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Introduction to CentOS netstat

The CentOS environment, the netstat tool, or utility will help understand network-related problems and troubleshoot network-related issues. The netstat word will be deriving from the words statistics and network. It is nothing but a command-line utility; the system administrator majorly uses it to analyze the network flow. It will give detailed information on a list of open or busy ports, multicast memberships, masquerade connections, routing table and the host system, etc.

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Note: By default, in the CentOS environment, the netstat tool is not available. We need to install the “net tools” utility in the CentOS environment. Once it will install, then only we can use the “netstat” utility.

Syntax of CentOS netstat

netstat [ DESCRIPTION ] [ OPTION ] delay

netstat: The netstat is nothing but a command-line utility. It will help to get the details about the network in the CentOS Environment. We can use the netstat keyword in the syntax or command. It will accept arguments like different DESCRIPTION, OPTIONS, etc. The netstat command will help to give detailed information about the network-related stuff.

DESCRIPTION: As per the requirement, we can use the different description option with the netstat command like –interfaces, –route, –masquerade, –statistics, –version, –help, etc.

OPTIONS: We can provide the different flags as the option that is compatible with the netstat command.

delay: As per the requirement, we can print the netstat output as the specific interval of time.

How CentOS netstat Works?

As we have discussed, the netstat is a command-line utility. It will help to analyze the network-related issues and help to fix them. As per the requirement or issues, we need to provide the different options to the netstat command. It will provide the output on the screen. As per the output, we need to take the correct action and fix the issue.

Below are the lists of option that are compatible with the “netstat” command.

–verbose, -v: It will update the user on what is going on (on the current state by verbose). Majorly, it will print the useful information on the screen like the unconfigured address families, etc.

–wide, -W: This option will not truncate the IP addresses by using output. (As wide as needed). In some cases, it will be optional for now to not break current scripts.

-numeric, -n: It will help print the numerical addresses instead of determining the symbolic host. It will also help in the port or user names also.

–numeric-hosts: It will print the numerical host addresses. But it will not affect the resolution of user names or port.

–numeric-ports: It will print the numerical port numbers but does not affect host or user names’ resolution.

numeric-users: It will display the numerical user IDs. But it will not affect the resolution of port names or hosts.

-c, –continuous: This option will cause the netstat to print the selected information every second. It will be a continuous operation.

-e, –extend: It will help to display the additional information. If we need max details information, then we need to use this option twice.

-o, –timers: It will help to display the information related to networking timers, etc.

-p, –program: This option will display the PID and name of the program to which each socket belongs to.

-l, –listening: It will help to print the only listening sockets. (By default, these things were omitted.)

-a, –all: It will help to print both the listening and the non-listening sockets information. (For TCP, this means the established connections). It will print the information with the –interfaces option. It will also show the interfaces that are not up.

-F: It will display the routing information from the FIB. (This is the default option.)

-C: It will display the routing table information from the route cache.

delay: With the help of this option, the netstat will cycle printing through statistics. The output information will be delay every second.

Examples to understand CentOS netstat.

Here are the following examples mention below

1. CentOS netstat: Get Network Routing Table

In the CentOS environment, we can get the details of the routing table.

Command:

netstat -nr

Explanation:

As per the above command, we are using the “-r” option with the netstat command to get the details of routing tables.

Output:

2. CentOS netstat : Get the Network Interphase Status

In the netstat command, we have the functionality to details of network interphases.

Command:

netstat -ai

Explanation:

As per the above command, we are using the “-ai” option with the netstat command to get the details of system network interphases.

Output:

3. CentOS netstat: Get Network Connection

Command:

netstat -ant

Explanation:

As per the above command, we are using the “-ant” option with the netstat command to get the system’s detailed network connection status.

Output:

Conclusion

We have seen the uncut concept of the “CentOS netstat” with the proper example, explanation, and command with different outputs. By default, the netstat command-line utility is not present in the CentOS system (with minimal installation). The netstat command will help to analyze the network and help to troubleshoot the network-related issues.

