Setting up SSH Keys via Terminal - Linux or macOS X

Setting up SSH Keys is straightforward and essential for enhancing security, especially when utilising the native Terminal applications available on Linux or macOS systems.

1.  Generating the Key Pair

Start by opening the Terminal program on your local machine and typing the following command to generate the keys:

Bash

ssh-keygen

• Generation Options: This command will prompt you with a few questions; it is recommended to accept the defaults for the file name (usually id_rsa).
• Passphrase: When asked for a Passphrase, we strongly recommend entering a strong passphrase. This adds an extra layer of security to your Private Key, preventing its use if the key file is compromised. (If you choose not to use one, simply press Return).

Result: Two keys will be generated in the default path (typically): ~/.ssh/

• Private Key: id_rsa
• Public Key: id_rsa.pub

2.  Copying the Public Key to the Server

Next, you need to copy the Public Key (id_rsa.pub) to the remote server you wish to log into and add it to the authorized_keys file. You can do this efficiently using the ssh-copy-id command:

Bash

ssh-copy-id -i ~/.ssh/id_rsa.pub username@ip.add.ress.here

Ensure you replace:

• username with the intended server access username.
• ip.add.ress.here with the IP address or domain name of your server.

 Specifying a Non-Standard Port

If your server uses an SSH port other than the default (22), you can specify it using the -p option (Example for port 2222):

Bash

ssh-copy-id -p 2222 -i ~/.ssh/id_rsa.pub username@ip.add.ress.here

• Authentication: When running this command, you will be prompted for the current password for that user on the server. Once entered, the key will be copied and the necessary permissions set automatically on the server.

3.  Verifying Security Permissions

After copying the key, you should ensure the file and directory permissions on the remote server are correctly set (to prevent authentication failures). SSH into your server (using the password one last time), and execute the following commands:

Bash

# Log in to the server
ssh username@domain.com

# Inside the server, set permissions:
chmod 700 ~/.ssh 
chmod 600 ~/.ssh/authorized_keys

• Note: The chown command is typically unnecessary if ssh-copy-id was used and executed by the correct user.

4.  Logging In with the Key

You can now test the connection. The server should automatically accept your Private Key without asking for a password (or it will ask for the passphrase you set for the key):

Bash

ssh username@domain.com

Updated on: 04/12/2025