All Errors

This error occurs when an SSH client cannot establish a TCP connection to the SSH server on the remote host. It typically indicates a network connectivity issue, incorrect hostname/port, or the SSH service isn't running or accessible.

The SSH daemon (sshd) cannot start because it cannot find or access its host keys. Host keys are cryptographic credentials that identify the SSH server to clients, and they must exist and be accessible for sshd to operate. This error typically occurs after a fresh installation, accidental deletion, or permission changes that prevent sshd from reading the keys.

This error occurs when the SSH server abruptly closes the connection during the key exchange phase, before authentication completes. Common causes include firewall blocks, IP bans, misconfigured SSH service, or network issues.

This error occurs when an SSH client (or server) exceeds the maximum number of authentication attempts. The SSH daemon disconnects the connection to prevent brute force attacks and excessive failed login attempts.

This error occurs when the SSH server (sshd) denies a channel opening request for port forwarding, tunneling, or subsystem operations. It means the server is configured to administratively prohibit the requested operation, even though the authentication succeeded.

This warning occurs when SSH stores different ECDSA keys for the same host accessed via both its hostname and IP address. It typically appears after a server reinstall, key regeneration, or when connecting via multiple identifiers. The warning is usually harmless but indicates SSH can't verify the connection is to the expected host.

The SSH client receives a connection reset error during the key exchange phase when attempting to establish an SSH connection. This typically indicates a network issue, firewall blocking, or SSH server misconfiguration.

This message appears in SSH logs when the SSH daemon (sshd) receives signal 15 (SIGTERM), a graceful termination request. It typically indicates a service restart or system shutdown, not necessarily a connection error.

SSH cannot translate the hostname to an IP address due to DNS resolution failures, incorrect hostname spelling, network connectivity issues, or misconfigured DNS settings. Fix by verifying hostname spelling, checking DNS resolution, updating /etc/hosts, or using the IP address directly.

This error occurs when the SSH client or server specifies an invalid or unsupported Message Authentication Code (MAC) algorithm in its configuration. It typically indicates a typo, deprecated algorithm, or incompatible SSH version.

SSH fails during the key-exchange identification handshake because the server closes the TCP connection before negotiation finishes. It's a connectivity or server-side issue (fail2ban, MaxStartups, firewall), not authentication.

This error occurs when the SSH server on a remote host unexpectedly closes the connection after accepting the TCP connection but before or immediately after authentication. It usually indicates server-side configuration issues, resource constraints, or authentication failures rather than network problems.

OpenSSH rejects the chroot directory because it has incorrect ownership or permissions. The directory must be owned by root and not writable by group or other users, for security reasons.

SSH automatically generates host keys when the SSH server starts for the first time. This message is normal and expected on new systems or fresh containers, but can be concerning if it happens unexpectedly on an existing server.

SSH local port forwarding fails when the specified local port is already in use by another process. This occurs when establishing tunnels with the -L flag and attempting to bind to a port that another service occupies.

This error occurs when your SSH client cannot establish a connection to the remote server on port 22. It typically indicates the SSH service is not running, the port is blocked by a firewall, or the server is unreachable.

SSH unknown option errors occur when an invalid or mistyped command-line flag is passed to the ssh command. This commonly happens due to typos, using double-dashes instead of single-dashes, or trying to use options that don't exist in your SSH version.

SSH fails with "Permission denied (publickey,keyboard-interactive)" when the server rejects both your public key and the interactive fallback. Usually missing/unauthorized keys, wrong permissions, or sshd config.

SSH port forwarding fails because the client or server cannot bind a listening socket on the requested port — usually because the port is already in use, is privileged, or a stale listener still holds it.

SSH fails to connect or initialize when your .ssh/config file contains invalid or misspelled configuration options. This error occurs during SSH parsing and prevents any connections from being established.