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Hadoop源碼分析三啟動及腳本剖析

 更新時(shí)間：2021年09月02日 17:24:07   作者：huserblog  
本篇是Hadoop源碼分析系列文章第三篇，主要介紹Hadoop啟動以及腳本的剖析，后續(xù)本系列文章會持續(xù)更新，有需要的朋友可以借鑒參考下

1、 啟動

hadoop的啟動是通過其sbin目錄下的腳本來啟動的。與啟動相關(guān)的叫腳本有以下幾個：

start-all.sh、start-dfs.sh、start-yarn.sh、hadoop-daemon.sh、yarn-daemon.sh。

hadoop-daemon.sh是用來啟動與hdfs相關(guān)的服務(wù)的

yarn-daemon.sh是用來啟動和yarn相關(guān)的服務(wù)

start-dfs.sh是用來啟動hdfs集群的

start-yarn.sh是用來啟動yarn集群

start-all.sh是用來啟動yarn和hdfs集群的

這幾個start開頭的腳本都是通過調(diào)用那兩個daemon腳本來啟動的。

2、 腳本分析

這里先從start-all.sh開始分析，然后逐步分析其腳本的調(diào)用。

start-all.sh腳本內(nèi)容如下：

#!/usr/bin/env bash

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# Start all hadoop daemons.  Run this on master node.

echo "This script is Deprecated. Instead use start-dfs.sh and start-yarn.sh"

bin=`dirname "${BASH_SOURCE-$0}"`
bin=`cd "$bin"; pwd`

DEFAULT_LIBEXEC_DIR="$bin"/../libexec
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh

# start hdfs daemons if hdfs is present
if [ -f "${HADOOP_HDFS_HOME}"/sbin/start-dfs.sh ]; then
  "${HADOOP_HDFS_HOME}"/sbin/start-dfs.sh --config $HADOOP_CONF_DIR
fi

# start yarn daemons if yarn is present
if [ -f "${HADOOP_YARN_HOME}"/sbin/start-yarn.sh ]; then
  "${HADOOP_YARN_HOME}"/sbin/start-yarn.sh --config $HADOOP_CONF_DIR
fi

這個腳本的重點(diǎn)在第31行到末尾，這里是兩個if語句，第一個if語句里（第34行）調(diào)用的是start-dfs.sh腳本，第二個if語句里（第37行）調(diào)用的是start-yarn.sh。

然后我們以start-dfs.sh為例，繼續(xù)向下分析。

start-dfs.sh的內(nèi)容如下：

#!/usr/bin/env bash

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


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

usage="Usage: start-dfs.sh [-upgrade|-rollback] [other options such as -clusterId]"

bin=`dirname "${BASH_SOURCE-$0}"`
bin=`cd "$bin"; pwd`

DEFAULT_LIBEXEC_DIR="$bin"/../libexec
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hdfs-config.sh

# get arguments
if [[ $# -ge 1 ]]; then
  startOpt="$1"
  shift
  case "$startOpt" in
    -upgrade)
      nameStartOpt="$startOpt"
    ;;
    -rollback)
      dataStartOpt="$startOpt"
    ;;
    *)
      echo $usage
      exit 1
    ;;
  esac
fi

#Add other possible options
nameStartOpt="$nameStartOpt $@"

#---------------------------------------------------------
# namenodes

NAMENODES=$($HADOOP_PREFIX/bin/hdfs getconf -namenodes)

echo "Starting namenodes on [$NAMENODES]"

"$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
  --config "$HADOOP_CONF_DIR" \
  --hostnames "$NAMENODES" \
  --script "$bin/hdfs" start namenode $nameStartOpt

#---------------------------------------------------------
# datanodes (using default slaves file)

if [ -n "$HADOOP_SECURE_DN_USER" ]; then
  echo \
    "Attempting to start secure cluster, skipping datanodes. " \
    "Run start-secure-dns.sh as root to complete startup."
else
  "$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
    --config "$HADOOP_CONF_DIR" \
    --script "$bin/hdfs" start datanode $dataStartOpt
fi

#---------------------------------------------------------
# secondary namenodes (if any)

SECONDARY_NAMENODES=$($HADOOP_PREFIX/bin/hdfs getconf -secondarynamenodes 2>/dev/null)

if [ -n "$SECONDARY_NAMENODES" ]; then
  echo "Starting secondary namenodes [$SECONDARY_NAMENODES]"

