q_datanode.sh

#!/bin/bash
usage(){
    echo "Usage: $0 hostname port"
    echo "Note: hostname can not be ip"
    exit 1
}

function valid_ip()
{
    local  ip=$1
    local  stat=1

    if [[ $ip =~ ^[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}$ ]]; then
        OIFS=$IFS
        IFS='.'
        ip=($ip)
        IFS=$OIFS
        [[ ${ip[0]} -le 255 && ${ip[1]} -le 255 \
            && ${ip[2]} -le 255 && ${ip[3]} -le 255 ]]
        stat=$?
    fi
    return $stat
}

# invoke  usage
# call usage() function if filename not supplied
[[ $# -ne 2 ]] && usage

host=$1
port=$2
username="hadoop"
CONN_TIMEOUT=15
localhost=`hostname`


# check hostname
if valid_ip $1; then
    usage
fi


# return value : 0 undetermined 1 killed 3 alive

# 1. try to kill the process
ssh -o ConnectTimeout=$CONN_TIMEOUT $username@$host "fuser -v -k -n tcp $port"
ret=$?
echo "$localhost ssh return value $ret" 
if [ $ret -eq 0 ]; then
    echo "$localhost: Kill the active namenode successfully!"
    exit 1
elif [ $ret -eq 2 ]; then
    echo "$localhost: Can not ssh when kill!"
    exit 0
elif [ $ret -eq 255 ]; then
    echo "$localhost: $host ssh service is down!"
    exit 0
else
# 2. check the port works
    ssh -o ConnectTimeout=$CONN_TIMEOUT $username@$host "nc -z $host $port"
    if [ $? -eq 0 ]; then
        echo "$localhost: Unable to fence - it is running but we cannot kill it!"
        exit 3
    elif [ $? -eq 2 ]; then
        echo "$localhost: Can not ssh when nc!"
        exit 0
    elif [ $? -eq 255 ]; then
        echo "$localhost: $host ssh service is down!"
        exit 0
    else
        echo "$localhost: Active namenode process have been killed!"
        exit 1
    fi
fi