Build private ethereum network and test step by step

9 min readAug 6, 2019

Avoid paywall : https://github.com/HyoungsungKim/Studying-ethereum/tree/master/study-in-geth/docs

**(Updated)You can see a way to use puppeth to make a genesis file in my github**

Let’s study ethereum using geth together

You can read it in my github

Build private network and test

Today we will build our own private network and test it is working well. However, we will use only 1 node for today. Let’s try multi-node later.

Index

Environment
Build private network
Test private network
Make a transaction for testing private network

Environment

Linux mint 19.1
Go (version 1.10 or later)
geth (go-ethereum)

Download and install geth

First clone geth from go-ethereum repository to GOPATH directory

my GOPATH is /home/hskim/go so i cloned geth to /home/hskim/go/src/github.com

git clone https://github.com/ethereum/go-ethereum.git

Then geth will be downloaded. after downloading, move to go-ethereum directory and open terminal

make all

If you want to use only geth console, then

make geth

is enough. However, If you want to test with multi-nodes someday, then you have to do make all

If build is successful then you can see geth in /go-ethereum/build/bin

Build private network

First of all you have to make a genesis.json. You can make it in any folder, any directory except a directory which need permission, but for convenience, I recommend make it in same folder with geth (/go-ethereum/build/bin)

{
    "config": {
        "chainId": 15, 
        "homesteadBlock": 0,
        "eip155Block": 0,
        "eip158Block": 0
    },  
    "difficulty": "400",
    "gasLimit": "2100000",
    "alloc": {
    }   
}

I got it from ethereum-wiki, however, changed something.

First, I changed chainId. chainId is the most important part of this .json Because, geth can recognize a network you want to access. In ethereum network, There are already defined chainID. you can see more detail from here

0: Olympic; Ethereum public pre-release testnet
1: Frontier; Homestead, Metropolis, the Ethereum public main network
1: Classic; The (un)forked public Ethereum Classic main network, chain ID 61
1: Expanse; An alternative Ethereum implementation, chain ID 2
2: Morden; The public Ethereum testnet, now Ethereum Classic testnet
3: Ropsten; The public cross-client Ethereum testnet
4: Rinkeby: The public Geth Ethereum testnet
42: Kovan; The public Parity Ethereum testnet
77: Sokol; The public POA testnet
99: POA; The public Proof of Authority Ethereum network
7762959: Musicoin; The music blockchain

Therefore, except these, you can use any chainId like 15 what i did.

Second, I changed difficulty for easy mining.

Third, I set alloc to empty. It is used for funding ether to a already generated accounts

For example, If you generate the account 7df9a875a174b3bc565e6424a0050ebc1b2d1d82 and .json is

{
    "config": {
        "chainId": 15,
        "homesteadBlock": 0,
        "eip155Block": 0,
        "eip158Block": 0
    },
    "difficulty": "400",
    "gasLimit": "2100000",
    "alloc": {
        "7df9a875a174b3bc565e6424a0050ebc1b2d1d82": { "balance": "300000" },
    }
}

then 300000 wei will charged after initiation. Don’t need to worry what is initiation. I will refer about it soon.

Now we have to make a directory to store information. I made geth-test folder. You can make it anywhere. my directory is /home/hskim/Documents/geth-test

Finally, We are ready to start.

