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<!DOCTYPE html>
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<title>Bitcoin Core: The Reference Implementation</title>
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<div class="sect1 data-line-2">
<h2 id="ch03_bitcoin_client">Bitcoin Core: The Reference Implementation</h2>
<div class="sectionbody">
<div class="paragraph data-line-4">
<p>Bitcoin is an <em>open source</em> project and the source code is available under an open (MIT) license, free to download and use for any purpose. Open source means more than simply free to use. It also means that bitcoin is developed by an open community of volunteers. At first, that community consisted of only Satoshi Nakamoto. By 2016, bitcoin’s source code had more than 400 contributors with about a dozen developers working on the code almost full-time and several dozen more on a part-time basis. Anyone can contribute to the code—including you!</p>
</div>
<div class="paragraph data-line-7">
<p>When bitcoin was created by Satoshi Nakamoto, the software was actually completed before the whitepaper reproduced in <a href="#satoshi_whitepaper">[satoshi_whitepaper]</a> was written. Satoshi wanted to make sure it worked before writing about it. That first implementation, then simply known as "Bitcoin" or "Satoshi client," has been heavily modified and improved. It has evolved into what is known as <em>Bitcoin Core</em>, to differentiate it from other compatible implementations. Bitcoin Core is the <em>reference implementation</em> of the bitcoin system, meaning that it is the authoritative reference on how each part of the technology should be implemented. Bitcoin Core implements all aspects of bitcoin, including wallets, a transaction and block validation engine, and a full network node in the peer-to-peer bitcoin network.</p>
</div>
<div class="admonitionblock warning data-line-10">
<table>
<tr>
<td class="icon">
<div class="title">Warning</div>
</td>
<td class="content">
<div class="paragraph data-line-11">
<p>Even though Bitcoin Core includes a reference implementation of a wallet, this is not intended to be used as a production wallet for users or for applications. Application developers are advised to build wallets using modern standards such as BIP-39 and BIP-32 (see <a href="#mnemonic_code_words">[mnemonic_code_words]</a> and <a href="#hd_wallets">[hd_wallets]</a>). BIP stands for <em>Bitcoin Improvement Proposal</em>.</p>
</div>
</td>
</tr>
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<div class="paragraph data-line-14">
<p><a href="#bitcoin_core_architecture">Bitcoin Core architecture (Source: Eric Lombrozo)</a> shows the architecture of Bitcoin Core.</p>
</div>
<div id="bitcoin_core_architecture" class="imageblock data-line-18">
<div class="content">
<img src="images/mbc2_0301.png" alt="Bitcoin Core Architecture">
</div>
<div class="title">Figure 1. Bitcoin Core architecture (Source: Eric Lombrozo)</div>
</div>
<div class="sect2 data-line-21">
<h3 id="_bitcoin_development_environment">Bitcoin Development Environment</h3>
<div class="paragraph data-line-23">
<p>If you’re a developer, you will want to set up a development environment with all the tools, libraries, and support software for writing bitcoin applications. In this highly technical chapter, we’ll walk through that process step-by-step. If the material becomes too dense (and you’re not actually setting up a development environment) feel free to skip to the next chapter, which is less technical.</p>
</div>
</div>
<div class="sect2 data-line-26">
<h3 id="compiling_core">Compiling Bitcoin Core from the Source Code</h3>
<div class="paragraph data-line-28">
<p>Bitcoin Core’s source code can be downloaded as a ZIP archive or by cloning the authoritative source repository from GitHub. On the <a href="https://github.com/bitcoin/bitcoin" data-href="https://github.com/bitcoin/bitcoin">GitHub bitcoin page</a>, select Download ZIP from the sidebar. Alternatively, use the git command line to create a local copy of the source code on your system.</p>
</div>
<div class="admonitionblock tip data-line-31">
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<td class="icon">
<div class="title">Tip</div>
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<td class="content">
<div class="paragraph data-line-32">
<p>In many of the examples in this chapter we will be using the operating system’s command-line interface (also known as a "shell"), accessed via a "terminal" application. The shell will display a prompt; you type a command; and the shell responds with some text and a new prompt for your next command. The prompt may look different on your system, but in the following examples it is denoted by a $ symbol. In the examples, when you see text after a $ symbol, don’t type the $ symbol but type the command immediately following it, then press Enter to execute the command. In the examples, the lines below each command are the operating system’s responses to that command. When you see the next $ prefix, you’ll know it’s a new command and you should repeat the process.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph data-line-35">
<p>In this example, we are using the git command to create a local copy ("clone") of the source code:</p>
</div>
<div class="listingblock data-line-37">
<div class="content">
<pre>$ git clone https://github.com/bitcoin/bitcoin.git
Cloning into 'bitcoin'...
