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BUILD.md

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+# Building etcher on Windows, Linux, and Mac
+
+> How do you build etcher? On Windows, Linux, Mac
+
+It’s the same on all systems:
+
+First clone the repository recursively:
+
+`git clone --recursive https://github.com:balena-io/etcher`
+
+```
+rm -rf node_modules
+make electron-develop
+npm start
+```
+
+To build packages for distribution, run `make electron-build` after the steps above.
+
+### Windows
+
+> What version of mingw and visual studio  are needed to build? Any other dependencies for windows? Instructions for how to install?
+
+Visual studio 2019 with:
+  * MSVC v142 x86-64 build tools
+  * Windows 10 SDK
+
+Also install Windows Driver Kit from https://docs.microsoft.com/en-us/windows-hardware/drivers/download-the-wdk
+ - you might have to look under "previous versions" for the windows wdk to match your windows sdk
+ - all you need from this page is the WDK, you can ignore everything else, just download it
+
+pip install -r requirements.txt
+
+Mingw64, install it from https://www.msys2.org/
+
+install choco: https://chocolatey.org/install
+install jq: choco install jq -y
+
+Add /c/msys64/usr/bin/ to path
+
+
+> It appears you’re supposed to use `npm i` and then `npm watch` and then `npm start` in order to build/run the electron app, but I’m getting the error:
+
+NODE_MODULE_VERSION 88. This version of Node.js requires
+NODE_MODULE_VERSION 80. Please try re-compiling or re-installing
+
+From the module `xxhash`
+
+This error means that a module wasn’t built for the correct runtime (node or electron) and version. In general it means that either you ran `npm i` instead of `make electron-develop` or you just updated the electron version.
+Remove the node_modules folder and run `make electron-develop`, that should fix it.
+
+If you want to use only npm, set up some env vars to target the correct runtime as in https://github.com/balena-io/EtcherProApplication/blob/v1.0.0/Dockerfile#L11-L13
+
+
+Each time you change a js file, you need to run `npm webpack` again. This is quite slow. To make it faster leave `npm run watch` running. It actually just runs `webpack --watch`
+
+https://github.com/electron/electron/blob/master/docs/tutorial/using-native-node-modules.md
+
+### Mac OS X
+
+Install XCode via the App Store
+
+> I get the error: `gyp: No Xcode or CLT version detected!`
+
+Fix with:
+
+```
+sudo xcodebuild -license accept
+```
+
+> I get the error: `xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance`
+
+Fix with:
+
+```
+sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
+```
+
+> I get the error: `[webpack-cli] Error: Could not find lzma_native binding`
+
+Try removing node_modules and running `make electron-develop` again.
+
+### Linux
+
+Should work OOTB, please create issue if not.
+
+* Note: Might have to downgrade to Node 14
+
+
+### FreeBSD
+
+Should work OOTB, please create issue if not.
+
+* Note: Might have to downgrade to Node 14