大資料時代之hadoop(一)：hadoop安裝

“兵馬未動，糧草先行”，要想深入的瞭解hadoop，我覺得啟動或停止hadoop的指令碼是必須要先了解的。說到底，hadoop就是一個分散式儲存和計算框架，但是這個分散式環境是如何啟動，管理的呢，我就帶著大家先從指令碼入手吧。說實話，hadoop的啟動指令碼寫的真好，裡面考慮的地方非常周全（比如說路徑中有空格，軟連線等）。

1、hadoop指令碼簡單介紹

   hadoop的指令碼分佈在$HADOOP_HOME下面的bin目錄下和conf資料夾下，主要介紹如下：

bin目錄下
        hadoop                 hadoop底層核心指令碼，所有分散式程式最終都是通過這個指令碼啟動的。
hadoop-config.sh       基本別的指令碼都會內嵌呼叫這個指令碼，這個指令碼作用就是解析命令列可選引數（--config ：hadoop conf資料夾路徑 和--hosts）
hadoop-daemon.sh       啟動或停止本機command引數所指定的分散式程式，通過呼叫hadoop指令碼實現。
hadoop-daemons.sh      啟動所有機器上的hadoop分散式程式，通過呼叫slaves.sh實現。
slaves.sh              在所有的機器上執行一組指定的命令（通過ssh無密碼登陸），供上層使用。
start-dfs.sh           在本機啟動namenode，在slaves機器上啟動datanode，在master機器上啟動secondarynamenode，通過呼叫hadoop-daemon.sh和hadoop-daemons.sh實現。
start-mapred.sh        在本機啟動jobtracker，在slaves機器上啟動tasktracker，通過呼叫hadoop-daemon.sh和hadoop-daemons.sh實現。
start-all.sh           啟動所有分散式hadoop程式，通過呼叫start-dfs.sh和start-mapred.sh實現。
start-balancer.sh      啟動hadoop分散式環境複雜均衡排程程式，平衡各節點儲存和處理能力。
還有幾個stop 指令碼，就不用詳細說了。

conf目錄下
hadoop-env.sh          配置hadoop執行時所需要的一些引數變數，比如JAVA_HOME,HADOOP_LOG_DIR,HADOOP_PID_DIR等。

2、指令碼的魅力（詳細解釋）

2.1、hadoop-config.sh

#軟連線解析
this="$0"
while [ -h "$this" ]; do
  ls=`ls -ld "$this"`
  link=`expr "$ls" : '.*-> \(.*\)$'`
  if expr "$link" : '.*/.*' > /dev/null; then
    this="$link"
  else
    this=`dirname "$this"`/"$link"
  fi
done

#絕對路徑解析
# convert relative path to absolute path
bin=`dirname "$this"`
script=`basename "$this"`
bin=`cd "$bin"; pwd`
this="$bin/$script"

# the root of the Hadoop installation
export HADOOP_HOME=`dirname "$this"`/..

#check to see if the conf dir is given as an optional argument
if [ $# -gt 1 ]
then
    if [ "--config" = "$1" ]
	  then
	      shift
	      confdir=$1
	      shift
	      HADOOP_CONF_DIR=$confdir
    fi
fi

#check to see it is specified whether to use the slaves or the
# masters file
if [ $# -gt 1 ]
then
    if [ "--hosts" = "$1" ]
    then
        shift
        slavesfile=$1
        shift
        export HADOOP_SLAVES="${HADOOP_CONF_DIR}/$slavesfile"
    fi
fi

# if no args specified, show usage
if [ $# = 0 ]; then
  echo "Usage: hadoop [--config confdir] COMMAND"
  echo "where COMMAND is one of:"
  echo "  namenode -format     format the DFS filesystem"
  echo "  secondarynamenode    run the DFS secondary namenode"
  echo "  namenode             run the DFS namenode"
  echo "  datanode             run a DFS datanode"
  echo "  dfsadmin             run a DFS admin client"
  echo "  mradmin              run a Map-Reduce admin client"
  echo "  fsck                 run a DFS filesystem checking utility"
  echo "  fs                   run a generic filesystem user client"
  echo "  balancer             run a cluster balancing utility"
  echo "  jobtracker           run the MapReduce job Tracker node" 
  echo "  pipes                run a Pipes job"
  echo "  tasktracker          run a MapReduce task Tracker node" 
  echo "  job                  manipulate MapReduce jobs"
  echo "  queue                get information regarding JobQueues" 
  echo "  version              print the version"
  echo "  jar <jar>            run a jar file"
  echo "  distcp <srcurl> <desturl> copy file or directories recursively"
  echo "  archive -archiveName NAME <src>* <dest> create a hadoop archive"
  echo "  daemonlog            get/set the log level for each daemon"
  echo " or"
  echo "  CLASSNAME            run the class named CLASSNAME"
  echo "Most commands print help when invoked w/o parameters."
  exit 1
fi

