Hadoop集羣的啓動腳本整理及守護線程源碼

在前三篇文章中，我們進行了HDFS的搭建，我們也使用start-dfs.sh腳本啓動了集羣環境，並且上傳了一個文件到HDFS上，還使用了mapreduce程序對HDFS上的這個文件進行了單詞統計。今天我們就來簡單瞭解一下啓動腳本的相關內容和HDFS的一些重要的默認配置屬性。

一、啓動腳本

hadoop的腳本/指令目錄，就兩個，一個是bin/，一個是sbin/。現在，就來看看幾個比較重要的腳本/指令。

1、sbin/start-all.sh

# Start all hadoop daemons.  Run this on master node.
# 開啓所有的hadoop守護進程，在主節點上運行
 
echo "This script is Deprecated. Instead use start-dfs.sh and start-yarn.sh"
#這個腳本已經被棄用，使用start-dfs.sh和start-yarn.sh替代
 
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
#運行libexe/hadoop-config.sh指令，加載配置文件
 
# 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
   #運行 sbin/start-dfs.sh指令
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
  #運行 sbin/start-yarn.sh指令
fi

我們可以看到，這個腳本的內容不多，實際上被棄用了，只不過是在這個start-all.sh腳本中，先執行hadoop-config.sh指令加載hadoop的一些環境變量，然後再分別執行start-dfs.sh腳本和start-yarn.sh腳本。

從此可以看出，我們也可以直接執行start-dfs.sh腳本來啓動hadoop集羣，無需執行start-all.sh腳本而已。（如果配置了yarn,再執行start-yarn.sh腳本）。

2、libexec/hadoop-config.sh

this="${BASH_SOURCE-$0}"
common_bin=$(cd -P -- "$(dirname -- "$this")" && pwd -P)
script="$(basename -- "$this")"
this="$common_bin/$script"
 
[ -f "$common_bin/hadoop-layout.sh" ] && . "$common_bin/hadoop-layout.sh"
 
HADOOP_COMMON_DIR=${HADOOP_COMMON_DIR:-"share/hadoop/common"}
HADOOP_COMMON_LIB_JARS_DIR=${HADOOP_COMMON_LIB_JARS_DIR:-"share/hadoop/common/lib"}
HADOOP_COMMON_LIB_NATIVE_DIR=${HADOOP_COMMON_LIB_NATIVE_DIR:-"lib/native"}
HDFS_DIR=${HDFS_DIR:-"share/hadoop/hdfs"}
HDFS_LIB_JARS_DIR=${HDFS_LIB_JARS_DIR:-"share/hadoop/hdfs/lib"}
YARN_DIR=${YARN_DIR:-"share/hadoop/yarn"}
YARN_LIB_JARS_DIR=${YARN_LIB_JARS_DIR:-"share/hadoop/yarn/lib"}
MAPRED_DIR=${MAPRED_DIR:-"share/hadoop/mapreduce"}
MAPRED_LIB_JARS_DIR=${MAPRED_LIB_JARS_DIR:-"share/hadoop/mapreduce/lib"}
 
# the root of the Hadoop installation
# See HADOOP-6255 for directory structure layout
HADOOP_DEFAULT_PREFIX=$(cd -P -- "$common_bin"/.. && pwd -P)
HADOOP_PREFIX=${HADOOP_PREFIX:-$HADOOP_DEFAULT_PREFIX}
export HADOOP_PREFIX
............................
...........省略細節，看重點..............
....................................
#  調用 hadoop-env.sh加載其他環境變量
if [ -f "${HADOOP_CONF_DIR}/hadoop-env.sh" ]; then
  . "${HADOOP_CONF_DIR}/hadoop-env.sh"
fi

這個腳本的作用，其實就是配置了一些hadoop集羣的所需要的環境變量而已，內部還執行了hadoop-env.sh腳本，加載其他的比較重要的環境變量，如jdk等等

3、sbin/start-dfs.sh

# Start hadoop dfs daemons.          #開啓HDFS的相關守護線程
# Optinally upgrade or rollback dfs state.   #可選升級或回滾DFS狀態
# Run this on master node.           #在主節點上運行這個腳本
 
