Run a GETH Ethereum Light Node

In this tutorial we will install the Geth implementation of Ethereum on Linux and we will be using the light sync mode which will get you up and running in minutes, which only downloads a couple of GBs.

Once we have our node setup we will be using the API and Web3 to interact with our ethereum node.

To understand the basics of blockchain better, you can read my post:

Environment Setup

We require go to be installed on our server, so from golang’s releases page get the latest version of Go and extract it:

cd /tmp
wget https://go.dev/dl/go1.17.4.linux-amd64.tar.gz
sudo tar -C /usr/local -xzf go1.17.4.linux-amd64.tar.gz

Setup environment for Go in /etc/profile.d/go.sh:

export GOROOT=/usr/local/go
export GOPATH=$HOME/go
export PATH=$PATH:$GOROOT/bin

While you are in your session, source the file:

source /etc/profile.d/go.sh

And verify that Go is installed:

go version
go version go1.17.4 linux/amd64

Download Geth

From the geth releases page, get the latest version, extract and setup a symlink to the latest version:

cd /tmp
wget https://gethstore.blob.core.windows.net/builds/geth-linux-amd64-1.10.13-7a0c19f8.tar.gz
tar -xvf geth-linux-amd64-1.10.13-7a0c19f8.tar.gz
sudo mkdir -p /usr/local/geth/1.10.13/bin
sudo mv geth-linux-amd64-1.10.13-7a0c19f8/geth /usr/local/geth/1.10.13/bin/geth
sudo ln -s /usr/local/geth/1.10.13 /usr/local/geth/current

Setup the environment for geth on /etc/profile.d/geth.sh:

export PATH=$PATH:/usr/local/geth/current/bin

Then source the file while you are still in your session:

source /etc/profile.d/geth.sh

You should be able to verify that geth is installed by running:

geth version
Geth
Version: 1.10.13-stable
Git Commit: eae3b1946a276ac099e0018fc792d9e8c3bfda6d
Git Commit Date: 20210929
Architecture: amd64
Go Version: go1.17
Operating System: linux
GOPATH=/home/ubuntu/go
GOROOT=/usr/local/go

Setup Geth

Create the data directory for geth and change the ownership of the directory to our user:

sudo mkdir -p /blockchain/ethereum/data
sudo chown -R ubuntu:ubuntu /blockchain/ethereum

Run geth in the foreground to test:

geth --ropsten \
--datadir /blockchain/ethereum/data --datadir.minfreedisk 1024 \
--cache 128 --syncmode "light" \
--http --http.addr 0.0.0.0 --http.port 8545 \
--metrics --metrics.addr 0.0.0.0 --metrics.port 6060

If everything goes okay, you can stop the process, and remove the ropsten testnet blockchain and state databases:

geth --ropsten removedb

Create the systemd unit file in /etc/systemd/system/geth.service:

[Unit]
Description=Geth Node
After=network.target auditd.service
Wants=network.target
[Service]
WorkingDirectory=/home/ubuntu
ExecStart=/usr/local/geth/current/bin/geth \
--ropsten \
--datadir /blockchain/ethereum/data \
--datadir.minfreedisk 1024 \
--cache 128 \
--syncmode "light" \
--http --http.addr 0.0.0.0 --http.port 8545 \
--http.api "admin,db,debug,eth,miner,net,personal,txpool,web3" \
--http.corsdomain "*" \
--metrics --metrics.addr 0.0.0.0 --metrics.port 6060 \
--whitelist 10920274=0xfd652086d220d506ae5b7cb80fde97d2f3f7028d346cc7d9d384a83d3d638532
User=ubuntu
Group=ubuntu
Restart=on-failure
RestartSec=120s
KillMode=process
KillSignal=SIGINT
TimeoutStopSec=600
[Install]
WantedBy=multi-user.target
Alias=geth.service

The values such as --whitelist can be retrieved from this issue or this post and extracted from the post:

