path: root/ssh_config.0

SSH_CONFIG(5)                 File Formats Manual                SSH_CONFIG(5)

NAME
     ssh_config M-bM-^@M-^S OpenSSH client configuration file

DESCRIPTION
     ssh(1) obtains configuration data from the following sources in the
     following order:

           1.   command-line options
           2.   user's configuration file (~/.ssh/config)
           3.   system-wide configuration file (/etc/ssh/ssh_config)

     Unless noted otherwise, for each parameter, the first obtained value will
     be used.  The configuration files contain sections separated by Host
     specifications, and that section is only applied for hosts that match one
     of the patterns given in the specification.  The matched host name is
     usually the one given on the command line (see the CanonicalizeHostname
     option for exceptions).

     Since the first obtained value for each parameter is used, more host-
     specific declarations should be given near the beginning of the file, and
     general defaults at the end.

     The file contains keyword-argument pairs, one per line.  Lines starting
     with M-bM-^@M-^X#M-bM-^@M-^Y and empty lines are interpreted as comments.  Arguments may
     optionally be enclosed in double quotes (") in order to represent
     arguments containing spaces.  Configuration options may be separated by
     whitespace or optional whitespace and exactly one M-bM-^@M-^X=M-bM-^@M-^Y; the latter format
     is useful to avoid the need to quote whitespace when specifying
     configuration options using the ssh, scp, and sftp -o option.

     The possible keywords and their meanings are as follows (note that
     keywords are case-insensitive and arguments are case-sensitive):

     Host    Restricts the following declarations (up to the next Host or
             Match keyword) to be only for those hosts that match one of the
             patterns given after the keyword.  If more than one pattern is
             provided, they should be separated by whitespace.  A single M-bM-^@M-^X*M-bM-^@M-^Y
             as a pattern can be used to provide global defaults for all
             hosts.  The host is usually the hostname argument given on the
             command line (see the CanonicalizeHostname keyword for
             exceptions).

             A pattern entry may be negated by prefixing it with an
             exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y).  If a negated entry is matched, then the
             Host entry is ignored, regardless of whether any other patterns
             on the line match.  Negated matches are therefore useful to
             provide exceptions for wildcard matches.

             See PATTERNS for more information on patterns.

     Match   Restricts the following declarations (up to the next Host or
             Match keyword) to be used only when the conditions following the
             Match keyword are satisfied.  Match conditions are specified
             using one or more criteria or the single token all which always
             matches.  The available criteria keywords are: canonical, final,
             exec, localnetwork, host, originalhost, tagged, user, and
             localuser.  The all criteria must appear alone or immediately
             after canonical or final.  Other criteria may be combined
             arbitrarily.  All criteria but all, canonical, and final require
             an argument.  Criteria may be negated by prepending an
             exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y).

             The canonical keyword matches only when the configuration file is
             being re-parsed after hostname canonicalization (see the
             CanonicalizeHostname option).  This may be useful to specify
             conditions that work with canonical host names only.

             The final keyword requests that the configuration be re-parsed
             (regardless of whether CanonicalizeHostname is enabled), and
             matches only during this final pass.  If CanonicalizeHostname is
             enabled, then canonical and final match during the same pass.

             The exec keyword executes the specified command under the user's
             shell.  If the command returns a zero exit status then the
             condition is considered true.  Commands containing whitespace
             characters must be quoted.  Arguments to exec accept the tokens
             described in the TOKENS section.

             The localnetwork keyword matches the addresses of active local
             network interfaces against the supplied list of networks in CIDR
             format.  This may be convenient for varying the effective
             configuration on devices that roam between networks.  Note that
             network address is not a trustworthy criteria in many situations
             (e.g. when the network is automatically configured using DHCP)
             and so caution should be applied if using it to control security-
             sensitive configuration.

             The other keywords' criteria must be single entries or comma-
             separated lists and may use the wildcard and negation operators
             described in the PATTERNS section.  The criteria for the host
             keyword are matched against the target hostname, after any
             substitution by the Hostname or CanonicalizeHostname options.
             The originalhost keyword matches against the hostname as it was
             specified on the command-line.  The tagged keyword matches a tag
             name specified by a prior Tag directive or on the ssh(1) command-
             line using the -P flag.  The user keyword matches against the
             target username on the remote host.  The localuser keyword
             matches against the name of the local user running ssh(1) (this
             keyword may be useful in system-wide ssh_config files).

     AddKeysToAgent
             Specifies whether keys should be automatically added to a running
             ssh-agent(1).  If this option is set to yes and a key is loaded
             from a file, the key and its passphrase are added to the agent
             with the default lifetime, as if by ssh-add(1).  If this option
             is set to ask, ssh(1) will require confirmation using the
             SSH_ASKPASS program before adding a key (see ssh-add(1) for
             details).  If this option is set to confirm, each use of the key
             must be confirmed, as if the -c option was specified to
             ssh-add(1).  If this option is set to no, no keys are added to
             the agent.  Alternately, this option may be specified as a time
             interval using the format described in the TIME FORMATS section
             of sshd_config(5) to specify the key's lifetime in ssh-agent(1),
             after which it will automatically be removed.  The argument must
             be no (the default), yes, confirm (optionally followed by a time
             interval), ask or a time interval.

     AddressFamily
             Specifies which address family to use when connecting.  Valid
             arguments are any (the default), inet (use IPv4 only), or inet6
             (use IPv6 only).

     BatchMode
             If set to yes, user interaction such as password prompts and host
             key confirmation requests will be disabled.  This option is
             useful in scripts and other batch jobs where no user is present
             to interact with ssh(1).  The argument must be yes or no (the
             default).

     BindAddress
             Use the specified address on the local machine as the source
             address of the connection.  Only useful on systems with more than
             one address.

     BindInterface
             Use the address of the specified interface on the local machine
             as the source address of the connection.

     CanonicalDomains
             When CanonicalizeHostname is enabled, this option specifies the
             list of domain suffixes in which to search for the specified
             destination host.

     CanonicalizeFallbackLocal
             Specifies whether to fail with an error when hostname
             canonicalization fails.  The default, yes, will attempt to look
             up the unqualified hostname using the system resolver's search
             rules.  A value of no will cause ssh(1) to fail instantly if
             CanonicalizeHostname is enabled and the target hostname cannot be
             found in any of the domains specified by CanonicalDomains.

     CanonicalizeHostname
             Controls whether explicit hostname canonicalization is performed.
             The default, no, is not to perform any name rewriting and let the
             system resolver handle all hostname lookups.  If set to yes then,
             for connections that do not use a ProxyCommand or ProxyJump,
             ssh(1) will attempt to canonicalize the hostname specified on the
             command line using the CanonicalDomains suffixes and
             CanonicalizePermittedCNAMEs rules.  If CanonicalizeHostname is
             set to always, then canonicalization is applied to proxied
             connections too.

             If this option is enabled, then the configuration files are
             processed again using the new target name to pick up any new
             configuration in matching Host and Match stanzas.  A value of
             none disables the use of a ProxyJump host.

