SSH Copy ID: Where Do Keys Get Stored?

SSH (Secure Shell) is a widely used protocol for secure remote logins, file transfers, and other operations. One of the essential tools when working with SSH is ssh-copy-id. This tool simplifies the process of securely copying your public SSH keys to the target server's .ssh/authorized_keys file. Below, we explore the details of how ssh-copy-id works and where it stores the keys it copies.

Understanding ssh-copy-id

ssh-copy-id is a Unix shell script, which is essentially a series of commands compiled into a single script for easier execution. If you wish to verify that you have the correct version installed, you can use the which command:

```shwhich ssh-copy-id```

Output: /usr/bin/ssh-copy-id

This script is written in a POSIX-compliant shell script and is likely stored as an ASCII text file, though non-printable characters (cljs*) may be present, which do not affect its functionality.

Inspecting the ssh-copy-id Script

For a detailed look at the script, you can use a text editor or less command to view the contents. When you run:

```shless /usr/bin/ssh-copy-id```

You will find the following structure:

Key Steps in the Script

ssh : This is the basic SSH command used to spawn a remote shell. cd : This command ensures that the remote shell returns to the user's home directory upon the script's completion. .ssh: The .ssh directory is automatically created if it does not already exist on the remote system. echo >> .ssh/authorized_keys: This line appends the user's public SSH key to the authorized_keys file in the corresponding directory.

Anatomy of a Public Key

Before understanding how ssh-copy-id works, it is crucial to know about the anatomy of an SSH public key. A typical public key has the following format:

```plaintextssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQD...```

This is a RSA public key. The ssh-rsa denotes the type of key, followed by the actual key data. When you generate a public-private key pair, you use a tool like ssh-keygen, and the output directory is usually the .ssh folder in your home directory.

How ssh-copy-id Copies Public Keys

When you run ssh-copy-id @, the following steps take place:

The script uses SSH to establish a connection to the specified remote host. This connection, once established, allows the script to execute the necessary commands on the remote host. The ssh-copy-id script will drop the user to a shell on the remote host. The script then ensures the .ssh directory exists. The .ssh/authorized_keys file is updated to include the user's public key.

Tips and Considerations

Understanding where and how ssh-copy-id operates can help you troubleshoot SSH issues more efficiently. Here are some tips for better management:

Ensure that the .ssh directory and the authorized_keys file are writable by the owner user. Use the -i option to specify a different public key file if needed. Use the -n option to get a dry run to see what changes would be made, without actually making any changes.

By following these steps, you can easily manage your SSH keys and increase your productivity while working with remote servers.

Conclusion

SSH is a fundamental tool in secure remote access, and ssh-copy-id is an essential command for managing and distributing public keys. Understanding how this command works helps in troubleshooting and leveraging the power of SSH for your projects.