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Explain The Concept Of A Class In C#

A class is one of the essential types in C#. We can think of a class as a blueprint for the objects relevant to the problem domain. It’s a template from which we create the objects, defining the structure and behavior that will be shared by the set of objects created from this class. In simple words, a class is a cookie-cutter, and the objects are the cookies themselves.

A class also enables encapsulation, which is an important concept in object-oriented programming. It means combining the data and the operations that work on the data in a single place and providing a simple API to the users of that object. A class allows us to encapsulate the data and hides the irrelevant details from other classes.

We can create a class by using the class keyword, followed by the name of the class.

public class User{    private string name;    private int salary;    public void Promote(){       salary += 1000;    } }

In the above example, User is a class that represents the users. The class encapsulates two pieces of data − name and salary. These are known as class fields, and hold the users’ name and salary. It also has a method named Promote(), which raises the user’s salary.

Each class has an associated access modifier that controls whether the class will be visible to other classes. Here are the five possible values we can provide for the access modifier.

Access ModifierDescriptionpublicUnlimited accessprotectedLimited access to the derived classesinternalLimited access to the assemblyprotected internalLimited access to the assembly or the derived classesprivateNo outside access

To create an instance of a class, we can use the new keyword. The new operator calculates the number of bytes required by the object’s data and allocates memory for the object. Then it returns a pointer (also called a reference) to the newly created object.

var alice = new User();    private string name;    private int salary;    public User(string name, int salary){       chúng tôi = name;       this.salary = salary;    }    public void Promote(){       salary += 1000;    } }

Having a constructor allows us to pass the name and the salary of a user when creating a new instance.

var alice = new User("Alice", 50000); var bob = new User("Bob", 45000);

It’s possible to have more than one constructor in a class. Having multiple constructors allows us to initialize the class in different ways. For example, we could add another constructor that only takes the user’s name and assigns a default salary.

public User(string name){    this.name = name;    this.salary = 50000; } Example

 Live Demo

using System; class Program{    static void Main(){       var alice = new User();       alice.Print();       var bob = new User();       bob.Print();       var chris = new User("Chris", 50000);       chris.Print();       var debs = new User("Debs", 45000);       debs.Print();       var scott = new User("Scott");       scott.Print();    } } public class User{    private string name;    private int salary;    public User(){    }    public User(string name){       chúng tôi = name;       this.salary = 50000;    }    public User(string name, int salary){       chúng tôi = name;       this.salary = salary;    }    public void Promote(){       salary += 1000;    }    public void Print(){       Console.WriteLine($"{name}: {salary}");    } } Output : 0 : 0 Chris: 50000 Debs: 45000 Scott: 50000

Learn The List Of Coreldraw Viewer

Introduction to CorelDraw Viewer

A CorelDraw Viewer is a program that helps the user to view the CorelDraw files without having to download the CorelDraw software. CorelDraw is a vector software that creates a specific file Extension .CDR.

.CDR is a file extension that cannot be viewed or opened on every software, just like the JPG format. To view the files with this extension, the user needs a definite program that helps them to do the same.

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List of CorelDraw Viewer

Some of the programs that help the user to view or edit .CDR files are finite but are either downloadable freeware programs or are available online instantly.

1. Imagine

This is a freeware program available in the market. The users can easily download the software and use it to view .CDR files. In addition, this program can create animations and batch sequence images as well. It is a useful program for graphic designers who are looking for open-source software. Following are the steps to view .CDR files:-

Download and install the software.

Open the software

Select the source folder where the .CDR file is saved to view the same

2. Inkscape

This program was created by SODIPODI developers. INKSCAPE is the successor of the Sodipodi program. This program is a vector graphics program, and it creates files in .SVG format (Scalable Vector Graphics). Other vector file formats such as .CDR can be viewed and edit within the software. The program proves to be functional and user-friendly. It has multiple features and can easily be used to create vector artworks.

Following are the steps to view .CDR files in the software:-

Download and install the program from the internet.

Open the CDR file. The program is also capable of modifying the artwork easily.

3. Irfan View

Following are the steps to view .CDR files in the software:-

Download and install the program from the internet.

Open the program

Select the CDR file that needs to be viewed

4. LibreOffice

To view a .CDR file, the user either needs CorelDraw Viewer or may convert the same file extension to other file formats. In this way, the user can view a .CDR file on any software.