  "$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
      --config "$HADOOP_CONF_DIR" \
      --hostnames "$SECONDARY_NAMENODES" \
      --script "$bin/hdfs" start secondarynamenode
fi

#---------------------------------------------------------
# quorumjournal nodes (if any)

SHARED_EDITS_DIR=$($HADOOP_PREFIX/bin/hdfs getconf -confKey dfs.namenode.shared.edits.dir 2>&-)

case "$SHARED_EDITS_DIR" in
qjournal://*)
  JOURNAL_NODES=$(echo "$SHARED_EDITS_DIR" | sed 's,qjournal://\([^/]*\)/.*,\1,g; s/;/ /g; s/:[0-9]*//g')
  echo "Starting journal nodes [$JOURNAL_NODES]"
  "$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
      --config "$HADOOP_CONF_DIR" \
      --hostnames "$JOURNAL_NODES" \
      --script "$bin/hdfs" start journalnode ;;
esac

#---------------------------------------------------------
# ZK Failover controllers, if auto-HA is enabled
AUTOHA_ENABLED=$($HADOOP_PREFIX/bin/hdfs getconf -confKey dfs.ha.automatic-failover.enabled)
if [ "$(echo "$AUTOHA_ENABLED" | tr A-Z a-z)" = "true" ]; then
  echo "Starting ZK Failover Controllers on NN hosts [$NAMENODES]"
  "$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
    --config "$HADOOP_CONF_DIR" \
    --hostnames "$NAMENODES" \
    --script "$bin/hdfs" start zkfc
fi

# eof

 首先是第23行到30行，這里是在處理hadoop的路徑。

然后是第32行到51行是在處理腳本傳入的參數(shù)。最后就啟動hdfs的各個角色了。

首先啟動的是namenode，在第60行到63行，這段代碼是調(diào)用了hadoop-daemons.sh腳本來啟動，這個腳本和之前提到的hadoop-daemon.sh腳本的區(qū)別在于這個腳本可以在集群的其他機(jī)器上啟動該啟動的角色，而hadoop-daemon.sh只能啟動當(dāng)前機(jī)器上的角色。其實(shí)hadoop-daemons.sh也是通過調(diào)用hadoop-daemon.sh來啟動的，這個稍后再分析。這個腳本還有幾個參數(shù)，其中最重要的是：start namenode。它表示啟動namenode。

然后是第65行到第76行，這里是在啟動datanode，啟動的方式和namenode相同。啟動DataNode的代碼在第73行。

然后是第78行到第90行，這里在啟動secondarynamenode。如果是配置了namenode的高可用，secondarynamenode便不會啟動。

然后是第92行到第105行，這里在啟動journalnode。如果配置了namenode的高可用，journalnode才會啟動。

最后是第107行到末尾，這里啟動的是zkfc。同樣這個也是要配置高可用才會啟動。

如果按照文檔（2）中配置的高可用來看，這里啟動的角色應(yīng)該為：namenode、datanode、journalnode、zkfc。

啟動上述角色調(diào)用的hadoop-daemons.sh腳本內(nèi)容如下：

#!/usr/bin/env bash
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# 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 $usage
  exit 1
fi
bin=`dirname "${BASH_SOURCE-$0}"`
bin=`cd "$bin"; pwd`
DEFAULT_LIBEXEC_DIR="$bin"/../libexec
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh
exec "$bin/slaves.sh" --config $HADOOP_CONF_DIR cd "$HADOOP_PREFIX" \; "$bin/hadoop-daemon.sh" --config $HADOOP_CONF_DIR "$@"

這個腳本的重點(diǎn)在最后一行。這里有兩個腳本slaves.sh和hadoop-daemon.sh。slaves.sh腳本會使用ssh登錄到指定的服務(wù)器中然后執(zhí)行其中的hadoop-daemon.sh腳本。這里就不分析slaves.sh腳本了。

我們繼續(xù)看hadoop-daemon.sh腳本。

其內(nèi)容如下：

#!/usr/bin/env bash

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


# Runs a Hadoop command as a daemon.
#
# Environment Variables
#
#   HADOOP_CONF_DIR  Alternate conf dir. Default is ${HADOOP_PREFIX}/conf.
#   HADOOP_LOG_DIR   Where log files are stored.  PWD by default.
#   HADOOP_MASTER    host:path where hadoop code should be rsync'd from
#   HADOOP_PID_DIR   The pid files are stored. /tmp by default.
#   HADOOP_IDENT_STRING   A string representing this instance of hadoop. $USER by default
#   HADOOP_NICENESS The scheduling priority for daemons. Defaults to 0.
##