     CanonicalizeMaxDots
             Specifies the maximum number of dot characters in a hostname
             before canonicalization is disabled.  The default, 1, allows a
             single dot (i.e. hostname.subdomain).

     CanonicalizePermittedCNAMEs
             Specifies rules to determine whether CNAMEs should be followed
             when canonicalizing hostnames.  The rules consist of one or more
             arguments of source_domain_list:target_domain_list, where
             source_domain_list is a pattern-list of domains that may follow
             CNAMEs in canonicalization, and target_domain_list is a pattern-
             list of domains that they may resolve to.

             For example, "*.a.example.com:*.b.example.com,*.c.example.com"
             will allow hostnames matching "*.a.example.com" to be
             canonicalized to names in the "*.b.example.com" or
             "*.c.example.com" domains.

             A single argument of "none" causes no CNAMEs to be considered for
             canonicalization.  This is the default behaviour.

     CASignatureAlgorithms
             Specifies which algorithms are allowed for signing of
             certificates by certificate authorities (CAs).  The default is:

                   ssh-ed25519,ecdsa-sha2-nistp256,
                   ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                   sk-ssh-ed25519@openssh.com,
                   sk-ecdsa-sha2-nistp256@openssh.com,
                   rsa-sha2-512,rsa-sha2-256

             If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the
             specified algorithms will be appended to the default set instead
             of replacing them.  If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y
             character, then the specified algorithms (including wildcards)
             will be removed from the default set instead of replacing them.

             ssh(1) will not accept host certificates signed using algorithms
             other than those specified.

     CertificateFile
             Specifies a file from which the user's certificate is read.  A
             corresponding private key must be provided separately in order to
             use this certificate either from an IdentityFile directive or -i
             flag to ssh(1), via ssh-agent(1), or via a PKCS11Provider or
             SecurityKeyProvider.

             Arguments to CertificateFile may use the tilde syntax to refer to
             a user's home directory, the tokens described in the TOKENS
             section and environment variables as described in the ENVIRONMENT
             VARIABLES section.

             It is possible to have multiple certificate files specified in
             configuration files; these certificates will be tried in
             sequence.  Multiple CertificateFile directives will add to the
             list of certificates used for authentication.

     ChannelTimeout
             Specifies whether and how quickly ssh(1) should close inactive
             channels.  Timeouts are specified as one or more M-bM-^@M-^\type=intervalM-bM-^@M-^]
             pairs separated by whitespace, where the M-bM-^@M-^\typeM-bM-^@M-^] must be the
             special keyword M-bM-^@M-^\globalM-bM-^@M-^] or a channel type name from the list
             below, optionally containing wildcard characters.

             The timeout value M-bM-^@M-^\intervalM-bM-^@M-^] is specified in seconds or may use
             any of the units documented in the TIME FORMATS section.  For
             example, M-bM-^@M-^\session=5mM-bM-^@M-^] would cause interactive sessions to
             terminate after five minutes of inactivity.  Specifying a zero
             value disables the inactivity timeout.

             The special timeout M-bM-^@M-^\globalM-bM-^@M-^] applies to all active channels,
             taken together.  Traffic on any active channel will reset the
             timeout, but when the timeout expires then all open channels will
             be closed.  Note that this global timeout is not matched by
             wildcards and must be specified explicitly.

             The available channel type names include:

             agent-connection
                     Open connections to ssh-agent(1).

             direct-tcpip, direct-streamlocal@openssh.com
                     Open TCP or Unix socket (respectively) connections that
                     have been established from a ssh(1) local forwarding,
                     i.e. LocalForward or DynamicForward.

             forwarded-tcpip, forwarded-streamlocal@openssh.com
                     Open TCP or Unix socket (respectively) connections that
                     have been established to a sshd(8) listening on behalf of
                     a ssh(1) remote forwarding, i.e. RemoteForward.

             session
                     The interactive main session, including shell session,
                     command execution, scp(1), sftp(1), etc.

             tun-connection
                     Open TunnelForward connections.

             x11-connection
                     Open X11 forwarding sessions.

             Note that in all the above cases, terminating an inactive session
             does not guarantee to remove all resources associated with the
             session, e.g. shell processes or X11 clients relating to the
             session may continue to execute.

             Moreover, terminating an inactive channel or session does not
             necessarily close the SSH connection, nor does it prevent a
             client from requesting another channel of the same type.  In
             particular, expiring an inactive forwarding session does not
             prevent another identical forwarding from being subsequently
             created.

             The default is not to expire channels of any type for inactivity.

     CheckHostIP
             If set to yes, ssh(1) will additionally check the host IP address
             in the known_hosts file.  This allows it to detect if a host key
             changed due to DNS spoofing and will add addresses of destination
             hosts to ~/.ssh/known_hosts in the process, regardless of the
             setting of StrictHostKeyChecking.  If the option is set to no
             (the default), the check will not be executed.

     Ciphers
             Specifies the ciphers allowed and their order of preference.
             Multiple ciphers must be comma-separated.  If the specified list
             begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified ciphers will be
             appended to the default set instead of replacing them.  If the
             specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified
             ciphers (including wildcards) will be removed from the default
             set instead of replacing them.  If the specified list begins with
             a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified ciphers will be placed at the
             head of the default set.

             The supported ciphers are:

                   3des-cbc
                   aes128-cbc
                   aes192-cbc
                   aes256-cbc
                   aes128-ctr
                   aes192-ctr
                   aes256-ctr
                   aes128-gcm@openssh.com
                   aes256-gcm@openssh.com
                   chacha20-poly1305@openssh.com

             The default is:

                   chacha20-poly1305@openssh.com,
                   aes128-ctr,aes192-ctr,aes256-ctr,
                   aes128-gcm@openssh.com,aes256-gcm@openssh.com

             The list of available ciphers may also be obtained using "ssh -Q
             cipher".

     ClearAllForwardings
             Specifies that all local, remote, and dynamic port forwardings
             specified in the configuration files or on the command line be
             cleared.  This option is primarily useful when used from the
             ssh(1) command line to clear port forwardings set in
             configuration files, and is automatically set by scp(1) and
             sftp(1).  The argument must be yes or no (the default).

     Compression
             Specifies whether to use compression.  The argument must be yes
             or no (the default).

     ConnectionAttempts
             Specifies the number of tries (one per second) to make before
             exiting.  The argument must be an integer.  This may be useful in
             scripts if the connection sometimes fails.  The default is 1.

     ConnectTimeout
             Specifies the timeout (in seconds) used when connecting to the
             SSH server, instead of using the default system TCP timeout.
             This timeout is applied both to establishing the connection and
             to performing the initial SSH protocol handshake and key
             exchange.

     ControlMaster
             Enables the sharing of multiple sessions over a single network
             connection.  When set to yes, ssh(1) will listen for connections
             on a control socket specified using the ControlPath argument.
             Additional sessions can connect to this socket using the same
             ControlPath with ControlMaster set to no (the default).  These
             sessions will try to reuse the master instance's network
             connection rather than initiating new ones, but will fall back to
             connecting normally if the control socket does not exist, or is
             not listening.

