SSH and SFTP errors on macOS

One page per exact message. Read which family your error belongs to first — applying a host key fix to an authentication problem is how a working setup gets worse.

Written and maintained by OnePasswordManager Ltd. Last checked against current documentation on 21 August 2026.

The pages below index SSH and SFTP error messages, written for people using a Mac. Each linked page takes one exact message, explains what the software is actually telling you, and ends with the command that resolves it. The pages are deliberately narrow: an error message is a precise thing, and a page that answers five of them answers none of them well.

Read the error before you fix it

SSH failures fall into two families, and telling them apart before you touch anything saves most of the time people lose to them. The first family is about the server proving its identity to you: messages mentioning host keys, known_hosts, or a changed fingerprint. Nothing about your own key is involved, and the correct response sometimes is to stop rather than to proceed. The second family is about you proving your identity to the server: messages mentioning publickey, authentication, or permission denied. Here the question is which key was offered and why the server refused it. Running the same fix from a search result against the wrong family is the most common way to make a working setup worse.

The one command worth learning first

ssh -v you@server.example.com

A single -v turns an unhelpful one-line refusal into a transcript of the negotiation, and it is almost always enough. In that output you can see which configuration files were read, which host key the server presented, which of your identities the client offered and in what order, and where the exchange stopped. Two more vs exist and are rarely needed. If you are about to ask anyone for help with an SSH problem, the output of ssh -v is the thing to bring; without it, every answer you get is a guess, including the ones you find in search results.

Error index

• Permission denied (publickey)

  The server rejected your key, or never saw it. On macOS the usual cause is the agent, not the file permissions that Linux-oriented guides start with.

• Host key verification failed

  Including the alarming REMOTE HOST IDENTIFICATION HAS CHANGED banner. When to clear the entry, and when clearing it is the wrong move.

Messages not covered yet, and the short answer for each

These do not have their own page. The one-line diagnosis is here so the page is still useful to you if yours is on this list, rather than leaving you with nothing.

Is an SFTP error the same as an SSH error?

Sometimes, and the distinction is worth holding onto. SFTP runs as a subsystem inside an already-established SSH connection, so every authentication and host key error above applies to SFTP identically — if ssh cannot connect, neither can sftp, for the same reason. Errors that appear only under SFTP are different: permission errors on individual files, messages about the subsystem not being available, or failures partway through a transfer. Those are about what the server lets your user account do once you are already logged in, or about the SFTP subsystem being disabled in sshd_config. If your problem reproduces with plain ssh, it is not an SFTP problem.