3、根據cmd設定執行時class

# figure out which class to run
if [ "$COMMAND" = "namenode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.namenode.NameNode'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_NAMENODE_OPTS"
elif [ "$COMMAND" = "secondarynamenode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_SECONDARYNAMENODE_OPTS"
elif [ "$COMMAND" = "datanode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.datanode.DataNode'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_DATANODE_OPTS"
elif [ "$COMMAND" = "fs" ] ; then
  CLASS=org.apache.hadoop.fs.FsShell
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "dfs" ] ; then
  CLASS=org.apache.hadoop.fs.FsShell
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "dfsadmin" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.DFSAdmin
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "mradmin" ] ; then
  CLASS=org.apache.hadoop.mapred.tools.MRAdmin
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "fsck" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.DFSck
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "balancer" ] ; then
  CLASS=org.apache.hadoop.hdfs.server.balancer.Balancer
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_BALANCER_OPTS"
elif [ "$COMMAND" = "jobtracker" ] ; then
  CLASS=org.apache.hadoop.mapred.JobTracker
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_JOBTRACKER_OPTS"
elif [ "$COMMAND" = "tasktracker" ] ; then
  CLASS=org.apache.hadoop.mapred.TaskTracker
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_TASKTRACKER_OPTS"
elif [ "$COMMAND" = "job" ] ; then
  CLASS=org.apache.hadoop.mapred.JobClient
elif [ "$COMMAND" = "queue" ] ; then
  CLASS=org.apache.hadoop.mapred.JobQueueClient
elif [ "$COMMAND" = "pipes" ] ; then
  CLASS=org.apache.hadoop.mapred.pipes.Submitter
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "version" ] ; then
  CLASS=org.apache.hadoop.util.VersionInfo
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "jar" ] ; then
  CLASS=org.apache.hadoop.util.RunJar
elif [ "$COMMAND" = "distcp" ] ; then
  CLASS=org.apache.hadoop.tools.DistCp
  CLASSPATH=${CLASSPATH}:${TOOL_PATH}
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "daemonlog" ] ; then
  CLASS=org.apache.hadoop.log.LogLevel
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "archive" ] ; then
  CLASS=org.apache.hadoop.tools.HadoopArchives
  CLASSPATH=${CLASSPATH}:${TOOL_PATH}
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
elif [ "$COMMAND" = "sampler" ] ; then
  CLASS=org.apache.hadoop.mapred.lib.InputSampler
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_CLIENT_OPTS"
else
  CLASS=$COMMAND
fi

# setup 'java.library.path' for native-hadoop code if necessary
JAVA_LIBRARY_PATH=''
if [ -d "${HADOOP_HOME}/build/native" -o -d "${HADOOP_HOME}/lib/native" ]; then
#通過執行一個java 類來決定當前平臺，挺有意思
  JAVA_PLATFORM=`CLASSPATH=${CLASSPATH} ${JAVA} -Xmx32m org.apache.hadoop.util.PlatformName | sed -e "s/ /_/g"`
  
  if [ -d "$HADOOP_HOME/build/native" ]; then
    JAVA_LIBRARY_PATH=${HADOOP_HOME}/build/native/${JAVA_PLATFORM}/lib
  fi
  
  if [ -d "${HADOOP_HOME}/lib/native" ]; then
    if [ "x$JAVA_LIBRARY_PATH" != "x" ]; then
      JAVA_LIBRARY_PATH=${JAVA_LIBRARY_PATH}:${HADOOP_HOME}/lib/native/${JAVA_PLATFORM}
    else
      JAVA_LIBRARY_PATH=${HADOOP_HOME}/lib/native/${JAVA_PLATFORM}
    fi
  fi
fi

 # run it
exec "$JAVA" $JAVA_HEAP_MAX $HADOOP_OPTS -classpath "$CLASSPATH" $CLASS "$@"

2.3、hadoop-daemon.sh       

usage="Usage: hadoop-daemon.sh [--config <conf-dir>] [--hosts hostlistfile] (start|stop) <hadoop-command> <args...>"

# if no args specified, show usage
if [ $# -le 1 ]; then
  echo $usage
  exit 1
fi

    首先內嵌執行hadoop-env.sh指令碼，然後設定HADOOP_PID_DIR等環境變數。

3、啟動或停止程式

case $startStop in

  (start)

    mkdir -p "$HADOOP_PID_DIR"

    if [ -f $pid ]; then
    #如果程式已經啟動的話，就停止，並退出。
      if kill -0 `cat $pid` > /dev/null 2>&1; then
        echo $command running as process `cat $pid`.  Stop it first.
        exit 1
      fi
    fi

    if [ "$HADOOP_MASTER" != "" ]; then
      echo rsync from $HADOOP_MASTER
      rsync -a -e ssh --delete --exclude=.svn --exclude='logs/*' --exclude='contrib/hod/logs/*' $HADOOP_MASTER/ "$HADOOP_HOME"
    fi
# rotate 當前已經存在的log
    hadoop_rotate_log $log
    echo starting $command, logging to $log
    cd "$HADOOP_HOME"
    #通過nohup 和bin/hadoop指令碼啟動相關程式
    nohup nice -n $HADOOP_NICENESS "$HADOOP_HOME"/bin/hadoop --config $HADOOP_CONF_DIR $command "$@" > "$log" 2>&1 < /dev/null &
    #獲取新啟動的程式pid並寫入到pid檔案中
    echo $! > $pid
    sleep 1; head "$log"
    ;;
          
