ssh-keygen to login without password

ssh-keygen.sh

# generate ssh key
$ ssh-keygen -t rsa

# create .ssh/authorized_keys on server
# and paste client ssh key
# and set permission
$ ssh $username@$hostname mkdir -p .ssh
$ cat .ssh/id_rsa.pub | ssh $username@$hostname 'cat >> .ssh/authorized_keys'
$ ssh $username@$hostname "chmod 700 .ssh; chmod 640 .ssh/authorized_keys"

# connect without password
$ ssh $username@$hostname