Using SSH Keys for VPS Login

31 Dec, 2025

This is a simple guide on how to get passwordless logins over ssh to a server up and running on a debian linux based system. By no means is this guide authoritative. It is more of a reminder for my future self on how I did this the next time I get a new VPS up and running again.

Generating a Local SSH Key

First, there must exist a local ssh key. On most unix/linux based systems, per user ssh information is stored in the user's home directory (~) in a dedicated .ssh subdirectory. If there is a key, such as id_ed25519 and a corresponding id_ed25519.pub, then this computer already has a private and public ssh key which can be used in the next steps. If not, the following command can be used to generate a new key:

ssh-keygen

This command first prompts for a location to store the new key and a filename. I would highly recommend sticking with the default here, unless there is a particular reason not to. Second, it asks for a password for the key. This password can be skipped by simply leaving it empty.¹

Uploading the SSH Key to the Server

Once a private/public key pair² exist, the public version of this key needs to be registered on the server as an allowed login key. The easiest way to do this is to use the ssh-copy-id tool as:

ssh-copy-id -i ~/.ssh/<new-key-name>.pub <user>@<server-ip-or-domain>

With the substitutions being:

<new-key-name> being the name of the ssh key. If left with the default name, this would most likely be id_ed25519
<user> being the user on the server for whom passwordless login is being created
<server-ip-or-domain> being the normal ssh access address for the server

Note: This command will ask you for your ssh login password to be able to modify the ssh configuration for the user on the server.

What `ssh-copy-id` Does

The above command makes a copy of the local public (.pub) version of the ssh key. Then, it logs into the server and appends this ssh key to the end of the authorized_keys configuration file.³ Both of these steps can also be done manually if that is preferred. The only caveat being to make sure not to delete any other ssh keys already previousely registered in the authorized_keys configuration file.

Ensure that PubkeyAuthentication is Enabled on the Server

Lastly, it might be worth while to double check that public key authentication is activated for the ssh daemon on the server. By default Debian linux should have this enabled, but the configuration can be double checked in the /etc/ssh/sshd_config file. There should be a line reading:

PubkeyAuthentication yes

Note: It is important to make a destinction between the ssh_config and sshd_config files here. the above mentioned config file is sshd_config. As a general rule of thumb, ssh is relevant for outbound connections and sshd refers to ssh daemon for inbound connections. So login settings will always be found in the sshd files.

Lastly, this private ssh key must be referenced in the ssh login command, as:

ssh -i ~/.ssh/<private-key-name> <user>@<server-ip-or-domain>

With:

<private-key-name> being the name of the private key (no .pub extention) that is the pair of the public key copied to the server
<user> being the user on the server for whom this passwordless login was set up
<server-ip-or-domain> being the server address such as www.example.com.

This command can also be aliased using something akin to this in whatever shell is being used on the local computer:

alias sshconnect="ssh -i ~/.ssh/<private-key-name> <user>@<server-ip-or-domain>

Footnotes

Theoretically, it might be slightly more secure if the ssh private key were to be encrypted with a password, however, if the base premise of using this ssh key is to create a passwordless login, then setting a password here would defeat the point.↩
The private and public key pair can be differentiated by the .pub extention on the public key. Only the public key should ever be shared off of the computer where it was created to maintain security.↩
The per user authorized_keys configuration file can normally be found in ~/.ssh/authorized_keys.↩

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