SSH_CONFIG(5)             NetBSD File Formats Manual             SSH_CONFIG(5)

NAME
     ssh_config -- OpenSSH SSH client configuration files

SYNOPSIS
     ~/.ssh/config
     /etc/ssh/ssh_config

DESCRIPTION
     ssh(1) obtains configuration data from the following sources in the fol-
     lowing 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 configu-
     ration 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 the one given on
     the command line.

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

     The configuration file has the following format:

     Empty lines and lines starting with `#' are comments.  Otherwise a line
     is of the format ``keyword arguments''.  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 speci-
     fying configuration options using the ssh, scp, and sftp -o option.
     Arguments may optionally be enclosed in double quotes (") in order to
     represent arguments containing spaces.

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

     Host    Restricts the following declarations (up to the next Host key-
             word) 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 pat-
             tern can be used to provide global defaults for all hosts.  The
             host is the hostname argument given on the command line (i.e. the
             name is not converted to a canonicalized host name before match-
             ing).

             A pattern entry may be negated by prefixing it with an exclama-
             tion 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.

     AddressFamily
             Specifies which address family to use when connecting.  Valid
             arguments are ``any'', ``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 is ``no''.

     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.  Note that this option does not work if
             UsePrivilegedPort is set to ``yes''.

     ChallengeResponseAuthentication
             Specifies whether to use challenge-response authentication.  The
             argument to this keyword must be ``yes'' or ``no''.  The default
             is ``yes''.

     CheckHostIP
             If this flag is set to ``yes'', ssh(1) will additionally check
             the host IP address in the known_hosts file.  This allows ssh to
             detect if a host key changed due to DNS spoofing.  If the option
             is set to ``no'', the check will not be executed.  The default is
             ``yes''.

     Cipher  Specifies the cipher to use for encrypting the session in proto-
             col version 1.  Currently, ``blowfish'', ``3des'', and ``des''
             are supported.  des is only supported in the ssh(1) client for
             interoperability with legacy protocol 1 implementations that do
             not support the 3des cipher.  Its use is strongly discouraged due
             to cryptographic weaknesses.  The default is ``3des''.

     Ciphers
             Specifies the ciphers allowed for protocol version 2 in order of
             preference.  Multiple ciphers must be comma-separated.  The sup-
             ported ciphers are ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'',
             ``aes256-cbc'', ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'',
             ``aes128-gcm@openssh.com'', ``aes256-gcm@openssh.com'',
             ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'',
             and ``cast128-cbc''.  The default is:

                aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
                aes128-gcm@openssh.com,aes256-gcm@openssh.com,
                aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
                aes256-cbc,arcfour

     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 configura-
             tion files, and is automatically set by scp(1) and sftp(1).  The
             argument must be ``yes'' or ``no''.  The default is ``no''.

     Compression
             Specifies whether to use compression.  The argument must be
             ``yes'' or ``no''.  The default is ``no''.

     CompressionLevel
             Specifies the compression level to use if compression is enabled.
             The argument must be an integer from 1 (fast) to 9 (slow, best).
             The default level is 6, which is good for most applications.  The
             meaning of the values is the same as in gzip(1).  Note that this
             option applies to protocol version 1 only.

     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 connec-
             tions on a control socket specified using the ControlPath argu-
             ment.  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 to listen for control con-
             nections, but require confirmation using the SSH_ASKPASS program
             before they are accepted (see ssh-add(1) for details).  If the
             ControlPath cannot be opened, ssh will continue without connect-
             ing to a master instance.

             X11 and ssh-agent(1) forwarding is supported over these multi-
             plexed connections, however the display and agent forwarded will
             be the one belonging to the master connection i.e. it is not pos-
             sible 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 shar-
             ing as described in the ControlMaster section above or the string
             ``none'' to disable connection sharing.  In the path, `%L' will
             be substituted by the first component of the local host name,
             `%l' will be substituted by the local host name (including any
             domain name), `%h' will be substituted by the target host name,
             `%n' will be substituted by the original target host name speci-
             fied on the command line, `%p' the port, `%r' by the remote login
             username, and `%u' by the username of the user running ssh(1).
             It is recommended that any ControlPath used for opportunistic
             connection sharing include at least %h, %p, and %r.  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 connec-
             tion has been closed.  If set to ``no'', then the master connec-
             tion will not be placed into the background, and will close as
             soon as the initial client connection is closed.  If set to
             ``yes'', then the master connection will remain in the background
             indefinitely (until killed or closed via a mechanism such as the
             ssh(1) ``-O exit'' option).  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 speci-
             fied 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 set-
             ting.  However, an explicit bind_address may be used to bind the
             connection to a specific address.  The bind_address of
             ``localhost'' indicates that the listening port be bound for
             local use only, while an empty address or `*' indicates that the
             port should be available from all interfaces.