             Setting this to ask will cause ssh(1) to listen for control
             connections, but require confirmation using ssh-askpass(1).  If
             the ControlPath cannot be opened, ssh(1) will continue without
             connecting to a master instance.

             X11 and ssh-agent(1) forwarding is supported over these
             multiplexed connections, however the display and agent forwarded
             will be the one belonging to the master connection i.e. it is not
             possible to forward multiple displays or agents.

             Two additional options allow for opportunistic multiplexing: try
             to use a master connection but fall back to creating a new one if
             one does not already exist.  These options are: auto and autoask.
             The latter requires confirmation like the ask option.

     ControlPath
             Specify the path to the control socket used for connection
             sharing as described in the ControlMaster section above or the
             string none to disable connection sharing.  Arguments to
             ControlPath may use the tilde syntax to refer to a user's home
             directory, the tokens described in the TOKENS section and
             environment variables as described in the ENVIRONMENT VARIABLES
             section.  It is recommended that any ControlPath used for
             opportunistic connection sharing include at least %h, %p, and %r
             (or alternatively %C) and be placed in a directory that is not
             writable by other users.  This ensures that shared connections
             are uniquely identified.

     ControlPersist
             When used in conjunction with ControlMaster, specifies that the
             master connection should remain open in the background (waiting
             for future client connections) after the initial client
             connection has been closed.  If set to no (the default), then the
             master connection will not be placed into the background, and
             will close as soon as the initial client connection is closed.
             If set to yes or 0, then the master connection will remain in the
             background indefinitely (until killed or closed via a mechanism
             such as the "ssh -O exit").  If set to a time in seconds, or a
             time in any of the formats documented in sshd_config(5), then the
             backgrounded master connection will automatically terminate after
             it has remained idle (with no client connections) for the
             specified time.

     DynamicForward
             Specifies that a TCP port on the local machine be forwarded over
             the secure channel, and the application protocol is then used to
             determine where to connect to from the remote machine.

             The argument must be [bind_address:]port.  IPv6 addresses can be
             specified by enclosing addresses in square brackets.  By default,
             the local port is bound in accordance with the GatewayPorts
             setting.  However, an explicit bind_address may be used to bind
             the connection to a specific address.  The bind_address of
             localhost indicates that the listening port be bound for local
             use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port
             should be available from all interfaces.

             Currently the SOCKS4 and SOCKS5 protocols are supported, and
             ssh(1) will act as a SOCKS server.  Multiple forwardings may be
             specified, and additional forwardings can be given on the command
             line.  Only the superuser can forward privileged ports.

     EnableEscapeCommandline
             Enables the command line option in the EscapeChar menu for
             interactive sessions (default M-bM-^@M-^X~CM-bM-^@M-^Y).  By default, the command
             line is disabled.

     EnableSSHKeysign
             Setting this option to yes in the global client configuration
             file /etc/ssh/ssh_config enables the use of the helper program
             ssh-keysign(8) during HostbasedAuthentication.  The argument must
             be yes or no (the default).  This option should be placed in the
             non-hostspecific section.  See ssh-keysign(8) for more
             information.

     EscapeChar
             Sets the escape character (default: M-bM-^@M-^X~M-bM-^@M-^Y).  The escape character
             can also be set on the command line.  The argument should be a
             single character, M-bM-^@M-^X^M-bM-^@M-^Y followed by a letter, or none to disable
             the escape character entirely (making the connection transparent
             for binary data).

     ExitOnForwardFailure
             Specifies whether ssh(1) should terminate the connection if it
             cannot set up all requested dynamic, tunnel, local, and remote
             port forwardings, (e.g. if either end is unable to bind and
             listen on a specified port).  Note that ExitOnForwardFailure does
             not apply to connections made over port forwardings and will not,
             for example, cause ssh(1) to exit if TCP connections to the
             ultimate forwarding destination fail.  The argument must be yes
             or no (the default).

     FingerprintHash
             Specifies the hash algorithm used when displaying key
             fingerprints.  Valid options are: md5 and sha256 (the default).

     ForkAfterAuthentication
             Requests ssh to go to background just before command execution.
             This is useful if ssh is going to ask for passwords or
             passphrases, but the user wants it in the background.  This
             implies the StdinNull configuration option being set to M-bM-^@M-^\yesM-bM-^@M-^].
             The recommended way to start X11 programs at a remote site is
             with something like ssh -f host xterm, which is the same as ssh
             host xterm if the ForkAfterAuthentication configuration option is
             set to M-bM-^@M-^\yesM-bM-^@M-^].

             If the ExitOnForwardFailure configuration option is set to M-bM-^@M-^\yesM-bM-^@M-^],
             then a client started with the ForkAfterAuthentication
             configuration option being set to M-bM-^@M-^\yesM-bM-^@M-^] will wait for all remote
             port forwards to be successfully established before placing
             itself in the background.  The argument to this keyword must be
             yes (same as the -f option) or no (the default).

     ForwardAgent
             Specifies whether the connection to the authentication agent (if
             any) will be forwarded to the remote machine.  The argument may
             be yes, no (the default), an explicit path to an agent socket or
             the name of an environment variable (beginning with M-bM-^@M-^X$M-bM-^@M-^Y) in which
             to find the path.

             Agent forwarding should be enabled with caution.  Users with the
             ability to bypass file permissions on the remote host (for the
             agent's Unix-domain socket) can access the local agent through
             the forwarded connection.  An attacker cannot obtain key material
             from the agent, however they can perform operations on the keys
             that enable them to authenticate using the identities loaded into
             the agent.

     ForwardX11
             Specifies whether X11 connections will be automatically
             redirected over the secure channel and DISPLAY set.  The argument
             must be yes or no (the default).

             X11 forwarding should be enabled with caution.  Users with the
             ability to bypass file permissions on the remote host (for the
             user's X11 authorization database) can access the local X11
             display through the forwarded connection.  An attacker may then
             be able to perform activities such as keystroke monitoring if the
             ForwardX11Trusted option is also enabled.

     ForwardX11Timeout
             Specify a timeout for untrusted X11 forwarding using the format
             described in the TIME FORMATS section of sshd_config(5).  X11
             connections received by ssh(1) after this time will be refused.
             Setting ForwardX11Timeout to zero will disable the timeout and
             permit X11 forwarding for the life of the connection.  The
             default is to disable untrusted X11 forwarding after twenty
             minutes has elapsed.

     ForwardX11Trusted
             If this option is set to yes, remote X11 clients will have full
             access to the original X11 display.

             If this option is set to no (the default), remote X11 clients
             will be considered untrusted and prevented from stealing or
             tampering with data belonging to trusted X11 clients.
             Furthermore, the xauth(1) token used for the session will be set
             to expire after 20 minutes.  Remote clients will be refused
             access after this time.

             See the X11 SECURITY extension specification for full details on
             the restrictions imposed on untrusted clients.

