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Generate the key pair in macOS Terminal with ssh-keygen, keep the private key on your Mac, and append only the matching .pub key to the VPS account’s ~/.ssh/authorized_keys. For a current OpenSSH installation, Ed25519 is the practical default:
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ssh-keygen -t ed25519 -C "[email protected]"Protect the private key with a passphrase, install the public key on the correct VPS user, set the server-side permissions to 700 for ~/.ssh and 600 for authorized_keys, then test with ssh [email protected]. This guide explains every step, where macOS stores the files, how to use a named key, and what to check when SSH still asks for a password.
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SSH public-key authentication uses two mathematically related files. The private key proves your identity and must remain on your Mac. The public key can be distributed to servers; it does not let someone derive or use the private key in normal operation.
When you connect, the SSH client offers a public-key identity. The VPS checks whether the corresponding public key appears in the target account’s ~/.ssh/authorized_keys. If it does, the client proves possession of the private key without sending that private key to the server. A password may still be enabled as a separate login method, but a correctly installed key normally lets you authenticate without typing the account password.
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macOS includes the OpenSSH client and the ssh-keygen utility. DigitalOcean’s OpenSSH documentation, last verified 13 July 2026, describes this same workflow. Your VPS provider may use a different username, hostname, port, or server policy, so substitute those values for the examples below.
Choose an algorithm before generating the key
Ed25519: the modern default
Use Ed25519 unless the VPS software is old or its provider specifically requires another algorithm. The command is short, the resulting public key is compact, and it is the modern default in the documented OpenSSH workflow.
RSA: a compatibility fallback
RSA can be appropriate when a legacy server, older SSH library, or provider control panel does not accept Ed25519. Do not assume RSA is universally better or worse: compatibility depends on the SSH software and policy on the VPS. If you need RSA, generate it explicitly and use a separate filename so it cannot overwrite an existing identity:
ssh-keygen -t rsa -b 4096 -C "[email protected]" -f ~/.ssh/id_rsa_vpsThe server must support the algorithm and any signature policy required by its SSH version. Check the VPS image documentation when compatibility is uncertain.
Hardware-backed Ed25519 security keys
OpenSSH also supports ed25519-sk, which uses a compatible FIDO authenticator to keep key operations tied to hardware. This is an advanced option, not a prerequisite for ordinary VPS access. Both your Mac’s OpenSSH build and the VPS must support the method, and the authenticator must be available whenever its protection is required.
Generate the key pair in Terminal
- Open Terminal. Use Spotlight, Applications › Utilities › Terminal, or another terminal emulator.
- Run the Ed25519 command.
ssh-keygen -t ed25519 -C "[email protected]"The comment is a label that helps you identify the key later; it is not a password. Replace the address with a useful label if desired.
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/Users/your-name/.ssh/id_ed25519, represented by the shorthand~/.ssh/id_ed25519. PressENTERto accept it when this is a new default identity. - Respond carefully if a file already exists. Do not overwrite a key that may still be used for another server, repository, or service. Enter a new path such as
~/.ssh/id_ed25519_vps2instead. You can always select that identity later with-i. - Enter a passphrase. Type it when prompted and repeat it. DigitalOcean recommends a passphrase because it protects the private-key file if your Mac is copied or compromised. You can press
ENTERto leave it empty, but an unencrypted private key provides less protection if the file is stolen.
On success, ssh-keygen creates two files. The private key is ~/.ssh/id_ed25519; the public key is ~/.ssh/id_ed25519.pub. For a named identity, replace id_ed25519 with the filename you selected. The public file is one line of text that normally begins with ssh-ed25519. Never upload, paste, or email the private file.
