Bitcoin

Let’s get your Bitcoin full node operational.

Bitcoin Core
Installation
1. Prepare data directory
2. Configuration
  1. Transaction indexing (optional)
Running bitcoind
1. Autostart on boot
2. Verification of bitcoind operations
Reduce ‘dbcache’ after full sync
Bitcoin Core upgrade

Bitcoin Core

The base of a sovereign Bitcoin node is a fully validating Bitcoin client. We are using Bitcoin Core, the reference implementation, but not the only option available. This application will download the whole blockchain from other peers and validate every single transaction that ever happened. After validation, the client can check all future transactions whether they are valid or not.

The validated blocks are also the base layer for other applications, like Electrs (to use with hardware wallets) or LND (the Lightning Network client).

Be already warned that the downloading and validation of all transactions since 2009, more than 600’000 blocks with a size of over 300 GB, is not an easy task. It’s great that the Raspberry Pi 4 can do it, even if it takes a few days, as this was simply not possible with the Raspberry Pi 3.

Installation

🚨 Familiarize yourself with signature verification An important part of the trust-minimization setup is to verify signatures of software you install. Take your time to read through a detailed guide from Luke-Jr.

We download the latest Bitcoin Core binaries (the application) and compare the file with the signed checksum. This is a precaution to make sure that this is an official release and not a malicious version trying to steal our money.

Get the latest download links at bitcoincore.org/en/download (ARM Linux 64 bit), they change with each update. Currently the latest one is 22.0, so the script has to be changed to the latest version available. Then run the following commands (with adjusted filenames) and check the output where indicated:

# Download Bitcoin Core binary
$ wget https://bitcoincore.org/bin/bitcoin-core-22.0/bitcoin-22.0-aarch64-linux-gnu.tar.gz

# Download the list of cryptographic checksums (SHA256 binary hashes):
$ wget https://bitcoincore.org/bin/bitcoin-core-22.0/SHA256SUMS

# Download the signatures attesting to validity of the checksums (SHA256 hash signatures):
$ wget https://bitcoincore.org/bin/bitcoin-core-22.0/SHA256SUMS.asc

# Download Bitcoin Core developer's keys list
$ wget https://raw.githubusercontent.com/bitcoin/bitcoin/master/contrib/builder-keys/keys.txt

# Fetch keys of builders and active developers, feed the list of fingerprints of the primary keys into gpg:
$ while read fingerprint keyholder_name; do gpg --keyserver hkps://keys.openpgp.org --recv-keys ${fingerprint}; done < ./keys.txt

# Check for keys update
$ gpg --keyserver hkp://keyserver.ubuntu.com --refresh-keys
$ gpg --refresh-keys

# Verify that the checksum of the release file is listed in the checksums file:
# (ignore the "lines are improperly formatted" warning)
$ sha256sum --ignore-missing --check SHA256SUMS
> bitcoin-22.0-aarch64-linux-gnu.tar.gz: OK
# Ensure the output lists "OK" after the name of the release file you downloaded.

$ gpg --verify SHA256SUMS.asc
# The command above will output a series of signature checks for each of the public keys that signed the checksums.
# Check at at least some signatures show the following text:
# A line that starts with: gpg: Good signature
# A complete line saying: Primary key fingerprint: E777 299F C265 DD04 7930  70EB 944D 35F9 AC3D B76A
# The output from the verify command may contain warnings that the "key is not certified with a trusted signature."

Extract the Bitcoin Core binaries, install them and check the version.

$ tar -xvf bitcoin-22.0-aarch64-linux-gnu.tar.gz
$ sudo install -m 0755 -o root -g root -t /usr/local/bin bitcoin-22.0/bin/*
$ bitcoind --version
> Bitcoin Core version v22.0.0

Prepare data directory

We use the Bitcoin daemon, called bitcoind, that runs in the background without user interface. It stores all data in a the directory /home/bitcoin/.bitcoin. Instead of creating a real directory, we create a link that points to a directory on the external hard disk.

Change to user “bitcoin” and add a symbolic link that points to the external drive.
```
$ sudo su - bitcoin
$ ln -s /mnt/ext/bitcoin /home/bitcoin/.bitcoin
```
Navigate to the home directory and check the symbolic link (the target must not be red). The content of this directory will actually be on the external drive.
```
$ ls -la
```

Configuration

Now, the configuration file for bitcoind needs to be created. Still as user “bitcoin”, open it with Nano and paste the configuration below. Save and exit.
🚨 Change the rpcpassword to your secure password [B].

$ nano /mnt/ext/bitcoin/bitcoin.conf

# RaspiNail: bitcoind configuration
# /mnt/ext/bitcoin/bitcoin.conf

# Bitcoin daemon
server=1
txindex=1

# Network
listen=1
listenonion=1
proxy=127.0.0.1:9050
bind=127.0.0.1

# Connections
rpcuser=raspinail
rpcpassword=PASSWORD_[B]
zmqpubrawblock=tcp://127.0.0.1:28332
zmqpubrawtx=tcp://127.0.0.1:28333

# Raspberry Pi optimizations
maxconnections=40
maxuploadtarget=5000

# Allows Electrs to bypass the "maxuploadtarget=" for local P2P used for Electrs indexing.
whitelist=download@127.0.0.1

# Initial block download optimizations
dbcache=2000
blocksonly=1

🔍 more: configuration options in Bitcoin Wiki

Transaction indexing (optional)

By default the above configuration enables transaction indexing. This allows other applications to query Bitcoin Core about any transaction. One example that needs this feature is the BTC RPC Explorer, your personal blockchain explorer.