remote: Counting objects: 66193, done.
remote: Total 66193 (delta 0), reused 0 (delta 0), pack-reused 66193
Receiving objects: 100% (66193/66193), 63.39 MiB | 574.00 KiB/s, done.
Resolving deltas: 100% (48395/48395), done.
Checking connectivity... done.
$</pre>
</div>
</div>
<div class="admonitionblock tip data-line-49">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="paragraph data-line-50">
<p>Git is the most widely used distributed version control system, an essential part of any software developer’s toolkit. You may need to install the git command, or a graphical user interface for git, on your operating system if you do not have it already.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph data-line-53">
<p>When the git cloning operation has completed, you will have a complete local copy of the source code repository in the directory <em>bitcoin</em>. Change to this directory by typing **cd bitcoin** at the prompt:</p>
</div>
<div class="listingblock data-line-55">
<div class="content">
<pre>$ cd bitcoin</pre>
</div>
</div>
<div class="sect3 data-line-59">
<h4 id="_selecting_a_bitcoin_core_release">Selecting a Bitcoin Core Release</h4>
<div class="paragraph data-line-60">
<p>By default, the local copy will be synchronized with the most recent code, which might be an unstable or beta version of bitcoin. Before compiling the code, select a specific version by checking out a release <em>tag</em>. This will synchronize the local copy with a specific snapshot of the code repository identified by a keyword tag. Tags are used by the developers to mark specific releases of the code by version number. First, to find the available tags, we use the git tag command:</p>
</div>
<div class="listingblock data-line-62">
<div class="content">
<pre>$ git tag
v0.1.5
v0.1.6test1
v0.10.0
...
v0.11.2
v0.11.2rc1
v0.12.0rc1
v0.12.0rc2
...</pre>
</div>
</div>
<div class="paragraph data-line-75">
<p>The list of tags shows all the released versions of bitcoin. By convention, <em>release candidates</em>, which are intended for testing, have the suffix "rc." Stable releases that can be run on production systems have no suffix. From the preceding list, select the highest version release, which at the time of writing was v0.11.2. To synchronize the local code with this version, use the git checkout command:</p>
</div>
<div class="listingblock data-line-77">
<div class="content">
<pre>$ git checkout v0.11.2
HEAD is now at 7e27892... Merge pull request #6975</pre>
</div>
</div>
<div class="paragraph data-line-82">
<p>You can confirm you have the desired version "checked out" by issuing the command git status:</p>
</div>
<div class="listingblock data-line-84">
<div class="content">
<pre>$ git status
HEAD detached at v0.11.2
nothing to commit, working directory clean</pre>
</div>
</div>
</div>
<div class="sect3 data-line-90">
<h4 id="_configuring_the_bitcoin_core_build">Configuring the Bitcoin Core Build</h4>
<div class="paragraph data-line-92">
<p>The source code includes documentation, which can be found in a number of files. Review the main documentation located in <em>README.md</em> in the <em>bitcoin</em> directory by typing **more README.md** at the prompt and using the spacebar to progress to the next page. In this chapter, we will build the command-line bitcoin client, also known as bitcoind on Linux. Review the instructions for compiling the bitcoind command-line client on your platform by typing **more doc/build-unix.md**. Alternative instructions for macOS and Windows can be found in the <em>doc</em> directory, as <em>build-osx.md</em> or <em>build-windows.md</em>, respectively.</p>
</div>
<div class="paragraph data-line-94">
<p>Carefully review the build prerequisites, which are in the first part of the build documentation. These are libraries that must be present on your system before you can begin to compile bitcoin. If these prerequisites are missing, the build process will fail with an error. If this happens because you missed a prerequisite, you can install it and then resume the build process from where you left off. Assuming the prerequisites are installed, you start the build process by generating a set of build scripts using the <em>autogen.sh</em> script.</p>
</div>
<div class="admonitionblock note data-line-97">
<table>
<tr>
<td class="icon">
<div class="title">Note</div>
</td>
<td class="content">
<div class="paragraph data-line-98">
<p>The Bitcoin Core build process was changed to use the autogen/configure/make system starting with version 0.9. Older versions use a simple Makefile and work slightly differently from the following example. Follow the instructions for the version you want to compile. The autogen/configure/make introduced in 0.9 is likely to be the build system used for all future versions of the code and is the system demonstrated in the following examples.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="listingblock data-line-101">
<div class="content">
<pre>$ ./autogen.sh
...