     GatewayPorts
             Specifies whether remote hosts are allowed to connect to local
             forwarded ports.  By default, ssh(1) binds local port forwardings
             to the loopback address.  This prevents other remote hosts from
             connecting to forwarded ports.  GatewayPorts can be used to
             specify that ssh should bind local port forwardings to the
             wildcard address, thus allowing remote hosts to connect to
             forwarded ports.  The argument must be yes or no (the default).

     GlobalKnownHostsFile
             Specifies one or more files to use for the global host key
             database, separated by whitespace.  The default is
             /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.

     GSSAPIAuthentication
             Specifies whether user authentication based on GSSAPI is allowed.
             The default is no.

     GSSAPIDelegateCredentials
             Forward (delegate) credentials to the server.  The default is no.

     HashKnownHosts
             Indicates that ssh(1) should hash host names and addresses when
             they are added to ~/.ssh/known_hosts.  These hashed names may be
             used normally by ssh(1) and sshd(8), but they do not visually
             reveal identifying information if the file's contents are
             disclosed.  The default is no.  Note that existing names and
             addresses in known hosts files will not be converted
             automatically, but may be manually hashed using ssh-keygen(1).

     HostbasedAcceptedAlgorithms
             Specifies the signature algorithms that will be used for
             hostbased authentication as a comma-separated list of patterns.
             Alternately if the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
             then the specified signature algorithms will be appended to the
             default set instead of replacing them.  If the specified list
             begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified signature
             algorithms (including wildcards) will be removed from the default
             set instead of replacing them.  If the specified list begins with
             a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified signature algorithms will be
             placed at the head of the default set.  The default for this
             option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ssh-ed25519@openssh.com,
                sk-ecdsa-sha2-nistp256@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             The -Q option of ssh(1) may be used to list supported signature
             algorithms.  This was formerly named HostbasedKeyTypes.

     HostbasedAuthentication
             Specifies whether to try rhosts based authentication with public
             key authentication.  The argument must be yes or no (the
             default).

     HostKeyAlgorithms
             Specifies the host key signature algorithms that the client wants
             to use in order of preference.  Alternately if the specified list
             begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified signature
             algorithms will be appended to the default set instead of
             replacing them.  If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y
             character, then the specified signature algorithms (including
             wildcards) will be removed from the default set instead of
             replacing them.  If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y
             character, then the specified signature algorithms will be placed
             at the head of the default set.  The default for this option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ecdsa-sha2-nistp256@openssh.com,
                sk-ssh-ed25519@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             If hostkeys are known for the destination host then this default
             is modified to prefer their algorithms.

             The list of available signature algorithms may also be obtained
             using "ssh -Q HostKeyAlgorithms".

     HostKeyAlias
             Specifies an alias that should be used instead of the real host
             name when looking up or saving the host key in the host key
             database files and when validating host certificates.  This
             option is useful for tunneling SSH connections or for multiple
             servers running on a single host.

     Hostname
             Specifies the real host name to log into.  This can be used to
             specify nicknames or abbreviations for hosts.  Arguments to
             Hostname accept the tokens described in the TOKENS section.
             Numeric IP addresses are also permitted (both on the command line
             and in Hostname specifications).  The default is the name given
             on the command line.

     IdentitiesOnly
             Specifies that ssh(1) should only use the configured
             authentication identity and certificate files (either the default
             files, or those explicitly configured in the ssh_config files or
             passed on the ssh(1) command-line), even if ssh-agent(1) or a
             PKCS11Provider or SecurityKeyProvider offers more identities.
             The argument to this keyword must be yes or no (the default).
             This option is intended for situations where ssh-agent offers
             many different identities.

     IdentityAgent
             Specifies the UNIX-domain socket used to communicate with the
             authentication agent.

             This option overrides the SSH_AUTH_SOCK environment variable and
             can be used to select a specific agent.  Setting the socket name
             to none disables the use of an authentication agent.  If the
             string "SSH_AUTH_SOCK" is specified, the location of the socket
             will be read from the SSH_AUTH_SOCK environment variable.
             Otherwise if the specified value begins with a M-bM-^@M-^X$M-bM-^@M-^Y character,
             then it will be treated as an environment variable containing the
             location of the socket.

             Arguments to IdentityAgent may use the tilde syntax to refer to a
             user's home directory, the tokens described in the TOKENS section
             and environment variables as described in the ENVIRONMENT
             VARIABLES section.

     IdentityFile
             Specifies a file from which the user's ECDSA, authenticator-
             hosted ECDSA, Ed25519, authenticator-hosted Ed25519 or RSA
             authentication identity is read.  You can also specify a public
             key file to use the corresponding private key that is loaded in
             ssh-agent(1) when the private key file is not present locally.
             The default is ~/.ssh/id_rsa, ~/.ssh/id_ecdsa,
             ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519 and ~/.ssh/id_ed25519_sk.
             Additionally, any identities represented by the authentication
             agent will be used for authentication unless IdentitiesOnly is
             set.  If no certificates have been explicitly specified by
             CertificateFile, ssh(1) will try to load certificate information
             from the filename obtained by appending -cert.pub to the path of
             a specified IdentityFile.

             Arguments to IdentityFile may use the tilde syntax to refer to a
             user's home directory or the tokens described in the TOKENS
             section.  Alternately an argument of none may be used to indicate
             no identity files should be loaded.

             It is possible to have multiple identity files specified in
             configuration files; all these identities will be tried in
             sequence.  Multiple IdentityFile directives will add to the list
             of identities tried (this behaviour differs from that of other
             configuration directives).

             IdentityFile may be used in conjunction with IdentitiesOnly to
             select which identities in an agent are offered during
             authentication.  IdentityFile may also be used in conjunction
             with CertificateFile in order to provide any certificate also
             needed for authentication with the identity.

     IgnoreUnknown
             Specifies a pattern-list of unknown options to be ignored if they
             are encountered in configuration parsing.  This may be used to
             suppress errors if ssh_config contains options that are
             unrecognised by ssh(1).  It is recommended that IgnoreUnknown be
             listed early in the configuration file as it will not be applied
             to unknown options that appear before it.

     Include
             Include the specified configuration file(s).  Multiple pathnames
             may be specified and each pathname may contain glob(7) wildcards
             and, for user configurations, shell-like M-bM-^@M-^X~M-bM-^@M-^Y references to user
             home directories.  Wildcards will be expanded and processed in
             lexical order.  Files without absolute paths are assumed to be in
             ~/.ssh if included in a user configuration file or /etc/ssh if
             included from the system configuration file.  Include directive
             may appear inside a Match or Host block to perform conditional
             inclusion.

     IPQoS   Specifies the IPv4 type-of-service or DSCP class for connections.
             Accepted values are af11, af12, af13, af21, af22, af23, af31,
             af32, af33, af41, af42, af43, cs0, cs1, cs2, cs3, cs4, cs5, cs6,
             cs7, ef, le, lowdelay, throughput, reliability, a numeric value,
             or none to use the operating system default.  This option may
             take one or two arguments, separated by whitespace.  If one
             argument is specified, it is used as the packet class
             unconditionally.  If two values are specified, the first is
             automatically selected for interactive sessions and the second
             for non-interactive sessions.  The default is af21 (Low-Latency
             Data) for interactive sessions and cs1 (Lower Effort) for non-
             interactive sessions.

