All Errors

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.

SSH fails when the server's chosen Diffie-Hellman Group Exchange modulus falls outside the bounds the client requested. Fix by aligning client GEX size limits or regenerating the server's /etc/ssh/moduli.

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 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 "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.

SSH rejects all offered authentication methods (publickey, gssapi-keyex, gssapi-with-mic). Usually a public key, permissions, or Kerberos/GSSAPI misconfiguration on the client or server.

SSH client and server cannot agree on an encryption algorithm. This occurs when connecting newer SSH clients to legacy servers, or when ciphers are disabled for security reasons.

This error occurs when your SSH private key has overly permissive file permissions. SSH refuses to use the key for security reasons, requiring file access restricted to your user only to prevent unauthorized access to your private key.

The SSH "no such identity" error appears when SSH cannot find the private key file specified in your config or command. Fix it by verifying the key exists and correcting its path.

OpenSSH fails to parse an SSH key file with "key_load_public: invalid format". Usually caused by PuTTY-format keys, BOM/CRLF corruption, or a wrong key format. Convert or regenerate the key in OpenSSH format to fix it.

"Could not open a connection to your authentication agent" means the SSH agent isn't running or SSH_AUTH_SOCK isn't set. Start the agent with eval and add your key.

This error appears when SSH tools like ssh-add try to reach the SSH agent, but SSH_AUTH_SOCK points to a missing or inaccessible socket. Usually the agent isn't running or the path is wrong.

The "This private key will be ignored" warning appears when your SSH private key file has permissions that are too permissive. SSH is strict about key file security and will refuse to use keys that are readable by other users. Fixing this requires restricting the file permissions to be readable only by the owner.