“due to the London upgrade you’ll probably end up on the chain that isn’t tracked by Etherscan and Metamask. To ensure you only retrieve blocks from peers on that chain, include the following string in your geth start command”

Since we created a new systemd unit file, reload the systemd daemon:

sudo systemctl daemon-reload

Enable and start geth:

sudo systemctl enable geth
sudo systemctl restart geth

You can tail the logs to ensure everything runs as it should:

sudo journalctl -fu geth

API

Following the JSON-RPC documentation, create your account:

curl -H "Content-Type: application/json" -XPOST http://localhost:8545/ -d '{"jsonrpc":"2.0","method":"personal_newAccount","params":["password"],"id":1}'

The response should provide your ropsten testnet address:

{
"jsonrpc":"2.0",
"id":1,
"result":"0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8"
}

We can list all our ethereum addresses by calling the eth_accounts method:

curl -H "Content-Type: application/json" -XPOST http://localhost:8545/ -d '{"jsonrpc":"2.0","method":"eth_accounts","params":[],"id":1}'

We can then check our balance with eth_getbalance, where we pass the ethereum address which is in hex format, followed by the block number, but we will use “latest”:

curl -H "Content-Type: application/json" -XPOST http://localhost:8545/ -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8", "latest"],"id":1}'

You can use the following faucets to send testnet funds to your account:

After sending funds to your account, we can check our balance again:

curl -H "Content-Type: application/json" -XPOST http://localhost:8545/ -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8", "latest"],"id":1}'

And our balances should reflect in our account:

{"jsonrpc":"2.0","id":1,"result":"0x429d069189e0000"}

Hexadecimal and Wei

As you can notice the value of our balance for our ethereum address is in hexadecimal format, we can convert it to decimal format:

echo $((0x429d069189e0000))
300000000000000000

We can use python to convert to decimal using the int() function, by passing the hexadecimal value and pass its base to convert it into an integer, the base for hexadecimal is 16:

>>> print(int('0x429d069189e0000', 16))
300000000000000000

The decimal value that was returned is the value in Wei, and the value of 1 ETH equals to 1,000,000,000,000,000,000 Wei.

Using gwei.io the conversions from 1 ETH are:

Wei: 1000000000000000000
Kwei: 1000000000000000
Mwei: 1000000000000
Gwei: 1000000000
Twei: 1000000
Pwei: 1000
ETH: 1

So now we can convert our balance from wei to ethereum:

  • your_balance_in_wei / unit_value_of_wei
  • 300000000000000000 / 1000000000000000000
python3 -c "print(300000000000000000 / 1000000000000000000)"
0.3

We can use this converter to make sure my math is correct

To get the current gas price in wei:

curl -H "Content-Type: application/json" -XPOST http://localhost:8545/ -d '{"jsonrpc":"2.0","method":"eth_gasPrice","params":[],"id":1}'{"jsonrpc":"2.0","id":1,"result":"0x73a20d04"}

CLI — Accounts

Create a password in /tmp/pass then:

geth --datadir /blockchain/ethereum/data --keystore /blockchain/ethereum/data/keystore account new --password /tmp/.passYour new key was generatedPublic address of the key:   0x5814D945EC909eb1307be4F133AaAB3dEF3572f0
Path of the secret key file: /blockchain/ethereum/data/keystore/UTC--2021-10-06T15-43-23.679655564Z--5814d945ec909eb1307be4f133aaab3def3572f0
- You can share your public address with anyone. Others need it to interact with you.
- You must NEVER share the secret key with anyone! The key controls access to your funds!
- You must BACKUP your key file! Without the key, it's impossible to access account funds!
- You must REMEMBER your password! Without the password, it's impossible to decrypt the key!

