hadoop - ubuntu: ssh: connect to host ubuntu port 22: Connection refused

Question

Ubuntu 16.04.1 LTS
Hadoop 3.3.1
I have mannually downloaded and installed java version "1.8.0_261"
when I run start-dfs.sh,

hadoop@ubuntu:~/hadoop/sbin$ start-dfs.sh
Starting namenodes on [ubuntu]
ubuntu: ssh: connect to host ubuntu port 22: Connection refused
Starting datanodes
localhost: ssh: connect to host localhost port 22: Connection refused
Starting secondary namenodes [ubuntu]
ubuntu: ssh: connect to host ubuntu port 22: Connection refused
2021-06-25 17:42:19,711 WARN util.NativeCodeLoader: Unable to load native-hadoop library for your platform... > using builtin-java classes where applicable

Answer 1

Try installing whole SSH package pack:

sudo apt-get install ssh