How to Copy SSH Keys with ssh-copy-id

ssh-copy-id is a utility that copies your local SSH public key to a remote server’s authorized_keys file. This sets up key-based authentication, allowing you to log in without entering a password. The command connects to the remote host over SSH to perform the installation.

In this guide, we will show you how to use the ssh-copy-id command with practical examples.

Prerequisites #

Before using ssh-copy-id, you need to have an SSH key pair. If you don’t have one, generate it with:

ssh-keygen -t ed25519

This creates a private key (~/.ssh/id_ed25519) and a public key (~/.ssh/id_ed25519.pub). For more details, see our guide on how to generate SSH keys on Linux .

Syntax #

The basic syntax of ssh-copy-id is:

ssh-copy-id [options] [user@]hostname

The command copies the public key to the remote server and appends it to the ~/.ssh/authorized_keys file. It also sets the correct permissions on the remote .ssh directory and authorized_keys file.

Copying the Default Key #

To copy your default public key to a remote server, run:

ssh-copy-id user@remote_host

You will be prompted to enter the remote user’s password:

/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/user/.ssh/id_ed25519.pub"
/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
user@remote_host's password:

Number of key(s) added: 1

After the key is copied, you can log in without a password:

ssh user@remote_host

Specifying a Key File #

If you have multiple SSH keys, use the -i option to specify which public key to copy:

ssh-copy-id -i ~/.ssh/id_ed25519.pub user@remote_host

Using a Non-Standard Port #

If the remote SSH server listens on a port other than the default 22, use the -p option:

ssh-copy-id -p 2222 user@remote_host

You can combine -i and -p:

ssh-copy-id -i ~/.ssh/id_ed25519.pub -p 2222 user@remote_host

Copying Keys Manually #

If ssh-copy-id is not available on your system, you can copy the key manually using cat and SSH:

cat ~/.ssh/id_ed25519.pub | ssh user@remote_host "mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat >> ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys"

This command does the following:

• Creates the ~/.ssh directory on the remote server if it does not exist.
• Sets the correct permissions (700) on the .ssh directory.
• Appends the public key to the authorized_keys file.
• Sets the correct permissions (600) on the authorized_keys file.

Common Options #

Troubleshooting #

Permission Denied #

If you get a “Permission denied” error, make sure that password authentication is enabled on the remote server. Check /etc/ssh/sshd_config for:

PasswordAuthentication yes

Restart the SSH service after making changes:

sudo systemctl restart sshd

Key Already Installed #

If the key is already in the remote authorized_keys file, ssh-copy-id will skip it and display:

/usr/bin/ssh-copy-id: WARNING: All keys were skipped because they already exist on the remote system.

Use the -f option to force installation if needed.

Quick Reference #

FAQ #

What does ssh-copy-id actually do?
It appends your public key to the ~/.ssh/authorized_keys file on the remote server and sets the correct file permissions. This enables key-based authentication.

Can I use ssh-copy-id on macOS?
Yes. ssh-copy-id is available through Homebrew: brew install ssh-copy-id. It is not included in macOS by default.

Is ssh-copy-id safe to use?
Yes. It only copies your public key, not your private key. The public key is meant to be shared.

What permissions does ssh-copy-id set?
It sets 700 on the ~/.ssh directory and 600 on the authorized_keys file. These permissions are required by the SSH server for security.

Can I copy keys to multiple servers?
Yes. Run ssh-copy-id once for each server. There is no built-in option to copy to multiple hosts at once, but you can use a loop: for host in server1 server2; do ssh-copy-id user@$host; done.

Conclusion #

The ssh-copy-id command is the simplest way to set up key-based SSH authentication. It copies your public key to a remote server and sets the correct permissions automatically.

If you have any questions, feel free to leave a comment below.

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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