glibtoolize: copying file 'build-aux/m4/libtool.m4'
glibtoolize: copying file 'build-aux/m4/ltoptions.m4'
glibtoolize: copying file 'build-aux/m4/ltsugar.m4'
glibtoolize: copying file 'build-aux/m4/ltversion.m4'
...
configure.ac:10: installing 'build-aux/compile'
configure.ac:5: installing 'build-aux/config.guess'
configure.ac:5: installing 'build-aux/config.sub'
configure.ac:9: installing 'build-aux/install-sh'
configure.ac:9: installing 'build-aux/missing'
Makefile.am: installing 'build-aux/depcomp'
...</pre>
</div>
</div>
<div class="paragraph data-line-118">
<p>The <em>autogen.sh</em> script creates a set of automatic configuration scripts that will interrogate your system to discover the correct settings and ensure you have all the necessary libraries to compile the code. The most important of these is the configure script that offers a number of different options to customize the build process. Type **./configure --help** to see the various options:</p>
</div>
<div class="listingblock data-line-120">
<div class="content">
<pre>$ ./configure --help
`configure' configures Bitcoin Core 0.11.2 to adapt to many kinds of systems.
Usage: ./configure [OPTION]... [VAR=VALUE]...
...
Optional Features:
--disable-option-checking ignore unrecognized --enable/--with options
--disable-FEATURE do not include FEATURE (same as --enable-FEATURE=no)
--enable-FEATURE[=ARG] include FEATURE [ARG=yes]
--enable-wallet enable wallet (default is yes)
--with-gui[=no|qt4|qt5|auto]
...</pre>
</div>
</div>
<div class="paragraph data-line-138">
<p>The configure script allows you to enable or disable certain features of bitcoind through the use of the --enable-FEATURE and --disable-FEATURE flags, where <span class="keep-together"><code>FEATURE</code></span> is replaced by the feature name, as listed in the help output. In this chapter, we will build the bitcoind client with all the default features. We won’t be using the configuration flags, but you should review them to understand what optional features are part of the client. If you are in an academic setting, computer lab restrictions may require you to install applications in your home directory (e.g., using --prefix=$HOME).</p>
</div>
<div class="paragraph data-line-140">
<p>Here are some useful options that override the default behavior of the configure script:</p>
</div>
<dl>
<dt><code>--prefix=$HOME</code></dt>
<dd><p>This overrides the default installation location (which is <em>/usr/local/</em>) for the resulting executable. Use <code>$HOME</code> to put everything in your home directory, or a different path.</p></dd>
<dt><code>--disable-wallet</code></dt>
<dd><p>This is used to disable the reference wallet implementation.</p></dd>
<dt><code>--with-incompatible-bdb</code></dt>
<dd><p>If you are building a wallet, allow the use of an incompatible version of the Berkeley DB library.</p></dd>
<dt><code>--with-gui=no</code></dt>
<dd><p>Don't build the graphical user interface, which requires the Qt library. This builds server and command-line bitcoin only.</p></dd>
</dl>
<div class="paragraph data-line-158">
<p>Next, run the configure script to automatically discover all the necessary libraries and create a customized build script for your system:</p>
</div>
<div class="listingblock data-line-160">
<div class="content">
<pre>$ ./configure
checking build system type... x86_64-unknown-linux-gnu
checking host system type... x86_64-unknown-linux-gnu
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for a thread-safe mkdir -p... /bin/mkdir -p
checking for gawk... gawk
checking whether make sets $(MAKE)... yes
...
