0 */5 * * *
The following key shows how each position in the cron pattern string is interpreted:
* * * * * * | | | | | | | | | | | day of week | | | | month | | | day of month | | hour | minute second (optional)
Cron Job lets you run a script to do a repetitive job in an efficient way, here's how you can schedule a cronjob for every 5 hours:
Step 1: Edit your cronjob file by running "crontab -e" command
Step 2: Add the following line for every 5 hours interval:
0 */5 * * * /home/ubuntu/backup.sh
Step 3: Save the file. Done!
Cron will then examine the modification time on all crontab and reload those which have changed. Thus cron need not be restarted whenever a crontab file is modified.
But if you just want to make sure its done anyway:
sudo service cron reload
sudo service cron restart
sudo systemctl reload crond
Hey peeps, Hope you all are safe & going well
Many entrepreneurs & startups are interested to start a crypto exchange platform by using a cryptocurrency exchange script, you know why??? Let me explain. Before that, you need to know what is a cryptocurrency exchange script???
Cryptocurrency Exchange Script is an upgrade version of all exchange platforms, it is also called ready-made script or software. By using the crypto exchange script you can launch your crypto trading platform instantly. It is one of the easiest and fastest ways to start your crypto exchange business. Also, it helps to launch your exchange platform within 7 days.
The More Important one is “Where to get the best bitcoin exchange script?”
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Are you wanting to be an Entrepreneur? A Business using cryptocurrency? Then this article is for you.
As a beginner, always one prefers fair play. But to the least, initiating business in the streams of cryptocurrency carries a varying degree of risks. We all know that, Every business packs the profit only if we are ready to take risks. But flabbergast is, you can avoid unnecessary risk, If you choose our Twisted HYIP Investment script. You don’t need to play poker with your hard-earned Money.
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How it works?
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HYIP projects are one of the growth trends of the internet and many investors are involved in it.
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Hyip concept is often referred to as a high-yield investment plan or scheme, while the main difference between this and other types of investments is high-yield and low-yield.
There are many HYIPs with different investment plans. Those are, Short and long term.
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Initial Coin Offering Projects:
In Today’s trend, ICO script also created a vast impact on collecting funds and gaining benefits valuable operations. The cost for building an ICO website is made easy as it is based on customers’ specifications of features.
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The product is furnished with more attractive and essential features that support
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Are you interested in starting a cryptocurrency exchange??? Congrats, you’ve chosen the right business idea at the right time!!! Because cryptocurrency is gonna boom in the upcoming days. Recently, many governments are legalizing cryptocurrency in their countries. And more importantly, the pride of cryptocurrencies “Bitcoin crossed more than $50K”. So this is the right time to originate your crypto exchange business. Now you will have a question like this “How to start a bitcoin exchange in a safe & secure way?” For your unanswered question. I suggest a simple solution, that is “Bitcoin Exchange Clone Script”. But there are lots of crypto exchange clone scripts in the crypto market. Here I listed the Top 10 Cryptocurrency Exchange Scripts check it out below.
Top 10 Cryptocurrency Exchange Scripts:
Among these clone scripts many cryptopreneurs & enthusiasts most commonly use only 3 cryptocurrency exchange scripts.
These are 3 cryptocurrency exchange clone scripts that are widely used in the crypto space. “Who Provides these cryptocurrency exchange scripts???” That’s really hard to find because many crypto exchange clone script firms are available in the crypto market. So, finding the best one will be a kind of complicated task. Don’t worry; I will help you. I’ve done some technical aspects to identify & find the best crypto exchange clone script provider, as the end of the result one script/software provider (Coinsclone) cleared all my technical & non-technical hurdles. Coinsclone is one of the professional crypto exchange clone script providers. Their software/script is 100% secured & bug-free because their primary motto is client stratification. So that they have clients from all over the world. Till now they have successfully delivered 100+ crypto projects (Crypto exchange, Wallets & Payment gateway) for their clients.
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The Substrate Knowledge Map provides information that you—as a Substrate hackathon participant—need to know to develop a non-trivial application for your hackathon submission.
The map covers 6 main sections:
Each section contains basic information on each topic, with links to additional documentation for you to dig deeper. Within each section, you'll find a mix of quizzes and labs to test your knowledge as your progress through the map. The goal of the labs and quizzes is to help you consolidate what you've learned and put it to practice with some hands-on activities.
One question we often get is why learn the Substrate framework when we can write smart contracts to build decentralized applications?
The short answer is that using the Substrate framework and writing smart contracts are two different approaches.
