Download the Native Client SDK

Follow the steps below to download and install the SDK:

Prerequisites:
- Make sure you have Python 2.6 or 2.7 installed, and that the Python executable is in your path.
  - On Mac/Linux, Python is probably preinstalled. Run the command "python ‑V" in a terminal window, and make sure that the version of Python you have is 2.6.x or 2.7.x (if it's not, upgrade to one of those versions).
  - On Windows, you may need to install Python. Go to http://www.python.org/download/ and select the latest 2.x version. In addition, be sure to add the Python directory (for example, C:\python27) to the PATH environment variable. After you've installed Python, run the command "python ‑V" in a Command Prompt window and verify that the version of Python you have is 2.6.x or 2.7.x.
  - Note that Python 3.x is not yet supported.
- On the Mac, you need to install the make command on your system before you can build and run the examples. One easy way to get make, along with several other useful tools, is to install Xcode Developer Tools. After installing Xcode, go to the Preferences menu, select Downloads and Components, and verify that Command Line Tools are installed. If you'd rather not install Xcode, you can download and build an open source version of make. In order to build the command you may also need to download and install a copy of gcc.
Download the SDK update utility: nacl_sdk.zip.
Unzip the SDK update utility:
- On Mac/Linux, run the command "unzip nacl_sdk.zip" in a Terminal window.
- On Windows, right-click on the .zip file and select "Extract All…". A dialog box will open; enter a location and click "Extract".
Unzipping the SDK update utility creates a directory called nacl_sdk with the following files and directories:
- naclsdk (and naclsdk.bat for Windows) – the front end of the update utility, i.e., the command you run to download the latest bundles
- sdk_cache – a directory with a manifest file that lists the bundles you have already downloaded
- sdk_tools – the back end of the update utility, also known as the "sdk_tools" bundle

Go to the nacl_sdk directory and run naclsdk with the "list" command to see a list of available bundles. The SDK includes a separate bundle for each version of Chrome/Pepper (see versioning information).

On Mac/Linux:

$ cd nacl_sdk
$ ./naclsdk list

On Windows:

> cd nacl_sdk
> naclsdk list

You should see output similar to this:

Available bundles:
  sdk_tools
    description: Native Client SDK Tools, revision 1.5
    stability: stable
    recommended: yes
    version: 1
    revision: 5
  pepper_14
    description: Chrome 14 bundle, revision 1052
    stability: stable
    recommended: yes
    version: 14
    revision: 1052
  pepper_15
    description: Chrome 15 bundle, revision 1208
    stability: beta
    recommended: no
    version: 15
    revision: 1208

Currently installed bundles:
  sdk_tools
    description: Native Client SDK Tools, revision 1.5
    stability: stable
    recommended: yes
    version: 1
    revision: 5

This sample output shows that there are three bundles available for download, and that you have already installed the latest revision of the sdk_tools bundle (it was included in the zip file you downloaded). In this example note that the pepper_15 bundle has the "recommended" attribute set to "no", meaning that the bundle is still experimental and not yet recommended for general use.

Run naclsdk with the "update" command to download particular bundles that are available.
On Mac/Linux:
```
$ ./naclsdk update
```
On Windows:
```
> naclsdk update
```
By default, naclsdk only downloads bundles that are recommended. Continuing with the earlier example, the "update" command would only download the sdk_tools and the pepper_14 bundles, since the pepper_15 bundle is not yet recommended. If you want the pepper_15 bundle, you must either ask for it explicitly, or ask to get all of the available bundles. Use one of the commands below:
```
$ ./naclsdk update pepper_15    # explicitly list the bundle you want to get, or
$ ./naclsdk update all          # get all available bundles, including experimental bundles
```
Continuing with the earlier example, if you run naclsdk with the "update all" command, you should see output similar to this:
```
sdk_tools is already up-to-date.
Updating bundle pepper_14 to version 14, revision 1052
Updating bundle pepper_15 to version 15, revision 1208
```
Note that the toolchains for Mac and Linux are around 150 MB, so the downloads can take a while, even on a fast Internet connection.

Run naclsdk with the "list" command again; this will show you the list of available bundles and verify which bundles are installed.

On Mac/Linux:

$ ./naclsdk list

On Windows:

> naclsdk list

Continuing with the earlier example, if you previously downloaded all of the available bundles, you should see output similar to this:

Available bundles:
  sdk_tools
    description: Native Client SDK Tools, revision 1.5
    stability: stable
    recommended: yes
    version: 1
    revision: 5
  pepper_14
    description: Chrome 14 bundle, revision 1052
    stability: stable
    recommended: yes
    version: 14
    revision: 1052
  pepper_15
    description: Chrome 15 bundle, revision 1208
    stability: beta
    recommended: no
    version: 15
    revision: 1208

Currently installed bundles:
  sdk_tools
    description: Native Client SDK Tools, revision 1.5
    stability: stable
    recommended: yes
    version: 1
    revision: 5
  pepper_14
    description: Chrome 14 bundle, revision 1052
    stability: stable
    recommended: yes
    version: 14
    revision: 1052
  pepper_15
    description: Chrome 15 bundle, revision 1208
    stability: beta
    recommended: no
    version: 15
    revision: 1208

Running naclsdk with the "update" command again will verify that your bundles are up-to-date, or warn if you there are new versions of previously installed bundles.
On Mac/Linux:
```
$ ./naclsdk update
```
On Windows:
```
> naclsdk update
```
Continuing with the earlier example in which the pepper_15 bundle is not yet recommended, you should see output similar to this:
```
sdk_tools is already up-to-date.
pepper_14 is already up-to-date.
```
If there is a new version of a previously installed bundle, the update utility will warn you with a message similar to this:
```
WARNING: pepper_14 already exists, but has an update available.
Run update with the --force option to overwrite the existing directory.
Warning: This will overwrite any modifications you have made within this directory.
```
To dowload the new version of a bundle and overwrite the existing directory for that bundle, run naclsdk with the --force option.

On Mac/Linux:
```
$ ./naclsdk update --force
```
On Windows:
```
> naclsdk update --force
```

Next steps:

Browse through the Release Notes for important information about the SDK and new bundles.
If you're just getting started with Native Client, we recommend reading the Technical Overview and walking through the Getting Started Tutorial.
If you'd rather dive into information about the toolchains, see Building Native Client Modules.