Provided by: ssh-krb5_3.8.1p1-10_i386 bug

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
     following 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
     configuration 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-
     specific 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 specifying configuration options using the ssh, scp and
     sftp -o option.

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

     Host    Restricts the following declarations (up to the next Host
             keyword) 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.
             In addition, the ServerAliveInterval and SetupTimeOut options
             will both 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 password, and where it is desirable to detect a
             broken network swiftly.  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
             protocol 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
             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.

     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 disable
             the escape character entirely (making the connection transparent
             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
             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.

     ForwardX11Trusted
             If the 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.

             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 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.

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

     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
             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
             specifications).

     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 protocol 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
             directory.  It is possible to have multiple identity files
             specified in configuration 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”.

     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
             command 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,
             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.  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
             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.  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
             command 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
             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.

     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.

     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 authentication
             agent is running.  The default is “yes”.  Note that this option
             applies to protocol version 1 only.

     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, or 300 if the BatchMode option is set.
             ProtocolKeepAlives is a Debian-specific compatibility alias for
             this option.

     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
             session.  It is important to note that the use of server alive
             messages is very different from TCPKeepAlive (below).  The server
             alive messages are sent through the encrypted channel and
             therefore will not be spoofable.  The TCP keepalive option
             enabled by TCPKeepAlive is spoofable.  The server alive mechanism
             is valuable when the client or server depend on knowing when a
             connection has become inactive.

             The default value is 3.  If, for example, ServerAliveInterval
             (above) 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 works when using
             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.

     SetupTimeOut
             Normally, ssh blocks indefinitely whilst waiting to receive the
             ssh banner and other setup protocol from the server, during the
             session setup.  This can cause ssh to hang under certain
             circumstances.  If this option is set, ssh will give up if no
             data from the server is received for the specified number of
             seconds.  The argument must be an integer.  The default is 0
             (disabled), or 300 if BatchMode is set.

     SmartcardDevice
             Specifies which smartcard device to use.  The argument to this
             keyword is the device ssh should use to communicate with a
             smartcard 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
             connect 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”.

     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”.

     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 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
             $HOME/.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.

     XAuthLocation
             Specifies the full pathname of the xauth(1) program.  The default
             is /usr/bin/X11/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.

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.