go/doc/install-source.html

<!--{
	"Title": "Installing Go from source",
	"Path": "/install/source/"
}-->

<h2 id="introduction">Introduction</h2>

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

<div class="detail">

<p>
There are two official Go compiler tool chains.
This document focuses on the <code>gc</code> Go
compiler and tools (<code>6g</code>, <code>8g</code> etc.).
For information on how to use <code>gccgo</code>, a more traditional
compiler using the GCC back end, see
<a href="/install/gccgo/">Setting up and using gccgo</a>.
</p>

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

<dl>
<dt>
	<code>amd64</code> (a.k.a. <code>x86-64</code>); <code>6g,6l,6c,6a</code>
</dt>
<dd>
	The most mature implementation. The compiler has an effective
	optimizer (registerizer) and generates good code (although
	<code>gccgo</code> can do noticeably better sometimes).
</dd>
<dt>
	<code>386</code> (a.k.a. <code>x86</code> or <code>x86-32</code>); <code>8g,8l,8c,8a</code>
</dt>
<dd>
	Comparable to the <code>amd64</code> port.
</dd>
<dt>
	<code>arm</code> (a.k.a. <code>ARM</code>); <code>5g,5l,5c,5a</code>
</dt>
<dd>
	Supports only Linux binaries. Less tested than the other ports.
</dd>
</dl>

<p>
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.
</p>

<p>
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
<a href="#environment">environment variables</a> below.
</p>

</div>

<h2 id="ctools">Install C tools, if needed</h2>

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

<p>
On OS X, a C compiler can be installed as part of
<a href="http://developer.apple.com/Xcode/">Xcode</a>. 
</p>

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

<p>
<font color="red">TODO: add Windows compiler info</font>
</p>

<h2 id="mercurial">Install Mercurial, if needed</h2>

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

<pre>
sudo easy_install mercurial==2.0
</pre>

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

<pre>apt-get install python-setuptools python-dev build-essential</pre>

<p>
If that fails, try installing manually from the
<a href="http://mercurial.selenic.com/wiki/Download">Mercurial Download</a>
page.</p>
</p>

<p>
Mercurial versions 1.7.x and up require the configuration of
<a href="http://mercurial.selenic.com/wiki/CACertificates">Certification Authorities</a>
(CAs). Error messages of the form:
</p>

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

<p>
when using Mercurial indicate that the CAs are missing.
Check your Mercurial version (<code>hg --version</code>) and
<a href="http://mercurial.selenic.com/wiki/CACertificates#Configuration_of_HTTPS_certificate_authorities">configure the CAs</a>
if necessary.
</p>


<h2 id="fetch">Fetch the repository</h2>

<p>
<p>Go will install to a directory named <code>go</code>.
Change to the directory that will be its parent
and make sure the <code>go</code> directory does not exist.
Then check out the repository:</p>

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

<h2 id="install">Install Go</h2>

<p>
To build the Go distribution, run
</p>

<pre>
$ cd go/src
$ ./all.bash
</pre>

<p>
(To build under Windows use <code>all.bat</code>.)
</p>

<p>
If all goes well, it will finish by printing output like:
</p>

<pre>
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.
</pre>

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

<div class="detail">
<p>
For more information about ways to control the build, see the discussion of
<a href="#environment">environment variables</a> below.
</p>
</div>


<h2 id="testing">Testing your installation</h2>

<p>
Check that Go is installed correctly by building a simple program.
</p>

<p>
Create a file named <code>hello.go</code> and put the following program in it:
</p>

<pre>
package main

import "fmt"

func main() {
    fmt.Printf("hello, world\n")
}
</pre>

<p>
Then run it with the <code>go</code> tool:
</p>

<pre>
$ go run hello.go
hello, world
</pre>

<p>
If you see the "hello, world" message then Go is installed correctly.
</p>


<h2 id="next">What's next</h2>

<p>
Start by taking <a href="http://code.google.com/p/go-tour/">A Tour of Go</a>
or reading the <a href="/doc/go_tutorial.html">Go Tutorial</a>.
</p>

<p>
For more detail about the process of building and testing Go programs
read <a href="/doc/code.html">How to Write Go Code</a>.
</p>

<p>
Build a web application by following the <a href="/doc/codelab/wiki/">Wiki
Codelab</a>.
</p>

<p>
Read <a href="/doc/effective_go.html">Effective Go</a> to learn about writing
idiomatic Go code.
</p>

