Linux Tutorial and something else.....

31 July 202231 July 2022

Apache command connection check

The netstat command has been deprecated and replaced by the ss command in most of the Linux distributions.

It reads various ‘/proc’ files to gather information. It would take more time when there are lots of connections to display.

1) Checking the number of concurrent Apache connections

Run following ss command to find the total number of concurrent connections to Apache:

# ss -ant | grep -E ':80|:443' | wc -l
500

Alternatively, you can get Apache concurrent connection using netstat command as shown below:

# netstat -ant | grep -E ':80|:443' | wc -l
430

2) Checking concurrent connections of Apache in detail

Run the below ss command to see detailed information of Apache connections instead of counting it.

It shows the active internet connections on the server on port 80 & 443:

# ss -ant | grep -E ':80|:443'

 LISTEN     0      128    10.10.6.160:80                       :                  
106.222.112.160:12650              
 TIME-WAIT  0      0      94.237.76.92:443                114.119.135.42:2366               
 TIME-WAIT  0      0      94.237.76.92:443                114.119.135.42:2406               
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38400              
 ESTAB      0      0      127.0.0.1:38454              94.237.76.92:443                     
 ESTAB      0      0      94.237.76.92:443                117.249.205.234:64685              
 ESTAB      0      0      94.237.76.92:443                192.99.9.25:33132              
 ESTAB      0      0      94.237.76.92:443                66.249.71.82:49611              
 ESTAB      0      0      94.237.76.92:443                106.222.112.160:12648              
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38412              
 ESTAB      0      0      127.0.0.1:38402              94.237.76.92:443                
 TIME-WAIT  0      0      94.237.76.92:443                157.46.105.172:45656              
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38340              
 ESTAB      0      151496 94.237.76.92:443                106.222.112.160:12656              
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38332              
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38396              
 ESTAB      0      0      127.0.0.1:38460              94.237.76.92:443                
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38374              
 ESTAB      0      0      94.237.76.92:80                 5.9.61.232:51082              
 ESTAB      0      0      94.237.76.92:443                60.8.123.152:64476              
 ESTAB      0      0      94.237.76.92:443                167.114.209.104:35758              
 ESTAB      0      0      94.237.76.92:80                 106.222.112.160:12643              
 ESTAB      0      0      94.237.76.92:443                167.114.158.215:53270                          
 ESTAB      0      0      94.237.76.92:443                66.249.71.147:56912              
 ESTAB      0      0      94.237.76.92:443                127.0.0.1:38454              
 ESTAB      0      0      94.237.76.92:443                127.0.0.1:38468                         
 ESTAB      0      0      94.237.76.92:443                127.0.0.1:38402              
 TIME-WAIT  0      0      94.237.76.92:443                127.0.0.1:38366

Check the same information using the netstat command as shown below:

# netstat -ant | grep -E ':80|:443'

3) Listing Apache connections sort by IP

To count the number of connections currently active in Apache from each IP address and to sort them, use the following command:

# ss -ant |grep -E ':80|:443'|grep ESTAB| awk '{print $5}' | cut -d":" -f1 | sort | uniq -c | sort -nr

       8 94.237.76.92
       8 127.0.0.1
       2 5.9.61.232
       2 106.222.112.160
       1 98.236.14.66
       1 66.249.72.22
       1 66.249.71.48
       1 192.99.9.25
       1 167.114.209.104
       1 167.114.158.215

Similarly, you can find the same information using netstat command as shown below:

# netstat -ant |grep -E ':80|:443'|grep ESTAB | awk '{print $5}' | cut -d":" -f1 | sort | uniq -c | sort -nr

      6 162.158.155.70
      5 127.0.0.1
      2 172.68.51.180
      2 172.68.215.98
      2 172.68.215.86
      2 172.68.215.77
      2 172.68.215.75
      2 172.68.215.113
      2 172.68.215.111
      2 172.68.215.109
      2 172.68.215.101
      2 172.68.215.100
      2 162.158.150.128
      2 162.158.150.120
      2 162.158.118.154
      2 141.101.96.253
      2 141.101.96.243
      2 141.101.76.234
      2 141.101.105.254
	  .
	  .

Bonus Tips: 1) Counting running Apache processes in Linux

ps command is used to display all running processes in Linux system. Use the following format, if you would like to count the running Apache processes in Linux:

# ps -auxw | grep httpd | grep -v grep | wc -l
12

1.a) Listing Apache processes with ps

Use the following command to see the running httpd processes in Linux:

# ps auxw | grep httpd | grep -v grep
nobody    7988  0.0  0.5 253280 23252 ?        S    14:32   0:00 /usr/sbin/httpd -k start
nobody    8050  0.0  0.6 253412 24276 ?        S    14:33   0:00 /usr/sbin/httpd -k start
nobody    8054  0.0  0.6 253280 23288 ?        S    14:33   0:00 /usr/sbin/httpd -k start
nobody    8158  0.0  0.6 253280 23296 ?        S    14:33   0:00 /usr/sbin/httpd -k start
nobody    8159  0.0  0.5 253280 23176 ?        S    14:33   0:00 /usr/sbin/httpd -k start
daygeek   8202  0.0  0.6 253416 23304 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8203  0.0  0.5 253280 23052 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8207  0.0  0.5 253280 23044 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8213  0.0  0.6 253280 23300 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8216  0.0  0.5 253280 23052 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8218  0.0  0.6 253416 23304 ?        S    14:34   0:00 /usr/sbin/httpd -k start
nobody    8266  0.0  0.5 253148 23052 ?        S    14:35   0:00 /usr/sbin/httpd -k start
nobody    8267  0.0  0.5 253144 22800 ?        S    14:35   0:00 /usr/sbin/httpd -k start
nobody    8391  0.3  0.5 253144 22800 ?        S    14:35   0:00 /usr/sbin/httpd -k start
nobody    8393  0.5  0.5 253012 21776 ?        S    14:35   0:00 /usr/sbin/httpd -k start
nobody    8394  1.0  0.5 253144 22800 ?        S    14:35   0:00 /usr/sbin/httpd -k start
root     30500  0.0  0.0 227356  3584 ?        Ss   Jul25   2:33 /usr/sbin/httpd -k start

