Introduction

Go is an open source project, distributed under a BSD-style license. This document explains how to check out the sources, build them on your own machine, and run them.

Most users don't need to do this, and will instead install from precompiled binary packages as described in Getting Started, a much simpler process. If you want to help develop what goes into those precompiled packages, though, read on.

Install Go compiler binaries

The Go toolchain is written in Go. To build it, you need a Go compiler installed. The scripts that do the initial build of the tools look for an existing Go tool chain in $GOROOT_BOOTSTRAP. If unset, the default value of GOROOT_BOOTSTRAP is $HOME/go1.4.

There are many options for the bootstrap toolchain. After obtaining one, set GOROOT_BOOTSTRAP to the directory containing the unpacked tree. For example, $GOROOT_BOOTSTRAP/bin/go should be the go command binary for the bootstrap toolchain.

To use a binary release as a bootstrap toolchain, see the downloads page or use any other packaged Go distribution.

To build a bootstrap toolchain from source, use either the git branch release-branch.go1.4 or go1.4-bootstrap-20171003.tar.gz, which contains the Go 1.4 source code plus accumulated fixes to keep the tools running on newer operating systems. (Go 1.4 was the last distribution in which the toolchain was written in C.) After unpacking the Go 1.4 source, cd to the src subdirectory, set CGO_ENABLED=0 in the environment, and run make.bash (or, on Windows, make.bat).

To cross-compile a bootstrap toolchain from source, which is necessary on systems Go 1.4 did not target (for example, linux/ppc64le), install Go on a different system and run bootstrap.bash.

When run as (for example)

$ GOOS=linux GOARCH=ppc64 ./bootstrap.bash

bootstrap.bash cross-compiles a toolchain for that GOOS/GOARCH combination, leaving the resulting tree in ../../go-${GOOS}-${GOARCH}-bootstrap. That tree can be copied to a machine of the given target type and used as GOROOT_BOOTSTRAP to bootstrap a local build.

To use gccgo as the bootstrap toolchain, you need to arrange for $GOROOT_BOOTSTRAP/bin/go to be the go tool that comes as part of gccgo 5. For example on Ubuntu Vivid:

$ sudo apt-get install gccgo-5
$ sudo update-alternatives --set go /usr/bin/go-5
$ GOROOT_BOOTSTRAP=/usr ./make.bash

Install Git, if needed

To perform the next step you must have Git installed. (Check that you have a git command before proceeding.)

If you do not have a working Git installation, follow the instructions on the Git downloads page.

(Optional) Install a C compiler

To build a Go installation with cgo support, which permits Go programs to import C libraries, a C compiler such as gcc or clang must be installed first. Do this using whatever installation method is standard on the system.

To build without cgo, set the environment variable CGO_ENABLED=0 before running all.bash or make.bash.

Fetch the repository

Go will install to a directory named go. Change to the directory that will be its parent and make sure the go directory does not exist. Then clone the repository and check out the latest release tag (go1.12, for example):

$ git clone https://go.googlesource.com/go
$ cd go
$ git checkout go1.12

(Optional) Switch to the master branch

If you intend to modify the go source code, and contribute your changes to the project, then move your repository off the release branch, and onto the master (development) branch. Otherwise, skip this step.

$ git checkout master

Install Go

To build the Go distribution, run

$ cd src
$ ./all.bash

(To build under Windows use all.bat.)

If all goes well, it will finish by printing output like:

ALL TESTS PASSED

---
Installed Go for linux/amd64 in /home/you/go.
Installed commands in /home/you/go/bin.
*** You need to add /home/you/go/bin to your $PATH. ***

where the details on the last few lines reflect the operating system, architecture, and root directory used during the install.

Testing your installation

Check that Go is installed correctly by building a simple program.

Create a file named hello.go and put the following program in it:

package main

import "fmt"

func main() {
	fmt.Printf("hello, world\n")
}

Then run it with the go tool:

$ go run hello.go
hello, world

If you see the "hello, world" message then Go is installed correctly.

Set up your work environment

You're almost done. You just need to do a little more setup.

Learn how to set up and use the Go tools

The How to Write Go Code document provides essential setup instructions for using the Go tools.

Install additional tools

The source code for several Go tools (including godoc) is kept in the go.tools repository. To install one of the tools (godoc in this case):

$ go get golang.org/x/tools/cmd/godoc

To install these tools, the go get command requires that Git be installed locally.

You must also have a workspace (GOPATH) set up; see How to Write Go Code for the details.

