source: trunk/third/openssh/ssh_config.0 @ 18759

SSH_CONFIG(5)             System File Formats Manual             SSH_CONFIG(5)

NAME
     ssh_config - OpenSSH SSH client configuration files

SYNOPSIS
     $HOME/.ssh/config
     /etc/ssh/ssh_config

DESCRIPTION
     ssh obtains configuration data from the following sources in the followM--
     ing order:
           1.   command-line options
           2.   user's configuration file ($HOME/.ssh/config)
           3.   system-wide configuration file (/etc/ssh/ssh_config)

     For each parameter, the first obtained value will be used.  The configuM--
     ration files contain sections bracketed 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-speM--
     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 whitesM--
     pace when specifying configuration options using the ssh, scp and sftp -o
     option.

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

     Host    Restricts the following declarations (up to the next Host keyM--
             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 proM--
             vide global defaults for all hosts.  The host is the hostname
             argument given on the command line (i.e., the name is not conM--
             verted to a canonicalized host name before matching).

     AFSTokenPassing
             Specifies whether to pass AFS tokens to remote host.  The arguM--
             ment to this keyword must be ``yes'' or ``no''.  This option
             applies to protocol version 1 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
             Specify the interface to transmit from on machines with multiple
             interfaces or aliased addresses.  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
             ``yes''.

     Cipher  Specifies the cipher to use for encrypting the session in protoM--
             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
             default is

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

     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 arguM--
             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.

     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 protoM--
             col is supported, and ssh will act as a SOCKS4 server.  Multiple
             forwardings may be specified, and additional forwardings can be
             given on the command line.  Only the superuser can forward priviM--
             leged ports.

     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 disM--
             able the escape character entirely (making the connection transM--
             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 rediM--
             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 X 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.

     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 conM--
             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.

     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
             database files.  This option is useful for tunneling ssh connecM--
             tions 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 specificaM--
             tions).

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

     KeepAlive
             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 temM--
             porarily, and some people find it annoying.

             The default is ``yes'' (to send keepalives), 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 keepalives, the value should be set to ``no''.

     KerberosAuthentication
             Specifies whether Kerberos authentication will be used.  The
             argument to this keyword must be ``yes'' or ``no''.

     KerberosTgtPassing
             Specifies whether a Kerberos TGT will be forwarded to the server.
             This will only work if the Kerberos server is actually an AFS
             kaserver.  The argument to this keyword must be ``yes'' or
             ``no''.

     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 a port number, and
             the second must be host:port.  IPv6 addresses can be specified
             with an alternative syntax: host/port.  Multiple forwardings may
             be specified, and additional forwardings can be given on the comM--
             mand line.  Only the superuser can forward privileged ports.

     LogLevel
             Gives the verbosity level that is used when logging messages from
             ssh.  The possible values are: QUIET, FATAL, ERROR, INFO, VERM--
             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 verM--
             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 warnM--
             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 comM--
             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 someM--
             where.  Host key management will be done using the HostName of
             the host being connected (defaulting to the name typed by the
             user).  Note that CheckHostIP is not available for connects with
             a proxy command.

     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 a port number, and the
             second must be host:port.  IPv6 addresses can be specified with
             an alternative syntax: host/port.  Multiple forwardings may be
             specified, and additional forwardings can be given on the command
             line.  Only the superuser can forward privileged ports.

     RhostsAuthentication
             Specifies whether to try rhosts based authentication.  Note that
             this declaration only affects the client side and has no effect
             whatsoever on security.  Most servers do not permit RhostsAuthenM--
             tication because it is not secure (see RhostsRSAAuthentication).
             The argument to this keyword must be ``yes'' or ``no''.  The
             default is ``no''.  This option applies to protocol version 1
             only and requires ssh to be setuid root and UsePrivilegedPort to
             be set to ``yes''.

     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 authenticaM--
             tion agent is running.  The default is ``yes''.  Note that this
             option applies to protocol version 1 only.

     SmartcardDevice
             Specifies which smartcard device to use. The argument to this
             keyword is the device ssh should use to communicate with a smartM--
             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 $HOME/.ssh/known_hosts file, and refuses to conM--
             nect to hosts whose host key has changed.  This provides maximum
             protection 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''.

     UsePrivilegedPort
             Specifies whether to use a privileged port for outgoing connecM--
             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'' if RhostsAuthentication and
             RhostsRSAAuthentication authentications are needed with older
             servers.

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

     UserKnownHostsFile
             Specifies a file to use for the user host key database instead of
             $HOME/.ssh/known_hosts.

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

FILES
     $HOME/.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.  This
             file does not usually contain any sensitive information, but the
             recommended permissions are read/write for the user, and not
             accessible by others.

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

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

SEE ALSO
     ssh(1)

BSD                           September 25, 1999                           BSD