why hadoop asks for password before starting any of the services?

why ssh login is required before starting hadoop? And why hadoop asks for password for starting any of the services?

shravilp@shravilp-HP-15-Notebook-PC:~/hadoop-2.6.3$ sbin/start-all.sh
This script is Deprecated. Instead use start-dfs.sh and start-yarn.sh
Starting namenodes on [localhost] 
shravilp@localhost's password: 
localhost: starting namenode, logging to /home/shravilp/hadoop-              


In Ubuntu, you can use the following one time set up steps to eliminate the need to enter password when running hadoop commands, for example, start-dfs.sh, start-yarn.sh:

sudo apt-get install openssh-server openssh-client
ssh-keygen -t rsa
ssh-copy-id user@localhost

replace user with your username. It was tested on Ubuntu 16.04.2, hadoop-2.7.3, jdk1.8.0_121

Note: 1. when execute "ssh-keygen -t rsa" command, you can simply press ENTER three times to accept the default values. 2. when execute "ssh-copy-id user@localhost" command, "Are you sure you want to continue connecting (yes/no)?" enter "yes", then your password

See this question also

It asks for password as it uses the SSH protocol, You could avoid this by adding your public key to all the ssh files of each node to make it passwordless.

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