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.

There are two official Go compiler tool chains. This document focuses on the gc Go compiler and tools (6g, 8g etc.). For information on how to work on gccgo, a more traditional compiler using the GCC back end, see Setting up and using gccgo.

The Go compilers support three instruction sets. There are important differences in the quality of the compilers for the different architectures.

amd64 (a.k.a. x86-64); 6g,6l,6c,6a
A mature implementation. The compiler has an effective optimizer (registerizer) and generates good code (although gccgo can do noticeably better sometimes).
386 (a.k.a. x86 or x86-32); 8g,8l,8c,8a
Comparable to the amd64 port.
arm (a.k.a. ARM); 5g,5l,5c,5a
Supports only Linux binaries. Less widely used than the other ports and therefore not as thoroughly tested.

Except for things like low-level operating system interface code, the run-time support is the same in all ports and includes a mark-and-sweep garbage collector, efficient array and string slicing, and support for efficient goroutines, such as stacks that grow and shrink on demand.

The compilers can target the FreeBSD, Linux, NetBSD, OpenBSD, OS X (Darwin), and Windows operating systems. The full set of supported combinations is listed in the discussion of environment variables below.

Install C tools, if needed

The Go tool chain is written in C. To build it, you need a C compiler installed.

On OS X, a C compiler is bundled in the command line tools for Xcode, and you don't need to install the whole Xcode to compile Go. If you have already installed Xcode 4.3+, you can install command line tools from the Components tab of the Downloads preferences panel. To verify you have a working compiler, just invoke gcc in a freshly created Terminal window, unless you see the "gcc: command not found" error, you are ready to go.

On Ubuntu/Debian, use sudo apt-get install gcc libc6-dev. If you want to build 32-bit binaries on a 64-bit system you'll also need the libc6-dev-i386 package.

On Windows, install gcc with MinGW. (Make sure you add its bin subdirectory to your PATH.)

Install Mercurial, if needed

To perform the next step you must have Mercurial installed. (Check that you have an hg command.)

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

Mercurial versions 1.7.x and up require the configuration of Certification Authorities (CAs). Error messages of the form: 

warning: code.google.com certificate with fingerprint b1:af: ... bc not verified (check hostfingerprints or web.cacerts config setting)

when using Mercurial indicate that the CAs are missing. Check your Mercurial version (hg --version) and configure the CAs if necessary.

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 check out the repository:

$ hg clone -u release https://code.google.com/p/go

Install Go

To build the Go distribution, run 

$ cd go/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.

For more information about ways to control the build, see the discussion of environment variables below.

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

The document How to Write Go Code explains how to set up a work environment in which to build and test Go code.

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

The Go project maintains a stable tag in its Mercurial repository: release.

The release tag refers to the current stable release of Go. Most Go users should use this version. New releases are announced on the golang-announce mailing list.

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

$ cd go/src
$ hg pull
$ hg update release
$ ./all.bash

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/go. 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 (Mac OS X 10.6 and above), freebsd, linux, netbsd, openbsd, plan9, and windows. Choices for $GOARCH are amd64 (64-bit x86, the most mature port), 386 (32-bit x86), and arm (32-bit ARM). The valid combinations of $GOOS and $GOARCH are:
$GOOS $GOARCH
darwin 386
darwin amd64
freebsd 386
freebsd amd64
linux 386
linux amd64
linux arm
netbsd 386
netbsd amd64
openbsd 386
openbsd amd64
plan9 386
windows 386
windows amd64

$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.

$GOARM (arm, default=6)

The ARM architecture version the run-time libraries should target. Setting $GOARM to 5 causes the linker to emit calls to a software floating point implementation instead of using hardware floating point support.

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 GOROOT=$HOME/go
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.