Datanode is not running - Datanode is missing - how to fix?

// Datanode is not up. Its not running. we need to do the following fix to make datanode up

jps
3317 NameNode
3785 SecondaryNameNode
5292 RunJar
21276 SparkSubmit
4350 NodeManager
5711 Jps
4063 ResourceManager
stop-all.sh

hadoop@hadoop:/usr/local/hadoop/etc/hadoop$ sudo gedit core-site.xml
see this :
<name>hadoop.tmp.dir</name>
<value>/app/hadoop/tmp</value> // this is the location we need to recreate
<description>A base for other temporary directories.</description>
</property>

// delete
sudo rm -Rf /app/hadoop/tmp

//recreate
sudo mkdir /app/hadoop/tmp
sudo chown -R hadoop:hadoop /app/hadoop/tmp
sudo chmod 777 /app/hadoop/tmp

format namenode
hdfs namenode -format

start-all.sh

jps
3317 NameNode
3785 SecondaryNameNode
5292 RunJar
21276 SparkSubmit
4350 NodeManager
3519 DataNode
5711 Jps
4063 ResourceManager