How to scp, ssh and rsync without prompting for password

For example, login in to some host linux box as root 172.16.0.155 and pass the command as,

ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /root/.ssh/id_rsa.
Your public key has been saved in /root/.ssh/id_rsa.pub.
The key fingerprint is:
35:50:28:70:2b:b0:9f:01:9a:8b:cb:0e:17:89:1d:a2 root@InVImFTSrv
The key's randomart image is:
+--[ RSA 2048]----+
|  o ... .o.      |
| o + .....       |
|+ o o ..  o      |
|o= + +   . .     |
|E + o   S        |
|.. .             |
|o..              |
|o.               |
| .               |
+-----------------+


now login to the host linux box as root 172.16.0.177 and copy,

scp -r root@172.16.0.155:/root/.ssh/id_rsa.pub /root/.ssh/

cd /root/.ssh/
cat id_rsa.pub >> authorized_keys
chmod 700 /root/.ssh/authorized_keys

now form 172.16.0.155 try ssh, scp or rsync as,

scp -r root@172.16.0.177:/usr/local/src/April /usr/local/src/

It won't prompt for any password.

Ref:-https://blogs.oracle.com/jkini/entry/how_to_scp_scp_and