[many pages of configuration tests follow]
...
$</pre>
</div>
</div>
<div class="paragraph data-line-176">
<p>If all went well, the configure command will end by creating the customized build scripts that will allow us to compile bitcoind. If there are any missing libraries or errors, the configure command will terminate with an error instead of creating the build scripts. If an error occurs, it is most likely because of a missing or incompatible library. Review the build documentation again and make sure you install the missing prerequisites. Then run configure again and see if that fixes the error.</p>
</div>
</div>
<div class="sect3 data-line-178">
<h4 id="_building_the_bitcoin_core_executables">Building the Bitcoin Core Executables</h4>
<div class="paragraph data-line-180">
<p>Next, you will compile the source code, a process that can take up to an hour to complete, depending on the speed of your CPU and available memory. During the compilation process you should see output every few seconds or every few minutes, or an error if something goes wrong. If an error occurs, or the compilation process is interrupted, it can be resumed any time by typing make again. Type **make** to start compiling the executable application:</p>
</div>
<div class="listingblock data-line-182">
<div class="content">
<pre>$ make
Making all in src
CXX crypto/libbitcoinconsensus_la-hmac_sha512.lo
CXX crypto/libbitcoinconsensus_la-ripemd160.lo
CXX crypto/libbitcoinconsensus_la-sha1.lo
CXX crypto/libbitcoinconsensus_la-sha256.lo
CXX crypto/libbitcoinconsensus_la-sha512.lo
CXX libbitcoinconsensus_la-hash.lo
CXX primitives/libbitcoinconsensus_la-transaction.lo
CXX libbitcoinconsensus_la-pubkey.lo
CXX script/libbitcoinconsensus_la-bitcoinconsensus.lo
CXX script/libbitcoinconsensus_la-interpreter.lo
[... many more compilation messages follow ...]
$</pre>
</div>
</div>
<div class="paragraph data-line-201">
<p>If all goes well, Bitcoin Core is now compiled. The final step is to install the various executables on your system using the sudo make install command. You may be prompted for your user password, because this step requires administrative privileges:</p>
</div>
<div class="listingblock data-line-203">
<div class="content">
<pre>$ sudo make install
Password:
Making install in src
../build-aux/install-sh -c -d '/usr/local/lib'
libtool: install: /usr/bin/install -c bitcoind /usr/local/bin/bitcoind
libtool: install: /usr/bin/install -c bitcoin-cli /usr/local/bin/bitcoin-cli
libtool: install: /usr/bin/install -c bitcoin-tx /usr/local/bin/bitcoin-tx
...
$</pre>
</div>
</div>
<div class="paragraph data-line-215">
<p>The default installation of bitcoind puts it in <em>/usr/local/bin</em>. You can confirm that Bitcoin Core is correctly installed by asking the system for the path of the executables, as follows:</p>
</div>
<div class="listingblock data-line-217">
<div class="content">
<pre>$ which bitcoind
/usr/local/bin/bitcoind
$ which bitcoin-cli
/usr/local/bin/bitcoin-cli</pre>
</div>
</div>
</div>
</div>
<div class="sect2 data-line-225">
<h3 id="_running_a_bitcoin_core_node">Running a Bitcoin Core Node</h3>
<div class="paragraph data-line-227">
<p>Bitcoin’s peer-to-peer network is composed of network "nodes," run mostly by volunteers and some of the businesses that build bitcoin applications. Those running bitcoin nodes have a direct and authoritative view of the bitcoin blockchain, with a local copy of all the transactions, independently validated by their own system. By running a node, you don’t have to rely on any third party to validate a transaction. Moreover, by running a bitcoin node you contribute to the bitcoin network by making it more robust.</p>
</div>
<div class="paragraph data-line-229">
