Generating an SSH Key and Copying it to Remote Server

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Aug 26, 2014
Last updated: Jan 25, 2021
Linux
2 minutes

1mkdir ~/.ssh && chmod 700 ~/.ssh
2touch ~/.ssh/authorized_keys && chmod 600 ~/.ssh/authorized_keys
3# copy key.pub to authorized_keys
4# nano /etc/ssh/sshd_config
5service ssh reload

Generate the Key (on local server)

1cd ~/.ssh && ssh-keygen -t ed25519

Ed25519 is a newer algorithm which is faster than RSA. Ed25519 is supported by OpenSSH so you should be good in almost all cases. Github recommends passing it your email with -C which is then uses as a label.

1cd ~/.ssh && ssh-keygen -t ed25519 -C "hello@example.com"

Add SSH key to macOS Keychain

1ssh-add --apple-use-keychain ~/.ssh/id_ed25519

Making Sure the Remote Server Accepts SSH Keys

view the server’s sshd_config file

1cat /etc/ssh/sshd_config

Check the following:

1RSAAuthentication yes
2PubkeyAuthentication yes
3AuthorizedKeysFile	~/.ssh/authorized_keys

Making sure the .ssh folder and authorized_keys file exists on Remote server

1sudo mkdir ~/.ssh && sudo touch ~/.sh/authorized_keys

Setting Permission on Remote Server

1sudo chmod go-w ~/ && sudo chmod 700 ~/.ssh && sudo chmod 600 ~/.ssh/authorized_keys

Copying SSH Public Key from Local to Remote Server

On macOS you can use the ssh-copy-id command to copy the SSH key to remote server

1ssh-copy-id -i ~/.ssh/mykey user@host

If you get the following error

/usr/bin/ssh-copy-id: WARNING: All keys were skipped because they already exist on the remote system.
		(if you think this is a mistake, you may want to use -f option)

then force copy it with -f flag

1ssh-copy-id -f -i <key_path> <remote_server>

Remote server can either be in the user@host form or a name of a saved Host in .ssh/config

Alternatively, you can copy the key output manually over SSH, like this:

1cat ~/.ssh/id_ed25519.pub | ssh username@example.com "cat >> ~/.ssh/authorized_keys"

replace id_ed25519.pub with your generated key.

Troubleshooting

make sure the authorized_keys file isn’t empty.
make sure you copied the correct authorized_keys file (.pub file that is)
make sure the user you are connecting to owns the .ssh folder and the authorized_keys file
make sure the permissions for the .ssh (700) folder and the authorized_keys (600) file are correct on the remote server
make sure the path given in ‘sshd_config’ is correct. /home/.ssh/authorized_keys and ~/.ssh/authorized_keys are different if the user you are connecting to isn’t root. ~/.ssh/authorized_keys is preferred since it is relative to the user.

Notes