Community resources

The usual community resources such as #go-nuts on the Freenode IRC server and the Go Nuts mailing list have active developers that can help you with problems with your installation or your development work. For those who wish to keep up to date, there is another mailing list, golang-checkins, that receives a message summarizing each checkin to the Go repository.

Bugs can be reported using the Go issue tracker.

Keeping up with releases

New releases are announced on the golang-announce mailing list. Each announcement mentions the latest release tag, for instance, go1.12.

To update an existing tree to the latest release, you can run:

$ cd go/src
$ git fetch
$ git checkout go1.12

Optional environment variables

The Go compilation environment can be customized by environment variables. None is required by the build, but you may wish to set some to override the defaults.

• $GOROOT

  The root of the Go tree, often $HOME/go1.X. Its value is built into the tree when it is compiled, and defaults to the parent of the directory where all.bash was run. There is no need to set this unless you want to switch between multiple local copies of the repository.

• $GOROOT_FINAL

  The value assumed by installed binaries and scripts when $GOROOT is not set explicitly. It defaults to the value of $GOROOT. If you want to build the Go tree in one location but move it elsewhere after the build, set $GOROOT_FINAL to the eventual location.

• $GOOS and $GOARCH

  The name of the target operating system and compilation architecture. These default to the values of $GOHOSTOS and $GOHOSTARCH respectively (described below).

Choices for $GOOS are darwin (macOS 10.10 and above and iOS), dragonfly, freebsd, linux, netbsd, openbsd, plan9, solaris and windows. Choices for $GOARCH are amd64 (64-bit x86, the most mature port), 386 (32-bit x86), arm (32-bit ARM), arm64 (64-bit ARM), ppc64le (PowerPC 64-bit, little-endian), ppc64 (PowerPC 64-bit, big-endian), mips64le (MIPS 64-bit, little-endian), mips64 (MIPS 64-bit, big-endian), mipsle (MIPS 32-bit, little-endian), mips (MIPS 32-bit, big-endian), and s390x (IBM System z 64-bit, big-endian). The valid combinations of $GOOS and $GOARCH are:

• $GOHOSTOS and $GOHOSTARCH

  The name of the host operating system and compilation architecture. These default to the local system's operating system and architecture.

Valid choices are the same as for $GOOS and $GOARCH, listed above. The specified values must be compatible with the local system. For example, you should not set $GOHOSTARCH to arm on an x86 system.

• $GOBIN

  The location where Go binaries will be installed. The default is $GOROOT/bin. After installing, you will want to arrange to add this directory to your $PATH, so you can use the tools. If $GOBIN is set, the go command installs all commands there.

• $GO386 (for 386 only, default is auto-detected if built on either 386 or amd64, 387 otherwise)

  This controls the code generated by gc to use either the 387 floating-point unit (set to 387) or SSE2 instructions (set to sse2) for floating point computations.

  • GO386=387: use x87 for floating point operations; should support all x86 chips (Pentium MMX or later).
  • GO386=sse2: use SSE2 for floating point operations; has better performance than 387, but only available on Pentium 4/Opteron/Athlon 64 or later.
• $GOARM (for arm only; default is auto-detected if building on the target processor, 6 if not)

  This sets the ARM floating point co-processor architecture version the run-time should target. If you are compiling on the target system, its value will be auto-detected.

  • GOARM=5: use software floating point; when CPU doesn't have VFP co-processor
  • GOARM=6: use VFPv1 only; default if cross compiling; usually ARM11 or better cores (VFPv2 or better is also supported)
  • GOARM=7: use VFPv3; usually Cortex-A cores

  If in doubt, leave this variable unset, and adjust it if required when you first run the Go executable. The GoARM page on the Go community wiki contains further details regarding Go's ARM support.

• $GOMIPS (for mips and mipsle only)
  $GOMIPS64 (for mips64 and mips64le only)

  These variables set whether to use floating point instructions. Set to "hardfloat" to use floating point instructions; this is the default. Set to "softfloat" to use soft floating point.

Note that $GOARCH and $GOOS identify the target environment, not the environment you are running on. In effect, you are always cross-compiling. By architecture, we mean the kind of binaries that the target environment can run: an x86-64 system running a 32-bit-only operating system must set GOARCH to 386, not amd64.

If you choose to override the defaults, set these variables in your shell profile ($HOME/.bashrc, $HOME/.profile, or equivalent). The settings might look something like this:

export GOARCH=amd64
export GOOS=linux

although, to reiterate, none of these variables needs to be set to build, install, and develop the Go tree.