Execute the below command:-

[root@cm ~]# java -XshowSettings:properties -version 2>&1 > /dev/null | grep 'java.home'
    java.home = /usr/java/jdk1.8.0_181-amd64/jre
 

You may get the below error while changing the password for users in linux machines:-

[root@hadoop3 ~]# passwd root
Changing password for user root.
passwd: Authentication token manipulation error

This can be fixed by running the command:-

[root@hadoop3 ~]# authconfig --updateall
 

HDFS Snapshots are read-only point-in-time copies of the file system.

HDFS snapshot is saved copy of an existing directory. Snapshots are used for  for restoring the corrupted data.

Apache Hadoop is an open-source software framework for distributed storage and distributed processing of very large data sets on computer clusters built from commodity hardware. All the modules in Hadoop are designed with a fundamental assumption that hardware failures are common and should be automatically handled by the framework.