HDFS2.7.0中hdfs namenode -format的示例分析

这篇文章将为大家详细讲解有关HDFS2.7.0中hdfs namenode -format的示例分析，小编觉得挺实用的，因此分享给大家做个参考，希望大家阅读完这篇文章后可以有所收获。

执行hadoop namenode -format后

实际上是执行

/root/hadoop-2.7.0-bin/bin/hdfs namenode -format

下面就来分析这个脚本

---

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

打印

bin=/root/hadoop-2.7.0-bin/bin

---

DEFAULT_LIBEXEC_DIR="$bin"/../libexec

打印'

DEFAULT_LIBEXEC_DIR=/root/hadoop-2.7.0-bin/bin/../libexec

---

cygwin=falsecase "$(uname)" inCYGWIN*) cygwin=true;;esac

这个不会执行，过滤

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接下来执行一个脚本

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

实际上执行的是

/root/hadoop-2.7.0-bin/libexec/hdfs-config.sh

这个脚本其实是调用另外一个脚本，调用的哪个脚本？读者可以自己去探索一下：）

---回到hdfs脚本

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  exitfi

这个太简单，就是一个函数而已，告诉用途

---

接下来到了最关键的时刻了，就是执行命令

if [ "$COMMAND" = "namenode" ] ; then  CLASS='org.apache.hadoop.hdfs.server.namenode.NameNode'  HADOOP_OPTS="$HADOOP_OPTS $HADOOP_NAMENODE_OPTS"

其中

HADOOP_OPTS= -Djava.net.preferIPv4Stack=true -Dhadoop.log.dir=/root/hadoop-2.7.0-bin/logs -Dhadoop.log.file=hadoop.log -Dhadoop.home.dir=/root/hadoop-2.7.0-bin -Dhadoop.id.str=root -Dhadoop.root.logger=INFO,console -Djava.library.path=/root/hadoop-2.7.0-bin/lib/native -Dhadoop.policy.file=hadoop-policy.xml -Djava.net.preferIPv4Stack=true -Dhadoop.security.logger=INFO,RFAS -Dhdfs.audit.logger=INFO,NullAppender

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剩下的一段是cgwin,忽略

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

赋值语句不多说

---

接下来的一个if-else语句，实际上执行的是最后一个分支

else  # run it  exec "$JAVA" -Dproc_$COMMAND $JAVA_HEAP_MAX $HADOOP_OPTS $CLASS "$@"fi

庐山真面目要出来了，打印执行语句

/usr/java/jdk1.8.0_45/bin/java -Dproc_namenode -Xmx1000m -Djava.net.preferIPv4Stack=true -Dhadoop.log.dir=/root/hadoop-2.7.0-bin/logs -Dhadoop.log.file=hadoop.log -Dhadoop.home.dir=/root/hadoop-2.7.0-bin -Dhadoop.id.str=root -Dhadoop.root.logger=INFO,console -Djava.library.path=/root/hadoop-2.7.0-bin/lib/native -Dhadoop.policy.file=hadoop-policy.xml -Djava.net.preferIPv4Stack=true -Dhadoop.security.logger=INFO,RFAS -Dhdfs.audit.logger=INFO,NullAppender -Dhadoop.security.logger=INFO,NullAppender org.apache.hadoop.hdfs.server.namenode.NameNode -format

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