#這是start-dfs.sh的用法                              單獨啓動一個clusterId
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}
#使用hdfs-config.sh加載環境變量
. $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]"
 
#執行hadoop-daemons.sh  調用bin/hdfs指令  啓動namenode守護線程
"$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
  --config "$HADOOP_CONF_DIR" \
  --hostnames "$NAMENODES" \
  --script "$bin/hdfs" start namenode $nameStartOpt
 
#---------------------------------------------------------
# datanodes (using default slaves file)
 
if [ -n "$HADOOP_SECURE_DN_USER" ]; then
  echo \
    "Attempting to start secure cluster, skipping datanodes. " \
    "Run start-secure-dns.sh as root to complete startup."
else
  #執行hadoop-daemons.sh  調用bin/hdfs指令 啓動datanode守護線程
  "$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]"
  #執行hadoop-daemons.sh  調用bin/hdfs指令 啓動secondarynamenode守護線程
  "$HADOOP_PREFIX/sbin/hadoop-daemons.sh" \
      --config "$HADOOP_CONF_DIR" \
      --hostnames "$SECONDARY_NAMENODES" \
      --script "$bin/hdfs" start secondarynamenode
fi
...................................
............省略細節.................
...................................
 
# eof

在start-dfs.sh腳本中，先執行hdfs-config.sh腳本加載環境變量，然後通過hadoop-daemons.sh腳本又調用bin/hdfs指令來分別開啓namenode、datanode以及secondarynamenode等守護進程。

如此我們也能發現，其實直接執行hadoop-daemons.sh腳本，配合其用法，也應該可以啓動HDFS等相關守護進程。

4、sbin/hadoop-daemons.sh

# 在所有的從節點上運行hadoop指令
# Run a Hadoop command on all slave hosts.
 
#hadoop-daemons.sh腳本的用法，                                            
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}
#調用hadoop-config.sh加載環境比那裏
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh
 
#調用sbin/slaves.sh腳本  加載配置文件，然後使用hadoop-daemon.sh腳本讀取配置文件
exec "$bin/slaves.sh" --config $HADOOP_CONF_DIR cd "$HADOOP_PREFIX" \; "$bin/hadoop-daemon.sh" --config $HADOOP_CONF_DIR "$@"

參考hadoop-daemons.sh的使用方法，不難發現直接使用hadoop-daemons.sh腳本，然後配合指令，就可以啓動相關守護線程，如：

hadoop-daemons.sh start namenode #啓動主節點
hadoop-daemons.sh start datanode #啓動從節點
hadoop-daemons.sh start secondarynamenode #啓動第二主節點

在這個腳本中，我們可以看到內部執行了slaves.sh腳本讀取環境變量，然後再調用了hadoop-daemon.sh腳本讀取相關配置信息並執行了hadoop指令。

5、sbin/slaves.sh

# Run a shell command on all slave hosts.
#
# Environment Variables
#
#   HADOOP_SLAVES    File naming remote hosts.
#     Default is ${HADOOP_CONF_DIR}/slaves.
#   HADOOP_CONF_DIR  Alternate conf dir. Default is ${HADOOP_PREFIX}/conf.
#   HADOOP_SLAVE_SLEEP Seconds to sleep between spawning remote commands.
#   HADOOP_SSH_OPTS Options passed to ssh when running remote commands.
##
 
#  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
 
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              #讀取環境變量
 
if [ -f "${HADOOP_CONF_DIR}/hadoop-env.sh" ]; then
  . "${HADOOP_CONF_DIR}/hadoop-env.sh"              #讀取環境變量
fi
 
# Where to start the script, see hadoop-config.sh
# (it set up the variables based on command line options)
if [ "$HADOOP_SLAVE_NAMES" != '' ] ; then
  SLAVE_NAMES=$HADOOP_SLAVE_NAMES
else
  SLAVE_FILE=${HADOOP_SLAVES:-${HADOOP_CONF_DIR}/slaves}
  SLAVE_NAMES=$(cat "$SLAVE_FILE" | sed  's/#.*$//;/^$/d')
fi
 