One of the programs that help the user to convert the .CDR files to any other file format is Bit Recover CDR CONVERTER WIZARD.

Following are the steps through which the user can covert the .CDR files to any other file format.

Download and install Bit Recover CDR Converter wizard from the internet

Select the .CDR Files that you need to convert.

Select the File extension you need to convert the .CDR files to

Select the destination folder in which the files needs to be saved

This program will help the user to convert the existing .CDR files to any other file format. With the program .CDR files can also be viewed in Adobe Photoshop or Adobe Illustrator programs.

Conclusion

To view CorelDraw files, the user can use some of the methods that are listed above. Since CorelDraw is a paid and expensive program, not every user can afford to purchase the software. In such a case, the user can use the open-source freeware programs to view or edit graphic artworks as per their requirements.

Furthermore, these open-source programs can only be used for viewing and simple editing. For complex and detailed modifications, the user will have to purchase CorelDraw software.

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Learn The Working Of The Math Library In Lua

Introduction to Lua math

In Lua, math is defined as a standard library that consists of mathematical functions that are used in Lua programs for dealing with mathematical concepts easily by declaring this library in the program. In general, Lua math is a standard library provided by Lua programming language to work with mathematical concepts using the functions that are defined in this library for solving mathematical related problems such as logarithmic functions (log), exponential functions (exp), trigonometric functions (sin, cos, tan, etc), rounding functions (floor, ceil) and many other functions like max, min, pi, etc are defined within this Lua math library which is an interface to standard C math library.

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Syntax:

math.function_name(argument_list or parameter);

In the above syntax, we can when we want to use any math functions then we need to use math library provided by Lua standard library and to define or use any kind of math functions then we have to use math library starting with math then followed by a dot and then followed by the function name along with the parameters that need to be declared or used in the function for calculations.

Working of math library in Lua programming language

The Lua math library can be included directly with its function name and the parameters are passed to this function to include the variable values that are needed to calculate according to the function defined. In Lua, there are various functions for different mathematical calculations in the math library and a few of them are listed in the below section. But before that, we will see a list of math functions that are defined within this math library.

math.sin(x), math.cos(x), math.tan(x), math.asin(x), math.acos(x), etc are some of the trigonometric functions for getting sine, cosine and tangent for radiant values that are passed as parameter to the function and asin and acos are for getting arc sine and arc cosine in radians for the given values in the parameter.

In Lua, the math library also provides random functions such as math.random([x [,y]]) to get random numbers.

Example:

In the below example let us see few math functions demonstration using math library.

print( "Demonstration of math library function in Lua programming language ") print("n") print("Rounding functions in math library are as follows:") a = 89.50983 print(" The floor value of a is ", math.floor(a)) print(" The ceil value of a is ", math.ceil(a)) print("n") print(" Comparative function are as follows: ") print(" The maximum of the given numbers is : ", math.max(30, 46, 29, 78, 56, 9)) print(" The minimum of the given numbers is : ",math.min(30, 46, 29, 78, 56,9)) print("n") print(" The trigonometric functions provided in the math library is as follows: ") print("n") p = math.rad(math.pi / 2) print("The pi value for calculating trigonometric values is : ", p) print("n") print("The sine value of the given radian which is 90 degree is : ", string.format("%.1f ", math.sin(p))) print("The cosine value of the given radian which is 90 degree is : ", string.format("%.1f ", math.cos(p))) print("The tangent value of the given radian which is 90 degree is : ", string.format("%.1f ", math.tan(p))) print("The sine hyperbolic value of the given radian which is 90 degree is : ", string.format("%.1f ", math.sinh(p))) print("The cosine hyperbolic value of the given radian which is 90 degree is : ", string.format("%.1f ", math.cosh(p))) print("The tangent hyperbolic value of the given radian which is 90 degree is : ", string.format("%.1f ", math.tanh(p)))

Output:

In the above program, we can see some of the math functions that are defined using the math library in the program. In the first we are finding the rounding of functions such as math.floor() which will round of to the previous value and math.ceil() will round off the value to the next value of the given number. Then we are defining comparative functions such as max and min which will display the maximum and minimum number in the given list of the numbers as parameters to this function. Then we have defined few trigonometric functions and to display the values for the radian with 90 degrees where we have converted the pi value to the radian value using rad() such as math.rad(math.pi / 2), whereas if we want to display the degree value then we can use deg() function as math.deg(math.pi / 2). In the above program, we have displayed the values of sine, cosine, and tangent along with its hyperbolic values also. The output of all these functions can be seen in the above screenshot.