Then when you attach your console session, you will be able to see the address that we created:

geth attach /blockchain/ethereum/data/geth.ipc
> eth.accounts[0]
"0x5814d945ec909eb1307be4f133aaab3def3572f0"

CLI — Attach

Run the geth console:

geth attach /blockchain/ethereum/data/geth.ipc
Welcome to the Geth JavaScript console!
instance: Geth/v1.10.13-stable-eae3b194/linux-amd64/go1.17
at block: 11173667 (Wed Oct 06 2021 08:00:44 GMT+0200 (SAST))
datadir: /blockchain/ethereum/data
modules: admin:1.0 debug:1.0 eth:1.0 ethash:1.0 les:1.0 net:1.0 personal:1.0 rpc:1.0 txpool:1.0 vflux:1.0 web3:1.0
To exit, press ctrl-d or type exit
>

We can run net to show us the peercounts:

> net
{
listening: true,
peerCount: 1,
version: "3",
getListening: function(callback),
getPeerCount: function(callback),
getVersion: function(callback)
}

Or if we just want to access the peerCount value:

> net.peerCount
1

To view the peers thats connected:

> admin.peers
[{
caps: ["eth/66", "les/2", "les/3", "les/4", "snap/1"],
enode: "enode://3b76ec5359e59048721de8b6ff97a064ea280233d37433222ce7efcdac700c987326734983c9b65f8f1914c40e1efd6b43999912a3bca208fcbb540a678db110@93.75.22.22:30308",
enr: "enr:-KO4QD2mp_FKB4ZDpfOAD_ziVnMXo1Mcd-FQl9Abj__EJKr9As6UE0frpdaiOnWjqzuGLGaabaAkG7e2CvfY8LulI9ENg2V0aMfGhHEZtrOAgmlkgnY0gmlwhF1LFhaDbGVzwQGJc2VjcDI1NmsxoQI7duxTWeWQSHId6Lb_l6Bk6igCM9N0MyIs5-_NrHAMmIRzbmFwwIN0Y3CCdmSDdWRwgnZk",
id: "a95433e1bcbcc64f5d1ad8bd2535557d1f5ed2191a760f704d42a925656bb8de",
name: "Geth/v1.10.9-stable-eae3b194/linux-amd64/go1.17",
network: {
inbound: false,
localAddress: "192.168.0.120:55166",
remoteAddress: "93.75.22.22:30308",
static: false,
trusted: false
},
protocols: {
les: {
difficulty: 35015228630523840,
head: "1aa1db0e6810f504f1542e8c3c49cecf17b0c3246b41f45bede42723d22b7c0c",
version: 4
}
}
}]

Check if the node is syncing:

> eth.syncing
{
currentBlock: 11176044,
highestBlock: 11176158,
knownStates: 40043719,
pulledStates: 39904521,
startingBlock: 0
}

We can view our accounts:

> eth.accounts
["0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8"]

And get the balance:

> eth.getBalance(eth.accounts[0])
300000000000000000

CLI — SendTransaction

The account that will be receiving the funds (host-a):

geth attach /blockchain/ethereum/data/geth.ipc
> eth.accounts[0]
"0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8"

It’s current balance:

> eth.getBalance(eth.accounts[0])
20485608293038927543

On the account that we will be sending from (host-b):

geth attach /blockchain/ethereum/data/geth.ipc
> eth.accounts[0]
"0xd490fb53c0e7d3c80153112a4bd135e2cf897282"

It’s current balance:

eth.getBalance(eth.accounts[0])
2001712477998186788

When we attempt to send 1ETH to the recipient address:

eth.sendTransaction({from: "0xd490fb53c0e7d3c80153112a4bd135e2cf897282", to: "0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8", value: "1000000000000000000"})
Error: authentication needed: password or unlock
at web3.js:6357:37(47)
at web3.js:5091:62(37)
at <eval>:1:20(10)

You will notice that we need to unlock our account first:

web3.personal.unlockAccount(web3.personal.listAccounts[0], null, 60)
Unlock account 0xd490fb53c0e7d3c80153112a4bd135e2cf897282
Passphrase:
true