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

     EnableSSHKeysign
             Setting this option to ``yes'' in the global client configuration
             file /etc/ssh/ssh_config enables the use of the helper program
             ssh-keysign(8) during HostbasedAuthentication.  The argument must
             be ``yes'' or ``no''.  The default is ``no''.  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 dis-
             able the escape character entirely (making the connection trans-
             parent 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.  The argument must be ``yes'' or ``no''.  The
             default is ``no''.

     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 is ``no''.

             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 redi-
             rected over the secure channel and DISPLAY set.  The argument
             must be ``yes'' or ``no''.  The default is ``no''.

             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 dis-
             play 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'', remote X11 clients will be con-
             sidered 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 min-
             utes.  Remote clients will be refused access after this time.

             The default is ``no''.

             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 spec-
             ify 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 is
             ``no''.

     GlobalKnownHostsFile
             Specifies one or more files to use for the global host key data-
             base, 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''.  Note that this option applies to protocol
             version 2 only.

     GSSAPIDelegateCredentials
             Forward (delegate) credentials to the server.  The default is
             ``no''.  Note that this option applies to protocol version 2
             only.

     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 iden-
             tifying 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 is ``no''.  This option applies to protocol version 2
             only and is similar to RhostsRSAAuthentication.

     HostKeyAlgorithms
             Specifies the protocol version 2 host key algorithms that the
             client wants to use in order of preference.  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-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
                ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
                ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
                ssh-rsa,ssh-dss

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

     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 data-
             base files.  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.  If the hostname
             contains the character sequence `%h', then this will be replaced
             with the host name specified on the command line (this is useful
             for manipulating unqualified names).  The default is the name
             given on the command line.  Numeric IP addresses are also permit-
             ted (both on the command line and in HostName specifications).

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

     IdentityFile
             Specifies a file from which the user's DSA, ECDSA or RSA authen-
             tication identity is read.  The default is ~/.ssh/identity for
             protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and
             ~/.ssh/id_rsa for protocol version 2.  Additionally, any identi-
             ties represented by the authentication agent will be used for
             authentication unless IdentitiesOnly is set.  ssh(1) will try to
             load certificate information from the filename obtained by
             appending -cert.pub to the path of a specified IdentityFile.

             The file name may use the tilde syntax to refer to a user's home
             directory or one of the following escape characters: `%d' (local
             user's home directory), `%u' (local user name), `%l' (local host
             name), `%h' (remote host name) or `%r' (remote user name).

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

             IdentityFile may be used in conjunction with IdentitiesOnly to
             select which identities in an agent are offered during authenti-
             cation.

     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 unrecog-
             nised 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.

     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'', or a numeric value.  This option may take one or
             two arguments, separated by whitespace.  If one argument is spec-
             ified, it is used as the packet class unconditionally.  If two
             values are specified, the first is automatically selected for
             interactive sessions and the second for non-interactive sessions.
             The default is ``lowdelay'' for interactive sessions and
             ``throughput'' for non-interactive sessions.

     KbdInteractiveAuthentication
             Specifies whether to use keyboard-interactive authentication.
             The argument to this keyword must be ``yes'' or ``no''.  The
             default is ``yes''.

     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'', ``pam'',
             and ``skey''.

     KexAlgorithms
             Specifies the available KEX (Key Exchange) algorithms.  Multiple
             algorithms must be comma-separated.  The default is:

                   ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
                   diffie-hellman-group-exchange-sha256,
                   diffie-hellman-group-exchange-sha1,
                   diffie-hellman-group14-sha1,
                   diffie-hellman-group1-sha1

     LocalCommand
             Specifies a command to execute on the local machine after suc-
             cessfully connecting to the server.  The command string extends
             to the end of the line, and is executed with the user's shell.
             The following escape character substitutions will be performed:
             `%d' (local user's home directory), `%h' (remote host name), `%l'
             (local host name), `%n' (host name as provided on the command
             line), `%p' (remote port), `%r' (remote user name) or `%u' (local
             user name).

             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 privi-
             leged 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 `*' indi-
             cates 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, VER-
             BOSE, 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 in protocol ver-
             sion 2 for data integrity protection.  Multiple algorithms must
             be comma-separated.  The algorithms that contain ``-etm'' calcu-
             late the MAC after encryption (encrypt-then-mac).  These are con-
             sidered safer and their use recommended.  The default is:

                   hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
                   umac-64-etm@openssh.com,umac-128-etm@openssh.com,
                   hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
                   hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
                   hmac-md5-96-etm@openssh.com,
                   hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
                   hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
                   hmac-sha1-96,hmac-md5-96

     NoHostAuthenticationForLocalhost
             This option can be used if the home directory is shared across
             machines.  In this case localhost will refer to a different
             machine on each of the machines and the user will get many warn-
             ings about changed host keys.  However, this option disables host
             authentication for localhost.  The argument to this keyword must
             be ``yes'' or ``no''.  The default is to check the host key for
             localhost.

