# ETH源码学习（1）创建私有链

By [point](https://paragraph.com/@point) · 2022-05-12

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下载geth，创建genesis.json

    {
        "config": {
            "chainId": 8888, //自行修改
            "homesteadBlock": 0,
            "daoForkBlock": 0,
            "daoForkSupport": true,
            "eip150Block": 0,
            "eip155Block": 0,
            "eip158Block": 0,
            "byzantiumBlock": 0,
            "constantinopleBlock": 0,
            "petersburgBlock": 0,
            "ethash": {}
        },
        "nonce": "0x42",
        "timestamp": "0x0",
        "extraData": "0x11bbe8db4e347b4e8c937c1c8370e4b5ed33adb3db69cbdb7a38e1e50b1b82fa",
        "gasLimit": "0xffffffff",
        "difficulty": "0x700000",//难度，越大挖矿越慢
        "alloc": {
            "093f59f1d91017d30d8c2caa78feb5beb0d2cfaf": {
                "balance": "0xffffffffffffffff"
            },
            "ddf7202cbe0aaed1c2d5c4ef05e386501a054406": {
                "balance": "0xffffffffffffffff"
            }
        }
    }
    

因为要分析源码，所以不是像网上命令行执行，而是使用goland debug

![执行命令](https://storage.googleapis.com/papyrus_images/af19010dce4685525a5478495e6a3470fbe712d1c8c3a0abd810a1dbd9f4003e.png)

执行命令

    参数
    --datadir "/Users/zhangnan/Downloads/self_eth/" init "/Users/zhangnan/Downloads/geth/genesis.json"
    

    初始化
    func initGenesis(ctx *cli.Context) error {
        // Make sure we have a valid genesis JSON
        genesisPath := ctx.Args().First()
        if len(genesisPath) == 0 {
            utils.Fatalf("Must supply path to genesis JSON file")
        }
        file, err := os.Open(genesisPath)
        if err != nil {
            utils.Fatalf("Failed to read genesis file: %v", err)
        }
        defer file.Close()
    
        genesis := new(core.Genesis)
        if err := json.NewDecoder(file).Decode(genesis); err != nil {
            utils.Fatalf("invalid genesis file: %v", err)
        }
    //以上是读初始化文件，下面开始第一个重要步骤，配置config
        // Open and initialise both full and light databases
        stack, _ := makeConfigNode(ctx)
        defer stack.Close()
    
        for _, name := range []string{"chaindata", "lightchaindata"} {
            chaindb, err := stack.OpenDatabase(name, 0, 0, "", false)
            if err != nil {
                utils.Fatalf("Failed to open database: %v", err)
            }
            _, hash, err := core.SetupGenesisBlock(chaindb, genesis)
            if err != nil {
                utils.Fatalf("Failed to write genesis block: %v", err)
            }
            chaindb.Close()
            log.Info("Successfully wrote genesis state", "database", name, "hash", hash)
        }
        return nil
    }

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*Originally published on [point](https://paragraph.com/@point/eth-1)*