Move to /go-ethereum/build/bin, open terminal and follow it

$ ./geth --datadir your_own_storage init genesis.json

For example, in my case

$ ./geth --datadir /home/hskim/Documents/geth-test init genesis.json

After initiation, check your own storage folder

INFO [08-06|20:49:41.266] Bumping default cache on mainnet         provided=1024 updated=4096
INFO [08-06|20:49:41.268] Maximum peer count                       ETH=50 LES=0 total=50
INFO [08-06|20:49:41.268] Smartcard socket not found, disabling    err="stat /run/pcscd/pcscd.comm: no such file or directory"
INFO [08-06|20:49:41.271] Allocated cache and file handles         database=/home/hskim/Documents/geth-test/geth/chaindata cache=16.00MiB handles=16
INFO [08-06|20:49:41.284] Writing custom genesis block 
INFO [08-06|20:49:41.284] Persisted trie from memory database      nodes=0 size=0.00B time=3.725µs gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B
INFO [08-06|20:49:41.285] Successfully wrote genesis state         database=chaindata hash=ab944c…55600c
INFO [08-06|20:49:41.285] Allocated cache and file handles         database=/home/hskim/Documents/geth-test/geth/lightchaindata cache=16.00MiB handles=16
INFO [08-06|20:49:41.302] Writing custom genesis block 
INFO [08-06|20:49:41.302] Persisted trie from memory database      nodes=0 size=0.00B time=3.632µs gcnodes=0 gcsize=0.00B gctime=0s livenodes=1 livesize=0.00B
INFO [08-06|20:49:41.303] Successfully wrote genesis state         database=lightchaindata hash=ab944c…55600c

If initiation is done well, then you can see geth and keystore folder in your storage

Now we can run our private network!

open terminal in /go-ethereum/build/bin and follow it!

$ ./geth --datadir Your_own_storage --networkid 15 console

We set the chainid as 15 in genesis.json Therefore our networkid is 15 too

In my case,

$ ./geth --datadir /home/hskim/Documents/geth-test --networkid 15 console

then you can see

INFO [08-06|21:27:43.867] Maximum peer count                       ETH=50 LES=0 total=50
INFO [08-06|21:27:43.867] Smartcard socket not found, disabling    err="stat /run/pcscd/pcscd.comm: no such file or directory"
INFO [08-06|21:27:43.870] Starting peer-to-peer node               instance=Geth/v1.9.2-unstable-aa6005b4-20190805/linux-amd64/go1.12.7
INFO [08-06|21:27:43.870] Allocated trie memory caches             clean=256.00MiB dirty=256.00MiB
INFO [08-06|21:27:43.870] Allocated cache and file handles         database=/home/hskim/Documents/geth-test/geth/chaindata cache=512.00MiB handles=524288
INFO [08-06|21:27:43.904] Opened ancient database                  database=/home/hskim/Documents/geth-test/geth/chaindata/ancient
INFO [08-06|21:27:43.904] Initialised chain configuration          config="{ChainID: 15 Homestead: 0 DAO: <nil> DAOSupport: false EIP150: <nil> EIP155: 0 EIP158: 0 Byzantium: <nil> Constantinople: <nil>  Petersburg: <nil> Engine: unknown}"
INFO [08-06|21:27:43.904] Disk storage enabled for ethash caches   dir=/home/hskim/Documents/geth-test/geth/ethash count=3
INFO [08-06|21:27:43.904] Disk storage enabled for ethash DAGs     dir=/home/hskim/.ethash count=2
INFO [08-06|21:27:43.904] Initialising Ethereum protocol           versions=[63] network=15 dbversion=7
INFO [08-06|21:27:43.944] Loaded most recent local header          number=0 hash=ab944c…55600c td=400 age=50y3mo3w
INFO [08-06|21:27:43.944] Loaded most recent local full block      number=0 hash=ab944c…55600c td=400 age=50y3mo3w
INFO [08-06|21:27:43.944] Loaded most recent local fast block      number=0 hash=ab944c…55600c td=400 age=50y3mo3w
INFO [08-06|21:27:43.945] Loaded local transaction journal         transactions=0 dropped=0
INFO [08-06|21:27:43.945] Regenerated local transaction journal    transactions=0 accounts=0
INFO [08-06|21:27:43.951] Allocated fast sync bloom                size=512.00MiB
INFO [08-06|21:27:43.951] Initialized fast sync bloom              items=0 errorrate=0.000 elapsed=37.353µs
INFO [08-06|21:27:43.997] New local node record                    seq=3 id=65c5b16ab4aa9e9f ip=127.0.0.1 udp=30303 tcp=30303
INFO [08-06|21:27:43.998] Started P2P networking                   self=enode://3e6e6cc9fd56954e02f3807813e086827ddf0576d0c969f67a915691ec3f879867332ba4911048fd513672856c63a2746063706005c6d777f670ae16c2c4a384@127.0.0.1:30303
INFO [08-06|21:27:43.999] IPC endpoint opened                      url=/home/hskim/Documents/geth-test/geth.ipc
WARN [08-06|21:27:44.088] Served eth_coinbase                      reqid=3 t=16.874µs err="etherbase must be explicitly specified"
Welcome to the Geth JavaScript console!