# start the daemons
for slave in $SLAVE_NAMES ; do
 ssh $HADOOP_SSH_OPTS $slave $"${@// /\\ }" \
   2>&1 | sed "s/^/$slave: /" &
 if [ "$HADOOP_SLAVE_SLEEP" != "" ]; then
   sleep $HADOOP_SLAVE_SLEEP
 fi
done

這個腳本也就是加載環境變量，然後通過ssh連接從節點。

6、sbin/hadoop-daemon.sh

#!/usr/bin/env bash
 
# Runs a Hadoop command as a daemon.     以守護進程的形式運行hadoop命令
 
.....................
.....................、
 
# 使用方法    command就是hadoop指令，下面有判讀
usage="Usage: hadoop-daemon.sh [--config <conf-dir>] [--hosts hostlistfile] [--script script] (start|stop) <hadoop-command> <args...>"
 
.....................
.....................
 
#使用hadoop-config.sh加載環境變量
DEFAULT_LIBEXEC_DIR="$bin"/../libexec
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh
 
#使用hadoop-env.sh加載環境變量
if [ -f "${HADOOP_CONF_DIR}/hadoop-env.sh" ]; then
  . "${HADOOP_CONF_DIR}/hadoop-env.sh"
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"
 
#判斷command是什麼指令，然後調用bin/hdfs指令 讀取配置文件，執行相關指令
    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
 ........................
........................
esac

在hadoop-daemon.sh腳本中，同樣讀取了環境變量，然後依據傳入的參數$@（上一個腳本中）來判斷要啓動的hadoop的守護線程($command)，最後調用bin/hdfs指令讀取配置信息並啓動hadoop的守護線程。

7、bin/hdfs

這是一個指令，而非shell腳本。我們可以發現，在啓動hadoop集羣時，不管使用什麼腳本，最終都指向了bin/hdfs這個指令，那麼這個指令裏到底是什麼呢，我們來看一下，就明白了。

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
 
#除了上面繼續加載環境變化外，這個函數其實就是提示我們在使用什麼
#比如namenode -format  是格式化DFS filesystem
#再比如 namenode    說的是運行一個DFS namenode
# 我們往下看
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
 
#   停停停，對就是這
#   我們可以看到，通過相應的hadoop指令，在加載相應的class文件
#   然後在jvm運行此程序。別忘記了，hadoop是用java語言開發的
 
if [ "$COMMAND" = "namenode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.namenode.NameNode'    #namenode守護線程對應的CLASS字節碼
  HADOOP_OPTS="$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'    #SecondaryNameNode守護線程對應的CLASS字節碼
  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_SECONDARYNAMENODE_OPTS"
elif [ "$COMMAND" = "datanode" ] ; then
  CLASS='org.apache.hadoop.hdfs.server.datanode.DataNode'           #DataNode守護線程對應的CLASS字節碼
  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"
 
.......................................
...............省略很多..............
.......................................
# 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
   #運行 java字節碼文件
  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
 
   #運行 java字節碼文件
  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
 
  #運行 java字節碼文件
  # run it
  exec "$JAVA" -Dproc_$COMMAND $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"
fi

看完懂了嗎？在這個指令中，加載了各個守護線程對應的CLASS字節碼文件，然後在JVM上來運行相應的守護線程。

hadoop的另一個指令bin/hadoop，內部也調用了bin/hdfs指令，感興趣的話，可以自己看看，我就不展示出來了。至於跟yarn有關的腳本和指令也是相同的邏輯關係，我也不一一展示了。