     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'' or ``no''.  The default is
             ``yes''.

     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 is ``no''.

     PKCS11Provider
             Specifies which PKCS#11 provider to use.  The argument to this
             keyword is the PKCS#11 shared library ssh(1) should use to commu-
             nicate 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 protocol 2
             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

     Protocol
             Specifies the protocol versions ssh(1) should support in order of
             preference.  The possible values are `1' and `2'.  Multiple ver-
             sions must be comma-separated.  When this option is set to
             ``2,1'' ssh will try version 2 and fall back to version 1 if ver-
             sion 2 is not available.  The default is `2'.

     ProxyCommand
             Specifies the command to use to connect to the server.  The com-
             mand string extends to the end of the line, and is executed with
             the user's shell.  In the command string, any occurrence of `%h'
             will be substituted by the host name to connect, `%p' by the
             port, and `%r' by the remote user name.  The command can be basi-
             cally 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).  Set-
             ting the command to ``none'' disables this option entirely.  Note
             that CheckHostIP is not available for connects with a proxy com-
             mand.

             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

     PubkeyAuthentication
             Specifies whether to try public key authentication.  The argument
             to this keyword must be ``yes'' or ``no''.  The default is
             ``yes''.  This option applies to protocol version 2 only.

     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 `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 docu-
             mented 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.  This option applies to protocol version 2 only.

     RemoteForward
             Specifies that a TCP port on the remote machine be forwarded over
             the secure channel to the specified host and port from the local
             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.  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 `*' or an empty
             string, then the forwarding is requested to listen on all inter-
             faces.  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).

     RhostsRSAAuthentication
             Specifies whether to try rhosts based authentication with RSA
             host authentication.  The argument must be ``yes'' or ``no''.
             The default is ``no''.  This option applies to protocol version 1
             only and requires ssh(1) to be setuid root.

     RSAAuthentication
             Specifies whether to try RSA authentication.  The argument to
             this keyword must be ``yes'' or ``no''.  RSA authentication will
             only be attempted if the identity file exists, or an authentica-
             tion agent is running.  The default is ``yes''.  Note that this
             option applies to protocol version 1 only.

     SendEnv
             Specifies what variables from the local environ(7) should be sent
             to the server.  Note that environment passing is only supported
             for protocol 2.  The server must also support it, and the server
             must be configured to accept these environment variables.  Refer
             to AcceptEnv in sshd_config(5) for how to configure the server.
             Variables are specified by name, which may contain wildcard char-
             acters.  Multiple environment variables may be separated by
             whitespace or spread across multiple SendEnv directives.  The
             default is not to send any environment variables.

             See PATTERNS for more information on patterns.

     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 there-
             fore will not be spoofable.  The TCP keepalive option enabled by
             TCPKeepAlive is spoofable.  The server alive mechanism is valu-
             able when the client or server depend on knowing when a connec-
             tion 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.  This option applies to protocol
             version 2 only.

     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.  This option applies to protocol version 2 only.

     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 con-
             nect to hosts whose host key has changed.  This provides maximum
             protection against trojan horse attacks, though it can be annoy-
             ing 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 ``no'', ssh will automatically add new host keys
             to the user known hosts files.  If this flag is set to ``ask'',
             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 automati-
             cally in all cases.  The argument must be ``yes'', ``no'', or
             ``ask''.  The default is ``ask''.

     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 tempo-
             rarily, 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''.

     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''.  Specifying ``yes''
             requests the default tunnel mode, which is ``point-to-point''.
             The default is ``no''.

     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''.

     UsePrivilegedPort
             Specifies whether to use a privileged port for outgoing connec-
             tions.  The argument must be ``yes'' or ``no''.  The default is
             ``no''.  If set to ``yes'', ssh(1) must be setuid root.  Note
             that this option must be set to ``yes'' for
             RhostsRSAAuthentication with older servers.

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

     UserKnownHostsFile
             Specifies one or more files to use for the user host key data-
             base, 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 argument must be ``yes'', ``no'', or ``ask''.  The
             default is ``no''.  Note that this option applies to protocol
             version 2 only.

             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 hex
             fingerprint string at login and for unknown host keys.  If this
             flag is set to ``no'', no fingerprint strings are printed at
             login and only the hex fingerprint string will be printed for
             unknown host keys.  The default is ``no''.

     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, `*' (a
     wildcard that matches zero or more characters), or `?' (a wildcard that
     matches exactly one character).  For example, to specify a set of decla-
     rations for any host in the ``.co.uk'' set of domains, the following pat-
     tern 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
     organisation except from the ``dialup'' pool, the following entry (in
     authorized_keys) could be used:

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

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 oth-
             ers.

     /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 cre-
     ated OpenSSH.  Markus Friedl contributed the support for SSH protocol
     versions 1.5 and 2.0.

NetBSD 6.0                       June 27 2013                       NetBSD 6.0

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