1. sudo vim /etc/profile

sudo into the profile file

2.

export JAVA_HOME=/usr/lib/jvm/jdk-1.8.0_212
export HADOOP_HOME=usr/local/hadoop
export PATH=.:$HADOOP_HOME/bin:$JAVA_HOME/bin:$PATH

Add the above three to the end of the profile file

Press i to edit first, press Esc after writing, then: wq save and exit

3.source /etc/profile

Update environment variables

This problem can be solved by the above three steps