instance: Geth/v1.9.2-unstable-aa6005b4-20190805/linux-amd64/go1.12.7
at block: 0 (Thu, 01 Jan 1970 09:00:00 KST)
 datadir: /home/hskim/Documents/geth-test
 modules: admin:1.0 debug:1.0 eth:1.0 ethash:1.0 miner:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0 web3:1.0
>

At last line, you can see console pointer(>). there are some lines we need to check

INFO [08-06|21:27:43.904] Initialised chain configuration          config="{ChainID: 15 Homestead: 0 DAO: <nil> DAOSupport: false EIP150: <nil> EIP155: 0 EIP158: 0 Byzantium: <nil> Constantinople: <nil>  Petersburg: <nil> Engine: unknown}"

In this line, we can check ChainID is 15 like we expected.

Now our private network is running!

Test private network

Now let’s test our private network

> eth.blockNumber
0
> eth.accounts
[]

eth.blockNumber check the number of blocks. We just generate this network. Therefore there is 0 block. eth.account check accounts of network. There are no accounts.

Let’s generate account

> personal.newAccount("Alice")
INFO [08-06|21:33:36.241] Your new key was generated               address=0xb8C941069cC2B71B1a00dB15E6E00A200d387039
WARN [08-06|21:33:36.241] Please backup your key file!             path=/home/hskim/Documents/geth-test/keystore/UTC--2019-08-06T12-33-34.442823142Z--b8c941069cc2b71b1a00db15e6e00a200d387039
WARN [08-06|21:33:36.241] Please remember your password! 
"0xb8c941069cc2b71b1a00db15e6e00a200d387039"

We just generated the address of Alice:0xb8C941069cC2B71B1a00dB15E6E00A200d387039. We can see it by using geth

> eth.accounts
["0xb8c941069cc2b71b1a00db15e6e00a200d387039"]

we will use it as miner’s address so block generation reward will be sent to Alice’s address

Before mining, let’s check Alice’s balance

> eth.getBalance("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
0
> eth.getBalance(eth.accounts[0])
0

There are 2 ways to check balance.

- First, using address directly
- Second, using random access of `eth.accounts`. Alice's account is first account of our network. so we can call it as `eth.account[0]`

I will use first one in this example to avoid confusion.

As we expect, there is no ether. now let’s mining.

First we have to set miner’s address

We will use 3 commands

miner.setEtherbase(address)

It sets miner’s address. Mining reward will be sent to this account

miner.start(number of threads)

Start mining. You can set how many threads you will use. I will use 1 thread

miner.stop()

Stop mining

> miner.setEtherbase("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
true
> miner.start(1)
null
INFO [08-06|21:42:38.198] Updated mining threads                   threads=1
INFO [08-06|21:42:38.198] Transaction pool price threshold updated price=1000000000
null
> INFO [08-06|21:42:38.198] Commit new mining work                   number=1 sealhash=4bb421…3f463a uncles=0 txs=0 gas=0 fees=0 elapsed=325.066µs
INFO [08-06|21:42:40.752] Successfully sealed new block            number=1 sealhash=4bb421…3f463a hash=4b2b78…4808f6 elapsed=2.554s
INFO [08-06|21:42:40.752] 🔨 mined potential block                  number=1 hash=4b2b78…4808f6.
.
.INFO [08-06|21:42:56.174] 🔨 mined potential block                  number=9 hash=2faebb…8be693
INFO [08-06|21:42:56.174] Commit new mining work                   number=10 sealhash=384aa6…cb0596 uncles=0 txs=0 gas=0 fees=0 elapsed=179.463µs
> miner.stop()
null

We finished mining. Now let’s check it worked well.

> eth.blockNumber
9

In my case, I mined 9 blocks until I stop it.