Let’s quickly look at the parameters

Serverlimit – Maximum number of Apache processes
StartServers – Number of processes to start when you start running Apache
MinSpareThreads/MaxSpareThreads – Number of threads to keep idle without being killed
ThreadsPerChild – Number of threads per process
MaxRequestWorkers – Number of concurrent connections to be supported. This is the main directive that you need to change to increase max connections in Apache
MaxConnectionsPerChild – Number of connections to be handled by each child before it is killed

22 July 202223 July 2022

Static Routing Contabo Problem solved

Destination Gateway Genmask Flags MSS Window irtt Iface

0.0.0.0 213.136.72.1 0.0.0.0 UG 0 0 0 eth0

213.136.72.0. 0.0.0.0. 255.255.255.0. U 0 0 0. eth0

Remove from static table route this to permit to reach the internal network ip always passing through the closed router

ip route del 213.136.72.0/24 via 0.0.0.0 dev eth0

[root@mail ~]# netstat -rn

Kernel IP routing table

Destination Gateway Genmask Flags MSS Window irtt Iface

0.0.0.0 213.136.72.1 0.0.0.0 UG 0 0 0 eth0

31 March 202231 March 2022

CIS Controls v8

12 March 202230 March 2022

Ways of Getting Data from API in React

from here

React library is a wonderful tool for building rich and highly scalable user interfaces. One of its powerful features is the possibility to fetch data for the web application from the outside and interact with it.

Why to Fetch Data?

When you are just starting developing web applications with React, you probably won’t need any external data at the beginning. You will build a simple applications like ToDo app or Counter and add your data to the state object of your application. And that is totally fine.

However, at some point you want to request real world data from an own or a third-party API. For example, if you want to build a book store or weather application, it is faster and convenient to use one of those free data sources available in the Internet.

Where to Do Data Fetching

Now that we have decided that we want to fetch data from external source, here comes the question – where exactly in our application we should do that?

This question depends the following criteria:

who is interested in data?
who will show the loading indicator in case data is pending?
where to show an optional error message when the request fails?

Usually this is a common parent component in the components tree who will do this job. It will fetch the data, store it to its local state and distribute it to the children:

1. On the first mounting of the component
We use this way when we want the data to be accessible when we first start the application. It means, we need to perform data fetching when our parent component is being mounted.

In class-based components the perfect place for data fetching is componentDidMount() lifecycle method.

In functional components it is useEffect() hook with an empty dependancy array because we need the data to be fetched once.

2. On event being triggered
We can fetch data on triggering an event (for example button click) by creating a function, which will make data fetching and then binding that function to the event.

Ways of Fetching Data

There are many ways to extract data from API in React:

using Fetch API
using Axios library
using async-await syntax
using custom hooks
using React Query library
using GrapthQL API

We will explore these ways now in details.

1. Fetching Data with Fetch API

Fetch API is built into most modern browsers on the window object (window.fetch) and enables us to make HTTP requests very easily using JavaScript promises.

In our CRA we can use fetch() method to get the data. This method accepts just an URL to the data.

To do so, we will create a method called fetchData(). It will call fetch() method with provided URL, then convert the result to JSON object and print it to the console:

const fetchData = () => {
return fetch("https://randomuser.me/api/")
      .then((response) => response.json())
      .then((data) => console.log(data));}

We can use this method now anywhere in the application. Here is an example how to use it in useEffect()hook:

import {useEffect} from "react";

useEffect(() => {
  fetchData();
  }, []);

2. Fetching Data with Axios library

It does the same job as Fetch, but the main difference is that it already returns the result as JSON object, so we don’t need to convert it.

First we need to install it using npm:

npm install axios

Than we need to import it to our project and we can use it in the same function fetchData() instead of fetch() method:

import axios from "axios"

const fetchData = () => {
return axios.get("https://randomuser.me/api/")
      .then((response) => console.log(response.data));}

What’s convenient about using Axios is that it has a much shorter syntax that allows us to cut down on our code and it includes a lot of tools and features which Fetch does not have in its API.

3.Fetching Data with Async-Await syntax

In ES7, it became possible to resolve promises using the async-await syntax. If you are not familiar with such function, check here.

The benefit of this is that it enables us to remove our .then() callbacks and simply get back our asynchronously resolved data.

Lets re-write our fetchData() function using this syntax:

async function fetchData() {
    try {
      const result = await axios.get("https://randomuser.me/api/")
      console.log(result.data));
    } catch (error) {
      console.error(error);
    }
  }

4.Fetching Data with Custom Hook

We can use the library React-Fetch-Hook to extract the data from API. It includes already several properties we can use: data, error for errors handling and isLoading for loading issues.

First it should be installed:

npm install react-fetch-hook

Then it should be imported and used on top of common parent component:

import useFetch from "react-fetch-hook"

const {data} = useFetch("https://randomuser.me/api/");
console.log(data);

There are other ways for data fetching as React Query library and GraphQL API, but this blog post is not covering them in depth, but you are free to explore those 🙂
Happy Fetching!!!

5 January 202230 March 2022

How to verify integrity of the file downloaded in windows

CertUtil -hashfile [FILENAME] SHA256

fciv [FILENAME] -sha1 > filename.txt

Linux Tutorial and something else…..

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