ssh-copy-id

To use the ssh-copy-id command effectively, follow the steps below. This command allows you to copy your SSH public key to a remote server, enabling passwordless login via SSH.

Prerequisites

  1. SSH Key Pair: Make sure you have an SSH key pair generated. The default location is:

    • Public key: ~/.ssh/id_rsa.pub
    • Private key: ~/.ssh/id_rsa

    If you don't have an SSH key, generate one with the following command:

    ssh-keygen -t rsa -b 4096 -C "your_email@example.com"

    Just hit Enter for all prompts to use the default location and settings.

  2. Remote Server Access: You need to have SSH access to the remote server using a password at least once to copy the key.

Steps to Use ssh-copy-id

1. Copy the Public Key to the Remote Server

Use the following command to copy your public key to the remote server:

ssh-copy-id user@remote-server-ip

Replace:

  • user: Your username on the remote server.
  • remote-server-ip: The IP address or hostname of the remote server.

Example:

ssh-copy-id john@192.168.1.10

2. Provide the Password

When prompted, enter the password for the user on the remote server. The ssh-copy-id command will:

  • Append your public key to the ~/.ssh/authorized_keys file on the remote server.
  • Set the correct permissions on the authorized_keys file and directory.

3. Test Passwordless Login

After the key is copied, try logging into the remote server to verify the setup:

ssh user@remote-server-ip

If everything is configured correctly, you won't be prompted for a password.

Optional: Specify a Custom SSH Key

If you are using a non-default SSH key (for example, ~/.ssh/my_custom_key), you can specify it with the -i option:

ssh-copy-id -i ~/.ssh/my_custom_key.pub user@remote-server-ip

Common Issues and Solutions

  • Permission Denied (Public Key): Ensure that:

    • The ~/.ssh directory on the remote server has 700 permissions.
    • The ~/.ssh/authorized_keys file has 600 permissions.

    You can set the correct permissions manually:

    chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys

  • No SSH Key Found: Make sure you generated the SSH key with ssh-keygen and the public key is available at ~/.ssh/id_rsa.pub.

Using ssh-copy-id is a convenient way to set up passwordless SSH access, improving both security and ease of use!

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