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):

           ·>   SendEnv LANG LC_*
           ·>   HashKnownHosts yes
           ·>   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-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.  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).

             A pattern entry may be negated by prefixing it with an exclamation mark (‘!’).  If a negated entry is matched, then the Host
             entry is ignored, regardless of whether any other patterns on the line match.  Negated matches are therefore useful to provide
             exceptions for wildcard matches.

             See PATTERNS for more information on patterns.

     AddressFamily
             Specifies which address family to use when connecting.  Valid arguments are “any”, “inet” (use IPv4 only), or “inet6” (use IPv6
             only).

     BatchMode
             If set to “yes”, passphrase/password querying will be disabled.  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 password, 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 connection.  Only useful on systems with more than
             one address.  Note that this option does not work if UsePrivilegedPort is set to “yes”.

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

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

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

     Ciphers
             Specifies the ciphers allowed for protocol version 2 in order of preference.  Multiple ciphers must be comma-separated.  The
             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 configuration files or on the command line be
             cleared.  This option is primarily useful when used from the ssh(1) command line to clear port forwardings set in 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.

     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 connection 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 sharing.  In the path, ‘%L’ will be substituted by the first component of the local host name, ‘%l’
             will be substituted by the local host name (including any domain name), ‘%h’ will be substituted by the target host name, ‘%n’
             will be substituted by the original target host name specified on the command line, ‘%p’ the port, ‘%r’ by the remote login
             username, and ‘%u’ by the username of the user running ssh(1).  It is recommended that any ControlPath used for opportunistic
             connection sharing include at least %h, %p, and %r.  This ensures that shared connections are uniquely identified.

     ControlPersist
             When used in conjunction with ControlMaster, specifies that the master connection should remain open in the background (waiting
             for future client connections) after the initial client 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 connection will automatically terminate after it has remained idle (with no client connections) 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 interfaces.

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

     EnableSSHKeysign
             Setting this option to “yes” in the global client configuration file /etc/ssh/ssh_config enables the use of the helper program
             ssh-keysign(8) during HostbasedAuthentication.  The argument must be “yes” or “no”.  The default is “no”.  This option should be
             placed in the non-hostspecific section.  See ssh-keysign(8) for more information.

     EscapeChar
             Sets the escape character (default: ‘~’).  The escape character can also be set on the command line.  The argument should be a
             single character, ‘^’ followed by a letter, or “none” to 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 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.

     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 one or more files to use for the global host key database, separated by whitespace.  The default is
             /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.

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

     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 disclosed.  The
             default is “no”.  Note that existing names and addresses in known hosts files will not be converted automatically, but may be
             manually hashed using ssh-keygen(1).  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 prefer their algorithms.

     HostKeyAlias
             Specifies an alias that should be used instead of the real host name when looking up or saving the host key in the host key
             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 command line (this is useful
             for manipulating unqualified names).  The default is the name given on the command 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 identities
             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.
             Multiple IdentityFile directives will add to the list of identities tried (this behaviour differs from that of other
             configuration directives).

     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 whitespace.  If one
             argument is specified, it is used as the packet class unconditionally.  If two values are specified, the first is automatically
             selected for interactive sessions and the second for non-interactive sessions.  The default is “lowdelay” for interactive
             sessions and “throughput” for non-interactive sessions.

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

     KbdInteractiveDevices
             Specifies the list of methods to use in keyboard-interactive authentication.  Multiple method names must be comma-separated.  The
             default is to use the server specified list.  The methods available vary depending on what the server supports.  For an OpenSSH
             server, it may be zero or more of: “bsdauth”, “pam”, and “skey”.

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

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

     LocalCommand
             Specifies a command to execute on the local machine after 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 interfaces.

     LogLevel
             Gives the verbosity level that is used when logging messages from ssh(1).  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,umac-64@openssh.com,
                   hmac-ripemd160,hmac-sha1-96,hmac-md5-96,
                   hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,
                   hmac-sha2-512-96

     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 providing the user's private RSA key.

     Port    Specifies the port number to connect on the remote host.  The default is 22.