     KbdInteractiveAuthentication
             Specifies whether to use keyboard-interactive authentication.
             The argument to this keyword must be yes (the default) or no.
             ChallengeResponseAuthentication is a deprecated alias for this.

     KbdInteractiveDevices
             Specifies the list of methods to use in keyboard-interactive
             authentication.  Multiple method names must be comma-separated.
             The default is to use the server specified list.  The methods
             available vary depending on what the server supports.  For an
             OpenSSH server, it may be zero or more of: bsdauth and pam.

     KexAlgorithms
             Specifies the permitted KEX (Key Exchange) algorithms that will
             be used and their preference order.  The selected algorithm will
             the the first algorithm in this list that the server also
             supports.  Multiple algorithms must be comma-separated.

             If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the
             specified algorithms will be appended to the default set instead
             of replacing them.  If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y
             character, then the specified algorithms (including wildcards)
             will be removed from the default set instead of replacing them.
             If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the
             specified algorithms will be placed at the head of the default
             set.

             The default is:

                   sntrup761x25519-sha512@openssh.com,
                   curve25519-sha256,curve25519-sha256@libssh.org,
                   ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
                   diffie-hellman-group-exchange-sha256,
                   diffie-hellman-group16-sha512,
                   diffie-hellman-group18-sha512,
                   diffie-hellman-group14-sha256

             The list of supported key exchange algorithms may also be
             obtained using "ssh -Q kex".

     KnownHostsCommand
             Specifies a command to use to obtain a list of host keys, in
             addition to those listed in UserKnownHostsFile and
             GlobalKnownHostsFile.  This command is executed after the files
             have been read.  It may write host key lines to standard output
             in identical format to the usual files (described in the
             VERIFYING HOST KEYS section in ssh(1)).  Arguments to
             KnownHostsCommand accept the tokens described in the TOKENS
             section.  The command may be invoked multiple times per
             connection: once when preparing the preference list of host key
             algorithms to use, again to obtain the host key for the requested
             host name and, if CheckHostIP is enabled, one more time to obtain
             the host key matching the server's address.  If the command exits
             abnormally or returns a non-zero exit status then the connection
             is terminated.

     LocalCommand
             Specifies a command to execute on the local machine after
             successfully connecting to the server.  The command string
             extends to the end of the line, and is executed with the user's
             shell.  Arguments to LocalCommand accept the tokens described in
             the TOKENS section.

             The command is run synchronously and does not have access to the
             session of the ssh(1) that spawned it.  It should not be used for
             interactive commands.

             This directive is ignored unless PermitLocalCommand has been
             enabled.

     LocalForward
             Specifies that a TCP port on the local machine be forwarded over
             the secure channel to the specified host and port from the remote
             machine.  The first argument specifies the listener and may be
             [bind_address:]port or a Unix domain socket path.  The second
             argument is the destination and may be host:hostport or a Unix
             domain socket path if the remote host supports it.

             IPv6 addresses can be specified by enclosing addresses in square
             brackets.  Multiple forwardings may be specified, and additional
             forwardings can be given on the command line.  Only the superuser
             can forward privileged ports.  By default, the local port is
             bound in accordance with the GatewayPorts setting.  However, an
             explicit bind_address may be used to bind the connection to a
             specific address.  The bind_address of localhost indicates that
             the listening port be bound for local use only, while an empty
             address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port should be available from
             all interfaces.  Unix domain socket paths may use the tokens
             described in the TOKENS section and environment variables as
             described in the ENVIRONMENT VARIABLES section.

     LogLevel
             Gives the verbosity level that is used when logging messages from
             ssh(1).  The possible values are: QUIET, FATAL, ERROR, INFO,
             VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.  The default is INFO.
             DEBUG and DEBUG1 are equivalent.  DEBUG2 and DEBUG3 each specify
             higher levels of verbose output.

     LogVerbose
             Specify one or more overrides to LogLevel.  An override consists
             of a pattern lists that matches the source file, function and
             line number to force detailed logging for.  For example, an
             override pattern of:

                   kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*

             would enable detailed logging for line 1000 of kex.c, everything
             in the kex_exchange_identification() function, and all code in
             the packet.c file.  This option is intended for debugging and no
             overrides are enabled by default.

     MACs    Specifies the MAC (message authentication code) algorithms in
             order of preference.  The MAC algorithm is used for data
             integrity protection.  Multiple algorithms must be comma-
             separated.  If the specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character,
             then the specified algorithms will be appended to the default set
             instead of replacing them.  If the specified list begins with a
             M-bM-^@M-^X-M-bM-^@M-^Y character, then the specified algorithms (including
             wildcards) will be removed from the default set instead of
             replacing them.  If the specified list begins with a M-bM-^@M-^X^M-bM-^@M-^Y
             character, then the specified algorithms will be placed at the
             head of the default set.

             The algorithms that contain "-etm" calculate the MAC after
             encryption (encrypt-then-mac).  These are considered safer and
             their use recommended.

             The default is:

                   umac-64-etm@openssh.com,umac-128-etm@openssh.com,
                   hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
                   hmac-sha1-etm@openssh.com,
                   umac-64@openssh.com,umac-128@openssh.com,
                   hmac-sha2-256,hmac-sha2-512,hmac-sha1

             The list of available MAC algorithms may also be obtained using
             "ssh -Q mac".

     NoHostAuthenticationForLocalhost
             Disable host authentication for localhost (loopback addresses).
             The argument to this keyword must be yes or no (the default).

     NumberOfPasswordPrompts
             Specifies the number of password prompts before giving up.  The
             argument to this keyword must be an integer.  The default is 3.

     ObscureKeystrokeTiming
             Specifies whether ssh(1) should try to obscure inter-keystroke
             timings from passive observers of network traffic.  If enabled,
             then for interactive sessions, ssh(1) will send keystrokes at
             fixed intervals of a few tens of milliseconds and will send fake
             keystroke packets for some time after typing ceases.  The
             argument to this keyword must be yes, no or an interval specifier
             of the form interval:milliseconds (e.g. interval:80 for 80
             milliseconds).  The default is to obscure keystrokes using a 20ms
             packet interval.  Note that smaller intervals will result in
             higher fake keystroke packet rates.

     PasswordAuthentication
             Specifies whether to use password authentication.  The argument
             to this keyword must be yes (the default) or no.

     PermitLocalCommand
             Allow local command execution via the LocalCommand option or
             using the !command escape sequence in ssh(1).  The argument must
             be yes or no (the default).

     PermitRemoteOpen
             Specifies the destinations to which remote TCP port forwarding is
             permitted when RemoteForward is used as a SOCKS proxy.  The
             forwarding specification must be one of the following forms:

                   PermitRemoteOpen host:port
                   PermitRemoteOpen IPv4_addr:port
                   PermitRemoteOpen [IPv6_addr]:port

             Multiple forwards may be specified by separating them with
             whitespace.  An argument of any can be used to remove all
             restrictions and permit any forwarding requests.  An argument of
             none can be used to prohibit all forwarding requests.  The
             wildcard M-bM-^@M-^X*M-bM-^@M-^Y can be used for host or port to allow all hosts or
             ports respectively.  Otherwise, no pattern matching or address
             lookups are performed on supplied names.

