</artifactId> <version>1.17.1</version> </dependency> <!-- .. -->

Add the following servlet snippet to your web.xml:

web.xml

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

<!-- .. --> <servlet> <servlet-name>jersey-serlvet</servlet-name> <servlet-class> com.sun.jersey.spi.container.servlet.ServletContainer </servlet-class> <init-param> <param-name>com.sun.jersey.config.property.packages</param-name> <param-value>ngdemo.rest</param-value> </init-param> <init-param> <param-name>com.sun.jersey.api.json.POJOMappingFeature</param-name> <param-value>true</param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>jersey-serlvet</servlet-name> <url-pattern>/rest/*</url-pattern> </servlet-mapping> <!-- .. -->

Enough configuration for now: Create a simple User object…

User.java

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

package ngdemo.domain; import javax.xml.bind.annotation.XmlRootElement; @XmlRootElement public class User { private String firstName; private String lastName; public String getFirstName() { return firstName; } public void setFirstName(String firstName) { this.firstName = firstName; } public String getLastName() { return lastName; } public void setLastName(String lastName) { this.lastName = lastName; } }

…and a service class…

UserService.java

1 2 3 4 5 6 7 8 9 10 11 12 13

package ngdemo.service; import ngdemo.domain.User; public class UserService { public User getDefaultUser() { User user = new User(); user.setFirstName("JonFromREST"); user.setLastName("DoeFromREST"); return user; } }

…and finally the RESTful Service… (Update 2015-08-07 small fix, thanks Jason):

UserRestService.java

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

package ngdemo.rest; import ngdemo.domain.User; import ngdemo.service.UserService; import javax.ws.rs.GET; import javax.ws.rs.Path; import javax.ws.rs.Produces; import javax.ws.rs.core.MediaType; @Path("/users") public class UserRestService { @GET @Produces(MediaType.APPLICATION_JSON) public User getDefaultUserInJSON() { UserService userService = new UserService(); return userService.getDefaultUser(); } }

Converting the User object to JSON via @Produces(MediaType.APPLICATION_JSON) requires jersey-json in web.xml (POJOMappingFeature).

Consuming web service from AngularJS (frontend)

Don’t forget to add angular-resources.js to your index.html…
Consuming the web service:

services.js

1 2 3 4 5 6 7 8 9 10 11

var services = angular.module('ngdemo.services', ['ngResource']); services.factory('UserFactory', function ($resource) { return $resource('/ngdemo/rest/users', {}, { query: { method: 'GET', params: {}, isArray: false } }) });

Usage in controller:

controller.js

1 2 3 4 5 6 7

var app = angular.module('ngdemo.controllers', []); app.controller('MyCtrl1', ['$scope', 'UserFactory', function ($scope, UserFactory) { UserFactory.get({}, function (userFactory) { $scope.firstname = userFactory.firstName; }) }]);

Usage in view:

1 2 3 4 5

<div> <p> Result from RESTful service is: {{ firstname }} </p> </div>

Et voila:

what are common commands in linux and unix Os

1. tar command examples

Create a new tar archive.

$ tar cvf archive_name.tar dirname/

Extract from an existing tar archive.

$ tar xvf archive_name.tar

View an existing tar archive.

$ tar tvf archive_name.tar

More tar examples: The Ultimate Tar Command Tutorial with 10 Practical Examples

2. grep command examples

Search for a given string in a file (case in-sensitive search).

$ grep -i "the" demo_file

Print the matched line, along with the 3 lines after it.

$ grep -A 3 -i "example" demo_text

Search for a given string in all files recursively

$ grep -r "ramesh" *

More grep examples: Get a Grip on the Grep! – 15 Practical Grep Command Examples

3. find command examples

Find files using file-name ( case in-sensitve find)

# find -iname "MyCProgram.c"

Execute commands on files found by the find command

$ find -iname "MyCProgram.c" -exec md5sum {} \;

Find all empty files in home directory

# find ~ -empty

More find examples: Mommy, I found it! — 15 Practical Linux Find Command Examples

4. ssh command examples

Login to remote host

ssh -l jsmith remotehost.example.com

Debug ssh client

ssh -v -l jsmith remotehost.example.com

Display ssh client version

$ ssh -V
OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003

More ssh examples: 5 Basic Linux SSH Client Commands

5. sed command examples

When you copy a DOS file to Unix, you could find \r\n in the end of each line. This example converts the DOS file format to Unix file format using sed command.

