我们都知道，在Hadoop 2.7.0中，系统刚开始执行时，需要执行一个命令就是
hadoop namenode -format下面我们就来逐行分析下，这个命令对应的脚本的真正内涵！
---
bin=`which $0`
bin=`dirname ${bin}`
bin=`cd "$bin"; pwd`打印出来的bin值为
/root/hadoop-2.7.0-bin/bin---
DEFAULT_LIBEXEC_DIR="$bin"/../libexec则导致DEFAULT_LIBEXEC_DIR的值为
/root/hadoop-2.7.0-bin/bin/../libexec---
cygwin=false
case "$(uname)" in
CYGWIN*) cygwin=true;;
esac这个一看就知道跟cywin相关，也就是如果你在windows下执行这个脚本才有意义，我的是linux,无视这段代码！
---
HADOOP_LIBEXEC_DIR=${HADOOP_LIBEXEC_DIR:-$DEFAULT_LIBEXEC_DIR}打印其值为
/root/hadoop-2.7.0-bin/bin/../libexec---
接下来执行一个脚本
. $HADOOP_LIBEXEC_DIR/hadoop-config.sh打印的值是/root/hadoop-2.7.0-bin/bin/../libexec/hadoop-config.sh
实际上也就是
/root/hadoop-2.7.0-bin/libexec/hadoop-config.sh所以先转向这个脚本看看
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---解析/root/hadoop-2.7.0-bin/libexec/hadoop-config.sh
刚开始是
this="${BASH_SOURCE-$0}"
common_bin=$(cd -P -- "$(dirname -- "$this")" && pwd -P)
script="$(basename -- "$this")"
this="$common_bin/$script"打印出所有的值为
this=/root/hadoop-2.7.0-bin/libexec/hadoop-config.sh
common_bin=/root/hadoop-2.7.0-bin/libexec
script=hadoop-config.sh---
然后执行一段脚本
[ -f "$common_bin/hadoop-layout.sh" ] && . "$common_bin/hadoop-layout.sh"谢天谢地，这里并没有这个脚本，所以不需要执行
---
接下来是一大波赋值语句
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=${MAPRED_LIB_JARS_DIR:-"share/hadoop/mapreduce/lib"}打印值如下：
HADOOP_COMMON_DIR=share/hadoop/common
HADOOP_COMMON_LIB_JARS_DIR=share/hadoop/common/lib
HADOOP_COMMON_LIB_NATIVE_DIR=lib/native
HDFS_DIR=share/hadoop/hdfs
HDFS_LIB_JARS_DIR=share/hadoop/hdfs/lib
YARN_DIR=share/hadoop/yarn
YARN_LIB_JARS_DIR=share/hadoop/yarn/lib
MAPRED_DIR=share/hadoop/mapreduce
MAPRED_LIB_JARS_DIR=share/hadoop/mapreduce/lib---
接下来是一小波赋值语句
HADOOP_DEFAULT_PREFIX=$(cd -P -- "$common_bin"/.. && pwd -P)
HADOOP_PREFIX=${HADOOP_PREFIX:-$HADOOP_DEFAULT_PREFIX}
export HADOOP_PREFIX打印值如下：
HADOOP_DEFAULT_PREFIX=/root/hadoop-2.7.0-bin
HADOOP_PREFIX=/root/hadoop-2.7.0-bin---
接下来是一段判断语句
#check to see if the conf dir is given as an optional argument
if [ $# -gt 1 ]
then
if [ "--config" = "$1" ]
then
shift
confdir=$1
if [ ! -d "$confdir" ]; then
echo "Error: Cannot find configuration directory: $confdir"
exit 1
fi
shift
HADOOP_CONF_DIR=$confdir
fi
fi执行结果如下：
本次命令下没有执行---
if [ $# -gt 1 ]
then
if [ "--loglevel" = "$1" ]