  (stop)

    if [ -f $pid ]; then
      if kill -0 `cat $pid` > /dev/null 2>&1; then
        echo stopping $command
        kill `cat $pid`
      else
        echo no $command to stop
      fi
    else
      echo no $command to stop
    fi
    ;;

  (*)
    echo $usage
    exit 1
    ;;
esac

2.4、slaves.sh

      在所有的機器上執行一組指定的命令（通過ssh無密碼登陸），供上層使用。

1、宣告使用方法

usage="Usage: slaves.sh [--config confdir] command..."

# if no args specified, show usage
if [ $# -le 0 ]; then
  echo $usage
  exit 1
fi

# If the slaves file is specified in the command line,
# then it takes precedence over the definition in 
# hadoop-env.sh. Save it here.
HOSTLIST=$HADOOP_SLAVES

if [ -f "${HADOOP_CONF_DIR}/hadoop-env.sh" ]; then
  . "${HADOOP_CONF_DIR}/hadoop-env.sh"
fi

if [ "$HOSTLIST" = "" ]; then
  if [ "$HADOOP_SLAVES" = "" ]; then
    export HOSTLIST="${HADOOP_CONF_DIR}/slaves"
  else
    export HOSTLIST="${HADOOP_SLAVES}"
  fi
fi

#挺重要，裡面技術含量也挺高，對遠端主機檔案進行去除特殊字元和刪除空行；對命令列進行空格替換，並通過ssh在目標主機執行命令；最後等待命令在所有目標主機執行完後，退出。
for slave in `cat "$HOSTLIST"|sed  "s/#.*$//;/^$/d"`; do
 ssh $HADOOP_SSH_OPTS $slave $"${@// /\\ }" \
   2>&1 | sed "s/^/$slave: /" &
 if [ "$HADOOP_SLAVE_SLEEP" != "" ]; then
   sleep $HADOOP_SLAVE_SLEEP
 fi
done

wait

2.5、hadoop-daemons.sh

# Run a Hadoop command on all slave hosts.

usage="Usage: hadoop-daemons.sh [--config confdir] [--hosts hostlistfile] [start|stop] command args..."

# if no args specified, show usage
if [ $# -le 1 ]; then
  echo $usage
  exit 1
fi

 #通過salves.sh來實現
 exec "$bin/slaves.sh" --config $HADOOP_CONF_DIR cd "$HADOOP_HOME" \; "$bin/hadoop-daemon.sh" --config $HADOOP_CONF_DIR "$@"

      在本機（呼叫此指令碼的主機）啟動namenode，在slaves機器上啟動datanode，在master機器上啟動secondarynamenode，通過呼叫hadoop-daemon.sh和hadoop-daemons.sh實現。

1、宣告使用方式

# Start hadoop dfs daemons.
# Optinally upgrade or rollback dfs state.
# Run this on master node.

usage="Usage: start-dfs.sh [-upgrade|-rollback]"

# start dfs daemons
# start namenode after datanodes, to minimize time namenode is up w/o data
# note: datanodes will log connection errors until namenode starts
#在本機（呼叫此指令碼的主機）啟動namenode
"$bin"/hadoop-daemon.sh --config $HADOOP_CONF_DIR start namenode $nameStartOpt
#在slaves機器上啟動datanode
"$bin"/hadoop-daemons.sh --config $HADOOP_CONF_DIR start datanode $dataStartOpt
#在master機器上啟動secondarynamenode
"$bin"/hadoop-daemons.sh --config $HADOOP_CONF_DIR --hosts masters start secondarynamenode

2.7、start-mapred.sh 

 # start mapred daemons
# start jobtracker first to minimize connection errors at startup
#在本機（呼叫此指令碼的主機）啟動jobtracker
"$bin"/hadoop-daemon.sh --config $HADOOP_CONF_DIR start jobtracker
#在master機器上啟動tasktracker
"$bin"/hadoop-daemons.sh --config $HADOOP_CONF_DIR start tasktracker

其他的指令碼就都已經非常簡單了，不用再詳細說明了，只要看下，大致都能看懂。

對了，最後再說下hadoop的指令碼里面用的shell直譯器的宣告吧。

#!/usr/bin/env bash