$sed 's/.$//' filename

Print file content in reverse order

$ sed -n '1!G;h;$p' thegeekstuff.txt

Add line number for all non-empty-lines in a file

$ sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'

More sed examples: Advanced Sed Substitution Examples

6. awk command examples

Remove duplicate lines using awk

$ awk '!($0 in array) { array[$0]; print }' temp

Print all lines from /etc/passwd that has the same uid and gid

$awk -F ':' '$3==$4' passwd.txt

Print only specific field from a file.

$ awk '{print $2,$5;}' employee.txt

More awk examples: 8 Powerful Awk Built-in Variables – FS, OFS, RS, ORS, NR, NF, FILENAME, FNR

7. vim command examples

Go to the 143rd line of file

$ vim +143 filename.txt

Go to the first match of the specified

$ vim +/search-term filename.txt

Open the file in read only mode.

$ vim -R /etc/passwd

More vim examples: How To Record and Play in Vim Editor

8. diff command examples

Ignore white space while comparing.

# diff -w name_list.txt name_list_new.txt

2c2,3
< John Doe --- > John M Doe
> Jason Bourne

More diff examples: Top 4 File Difference Tools on UNIX / Linux – Diff, Colordiff, Wdiff, Vimdiff

9. sort command examples

Sort a file in ascending order

$ sort names.txt

Sort a file in descending order

$ sort -r names.txt

Sort passwd file by 3rd field.

$ sort -t: -k 3n /etc/passwd | more

10. export command examples

To view oracle related environment variables.

$ export | grep ORACLE
declare -x ORACLE_BASE="/u01/app/oracle"
declare -x ORACLE_HOME="/u01/app/oracle/product/10.2.0"
declare -x ORACLE_SID="med"
declare -x ORACLE_TERM="xterm"

To export an environment variable:

$ export ORACLE_HOME=/u01/app/oracle/product/10.2.0

11. xargs command examples

Copy all images to external hard-drive

# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory

Search all jpg images in the system and archive it.

# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz

Download all the URLs mentioned in the url-list.txt file

# cat url-list.txt | xargs wget –c

12. ls command examples

Display filesize in human readable format (e.g. KB, MB etc.,)

$ ls -lh
-rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz

Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr

$ ls -ltr

Visual Classification of Files With Special Characters Using ls -F

$ ls -F

More ls examples: Unix LS Command: 15 Practical Examples

13. pwd command

pwd is Print working directory. What else can be said about the good old pwd who has been printing the current directory name for ages.

14. cd command examples

Use “cd -” to toggle between the last two directories
Use “shopt -s cdspell” to automatically correct mistyped directory names on cd
More cd examples: 6 Awesome Linux cd command Hacks

15. gzip command examples

To create a *.gz compressed file:

$ gzip test.txt

To uncompress a *.gz file:

$ gzip -d test.txt.gz

Display compression ratio of the compressed file using gzip -l

$ gzip -l *.gz
         compressed        uncompressed  ratio uncompressed_name
              23709               97975  75.8% asp-patch-rpms.txt

16. bzip2 command examples

To create a *.bz2 compressed file:

$ bzip2 test.txt

To uncompress a *.bz2 file:

bzip2 -d test.txt.bz2

More bzip2 examples: BZ is Eazy! bzip2, bzgrep, bzcmp, bzdiff, bzcat, bzless, bzmore examples

17. unzip command examples

To extract a *.zip compressed file:

$ unzip test.zip

View the contents of *.zip file (Without unzipping it):

$ unzip -l jasper.zip
Archive:  jasper.zip
  Length     Date   Time    Name
 --------    ----   ----    ----
    40995  11-30-98 23:50   META-INF/MANIFEST.MF
    32169  08-25-98 21:07   classes_
    15964  08-25-98 21:07   classes_names
    10542  08-25-98 21:07   classes_ncomp

18. shutdown command examples

Shutdown the system and turn the power off immediately.

# shutdown -h now

Shutdown the system after 10 minutes.

# shutdown -h +10

Reboot the system using shutdown command.

# shutdown -r now

Force the filesystem check during reboot.

# shutdown -Fr now

19. ftp command examples

Both ftp and secure ftp (sftp) has similar commands. To connect to a remote server and download multiple files, do the following.

