Linux: Adding SSH Keys with ssh-copy-id

If you are attempting to add an SSH key (to a Linux host), from another Linux host, you can use a built-in utility called, ssh-copy-id .

Due to its simplicity, this method is highly recommended if available. If you do not have ssh-copy-id available to you on your client machine, you may use one of the two alternate methods provided in this section (copying via password-based SSH, or manually copying the key).

Using ssh-copy-id

The ssh-copy-id tool is included by default in many operating systems, so you may have it available on your local system. For this method to work, you must already have password-based SSH access to your server.

To use the utility, you specify the remote host that you would like to connect to, and the user account that you have password-based SSH access to. This is the account to which your public SSH key will be copied.

The syntax is:

ssh-copy-id username@remote_host

You may see the following message:

OutputThe authenticity of host '203.0.113.1 (203.0.113.1)' can't be established.
ECDSA key fingerprint is fd:fd:d4:f9:77:fe:73:84:e1:55:00:ad:d6:6d:22:fe.
Are you sure you want to continue connecting (yes/no)? yes

This means that your local computer does not recognize the remote host. This will happen the first time you connect to a new host. Type “yes” and press ENTER to continue.

Next, the utility will scan your local account for the id_rsa.pub key that we created earlier. When it finds the key, it will prompt you for the password of the remote user’s account:

Output/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
username@203.0.113.1's password:

Type in the password (your typing will not be displayed, for security purposes) and press ENTER.

The utility will connect to the account on the remote host using the password you provided.

It will then copy the contents of your ~/.ssh/id_rsa.pub key into a file in the remote account’s home ~/.ssh directory called authorized_keys.

You should see the following output:

OutputNumber of key(s) added: 1

Now try logging into the machine, with:   "ssh 'username@203.0.113.1'"
and check to make sure that only the key(s) you wanted were added.