1.概述
最近，有小伙伴涉及到源码编译。然而，在编译期间也是遇到各种坑，在求助于搜索引擎，技术博客，也是难以解决自身所遇到的问题。笔者在被询问多 次的情况下，今天打算为大家来写一篇文章来剖析下编译的细节，以及遇到编译问题后，应该如何去解决这样类似的问题。因为，编译的问题，对于后期业务拓展， 二次开发，编译打包是一个基本需要面临的问题。
2.编译准备
在编译源码之前，我们需要准备编译所需要的基本环境。下面给大家列举本次编译的基础环境，如下所示：
- 硬件环境
| 操作系统 | CentOS6.6 |
| CPU | I7 |
| 内存 | 16G |
| 硬盘 | 闪存 |
| 核数 | 4核 |
- 软件环境
| JDK | 1.7 |
| Maven | 3.2.3 |
| ANT | 1.9.6 |
| Protobuf | 2.5.0 |
在准备好这些环境之后，我们需要去将这些环境安装到操作系统当中。步骤如下：
2.1 基础环境安装
关于JDK，Maven，ANT的安装较为简单，这里就不多做赘述了，将其对应的压缩包解压，然后在/etc/profile文件当中添加对应 的路径到PATH中即可。下面笔者给大家介绍安装Protobuf，其安装需要对Protobuf进行编译，故我们需要编译的依赖环境gcc、gcc- c++、cmake、openssl-devel、ncurses-devel，安装命令如下所示：
yum -y install gcc
yum -y install gcc-c++
yum -y install cmake
yum -y install openssl-devel
yum -y install ncurses-devel验证GCC是否安装成功，命令如下所示：
验证Make核CMake是否安装成功，命令如下所示：
在准备完这些环境之后，开始去编译Protobuf，编译命令如下所示：
[hadoop@nna ~]$ cd protobuf-2.5.0/
[hadoop@nna protobuf-2.5.0]$ ./configure --prefix=/usr/local/protoc
[hadoop@nna protobuf-2.5.0]$ make
[hadoop@nna protobuf-2.5.0]$ make installPS：这里安装的时候有可能提示权限不足，若出现该类问题，使用sudo进行安装。
验证Protobuf安装是否成功，命令如下所示：
下面，我们开始进入编译环境，在编译的过程当中会遇到很多问题，大家遇到问题的时候，要认真的去分析这些问题产生的原因，这里先给大家列举一些 可以避免的问题，在使用Maven进行编译的时候，若使用默认的JVM参数，在编译到hadoop-hdfs模块的时候，会出现溢出现象。异常信息如下所 示：
java.lang.OutOfMemoryError: Java heap space 这里，我们在编译Hadoop源码之前，可以先去环境变量中设置其参数即可，内容修改如下：
export MAVEN_OPTS="-Xms256m -Xmx512m"
接下来，我们进入到Hadoop的源码，这里笔者使用的是Hadoop2.6的源码进行编译，更高版本的源码进行编译，估计会有些许差异，编译命令如下所示：
[hadoop@nna tar]$ cd hadoop-2.6.0-src
[hadoop@nna tar]$ mvn package -DskipTests -Pdist,nativePS：这里笔者是直接将其编译为文件夹，若需要编译成tar包，可以在后面加上tar的参数，命令为 mvn package -DskipTests -Pdist,native -Dtar
笔者在编译过程当中，出现过在编译KMS模块时，下载tomcat不完全的问题，Hadoop采用的tomcat是apache- tomcat-6.0.41.tar.gz，若是在此模块下出现异常，可以使用一下命令查看tomcat的文件大小，该文件正常大小为6.9M左右。查看 命令如下所示：
[hadoop@nna downloads]$ du -sh *
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary:
[INFO]
[INFO] Apache Hadoop Main ................................. SUCCESS [ 1.162 s]
[INFO] Apache Hadoop Project POM .......................... SUCCESS [ 0.690 s]
[INFO] Apache Hadoop Annotations .......................... SUCCESS [ 1.589 s]
[INFO] Apache Hadoop Assemblies ........................... SUCCESS [ 0.164 s]
[INFO] Apache Hadoop Project Dist POM ..................... SUCCESS [ 1.064 s]
[INFO] Apache Hadoop Maven Plugins ........................ SUCCESS [ 2.260 s]
[INFO] Apache Hadoop MiniKDC .............................. SUCCESS [ 1.492 s]
[INFO] Apache Hadoop Auth ................................. SUCCESS [ 2.233 s]
[INFO] Apache Hadoop Auth Examples ........................ SUCCESS [ 2.102 s]
[INFO] Apache Hadoop Common ............................... SUCCESS [01:00 min]
[INFO] Apache Hadoop NFS .................................. SUCCESS [ 3.891 s]
[INFO] Apache Hadoop KMS .................................. SUCCESS [ 5.872 s]
[INFO] Apache Hadoop Common Project ....................... SUCCESS [ 0.019 s]
[INFO] Apache Hadoop HDFS ................................. SUCCESS [04:04 min]
[INFO] Apache Hadoop HttpFS ............................... SUCCESS [01:47 min]
[INFO] Apache Hadoop HDFS BookKeeper Journal .............. SUCCESS [04:58 min]
[INFO] Apache Hadoop HDFS-NFS ............................. SUCCESS [ 2.492 s]
[INFO] Apache Hadoop HDFS Project ......................... SUCCESS [ 0.020 s]
[INFO] hadoop-yarn ........................................ SUCCESS [ 0.018 s]
[INFO] hadoop-yarn-api .................................... SUCCESS [01:05 min]
[INFO] hadoop-yarn-common ................................. SUCCESS [01:00 min]
[INFO] hadoop-yarn-server ................................. SUCCESS [ 0.029 s]
[INFO] hadoop-yarn-server-common .......................... SUCCESS [01:03 min]
