Tutorial for bitcoin regtest

generate_blocks.sh

# Script to generate a new block every minute
# Put this script at the root of your unpacked folder
#!/bin/bash

echo "Generating a block every minute. Press [CTRL+C] to stop.."

address=`./bin/bitcoin-cli getnewaddress`

while :
do
        echo "Generate a new block `date '+%d/%m/%Y %H:%M:%S'`"
        ./bin/bitcoin-cli generatetoaddress 1 $address
        sleep 60
done

how_to_regtest.md

How to Bitcoin regtest

Setup

1. Download bitcoin core
2. Unpack it wherever you want.
3. Create a directory named data inside the unpacked folder.
4. Create a directory named .bitcoin inside your home folder: mkdir ~/.bitcoin
5. Copy bitcoin.conf into ~/.bitcoin
6. Copy rpcauth into <unpacked_folder>/share/rpcauth
7. Run <unpacked_folder>/share/rpcauth/rpcauth.py <YOUR_USERNAME>. Keep the output somewhere, you'll need it later.
8. Edit your bitcoin.conf.
9. Uncomment regtest=0 and enable it: regtest=1
10. Uncomment rpcuser=alice and replace the value with your username.
11. Uncomment rpcpassword=... and replace the value with the password you got from rpcauth.
12. Uncomment rpcauth=bob:... and replace the value with the line you got from rpcauth.
13. (Optional) Append datadir=<unpacked_folder>/data to the end of the file, where <unpacked_folder> is the absolute path to your unpacked folder.
14. Run <unpacked_folder>/bin/bitcoind
15. Open another terminal, and run <unpacked_folder>/bin/bitcoin-cli getbalance. It should return 0.

Your first node is set. Now let's setup another one to connect to. We need to use another port and another data dir.

Run: bitcoind -port=18445 -rpcport=8333 -datadir=<unpacked_folder>/data2

Generate a new address

We'll start by generating a new wallet address. We will use it for all our future operations, so keep it somewhere.

bitcoin-cli getnewaddress

Generate some blocks

bitcoin-cli generatetoaddress 50 <youraddress>

# Check the blocks are mined
bitcoin-cli getblockcount # Should return 50

Connect to other nodes

Let's connect to our second node: bitcoin-cli addnode "127.0.0.1:18445" add.
To keep the connection after a restart, add the following to your bitcoin.conf: addnode=127.0.0.1:18445

Check if your nodes are connected: bitcoin-cli getaddednodeinfo.

Now check if the second node is synchronized: bitcoin-cli -rpcport=8333 getblockcount.

Let's mine some blocks and check if everything is synchronized:

bitcoin-cli generatetoaddress 25 "<your_address>"
bitcoin-cli getblockcount # Should return 75
bitcoin-cli -rpcport=8333 getblockcount # Should return 75 

Transfer funds

We got some funds from mining the first blocks. We will transfer them to our wallet on the second node.

address=`bitcoin-cli -rpcport=8333 getnewaddress`
bitcoin-cli sendtoaddress "$1" 10

# Check the funds have been received
bitcoin-cli -rpcport=8333 getwalletinfo

Double spend

As we only have two nodes in the network, it's easy to make a 51% attack. We're going to double spend some bitcoin.

# Get a unspent output with a non-zero output
bitcoin-cli listunspent

# Create a raw transaction and sign it
# Don't forget to set the amount of your vout a little bit lower than the amount of your utxo so your tx has fees
transaction=`bitcoin-cli createrawtransaction '[{"txid":"<TX_ID>","vout":0}]' '{"$address":12.49}'`
bitcoin-cli signrawtransactionwithwallet "$transaction"

Keep the generated hex of the signed transaction. We need to disconnect both nodes and broadcast the transaction from the other node.

# Disconnect nodes
bitcoin-cli disconnectnode "127.0.0.1:18445"
bitcoin-cli -rpcport=8333 disconnectnode "127.0.0.1:18444"

# Broadcast from other node
bitcoin-cli -rpcport=8333 sendrawtransaction "<HEX>"

To make a double spend, we need to create another transaction with the same utxo and broadcast it on the chain where the first one wasn't broadcasted.

# Generate a second address to make it easier to differenciate both transactions
address=`bitcoin-cli -rpcport=8333 getnewaddress`

transaction=`bitcoin-cli createrawtransaction '[{"txid":"<TX_ID>","vout":0}]' '{"$address":12.49}'`
bitcoin-cli signrawtransactionwithwallet "$transaction"
bitcoin-cli sendrawtransaction "<HEX>"

We need to mine some blocks so when we join the two nodes, the longest chain is kept. (In our case, the one with the second transaction).

bitcoin-cli generate 50

# Join
bitcoin-cli addnode "127.0.0.1:18445" add

Check that the first transaction doesn't exist anymore:

bitcoin-cli -rpcport=8333 listtransactions

The last one should have the address we used for the second transaction. The double-spend worked!

Hi I am running two regtest nodes according to the method described in the gist but when I use addnode the first node just adds the second one in the addednode list but doesn't connect. Please suggest a fix.

[
  {
    "addednode": "127.0.0.1:18445",
    "connected": false,
    "addresses": [
    ]
  }
]

Also when I mistakenly ran the second node with regtest=0 , the two nodes were able to connect.

bitcoind logs for the second node show this

[net:error] Unable to bind to 0.0.0.0:18445 on this computer. Bitcoin Core is probably already running.

@110CodingP Are you sure you don't have another program running listening on port 18455? The message shows that the second node could not be started because it failed to bind to 0.0.0.0:18445.

@System-Glitch , I am not sure but on doing ps aux | grep -i 'bitcoin' and ps aux | grep -i 'bitcoind' I can't find any bitcoin processes running...