[Ubuntu] SSH without password

The spirit is: Put your public key, say id_rsa.pub, into the target machine’s list, say authorized_key.  Please node that this is one-way function, if you want mutual password-free ssh connections, do it again in opposite direction!

Example:
server_node
client_node

server_node to client_node

Generate private and public keys from server

server_node$: ssh-keygen

Leave all the setting default by pressing enter (you can also enter a strong passphrase for security)
Send the key to the client

ssh-copy-id client_node

This is a shortcut to 
1. copy the the public key (id_rsa.pub) to the client_node 

server_node$: scp ~/.ssh/id_rsa.pub client_node/.ssh

2. copy the contend of id_rsa.pub from server_node to the list (authorized_key) in the client_node

client_node$: cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys

Test whether it works

server_node$: ssh client_node

If you are required to enter password/passphrase, do the following

server_node$:  sudo apt-get install keychain

Add the following to your ~/.bashrc (depend on your shell)

if type keychain >/dev/null 2>/dev/null; then      keychain --nogui -q id_rsa      [ -f ~/.keychain/${HOSTNAME}-sh ] && . ~/.keychain/${HOSTNAME}-sh      [ -f ~/.keychain/${HOSTNAME}-sh-gpg ] && . ~/.keychain/${HOSTNAME}-sh-gpg

If you encounter syntax problems, please check the indent, make sure the indent are 4 spaces.


This is just one way process, if you want to mutual password-free, do it again on the client_node.  OR copy your .ssh files file server_node to client_node.

NOTE: If you manually copy id_rsa.pub, be aware of not overriding the key, rename the name before transmitting.