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Prerequisites

Before setting up captaind, ensure you have:
1

Bitcoin Core node

Running Bitcoin Core v24.0+ with:
  • txindex=1 enabled
  • RPC access configured
  • Fully synced for your target network (mainnet, testnet, or signet)
2

PostgreSQL database

PostgreSQL v13+ installed and running
  • Create a dedicated database for captaind
  • Note the connection credentials
3

System resources

  • 4GB+ RAM available
  • 50GB+ free disk space (SSD recommended)
  • Stable network connection

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Installation

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From Pre-built Binaries

Download the latest release from the bark repository: 
# Download for your platform
wget https://gitlab.com/ark-bitcoin/bark/-/releases/download/v0.1.0-beta.7/bark-linux-x86_64.tar.gz

# Extract
tar -xzf bark-linux-x86_64.tar.gz

# Move to PATH
sudo mv captaind /usr/local/bin/

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Building from Source

Requires Rust 1.74 or later. Install Rust from rustup.rs.
# Clone the repository
git clone https://gitlab.com/ark-bitcoin/bark.git
cd bark

# Build captaind
cargo build --release --bin captaind

# Binary will be at target/release/captaind
sudo cp target/release/captaind /usr/local/bin/

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Initial Configuration

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1. Create Configuration File

Copy the default configuration template: 
# Create config directory
mkdir -p ~/.config/captaind

# Copy default config (from source directory)
cp server/captaind.default.toml ~/.config/captaind/captaind.toml

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2. Configure Essential Settings

Edit ~/.config/captaind/captaind.toml with your settings:
captaind.toml
# Data directory for wallet and state
data_dir = "./bark-server"

# Bitcoin network: "mainnet", "testnet", "signet", or "regtest"
network = "signet"

# VTXO lifetime in blocks (default: 30 days)
vtxo_lifetime = 4320

# Round interval (how often to run payment rounds)
round_interval = "10s"

# PostgreSQL connection
[postgres]
host = "localhost"
port = 5432
name = "bark-server-db"
user = "postgres"
password = "your_password_here"
max_connections = 10

# Bitcoin Core RPC connection
[bitcoind]
url = "http://127.0.0.1:38332"  # Signet port

# Option 1: Use cookie file authentication
cookie = "/home/bitcoin/.bitcoin/signet/.cookie"

# Option 2: Use username/password (comment out cookie if using this)
# rpc_user = "bitcoinrpc"
# rpc_pass = "your_password_here"
Authentication Required: You must configure exactly one authentication method for Bitcoin Core - either cookie OR (rpc_user + rpc_pass), not both.

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3. Create Database

Create the PostgreSQL database: 
CREATE DATABASE "bark-server-db";
Or using psql: 
psql -U postgres -c 'CREATE DATABASE "bark-server-db";'

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4. Initialize Server

Run the create command to initialize captaind: 
captaind -C ~/.config/captaind/captaind.toml create
This will:
  • Generate a new BIP39 mnemonic seed phrase
  • Save the mnemonic to <data_dir>/mnemonic.txt
  • Initialize the database schema
  • Create wallet state
Backup Your Mnemonic: The seed phrase in mnemonic.txt controls all server funds. Back it up securely and never share it.

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5. Retrieve Your Mnemonic (if needed)

To view your server’s mnemonic later: 
captaind -C ~/.config/captaind/captaind.toml get-mnemonic

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Starting the Server

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Run in Foreground

For testing or development: 
captaind -C ~/.config/captaind/captaind.toml start
The server will:
  • Connect to Bitcoin Core and PostgreSQL
  • Start the RPC server on port 3535 (default)
  • Begin running payment rounds
  • Display logs to stdout

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Run as a Service (Production)

Create a systemd service file:
/etc/systemd/system/captaind.service
[Unit]
Description=Bark Ark Server (captaind)
After=network.target postgresql.service bitcoind.service
Requires=postgresql.service
Wants=bitcoind.service

[Service]
Type=simple
User=bark
Group=bark
ExecStart=/usr/local/bin/captaind -C /etc/captaind/captaind.toml start
Restart=on-failure
RestartSec=10

# Security hardening
NoNewPrivileges=true
PrivateTmp=true
ProtectSystem=full
ProtectHome=true

[Install]
WantedBy=multi-user.target
Enable and start the service: 
# Reload systemd
sudo systemctl daemon-reload

# Enable auto-start on boot
sudo systemctl enable captaind

# Start the service
sudo systemctl start captaind

# Check status
sudo systemctl status captaind

# View logs
journalctl -u captaind -f

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Verification

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Check Server Status

Use the admin RPC to verify the server is running: 
captaind -C ~/.config/captaind/captaind.toml rpc wallet
Expected output: 
{
  "rounds": {
    "address": "tb1q...",
    "total_balance": 0,
    "trusted_pending_balance": 0,
    "untrusted_pending_balance": 0,
    "confirmed_balance": 0,
    "confirmed_utxos": 0,
    "unconfirmed_utxos": 0
  }
}

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Fund the Server Wallet

Get a receiving address: 
captaind -C ~/.config/captaind/captaind.toml rpc wallet | jq -r '.rounds.address'
Send Bitcoin to this address to fund the server’s round wallet. This Bitcoin is used to:
  • Create round funding transactions
  • Pay transaction fees
  • Provide change outputs in rounds

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Connect a Client

Test connectivity with a bark client: 
# If running bark CLI wallet
bark --server 127.0.0.1:3535 info

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Next Steps

Configuration

Customize server settings and fees

Lightning Setup

Configure CLN for Lightning payments

Monitoring

Set up observability and alerts

Rounds Management

Understand and manage payment rounds

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Common Issues

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”Error loading config file”

  • Verify the config file path is correct
  • Check TOML syntax for errors
  • Ensure all required fields are present

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”Failed to connect to bitcoind”

  • Verify Bitcoin Core is running and synced
  • Check the RPC URL and port match your bitcoin.conf
  • Verify authentication credentials (cookie or user/pass)
  • Ensure txindex=1 is enabled in bitcoin.conf

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”Failed to connect to db”

  • Verify PostgreSQL is running
  • Check database name, user, and password
  • Ensure the database was created
  • Verify network connectivity to PostgreSQL

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”Mnemonic file already exists”

  • Server was already initialized
  • Use start command instead of create
  • To start fresh, delete the data directory (will lose funds!)

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