<p>
For the full story, consult Go's extensive 
<a href="/doc/">documentation</a>.
</p>


<h2 id="community">Community resources</h2>

<p>
For real-time help, there may be users or developers on
<code>#go-nuts</code> on the <a href="http://freenode.net/">Freenode</a> IRC server.
</p>

<p>
The official mailing list for discussion of the Go language is
<a href="http://groups.google.com/group/golang-nuts">Go Nuts</a>.
</p>

<p>
Bugs can be reported using the <a href="http://code.google.com/p/go/issues/list">Go issue tracker</a>.
</p>

<p>
For those who wish to keep up with development,
there is another mailing list, <a href="http://groups.google.com/group/golang-checkins">golang-checkins</a>,
that receives a message summarizing each checkin to the Go repository.
</p>


<h2 id="releases">Keeping up with releases</h2>

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

<p>
Most Go users will want to keep their Go installation at the latest
<code>release</code> tag.
New releases are announced on the
<a href="http://groups.google.com/group/golang-announce">golang-announce</a>
mailing list.
</p>

<p>
To update an existing tree to the latest release, you can run:
</p>

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

<p>
To use the <code>weekly</code> tag run <code>hg update weekly</code> instead.
</p>


<h2 id="environment">Optional environment variables</h2>

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

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

<dt>
	<code>$GOROOT_FINAL</code>
</dt>
<dd>
	<p>
	The value assumed by installed binaries and scripts when
	<code>$GOROOT</code> is not set.
	It defaults to the value used for <code>$GOROOT</code>.
	If you want to build the Go tree in one location
	but move it elsewhere after the build, set 
	<code>$GOROOT_FINAL</code> to the eventual location.
</dd>

<dt>
<code>$GOOS</code> and <code>$GOARCH</code>
</dt>
<dd>
	<p>
	The name of the target operating system and compilation architecture.
	These default to the values of <code>$GOHOSTOS</code> and
	<code>$GOHOSTARCH</code> respectively (described below).

	<p>
	Choices for <code>$GOOS</code> are
	<code>darwin</code> (Mac OS X 10.5 and above), <code>freebsd</code>,
	<code>linux</code>, <code>netbsd</code>, <code>openbsd</code>, 
	<code>plan9</code>, and <code>windows</code>.
	Choices for <code>$GOARCH</code> are
	<code>amd64</code> (64-bit x86, the most mature port),
	<code>386</code> (32-bit x86), and <code>arm</code> (32-bit ARM).
	The valid combinations of <code>$GOOS</code> and <code>$GOARCH</code> are:
	<table cellpadding="0">
	<tr>
	<th width="50"><th align="left" width="100"><code>$GOOS</code></th> <th align="left" width="100"><code>$GOARCH</code></th> <th align="left"></th>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>darwin</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>freebsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>linux</code></td> <td><code>arm</code></td>
	</tr>
	<tr>
	<td></td><td><code>netbsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>netbsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>openbsd</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>openbsd</code></td> <td><code>amd64</code></td>
	</tr>
	<tr>
	<td></td><td><code>plan9</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>windows</code></td> <td><code>386</code></td>
	</tr>
	<tr>
	<td></td><td><code>windows</code></td> <td><code>amd64</code></td>
	</tr>
	</table>
	<p>
</dd>

<dt>
<code>$GOHOSTOS</code> and <code>$GOHOSTARCH</code>
</dt>
<dd>
	<p>
	The name of the host operating system and compilation architecture.
	These default to the local system's operating system and
	architecture.

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

<dt>
<code>$GOBIN</code>
</dt>
<dd>
	<p>
	The location where binaries will be installed.
	The default is <code>$GOROOT/bin</code>.
	After installing, you will want to arrange to add this
	directory to your <code>$PATH</code>, so you can use the tools.
</dd>

<dt>
<code>$GOARM</code> (arm, default=6)
</dt>
<dd>
	<p>
	The ARM architecture version the run-time libraries should target.
	Setting <code>$GOARM</code> to 5 causes the linker to emit calls
	to a software floating point implementation instead of using
	hardware floating point support.
</dd>
</dl>

<p>
Note that <code>$GOARCH</code> and <code>$GOOS</code> identify the
<em>target</em> 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 <code>GOARCH</code> to <code>386</code>,
not <code>amd64</code>.
</p>

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

<pre>
export GOROOT=$HOME/go
export GOARCH=amd64
export GOOS=linux
</pre>