Cheatsheet

Chapter 57: Quick Reference Cheat Sheet

Overview

This is your quick reference guide for blockchain node operations. Print or bookmark this page for quick access during your interview.

Quick Commands

Geth (Ethereum)

# Install Geth
wget https://gethstore.blob.core.windows.net/builds/geth-linux-amd64-1.13.14.tar.gz
tar -xzf geth-linux-amd64-1.13.14.tar.gz
sudo mv geth /usr/local/bin/

# Start node with snap sync (RECOMMENDED)
geth --syncmode snap --http --http.port 8545

# Start full node
geth --syncmode full --http --http.port 8545

# Start light node
geth --syncmode light --http --http.port 8545

# Start on testnet
geth --sepolia --syncmode snap --http --http.port 8545

JSON-RPC Quick Reference

Essential RPC Calls

# Get latest block number
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_blockNumber","params":[],"id":1}'

# Get block by number
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["latest", true],"id":1}'

# Get account balance
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getBalance","params":["0x...", "latest"],"id":1}'

# Send transaction
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_sendRawTransaction","params":["0x..."],"id":1}'

# Get transaction receipt
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_getTransactionReceipt","params":["0x..."],"id":1}'

# Check sync status
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_syncing","params":[],"id":1}'

# Get peer count
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"net_peerCount","params":[],"id":1}'

# Get chain ID
curl -X POST http://localhost:8545 \
  -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"eth_chainId","params":[],"id":1}'

Important Ports

Service	Port	Description
P2P (TCP/UDP)	30303	Node-to-node communication
HTTP RPC	8545	JSON-RPC over HTTP
WebSocket	8546	WebSocket API
Metrics	6060	Prometheus metrics
pprof	6061	Profiling API

Network Chain IDs

Network	Chain ID	Network ID
Ethereum Mainnet	1	1
Sepolia	11155111	11155111
Goerli	5	5
Holesky	17000	17000

Sync Status Check

// In Geth console
geth attach http://localhost:8545

// Check sync status
eth.syncing
// Returns object when syncing, false when synced

// Get current block
eth.blockNumber

Important Geth Flags

# Sync mode
--syncmode snap      # Default, fastest
--syncmode full      # Full verification
--syncmode light    # Light client

# RPC/HTTP
--http              # Enable HTTP RPC
--http.addr         # Bind address (default: 127.0.0.1)
--http.port         # Port (default: 8545)
--http.api          # Enabled APIs
--http.corsdomain   # CORS allowed domains

# WebSocket
--ws                # Enable WebSocket
--ws.port           # Port (default: 8546)

# Storage
--datadir           # Data directory path
--cache             # Memory cache in MB

# Network
--port              # P2P port (default: 30303)
--maxpeers          # Max peers (default: 50)
--bootnodes         # Bootnodes

# Monitoring
--metrics           # Enable metrics
--metrics.port      # Metrics port (default: 6060)
--pprof             # Enable pprof

Hardware Requirements

Ethereum Full Node

Component	Minimum	Recommended
CPU	4 cores	8+ cores
RAM	8 GB	16-32 GB
Storage	1 TB SSD	2 TB NVMe
Network	25 Mbps	100 Mbps

Ethereum Archive Node

Component	Requirement
Storage	10-12 TB
RAM	32-64 GB

Ethereum 2.0 (Post-Merge)

Running a Validator

You need TWO clients:

Execution Client: Geth, Erigon, Nethermind
Consensus Client: Lighthouse, Prysm, Teku

Communication via Engine API (JWT auth).

Validator Commands

# Lighthouse (consensus)
lighthouse validator \
  --beacon-node http://localhost:5052 \
  --wallet-path /path/to/wallet

# Prysm (consensus)
prysm validator \
  --beacon-rpc-provider localhost:4000

Common Interview Answers

Q: How to make node fully sync?

A: Use --syncmode snap and wait 2-4 hours. Check with eth.syncing - returns false when synced.

Q: What’s the difference between full and light nodes?

A: Full nodes store entire blockchain (~1.2TB); light nodes only headers (~1GB). Full nodes verify everything; light nodes trust full nodes for data.

Q: What is The Merge?

A: Ethereum’s transition from PoW to PoS (September 2022). Now uses dual-client architecture (execution + consensus clients).

Q: What is gas in Ethereum?

A: Unit of computation. Transaction fee = Gas Used × Gas Price. EIP-1559 introduced base fee (burned) + priority fee (to validator).

Q: What does the mempool do?

A: Memory pool - holds pending transactions before they’re included in a block.

Troubleshooting Quick Fixes

Problem	Solution
No peers	Check network, firewall, try different bootnodes
Slow sync	Increase peers, check CPU/disk
Stuck at header	Remove chaindata, restart sync
RPC slow	Add caching, increase cache size
Out of disk	Enable pruning, use snap sync

Filesystem Layout

/data/ethereum/
├── geth/
│   ├── chaindata/      # Blockchain data
│   ├── triecache/      # Trie cache
│   └── nodes/          # Peer information
├── keystore/           # Account keys (if any)
└── history/            # Historical state (if enabled)

Backup Commands

# Backup keystore
cp -r /data/ethereum/keystore /backup/

# Backup wallet (Ledger, etc.)
# Do NOT backup raw private keys - use hardware wallet

# Backup node data
tar -czf eth-node-backup.tar.gz /data/ethereum/

Security Checklist

Quick Links

Ethereum Docs: https://ethereum.org/developers/
Geth Docs: https://geth.ethereum.org/
Etherscan: https://etherscan.io
Ethereum Block Explorer: https://etherscan.io

Last Minute Interview Tips

When asked to set up a node: Start with geth --syncmode snap --http
To check sync: Use eth.syncing - returns false when done
Quick verification: Compare your block number with etherscan.io
Don’t panic: It’s okay to say “Let me check the documentation”
Explain what you’re doing: Talk through your steps

Good Luck! 🍀

You’ve prepared well. Remember:

Stay calm
Think out loud
Use the cheat sheet
Ask clarifying questions if needed

Last Updated: 2026-02-20