使用圖片重寫整理了一下啓動腳本的執行先後順序：

使用文字再次整理一下：

#一個腳本啓動所有線程
start-all.sh         #執行此腳本可以啓動所有線程
    1. hadoop-config.sh
        a. hadoop-env.sh    
    2. start-dfs.sh  #執行此腳本可以啓動HDFS相關線程
        a.hadoop-config.sh
        b.hadoop-daemons.sh   hdfs  namenode
          hadoop-daemons.sh   hdfs  datanode
          hadoop-daemons.sh   hdfs  secondarynamenode   
    3. start-yarn.sh  #執行此腳本可以啓動YARN相關線程

#啓動單個線程
#方法1：
hadoop-daemons.sh   --config   [start|stop]  command
    1. hadoop-config.sh
        a. hadoop-env.sh
    2. slaves.sh
        a. hadoop-config.sh
        b. hadoop-env.sh
    3. hadoop-daemon.sh --config  [start|stop]  command
        a.hdfs $command
#方法2：
hadoop-daemon.sh   --config   [start|stop]  command
    1. hadoop-config.sh
        a. hadoop-env.sh
    2. hdfs $command

二、底層源碼查看

我們通過捋順啓動腳本發現，啓動namenode對應的字節碼文件是：org.apache.hadoop.hdfs.server.namenode.NameNode。啓動datanode對應的字節碼文件是：org.apache.hadoop.hdfs.server.datanode.DataNode。而啓動secondarynamenode對應的字節碼文件是：org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode。

這些源碼所在的har包：hadoop-hdfs-2.7.3-sources.jar

1、namenode的源碼

package org.apache.hadoop.hdfs.server.namenode;
 
.......................
import org.apache.hadoop.hdfs.HdfsConfiguration;
..........................
@InterfaceAudience.Private
public class NameNode implements NameNodeStatusMXBean {
  static{   //靜態塊
    HdfsConfiguration.init();     //調用HdfsConfiguration的init方法，進行讀取配置文件
  }
  ...................
  public static void main(String argv[]) throws Exception {
    if (DFSUtil.parseHelpArgument(argv, NameNode.USAGE, System.out, true)) {
      System.exit(0);
    }
 
    try {
      StringUtils.startupShutdownMessage(NameNode.class, argv, LOG);
      NameNode namenode = createNameNode(argv, null);  //創建namenode
      if (namenode != null) {
        namenode.join();   //啓動namenode線程
      }
    } catch (Throwable e) {
      LOG.error("Failed to start namenode.", e);
      terminate(1, e);
    }
  }
...........
}

看一下HdfsConfiguration類

package org.apache.hadoop.hdfs;
 
/**
 * Adds deprecated keys into the configuration.
 */
@InterfaceAudience.Private
public class HdfsConfiguration extends Configuration {
  static {       //靜態塊
    addDeprecatedKeys();
    // adds the default resources
    Configuration.addDefaultResource("hdfs-default.xml");       //取默認配置文件
    Configuration.addDefaultResource("hdfs-site.xml");          //讀取個人設置文件
 
  }
  
  public static void init() {}
 
  private static void addDeprecatedKeys() {}
 
  public static void main(String[] args) {
    init();
    Configuration.dumpDeprecatedKeys();
  }
}

2、datanode源碼

package org.apache.hadoop.hdfs.server.datanode;
..............
import org.apache.hadoop.hdfs.HdfsConfiguration;
..............
@InterfaceAudience.Private
public class DataNode extends ReconfigurableBase
    implements InterDatanodeProtocol, ClientDatanodeProtocol,
        TraceAdminProtocol, DataNodeMXBean {
  public static final Log LOG = LogFactory.getLog(DataNode.class);
  
  static{
    HdfsConfiguration.init();    //同樣在靜態塊中調用了HdfsConfiguration類，用於加載配置文件
  }
}

Hadoop集羣的啓動腳本整理及守護線程源碼

一、啓動腳本

1、sbin/start-all.sh

2、libexec/hadoop-config.sh

3、sbin/start-dfs.sh

4、sbin/hadoop-daemons.sh

5、sbin/slaves.sh

6、sbin/hadoop-daemon.sh

7、bin/hdfs

二、底層源碼查看

1、namenode的源碼

2、datanode源碼

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