Provided by: openssh-client_9.0p1-1ubuntu8_amd64 bug

NAME

     ssh_config — 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)

     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.

     Note that the Debian openssh-client package sets several options as standard in
     /etc/ssh/ssh_config which are not the default in ssh(1):

              Include /etc/ssh/ssh_config.d/*.conf
              SendEnv LANG LC_*
              HashKnownHosts yes
              GSSAPIAuthentication yes

     /etc/ssh/ssh_config.d/*.conf files are included at the start of the system-wide
     configuration file, so options set there will override those in /etc/ssh/ssh_config.

     The file contains keyword-argument pairs, one per line.  Lines starting with ‘#’ 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 ‘=’; 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
             ‘*’ 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 (‘!’).  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, host,
             originalhost, 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 (‘!’).

             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 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
             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.  In addition, the ServerAliveInterval option will be set
             to 300 seconds by default (Debian-specific).  This option is useful in scripts and
             other batch jobs where no user is present to interact with ssh(1), and where it is
             desirable to detect a broken network swiftly.  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 ‘+’ character, then the specified algorithms
             will be appended to the default set instead of replacing them.  If the specified
             list begins with a ‘-’ 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.

     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 ‘+’ character, then the
             specified ciphers will be appended to the default set instead of replacing them.  If
             the specified list begins with a ‘-’ 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 ‘^’ 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 ‘*’ 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.

     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: ‘~’).  The escape character can also be set on
             the command line.  The argument should be a single character, ‘^’ 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 “yes”.
             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 “yes”.

             If the ExitOnForwardFailure configuration option is set to “yes”, then a client
             started with the ForkAfterAuthentication configuration option being set to “yes”
             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 ‘$’) 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, (the Debian-specific default), remote X11 clients will
             have full access to the original X11 display.

             If this option is set to no (the upstream 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.

     GSSAPIClientIdentity
             If set, specifies the GSSAPI client identity that ssh should use when connecting to
             the server. The default is unset, which means that the default identity will be
             used.

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

     GSSAPIKeyExchange
             Specifies whether key exchange based on GSSAPI may be used. When using GSSAPI key
             exchange the server need not have a host key.  The default is “no”.

     GSSAPIRenewalForcesRekey
             If set to “yes” then renewal of the client's GSSAPI credentials will force the
             rekeying of the ssh connection. With a compatible server, this will delegate the
             renewed credentials to a session on the server.

             Checks are made to ensure that credentials are only propagated when the new
             credentials match the old ones on the originating client and where the receiving
             server still has the old set in its cache.

             The default is “no”.

             For this to work GSSAPIKeyExchange needs to be enabled in the server and also used
             by the client.

     GSSAPIServerIdentity
             If set, specifies the GSSAPI server identity that ssh should expect when connecting
             to the server. The default is unset, which means that the expected GSSAPI server
             identity will be determined from the target hostname.

     GSSAPITrustDns
             Set to “yes” to indicate that the DNS is trusted to securely canonicalize the name
             of the host being connected to. If “no”, the hostname entered on the command line
             will be passed untouched to the GSSAPI library.  The default is “no”.

     GSSAPIKexAlgorithms
             The list of key exchange algorithms that are offered for GSSAPI key exchange.
             Possible values are

                gss-gex-sha1-,
                gss-group1-sha1-,
                gss-group14-sha1-,
                gss-group14-sha256-,
                gss-group16-sha512-,
                gss-nistp256-sha256-,

                gss-curve25519-sha256-
             The default is
             “gss-group14-sha256-,gss-group16-sha512-,gss-nistp256-sha256-,gss-curve25519-sha256-,gss-gex-sha1-,gss-group14-sha1-”.
             This option only applies to connections using GSSAPI.

     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).  Use of this option may break facilities such as tab-completion that
             rely on being able to read unhashed host names from ~/.ssh/known_hosts.

     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
             ‘+’ character, then the specified signature algorithms will be appended to the
             default set instead of replacing them.  If the specified list begins with a ‘-’
             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 ‘^’ 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 ‘+’ character, then the
             specified signature algorithms will be appended to the default set instead of
             replacing them.  If the specified list begins with a ‘-’ 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 ‘^’
             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 ‘$’ 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 DSA, ECDSA, authenticator-hosted ECDSA,
             Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.  The
             default is ~/.ssh/id_rsa, ~/.ssh/id_ecdsa, ~/.ssh/id_ecdsa_sk, ~/.ssh/id_ed25519,
             ~/.ssh/id_ed25519_sk and ~/.ssh/id_dsa.  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.

             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 ‘~’ 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 lowdelay for interactive sessions and throughput 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 available KEX (Key Exchange) algorithms.  Multiple algorithms must be
             comma-separated.  If the specified list begins with a ‘+’ character, then the
             specified algorithms will be appended to the default set instead of replacing them.
             If the specified list begins with a ‘-’ 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 ‘^’ 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 available 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 ‘*’ 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 ‘+’ character, then the
             specified algorithms will be appended to the default set instead of replacing them.
             If the specified list begins with a ‘-’ 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 ‘^’ 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.

     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
             ‘*’ 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 ‘exec’ 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 ‘+’
             character, then the algorithms after it will be appended to the default instead of
             replacing it.  If the specified list begins with a ‘-’ 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 ‘^’ 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 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 ‘K’, ‘M’, or ‘G’ to indicate Kilobytes, Megabytes, or
             Gigabytes, respectively.  The default is between ‘1G’ and ‘4G’, 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 ‘*’ 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).

     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).

     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 ‘$’ 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, or 300 if the BatchMode option is set (Debian-specific).
             ProtocolKeepAlives and SetupTimeOut are Debian-specific compatibility aliases for
             this option.

     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.  This option only uses TCP keepalives (as opposed to using ssh
             level keepalives), so takes a long time to notice when the connection dies.  As
             such, you probably want the ServerAliveInterval option as well.  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.

     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.  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/bin/xauth.

PATTERNS

     A pattern consists of zero or more non-whitespace characters, ‘*’ (a wildcard that matches
     zero or more characters), or ‘?’ (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 (‘!’).  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 ‘%’.
           %C    Hash of %l%h%p%r.
           %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.
           %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, and UserKnownHostsFile accept the tokens %%, %C,
     %d, %h, %i, %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 accepts the tokens %%, %h, %n, %p, and %r.

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.  It may be group-writable provided that the group in question contains only
             the user.

     /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.