SSH key already in use
A service rejects a public key because that exact identity is already attached to another account, repository, or ownership boundary.
Ed25519 or RSA SSH key
The user needs a new key but must choose an algorithm that the client, server, policy, and recovery process all support.
Hashed SSH known_hosts entries
The known_hosts file hides hostnames with keyed hashes, making manual searches confusing while preserving host-key verification.
SSH known_hosts for a custom port
A host on a nondefault port is stored as a bracketed host-and-port identity, so ordinary hostname removal or lookup misses it.
Fix SSH error in libcrypto
The client cannot parse the private key material it was given, often after a CI secret lost line breaks or a key format changed.
Lost SSH private key recovery
The private key is missing or unreadable; because private keys cannot be reconstructed from public keys, access must be recovered through another trusted path.
SSH MaxSessions limit reached
One authenticated transport cannot open another shell, command, subsystem, or forwarded session because its channel limit is exhausted.
SSH MFA prompt missing
The expected TOTP, push, or broker challenge never appears because client methods, sshd AuthenticationMethods, PAM, or non-interactive execution do not align.
SSH multiplexing stale socket
A reused ControlMaster connection or control socket points to dead state, the wrong target, or credentials that should no longer be shared.
SSH PAM authentication failure
Sshd reaches PAM, but one account, policy, module, or session step denies or aborts the login.
SSH permission denied (publickey)
The network connection succeeds, but the server rejects every public key the client offers.
SSH PKCS#11 smartcard not working
The SSH client or agent cannot load, enumerate, or use a key through the intended PKCS#11 provider.
SSH port forwarding not working
SSH authenticates, but the local, remote, or dynamic forwarding endpoint cannot carry the expected application traffic.
SSH post-quantum key exchange warning
A current OpenSSH client warns that the connection negotiated only classical key exchange instead of a hybrid post-quantum method.
SSH ProxyJump not working
The client cannot complete one of the distinct hops from local machine to bastion to target.
SSH disconnects during rekey
A long-lived or high-volume session fails when the transport rotates keys and one peer mishandles rekey protocol behavior.
SSH remote port forwarding denied
Authentication succeeds, but the server refuses or cannot bind the requested -R listening endpoint.
SSH root login denied
The network and SSH service work, but direct root authentication is prohibited by policy, key restrictions, cloud image defaults, or account state.
Rsync over SSH exit code 23
Rsync completed only a partial transfer because at least one file, attribute, path, or remote operation failed.
SCP legacy protocol compatibility
Modern scp uses SFTP by default, but an older server or unusual shell expects legacy SCP behavior and fails differently.
SCP no such file or directory
The copy command resolves a source or destination on a different side, shell, home directory, or protocol than the user expects.
SFTP chroot ownership error
An internal-sftp account authenticates but sshd refuses the chroot because a path component is writable or owned by an unsafe identity.
SFTP or SCP fails over SSH
Interactive SSH works, but file transfer fails because its subsystem, path, permissions, shell output, or protocol assumptions differ.
SSH agent not working
A key exists, but the current process cannot reach the intended agent or the agent does not hold the expected identity.