path: root/ssh_config.0

SSH_CONFIG(5)                 File Formats Manual                SSH_CONFIG(5)

NAME
     ssh_config M-bM-^@M-^S OpenSSH SSH client configuration files

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.

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

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

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

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

             See PATTERNS for more information on patterns.

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

             The canonical keyword matches only when the configuration file is
             being re-parsed after hostname canonicalization (see the
             CanonicalizeHostname option.)  This may be useful to specify
             conditions that work with canonical host names only.  The 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.  The argument must be yes, confirm, ask, or no (the
             default).

     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, passphrase/password querying will be disabled.
             This option is useful in scripts and other batch jobs where no
             user is present to supply the password.  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, 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.

     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.

     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.

             Arguments to CertificateFile 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 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.

     ChallengeResponseAuthentication
             Specifies whether to use challenge-response authentication.  The
             argument to this keyword must be yes (the default) or no.

     CheckHostIP
             If set to yes (the default), 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 check will not be executed.

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

             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 value is used only when the target is down or really
             unreachable, not when it refuses the connection.

     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 or the tokens described in the TOKENS 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, then the master
             connection will not be placed into the background, and will close
             as soon as the initial client connection is closed.  If set to
             yes or 0, then the master connection will remain in the
             background indefinitely (until killed or closed via a mechanism
             such as the "ssh -O exit").  If set to a time in seconds, or a
             time in any of the formats documented in sshd_config(5), then the
             backgrounded master connection will automatically terminate after
             it has remained idle (with no client connections) for the
             specified time.

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

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

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

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

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

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

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

     ForwardAgent
             Specifies whether the connection to the authentication agent (if
             any) will be forwarded to the remote machine.  The argument must
             be yes or no (the default).

             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.
             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 reveal
             identifying information should the file's contents be 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).

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

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

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

             The -Q option of ssh(1) may be used to list supported key types.

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

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

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

             The list of available key types may also be obtained using "ssh
             -Q key".

     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 authentication identity
             and certificate files explicitly configured in the ssh_config
             files or passed on the ssh(1) command-line, even if ssh-agent(1)
             or a PKCS11Provider 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.

             Arguments to IdentityAgent may use the tilde syntax to refer to a
             user's home directory or the tokens described in the TOKENS
             section.

     IdentityFile
             Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
             authentication identity is read.  The default is ~/.ssh/id_dsa,
             ~/.ssh/id_ecdsa, ~/.ssh/id_ed25519 and ~/.ssh/id_rsa.
             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 M-bM-^@M-^X~M-bM-^@M-^Y references to user
             home directories.  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, 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.

     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.  Alternately if the specified
             value begins with a M-bM-^@M-^X+M-bM-^@M-^Y character, then the specified methods
             will be appended to the default set instead of replacing them.
             If the specified value begins with a M-bM-^@M-^X-M-bM-^@M-^Y character, then the
             specified methods (including wildcards) will be removed from the
             default set instead of replacing them.  The default is:

                   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-group-exchange-sha1,
                   diffie-hellman-group14-sha256,
                   diffie-hellman-group14-sha1

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

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

     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.

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

             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).

     PKCS11Provider
             Specifies which PKCS#11 provider to use.  The argument to this
             keyword is the PKCS#11 shared library ssh(1) should use to
             communicate with a PKCS#11 token providing the user's private RSA
             key.

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

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

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

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

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

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

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

     ProxyJump
             Specifies one or more jump proxies as either [user@]host[:port]
             or an ssh URI.  Multiple proxies may be separated by comma
             characters and will be visited sequentially.  Setting this option
             will cause ssh(1) to connect to the target host by first making a
             ssh(1) connection to the specified ProxyJump host and then
             establishing a TCP forwarding to the ultimate target from there.

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

     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.

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

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

             The list of available key types may also be obtained using "ssh
             -Q key".

     PubkeyAuthentication
             Specifies whether to try public key authentication.  The argument
             to this keyword must be yes (the default) or no.

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

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

     RemoteForward
             Specifies that a TCP port on the remote machine be forwarded over
             the secure channel.  The remote port may either be forwarded to a
             specified host and port from the local machine, or may act as a
             SOCKS 4/5 proxy that allows a remote client to connect to
             arbitrary destinations from the local machine.  The first
             argument must be [bind_address:]port If forwarding to a specific
             destination then the second argument must be host:hostport,
             otherwise if no destination argument is specified then the remote
             forwarding will be established as a SOCKS proxy.

             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.

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

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

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

     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).

     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 inactive.

             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.

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

     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 M-bM-^@M-^\accept-newM-bM-^@M-^] then ssh will automatically
             add new host keys to the user known hosts files, but will not
             permit connections to hosts with changed host keys.  If this flag
             is set to M-bM-^@M-^\noM-bM-^@M-^] or M-bM-^@M-^\offM-bM-^@M-^], 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.

     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 (the default) or ask.  Enabling 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.  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.  The default is
             ~/.ssh/known_hosts, ~/.ssh/known_hosts2.

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

             See also VERIFYING HOST KEYS in ssh(1).

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

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

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

           Host *.co.uk

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

           Host 192.168.0.?

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

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

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

           from="!host1,!host2"

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

           from="!host1,!host2,*"

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

           %%    A literal M-bM-^@M-^X%M-bM-^@M-^Y.
           %C    Hash of %l%h%p%r.
           %d    Local user's home directory.
           %h    The remote hostname.
           %i    The local user ID.
           %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.
           %u    The local username.

     Match exec accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.

     CertificateFile accepts the tokens %%, %d, %h, %i, %l, %r, and %u.

     ControlPath accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and
     %u.

     HostName accepts the tokens %% and %h.

     IdentityAgent and IdentityFile accept the tokens %%, %d, %h, %i, %l, %r,
     and %u.

     LocalCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T,
     and %u.

     ProxyCommand accepts the tokens %%, %h, %p, and %r.

     RemoteCommand accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and
     %u.

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 accessible by
             others.

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

SEE ALSO
     ssh(1)

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

OpenBSD 6.4                      July 23, 2018                     OpenBSD 6.4