All Errors

This error occurs when your SSH client and server cannot agree on a compatible key exchange algorithm. Older servers may only support deprecated algorithms that modern SSH clients disable by default for security.

The remote server's SSH host key no longer matches what's stored in your known_hosts file. This warning protects against man-in-the-middle attacks but usually indicates a legitimate server change. You can safely resolve it by removing the old key.

This error occurs when your SSH client and server cannot agree on a host key algorithm for authentication. Modern OpenSSH versions (8.8+) disabled legacy algorithms like ssh-rsa for security reasons, causing connection failures with older servers still using these algorithms.

This error occurs when your SSH configuration file (~/.ssh/config) contains an unrecognized or unsupported option. It's typically caused by typos, unsupported options for your SSH version, or platform-specific settings used on an incompatible system.

This warning appears when SSH connects to a server for the first time (or after the server's host key changes) and stores the host's public key fingerprint in your known_hosts file. It's an informational message, not an error, but indicates that SSH is learning a new host identity for future verification.

X11 forwarding fails when SSH is misconfigured or missing required dependencies. This error occurs when the SSH server cannot establish an X11 tunnel to display graphical applications on your local machine.

SSH remote port forwarding (reverse tunneling) fails when the remote server cannot bind to the specified port. This typically happens due to port conflicts, privilege restrictions, or SSH server misconfiguration.

The SSH daemon (sshd) cannot bind to port 22 because another process is already using it, or a previous sshd instance hasn't fully released the port. This error specifically indicates an IPv6 binding conflict (the :: address) and occurs during server startup.

This error occurs when SSH cannot write a key file to disk. Common causes include permission issues on the .ssh directory, insufficient disk space, or a read-only filesystem. The fix depends on identifying whether the problem is permissions, storage, or file system access.

This error occurs when OpenSSH client and server cannot agree on Diffie-Hellman key exchange parameters. Modern OpenSSH requires minimum 2048-bit moduli, but some legacy systems only support 1024-bit keys, causing the connection to fail.

The "Corrupted MAC on input" error occurs when SSH's Message Authentication Code (MAC) verification fails during connection, indicating either network packet corruption, MAC algorithm incompatibility between client and server, or hardware issues. This error prevents successful SSH authentication and can usually be resolved by changing the MAC algorithm or investigating network stability.

This error occurs when the SSH daemon (sshd) cannot bind to port 22 because another process is already listening on it. Common causes include duplicate sshd instances, IPv6/IPv4 binding conflicts, or configuration issues.

This error occurs when you try to generate an SSH key with a type that ssh-keygen doesn't recognize or support. It's usually caused by a typo in the key type name, using an unsupported algorithm on your OpenSSH version, or trying to use deprecated key types.

The "Saving key failed" error occurs when ssh-keygen cannot write the generated SSH key files to the specified directory. This is typically caused by missing .ssh directory, incorrect file permissions, or insufficient disk space. Fix it by ensuring the directory exists with proper permissions and disk space is available.

The SSH "no hostkey alg" error occurs when the SSH client and server cannot agree on a compatible host key algorithm. This typically happens when connecting older SSH clients to newer servers with strict algorithm policies.

The "Connection from hostname port XXXXX on hostname port 22 rdomain" message is a standard informational log entry from sshd (SSH daemon) that records incoming client connections. It indicates a successful socket connection before authentication attempts.

This error indicates the SSH client cannot establish a network path to the remote host. It typically means the target server is unreachable due to network connectivity issues, firewall blocks, routing problems, or the host being offline.

This message appears when the SSH server you're connected to is shutting down or rebooting. The connection is abruptly closed by the remote system, usually due to scheduled maintenance, manual shutdown command, or system crash.

The SSH connection unexpectedly closed because the TCP connection was terminated. This usually happens when an idle session times out or network connectivity is lost.

This error occurs when an SSH connection is unexpectedly terminated, typically due to network inactivity, firewall timeouts, or server disconnection. The connection breaks while attempting to send data to the remote host.