$ ftp IP/hostname
ftp> mget *.html

To view the file names located on the remote server before downloading, mls ftp command as shown below.

ftp> mls *.html -
/ftptest/features.html
/ftptest/index.html
/ftptest/othertools.html
/ftptest/samplereport.html
/ftptest/usage.html

More ftp examples: FTP and SFTP Beginners Guide with 10 Examples

20. crontab command examples

View crontab entry for a specific user

# crontab -u john -l

Schedule a cron job every 10 minutes.

*/10 * * * * /home/ramesh/check-disk-space

More crontab examples: Linux Crontab: 15 Awesome Cron Job Examples

21. service command examples

Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command.
Check the status of a service:

# service ssh status

Check the status of all the services.

service --status-all

Restart a service.

# service ssh restart

22. ps command examples

ps command is used to display information about the processes that are running in the system.
While there are lot of arguments that could be passed to a ps command, following are some of the common ones.
To view current running processes.

$ ps -ef | more

To view current running processes in a tree structure. H option stands for process hierarchy.

$ ps -efH | more

23. free command examples

This command is used to display the free, used, swap memory available in the system.
Typical free command output. The output is displayed in bytes.

$ free
             total       used       free     shared    buffers     cached
Mem:       3566408    1580220    1986188          0     203988     902960
-/+ buffers/cache:     473272    3093136
Swap:      4000176          0    4000176

If you want to quickly check how many GB of RAM your system has use the -g option. -b option displays in bytes, -k in kilo bytes, -m in mega bytes.

$ free -g
             total       used       free     shared    buffers     cached
Mem:             3          1          1          0          0          0
-/+ buffers/cache:          0          2
Swap:            3          0          3

If you want to see a total memory ( including the swap), use the -t switch, which will display a total line as shown below.

ramesh@ramesh-laptop:~$ free -t
             total       used       free     shared    buffers     cached
Mem:       3566408    1592148    1974260          0     204260     912556
-/+ buffers/cache:     475332    3091076
Swap:      4000176          0    4000176
Total:     7566584    1592148    5974436

24. top command examples

top command displays the top processes in the system ( by default sorted by cpu usage ). To sort top output by any column, Press O (upper-case O) , which will display all the possible columns that you can sort by as shown below.

Current Sort Field:  P  for window 1:Def
Select sort field via field letter, type any other key to return

  a: PID        = Process Id              v: nDRT       = Dirty Pages count
  d: UID        = User Id                 y: WCHAN      = Sleeping in Function
  e: USER       = User Name               z: Flags      = Task Flags
  ........

To displays only the processes that belong to a particular user use -u option. The following will show only the top processes that belongs to oracle user.

$ top -u oracle

More top examples: Can You Top This? 15 Practical Linux Top Command Examples

25. df command examples

Displays the file system disk space usage. By default df -k displays output in bytes.

$ df -k
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda1             29530400   3233104  24797232  12% /
/dev/sda2            120367992  50171596  64082060  44% /home

df -h displays output in human readable form. i.e size will be displayed in GB’s.

ramesh@ramesh-laptop:~$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              29G  3.1G   24G  12% /
/dev/sda2             115G   48G   62G  44% /home

Use -T option to display what type of file system.

ramesh@ramesh-laptop:~$ df -T
Filesystem    Type   1K-blocks      Used Available Use% Mounted on
/dev/sda1     ext4    29530400   3233120  24797216  12% /
/dev/sda2     ext4   120367992  50171596  64082060  44% /home

26. kill command examples

Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process.

$ ps -ef | grep vim
ramesh    7243  7222  9 22:43 pts/2    00:00:00 vim

$ kill -9 7243

More kill examples: 4 Ways to Kill a Process – kill, killall, pkill, xkill

27. rm command examples

Get confirmation before removing the file.

$ rm -i filename.txt

It is very useful while giving shell metacharacters in the file name argument.
Print the filename and get confirmation before removing the file.

$ rm -i file*

Following example recursively removes all files and directories under the example directory. This also removes the example directory itself.

$ rm -r example

28. cp command examples

Copy file1 to file2 preserving the mode, ownership and timestamp.

$ cp -p file1 file2

Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it.

$ cp -i file1 file2

29. mv command examples

Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it.

$ mv -i file1 file2

Note: mv -f is just the opposite, which will overwrite file2 without prompting.
mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument.