then
shift
HADOOP_LOGLEVEL=$1
shift
fi
fi
HADOOP_LOGLEVEL="${HADOOP_LOGLEVEL:-INFO}"执行结果为
HADOOP_LOGLEVEL=INFO---
# Allow alternate conf dir location.
if [ -e "${HADOOP_PREFIX}/conf/hadoop-env.sh" ]; then
DEFAULT_CONF_DIR="conf"
else
DEFAULT_CONF_DIR="etc/hadoop"
fi
export HADOOP_CONF_DIR="${HADOOP_CONF_DIR:-$HADOOP_PREFIX/$DEFAULT_CONF_DIR}"打印为
HADOOP_CONF_DIR=/root/hadoop-2.7.0-bin/etc/hadoop---
接下来是判断脚本
# User can specify hostnames or a file where the hostnames are (not both)
if [[ ( "$HADOOP_SLAVES" != '' ) && ( "$HADOOP_SLAVE_NAMES" != '' ) ]] ; then
echo \
"Error: Please specify one variable HADOOP_SLAVES or " \
"HADOOP_SLAVE_NAME and not both."
exit 1
fi结果为
通过---
# Process command line options that specify hosts or file with host
# list
if [ $# -gt 1 ]
then
if [ "--hosts" = "$1" ]
then
shift
export HADOOP_SLAVES="${HADOOP_CONF_DIR}/$1"
shift
elif [ "--hostnames" = "$1" ]
then
shift
export HADOOP_SLAVE_NAMES=$1
shift
fi
fi执行结果为
很抱歉，任何一个分支都没有被执行---
# User can specify hostnames or a file where the hostnames are (not both)
# (same check as above but now we know it's command line options that cause
# the problem)
if [[ ( "$HADOOP_SLAVES" != '' ) && ( "$HADOOP_SLAVE_NAMES" != '' ) ]] ; then
echo \
"Error: Please specify one of --hosts or --hostnames options and not both."
exit 1
fi显然执行结果为不执行
---
接下来又执行另一个脚本
if [ -f "${HADOOP_CONF_DIR}/hadoop-env.sh" ]; then
. "${HADOOP_CONF_DIR}/hadoop-env.sh"
fi路径为：
/root/hadoop-2.7.0-bin/etc/hadoop/hadoop-env.sh下面来执行这个脚本
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---/root/hadoop-2.7.0-bin/etc/hadoop/hadoop-env.sh
这个脚本，全部是export,就不细细分析了。让我们再回到hadoop-config.sh
---
接下来是
# check if net.ipv6.bindv6only is set to 1
bindv6only=$(/sbin/sysctl -n net.ipv6.bindv6only 2> /dev/null)
if [ -n "$bindv6only" ] && [ "$bindv6only" -eq "1" ] && [ "$HADOOP_ALLOW_IPV6" != "yes" ]
then
echo "Error: \"net.ipv6.bindv6only\" is set to 1 - Java networking could be broken"
echo "For more info: http://wiki.apache.org/hadoop/HadoopIPv6"