     PKCS11Provider
             Specifies which PKCS#11 provider to use or none to indicate that
             no provider should be used (the default).  The argument to this
             keyword is a path to the PKCS#11 shared library ssh(1) should use
             to communicate with a PKCS#11 token providing keys for user
             authentication.

     Port    Specifies the port number to connect on the remote host.  The
             default is 22.

     PreferredAuthentications
             Specifies the order in which the client should try authentication
             methods.  This allows a client to prefer one method (e.g.
             keyboard-interactive) over another method (e.g. password).  The
             default is:

                   gssapi-with-mic,hostbased,publickey,
                   keyboard-interactive,password

     ProxyCommand
             Specifies the command to use to connect to the server.  The
             command string extends to the end of the line, and is executed
             using the user's shell M-bM-^@M-^XexecM-bM-^@M-^Y directive to avoid a lingering
             shell process.

             Arguments to ProxyCommand accept the tokens described in the
             TOKENS section.  The command can be basically anything, and
             should read from its standard input and write to its standard
             output.  It should eventually connect an sshd(8) server running
             on some machine, or execute sshd -i somewhere.  Host key
             management will be done using the Hostname of the host being
             connected (defaulting to the name typed by the user).  Setting
             the command to none disables this option entirely.  Note that
             CheckHostIP is not available for connects with a proxy command.

             This directive is useful in conjunction with nc(1) and its proxy
             support.  For example, the following directive would connect via
             an HTTP proxy at 192.0.2.0:

                ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p

     ProxyJump
             Specifies one or more jump proxies as either [user@]host[:port]
             or an ssh URI.  Multiple proxies may be separated by comma
             characters and will be visited sequentially.  Setting this option
             will cause ssh(1) to connect to the target host by first making a
             ssh(1) connection to the specified ProxyJump host and then
             establishing a TCP forwarding to the ultimate target from there.
             Setting the host to none disables this option entirely.

             Note that this option will compete with the ProxyCommand option -
             whichever is specified first will prevent later instances of the
             other from taking effect.

             Note also that the configuration for the destination host (either
             supplied via the command-line or the configuration file) is not
             generally applied to jump hosts.  ~/.ssh/config should be used if
             specific configuration is required for jump hosts.

     ProxyUseFdpass
             Specifies that ProxyCommand will pass a connected file descriptor
             back to ssh(1) instead of continuing to execute and pass data.
             The default is no.

     PubkeyAcceptedAlgorithms
             Specifies the signature algorithms that will be used for public
             key authentication as a comma-separated list of patterns.  If the
             specified list begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the algorithms
             after it will be appended to the default instead of replacing it.
             If the specified list begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the
             specified algorithms (including wildcards) will be removed from
             the default set instead of replacing them.  If the specified list
             begins with a M-bM-^@M-^X^M-bM-^@M-^Y character, then the specified algorithms will
             be placed at the head of the default set.  The default for this
             option is:

                ssh-ed25519-cert-v01@openssh.com,
                ecdsa-sha2-nistp256-cert-v01@openssh.com,
                ecdsa-sha2-nistp384-cert-v01@openssh.com,
                ecdsa-sha2-nistp521-cert-v01@openssh.com,
                sk-ssh-ed25519-cert-v01@openssh.com,
                sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
                rsa-sha2-512-cert-v01@openssh.com,
                rsa-sha2-256-cert-v01@openssh.com,
                ssh-ed25519,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                sk-ssh-ed25519@openssh.com,
                sk-ecdsa-sha2-nistp256@openssh.com,
                rsa-sha2-512,rsa-sha2-256

             The list of available signature algorithms may also be obtained
             using "ssh -Q PubkeyAcceptedAlgorithms".

     PubkeyAuthentication
             Specifies whether to try public key authentication.  The argument
             to this keyword must be yes (the default), no, unbound or
             host-bound.  The final two options enable public key
             authentication while respectively disabling or enabling the
             OpenSSH host-bound authentication protocol extension required for
             restricted ssh-agent(1) forwarding.

     RekeyLimit
             Specifies the maximum amount of data that may be transmitted or
             received before the session key is renegotiated, optionally
             followed by a maximum amount of time that may pass before the
             session key is renegotiated.  The first argument is specified in
             bytes and may have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate
             Kilobytes, Megabytes, or Gigabytes, respectively.  The default is
             between M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher.  The optional
             second value is specified in seconds and may use any of the units
             documented in the TIME FORMATS section of sshd_config(5).  The
             default value for RekeyLimit is default none, which means that
             rekeying is performed after the cipher's default amount of data
             has been sent or received and no time based rekeying is done.

     RemoteCommand
             Specifies a command to execute on the remote machine after
             successfully connecting to the server.  The command string
             extends to the end of the line, and is executed with the user's
             shell.  Arguments to RemoteCommand accept the tokens described in
             the TOKENS section.

     RemoteForward
             Specifies that a TCP port on the remote machine be forwarded over
             the secure channel.  The remote port may either be forwarded to a
             specified host and port from the local machine, or may act as a
             SOCKS 4/5 proxy that allows a remote client to connect to
             arbitrary destinations from the local machine.  The first
             argument is the listening specification and may be
             [bind_address:]port or, if the remote host supports it, a Unix
             domain socket path.  If forwarding to a specific destination then
             the second argument must be host:hostport or a Unix domain socket
             path, otherwise if no destination argument is specified then the
             remote forwarding will be established as a SOCKS proxy.  When
             acting as a SOCKS proxy, the destination of the connection can be
             restricted by PermitRemoteOpen.

             IPv6 addresses can be specified by enclosing addresses in square
             brackets.  Multiple forwardings may be specified, and additional
             forwardings can be given on the command line.  Privileged ports
             can be forwarded only when logging in as root on the remote
             machine.  Unix domain socket paths may use the tokens described
             in the TOKENS section and environment variables as described in
             the ENVIRONMENT VARIABLES section.

             If the port argument is 0, the listen port will be dynamically
             allocated on the server and reported to the client at run time.

             If the bind_address is not specified, the default is to only bind
             to loopback addresses.  If the bind_address is M-bM-^@M-^X*M-bM-^@M-^Y or an empty
             string, then the forwarding is requested to listen on all
             interfaces.  Specifying a remote bind_address will only succeed
             if the server's GatewayPorts option is enabled (see
             sshd_config(5)).

     RequestTTY
             Specifies whether to request a pseudo-tty for the session.  The
             argument may be one of: no (never request a TTY), yes (always
             request a TTY when standard input is a TTY), force (always
             request a TTY) or auto (request a TTY when opening a login
             session).  This option mirrors the -t and -T flags for ssh(1).

