Build instructions for Hadoop

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Requirements:

* Unix System
* JDK 1.6+
* Maven 3.0 or later
* Findbugs 1.3.9 (if running findbugs)
* ProtocolBuffer 2.5.0
* CMake 2.6 or newer (if compiling native code)
* Internet connection for first build (to fetch all Maven and Hadoop dependencies)

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Maven main modules:

  hadoop                            (Main Hadoop project)
         - hadoop-project           (Parent POM for all Hadoop Maven modules.             )
                                    (All plugins & dependencies versions are defined here.)
         - hadoop-project-dist      (Parent POM for modules that generate distributions.)
         - hadoop-annotations       (Generates the Hadoop doclet used to generated the Javadocs)
         - hadoop-assemblies        (Maven assemblies used by the different modules)
         - hadoop-common-project    (Hadoop Common)
         - hadoop-hdfs-project      (Hadoop HDFS)
         - hadoop-mapreduce-project (Hadoop MapReduce)
         - hadoop-tools             (Hadoop tools like Streaming, Distcp, etc.)
         - hadoop-dist              (Hadoop distribution assembler)

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Where to run Maven from?

  It can be run from any module. The only catch is that if not run from utrunk
  all modules that are not part of the build run must be installed in the local
  Maven cache or available in a Maven repository.

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Maven build goals:

 * Clean                     : mvn clean
 * Compile                   : mvn compile [-Pnative]
 * Run tests                 : mvn test [-Pnative]
 * Create JAR                : mvn package
 * Run findbugs              : mvn compile findbugs:findbugs
 * Run checkstyle            : mvn compile checkstyle:checkstyle
 * Install JAR in M2 cache   : mvn install
 * Deploy JAR to Maven repo  : mvn deploy
 * Run clover                : mvn test -Pclover [-DcloverLicenseLocation=${user.name}/.clover.license]
 * Run Rat                   : mvn apache-rat:check
 * Build javadocs            : mvn javadoc:javadoc
 * Build distribution        : mvn package [-Pdist][-Pdocs][-Psrc][-Pnative][-Dtar]
 * Change Hadoop version     : mvn versions:set -DnewVersion=NEWVERSION

 Build options:

  * Use -Pnative to compile/bundle native code
  * Use -Pdocs to generate & bundle the documentation in the distribution (using -Pdist)
  * Use -Psrc to create a project source TAR.GZ
  * Use -Dtar to create a TAR with the distribution (using -Pdist)

 Snappy build options:

   Snappy is a compression library that can be utilized by the native code.
   It is currently an optional component, meaning that Hadoop can be built with
   or without this dependency.

  * Use -Drequire.snappy to fail the build if libsnappy.so is not found.
    If this option is not specified and the snappy library is missing,
    we silently build a version of libhadoop.so that cannot make use of snappy.
    This option is recommended if you plan on making use of snappy and want
    to get more repeatable builds.

  * Use -Dsnappy.prefix to specify a nonstandard location for the libsnappy
    header files and library files. You do not need this option if you have
    installed snappy using a package manager.
  * Use -Dsnappy.lib to specify a nonstandard location for the libsnappy library
    files.  Similarly to snappy.prefix, you do not need this option if you have
    installed snappy using a package manager.
  * Use -Dbundle.snappy to copy the contents of the snappy.lib directory into
    the final tar file. This option requires that -Dsnappy.lib is also given,
    and it ignores the -Dsnappy.prefix option.

   Tests options:

  * Use -DskipTests to skip tests when running the following Maven goals:
    'package',  'install', 'deploy' or 'verify'
  * -Dtest=<TESTCLASSNAME>,<TESTCLASSNAME#METHODNAME>,....
  * -Dtest.exclude=<TESTCLASSNAME>
  * -Dtest.exclude.pattern=**/<TESTCLASSNAME1>.java,**/<TESTCLASSNAME2>.java

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Building components separately

If you are building a submodule directory, all the hadoop dependencies this
submodule has will be resolved as all other 3rd party dependencies. This is,
from the Maven cache or from a Maven repository (if not available in the cache
or the SNAPSHOT 'timed out').
An alternative is to run 'mvn install -DskipTests' from Hadoop source top
level once; and then work from the submodule. Keep in mind that SNAPSHOTs
time out after a while, using the Maven '-nsu' will stop Maven from trying
to update SNAPSHOTs from external repos.