If you know that you don’t need this feature, you can delete the line txindex=1 in the configuration above. This results in a faster initial blockchain verification, and saves about 20 GB of storage. If in doubt, just leave it as-is, otherwise you might need to enable it later and reindex the whole blockchain again.

Running bitcoind

Still logged in as user “bitcoin”, let’s start “bitcoind” manually. Monitor the log file a few minutes to see if it works fine (it may stop at “dnsseed thread exit”, that’s ok). Stop “bitcoind” with Ctrl-C.

$ bitcoind

Note: the following screencast skips longer waiting times, the initial start is longer in real life.

Autostart on boot

The system needs to run the bitcoin daemon automatically in the background, even when nobody is logged in. We use “systemd“, a daemon that controls the startup process using configuration files.

Exit the “bitcoin” user session back to user “admin”
```
$ exit
```

Create the configuration file in the Nano text editor and copy the following paragraph. Save and exit.

$ sudo nano /etc/systemd/system/bitcoind.service

# RaspiNail: systemd unit for bitcoind
# /etc/systemd/system/bitcoind.service

[Unit]
Description=Bitcoin daemon
After=network.target

[Service]

# Service execution
###################

ExecStart=/usr/local/bin/bitcoind -daemon \
                                  -pid=/run/bitcoind/bitcoind.pid \
                                  -conf=/mnt/ext/bitcoin/bitcoin.conf \
                                  -datadir=/mnt/ext/bitcoin


# Process management
####################

Type=forking
PIDFile=/run/bitcoind/bitcoind.pid
Restart=on-failure
TimeoutSec=300
RestartSec=30


# Directory creation and permissions
####################################

# Run as bitcoin:bitcoin
User=bitcoin
Group=bitcoin

# /run/bitcoind
RuntimeDirectory=bitcoind
RuntimeDirectoryMode=0710


# Hardening measures
####################

# Provide a private /tmp and /var/tmp.
PrivateTmp=true

# Mount /usr, /boot/ and /etc read-only for the process.
ProtectSystem=full

# Deny access to /home, /root and /run/user
ProtectHome=true

# Disallow the process and all of its children to gain
# new privileges through execve().
NoNewPrivileges=true

# Use a new /dev namespace only populated with API pseudo devices
# such as /dev/null, /dev/zero and /dev/random.
PrivateDevices=true

# Deny the creation of writable and executable memory mappings.
MemoryDenyWriteExecute=true

[Install]
WantedBy=multi-user.target

Enable the service

$ sudo systemctl enable bitcoind.service

Link the Bitcoin data directory in the user “admin” home. As a member or the group “bitcoin”, admin has read-only access to certain files.
```
$ ln -s /mnt/ext/bitcoin/ /home/admin/.bitcoin
```
Restart the Raspberry Pi
```
$ sudo reboot
```

Verification of bitcoind operations

After rebooting, the bitcoind should start and begin to sync and validate the Bitcoin blockchain.

Wait a bit, reconnect via SSH and login with the user “admin”.
Check the status of the bitcoin daemon that was started by systemd (exit with Ctrl-C)
```
$ systemctl status bitcoind.service
```
See bitcoind in action by monitoring its log file (exit with Ctrl-C)
```
$ sudo tail -f /mnt/ext/bitcoin/debug.log
```
Use the Bitcoin Core client bitcoin-cli to get information about the current blockchain
```
$ bitcoin-cli getblockchaininfo
```
Please note:
- When “bitcoind” is still starting, you may get an error message like “verifying blocks”. That’s normal, just give it a few minutes.
- Among other infos, the “verificationprogress” is shown. Once this value reaches almost 1 (0.999…), the blockchain is up-to-date and fully validated.

🚨 Please let Bitcoin Core sync fully before proceeding.

This can take up to a week when using a Raspberry Pi 4, depending mostly on your external drive (SSD good, HDD bad; USB3 good, USB2 bad).

Reduce ‘dbcache’ after full sync

Once Bitcoin Core is fully synced, we can reduce the size of the database cache. A bigger cache speeds up the initial block download, now we want to reduce memory consumption to allow LND and Electrs to run in parallel. We also now want to enable the node to listen to and relay transactions.

As user “admin”, comment the following lines out (add a # at the beginning) in the Bitcoin settings file. Bitcoin Core will then just use the default of 300 MB instead of 2 GB. Save and exit.
```
$ sudo nano /mnt/ext/bitcoin/bitcoin.conf
```
```
#dbcache=2000
#blocksonly=1
```
Restart Bitcoin Core for the settings to take effect.
```
$ sudo systemctl restart bitcoind
```

Bitcoin Core upgrade

If you want to upgrade to a new release of Bitcoin Core in the future, check out the FAQ section: How to upgrade Bitcoin Core

Next: Lightning »