Now we can send the transaction:

eth.sendTransaction({from: "0xd490fb53c0e7d3c80153112a4bd135e2cf897282", to: "0x2b1718cdf7dbcc381267ccf43d320c6e194d6aa8", value: "1000000000000000000"})
"0x4bffabf28b71e6f83a48f0accb850b232dc3f482e30d942be3a2eb53d639d4bd"

And the transaction id can be looked up on the ropsten blockexplorer:

And after the confirmations has been confirmed, we can see in our receiving account, we received the funds:

> eth.getBalance(eth.accounts[0])
21485608293038927543

Web3

Run a python environment:

docker run -it python:3.8.5-slim bash

Install dependencies:

apt update
apt install python3-dev gcc -y
pip install web3[tester]

The examples I will be following was extracted from the documentation:

Instantiate a client and connect to your geth node, [this documentation] provides different methods of connecting, but I will be using the HTTPProvider to connect over the network:

>>> from web3 import Web3
>>> w3 = Web3(Web3.HTTPProvider('http://192.168.0.120:8545'))
>>> w3.isConnected()
True

List the accounts:

>>> w3.eth.accounts
['0x2b1718CdF7dBcc381267CCF43D320C6e194D6aa8']

Get the balance in Wei:

>>> account = w3.eth.accounts[0]
>>> w3.eth.get_balance(account)
300000000000000000

Convert from Wei to ETH:

>>> balance_wei = w3.eth.get_balance(account)
>>> w3.fromWei(balance_wei, 'ether')
Decimal('0.3')

Get the information about the latest block:

>>> w3.eth.get_block('latest')
AttributeDict({'baseFeePerGas': 9, 'difficulty': 2073277081, 'extraData': HexBytes('0x63732e7064782e65647520676574682076312e31302e38'), 'gasLimit': 8000000, 'gasUsed': 3361330, 'hash': HexBytes('0xd06a7a734413bcffa4d56617b7efb9ebd8e684c5fcc7fd4f3ec85b8b809b1a0b'), 'logsBloom': HexBytes('0x00000004080000000001000000000000000000000000000000000000000000860000000000000400000000010000000000000000001000000000000080240000000000000000000000000018000000000000000000040000000000000000000002000000020000000000000000000800000000000000200000000010000000800000000000000002000000020000000040000000000000000001000000000000020800000000000000000000000000000000000000000000000000000000800000004002008000000001000000800000000000000000000000000000000062004010202800004000000000000000000000000040000000000002200000000000'), 'miner': '0xe9e7034AeD5CE7f5b0D281CFE347B8a5c2c53504', 'mixHash': HexBytes('0x42641ef2d13826f9cb070516f81515464af9c5c0a36edaa7c250fec62d18a193'), 'nonce': HexBytes('0x670ce792aed73895'), 'number': 11173874, 'parentHash': HexBytes('0xe26e265b264e5158a46ee213d39150d90b532db061497027f35ad36e98458895'), 'receiptsRoot': HexBytes('0x08c15b7365caa993a3047a3093ae641d5b97c51aff058952ab48a56bdee9240b'), 'sha3Uncles': HexBytes('0x1dcc4de8dec75d7aab85b567b6ccd41ad312451b948a7413f0a142fd40d49347'), 'size': 16130, 'stateRoot': HexBytes('0x9e2d99e11b4c71b93f14a563a87945c0ed89e577eefc860a7909bd6f3b8e669f'), 'timestamp': 1633502988, 'totalDifficulty': 35015626783987398, 'transactions': [HexBytes('0x9013555031ca4510e619968814b75ff428c595488c46a387a6b57774313f4686'), HexBytes('0x899f3dfa8cc0ce7eac397500a014dd624d50c0024e112fa3989403da5669b838'), HexBytes('0xf0c08c7e6849be5d23e0c603b405012a1baa4252884f8efac3244d3ed77b8622'), HexBytes('0xb6e03e10e0d6ced0a791f3a9474d760d7248301dc489c5b191aa82b1ef23e677'), HexBytes('0xb424a4da501df145346027c9c839ae9bf9a25f3672bf13fe097c39f46eda5028'), HexBytes('0xcb74ac5580485542ca532f5dc46798b84cb26d34ebc127871d6e2ffead6c32c7'), HexBytes('0xb61cf0eb92798885e4a6309d228e8a31e892e4353810593ba14a2737c1fcd53a'), HexBytes('0x20b27640c1b674be98d3051fac5dcf5ae50d5b7e957defc2336f07b99053fb2c'), HexBytes('0x2929a7384e5b47c4e414142623911a2deca95996e761bc10ccedf607342156af'), HexBytes('0x698af438f73bf384b7c35d4448c0e098d7744b4ce58327dc258a3d5706421c7e')], 'transactionsRoot': HexBytes('0x33cca53eabc2aed8cb0c8a5a7b771b9f14fd2e2aa2561195250411f0714ec768'), 'uncles': []})