exit 1
fi显然不执行
---
接下来是
# Newer versions of glibc use an arena memory allocator that causes virtual
# memory usage to explode. This interacts badly with the many threads that
# we use in Hadoop. Tune the variable down to prevent vmem explosion.
export MALLOC_ARENA_MAX=${MALLOC_ARENA_MAX:-4}打印
MALLOC_ARENA_MAX=4---
接下来是JAVA_HOME
# Attempt to set JAVA_HOME if it is not set
if [[ -z $JAVA_HOME ]]; then
# On OSX use java_home (or /Library for older versions)
if [ "Darwin" == "$(uname -s)" ]; then
if [ -x /usr/libexec/java_home ]; then
export JAVA_HOME=($(/usr/libexec/java_home))
else
export JAVA_HOME=(/Library/Java/Home)
fi
fi
# Bail if we did not detect it
if [[ -z $JAVA_HOME ]]; then
echo "Error: JAVA_HOME is not set and could not be found." 1>&2
exit 1
fi
fi打印
JAVA_HOME=/usr/java/jdk1.8.0_45---
JAVA=$JAVA_HOME/bin/java
# some Java parameters
JAVA_HEAP_MAX=-Xmx1000m
# check envvars which might override default args
if [ "$HADOOP_HEAPSIZE" != "" ]; then
#echo "run with heapsize $HADOOP_HEAPSIZE"
JAVA_HEAP_MAX="-Xmx""$HADOOP_HEAPSIZE""m"
#echo $JAVA_HEAP_MAX
fi打印值为
JAVA_HEAP_MAX=-Xmx1000m---
# CLASSPATH initially contains $HADOOP_CONF_DIR
CLASSPATH="${HADOOP_CONF_DIR}"打印
CLASSPATH=/root/hadoop-2.7.0-bin/etc/hadoop---
# so that filenames w/ spaces are handled correctly in loops below
IFS=
if [ "$HADOOP_COMMON_HOME" = "" ]; then
if [ -d "${HADOOP_PREFIX}/$HADOOP_COMMON_DIR" ]; then
export HADOOP_COMMON_HOME=$HADOOP_PREFIX
fi
fi打印
HADOOP_COMMON_HOME=/root/hadoop-2.7.0-bin---
# for releases, add core hadoop jar & webapps to CLASSPATH
if [ -d "$HADOOP_COMMON_HOME/$HADOOP_COMMON_DIR/webapps" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_COMMON_HOME/$HADOOP_COMMON_DIR
fi
if [ -d "$HADOOP_COMMON_HOME/$HADOOP_COMMON_LIB_JARS_DIR" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_COMMON_HOME/$HADOOP_COMMON_LIB_JARS_DIR'/*'
fi
CLASSPATH=${CLASSPATH}:$HADOOP_COMMON_HOME/$HADOOP_COMMON_DIR'/*'打印值
CLASSPATH=/root/hadoop-2.7.0-bin/etc/hadoop:/root/hadoop-2.7.0-bin/share/hadoop/common/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/common/*---
# default log directory & file
if [ "$HADOOP_LOG_DIR" = "" ]; then
HADOOP_LOG_DIR="$HADOOP_PREFIX/logs"
fi
if [ "$HADOOP_LOGFILE" = "" ]; then
HADOOP_LOGFILE='hadoop.log'
fi
# default policy file for service-level authorization
if [ "$HADOOP_POLICYFILE" = "" ]; then
HADOOP_POLICYFILE="hadoop-policy.xml"
fi
# restore ordinary behaviour
unset IFS打印
HADOOP_LOG_DIR=/root/hadoop-2.7.0-bin/logs
HADOOP_LOGFILE=hadoop.log
HADOOP_POLICYFILE=hadoop-policy.xml---
# setup 'java.library.path' for native-hadoop code if necessary
if [ -d "${HADOOP_PREFIX}/build/native" -o -d "${HADOOP_PREFIX}/$HADOOP_COMMON_LIB_NATIVE_DIR" ]; then
if [ -d "${HADOOP_PREFIX}/$HADOOP_COMMON_LIB_NATIVE_DIR" ]; then
if [ "x$JAVA_LIBRARY_PATH" != "x" ]; then
JAVA_LIBRARY_PATH=${JAVA_LIBRARY_PATH}:${HADOOP_PREFIX}/$HADOOP_COMMON_LIB_NATIVE_DIR
else
JAVA_LIBRARY_PATH=${HADOOP_PREFIX}/$HADOOP_COMMON_LIB_NATIVE_DIR
fi
fi
fi打印
JAVA_LIBRARY_PATH=/root/hadoop-2.7.0-bin/lib/native---