> eth.getBalance("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
45000000000000000000

Wow! we got a reward. Exactly wei, not ether. wei is small unit of ether like satoshi of bitcoin

1 ether = 10^18 wei

We can convert it to ether by command

> web3.fromWei(eth.getBalance("0xb8c941069cc2b71b1a00db15e6e00a200d387039"), "ether")
45

Yeah! we got 45 ether. But why 45 ether? To know it, we have to see the source code of geth(go-ethereum)

//go-ethereum/consensus/ethash/consensus.go
func accumulateRewards(config *params.ChainConfig, state *state.StateDB, header *types.Header, uncles []*types.Header) {
	// Select the correct block reward based on chain progression
	blockReward := FrontierBlockReward
	if config.IsByzantium(header.Number) {
		blockReward = ByzantiumBlockReward
	}
	if config.IsConstantinople(header.Number) {
		blockReward = ConstantinopleBlockReward
	}
	// Accumulate the rewards for the miner and any included uncles
	reward := new(big.Int).Set(blockReward)
	r := new(big.Int)
	for _, uncle := range uncles {
		r.Add(uncle.Number, big8)
		r.Sub(r, header.Number)
		r.Mul(r, blockReward)
		r.Div(r, big8)
		state.AddBalance(uncle.Coinbase, r)		r.Div(blockReward, big32)
		reward.Add(reward, r)
	}
	state.AddBalance(header.Coinbase, reward)
}

In this function, blockReward is initialized as FrontierBlockReward.

Let’s see what is FrontierBlockReward

//go-ethereum/consensus/ethash/consensus.go
var (
	FrontierBlockReward       = big.NewInt(5e+18) // Block reward in wei for successfully mining a block
	ByzantiumBlockReward      = big.NewInt(3e+18) // Block reward in wei for successfully mining a block upward from Byzantium
	ConstantinopleBlockReward = big.NewInt(2e+18) // Block reward in wei for successfully mining a block upward from Constantinople
	maxUncles                 = 2                 // Maximum number of uncles allowed in a single block
	allowedFutureBlockTime    = 15 * time.Second  // Max time from current time allowed for blocks, before they're considered future blocks
.
.
.
)

FrontierBlockReward is set as 5 * 10^18 and it is 5 ether. Alice generated 9 blocks and got 5 ether per generation. Therefore Alice has 45 ether.

Make a transaction for testing private network

Generate new account

> personal.newAccout("Bob")
INFO [08-06|22:00:23.416] Your new key was generated               address=0xf39Cf42Cd233261cd2b45ADf8fb1E5A1e61A6f90
WARN [08-06|22:00:23.416] Please backup your key file!             path=/home/hskim/Documents/geth-test/keystore/UTC--2019-08-06T13-00-21.621172635Z--f39cf42cd233261cd2b45adf8fb1e5a1e61a6f90
WARN [08-06|22:00:23.416] Please remember your password! 
"0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90"> eth.getBalance("0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90")
0

I got the account of Bob:0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90 Alice will send ether to Bob's account

> eth.sendTransaction({from: "0xb8c941069cc2b71b1a00db15e6e00a200d387039", to: "0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90", value: web3.toWei(5, "ether")})

Let’s send 5 ether to Bob’s account

Alice’s account : 0xb8c941069cc2b71b1a00db15e6e00a200d387039
Bob’s account : 0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90

Or we can initialize these using variable

> from = "0xb8c941069cc2b71b1a00db15e6e00a200d387039"
> to = "0xb8c941069cc2b71b1a00db15e6e00a200d387039"
> eth.sendTransaction({from: from, to: to, value: web3.toWei(5, "ether")})

We sent ether, however, don’t forget we never use private key of Alice. Therefore we met Error

WARN [08-06|22:04:55.407] Served eth_sendTransaction               reqid=25 t=3.461656ms err="authentication needed: password or unlock"
Error: authentication needed: password or unlock
    at web3.js:3143:20
    at web3.js:6347:15
    at web3.js:5081:36
    at <anonymous>:1:1

We have to unlock Alice’s account. Let’s see status of Alice’s account.

