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SSH_CONFIG(5)			     BSD 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 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 the one
     given on the command line.

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

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

	   o   SendEnv LANG LC_*
	   o   HashKnownHosts yes
	   o   GSSAPIAuthentication yes

     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 specifying 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 keywords are case-insen-
     sitive and arguments are case-sensitive):

     Host    Restricts the following declarations (up to the next Host keyword) to be only for
	     those hosts that match one of the patterns given after the keyword.  If more than
	     one pattern is provided, they should be separated by whitespace.  A single '*' as a
	     pattern can be used to provide global defaults for all hosts.  The host is the
	     hostname argument given on the command line (i.e. the name is not converted to a
	     canonicalized host name before matching).

	     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.	In addition, the
	     ServerAliveInterval option will be set to 300 seconds by default.	This option is
	     useful in scripts and other batch jobs where no user is present to supply the pass-
	     word, and where it is desirable to detect a broken network swiftly.  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 connec-
	     tion.  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 protocol version 1.  Cur-
	     rently, ``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 crypto-
	     graphic weaknesses.  The default is ``3des''.

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

		aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
		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 con-
	     figuration 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 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 to listen for control connections, 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 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 con-
	     nection 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 shar-
	     ing.  In the path, '%l' will be substituted by the local host name, '%h' will be
	     substituted by the target host name, '%p' the port, and '%r' by the remote login
	     username.	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 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'', 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 con-
	     nection will automatically terminate after it has remained idle (with no client con-
	     nections) for the specified time.

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

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

	     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 let-
	     ter, 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.  The argument must be
	     ``yes'' or ``no''.  The default is ``no''.

     ForwardAgent
	     Specifies whether the connection to the authentication agent (if any) will be for-
	     warded 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 redirected 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 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'', 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.

	     The default is ``yes'' (Debian-specific).

	     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 is ``no''.

     GlobalKnownHostsFile
	     Specifies a file to use for the global host key database instead of
	     /etc/ssh/ssh_known_hosts.

     GSSAPIAuthentication
	     Specifies whether user authentication based on GSSAPI is allowed.	The default is
	     ``no''.  Note that this option applies to protocol version 2 only.

     GSSAPIKeyExchange
	     Specifies whether key exchange based on GSSAPI may be used. When using GSSAPI key
	     exchange the server need not have a host key.  The default is ``no''.  Note that
	     this option applies to protocol version 2 only.

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

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

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

     GSSAPIRenewalForcesRekey
	     If set to ``yes'' then renewal of the client's GSSAPI credentials will force the
	     rekeying of the ssh connection. With a compatible server, this can delegate the
	     renewed credentials to a session on the server.  The default is ``no''.

     GSSAPITrustDns
	     Set to ``yes to indicate that the DNS is trusted to securely canonicalize'' the name
	     of the host being connected to. If ``no, the hostname entered on the'' command line
	     will be passed untouched to the GSSAPI library.  The default is ``no''.  This option
	     only applies to protocol version 2 connections using GSSAPI.

     HashKnownHosts
	     Indicates that ssh(1) should hash host names and addresses when they are added to
	     ~/.ssh/known_hosts.  These hashed names may be used normally by ssh(1) and sshd(8),
	     but they do not reveal identifying information should the file's contents be dis-
	     closed.  The default is ``no''.  Note that existing names and addresses in known
	     hosts files will not be converted automatically, but may be manually hashed using
	     ssh-keygen(1).  Use of this option may break facilities such as tab-completion that
	     rely on being able to read unhashed host names from ~/.ssh/known_hosts.

     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 pre-
	     fer 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 database 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 commandline (this is use-
	     ful for manipulating unqualified names).  The default is the name given on the com-
	     mand line.  Numeric IP addresses are also permitted (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) 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 DSA authentication 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.
	     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 configuration files; all
	     these identities will be tried in sequence.

     IPQoS   Specifies the IPv4 type-of-service or DSCP class for connections.	Accepted values
	     are ``af11'', ``af12'', ``af13'', ``af14'', ``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 white-
	     space.  If one argument is specified, it is used as the packet class uncondition-
	     ally.  If two values are specified, the first is automatically selected for interac-
	     tive sessions and the second for non-interactive sessions.  The default is
	     ``lowdelay'' for interactive sessions and ``throughput'' for non-interactive ses-
	     sions.