# setup a default TOOL_PATH
TOOL_PATH="${TOOL_PATH:-$HADOOP_PREFIX/share/hadoop/tools/lib/*}"
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.dir=$HADOOP_LOG_DIR"
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.log.file=$HADOOP_LOGFILE"
HADOOP_HOME=$HADOOP_PREFIX
if $cygwin; then
HADOOP_HOME=$(cygpath -w "$HADOOP_HOME" 2>/dev/null)
fi
export HADOOP_HOME
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.home.dir=$HADOOP_HOME"
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.id.str=$HADOOP_IDENT_STRING"
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.root.logger=${HADOOP_ROOT_LOGGER:-${HADOOP_LOGLEVEL},console}"
if [ "x$JAVA_LIBRARY_PATH" != "x" ]; then
if $cygwin; then
JAVA_LIBRARY_PATH=$(cygpath -w "$JAVA_LIBRARY_PATH" 2>/dev/null)
fi
HADOOP_OPTS="$HADOOP_OPTS -Djava.library.path=$JAVA_LIBRARY_PATH"
export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$JAVA_LIBRARY_PATH
fi
HADOOP_OPTS="$HADOOP_OPTS -Dhadoop.policy.file=$HADOOP_POLICYFILE"
# Disable ipv6 as it can cause issues
HADOOP_OPTS="$HADOOP_OPTS -Djava.net.preferIPv4Stack=true"一大波赋值语句就不多说了。
---
# put hdfs in classpath if present
if [ "$HADOOP_HDFS_HOME" = "" ]; then
if [ -d "${HADOOP_PREFIX}/$HDFS_DIR" ]; then
export HADOOP_HDFS_HOME=$HADOOP_PREFIX
fi
fi打印
HADOOP_HDFS_HOME=/root/hadoop-2.7.0-bin---
if [ -d "$HADOOP_HDFS_HOME/$HDFS_DIR/webapps" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_HDFS_HOME/$HDFS_DIR
fi
if [ -d "$HADOOP_HDFS_HOME/$HDFS_LIB_JARS_DIR" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_HDFS_HOME/$HDFS_LIB_JARS_DIR'/*'
fi
CLASSPATH=${CLASSPATH}:$HADOOP_HDFS_HOME/$HDFS_DIR'/*'打印
CLASSPATH=/root/hadoop-2.7.0-bin/etc/hadoop:/root/hadoop-2.7.0-bin/share/hadoop/common/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/common/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/*---
# put yarn in classpath if present
if [ "$HADOOP_YARN_HOME" = "" ]; then
if [ -d "${HADOOP_PREFIX}/$YARN_DIR" ]; then
export HADOOP_YARN_HOME=$HADOOP_PREFIX
fi
fi打印
HADOOP_YARN_HOME=/root/hadoop-2.7.0-bin---
if [ -d "$HADOOP_YARN_HOME/$YARN_DIR/webapps" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_YARN_HOME/$YARN_DIR
fi
if [ -d "$HADOOP_YARN_HOME/$YARN_LIB_JARS_DIR" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_YARN_HOME/$YARN_LIB_JARS_DIR'/*'
fi
CLASSPATH=${CLASSPATH}:$HADOOP_YARN_HOME/$YARN_DIR'/*'
# put mapred in classpath if present AND different from YARN
if [ "$HADOOP_MAPRED_HOME" = "" ]; then
if [ -d "${HADOOP_PREFIX}/$MAPRED_DIR" ]; then
export HADOOP_MAPRED_HOME=$HADOOP_PREFIX
fi
fi
if [ "$HADOOP_MAPRED_HOME/$MAPRED_DIR" != "$HADOOP_YARN_HOME/$YARN_DIR" ] ; then
if [ -d "$HADOOP_MAPRED_HOME/$MAPRED_DIR/webapps" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_MAPRED_HOME/$MAPRED_DIR
fi
if [ -d "$HADOOP_MAPRED_HOME/$MAPRED_LIB_JARS_DIR" ]; then
CLASSPATH=${CLASSPATH}:$HADOOP_MAPRED_HOME/$MAPRED_LIB_JARS_DIR'/*'
fi
CLASSPATH=${CLASSPATH}:$HADOOP_MAPRED_HOME/$MAPRED_DIR'/*'
fi打印