$ mv -v file1 file2

30. cat command examples

You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout.

$ cat file1 file2

While displaying the file, following cat -n command will prepend the line number to each line of the output.

$ cat -n /etc/logrotate.conf
    1 /var/log/btmp {
    2     missingok
    3     monthly
    4     create 0660 root utmp
    5     rotate 1
    6 }

31. mount command examples

To mount a file system, you should first create a directory and mount it as shown below.

# mkdir /u01

# mount /dev/sdb1 /u01

You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted.

/dev/sdb1 /u01 ext2 defaults 0 2

32. chmod command examples

chmod command is used to change the permissions for a file or directory.
Give full access to user and group (i.e read, write and execute ) on a specific file.

$ chmod ug+rwx file.txt

Revoke all access for the group (i.e read, write and execute ) on a specific file.

$ chmod g-rwx file.txt

Apply the file permissions recursively to all the files in the sub-directories.

$ chmod -R ug+rwx file.txt

More chmod examples: 7 Chmod Command Examples for Beginners

33. chown command examples

chown command is used to change the owner and group of a file. \
To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.

$ chown oracle:dba dbora.sh

Use -R to change the ownership recursively.

$ chown -R oracle:dba /home/oracle

34. passwd command examples

Change your password from command line using passwd. This will prompt for the old password followed by the new password.

$ passwd

Super user can use passwd command to reset others password. This will not prompt for current password of the user.

# passwd USERNAME

Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.

# passwd -d USERNAME

35. mkdir command examples

Following example creates a directory called temp under your home directory.

$ mkdir ~/temp

Create nested directories using one mkdir command. If any of these directories exist already, it will not display any error. If any of these directories doesn’t exist, it will create them.

$ mkdir -p dir1/dir2/dir3/dir4/

36. ifconfig command examples

Use ifconfig command to view or configure a network interface on the Linux system.
View all the interfaces along with status.

$ ifconfig -a

Start or stop a specific interface using up and down command as shown below.

$ ifconfig eth0 up

$ ifconfig eth0 down

More ifconfig examples: Ifconfig: 7 Examples To Configure Network Interface

37. uname command examples

Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number,
Processor type, etc.,
Sample uname output from a Ubuntu laptop is shown below.

$ uname -a
Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux

38. whereis command examples

When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command.

$ whereis ls
ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz

When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available.

$ whereis -u -B /tmp -f lsmk
lsmk: /tmp/lsmk

39. whatis command examples

Whatis command displays a single line description about a command.

$ whatis ls
ls  (1)  - list directory contents

$ whatis ifconfig
ifconfig (8)         - configure a network interface

40. locate command examples

Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb.
The example below shows all files in the system that contains the word crontab in it.

$ locate crontab
/etc/anacrontab
/etc/crontab
/usr/bin/crontab
/usr/share/doc/cron/examples/crontab2english.pl.gz
/usr/share/man/man1/crontab.1.gz
/usr/share/man/man5/anacrontab.5.gz
/usr/share/man/man5/crontab.5.gz
/usr/share/vim/vim72/syntax/crontab.vim

41. man command examples

Display the man page of a specific command.

$ man crontab

When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below.

$ man SECTION-NUMBER commandname

Following 8 sections are available in the man page.

1. General commands
2. System calls
3. C library functions
4. Special files (usually devices, those found in /dev) and drivers
5. File formats and conventions
6. Games and screensavers
7. Miscellaneous
8. System administration commands and daemons

For example, when you do whatis crontab, you’ll notice that crontab has two man pages (section 1 and section 5). To view section 5 of crontab man page, do the following.

$ whatis crontab
crontab (1)          - maintain crontab files for individual users (V3)
crontab (5)          - tables for driving cron

$ man 5 crontab

42. tail command examples

Print the last 10 lines of a file by default.

$ tail filename.txt

Print N number of lines from the file named filename.txt

$ tail -n N filename.txt

View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C.

$ tail -f log-file

More tail examples: 3 Methods To View tail -f output of Multiple Log Files in One Terminal

43. less command examples

less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening.

$ less huge-log-file.log

One you open a file using less command, following two keys are very helpful.

CTRL+F – forward one window
CTRL+B – backward one window

More less examples: Unix Less Command: 10 Tips for Effective Navigation

44. su command examples

Switch to a different user account using su command. Super user can switch to any other user without entering their password.

