All Errors

SSH refuses to use private key files with overly permissive permissions (0644, 0755, etc). Private keys must be restricted to the owner only (mode 600 or 400) for security.

SSH shows this warning when the remote host's key fingerprint has changed or doesn't match your stored record. This is a critical security alert that requires verification before proceeding, as it could indicate a man-in-the-middle attack or a legitimate server change.

SSH authentication fails when the SSH agent cannot sign your key. This typically occurs when your SSH key isn't loaded in the agent or the agent has configuration issues, preventing authentication to GitHub or other SSH servers.

SSH authentication failed occurs when the server rejects your login credentials or keys. This can happen due to incorrect credentials, permission issues with key files, wrong key usage, or server configuration mismatches.

SSH shows 'type -1' when it cannot find or load an identity file. This usually means the key file doesn't exist at the specified path or cannot be read. While often a harmless informational message, it indicates SSH is falling back to other authentication methods.

The "client_loop: send disconnect: Broken pipe" error occurs when an idle SSH connection is terminated by the server, firewall, or NAT device due to inactivity timeout. It's common in remote work and cloud environments where keepalive settings aren't configured.

PuTTY's "Server unexpectedly closed network connection" most often means sshd dropped you at connection setup (fail2ban ban, MaxStartups, TCP wrappers, cipher/kex mismatch); idle timeouts are a less common cause.

This SSH error appears when authentication fails due to incorrect credentials, disabled password authentication, or mismatched SSH keys. It typically occurs when logging in with password or public key authentication. Resolve it by verifying credentials, enabling password authentication on the server, or ensuring your SSH keys are properly configured.

This error occurs when SSH cannot verify the authenticity of a remote host's key because it doesn't exist in your known_hosts file or has changed. It's a security feature that prevents man-in-the-middle attacks but requires manual verification the first time you connect to a host.

This error occurs when SSH cannot resolve a hostname due to DNS failures. Check your internet connection, verify DNS server configuration, and ensure your firewall isn't blocking DNS queries (port 53).

This error occurs when the SSH server abruptly closes the connection during the protocol handshake, before authentication is completed. It typically indicates server-side configuration issues, resource constraints, or firewall restrictions rather than a networking connectivity problem.

The SSH daemon (sshd) fails to start with "fatal: Cannot bind any address" when it cannot listen on the configured address or port. Common causes include address family mismatches, ports already in use, network startup timing issues, and SELinux permission restrictions. Most solutions involve fixing sshd configuration or checking service startup order.

This error appears when SSH detects that a host's key has changed since you last connected. It's a critical security check that prevents man-in-the-middle attacks, but is often triggered legitimately when servers are reinstalled, IP addresses are reassigned, or infrastructure is recreated.

The ssh-keygen command prompts for confirmation when an SSH key file already exists at the target location. You need to decide whether to overwrite the existing key, use a different filename, or keep the existing key.

This error occurs when the SSH client tries too many authentication methods before the server's maximum attempt limit is reached. The server disconnects to prevent brute force attacks. Usually caused by offering too many SSH keys or having multiple identity files configured.

The SSH server reset the connection during key exchange. Fix by checking firewall/fail2ban, MaxStartups, or port 443 SSH.

This error occurs when the SSH server abruptly terminates the connection during the key exchange phase, before authentication completes. It's typically caused by firewall blocking, network issues, server misconfiguration, or resource exhaustion.

The 'Network is unreachable' SSH error occurs when the client machine cannot establish a network route to the remote host. This typically results from missing network connectivity, incorrect routing configuration, firewall blocking, or the remote host being offline. Unlike connection refused errors, this indicates the network path itself is unavailable, not that the SSH service is unreachable.

This error occurs when the SSH client detects that a server's ECDSA host key has changed from what is stored locally. It's a security warning that prevents automatic connection to the server, requiring you to verify that the host hasn't been compromised or replaced.

This error occurs when the SSH client or server encounters an invalid or misspelled configuration option. It typically indicates a typo in your SSH config file, use of a deprecated option, or an option that's not supported by your SSH version.