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

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

bin=`dirname "${BASH_SOURCE-$0}"`
bin=`cd "$bin"; pwd`

DEFAULT_LIBEXEC_DIR="$bin"/../libexec
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh

# get arguments

#default value
hadoopScript="$HADOOP_PREFIX"/bin/hadoop
if [ "--script" = "$1" ]
  then
    shift
    hadoopScript=$1
    shift
fi
startStop=$1
shift
command=$1
shift

hadoop_rotate_log ()
{
    log=$1;
    num=5;
    if [ -n "$2" ]; then
	num=$2
    fi
    if [ -f "$log" ]; then # rotate logs
	while [ $num -gt 1 ]; do
	    prev=`expr $num - 1`
	    [ -f "$log.$prev" ] && mv "$log.$prev" "$log.$num"
	    num=$prev
	done
	mv "$log" "$log.$num";
    fi
}

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

# Determine if we're starting a secure datanode, and if so, redefine appropriate variables
if [ "$command" == "datanode" ] && [ "$EUID" -eq 0 ] && [ -n "$HADOOP_SECURE_DN_USER" ]; then
  export HADOOP_PID_DIR=$HADOOP_SECURE_DN_PID_DIR
  export HADOOP_LOG_DIR=$HADOOP_SECURE_DN_LOG_DIR
  export HADOOP_IDENT_STRING=$HADOOP_SECURE_DN_USER
  starting_secure_dn="true"
fi

#Determine if we're starting a privileged NFS, if so, redefine the appropriate variables
if [ "$command" == "nfs3" ] && [ "$EUID" -eq 0 ] && [ -n "$HADOOP_PRIVILEGED_NFS_USER" ]; then
    export HADOOP_PID_DIR=$HADOOP_PRIVILEGED_NFS_PID_DIR
    export HADOOP_LOG_DIR=$HADOOP_PRIVILEGED_NFS_LOG_DIR
    export HADOOP_IDENT_STRING=$HADOOP_PRIVILEGED_NFS_USER
    starting_privileged_nfs="true"
fi

if [ "$HADOOP_IDENT_STRING" = "" ]; then
  export HADOOP_IDENT_STRING="$USER"
fi


# get log directory
if [ "$HADOOP_LOG_DIR" = "" ]; then
  export HADOOP_LOG_DIR="$HADOOP_PREFIX/logs"
fi

if [ ! -w "$HADOOP_LOG_DIR" ] ; then
  mkdir -p "$HADOOP_LOG_DIR"
  chown $HADOOP_IDENT_STRING $HADOOP_LOG_DIR
fi

if [ "$HADOOP_PID_DIR" = "" ]; then
  HADOOP_PID_DIR=/tmp
fi

# some variables
export HADOOP_LOGFILE=hadoop-$HADOOP_IDENT_STRING-$command-$HOSTNAME.log
export HADOOP_ROOT_LOGGER=${HADOOP_ROOT_LOGGER:-"INFO,RFA"}
export HADOOP_SECURITY_LOGGER=${HADOOP_SECURITY_LOGGER:-"INFO,RFAS"}
export HDFS_AUDIT_LOGGER=${HDFS_AUDIT_LOGGER:-"INFO,NullAppender"}
log=$HADOOP_LOG_DIR/hadoop-$HADOOP_IDENT_STRING-$command-$HOSTNAME.out
pid=$HADOOP_PID_DIR/hadoop-$HADOOP_IDENT_STRING-$command.pid
HADOOP_STOP_TIMEOUT=${HADOOP_STOP_TIMEOUT:-5}

# Set default scheduling priority
if [ "$HADOOP_NICENESS" = "" ]; then
    export HADOOP_NICENESS=0
fi

case $startStop in

  (start)