     RequiredRSASize
             Specifies the minimum RSA key size (in bits) that ssh(1) will
             accept.  User authentication keys smaller than this limit will be
             ignored.  Servers that present host keys smaller than this limit
             will cause the connection to be terminated.  The default is 1024
             bits.  Note that this limit may only be raised from the default.

     RevokedHostKeys
             Specifies revoked host public keys.  Keys listed in this file
             will be refused for host authentication.  Note that if this file
             does not exist or is not readable, then host authentication will
             be refused for all hosts.  Keys may be specified as a text file,
             listing one public key per line, or as an OpenSSH Key Revocation
             List (KRL) as generated by ssh-keygen(1).  For more information
             on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
             Arguments to RevokedHostKeys may use the tilde syntax to refer to
             a user's home directory, the tokens described in the TOKENS
             section and environment variables as described in the ENVIRONMENT
             VARIABLES section.

     SecurityKeyProvider
             Specifies a path to a library that will be used when loading any
             FIDO authenticator-hosted keys, overriding the default of using
             the built-in USB HID support.

             If the specified value begins with a M-bM-^@M-^X$M-bM-^@M-^Y character, then it will
             be treated as an environment variable containing the path to the
             library.

     SendEnv
             Specifies what variables from the local environ(7) should be sent
             to the server.  The server must also support it, and the server
             must be configured to accept these environment variables.  Note
             that the TERM environment variable is always sent whenever a
             pseudo-terminal is requested as it is required by the protocol.
             Refer to AcceptEnv in sshd_config(5) for how to configure the
             server.  Variables are specified by name, which may contain
             wildcard characters.  Multiple environment variables may be
             separated by whitespace or spread across multiple SendEnv
             directives.

             See PATTERNS for more information on patterns.

             It is possible to clear previously set SendEnv variable names by
             prefixing patterns with -.  The default is not to send any
             environment variables.

     ServerAliveCountMax
             Sets the number of server alive messages (see below) which may be
             sent without ssh(1) receiving any messages back from the server.
             If this threshold is reached while server alive messages are
             being sent, ssh will disconnect from the server, terminating the
             session.  It is important to note that the use of server alive
             messages is very different from TCPKeepAlive (below).  The server
             alive messages are sent through the encrypted channel and
             therefore will not be spoofable.  The TCP keepalive option
             enabled by TCPKeepAlive is spoofable.  The server alive mechanism
             is valuable when the client or server depend on knowing when a
             connection has become unresponsive.

             The default value is 3.  If, for example, ServerAliveInterval
             (see below) is set to 15 and ServerAliveCountMax is left at the
             default, if the server becomes unresponsive, ssh will disconnect
             after approximately 45 seconds.

     ServerAliveInterval
             Sets a timeout interval in seconds after which if no data has
             been received from the server, ssh(1) will send a message through
             the encrypted channel to request a response from the server.  The
             default is 0, indicating that these messages will not be sent to
             the server.

     SessionType
             May be used to either request invocation of a subsystem on the
             remote system, or to prevent the execution of a remote command at
             all.  The latter is useful for just forwarding ports.  The
             argument to this keyword must be none (same as the -N option),
             subsystem (same as the -s option) or default (shell or command
             execution).

     SetEnv  Directly specify one or more environment variables and their
             contents to be sent to the server.  Similarly to SendEnv, with
             the exception of the TERM variable, the server must be prepared
             to accept the environment variable.

     StdinNull
             Redirects stdin from /dev/null (actually, prevents reading from
             stdin).  Either this or the equivalent -n option must be used
             when ssh is run in the background.  The argument to this keyword
             must be yes (same as the -n option) or no (the default).

     StreamLocalBindMask
             Sets the octal file creation mode mask (umask) used when creating
             a Unix-domain socket file for local or remote port forwarding.
             This option is only used for port forwarding to a Unix-domain
             socket file.

             The default value is 0177, which creates a Unix-domain socket
             file that is readable and writable only by the owner.  Note that
             not all operating systems honor the file mode on Unix-domain
             socket files.

     StreamLocalBindUnlink
             Specifies whether to remove an existing Unix-domain socket file
             for local or remote port forwarding before creating a new one.
             If the socket file already exists and StreamLocalBindUnlink is
             not enabled, ssh will be unable to forward the port to the Unix-
             domain socket file.  This option is only used for port forwarding
             to a Unix-domain socket file.

             The argument must be yes or no (the default).

     StrictHostKeyChecking
             If this flag is set to yes, ssh(1) will never automatically add
             host keys to the ~/.ssh/known_hosts file, and refuses to connect
             to hosts whose host key has changed.  This provides maximum
             protection against man-in-the-middle (MITM) attacks, though it
             can be annoying when the /etc/ssh/ssh_known_hosts file is poorly
             maintained or when connections to new hosts are frequently made.
             This option forces the user to manually add all new hosts.

             If this flag is set to accept-new then ssh will automatically add
             new host keys to the user's known_hosts file, but will not permit
             connections to hosts with changed host keys.  If this flag is set
             to no or off, ssh will automatically add new host keys to the
             user known hosts files and allow connections to hosts with
             changed hostkeys to proceed, subject to some restrictions.  If
             this flag is set to ask (the default), new host keys will be
             added to the user known host files only after the user has
             confirmed that is what they really want to do, and ssh will
             refuse to connect to hosts whose host key has changed.  The host
             keys of known hosts will be verified automatically in all cases.

     SyslogFacility
             Gives the facility code that is used when logging messages from
             ssh(1).  The possible values are: DAEMON, USER, AUTH, LOCAL0,
             LOCAL1, LOCAL2, LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.  The
             default is USER.

     TCPKeepAlive
             Specifies whether the system should send TCP keepalive messages
             to the other side.  If they are sent, death of the connection or
             crash of one of the machines will be properly noticed.  However,
             this means that connections will die if the route is down
             temporarily, and some people find it annoying.

             The default is yes (to send TCP keepalive messages), and the
             client will notice if the network goes down or the remote host
             dies.  This is important in scripts, and many users want it too.

             To disable TCP keepalive messages, the value should be set to no.
             See also ServerAliveInterval for protocol-level keepalives.

     Tag     Specify a configuration tag name that may be later used by a
             Match directive to select a block of configuration.

     Tunnel  Request tun(4) device forwarding between the client and the
             server.  The argument must be yes, point-to-point (layer 3),
             ethernet (layer 2), or no (the default).  Specifying yes requests
             the default tunnel mode, which is point-to-point.

     TunnelDevice
             Specifies the tun(4) devices to open on the client (local_tun)
             and the server (remote_tun).

             The argument must be local_tun[:remote_tun].  The devices may be
             specified by numerical ID or the keyword any, which uses the next
             available tunnel device.  If remote_tun is not specified, it
             defaults to any.  The default is any:any.

     UpdateHostKeys
             Specifies whether ssh(1) should accept notifications of
             additional hostkeys from the server sent after authentication has
             completed and add them to UserKnownHostsFile.  The argument must
             be yes, no or ask.  This option allows learning alternate
             hostkeys for a server and supports graceful key rotation by
             allowing a server to send replacement public keys before old ones
             are removed.