> personal.listWallets[0].status
"Locked"

Yes… It is locked… So we have to unlock it to send ether from Alice to Bob

> web3.personal.unlockAccount("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
Unlock account 0xb8c941069cc2b71b1a00db15e6e00a200d387039

Alice’s address is 0xb8c941069cc2b71b1a00db15e6e00a200d387039. However we have to type a Passphrase of Alice. passphrase is Alice cause we generate this address using Alice

Remember it!
> personal.newAccount(“Alice”)

Passphrase: Alice
true

Now Alice’s account is unlocked. Let’s go back to transaction. We can see pending transactions

> eth.pendingTransactions
[]

Until now, there is not any transaction. We just unlocked Alice’s account. Let’s make a transaction again.

> eth.sendTransaction({from: "0xb8c941069cc2b71b1a00db15e6e00a200d387039", to: "0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90", value: web3.toWei(5, "ether")})
INFO [08-06|22:16:09.274] Setting new local account                address=0xb8C941069cC2B71B1a00dB15E6E00A200d387039
INFO [08-06|22:16:09.275] Submitted transaction                    fullhash=0x926f1bb71d5b48a306e6cde2d45c01f8af2107febf94b166a7e5f8e025dc8adc recipient=0xf39Cf42Cd233261cd2b45ADf8fb1E5A1e61A6f90
"0x926f1bb71d5b48a306e6cde2d45c01f8af2107febf94b166a7e5f8e025dc8adc"

There is no error. Let’s see pending transactions

> eth.pendingTransactions
[{
    blockHash: null,
    blockNumber: null,
    from: "0xb8c941069cc2b71b1a00db15e6e00a200d387039",
    gas: 21000,
    gasPrice: 1000000000,
    hash: "0x926f1bb71d5b48a306e6cde2d45c01f8af2107febf94b166a7e5f8e025dc8adc",
    input: "0x",
    nonce: 0,
    r: "0x70484271bdc85f7233e715423d8d0be5c669a323385b5ec0ff080a52cf3c654c",
    s: "0x1b55a792995f61128c10a48ce1e0869893c863d38489f574d84ae3a96b031cef",
    to: "0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90",
    transactionIndex: null,
    v: "0x42",
    value: 5000000000000000000
}]

Yeah! There is a transaction.

> eth.getBalance("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
45000000000000000000
> eth.getBalance("0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90")
0

We didn’t mine any block. so There is no change of balance yet. Let’s mine again!

> miner.start(1)
INFO [08-06|22:19:53.061] Updated mining threads                   threads=1
INFO [08-06|22:19:53.061] Transaction pool price threshold updated price=1000000000
null
> INFO [08-06|22:19:53.062] Commit new mining work                   number=10 sealhash=f69cfb…273c0d uncles=0 txs=0 gas=0 fees=0 elapsed=265.557µs
INFO [08-06|22:19:53.062] Commit new mining work                   number=10 sealhash=a018f5…65f494 uncles=0 txs=1 gas=21000 fees=2.1e-05 elapsed=1.022ms
INFO [08-06|22:19:54.718] Successfully sealed new block            number=10 sealhash=a018f5….
.
.INFO [08-06|22:20:05.086] 🔨 mined potential block                  number=16 hash=e7688a…09ed64
INFO [08-06|22:20:05.086] Commit new mining work                   number=17 sealhash=6b297d…b76b19 uncles=0 txs=0 gas=0     fees=0       elapsed=252.945µs
> miner.stop()
null> eth.blockNumber
16

Last time Alice mined 9 blocks and this time mined 7 blocks more. So We can expect Alice has 75 ether (80 ether block reward — 5 ether sent to Bob = 75 ether). Let’s check.

First,

> eth.pendingTransactions
[]

There is no pending transaction. Alice and Bob’s transaction is done!

Let’s see balance of them

> eth.getBalance("0xb8c941069cc2b71b1a00db15e6e00a200d387039")
75000000000000000000
> eth.getBalance("0xf39cf42cd233261cd2b45adf8fb1e5a1e61a6f90")
5000000000000000000

As we expected, Alice has 75 ether, Bob has 5 ether. We did it!

That is all what i have prepared. My goal is changing consensus algorithm of geth for studying. So if my process is successful, I will be back with new posts. Please pray for me and next posts.. T_T

If there are errors or you want to add more details, please contribute it

Github : https://github.com/HyoungsungKim/Studying-ethereum/tree/master/study-in-geth/docs