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A fast & nimble SPV Server for Bitcoin Cash
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A fast & nimble SPV server for Bitcoin Cash.


(C) 2019-2020 Calin Culianu


GPLv3. See the included LICENSE.txt file or visit and read the license.

Image Fulcrum


  • Fast: Written in 100% modern C++17 using multi-threaded and asynchronous programming techniques.
  • A drop-in replacement for ElectronX/ElectrumX: The initial release of this server is 100% protocol-level compatible with the ElectronX/ElectrumX 1.4.2 protocol. Existing server admins should feel right at home with this software since installation and management of it is nearly identical to ElectronX/ElectrumX server.
  • Cross-platform: While this codebase was mainly developed and tested on MacOS, Windows and Linux, it should theoretically work on any modern OS (such as *BSD) that has Qt5 Core and Qt5 Networking available.


  • Qt Core & Qt Networking libraries 5.12.5 or above (I use 5.13.2 myself). Qt 5.12.4 (or earlier) is not supported.
  • A modern, 64-bit C++17 compiler. clang is recommended but G++ also works. MSVC on Windows is not supported (please use MinGW G++ instead, which ships with Qt Open Source Edition for Windows).

How To Compile

It's recommended you use Qt Creator.

  1. Get the latest version of Qt Open Source Edition for your platform.
  2. Point the Qt Creator IDE at the file.
  3. Set the build configuration to "Release". Hit Build. It should "just work".

You may also build from the CLI (on Linux and MacOS):

  1. Make sure you have qmake in your path and all the requisite Qt5 dev libs installed.
  2. qmake (to generate the Makefile)
  3. make -j8 (replace 8 here with the number of cores on your machine)

A note for Linux users: You may have to install the Qt5 networking package separately such as libqt5network5 (depending on your distribution). You also need libbz2-dev otherwise compilation will fail. If you are having trouble finding the required Qt versions, you can try this link: (for Ubuntu/Debian ppas).

A note for Windows users: Qt 5.13.2 (or above) with MinGW G++ 7.x.x is the compiler/Qt kit you should be using. MSVC is not supported by this codebase at the present time.

What to do if compiling fails

If you have problems compiling, the most likely culprit would be your compiler not being C++17 compliant (please use a recent verson of GCC or clang on Linux, Apple's Xcode on Mac, or MinGW G++ 7.x on Windows).

The other likely culprit is the fact that at the present time I have included a statically-built librocksdb in the codebase. There are versions of this library for Windows, Mac, and Linux included right in the source tree, and looks for them and links to them. Instructions are included within the project file about how to build your own static librocksdb if the bundled one does not work on your system.

If you are still having trouble, file an issue here in this github.

Linking against the system (experimental)

You may optionally build against the system rocksdb (Linux only) if your distribution offers rocksdb version 6.5.x or newer.

  1. qmake features= (to generate the Makefile without the staticlibs feature)
  2. make clean && make -j8 (replace 8 here with the number of cores on your machine)

Note: Some Linux distributions have been known to package incorrectly. See here for an example, so until I can be confident most distributions do it right, I am considering using the system an experimental feature for the time being (in principle it should work ok if the library is compiled correctly).

Running Fulcrum

Execute the binary, with -h to see the built-in help, e.g. ./Fulcrum -h. You can set most options from the CLI, but you can also specify a config file as an argument. See:

Fulcrum requires a bitcoind instance running either on testnet or mainnet (or regtest for testing), which you must tell it about via the CLI options or via the config file. You also need to tell it what port(s) to listen on and optionally what SSL certificates to use (if using SSL). Note: Electron Cash at this time no longer supports connecting to non-SSL servers, so you should probably configure SSL for production use.

It is recommended you specify a data dir (-D via CLI or datadir= via config file) on an SSD drive for best results. Synching against testnet should take you about 10-20 minutes (more on slower machines), and mainnet can take anywhere from 4 hours to 20+ hours, depending on machine and drive speed. I have not tried synching against mainnet on an HDD and it will probably take days if you are lucky.

Once the server finishes synching it will behave like an ElectronX/ElectrumX server and it can receive requests from Electron Cash.

You may also wish to read the Fulcrum manpage.

Admin Script: FulcrumAdmin

Fulcrum comes with an admin script (Python 3.6+ is required on the system to run this script). You may send commands to Fulcrum using this script. The script requires that an admin port (config var admin=, CLI arg -a) be configured for your server. To run the script, execute ./FulcrumAdmin -h and you will see a list of possible subcommands that you can send to Fulcrum. Here are two of the most popular commands to try (the below assumes the admin port is on port 8000):

$ ./FulcrumAdmin -p 8000 peers
$ ./FulcrumAdmin -p 8000 clients
$ ./FulcrumAdmin -p 8000 getinfo

(This section is incomplete for now, all apologies -- more documentation is coming soon!)

Platform Notes

Big Endian Architectures

The code is more or less configured to assume a "little endian" architecture by default (which is what all Intel x86/x86_64 are). If you're on a big endian machine, on Linux it should just auto-detect that fact. However, on other OS's such as BSD, if you're on a big endian machine, you may need to uncomment this line from the .pro file:



This codebase will not compile correctly (or at all) using MSVC. Please use the MinGW and/or G++ kit in Qt Creator to build this software.


If you have clang on your system, configure the project to use it as the compiler preferentially over G++. G++ works too, but clang is preferred.


Everything should just work (I use MacOS as my dev machine).


Q: Why Qt? This isn't a GUI app!

A: Yes, I know. However, Qt is a very robust, cross-platform and fast application framework. You can use its "Core" library for console apps, servers, etc. It has great network support and other basic things a programmer needs to get stuff done.


Sure! Send BCH here:



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