Run hadoop fsck and determine if our HDFS is corrupt in some way. This is very basic and could be extended further to tell you what the corruption really is.

check_hdfs.sh

#!/bin/sh

if [ -x /usr/bin/hadoop ] ; then
    chk_hdfs=`/usr/bin/hadoop fsck / | grep 'filesystem under path'`

    case $chk_hdfs in
        *HEALTHY*)
            echo "OK - HDFS is healthy"
            exit 0
        ;;
        *)
            echo "CRITICAL - HDFS is corrupt!"
            exit 2
        ;;
    esac
else
    echo "UNKNOWN - can't execute /usr/bin/hadoop"
    exit 3
fi