ssh-copy-id: Copy SSH Public Key

Overview

ssh-copy-id automates the process of setting up SSH public key authentication, enabling users to securely connect to remote servers without a password. This command by default uses standard public key files like ~/.ssh/id_rsa.pub or ~/.ssh/id_dsa.pub, but you can also specify a particular key file.

Key Features

Copies SSH public key to the remote server
Automatically sets permissions for the authorized_keys file
Supports establishing passwordless SSH connections
Prevents duplicate key additions even when run multiple times (idempotency)

Key Options

The ssh-copy-id command offers several useful options to finely control the key copying process.

Key and Connection Settings

Execution Modes

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Usage Examples

Various scenarios for copying SSH public keys to a remote server using ssh-copy-id.

Basic Usage

ssh-copy-id user@remote_host

Copies the default public key (e.g., ~/.ssh/id_rsa.pub) to the 'user' account on 'remote_host'. You will be prompted to enter the password.

Specify a Specific Key File

ssh-copy-id -i ~/.ssh/my_custom_key.pub user@remote_host

Copies the key using a specified public key file (e.g., ~/.ssh/my_custom_key.pub).

Using a Non-Standard SSH Port

ssh-copy-id -p 2222 user@remote_host

Use this when the remote server runs its SSH service on a port other than the default (22), such as port 2222.

Combining Multiple Options

ssh-copy-id -i ~/.ssh/another_key.pub -p 2222 user@remote_host

An example of copying a key to a non-standard port using a specific key file.

Tips & Precautions

Useful tips and precautions when using ssh-copy-id.

Prerequisites

Before using ssh-copy-id, please check the following:

Generate Public Key: If you don't have an SSH key pair yet, you must generate one first using the `ssh-keygen` command.
Remote Server Access: You need to have a password or another authentication method to access the remote server via SSH. ssh-copy-id requires a password for this initial authentication.

Permission Issues

ssh-copy-id automatically sets the correct permissions for the `~/.ssh` directory and the `~/.ssh/authorized_keys` file on the remote server. If you copied the key manually, you must set the permissions correctly using the commands `chmod 700 ~/.ssh` and `chmod 600 ~/.ssh/authorized_keys`.

Idempotency

ssh-copy-id does not add a key that has already been copied. Therefore, running it multiple times will not result in duplicate keys accumulating in the authorized_keys file. This is a very convenient feature for use in scripts.