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Know where macOS stores SSH files
The tilde (~) means your macOS home directory. Therefore:
| Item | Typical path | Purpose |
|---|---|---|
| Private Ed25519 key | ~/.ssh/id_ed25519 |
Secret proof held on the Mac |
| Public Ed25519 key | ~/.ssh/id_ed25519.pub |
Copy this line to the VPS account |
| Named private key | ~/.ssh/id_ed25519_vps2 (example) |
Separate identity for a particular server or purpose |
| Named public key | ~/.ssh/id_ed25519_vps2.pub |
Matching public half of the named key |
To inspect the directory without displaying the private key, run:
ls -la ~/.sshIt is safe to display the public key when you are installing it. If you need to inspect its exact one-line contents, use:
cat ~/.ssh/id_ed25519.pubDo not run cat on the private-key file in a chat, ticket, web form, or shell transcript that others can read.
Install the public key on the VPS
The public key must be added to the target account’s ~/.ssh/authorized_keys. Uploading the file somewhere else on the VPS, placing it in the wrong user’s home directory, or leaving it only on your Mac does not enable login.
One-command installation when password login works
From your Mac, run this command with the VPS username and address supplied by your provider:
cat ~/.ssh/id_ed25519.pub | ssh [email protected] "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"The first cat reads the public key locally. The pipe sends that line through an SSH session authenticated with your existing password. On the VPS, mkdir -p creates the directory if necessary, and >> appends the key rather than replacing existing keys. Enter the VPS account password when prompted.
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For a named key, change only the local filename:
cat ~/.ssh/id_ed25519_vps2.pub | ssh [email protected] "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"Using ssh-copy-id
Some macOS setups have ssh-copy-id available, although it is not present in every installation. Where it exists, use:
ssh-copy-id -i ~/.ssh/id_ed25519.pub [email protected]It performs the same basic task: authenticate with the current method and append the selected public key to the account’s authorized-key file. If the command is unavailable, use the pipe-and-SSH method above or follow your provider’s console instructions.
Manual installation from a provider console
If password SSH is disabled but the VPS offers a web or serial console, open a shell as the target account, create ~/.ssh, and append the complete public-key line to ~/.ssh/authorized_keys. Keep the key on one line; do not add wrapping or omit the key type, encoded key, or comment. The file belongs to the account that will log in, not automatically to the administrative account.
Set permissions that OpenSSH accepts
SSH can reject a key when the account’s SSH directory or authorized-key file is writable by other users. On the VPS, run:
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chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keysAlso verify that the directory and file are owned by the intended login account. If the key is installed under a different account’s home directory, move it to that account’s ~/.ssh/authorized_keys or connect using the account that owns it. Your provider’s image documentation may impose additional SSH restrictions.
The private key on your Mac should likewise be accessible only to you. If macOS reports that the key permissions are too open, restrict the file:
chmod 600 ~/.ssh/id_ed25519Apply the same command to a named private key, changing the path accordingly.
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Test key-based login
- Run the basic connection command:
ssh [email protected]Replace user and server.example with the exact VPS account and address. The first connection may show a host-authenticity warning and ask whether you want to continue. Before accepting, compare the displayed fingerprint with the fingerprint shown in your provider’s trusted control panel or console. The available documentation demonstrates the prompt but does not define one universal verification procedure for every provider.
- If the key has a non-default filename, identify it explicitly:
ssh -i ~/.ssh/id_ed25519_vps2 [email protected]- After successful authentication, confirm that you reached the expected VPS and account. A shell prompt alone does not prove that you selected the intended server or username.
Once the key works, you can optionally configure an SSH host alias in ~/.ssh/config so you do not have to type -i repeatedly. Keep any configuration entry limited to the host, user, and identity you intend to use, and protect the file from other local users.
Use ssh-agent for passphrase convenience
A passphrase encrypts the private key at rest, but entering it for every connection can be inconvenient. An SSH agent can hold an unlocked key in memory for repeated use during your session. Start or access the agent and add the key:
eval "$(ssh-agent -s)"
ssh-add ~/.ssh/id_ed25519Enter the key’s passphrase when ssh-add requests it. For a named identity, substitute its path. The agent stores the usable key material for the session according to the agent and macOS behavior; it does not copy the private key to the VPS. Remove a key from the agent when it is no longer needed with:
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ssh-add -d ~/.ssh/id_ed25519Agent behavior and persistence can vary by macOS release and shell setup. If you use a shared Mac account, treat an unlocked agent as a sensitive credential.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why SSH still asks for a password
A password prompt can mean either that the key was not offered or that the server rejected it. Work through these checks in order.
