[root@test ~]# 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:
79:a9:66:cd:1a:a5:7c:82:80:c3:06:ec:44:13:b9:7a root@test
The key's randomart image is:
+--[ RSA 2048]----+
| +o |
|o.. |
|.o. |
|o+ . . . |
|..= . S + |
|..E. . o B |
| . . O + |
| o = |
| . |
+-----------------+

[root@test ~]# ls .ssh/
authorized_keys id_rsa id_rsa.pub
[root@test ~]#
[root@test ~]# ssh-copy-id -i /root/.ssh/id_rsa.pub root@192.168.0.178
The authenticity of host '192.168.0.178 (192.168.0.178)' can't be established.
RSA key fingerprint is 53:bd:d7:e6:27:96:f3:70:f1:4b:4d:35:a4:38:1d:69.
Are you sure you want to continue connecting (yes/no)"ssh 'root@192.168.0.178'", and check in:
.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
[root@test ~]#

[root@test ~]# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:0c:29:7e:1f:f6 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.177/24 brd 192.168.0.255 scope global eth0
inet6 fe80::20c:29ff:fe7e:1ff6/64 scope link
valid_lft forever preferred_lft forever
[root@test ~]#
[root@test ~]# ssh 192.168.0.178
Last login: Sat Sep 24 14:00:49 2016 from 192.168.0.103
[root@test ~]#ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:0c:29:36:93:06 brd ff:ff:ff:ff:ff:ff
inet 192.168.0.178/24 brd 192.168.0.255 scope global eth0
inet6 fe80::20c:29ff:fe36:9306/64 scope link
valid_lft forever preferred_lft forever

[root@test .ssh]# cat authorized_keys
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEA+I6LXDE5DvSmQJcX98FpzScXoGpJ6fD47yXzp/tp/HTpOTQgNbiTjH6s6yNMsd5LQlBED8a5CTx5wKm+H7rT0po2xD+AZcF69js+4SwO8/xFwHLZ/8O64hsvn68GmxqO9vP8giWWcZNy/CsmOecllOB1NFXpCwQ1TBw+P4n84oj2YHwdSzGcre8j/OiAChHl6QHFtAuFvOdVRYFeyurFM8KP6Bb6tEeDDrqILboaQtTJOwRD2Fkt33C5lpuZNNGqc+DmRjDabgC3ZgzRCe3OyYbhaRlfiwVHFPYt7pDQMnrp/dUmyBSs/6gwd2CiK3cV4ZvpOzyGdynPqXsxIIBIKw== root@test