How to ssh/scp w/o password prompt

Sometimes, we'd like to automate a file transfer process between main server and backup server. We can use scp to transfer files but usually scp requires input for password prompt. Belows are quick steps to remove the password prompt for scp/ssh.Basically, there are two steps needed:

1. create public and private key in the ssh client
   
2. copy or append the public key content to the ssh server

If you are using SSH version 2, follow the following steps:

1. at the client machine, login as the user who will execute the ssh or scp, then create pair of public and private key using dsa to ~/.ssh/id_dsa with the following command:

   $ ssh-keygen -t dsa -f .ssh/id_dsa

   (If there's a prompt asking for password, leave it blank. There will be two files created on ~/.ssh/ : id_dsa (private key) and id_dsa.pub (public key))
2. Copy or append the content of id_dsa.pub (public key) above to the ssh server at the home directory of the ssh user: ~/.ssh/authorized_keys2

If you are using SSH version 1, follow the following steps (very similar):

1. At the client machine, login as the user who will execute the ssh or scp, then create pair of public and private key using rsa to ~/.ssh/id_rsa with the following command:

   $ ssh-keygen -t rsa -f .ssh/id_rsa

   (If there's a prompt asking for password, leave it blank, there will be two files created.)
2. Copy or append the content of id_rsa.pub (public key) above to the ssh server at the home directory of the ssh user: ~/.ssh/authorized_keys

That's all :)

Update:
Don't forget to set the file permission for the public key file in ssh server:

chmod 600 ~/.ssh/authorized_keys or chmod 600 ~/.ssh/authorized_keys2

That's all :)