<p>Running a node, however, requires a permanently connected system with enough resources to process all bitcoin transactions. Depending on whether you choose to index all transactions and keep a full copy of the blockchain, you may also need a lot of disk space and RAM. As of late 2016, a full-index node needs 2 GB of RAM and 125 GB of disk space so that it has room to grow. Bitcoin nodes also transmit and receive bitcoin transactions and blocks, consuming internet bandwidth. If your internet connection is limited, has a low data cap, or is metered (charged by the gigabit), you should probably not run a bitcoin node on it, or run it in a way that constrains its bandwidth (see <a href="#constrained_resources">Sample configuration of a resource-constrained system</a>).</p>
</div>
<div class="admonitionblock tip data-line-232">
<table>
<tr>
<td class="icon">
<div class="title">Tip</div>
</td>
<td class="content">
<div class="paragraph data-line-233">
<p>Bitcoin Core keeps a full copy of the blockchain by default, with every transaction that has ever occurred on the bitcoin network since its inception in 2009. This dataset is dozens of gigabytes in size and is downloaded incrementally over several days or weeks, depending on the speed of your CPU and internet connection. Bitcoin Core will not be able to process transactions or update account balances until the full blockchain dataset is downloaded. Make sure you have enough disk space, bandwidth, and time to complete the initial synchronization. You can configure Bitcoin Core to reduce the size of the blockchain by discarding old blocks (see <a href="#constrained_resources">Sample configuration of a resource-constrained system</a>), but it will still download the entire dataset before discarding data.</p>
</div>
</td>
</tr>
</table>
</div>
<div class="paragraph data-line-236">
<p>Despite these resource requirements, thousands of volunteers run bitcoin nodes. Some are running on systems as simple as a Raspberry Pi (a $35 USD computer the size of a pack of cards). Many volunteers also run bitcoin nodes on rented servers, usually some variant of Linux. A <em>Virtual Private Server</em> (VPS) or <em>Cloud Computing Server</em> instance can be used to run a bitcoin node. Such servers can be rented for $25 to $50 USD per month from a variety of providers.</p>
</div>
<div class="paragraph data-line-238">
<p>Why would you want to run a node? Here are some of the most common reasons:</p>
</div>
<div class="ulist data-line-240">
<ul>
<li class="data-line-240">
<p>If you are developing bitcoin software and need to rely on a bitcoin node for programmable (API) access to the network and blockchain.</p>
</li>
<li class="data-line-242">
<p>If you are building applications that must validate transactions according to bitcoin’s consensus rules. Typically, bitcoin software companies run several nodes.</p>
</li>
<li class="data-line-244">
<p>If you want to support bitcoin. Running a node makes the network more robust and able to serve more wallets, more users, and more transactions.</p>
</li>
<li class="data-line-246">
<p>If you do not want to rely on any third party to process or validate your transactions.</p>
</li>
</ul>
</div>
<div class="paragraph data-line-248">
<p>If you’re reading this book and interested in developing bitcoin software, you should be running your own node.</p>
</div>
<div class="sect3 data-line-250">
<h4 id="_running_bitcoin_core_for_the_first_time">Running Bitcoin Core for the First Time</h4>
<div class="paragraph data-line-252">
<p>When you first run bitcoind, it will remind you to create a configuration file with a strong password for the JSON-RPC interface. This password controls access to the application programming interface (API) offered by Bitcoin Core.</p>
</div>
<div class="paragraph data-line-254">
<p>Run bitcoind by typing **bitcoind** into the terminal:</p>
</div>
<div class="listingblock data-line-256">
<div class="content">
<pre>$ bitcoind
Error: To use the "-server" option, you must set a rpcpassword in the configuration file:
/home/ubuntu/.bitcoin/bitcoin.conf
It is recommended you use the following random password:
rpcuser=bitcoinrpc
rpcpassword=2XA4DuKNCbtZXsBQRRNDEwEY2nM6M4H9Tx5dFjoAVVbK
(you do not need to remember this password)
The username and password MUST NOT be the same.
If the file does not exist, create it with owner-readable-only file permissions.