Traditional smart contract platforms allow users to publish additional logic on top of some core blockchain logic. Since smart contract logic can be published by anyone, including malicious actors and inexperienced developers, there are a number of intentional safeguards and restrictions built around these public smart contract platforms. For example:
Fees: Smart contract developers must ensure that contract users are charged for the computation and storage they impose on the computers running their contract. With fees, block creators are protected from abuse of the network.
Sandboxed: A contract is not able to modify core blockchain storage or storage items of other contracts directly. Its power is limited to only modifying its own state, and the ability to make outside calls to other contracts or runtime functions.
Reversion: Contracts can be prone to undesirable situations that lead to logical errors when wanting to revert or upgrade them. Developers need to learn additional patterns such as splitting their contract's logic and data to ensure seamless upgrades.
These safeguards and restrictions make running smart contracts slower and more costly. However, it's important to consider the different developer audiences for contract development versus Substrate runtime development.
Building decentralized applications with smart contracts allows your community to extend and develop on top of your runtime logic without worrying about proposals, runtime upgrades, and so on. You can also use smart contracts as a testing ground for future runtime changes, but done in an isolated way that protects your network from any errors the changes might introduce.
In summary, smart contract development:
Unlike traditional smart contract development, Substrate runtime development offers none of the network protections or safeguards. Instead, as a runtime developer, you have total control over how the blockchain behaves. However, this level of control also means that there is a higher barrier to entry.
Substrate is a framework for building blockchains, which almost makes comparing it to smart contract development like comparing apples and oranges. With the Substrate framework, developers can build smart contracts but that is only a fraction of using Substrate to its full potential.
With Substrate, you have full control over the underlying logic that your network's nodes will run. You also have full access for modifying and controlling each and every storage item across your runtime modules. As you progress through this map, you'll discover concepts and techniques that will help you to unlock the potential of the Substrate framework, giving you the freedom to build the blockchain that best suits the needs of your application.
You'll also discover how you can upgrade the Substrate runtime with a single transaction instead of having to organize a community hard-fork. Upgradeability is one of the primary design features of the Substrate framework.
In summary, runtime development:
If you need any community support, please join the following channels based on the area where you need help:
Alternatively, also look for support on Stackoverflow where questions are tagged with "substrate" or on the Parity Subport repo.
Use the following links to explore the sites and resources available on each:
Substrate Developer Hub has the most comprehensive all-round coverage about Substrate, from a "big picture" explanation of architecture to specific technical concepts. The site also provides tutorials to guide you as your learn the Substrate framework and the API reference documentation. You should check this site first if you want to look up information about Substrate runtime development. The site consists of:
Knowledge Base: Explaining the foundational concepts of building blockchain runtimes using Substrate.
Tutorials: Hand-on tutorials for developers to follow. The first SIX tutorials show the fundamentals in Substrate and are recommended for every Substrate learner to go through.
How-to Guides: These resources are like the O'Reilly cookbook series written in a task-oriented way for readers to get the job done. Some examples of the topics overed include:
API docs: Substrate API reference documentation.
Substrate Node Template provides a light weight, minimal Substrate blockchain node that you can set up as a local development environment.
Substrate Front-end template provides a front-end interface built with React using Polkadot-JS API to connect to any Substrate node. Developers are encouraged to start new Substrate projects based on these templates.
If you face any technical difficulties and need support, feel free to join the Substrate Technical matrix channel and ask your questions there.
Polkadot Wiki documents the specific behavior and mechanisms of the Polkadot network. The Polkadot network allows multiple blockchains to connect and pass messages to each other. On the wiki, you can learn about how Polkadot—built using Substrate—is customized to support inter-blockchain message passing.
👉 Submit your answers to Quiz #1
Here you will set up your local machine to install the Rust compiler—ensuring that you have both stable and nightly versions installed. Both stable and nightly versions are required because currently a Substrate runtime is compiled to a native binary using the stable Rust compiler, then compiled to a WebAssembly (WASM) binary, which only the nightly Rust compiler can do.
Also refer to:
👉 Complete Lab #1: Run a Substrate node
Polkadot JS Apps is the canonical front-end to interact with any Substrate-based chain.
You can configure whichever endpoint you want it to connected to, even to your
localhost running node. Refer to the following two diagrams.
👉 Complete Quiz #2
👉 Complete Lab #2: Using Polkadot-JS Apps
Notes: If you are connecting Apps to a custom chain (or your locally-running node), you may need to specify your chain's custom data types in JSON under Settings > Developer.
Polkadot-JS Apps only receives a series of bytes from the blockchain. It is up to the developer to tell it how to decode and interpret these custom data type. To learn more on this, refer to:
You will also need to create an account. To do so, follow these steps on account generation. You'll learn that you can also use the Polkadot-JS Browser Plugin (a Metamask-like browser extension to manage your Substrate accounts) and it will automatically be imported into Polkadot-JS Apps.