Mining

Note: Light clients do not support mining

From another node, I’m running the fast sync mode on ropsten:

--syncmode "fast"

To see your hashrate:

> eth.hashrate
43949

Fore more information on mining, see:

Delete Data

If we look at a fully synced ropsten “fast” node:

du -h /blockchain/ethereum/
4.0K /blockchain/ethereum/data/keystore
856K /blockchain/ethereum/data/geth/triecache
58G /blockchain/ethereum/data/geth/chaindata/ancient
69G /blockchain/ethereum/data/geth/chaindata
2.2M /blockchain/ethereum/data/geth/nodes
188M /blockchain/ethereum/data/geth/ethash
69G /blockchain/ethereum/data/geth
69G /blockchain/ethereum/data
69G /blockchain/ethereum/

Remove the data with removedb:

geth --datadir /blockchain/ethereum/data removedbINFO [10-06|20:01:52.061] Maximum peer count                       ETH=50 LES=0 total=50
INFO [10-06|20:01:52.061] Smartcard socket not found, disabling err="stat /run/pcscd/pcscd.comm: no such file or directory"
INFO [10-06|20:01:52.062] Set global gas cap cap=50,000,000
Remove full node state database (/blockchain/ethereum/data/geth/chaindata)? [y/n] y
Remove full node state database (/blockchain/ethereum/data/geth/chaindata)? [y/n] y
INFO [10-06|20:01:57.141] Database successfully deleted path=/blockchain/ethereum/data/geth/chaindata elapsed=2.482s
Remove full node ancient database (/blockchain/ethereum/data/geth/chaindata/ancient)? [y/n] y
Remove full node ancient database (/blockchain/ethereum/data/geth/chaindata/ancient)? [y/n] y
INFO [10-06|20:02:05.645] Database successfully deleted path=/blockchain/ethereum/data/geth/chaindata/ancient elapsed=589.737ms
INFO [10-06|20:02:05.645] Light node database missing path=/blockchain/ethereum/data/geth/lightchaindata

Now when we list the data directory, we can see the data was removed:

du -h /blockchain/ethereum/
8.0K /blockchain/ethereum/data/keystore
868K /blockchain/ethereum/data/geth/triecache
4.0K /blockchain/ethereum/data/geth/chaindata/ancient
180K /blockchain/ethereum/data/geth/chaindata
1.4M /blockchain/ethereum/data/geth/nodes
188M /blockchain/ethereum/data/geth/ethash
190M /blockchain/ethereum/data/geth
190M /blockchain/ethereum/data
190M /blockchain/ethereum/

Resources

Thank You

Thanks for reading, if you like my content, check out my or follow me at @ruanbekker on Twitter.

Originally published at https://blog.ruanbekker.com on December 5, 2021.

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DevOps Engineer and Open Source Enthusiast

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Ruan Bekker

Ruan Bekker

DevOps Engineer and Open Source Enthusiast

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