[INFO] hadoop-yarn-server-nodemanager ..................... SUCCESS [01:10 min]
[INFO] hadoop-yarn-server-web-proxy ....................... SUCCESS [ 1.810 s]
[INFO] hadoop-yarn-server-applicationhistoryservice ....... SUCCESS [ 4.041 s]
[INFO] hadoop-yarn-server-resourcemanager ................. SUCCESS [ 11.739 s]
[INFO] hadoop-yarn-server-tests ........................... SUCCESS [ 3.332 s]
[INFO] hadoop-yarn-client ................................. SUCCESS [ 4.762 s]
[INFO] hadoop-yarn-applications ........................... SUCCESS [ 0.017 s]
[INFO] hadoop-yarn-applications-distributedshell .......... SUCCESS [ 1.586 s]
[INFO] hadoop-yarn-applications-unmanaged-am-launcher ..... SUCCESS [ 1.233 s]
[INFO] hadoop-yarn-site ................................... SUCCESS [ 0.018 s]
[INFO] hadoop-yarn-registry ............................... SUCCESS [ 3.270 s]
[INFO] hadoop-yarn-project ................................ SUCCESS [ 2.164 s]
[INFO] hadoop-mapreduce-client ............................ SUCCESS [ 0.032 s]
[INFO] hadoop-mapreduce-client-core ....................... SUCCESS [ 13.047 s]
[INFO] hadoop-mapreduce-client-common ..................... SUCCESS [ 10.890 s]
[INFO] hadoop-mapreduce-client-shuffle .................... SUCCESS [ 2.534 s]
[INFO] hadoop-mapreduce-client-app ........................ SUCCESS [ 6.429 s]
[INFO] hadoop-mapreduce-client-hs ......................... SUCCESS [ 4.866 s]
[INFO] hadoop-mapreduce-client-jobclient .................. SUCCESS [02:04 min]
[INFO] hadoop-mapreduce-client-hs-plugins ................. SUCCESS [ 1.183 s]
[INFO] Apache Hadoop MapReduce Examples ................... SUCCESS [ 3.655 s]
[INFO] hadoop-mapreduce ................................... SUCCESS [ 1.775 s]
[INFO] Apache Hadoop MapReduce Streaming .................. SUCCESS [ 11.478 s]
[INFO] Apache Hadoop Distributed Copy ..................... SUCCESS [ 15.399 s]
[INFO] Apache Hadoop Archives ............................. SUCCESS [ 1.359 s]
[INFO] Apache Hadoop Rumen ................................ SUCCESS [ 3.736 s]
[INFO] Apache Hadoop Gridmix .............................. SUCCESS [ 2.822 s]
[INFO] Apache Hadoop Data Join ............................ SUCCESS [ 1.791 s]
[INFO] Apache Hadoop Ant Tasks ............................ SUCCESS [ 1.350 s]
[INFO] Apache Hadoop Extras ............................... SUCCESS [ 1.858 s]
[INFO] Apache Hadoop Pipes ................................ SUCCESS [ 5.805 s]
[INFO] Apache Hadoop OpenStack support .................... SUCCESS [ 3.061 s]
[INFO] Apache Hadoop Amazon Web Services support .......... SUCCESS [07:14 min]
[INFO] Apache Hadoop Client ............................... SUCCESS [ 2.986 s]
[INFO] Apache Hadoop Mini-Cluster ......................... SUCCESS [ 0.053 s]
[INFO] Apache Hadoop Scheduler Load Simulator ............. SUCCESS [ 2.917 s]
[INFO] Apache Hadoop Tools Dist ........................... SUCCESS [ 5.702 s]
[INFO] Apache Hadoop Tools ................................ SUCCESS [ 0.015 s]
[INFO] Apache Hadoop Distribution ......................... SUCCESS [ 8.587 s]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 28:25 min
[INFO] Finished at: 2015-10-22T15:12:10+08:00
[INFO] Final Memory: 89M/451M
[INFO] ------------------------------------------------------------------------在编译完成之后，会在Hadoop源码的dist目录下生成编译好的文件，如下图所示：
图中hadoop-2.6.0即表示编译好的文件。
3.总结
在编译的过程当中，会出现各种各样的问题，有些问题可以借助搜索引擎去帮助我们解决，有些问题搜索引擎却难以直接的给出解决方案，这时，我们需 要冷静的分析编译错误信息，大胆的去猜测，然后去求证我们的想法。简而言之，解决问题的方法是有很多的。当然，大家也可以在把遇到的编译问题，贴在评论下 方，供后来者参考或借鉴。
4.结束语
这篇文章就和大家分享到这里，如果大家在研究和学习的过程中有什么疑问，可以加群进行讨论或发送邮件给我，我会尽我所能为您解答，与君共勉！