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Protocol Buffer compiler

The version of Protocol Buffer compiler, protoc, must match the version of the
protobuf JAR.

If you have multiple versions of protoc in your system, you can set in your 
build shell the HADOOP_PROTOC_PATH environment variable to point to the one you 
want to use for the Hadoop build. If you don't define this environment variable,
protoc is looked up in the PATH.
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Importing projects to eclipse

When you import the project to eclipse, install hadoop-maven-plugins at first.

  $ cd hadoop-maven-plugins
  $ mvn install

Then, generate eclipse project files.

  $ mvn eclipse:eclipse -DskipTests

At last, import to eclipse by specifying the root directory of the project via
[File] > [Import] > [Existing Projects into Workspace].

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Building distributions:

Create binary distribution without native code and without documentation:

  $ mvn package -Pdist -DskipTests -Dtar

Create binary distribution with native code and with documentation:

  $ mvn package -Pdist,native,docs -DskipTests -Dtar

Create source distribution:

  $ mvn package -Psrc -DskipTests

Create source and binary distributions with native code and documentation:

  $ mvn package -Pdist,native,docs,src -DskipTests -Dtar

Create a local staging version of the website (in /tmp/hadoop-site)

  $ mvn clean site; mvn site:stage -DstagingDirectory=/tmp/hadoop-site

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Handling out of memory errors in builds

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If the build process fails with an out of memory error, you should be able to fix
it by increasing the memory used by maven -which can be done via the environment
variable MAVEN_OPTS.

Here is an example setting to allocate between 256 and 512 MB of heap space to
Maven

export MAVEN_OPTS="-Xms256m -Xmx512m"

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Building on OS/X

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A one-time manual step is required to enable building Hadoop OS X with Java 7
every time the JDK is updated.
see: https://issues.apache.org/jira/browse/HADOOP-9350

$ sudo mkdir `/usr/libexec/java_home`/Classes
$ sudo ln -s `/usr/libexec/java_home`/lib/tools.jar `/usr/libexec/java_home`/Classes/classes.jar

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Building on Windows

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Requirements:

* Windows System
* JDK 1.6+
* Maven 3.0 or later
* Findbugs 1.3.9 (if running findbugs)
* ProtocolBuffer 2.5.0
* Windows SDK or Visual Studio 2010 Professional
* Unix command-line tools from GnuWin32 or Cygwin: sh, mkdir, rm, cp, tar, gzip
* Internet connection for first build (to fetch all Maven and Hadoop dependencies)

If using Visual Studio, it must be Visual Studio 2010 Professional (not 2012).
Do not use Visual Studio Express.  It does not support compiling for 64-bit,
which is problematic if running a 64-bit system.  The Windows SDK is free to
download here:

http://www.microsoft.com/en-us/download/details.aspx?id=8279

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Building:

Keep the source code tree in a short path to avoid running into problems related
to Windows maximum path length limitation.  (For example, C:\hdc).

Run builds from a Windows SDK Command Prompt.  (Start, All Programs,
Microsoft Windows SDK v7.1, Windows SDK 7.1 Command Prompt.)

JAVA_HOME must be set, and the path must not contain spaces.  If the full path
would contain spaces, then use the Windows short path instead.

You must set the Platform environment variable to either x64 or Win32 depending
on whether you're running a 64-bit or 32-bit system.  Note that this is
case-sensitive.  It must be "Platform", not "PLATFORM" or "platform".
Environment variables on Windows are usually case-insensitive, but Maven treats
them as case-sensitive.  Failure to set this environment variable correctly will
cause msbuild to fail while building the native code in hadoop-common.

set Platform=x64 (when building on a 64-bit system)
set Platform=Win32 (when building on a 32-bit system)

Several tests require that the user must have the Create Symbolic Links
privilege.

All Maven goals are the same as described above with the exception that
native code is built by enabling the 'native-win' Maven profile. -Pnative-win 
is enabled by default when building on Windows since the native components 
are required (not optional) on Windows.

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Building distributions:

 * Build distribution with native code    : mvn package [-Pdist][-Pdocs][-Psrc][-Dtar]