Notes: When you run a Substrate chain in development mode (with the
--devflag), well-known accounts (
Charlie, etc.) are always created for you.
👉 Complete Lab #3: Create an Account
You need to know some Rust programming concepts and have a good understanding on how blockchain technology works in order to make the most of developing with Substrate. The following resources will help you brush up in these areas.
You will need familiarize yourself with Rust to understand how Substrate is built and how to make the most of its capabilities.
If you are new to Rust, or need a brush up on your Rust knowledge, please refer to The Rust Book. You could still continue learning about Substrate without knowing Rust, but we recommend you come back to this section whenever in doubt about what any of the Rust syntax you're looking at means. Here are the parts of the Rust book we recommend you familiarize yourself with:
Given that you'll be writing a blockchain runtime, you need to know what a blockchain is, and how it works. The **Web3 Blockchain Fundamental MOOC Youtube video series provides a good basis for understanding key blockchain concepts and how blockchains work.
The lectures we recommend you watch are: lectures 1 - 7 and lecture 10. That's 8 lectures, or about 4 hours of video.
👉 Complete Quiz #3
In this document, we assume you will develop a Substrate runtime with FRAME (v2). This is what a Substrate node consists of.
Each node has many components that manage things like the transaction queue, communicating over a P2P network, reaching consensus on the state of the blockchain, and the chain's actual runtime logic (aka the blockchain runtime). Each aspect of the node is interesting in its own right, and the runtime is particularly interesting because it contains the business logic (aka "state transition function") that codifies the chain's functionality. The runtime contains a collection of pallets that are configured to work together.
On the node level, Substrate leverages libp2p for the p2p networking layer and puts the transaction pool, consensus mechanism, and underlying data storage (a key-value database) on the node level. These components all work "under the hood", and in this knowledge map we won't cover them in detail except for mentioning their existence.
👉 Complete Quiz #4
In our Developer Hub, we have a thorough coverage on various subjects you need to know to develop with Substrate. So here we just list out the key topics and reference back to Developer Hub. Please go through the following key concepts and the directed resources to know the fundamentals of runtime development.
Key Concept: Runtime, this is where the blockchain state transition function (the blockchain application-specific logic) is defined. It is about composing multiple pallets (can be understood as Rust modules) together in the runtime and hooking them up together.
Runtime Development: Execution, this article describes how a block is produced, and how transactions are selected and executed to reach the next "stage" in the blockchain.
Runtime Develpment: Pallets, this article describes what the basic structure of a Substrate pallet is consists of.
Runtime Development: FRAME, this article gives a high level overview of the system pallets Substrate already implements to help you quickly develop as a runtime engineer. Have a quick skim so you have a basic idea of the different pallets Substrate is made of.
👉 Complete Lab #4: Adding a Pallet into a Runtime
Runtime Development: Storage, this article describes how data is stored on-chain and how you could access them.
Runtime Development: Events & Errors, this page describe how external parties know what has happened in the blockchain, via the emitted events and errors when executing transactions.
Notes: All of the above concepts we leverage on the
#[pallet::*]macro to define them in the code. If you are interested to learn more about what other types of pallet macros exist go to the FRAME macro API documentation and this doc on some frequently used Substrate macros.
👉 Complete Lab #5: Building a Proof-of-Existence dApp
👉 Complete Lab #6: Building a Substrate Kitties dApp
👉 Complete Quiz #5
The Substrate Front-end Template is an example of using Polkadot JS API in a React front-end.
👉 Complete Lab #7: Using Polkadot-JS API
👉 Complete Quiz #6: Using Polkadot-JS API
Learn about the difference between smart contract development vs Substrate runtime development, and when to use each here.
In Substrate, you can program smart contracts using ink!.
👉 Complete Quiz #7: Using ink!
A lot 😄
On-chain runtime upgrades. We have a tutorial on On-chain (forkless) Runtime Upgrade. This tutorial introduces how to perform and schedule a runtime upgrade as an on-chain transaction.
There are certain limits to on-chain logic. For instance, computation cannot be too intensive that it affects the block output time, and computation must be deterministic. This means that computation that relies on external data fetching cannot be done on-chain. In Substrate, developers can run these types of computation off-chain and have the result sent back on-chain via extrinsics.
Tightly- and Loosely-coupled pallets, calling one pallet's functions from another pallet via trait specification.
Parachains: one key feature of Substrate is the capability of becoming a parachain for relay chains like Polkadot. You can develop your own application-specific logic in your chain and rely on the validator community of the relay chain to secure your network, instead of building another validator community yourself. Learn more with the following resources:
Source Code: https://github.com/substrate-developer-hub/hackathon-knowledge-map