    [ -w "$HADOOP_PID_DIR" ] ||  mkdir -p "$HADOOP_PID_DIR"

    if [ -f $pid ]; then
      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_PREFIX"
    fi

    hadoop_rotate_log $log
    echo starting $command, logging to $log
    cd "$HADOOP_PREFIX"
    case $command in
      namenode|secondarynamenode|datanode|journalnode|dfs|dfsadmin|fsck|balancer|zkfc)
        if [ -z "$HADOOP_HDFS_HOME" ]; then
          hdfsScript="$HADOOP_PREFIX"/bin/hdfs
        else
          hdfsScript="$HADOOP_HDFS_HOME"/bin/hdfs
        fi
        nohup nice -n $HADOOP_NICENESS $hdfsScript --config $HADOOP_CONF_DIR $command "$@" > "$log" 2>&1 < /dev/null &
      ;;
      (*)
        nohup nice -n $HADOOP_NICENESS $hadoopScript --config $HADOOP_CONF_DIR $command "$@" > "$log" 2>&1 < /dev/null &
      ;;
    esac
    echo $! > $pid
    sleep 1
    head "$log"
    # capture the ulimit output
    if [ "true" = "$starting_secure_dn" ]; then
      echo "ulimit -a for secure datanode user $HADOOP_SECURE_DN_USER" >> $log
      # capture the ulimit info for the appropriate user
      su --shell=/bin/bash $HADOOP_SECURE_DN_USER -c 'ulimit -a' >> $log 2>&1
    elif [ "true" = "$starting_privileged_nfs" ]; then
        echo "ulimit -a for privileged nfs user $HADOOP_PRIVILEGED_NFS_USER" >> $log
        su --shell=/bin/bash $HADOOP_PRIVILEGED_NFS_USER -c 'ulimit -a' >> $log 2>&1
    else
      echo "ulimit -a for user $USER" >> $log
      ulimit -a >> $log 2>&1
    fi
    sleep 3;
    if ! ps -p $! > /dev/null ; then
      exit 1
    fi
    ;;

  (stop)

    if [ -f $pid ]; then
      TARGET_PID=`cat $pid`
      if kill -0 $TARGET_PID > /dev/null 2>&1; then
        echo stopping $command
        kill $TARGET_PID
        sleep $HADOOP_STOP_TIMEOUT
        if kill -0 $TARGET_PID > /dev/null 2>&1; then
          echo "$command did not stop gracefully after $HADOOP_STOP_TIMEOUT seconds: killing with kill -9"
          kill -9 $TARGET_PID
        fi
      else
        echo no $command to stop
      fi
      rm -f $pid
    else
      echo no $command to stop
    fi
    ;;

  (*)
    echo $usage
    exit 1
    ;;

esac

這段代碼的重點(diǎn)在第131行到結(jié)束。這里是真正在啟動服務(wù)的代碼，這個文件在調(diào)用的時(shí)候，會傳入兩個重要的參數(shù)start/stop xxx。用于啟動或停止某些服務(wù)。以啟動服務(wù)為例，其重點(diǎn)在第153行，這里會執(zhí)行一個hdfsScript腳本。這個參數(shù)的定義在第155行，

這里可以看見它實(shí)際是hadoop的bin目錄下的hdfs文件

文件的內(nèi)容如下：

#!/usr/bin/env bash

# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements.  See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You under the Apache License, Version 2.0
# (the "License"); you may not use this file except in compliance with
# the License.  You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

# Environment Variables
#
#   JSVC_HOME  home directory of jsvc binary.  Required for starting secure
#              datanode.
#
#   JSVC_OUTFILE  path to jsvc output file.  Defaults to
#                 $HADOOP_LOG_DIR/jsvc.out.
#
#   JSVC_ERRFILE  path to jsvc error file.  Defaults to $HADOOP_LOG_DIR/jsvc.err.

