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:
The key's randomart image is:
+--[ RSA 2048]----+
| o ... .o. |
| o + ..... |
|+ o o .. o |
|o= + + . . |
|E + o S |
|.. . |
| . |
now login to the host linux box as root 172.16.0.177 and copy,
scp -r firstname.lastname@example.org:/root/.ssh/id_rsa.pub /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 email@example.com:/usr/local/src/April /usr/local/src/
It won't prompt for any password.