     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.  Multi-
	     ple method names must be comma-separated.	The default is to use the server speci-
	     fied 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 successfully 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 privileged ports.  By default, the local port is bound in
	     accordance with the GatewayPorts setting.	However, an explicit bind_address may be
	     used to bind the connection to a specific address.  The bind_address of
	     ``localhost'' indicates that the listening port be bound for local use only, while
	     an empty address or '*' indicates that the port should be available from all inter-
	     faces.

     LogLevel
	     Gives the verbosity level that is used when logging messages from ssh(1).	The pos-
	     sible 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 in protocol version 2 for data integrity protection.  Mul-
	     tiple algorithms must be comma-separated.	The default is:

		   hmac-md5,hmac-sha1,umac-64@openssh.com,
		   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 warnings 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 communicate with a PKCS#11 token provid-
	     ing 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 meth-
	     ods.  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 versions must be comma-separated.  When
	     this option is set to ``2,1'' ssh will try version 2 and fall back to version 1 if
	     version 2 is not available.  The default is '2'.

     ProxyCommand
	     Specifies the command to use to connect to the server.  The command 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 basically any-
	     thing, 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 exam-
	     ple, 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.  The argument is the number of bytes, with an optional suffix of
	     'K', 'M', or 'G' to indicate Kilobytes, Megabytes, or Gigabytes, respectively.  The
	     default is between '1G' and '4G', depending on the cipher.  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 interfaces.  Specifying a remote bind_address will only
	     succeed if the server's GatewayPorts option is enabled (see sshd_config(5)).

     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 authentication 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 vari-
	     ables.  Refer to AcceptEnv in sshd_config(5) for how to configure the server.  Vari-
	     ables are specified by name, which may contain wildcard characters.  Multiple envi-
	     ronment 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 mes-
	     sages 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 unrespon-
	     sive, ssh will disconnect after approximately 45 seconds.	This option applies to
	     protocol version 2 only; in protocol version 1 there is no mechanism to request a
	     response from the server to the server alive messages, so disconnection is the
	     responsibility of the TCP stack.

     ServerAliveInterval
	     Sets a timeout interval in seconds after which if no data has been received from the
	     server, ssh(1) will send a message through the encrypted channel to request a
	     response from the server.	The default is 0, indicating that these messages will not
	     be sent to the server, or 300 if the BatchMode option is set.  This option applies
	     to protocol version 2 only.  ProtocolKeepAlives and SetupTimeOut are Debian-specific
	     compatibility aliases for this option.

     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 trojan horse attacks, though it can be
	     annoying when the /etc/ssh/ssh_known_hosts file is poorly maintained or when connec-
	     tions 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 automatically 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.	This option only uses TCP keepalives (as opposed to using ssh
	     level keepalives), so takes a long time to notice when the connection dies.  As
	     such, you probably want the ServerAliveInterval option as well.  However, this means
	     that connections will die if the route is down temporarily, and some people find it
	     annoying.

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

	     To disable TCP keepalive messages, the value should be set to ``no''.

     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 numer-
	     ical 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''.

     UseBlacklistedKeys
	     Specifies whether ssh(1) should use keys recorded in its blacklist of known-compro-
	     mised keys (see ssh-vulnkey(1)) for authentication.  If ``yes'', then attempts to
	     use compromised keys for authentication will be logged but accepted.  It is strongly
	     recommended that this be used only to install new authorized keys on the remote sys-
	     tem, and even then only with the utmost care.  If ``no'', then attempts to use com-
	     promised keys for authentication will be prevented.  The default is ``no''.

     UsePrivilegedPort
	     Specifies whether to use a privileged port for outgoing connections.  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 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 a file to use for the user host key database instead of
	     ~/.ssh/known_hosts.

     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 finger-
	     print 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 proto-
	     col 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/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 exam-
     ple, to specify a set of declarations for any host in the ``.co.uk'' set of domains, the
     following pattern could be used:

	   Host *.co.uk

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

	   Host 192.168.0.?

     A pattern-list is a comma-separated list of patterns.  Patterns within pattern-lists may be
     negated by preceding them with an exclamation mark ('!').	For example, to allow a key to be
     used from anywhere within an 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 others.  It may be group-writable provided that the group in question contains
	     only the user.

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

SEE ALSO
     ssh(1)

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

BSD					  April 28, 2017				      BSD
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