     PreferredAuthentications
             Specifies the order in which the client should try protocol 2 authentication methods.  This allows a client to prefer one method
             (e.g. keyboard-interactive) over another method (e.g. password).  The default is:

                   gssapi-with-mic,hostbased,publickey,
                   keyboard-interactive,password

     Protocol
             Specifies the protocol versions ssh(1) should support in order of preference.  The possible values are ‘1’ and ‘2’.  Multiple
             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 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.

             This directive is useful in conjunction with nc(1) and its proxy support.  For example, the following directive would connect via
             an HTTP proxy at 192.0.2.0:

                ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p

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

     RekeyLimit
             Specifies the maximum amount of data that may be transmitted before the session key is renegotiated.  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)).

     RequestTTY
             Specifies whether to request a pseudo-tty for the session.  The argument may be one of: “no” (never request a TTY), “yes” (always
             request a TTY when standard input is a TTY), “force” (always request a TTY) or “auto” (request a TTY when opening a login
             session).  This option mirrors the -t and -T flags for ssh(1).

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

     RSAAuthentication
             Specifies whether to try RSA authentication.  The argument to this keyword must be “yes” or “no”.  RSA authentication will only
             be attempted if the identity file exists, or an 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 variables.  Refer
             to AcceptEnv in sshd_config(5) for how to configure the server.  Variables are specified by name, which may contain wildcard
             characters.  Multiple environment variables may be separated by whitespace or spread across multiple SendEnv directives.  The
             default is not to send any environment variables.

             See PATTERNS for more information on patterns.

     ServerAliveCountMax
             Sets the number of server alive messages (see below) which may be sent without ssh(1) receiving any messages back from the
             server.  If this threshold is reached while server alive messages are being sent, ssh will disconnect from the server,
             terminating the session.  It is important to note that the use of server alive messages is very different from TCPKeepAlive
             (below).  The server alive messages are sent through the encrypted channel and 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 unresponsive, 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 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”.

     Tunnel  Request tun(4) device forwarding between the client and the server.  The argument must be “yes”, “point-to-point” (layer 3),
             “ethernet” (layer 2), or “no”.  Specifying “yes” requests the default tunnel mode, which is “point-to-point”.  The default is
             “no”.

     TunnelDevice
             Specifies the tun(4) devices to open on the client (local_tun) and the server (remote_tun).

             The argument must be local_tun[:remote_tun].  The devices may be specified by numerical ID or the keyword “any”, which uses the
             next available tunnel device.  If remote_tun is not specified, it defaults to “any”.  The default is “any:any”.

     UseBlacklistedKeys
             Specifies whether ssh(1) should use keys recorded in its blacklist of known-compromised 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 system, and even then only with the utmost care.
             If “no”, then attempts to use compromised 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 one or more files to use for the user host key database, separated by whitespace.  The default is ~/.ssh/known_hosts,
             ~/.ssh/known_hosts2.

     VerifyHostKeyDNS
             Specifies whether to verify the remote key using DNS and SSHFP resource records.  If this option is set to “yes”, the client will
             implicitly trust keys that match a secure fingerprint from DNS.  Insecure fingerprints will be handled as if this option was set
             to “ask”.  If this option is set to “ask”, information on fingerprint match will be displayed, but the user will still need to
             confirm new host keys according to the StrictHostKeyChecking option.  The argument must be “yes”, “no”, or “ask”.  The default is
             “no”.  Note that this option applies to protocol version 2 only.

             See also VERIFYING HOST KEYS in ssh(1).

     VisualHostKey
             If this flag is set to “yes”, an ASCII art representation of the remote host key fingerprint is printed in addition to the hex
             fingerprint string at login and for unknown host keys.  If this flag is set to “no”, no fingerprint strings are printed at login
             and only the hex fingerprint string will be printed for unknown host keys.  The default is “no”.

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

PATTERNS

     A pattern consists of zero or more non-whitespace characters, ‘*’ (a wildcard that matches zero or more characters), or ‘?’ (a wildcard
     that matches exactly one character).  For example, to specify a set of 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.
 

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