Example:

print( "Demonstration of some other math library function in Lua programming language ") print("n") print("The squareroot of given number a is :", math.sqrt(24)) print("n") print("The 2 to the power of 5 is :", math.pow(2,5)) print("n") print("The absolute value of the given number is :", math.abs(-45)) print("n") print("The exponential value of the given number is :", math.exp(4)) print("n") print("The logarithmic value of the given number is :",math.log(2)) print("n") print("Random number between 70 and 80 is ",math.random(70,80))

Output:

In the above program, we can see we have defined some other math function provided by the math library such as math.sqrt() will display the square root of the specified number, math.pow() will specify the powers of the given number in the above program, it is 2 ^ 5 =32, then we saw math.abs() which will display the absolute value which will always display positive number, then math.exp() will display the exponential value, math.log() displays logarithmic values, then we have also defined the math.random() function to display the random number. The output in the above screenshot will show the result of these functions respectively.

Conclusion

In this article, we conclude that Lua provides a standard library that contains mathematical functions for some mathematical calculations in the program and it is provided by the math library. In this, we don’t need to separately import or include the math library we can directly use it with the math function with a dot followed by the math function name. Therefore unlike other programming languages, this also has a simple math library for mathematical operations.

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Learn The Architecture Of Firewall In Detail

Introduction to Firewall

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The basic concept of a firewall is to protect the internal or organizational environment from any external security attack. Similarly, three major aspects will define the firewall’s configuration, like the network’s objective regarding the organization’s point of view, the development ability, and how we need to implement it. While considering it in terms of the hardware level, then we need to consider the budget also.

Firewall Architecture in Detail

There are different types of architecture available in the firewall.

1 Screened host firewall architecture

We have improved the packet filtering routers firewall architecture in the screened host firewall architecture. In this architecture, we use the packet filtering routers firewall technique with the dedicated or the separate firewall. It is known as the application proxy server. In the packet filtering router’s firewall architecture, we have a very big overhead to filter the network traffic (once the access control list increases). Due to this, we are facing lots of issues. Here, we have tried to overcome it and added a dedicated firewall. This technique will allow the router to access the firewall. Due to this architecture, the routers will pre-screen the network traffic or the packets to minimize the network overhead. It will also help to distribute the load as well.

Work Flow: As per the above architecture, a separate host is available, i.e., the bastion host. It acts like a proxy server to balance the load on the firewall. The firewall holds all the set of rules and access control. The Bastion server will help to filter out the network traffic. If it is a valid packet, it will allow it via proxy access to the internal filter router, moving further in the internal network.

2. Packet filtering routers’ firewall architecture

Many organizations want internet connectivity. If we enable internet connectivity, the organization without a firewall will be exposed to the external world. We need to install and configure the firewall to avoid an external security attack. In the packet filtering routers, we have the router concept. Here, the router interface acts as the internet provider to the organization. The router acts as an intermediate between the organization and the internet provider. On the same level, we are enabling the network packet filtering process.

If any unwanted packets may come, so it will filter them out on the same level. Hence the packages will drop or be rejected. It will not come in the organization-level network. It is a very simple way to implement it. It will also help to lower the risk of external security threats. But it has a few concerns also. If we go with the packet filtering routers, there will be less auditing of the network traffic. Similarly, we are also having the drawback of the strong authentication mechanism. Day by day, the access control list will grow. Hence, it will be a very big overhead to filter the incoming network packets. Due to this, it will decrease the network performance also. In a few cases, we will face a lag.

