ssh_config(5) — Linux manual page

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SSH_CONFIG(5)              File Formats Manual             SSH_CONFIG(5)

NAME         top

       ssh_config — OpenSSH client configuration file

DESCRIPTION         top

       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 ‘#’ 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,
               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 (‘!’).

               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 ‘+’ 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.

       ChannelTimeout
               Specifies whether and how quickly ssh(1) should close
               inactive channels.  Timeouts are specified as one or more
               “type=interval” pairs separated by whitespace, where the
               “type” must be the special keyword “global” or a channel
               type name from the list below, optionally containing
               wildcard characters.

               The timeout value “interval” is specified in seconds or
               may use any of the units documented in the “TIME FORMATS”
               section.  For example, “session=5m” would cause
               interactive sessions to terminate after five minutes of
               inactivity.  Specifying a zero value disables the
               inactivity timeout.

               The special timeout “global” 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 ‘+’ 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.

       EnableEscapeCommandline
               Enables the command line option in the EscapeChar menu
               for interactive sessions (default ‘~C’).  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: ‘~’).  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, 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 ‘+’ 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.  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, ~/.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.  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 ‘~’ 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 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.

       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 ‘*’ 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 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 ‘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).

       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 ‘$’ 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         top

       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         top

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

             %%    A literal ‘%’.
             %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         top

       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         top

       ~/.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         top

       ssh(1)

AUTHORS         top

       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.

COLOPHON         top

       This page is part of the openssh (Portable OpenSSH) project.
       Information about the project can be found at
       http://www.openssh.com/portable.html.  If you have a bug report
       for this manual page, see ⟨http://www.openssh.com/report.html⟩.
       This page was obtained from the tarball openssh-9.7p1.tar.gz
       fetched from
       ⟨http://ftp.eu.openbsd.org/pub/OpenBSD/OpenSSH/portable/⟩ on
       2024-06-14.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-
       to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not
       part of the original manual page), send a mail to
       man-pages@man7.org

GNU                         February 21, 2024              SSH_CONFIG(5)

Pages that refer to this page: sshfs(1)systemd-ssh-proxy(1)