In linux, how can I avoid password prompts when using the remote Copy command scp?

In linux, if you use the remote Copy command scp, how can I avoid the password prompt-Linux Enterprise Application-Linux server application information? For details, see the following. Write the ssh public key file of your local host user to the remote host user ~ /. Ssh/authorized_keys file, the specific method
Assume that the local host test1 and remote host test2

1. users in the test1 host
Run ssh-keygen-t rsa
The result is as follows:
Generating public/private rsa key pair.

Enter file in which to save the key (/home/. username/ssh/id_rsa): # Press Enter

Enter passphrase (empty for no passphrase): # Press Enter

Enter same passphrase again: # Press Enter

Your identification has been saved in/home/. username/. ssh/id_rsa.

Your public key has been saved in/home/. username/. ssh/id_rsa.pub.

The key fingerprint is:

38: 25: c1: 4d: 5d: d3: 89: bb: 46: 67: bf: 52: af: c3: 17: 0c username @ localhost

Generating RSA keys:

Key generation complete.
Will be in the user directory ~ /. Ssh/generate two files: id_rsa, id_rsa.pub

2. Copy the id_rsa.pub file to the user directory of the test2 host.
Cat id_rsa.pub> ~ /. Ssh/authorized_keys
You can.

In this way, users of the test1 host can log on to the test2 host through ssh without a password.