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_exit
__syscall
 
FreeBSD/Linux/UNIX General Commands Manual
Hypertext Man Pages
ssh_config
 
SSH_CONFIG(5)		  FreeBSD File Formats Manual		 SSH_CONFIG(5)

NAME
     ssh_config -- OpenSSH SSH client configuration files

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

DESCRIPTION
     ssh obtains configuration data from the following sources in the follow-
     ing 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 white-
     space when specifying configuration options using the ssh, scp and sftp
     -o option.

     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.  `*' and `?' can be used as wildcards in
	     the patterns.  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).

     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 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
	     ``no''.

     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 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'',
	     ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'',
	     and ``cast128-cbc''.  The default is

	       ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
		 arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
		 aes192-ctr,aes256-ctr''

     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
	     command line to clear port forwardings set in configuration
	     files, and is automatically set by scp(1) and sftp(1).  The argu-
	     ment 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 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 reuse the master instance's network connec-
	     tion rather than initiating new ones.  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 can
	     not be opened, ssh will continue without connecting to a master
	     instance.

	     X11 and ssh-agent(1) forwarding is supported over these multi-
	     plexed connections, however the display and agent fowarded 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, `%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 all
	     three of these escape sequences.  This ensures that shared con-
	     nections are uniquely identified.

     DynamicForward
	     Specifies that a TCP/IP 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 a port number.  Currently the SOCKS4 and
	     SOCKS5 protocols are supported, and ssh 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).

     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.

     ForwardX11Trusted
	     If this option is set to ``yes'' then remote X11 clients will
	     have full access to the original X11 display.

	     If this option is set to ``no'' then 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 ``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 binds local port forwardings to
	     the loopback address.  This prevents other remote hosts from con-
	     necting 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.

     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 should hash host names and addresses when they
	     are added to ~/.ssh/known_hosts.  These hashed names may be used
	     normally by ssh and sshd, but they do not reveal identifying
	     information should the file's contents be disclosed.  The default
	     is ``no''.  Note that hashing of names and addresses will not be
	     retrospectively applied to existing known hosts files, but these
	     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: ``ssh-rsa,ssh-dss''.

     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.  Default is the
	     name given on the command line.  Numeric IP addresses are also
	     permitted (both on the command line and in HostName specifica-
	     tions).

     IdentityFile
	     Specifies a file from which the user's RSA or DSA authentication
	     identity is read.	The default is ~/.ssh/identity for protocol
	     version 1, and ~/.ssh/id_rsa and ~/.ssh/id_dsa for protocol ver-
	     sion 2.  Additionally, any identities represented by the authen-
	     tication agent will be used for authentication.  The file name
	     may use the tilde syntax to refer to a user's home directory.  It
	     is possible to have multiple identity files specified in configu-
	     ration files; all these identities will be tried in sequence.

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

     LocalForward
	     Specifies that a TCP/IP 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 or by
	     using an alternative syntax: [bind_address/]port and
	     host/hostport.  Multiple forwardings may be specified, and addi-
	     tional 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.  How-
	     ever, an explicit bind_address may be used to bind the connection
	     to a specific address.  The bind_address of ``localhost'' indi-
	     cates that the listening port be bound for local use only, while
	     an empty address or `*' indicates that the port should be avail-
	     able from all interfaces.

     LogLevel
	     Gives the verbosity level that is used when logging messages from
	     ssh.  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 default is
	     ``hmac-md5,hmac-sha1,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.  Default is 3.

     PasswordAuthentication
	     Specifies whether to use password authentication.	The argument
	     to this keyword must be ``yes'' or ``no''.  The default is
	     ``yes''.

     Port    Specifies the port number to connect on the remote host.  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 for this option is:
	     ``hostbased,publickey,keyboard-interactive,password''.

     Protocol
	     Specifies the protocol versions ssh should support in order of
	     preference.  The possible values are ``1'' and ``2''.  Multiple
	     versions must be comma-separated.	The default is ``2,1''.  This
	     means that ssh tries version 2 and falls back to version 1 if
	     version 2 is not available.

     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
	     /bin/sh.  In the command string, `%h' will be substituted by the
	     host name to connect and `%p' by the port.  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 some-
	     where.  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

     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.

     RemoteForward
	     Specifies that a TCP/IP 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 or by
	     using an alternative syntax: [bind_address/]port and
	     host/hostport.  Multiple forwardings may be specified, and addi-
	     tional forwardings can be given on the command line.  Only the
	     superuser can forward privileged ports.

	     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)).

     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 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 the wildcard
	     characters `*' and `?'.  Multiple environment variables may be
	     separated by whitespace or spread across multiple SendEnv direc-
	     tives.  The default is not to send any environment variables.

     ServerAliveInterval
	     Sets a timeout interval in seconds after which if no data has
	     been received from the server, ssh 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.

     ServerAliveCountMax
	     Sets the number of server alive messages (see above) which may be
	     sent without ssh 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 ses-
	     sion.  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 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
	     (above) is set to 15, and ServerAliveCountMax is left at the
	     default, if the server becomes unresponsive ssh will disconnect
	     after approximately 45 seconds.

     SmartcardDevice
	     Specifies which smartcard device to use.  The argument to this
	     keyword is the device ssh should use to communicate with a smart-
	     card used for storing the user's private RSA key.	By default, no
	     device is specified and smartcard support is not activated.

     StrictHostKeyChecking
	     If this flag is set to ``yes'', ssh 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 pro-
	     tection against trojan horse attacks, however, can be annoying
	     when the /etc/ssh/ssh_known_hosts file is poorly maintained, or
	     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 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.  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''.

     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 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 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
	     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.

     VersionAddendum
	     Specifies a string to append to the regular version string to
	     identify OS- or site-specific modifications.  The default is
	     ``FreeBSD-20050903''.

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

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.

FreeBSD 6.1		      September 25, 1999		   FreeBSD 6.1
=12418
+210
(36)