By far this is the easiest way:
ssh-copy-id -i path/to/id_rsa.pub user@ipaddress
You can do this also manually, which is does the same as the ssh-copy-id command:
1. Check if you have already an rsa key-pair in ~/.ssh directory. You should have the files id_rsa and id_rsa.pub (or another name-combo, f.e. loboloco and loboloco.pub)
If there isn't such a file combo, proceed with the next step, otherwise skip to step 3.
2. first generate an rsa key-pair on your local machine in ~/.ssh:
ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/dewolfth/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/loboloco/.ssh/id_rsa.
Your public key has been saved in /home/loboloco/.ssh/id_rsa.pub.
The key fingerprint is:
The key's randomart image is:
+--[ RSA 2048]----+
| o. |
| . o o|
| o . o|
| o . o ++|
| ES . . oo+|
| . o.= o|
| . o o.+.|
| o .. . |
| . .. . |
3. Copy the .pub file to the destination server (scp, rsync)
4. Connect to the server via ssh
5. Copy the .pub file to the file ~/.ssh/authorized_keys: cat id_rsa.pub >> .ssh/authorized_keys
That should be it, when you connect again you won't have to enter your password anymore. Very handy if you have to commit code via ssh.