$ su - USERNAME

Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john’s account.

[john@dev-server]$ su - raj -c 'ls'

[john@dev-server]$

Login to a specified user account, and execute the specified shell instead of the default shell.

$ su -s 'SHELLNAME' USERNAME

45. mysql command examples

mysql is probably the most widely used open source database on Linux. Even if you don’t run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server.
To connect to a remote mysql database. This will prompt for a password.

$ mysql -u root -p -h 192.168.1.2

To connect to a local mysql database.

$ mysql -u root -p

If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space).

46. yum command examples

To install apache using yum.

$ yum install httpd

To upgrade apache using yum.

$ yum update httpd

To uninstall/remove apache using yum.

$ yum remove httpd

47. rpm command examples

To install apache using rpm.

# rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm

To upgrade apache using rpm.

# rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm

To uninstall/remove apache using rpm.

# rpm -ev httpd

More rpm examples: RPM Command: 15 Examples to Install, Uninstall, Upgrade, Query RPM Packages

48. ping command examples

Ping a remote host by sending only 5 packets.

$ ping -c 5 gmail.com

More ping examples: Ping Tutorial: 15 Effective Ping Command Examples

49. date command examples

Set the system date:

# date -s "01/31/2010 23:59:53"

Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.

# hwclock –systohc

# hwclock --systohc –utc

50. wget command examples

The quick and effective method to download software, music, video from internet is using wget command.

$ wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz

Download and store it with a different name.

$ wget -O taglist.zip http://www.vim.org/scripts/download_script.php?src_id=7701

Java Technical interview question and answer? faced by us

1.     Multiple servlet handle in a single servlet?example

A: http://stackoverflow.com/questions/27765547/how-does-a-single-servlet-handle-multiple-requests-from-client-side

2.     Does Parameterized constructor in servlet?

A: http://stackoverflow.com/questions/945778/parameterized-constructor-in-servlet

3.     what is the significance of load factor in hashmap?

4.     Capacity & Load Factor in setmap?

5.     Object. Clone without clone Method ?

Differences between a Web container, Web server, servlet container and an application server?

A Web application runs within a Web container of a Web server. The Web container provides the runtime environment through components that provide naming context and life cycle management. Some Web servers may also provide additional services such as security and concurrency control. A Web server may work with an EJB server to provide some of those services. A Web server, however, does not need to be located on the same machine as an EJB server.

Web applications are composed of web components and other data such as HTML pages. Web components can be servlets, JSP pages created with the JavaServer Pages™ technology, web filters, and web event listeners. These components typically execute in a web server and may respond to HTTP requests from web clients. Servlets, JSP pages, and filters may be used to generate HTML pages that are an application’s user interface. They may also be used to generate XML or other format data that is consumed by other application components

In Java: Web Container or Servlet Container or Servlet Engine : is used to manage the components like servlets, JSP.It is a part of the web server.
Web Server or HTTP Server: a server which is capable of handling HTTP request send by a client and respond back with a HTTP response.
Application Server or App Server: can handle all application operations between users and an organization's back end business applications or databases.It is frequently viewed as part of a three-tier application with: Presentaiton tier, logic tier,Data tier.

Most of the times these terms Web Server and Application server are used interchangeably.
Following are some of the key differences in features of Web Server and Application Server:

• Web Server is designed to serve HTTP Content. App Server can also serve HTTP Content but is not limited to just HTTP. It can be provided other protocol support such as RMI/RPC
• Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like Perl, PHP, ASP, JSP etc. through which these servers can generate dynamic HTTP content.
• Most of the application servers have Web Server as integral part of them, that means App Server can do whatever Web Server is capable of. Additionally App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.
• As web servers are well suited for static content and app servers for dynamic content, most of the production environments have web server acting as reverse proxy to app server. That means while servicing a page request, static contents (such as images/Static HTML) are served by web server that interprets the request. Using some kind of filtering technique (mostly extension of requested resource) web server identifies dynamic content request and transparently forwards to app server

Example of such configuration is Apache Tomcat HTTP Server and Oracle (formerly BEA) WebLogic Server. Apache Tomcat HTTP Server is Web Server and Oracle WebLogic is Application Server.
In some cases the servers are tightly integrated such as IIS and .NET Runtime. IIS is web server. When equipped with .NET runtime environment, IIS is capable of providing application services.