how to ssh logon remote host without password

ou want to connect from machine "left" to machine "right".

Log into left:
mkdir ~/.ssh
cd ~/.ssh
ssh-keygen -b 1024 -t rsa1 -C "you@yourdomain.com" -N ""
ssh-keygen -b 1024 -t rsa -C "you@yourdomain.com" -N ""
ssh-keygen -b 1024 -t dsa -C "you@yourdomain.com" -N ""

This creates six files in your ~/.ssh directory:
identity
identity.pub
id_rsa
id_rsa.pub
id_dsa
id_dsa.pub

Log into right:
mkdir ~/.ssh
cd ~/.ssh

On right, create a file called "authorized_keys" (in the ~/.ssh directory). Paste the contents of the three .pub files created earlier into this file (you will have to work out for yourself the best way to do this).

Now test it out. On left:
ssh username@right

It should let you in without a password. If it does not, the first thing to check is your file permissions. The ~/.ssh directories on both sides should not be writable by anyone but the owner. The .pub files should be readable by everyone, but the other key files should only be readable by their owner. The permissions should be set correctly by ssh-keygen, but you never know. There are a lot of things that can go wrong here; troubleshooting is complicated and well beyond the scope of these instructions.