Guys,

I finally solved ALL the Errors: in  ...datanode*.log  after trying to start the node with "service datanode start".
The errors were:
- conflicting NN DD ids - solved through reformatting NN.
- could not connect to 127.0.0.1:8020 - Connection refused - solved through correcting a typo inside hdfs-site.xml under dfs.namenode.http-address; somehow had the default value i/o localhost. (Running pseudo-mode)
- conf was pointing to the wrong sLink - solved by running alternatives -set hadoop-conf <conf.myconf>

However, when I run "service -status-all", still see that datanode [FAILED] message. All others, NN, SNN, JT, TT are running [OK].
1.       Starting daemons, all seems OK:
Starting Hadoop datanode:                                  [  OK  ]
starting datanode, logging to /home/hadoop/logs/hadoop-root-datanode-ip-10-204-47-138.out
Starting Hadoop namenode:                                  [  OK  ]
starting namenode, logging to /home/hadoop/logs/hadoop-hdfs-namenode-ip-10-204-47-138.out
Starting Hadoop secondarynamenode:                         [  OK  ]
starting secondarynamenode, logging to /home/hadoop/logs/hadoop-hdfs-secondarynamenode-ip-10-204-47-138.out

2.
running service -status-all command and get:
Hadoop datanode is not running                             [FAILED]
Hadoop namenode is running                                 [  OK  ]
Hadoop secondarynamenode is running                        [  OK  ]

3.
Here is log file on DN:
2012-10-25 15:33:37,554 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: STARTUP_MSG:
/************************************************************
STARTUP_MSG: Starting DataNode
STARTUP_MSG:   host = ip-10-204-47-138.ec2.internal/10.204.47.138
STARTUP_MSG:   args = []
STARTUP_MSG:   version = 2.0.0-cdh4.1.1
STARTUP_MSG:   classpath = /etc/ha..........
...............................
..............................
2012-10-25 15:33:38,098 WARN org.apache.hadoop.hdfs.server.common.Util: Path /home/hadoop/dfs/data should be specified as a URI in configuration files. Please update hdfs configuration.
2012-10-25 15:33:41,589 INFO org.apache.hadoop.metrics2.impl.MetricsConfig: loaded properties from hadoop-metrics2.properties
2012-10-25 15:33:42,125 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: Scheduled snapshot period at 10 second(s).
2012-10-25 15:33:42,125 INFO org.apache.hadoop.metrics2.impl.MetricsSystemImpl: DataNode metrics system started
2012-10-25 15:33:42,204 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Configured hostname is ip-10-204-47-138.ec2.internal
2012-10-25 15:33:42,319 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Opened streaming server at /0.0.0.0:50010
2012-10-25 15:33:42,323 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Balancing bandwith is 1048576 bytes/s
2012-10-25 15:33:42,412 INFO org.mortbay.log: Logging to org.slf4j.impl.Log4jLoggerAdapter(org.mortbay.log) via org.mortbay.log.Slf4jLog
2012-10-25 15:33:42,603 INFO org.apache.hadoop.http.HttpServer: Added global filter 'safety' (class=org.apache.hadoop.http.HttpServer$QuotingInputFilter)
2012-10-25 15:33:42,607 INFO org.apache.hadoop.http.HttpServer: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context datanode
2012-10-25 15:33:42,607 INFO org.apache.hadoop.http.HttpServer: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context logs
2012-10-25 15:33:42,607 INFO org.apache.hadoop.http.HttpServer: Added filter static_user_filter (class=org.apache.hadoop.http.lib.StaticUserWebFilter$StaticUserFilter) to context static
2012-10-25 15:33:42,682 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Opened info server at 0.0.0.0:50075
2012-10-25 15:33:42,690 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: dfs.webhdfs.enabled = false
2012-10-25 15:33:42,690 INFO org.apache.hadoop.http.HttpServer: Jetty bound to port 50075
2012-10-25 15:33:42,690 INFO org.mortbay.log: jetty-6.1.26.cloudera.2
2012-10-25 15:33:43,601 INFO org.mortbay.log: Started SelectChannelConnector@0.0.0.0:50075
2012-10-25 15:33:43,787 INFO org.apache.hadoop.ipc.Server: Starting Socket Reader #1 for port 50020
2012-10-25 15:33:43,905 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Opened IPC server at /0.0.0.0:50020
2012-10-25 15:33:43,917 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Refresh request received for nameservices: null
2012-10-25 15:33:43,943 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Starting BPOfferServices for nameservices: <default>
2012-10-25 15:33:43,950 WARN org.apache.hadoop.hdfs.server.common.Util: Path /home/hadoop/dfs/data should be specified as a URI in configuration files. Please update hdfs configuration.
2012-10-25 15:33:43,958 INFO org.apache.hadoop.hdfs.server.datanode.DataNode: Block pool <registering> (storage id unknown) service to localhost/127.0.0.1:8020 starting to offer service
2012-10-25 15:33:44,297 INFO org.apache.hadoop.ipc.Server: IPC Server Responder: starting
2012-10-25 15:33:44,304 INFO org.apache.hadoop.ipc.Server: IPC Server listener on 50020: starting
2012-10-25 15:33:45,551 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 0 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
2012-10-25 15:33:46,605 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 1 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
2012-10-25 15:33:47,865 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 2 time(s); retry policy is RetryUpToMaximumCountWithFixedSleep(maxRetries=10, sleepTime=1 SECONDS)
2012-10-25 15:33:48,945 INFO org.apache.hadoop.ipc.Client: Retrying connect to server: localhost/127.0.0.1:8020. Already tried 3 time(s); retry policy is RetryUpToMaximu