bin=`which $0`
bin=`dirname ${bin}`
bin=`cd "$bin" > /dev/null; pwd`

DEFAULT_LIBEXEC_DIR="$bin"/../libexec

HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hdfs-config.sh

function print_usage(){
  echo "Usage: hdfs [--config confdir] [--loglevel loglevel] COMMAND"
  echo "       where COMMAND is one of:"
  echo "  dfs                  run a filesystem command on the file systems supported in Hadoop."
  echo "  classpath            prints the classpath"
  echo "  namenode -format     format the DFS filesystem"
  echo "  secondarynamenode    run the DFS secondary namenode"
  echo "  namenode             run the DFS namenode"
  echo "  journalnode          run the DFS journalnode"
  echo "  zkfc                 run the ZK Failover Controller daemon"
  echo "  datanode             run a DFS datanode"
  echo "  dfsadmin             run a DFS admin client"
  echo "  haadmin              run a DFS HA admin client"
  echo "  fsck                 run a DFS filesystem checking utility"
  echo "  balancer             run a cluster balancing utility"
  echo "  jmxget               get JMX exported values from NameNode or DataNode."
  echo "  mover                run a utility to move block replicas across"
  echo "                       storage types"
  echo "  oiv                  apply the offline fsimage viewer to an fsimage"
  echo "  oiv_legacy           apply the offline fsimage viewer to an legacy fsimage"
  echo "  oev                  apply the offline edits viewer to an edits file"
  echo "  fetchdt              fetch a delegation token from the NameNode"
  echo "  getconf              get config values from configuration"
  echo "  groups               get the groups which users belong to"
  echo "  snapshotDiff         diff two snapshots of a directory or diff the"
  echo "                       current directory contents with a snapshot"
  echo "  lsSnapshottableDir   list all snapshottable dirs owned by the current user"
  echo "						Use -help to see options"
  echo "  portmap              run a portmap service"
  echo "  nfs3                 run an NFS version 3 gateway"
  echo "  cacheadmin           configure the HDFS cache"
  echo "  crypto               configure HDFS encryption zones"
  echo "  storagepolicies      list/get/set block storage policies"
  echo "  version              print the version"
  echo ""
  echo "Most commands print help when invoked w/o parameters."
  # There are also debug commands, but they don't show up in this listing.
}

if [ $# = 0 ]; then
  print_usage
  exit
fi

COMMAND=$1
shift

case $COMMAND in
  # usage flags
  --help|-help|-h)
    print_usage
    exit
    ;;
esac

# Determine if we're starting a secure datanode, and if so, redefine appropriate variables
if [ "$COMMAND" == "datanode" ] && [ "$EUID" -eq 0 ] && [ -n "$HADOOP_SECURE_DN_USER" ]; then
  if [ -n "$JSVC_HOME" ]; then
    if [ -n "$HADOOP_SECURE_DN_PID_DIR" ]; then
      HADOOP_PID_DIR=$HADOOP_SECURE_DN_PID_DIR
    fi

    if [ -n "$HADOOP_SECURE_DN_LOG_DIR" ]; then
      HADOOP_LOG_DIR=$HADOOP_SECURE_DN_LOG_DIR
      HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.dir=$HADOOP_LOG_DIR"
    fi

    HADOOP_IDENT_STRING=$HADOOP_SECURE_DN_USER
    HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.id.str=$HADOOP_IDENT_STRING"
    starting_secure_dn="true"
  else
    echo "It looks like you're trying to start a secure DN, but \$JSVC_HOME"\
      "isn't set. Falling back to starting insecure DN."
  fi
fi

# Determine if we're starting a privileged NFS daemon, and if so, redefine appropriate variables
if [ "$COMMAND" == "nfs3" ] && [ "$EUID" -eq 0 ] && [ -n "$HADOOP_PRIVILEGED_NFS_USER" ]; then
  if [ -n "$JSVC_HOME" ]; then
    if [ -n "$HADOOP_PRIVILEGED_NFS_PID_DIR" ]; then
      HADOOP_PID_DIR=$HADOOP_PRIVILEGED_NFS_PID_DIR
    fi

    if [ -n "$HADOOP_PRIVILEGED_NFS_LOG_DIR" ]; then
      HADOOP_LOG_DIR=$HADOOP_PRIVILEGED_NFS_LOG_DIR
      HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.dir=$HADOOP_LOG_DIR"
    fi

    HADOOP_IDENT_STRING=$HADOOP_PRIVILEGED_NFS_USER
    HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.id.str=$HADOOP_IDENT_STRING"
    starting_privileged_nfs="true"
  else
    echo "It looks like you're trying to start a privileged NFS server, but"\
      "\$JSVC_HOME isn't set. Falling back to starting unprivileged NFS server."
  fi
fi

