login with ssh-key

[root@local-linux ~]# cd ~/.ssh
[root@local-linux .ssh]# ssh-keygen
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:
SHA256:U9+M6TKXwZ6GAj1i7SCOFesWDCyQYC46JG4g9FtStN4 root@local-linux
The key's randomart image is:
+---[RSA 2048]----+
|++  .o           |
|*.. . .          |
|*ooo.o    .      |
|O. o=o.o . o =   |
|oo .*.=ES   * o  |
|.. = + = o + +   |
|  . +   o + B    |
|   .     . =     |
|                 |
+----[SHA256]-----+

[root@local-linux .ssh]# ls -laht
total 16K
drwx------.  2 root root   54 May  5 13:45 .
-rw-------.  1 root root 1.7K May  5 13:45 id_rsa
-rw-r--r--.  1 root root  402 May  5 13:45 id_rsa.pub
-rw-r--r--.  1 root root 3.0K May  5 13:44 known_hosts
dr-xr-x---. 21 root root 4.0K May  3 07:06 ..

[root@local-linux .ssh]# ssh-copy-id some.user@78.141.215.162
/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/root/.ssh/id_rsa.pub"
/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
some.user@78.141.215.162's password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'some.user@78.141.215.162'"
and check to make sure that only the key(s) you wanted were added.

[root@local-linux .ssh]# ssh some.user@78.141.215.162
Activate the web console with: systemctl enable --now cockpit.socket

Last login: Wed May  5 10:50:02 2021 from 85.23.146.80
[some.user@remote-linux ~]$ exit
logout
Connection to 78.141.215.162 closed.