It is also recommended to set alertnotify so you are notified of problems;
for example: alertnotify=echo %s | mail -s "Bitcoin Alert" admin@foo.com</pre>
</div>
</div>
<div class="paragraph data-line-270">
<p>As you can see, the first time you run bitcoind it tells you that you need to build a configuration file, with at least an rpcuser and rpcpassword entry. Additionally, it is recommended that you set up the alerting mechanism. In the next section we will examine the various configuration options and set up a configuration file.</p>
</div>
</div>
<div class="sect3 data-line-272">
<h4 id="_configuring_the_bitcoin_core_node">Configuring the Bitcoin Core Node</h4>
<div class="paragraph data-line-274">
<p>Edit the configuration file in your preferred editor and set the parameters, replacing the password with a strong password as recommended by bitcoind. Do <em>not</em> use the password shown in the book. Create a file inside the <em>.bitcoin</em> directory (under your user’s home directory) so that it is named <em>.bitcoin/bitcoin.conf</em> and provide a username and password:</p>
</div>
<div class="listingblock data-line-277">
<div class="content">
<pre class="highlight"><code class="language-ini" data-lang="ini">rpcuser=bitcoinrpc
rpcpassword=CHANGE_THIS</code></pre>
</div>
</div>
<div class="paragraph data-line-282">
<p>In addition to the rpcuser and rpcpassword options, Bitcoin Core offers more than 100 configuration options that modify the behavior of the network node, the storage of the blockchain, and many other aspects of its operation. To see a listing of these options, run bitcoind --help:</p>
</div>
<div class="listingblock data-line-284">
<div class="content">
<pre> bitcoind --help
Bitcoin Core Daemon version v0.11.2
Usage:
bitcoind [options] Start Bitcoin Core Daemon
Options:
-?
This help message
-alerts
Receive and display P2P network alerts (default: 1)
-alertnotify=<cmd>
Execute command when a relevant alert is received or we see a really
long fork (%s in cmd is replaced by message)
...
[many more options]
...
-rpcsslciphers=<ciphers>
Acceptable ciphers (default:
TLSv1.2+HIGH:TLSv1+HIGH:!SSLv2:!aNULL:!eNULL:!3DES:@STRENGTH)</pre>
</div>
</div>
<div class="paragraph data-line-311">
<p>Here are some of the most important options that you can set in the configuration file, or as command-line parameters to bitcoind:</p>
</div>
<div class="dlist data-line-313">
<dl>
<dt class="hdlist1">alertnotify</dt>
<dd>
<p>Run a specified command or script to send emergency alerts to the owner of this node, usually by email.</p>
</dd>
<dt class="hdlist1">conf</dt>
<dd>
<p>An alternative location for the configuration file. This only makes sense as a command-line parameter to bitcoind, as it can’t be inside the configuration file it refers to.</p>
</dd>
<dt class="hdlist1">datadir</dt>
<dd>
<p>Select the directory and filesystem in which to put all the blockchain data. By default this is the <em>.bitcoin</em> subdirectory of your home directory. Make sure this filesystem has several gigabytes of free space.</p>
</dd>
<dt class="hdlist1">prune</dt>
<dd>
<p>Reduce the disk space requirements to this many megabytes, by deleting old blocks. Use this on a resource-constrained node that can’t fit the full blockchain.</p>
</dd>
<dt class="hdlist1">txindex</dt>
<dd>
<p>Maintain an index of all transactions. This means a complete copy of the blockchain that allows you to programmatically retrieve any transaction by ID.</p>
</dd>
<dt class="hdlist1">maxconnections</dt>
<dd>
<p>Set the maximum number of nodes from which to accept connections. Reducing this from the default will reduce your bandwidth consumption. Use if you have a data cap or pay by the gigabyte.</p>
</dd>
<dt class="hdlist1">maxmempool</dt>
<dd>
<p>Limit the transaction memory pool to this many megabytes. Use it to reduce memory use of the node.</p>
</dd>
<dt class="hdlist1">maxreceivebuffer/maxsendbuffer</dt>
<dd>
<p>Limit per-connection memory buffer to this many multiples of 1000 bytes. Use on memory-constrained nodes.</p>
</dd>
<dt class="hdlist1">minrelaytxfee</dt>
<dd>
<p>Set the minimum fee transaction you will relay. Below this value, the transaction is treated as zero fee. Use this on memory-constrained nodes to reduce the size of the in-memory transaction pool.</p>
</dd>
</dl>
</div>
<div id="txindex" class="sidebarblock data-line-334">