if [ "$COMMAND" = "namenode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.namenode.NameNode'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_NAMENODE_OPTS"
elif [ "$COMMAND" = "zkfc" ] ; then
  CLASS='org.apache.hadoop.hdfs.tools.DFSZKFailoverController'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_ZKFC_OPTS"
elif [ "$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'
  if [ "$starting_secure_dn" = "true" ]; then
    HADOOP_OPTS="$HADOOP_OPTS -jvm server $HADOOP_DATANODE_OPTS"
  else
    HADOOP_OPTS="$HADOOP_OPTS -server $HADOOP_DATANODE_OPTS"
  fi
elif [ "$COMMAND" = "journalnode" ] ; then
  CLASS='org.apache.hadoop.hdfs.qjournal.server.JournalNode'
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_JOURNALNODE_OPTS"
elif [ "$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" = "haadmin" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.DFSHAAdmin
  CLASSPATH=${CLASSPATH}:${TOOL_PATH}
  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" = "mover" ] ; then
  CLASS=org.apache.hadoop.hdfs.server.mover.Mover
  HADOOP_OPTS="${HADOOP_OPTS} ${HADOOP_MOVER_OPTS}"
elif [ "$COMMAND" = "storagepolicies" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.StoragePolicyAdmin
elif [ "$COMMAND" = "jmxget" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.JMXGet
elif [ "$COMMAND" = "oiv" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.offlineImageViewer.OfflineImageViewerPB
elif [ "$COMMAND" = "oiv_legacy" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.offlineImageViewer.OfflineImageViewer
elif [ "$COMMAND" = "oev" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.offlineEditsViewer.OfflineEditsViewer
elif [ "$COMMAND" = "fetchdt" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.DelegationTokenFetcher
elif [ "$COMMAND" = "getconf" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.GetConf
elif [ "$COMMAND" = "groups" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.GetGroups
elif [ "$COMMAND" = "snapshotDiff" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.snapshot.SnapshotDiff
elif [ "$COMMAND" = "lsSnapshottableDir" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.snapshot.LsSnapshottableDir
elif [ "$COMMAND" = "portmap" ] ; then
  CLASS=org.apache.hadoop.portmap.Portmap
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_PORTMAP_OPTS"
elif [ "$COMMAND" = "nfs3" ] ; then
  CLASS=org.apache.hadoop.hdfs.nfs.nfs3.Nfs3
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_NFS3_OPTS"
elif [ "$COMMAND" = "cacheadmin" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.CacheAdmin
elif [ "$COMMAND" = "crypto" ] ; then
  CLASS=org.apache.hadoop.hdfs.tools.CryptoAdmin
elif [ "$COMMAND" = "version" ] ; then
  CLASS=org.apache.hadoop.util.VersionInfo
elif [ "$COMMAND" = "debug" ]; then
  CLASS=org.apache.hadoop.hdfs.tools.DebugAdmin
elif [ "$COMMAND" = "classpath" ]; then
  if [ "$#" -gt 0 ]; then
    CLASS=org.apache.hadoop.util.Classpath
  else
    # No need to bother starting up a JVM for this simple case.
    if $cygwin; then
      CLASSPATH=$(cygpath -p -w "$CLASSPATH" 2>/dev/null)
    fi
    echo $CLASSPATH
    exit 0
  fi
else
  CLASS="$COMMAND"
fi

# cygwin path translation
if $cygwin; then
  CLASSPATH=$(cygpath -p -w "$CLASSPATH" 2>/dev/null)
  HADOOP_LOG_DIR=$(cygpath -w "$HADOOP_LOG_DIR" 2>/dev/null)
  HADOOP_PREFIX=$(cygpath -w "$HADOOP_PREFIX" 2>/dev/null)
  HADOOP_CONF_DIR=$(cygpath -w "$HADOOP_CONF_DIR" 2>/dev/null)
  HADOOP_COMMON_HOME=$(cygpath -w "$HADOOP_COMMON_HOME" 2>/dev/null)
  HADOOP_HDFS_HOME=$(cygpath -w "$HADOOP_HDFS_HOME" 2>/dev/null)
  HADOOP_YARN_HOME=$(cygpath -w "$HADOOP_YARN_HOME" 2>/dev/null)
  HADOOP_MAPRED_HOME=$(cygpath -w "$HADOOP_MAPRED_HOME" 2>/dev/null)
fi

export CLASSPATH=$CLASSPATH

HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.security.logger=${HADOOP_SECURITY_LOGGER:-INFO,NullAppender}"

# Check to see if we should start a secure datanode
if [ "$starting_secure_dn" = "true" ]; then
  if [ "$HADOOP_PID_DIR" = "" ]; then
    HADOOP_SECURE_DN_PID="/tmp/hadoop_secure_dn.pid"
  else
    HADOOP_SECURE_DN_PID="$HADOOP_PID_DIR/hadoop_secure_dn.pid"
  fi