Confirm the username and address
The authorized key is valid only for the account in whose home directory it is installed. Check the provider’s exact login username, VPS address, and any nonstandard port. Installing the key for one account and connecting as another produces a public-key failure even when the key text is correct.
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Confirm that the complete public key was appended
On the VPS, inspect the target account’s ~/.ssh/authorized_keys and compare the line with the output of cat ~/.ssh/id_ed25519.pub on your Mac. The key type, encoded body, and comment must remain together on one line. Do not accidentally paste the private key or introduce line breaks.
Check server-side path, ownership, and permissions
Make sure the file is exactly ~/.ssh/authorized_keys for the account you are using, that ~/.ssh is mode 700, and that authorized_keys is mode 600. Verify ownership as well. A key in /root/.ssh/authorized_keys does not authenticate a regular user, and a file owned by the wrong account may be ignored.
See which identity the client offers
Run SSH in verbose mode:
ssh -v [email protected]The diagnostic output shows the identities the client searches for and offers. Look for your intended private-key path. If it is absent, use -i explicitly:
ssh -v -i ~/.ssh/id_ed25519_vps2 [email protected]Do not publish verbose output if it contains hostnames, usernames, or other operational details that your organization treats as sensitive.
Do not assume every provider has the same SSH policy
The documented workflow does not establish every VPS provider’s server configuration. An image may disable password login, restrict accepted algorithms, use a custom SSH port, or apply account-specific settings. Consult the image or provider documentation when the local key, remote path, ownership, and permissions are correct but authentication still fails.
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- Keep private keys private. Never paste them into a VPS control panel, ticket, chat, repository, or command intended to install a public key.
- Use one identity per purpose when practical. A named key for a VPS makes revocation and troubleshooting easier than reusing one key everywhere.
- Do not overwrite blindly. When
ssh-keygenreports an existing file, choose a new filename unless you have confirmed that the old key is no longer needed. - Preserve the public/private pairing. The
.pubfile must match the private key you offer. Installing a public key generated from a different private key will always fail. - Rotate deliberately. Generate a replacement key, append its public half, test it in a new session, and only then remove the old line from
authorized_keys. This avoids locking yourself out. - Back up securely. A passphrase-protected private key can be stored in an encrypted backup, but never leave an unprotected copy in cloud-sync folders or shared storage.
Ed25519 versus RSA at a glance
| Decision point | Ed25519 | RSA |
|---|---|---|
| Role in this workflow | Modern default for current OpenSSH deployments | Fallback for legacy or restricted servers |
| Generation example | ssh-keygen -t ed25519 -C "[email protected]" |
ssh-keygen -t rsa -b 4096 -C "[email protected]" -f ~/.ssh/id_rsa_vps |
| Compatibility | Requires server support for Ed25519 | Broad legacy compatibility, subject to the server’s RSA signature policy |
| File handling | Private key stays on Mac; matching .pub line goes in authorized_keys |
Same handling rules; use a distinct filename if another key exists |
| Choice when VPS version is unknown | Try first on a current image; verify provider support | Use only when compatibility evidence calls for it |
No single algorithm is guaranteed for every VPS. The server’s SSH implementation and provider policy determine what can be accepted.
Quick Recap
A repeatable checklist
- Open Terminal on the Mac.
- Generate Ed25519, or RSA only for a documented compatibility reason.
- Accept
~/.ssh/id_ed25519or choose a new filename without overwriting a needed key. - Set a strong passphrase and keep the private file on the Mac.
- Append only the matching
.publine to the target account’s~/.ssh/authorized_keys. - Set VPS permissions to 700 for
~/.sshand 600 forauthorized_keys; verify ownership. - Test with the exact provider-supplied username and address.
- Use
ssh -iandssh -vwhen a named key is not automatically offered. - Verify the host fingerprint through a trusted provider channel on the first connection.
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