CLASSPATH=/root/hadoop-2.7.0-bin/etc/hadoop:/root/hadoop-2.7.0-bin/share/hadoop/common/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/common/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/*:/root/hadoop-2.7.0-bin/share/hadoop/yarn/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/yarn/*:/root/hadoop-2.7.0-bin/share/hadoop/mapreduce/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/mapreduce/*---
# Add the user-specified CLASSPATH via HADOOP_CLASSPATH
# Add it first or last depending on if user has
# set env-var HADOOP_USER_CLASSPATH_FIRST
# if the user set HADOOP_USE_CLIENT_CLASSLOADER, HADOOP_CLASSPATH is not added
# to the classpath
if [[ ( "$HADOOP_CLASSPATH" != "" ) && ( "$HADOOP_USE_CLIENT_CLASSLOADER" = "" ) ]]; then
# Prefix it if its to be preceded
if [ "$HADOOP_USER_CLASSPATH_FIRST" != "" ]; then
CLASSPATH=${HADOOP_CLASSPATH}:${CLASSPATH}
else
CLASSPATH=${CLASSPATH}:${HADOOP_CLASSPATH}
fi
fi打印
CLASSPATH=/root/hadoop-2.7.0-bin/etc/hadoop:/root/hadoop-2.7.0-bin/share/hadoop/common/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/common/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/hdfs/*:/root/hadoop-2.7.0-bin/share/hadoop/yarn/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/yarn/*:/root/hadoop-2.7.0-bin/share/hadoop/mapreduce/lib/*:/root/hadoop-2.7.0-bin/share/hadoop/mapreduce/*:/contrib/capacity-scheduler/*.jar---然后再回到最开始的hadoop脚本
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---继续执行
function print_usage(){
echo "Usage: hadoop [--config confdir] [COMMAND | CLASSNAME]"
echo " CLASSNAME run the class named CLASSNAME"
echo " or"
echo " where COMMAND is one of:"
echo " fs run a generic filesystem user client"
echo " version print the version"
echo " jar <jar> run a jar file"
echo " note: please use \"yarn jar\" to launch"
echo " YARN applications, not this command."
echo " checknative [-a|-h] check native hadoop and compression libraries availability"
echo " distcp <srcurl> <desturl> copy file or directories recursively"
echo " archive -archiveName NAME -p <parent path> <src>* <dest> create a hadoop archive"
echo " classpath prints the class path needed to get the"
echo " credential interact with credential providers"
echo " Hadoop jar and the required libraries"
echo " daemonlog get/set the log level for each daemon"
echo " trace view and modify Hadoop tracing settings"
echo ""
echo "Most commands print help when invoked w/o parameters."
}这个就不多说了
不多细说---
if [ $# = 0 ]; then
print_usage
exit
fi这个就不用我多说了。
---接下来开始执行命令
走的分支为
#hdfs commands
namenode|secondarynamenode|datanode|dfs|dfsadmin|fsck|balancer|fetchdt|oiv|dfsgroups|portmap|nfs3)
exit
echo "DEPRECATED: Use of this script to execute hdfs command is deprecated." 1>&2
echo "Instead use the hdfs command for it." 1>&2
echo "" 1>&2
#try to locate hdfs and if present, delegate to it.
shift
if [ -f "${HADOOP_HDFS_HOME}"/bin/hdfs ]; then
exec "${HADOOP_HDFS_HOME}"/bin/hdfs ${COMMAND/dfsgroups/groups} "$@"
elif [ -f "${HADOOP_PREFIX}"/bin/hdfs ]; then
exec "${HADOOP_PREFIX}"/bin/hdfs ${COMMAND/dfsgroups/groups} "$@"
else
echo "HADOOP_HDFS_HOME not found!"
exit 1
fi
;;最终执行的是
/root/hadoop-2.7.0-bin/bin/hdfs namenode -format下一篇来讲解这个命令。
来源：oschina
链接：https://my.oschina.net/u/1382024/blog/423648