  JSVC=$JSVC_HOME/jsvc
  if [ ! -f $JSVC ]; then
    echo "JSVC_HOME is not set correctly so jsvc cannot be found. jsvc is required to run secure datanodes. "
    echo "Please download and install jsvc from http://archive.apache.org/dist/commons/daemon/binaries/ "\
      "and set JSVC_HOME to the directory containing the jsvc binary."
    exit
  fi

  if [[ ! $JSVC_OUTFILE ]]; then
    JSVC_OUTFILE="$HADOOP_LOG_DIR/jsvc.out"
  fi

  if [[ ! $JSVC_ERRFILE ]]; then
    JSVC_ERRFILE="$HADOOP_LOG_DIR/jsvc.err"
  fi

  exec "$JSVC" \
           -Dproc_$COMMAND -outfile "$JSVC_OUTFILE" \
           -errfile "$JSVC_ERRFILE" \
           -pidfile "$HADOOP_SECURE_DN_PID" \
           -nodetach \
           -user "$HADOOP_SECURE_DN_USER" \
            -cp "$CLASSPATH" \
           $JAVA_HEAP_MAX $HADOOP_OPTS \
           org.apache.hadoop.hdfs.server.datanode.SecureDataNodeStarter "$@"
elif [ "$starting_privileged_nfs" = "true" ] ; then
  if [ "$HADOOP_PID_DIR" = "" ]; then
    HADOOP_PRIVILEGED_NFS_PID="/tmp/hadoop_privileged_nfs3.pid"
  else
    HADOOP_PRIVILEGED_NFS_PID="$HADOOP_PID_DIR/hadoop_privileged_nfs3.pid"
  fi

  JSVC=$JSVC_HOME/jsvc
  if [ ! -f $JSVC ]; then
    echo "JSVC_HOME is not set correctly so jsvc cannot be found. jsvc is required to run privileged NFS gateways. "
    echo "Please download and install jsvc from http://archive.apache.org/dist/commons/daemon/binaries/ "\
      "and set JSVC_HOME to the directory containing the jsvc binary."
    exit
  fi

  if [[ ! $JSVC_OUTFILE ]]; then
    JSVC_OUTFILE="$HADOOP_LOG_DIR/nfs3_jsvc.out"
  fi

  if [[ ! $JSVC_ERRFILE ]]; then
    JSVC_ERRFILE="$HADOOP_LOG_DIR/nfs3_jsvc.err"
  fi

  exec "$JSVC" \
           -Dproc_$COMMAND -outfile "$JSVC_OUTFILE" \
           -errfile "$JSVC_ERRFILE" \
           -pidfile "$HADOOP_PRIVILEGED_NFS_PID" \
           -nodetach \
           -user "$HADOOP_PRIVILEGED_NFS_USER" \
           -cp "$CLASSPATH" \
           $JAVA_HEAP_MAX $HADOOP_OPTS \
           org.apache.hadoop.hdfs.nfs.nfs3.PrivilegedNfsGatewayStarter "$@"
else
  # run it
  exec "$JAVA" -Dproc_$COMMAND $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"
fi

這段代碼的重點(diǎn)在第134行到219行和第304行。首先看第134行到219行，這段代碼雖然很長但全是一堆if else語句。其邏輯也很簡單，就是根據(jù)傳入的COMMAND的值來為CLASS和HADOOP_OPTS賦值。然后是第304行，執(zhí)行CLASS類。以第134行的namenode類為例，這里CLASS的值為org.apache.hadoop.hdfs.server.namenode.NameNode，這是一個java類隨后便會執(zhí)行這個類啟動namenode。

如果想要debug hdfs的源碼，最好在這里設(shè)置遠(yuǎn)程調(diào)試。因?yàn)檫@里有單個的服務(wù)類與啟動參數(shù)，可以準(zhǔn)確的定位需要的服務(wù)。

以上就是Hadoop源碼分析之啟動及腳本剖析的詳細(xì)內(nèi)容，本系列下一篇文章傳送門Hadoop源碼分析四遠(yuǎn)程debug調(diào)試更多關(guān)于Hadoop源碼分析分析的資料請繼續(xù)關(guān)注腳本之家其它相關(guān)文章！

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