Bitcoin

Chapter 53: Bitcoin Nodes

Overview

Bitcoin is the first and largest cryptocurrency. Running a Bitcoin node supports network decentralization and gives you private, trustless access to the chain. Bitcoin Core (BTC Core) is the reference implementation.

53.1 Bitcoin Basics

Feature	Value
Consensus	Proof of Work (SHA-256)
Block Time	~10 minutes
Block Size	1-4 MB (SegWit/weight units)
Finality	Probabilistic — confirmations build confidence over time
Token	BTC

53.2 Node Types

Type	Description
Full Node	Downloads and validates the entire chain (~600+ GB, growing)
Pruned Node	Runs the same validation but keeps only the last ~550 MiB-5 GB of blocks
Lightweight (SPV)	Headers-only + Merkle proofs, trusts full nodes for data

How Initial Sync Works: Headers-First + AssumeValid

Bitcoin Core does headers-first sync:

┌─────────────────────────────────────────────────────────────┐
│                INITIAL BLOCK DOWNLOAD (IBD)                 │
├─────────────────────────────────────────────────────────────┤
│                                                              │
│  1. Download ALL block headers first (cheapest part)        │
│     → compute the header chain, detect forks                 │
│                                                              │
│  2. Walk an "assumed valid" checkpoint (assumevalid=...):   │
│     at that height, transactions are NOT fully re-validated │
│     (they were already considered valid); blocks after it   │
│     are fully validated                                      │
│                                                              │
│  3. Swap to normal validation as the tip approaches          │
│                                                              │
└─────────────────────────────────────────────────────────────┘

-assumevalid (a hash in the release binary) trades a tiny amount of historical re-validation for massively faster IBD — the node still validates the UTXO set, policy, and every block after the checkpoint.

53.3 Running Bitcoin Core

Install

# Install dependencies (bsdmainutils is no longer needed on modern Ubuntu —
# it was removed from the dependency list in recent Bitcoin Core releases)
sudo apt-get install build-essential libtool autotools-dev \
  automake pkg-config python3 libevent-dev libboost-dev

# Clone and build
git clone https://github.com/bitcoin/bitcoin.git
cd bitcoin
./autogen.sh
./configure --with-gui=no
make -j$(nproc)
sudo make install

Configuration

mkdir -p ~/.bitcoin
nano ~/.bitcoin/bitcoin.conf

# bitcoin.conf
server=1
rpcuser=user
rpcpassword=change-this-long-random-string
rpcbind=127.0.0.1
rpcport=8332
prune=550            # MiB — minimum is 550; on a pruned node no txindex
# txindex=1          # enable FULL tx index (required for getrawtransaction by txid
#                    # on historical txs; incompatible with pruning)
# blocksonly=1       # only announce blocks, never relay mempool txs
daemon=1

⚠️ Use a long random rpcpassword — the RPC server is unauthenticated-by-default and a weak password invites theft (a classic Bitcoin node attack).

53.4 Commands

Start Node

# Start daemon (reads ~/.bitcoin/bitcoin.conf; --daemon forks to background)
bitcoind

# Or explicit pruning
bitcoind -prune=550

RPC Commands

# Sync/chain status (the go-to health check)
bitcoin-cli getblockchaininfo
# → { "chain": "main", "blocks": N, "headers": M, "verificationprogress": 0.9999, ... }

# Get block count
bitcoin-cli getblockcount

# Network + peers
bitcoin-cli getnetworkinfo
bitcoin-cli getpeerinfo | jq 'length'

# Mempool size
bitcoin-cli getmempoolinfo

# Balance (if watching a wallet)
bitcoin-cli getbalance

# Send transaction
bitcoin-cli sendtoaddress "address" amount

Reading the health output: verificationprogress → 1.0 means fully synced; blocks vs headers gap means the node is still downloading headers/blocks.

Ports

Port	Purpose
8333 (TCP)	P2P — mainnet (public)
8332 (TCP)	JSON-RPC — mainnet (localhost only!)
18333 / 18332	Testnet P2P / RPC
18444 / 18443	Regtest P2P / RPC

Pinning Peers

# bitcoin.conf — deterministic connectivity:
addnode=1.2.3.4:8333      # keep a connection to this peer, both directions
# connect=1.2.3.4:8333    # ONLY connect to these (isolated/private setups)

53.5 Operational Notes

IBD time: on modern hardware + assumevalid + fast NVMe, mainnet IBD is ~1-2 days (was weeks before headers-first + assumevalid).
Disk: prune to save space (-prune=550 is the floor); full archive grows faster than storage costs (Chapter 30/pruning principles apply).
Privacy: run -onlynet=onion + Tor if you want to avoid revealing your IP; trim -rpcbind to loopback.
Monitoring: Bitcoin Core metrics: getblockchaininfo (tip/progress), getmempoolinfo, getpeerinfo; alert when verificationprogress < 1 for too long, peers drop to 0, or disk fills — same alerting model as Chapter 38.

Summary

Bitcoin uses PoW; finality is probabilistic (confirmations)
Headers-first IBD + assumevalid make initial sync practical
Full node ~600 GB+; pruned node validates identically with far less disk
Secure the RPC (rpcpassword, loopback-only), keep P2P 8333 open
Health = getblockchaininfo (progress + tip) + getpeerinfo

End of Guide

This completes the Blockchain Node Guide. Review the chapters and practice the hands-on tasks before your interview!

Last Updated: 2026-09-28