## 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.

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 use `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`
  The most 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 tested than the other ports.

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 can be installed as part of Xcode.

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.

TODO: add Windows compiler info

## Install Mercurial, if needed

To perform the next step you must have Mercurial installed. (Check that you have an `hg` command.) This suffices to install Mercurial on most systems:

    sudo easy_install mercurial==2.0

On Ubuntu/Debian, the Mercurial in your distribution's package repository is most likely old and broken. You might try this first:

    apt-get install python-setuptools python-dev build-essential

If that fails, try installing manually from the Mercurial Download 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. ***
    The compiler is 6g.

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.

## What's next

Start by taking A Tour of Go or reading the Go Tutorial.

For more detail about the process of building and testing Go programs read How to Write Go Code.

Build a web application by following the Wiki Codelab.

Read Effective Go to learn about writing idiomatic Go code.

For the full story, consult Go's extensive documentation.

## Community resources

For real-time help, there may be users or developers on `#go-nuts` on the Freenode IRC server.

The official mailing list for discussion of the Go language is Go Nuts.

Bugs can be reported using the Go issue tracker.

For those who wish to keep up with development, there is another mailing list, golang-checkins, that receives a message summarizing each checkin to the Go repository.

## Keeping up with releases

The Go project maintains two stable tags in its Mercurial repository: `release` and `weekly`. The `weekly` tag is updated about once a week, and should be used by those who want to track the project's development. The `release` tag is given, less often, to those weekly releases that have proven themselves to be robust.

Most Go users will want to keep their Go installation at the latest `release` tag. 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

To use the `weekly` tag run `hg update weekly` instead.

## Optional environment variables

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

`$GOROOT`

  The root of the Go tree, often `$HOME/go`. This defaults to the parent of the directory where `all.bash` is run. If you choose not to set `$GOROOT`, you must run `gomake` instead of `make` or `gmake` when developing Go programs using the conventional makefiles.

`$GOROOT_FINAL`

  The value assumed by installed binaries and scripts when `$GOROOT` is not set. It defaults to the value used for `$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 `$GOOS` are `darwin` (Mac OS X 10.5 and above), `freebsd`, `linux`, `netbsd`, `openbsd`, `plan9`, and `windows`. Choices for `$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 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.

`$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