Reasons why the NameNode fails to start and solutions

Problem: After starting Hadoop, I checked with JPS and found no NameNode

The NAMenode Format creates a new NAMenodeld every time, and TMP/DFS /data contains the ID under the last format. The Namenode Format clears the data under the Namenode, but does not clean the data under the Datanode, which causes startup failure.
Solutions:

stop running hadoop

stop -dfs.sh

delete the file items mapped by hadoop.tmp.dir in the core-site configuration file, generally hadoop/ TMP folder

sudo rm -r tmp

performs formatting

./bin/hdfs namenode -format

restart

start-hdfs.sh