             Additional hostkeys are only accepted if the key used to
             authenticate the host was already trusted or explicitly accepted
             by the user, the host was authenticated via UserKnownHostsFile
             (i.e. not GlobalKnownHostsFile) and the host was authenticated
             using a plain key and not a certificate.

             UpdateHostKeys is enabled by default if the user has not
             overridden the default UserKnownHostsFile setting and has not
             enabled VerifyHostKeyDNS, otherwise UpdateHostKeys will be set to
             no.

             If UpdateHostKeys is set to ask, then the user is asked to
             confirm the modifications to the known_hosts file.  Confirmation
             is currently incompatible with ControlPersist, and will be
             disabled if it is enabled.

             Presently, only sshd(8) from OpenSSH 6.8 and greater support the
             "hostkeys@openssh.com" protocol extension used to inform the
             client of all the server's hostkeys.

     User    Specifies the user to log in as.  This can be useful when a
             different user name is used on different machines.  This saves
             the trouble of having to remember to give the user name on the
             command line.

     UserKnownHostsFile
             Specifies one or more files to use for the user host key
             database, separated by whitespace.  Each filename may use tilde
             notation to refer to the user's home directory, the tokens
             described in the TOKENS section and environment variables as
             described in the ENVIRONMENT VARIABLES section.  A value of none
             causes ssh(1) to ignore any user-specific known hosts files.  The
             default is ~/.ssh/known_hosts, ~/.ssh/known_hosts2.

     VerifyHostKeyDNS
             Specifies whether to verify the remote key using DNS and SSHFP
             resource records.  If this option is set to yes, the client will
             implicitly trust keys that match a secure fingerprint from DNS.
             Insecure fingerprints will be handled as if this option was set
             to ask.  If this option is set to ask, information on fingerprint
             match will be displayed, but the user will still need to confirm
             new host keys according to the StrictHostKeyChecking option.  The
             default is no.

             See also VERIFYING HOST KEYS in ssh(1).

     VisualHostKey
             If this flag is set to yes, an ASCII art representation of the
             remote host key fingerprint is printed in addition to the
             fingerprint string at login and for unknown host keys.  If this
             flag is set to no (the default), no fingerprint strings are
             printed at login and only the fingerprint string will be printed
             for unknown host keys.

     XAuthLocation
             Specifies the full pathname of the xauth(1) program.  The default
             is /usr/X11R6/bin/xauth.

PATTERNS
     A pattern consists of zero or more non-whitespace characters, M-bM-^@M-^X*M-bM-^@M-^Y (a
     wildcard that matches zero or more characters), or M-bM-^@M-^X?M-bM-^@M-^Y (a wildcard that
     matches exactly one character).  For example, to specify a set of
     declarations for any host in the ".co.uk" set of domains, the following
     pattern could be used:

           Host *.co.uk

     The following pattern would match any host in the 192.168.0.[0-9] network
     range:

           Host 192.168.0.?

     A pattern-list is a comma-separated list of patterns.  Patterns within
     pattern-lists may be negated by preceding them with an exclamation mark
     (M-bM-^@M-^X!M-bM-^@M-^Y).  For example, to allow a key to be used from anywhere within an
     organization except from the "dialup" pool, the following entry (in
     authorized_keys) could be used:

           from="!*.dialup.example.com,*.example.com"

     Note that a negated match will never produce a positive result by itself.
     For example, attempting to match "host3" against the following pattern-
     list will fail:

           from="!host1,!host2"

     The solution here is to include a term that will yield a positive match,
     such as a wildcard:

           from="!host1,!host2,*"

TOKENS
     Arguments to some keywords can make use of tokens, which are expanded at
     runtime:

           %%    A literal M-bM-^@M-^X%M-bM-^@M-^Y.
           %C    Hash of %l%h%p%r%j.
           %d    Local user's home directory.
           %f    The fingerprint of the server's host key.
           %H    The known_hosts hostname or address that is being searched
                 for.
           %h    The remote hostname.
           %I    A string describing the reason for a KnownHostsCommand
                 execution: either ADDRESS when looking up a host by address
                 (only when CheckHostIP is enabled), HOSTNAME when searching
                 by hostname, or ORDER when preparing the host key algorithm
                 preference list to use for the destination host.
           %i    The local user ID.
           %j    The contents of the ProxyJump option, or the empty string if
                 this option is unset.
           %K    The base64 encoded host key.
           %k    The host key alias if specified, otherwise the original
                 remote hostname given on the command line.
           %L    The local hostname.
           %l    The local hostname, including the domain name.
           %n    The original remote hostname, as given on the command line.
           %p    The remote port.
           %r    The remote username.
           %T    The local tun(4) or tap(4) network interface assigned if
                 tunnel forwarding was requested, or "NONE" otherwise.
           %t    The type of the server host key, e.g.  ssh-ed25519.
           %u    The local username.

     CertificateFile, ControlPath, IdentityAgent, IdentityFile,
     KnownHostsCommand, LocalForward, Match exec, RemoteCommand,
     RemoteForward, RevokedHostKeys, and UserKnownHostsFile accept the tokens
     %%, %C, %d, %h, %i, %j, %k, %L, %l, %n, %p, %r, and %u.

     KnownHostsCommand additionally accepts the tokens %f, %H, %I, %K and %t.

     Hostname accepts the tokens %% and %h.

     LocalCommand accepts all tokens.

     ProxyCommand and ProxyJump accept the tokens %%, %h, %n, %p, and %r.

     Note that some of these directives build commands for execution via the
     shell.  Because ssh(1) performs no filtering or escaping of characters
     that have special meaning in shell commands (e.g. quotes), it is the
     user's responsibility to ensure that the arguments passed to ssh(1) do
     not contain such characters and that tokens are appropriately quoted when
     used.

ENVIRONMENT VARIABLES
     Arguments to some keywords can be expanded at runtime from environment
     variables on the client by enclosing them in ${}, for example
     ${HOME}/.ssh would refer to the user's .ssh directory.  If a specified
     environment variable does not exist then an error will be returned and
     the setting for that keyword will be ignored.

     The keywords CertificateFile, ControlPath, IdentityAgent, IdentityFile,
     KnownHostsCommand, and UserKnownHostsFile support environment variables.
     The keywords LocalForward and RemoteForward support environment variables
     only for Unix domain socket paths.

FILES
     ~/.ssh/config
             This is the per-user configuration file.  The format of this file
             is described above.  This file is used by the SSH client.
             Because of the potential for abuse, this file must have strict
             permissions: read/write for the user, and not writable by others.

     /etc/ssh/ssh_config
             Systemwide configuration file.  This file provides defaults for
             those values that are not specified in the user's configuration
             file, and for those users who do not have a configuration file.
             This file must be world-readable.

SEE ALSO
     ssh(1)

AUTHORS
     OpenSSH is a derivative of the original and free ssh 1.2.12 release by
     Tatu Ylonen.  Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
     de Raadt and Dug Song removed many bugs, re-added newer features and
     created OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.

OpenBSD 7.5                      June 17, 2024                     OpenBSD 7.5