Work Flow: It is the basic technique to implement the firewall. Here, the ISP will provide an internet connection to the organization. Then, it is attached to the external filter router. First, we need to add the list of ACLs and configurations on the firewall. Then, with the help of the same configuration, the network traffic will filter and pass to the internal filter router. Further, the internal filter router will separate the network traffic into the internal organization-level network.

3. Dual-homed firewall architecture

The architectural complexity is increasing because we need high performance and less network lag. We use the single network interphase card in the previous firewall architecture. But when using such firewall architecture, the bastion host will contain the two different network interphase cards. In this architecture, one network interphase card will connect with the external network, and the other will connect with the internal network. Here, all the network traffic will physically travel from the firewall between internal and external network interphase cards.

Work Flow: In this architecture, there is no separate proxy server. In this firewall architecture, there are two different NIC’s available. In one NIC, the external ISP connection will connect. In the second NIC, the internal network will connect. Once the traffic comes, the firewall will filter the traffic and pass it to the internal network. If the traffic is not valid, the firewall will drop the packet and not flow it further.

Conclusion

We have seen the uncut concept of the “firewall architecture” with the proper explanation. Several firewall architectures are available; we must choose them per our requirements and budget. The firewall will track the traffic on the application level also.

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Learn The Overview And Examples Of Jmeter Script

Introduction to JMeter Script JMeter script overview

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JMeter script run

The procedure to execute JMeter scripts and Loadrunner configuration, and runtime configuration is explained below.

Install the JMeter, the latest version 64-bit JDK or JRE, in all the load generator machines where the script needs to be executed.

Compose the scripts in JMeter and save them in a local folder. The script should be saved in ZIP format and have all the files in the test script folder. The file’s path in the script folder should not surpass 260 characters.

CSV files can be downloaded manually on the load generator executed on JMeter concerning the path in the script location.

Upload the script of the JMeter into the Loadrunner enterprise.

In the navigation toolbar, choose test management. Next, choose the destination folder, or the user can create a new one.

Choose the upload script button from the navigation pane.

Upload settings should be configured and update the selected scripts in the destination folder.

After uploading the scripts of JMeter to Loadrunner, then choose the script in the test management tree and display the script to view the description.

In the workload and group view option, choose Vuser groups and edit runtime. After which, the dialog box pops up with JMeter runtime settings.

The JMX measurement is a UI element used to enable the JMX measurements at performance test execution.

The JMeter path is used to enter the default values in the JMeter script by including environment variables of %JMETER_HOME%

JMeter port is used to select the default port, which begins from 4000, and it uses the alternate port if the default port is already occupied. The range of the JMeter port lies from 4445 to 4455.

Remote testing is used to execute JMeter in node mode or server mode. Execution of JMeter can replicate the test among low version computers which simulate maximum load on the server.

JMeter additional file is used to give the local path for remote load generator, which can also be used as remote JMeter nodes or JMeter controller. It is enabled when remote testing is selected. Ensure that added properties are placed in the local path of the remote load generator, which is used as remote JMeter nodes or controllers when the test is executed.

Give a LoadRunner enterprise test and align the JMeter script with it.

Execute the test from the JMeter.

JMeter script with Examples

Cloud provisioning can be implemented to make the JMeter scripts more reliable to the host machine. Furthermore, it signifies that the JMX scripts on the cloud give effective cloud provisioning methods where the customer doesn’t want to pay and use it for free to execute the cloud test. To define the cloud location, choose the list of available locations, fetch cloud tokens from API keys and run the modules. If the user wants to specify multiple cloud locations for the same execution, it distributes the throughput and concurrency among all the locations.

The JMeter scripting can also be automated with Jenkins to achieve maximum efficacy. Continuous delivery becomes more fascinating in Software as a service company to create a new website and continuously work to enhance it. Software development has been growing in terms of automating the process, testing the behind lags, increasing the performance, minimizing the execution time, finding the bugs easily, and so on. By using Jenkins in executing a shell in JMeter, the project configuration is executed to make an effective continuous delivery cycle.

Conclusion

The JMeter script is used to access reporting services. For example, many testing tools aim at execution; the reporting features help access the test results in an interactive method. In addition, monitoring execution time helps find and access the JMeter scripting in a better method.

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