<div class="content">
<div class="title">Transaction Database Index and txindex Option</div>
<div class="paragraph data-line-335">
<p>By default, Bitcoin Core builds a database containing <em>only</em> the transactions related to the user’s wallet. If you want to be able to access <em>any</em> transaction with commands like getrawtransaction (see <a href="#exploring_and_decoding_transanctions">Exploring and Decoding Transactions</a>), you need to configure Bitcoin Core to build a complete transaction index, which can be achieved with the txindex option. Set txindex=1 in the Bitcoin Core configuration file. If you don’t set this option at first and later set it to full indexing, you need to restart bitcoind with the -reindex option and wait for it to rebuild the index.</p>
</div>
</div>
</div>
<div class="paragraph data-line-338">
<p><a href="#full_index_node">Sample configuration of a full-index node</a> shows how you might combine the preceding options, with a fully indexed node, running as an API backend for a bitcoin application.</p>
</div>
<div id="full_index_node" class="exampleblock data-line-342">
<div class="title">Example 1. Sample configuration of a full-index node</div>
<div class="content">
<div class="listingblock data-line-343">
<div class="content">
<pre>alertnotify=myemailscript.sh "Alert: %s"
datadir=/lotsofspace/bitcoin
txindex=1
rpcuser=bitcoinrpc
rpcpassword=CHANGE_THIS</pre>
</div>
</div>
</div>
</div>
<div class="paragraph data-line-352">
<p><a href="#constrained_resources">Sample configuration of a resource-constrained system</a> shows a resource-constrained node running on a smaller server.</p>
</div>
<div id="constrained_resources" class="exampleblock data-line-356">
<div class="title">Example 2. Sample configuration of a resource-constrained system</div>
<div class="content">
<div class="listingblock data-line-357">
<div class="content">
<pre>alertnotify=myemailscript.sh "Alert: %s"
maxconnections=15
prune=5000
minrelaytxfee=0.0001
maxmempool=200
maxreceivebuffer=2500
maxsendbuffer=500
rpcuser=bitcoinrpc
rpcpassword=CHANGE_THIS</pre>
</div>
</div>
</div>
</div>
<div class="paragraph data-line-370">
<p>Once you’ve edited the configuration file and set the options that best represent your needs, you can test bitcoind with this configuration. Run Bitcoin Core with the option printtoconsole to run in the foreground with output to the console:</p>
</div>
<div class="listingblock data-line-372">
<div class="content">
<pre>$ bitcoind -printtoconsole
Bitcoin version v0.11.20.0
Using OpenSSL version OpenSSL 1.0.2e 3 Dec 2015
Startup time: 2015-01-02 19:56:17
Using data directory /tmp/bitcoin
Using config file /tmp/bitcoin/bitcoin.conf
Using at most 125 connections (275 file descriptors available)
Using 2 threads for script verification
scheduler thread start
HTTP: creating work queue of depth 16
No rpcpassword set - using random cookie authentication
Generated RPC authentication cookie /tmp/bitcoin/.cookie
HTTP: starting 4 worker threads
Bound to [::]:8333
Bound to 0.0.0.0:8333
Cache configuration:
* Using 2.0MiB for block index database
* Using 32.5MiB for chain state database
* Using 65.5MiB for in-memory UTXO set
init message: Loading block index...
Opening LevelDB in /tmp/bitcoin/blocks/index
Opened LevelDB successfully
[... more startup messages ...]</pre>
</div>
</div>
<div class="paragraph data-line-400">
<p>You can hit Ctrl-C to interrupt the process once you are satisfied that it is loading the correct settings and running as you expect.</p>
</div>
<div class="paragraph data-line-402">
<p>To run Bitcoin Core in the background as a process, start it with the daemon option, as bitcoind -daemon.</p>
</div>
<div class="paragraph data-line-404">
<p>To monitor the progress and runtime status of your bitcoin node, use the command bitcoin-cli getinfo:</p>
</div>
<div class="listingblock data-line-406">
<div class="content">
<pre>$ bitcoin-cli getinfo</pre>
</div>
</div>
<div class="listingblock data-line-411">
<div class="content">
<pre class="highlight"><code class="language-json" data-lang="json">{
"version" : 110200,
"protocolversion" : 70002,
"blocks" : 396328,
"timeoffset" : 0,
"connections" : 15,
"proxy" : "",
"difficulty" : 120033340651.23696899,
"testnet" : false,
"relayfee" : 0.00010000,
"errors" : ""
}</code></pre>
</div>