2 .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3 .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4 .\" All rights reserved
6 .\" As far as I am concerned, the code I have written for this software
7 .\" can be used freely for any purpose. Any derived versions of this
8 .\" software must be clearly marked as such, and if the derived work is
9 .\" incompatible with the protocol description in the RFC file, it must be
10 .\" called by a name other than "ssh" or "Secure Shell".
12 .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13 .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14 .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16 .\" Redistribution and use in source and binary forms, with or without
17 .\" modification, are permitted provided that the following conditions
19 .\" 1. Redistributions of source code must retain the above copyright
20 .\" notice, this list of conditions and the following disclaimer.
21 .\" 2. Redistributions in binary form must reproduce the above copyright
22 .\" notice, this list of conditions and the following disclaimer in the
23 .\" documentation and/or other materials provided with the distribution.
25 .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26 .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27 .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28 .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29 .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30 .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31 .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32 .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33 .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34 .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36 .\" $OpenBSD: ssh_config.5,v 1.153 2011/08/02 01:22:11 djm Exp $
37 .Dd $Mdocdate: August 2 2011 $
42 .Nd OpenSSH SSH client configuration files
45 .Nm /etc/ssh/ssh_config
48 obtains configuration data from the following sources in
51 .Bl -enum -offset indent -compact
55 user's configuration file
58 system-wide configuration file
59 .Pq Pa /etc/ssh/ssh_config
62 For each parameter, the first obtained value
64 The configuration files contain sections separated by
66 specifications, and that section is only applied for hosts that
67 match one of the patterns given in the specification.
68 The matched host name is the one given on the command line.
70 Since the first obtained value for each parameter is used, more
71 host-specific declarations should be given near the beginning of the
72 file, and general defaults at the end.
74 The configuration file has the following format:
76 Empty lines and lines starting with
79 Otherwise a line is of the format
80 .Dq keyword arguments .
81 Configuration options may be separated by whitespace or
82 optional whitespace and exactly one
84 the latter format is useful to avoid the need to quote whitespace
85 when specifying configuration options using the
92 Arguments may optionally be enclosed in double quotes
94 in order to represent arguments containing spaces.
97 keywords and their meanings are as follows (note that
98 keywords are case-insensitive and arguments are case-sensitive):
101 Restricts the following declarations (up to the next
103 keyword) to be only for those hosts that match one of the patterns
104 given after the keyword.
105 If more than one pattern is provided, they should be separated by whitespace.
108 as a pattern can be used to provide global
109 defaults for all hosts.
112 argument given on the command line (i.e. the name is not converted to
113 a canonicalized host name before matching).
115 A pattern entry may be negated by prefixing it with an exclamation mark
117 If a negated entry is matched, then the
119 entry is ignored, regardless of whether any other patterns on the line
121 Negated matches are therefore useful to provide exceptions for wildcard
126 for more information on patterns.
128 Specifies which address family to use when connecting.
138 passphrase/password querying will be disabled.
139 This option is useful in scripts and other batch jobs where no user
140 is present to supply the password.
148 Use the specified address on the local machine as the source address of
150 Only useful on systems with more than one address.
151 Note that this option does not work if
152 .Cm UsePrivilegedPort
155 .It Cm ChallengeResponseAuthentication
156 Specifies whether to use challenge-response authentication.
157 The argument to this keyword must be
164 If this flag is set to
167 will additionally check the host IP address in the
170 This allows ssh to detect if a host key changed due to DNS spoofing.
171 If the option is set to
173 the check will not be executed.
177 Specifies the cipher to use for encrypting the session
178 in protocol version 1.
186 is only supported in the
188 client for interoperability with legacy protocol 1 implementations
189 that do not support the
192 Its use is strongly discouraged due to cryptographic weaknesses.
196 Specifies the ciphers allowed for protocol version 2
197 in order of preference.
198 Multiple ciphers must be comma-separated.
199 The supported ciphers are
214 .Bd -literal -offset 3n
215 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
216 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
219 .It Cm ClearAllForwardings
220 Specifies that all local, remote, and dynamic port forwardings
221 specified in the configuration files or on the command line be
223 This option is primarily useful when used from the
225 command line to clear port forwardings set in
226 configuration files, and is automatically set by
237 Specifies whether to use compression.
244 .It Cm CompressionLevel
245 Specifies the compression level to use if compression is enabled.
246 The argument must be an integer from 1 (fast) to 9 (slow, best).
247 The default level is 6, which is good for most applications.
248 The meaning of the values is the same as in
250 Note that this option applies to protocol version 1 only.
251 .It Cm ConnectionAttempts
252 Specifies the number of tries (one per second) to make before exiting.
253 The argument must be an integer.
254 This may be useful in scripts if the connection sometimes fails.
256 .It Cm ConnectTimeout
257 Specifies the timeout (in seconds) used when connecting to the
258 SSH server, instead of using the default system TCP timeout.
259 This value is used only when the target is down or really unreachable,
260 not when it refuses the connection.
262 Enables the sharing of multiple sessions over a single network connection.
266 will listen for connections on a control socket specified using the
269 Additional sessions can connect to this socket using the same
276 These sessions will try to reuse the master instance's network connection
277 rather than initiating new ones, but will fall back to connecting normally
278 if the control socket does not exist, or is not listening.
283 to listen for control connections, but require confirmation using the
285 program before they are accepted (see
291 ssh will continue without connecting to a master instance.
295 forwarding is supported over these multiplexed connections, however the
296 display and agent forwarded will be the one belonging to the master
297 connection i.e. it is not possible to forward multiple displays or agents.
299 Two additional options allow for opportunistic multiplexing: try to use a
300 master connection but fall back to creating a new one if one does not already
306 The latter requires confirmation like the
310 Specify the path to the control socket used for connection sharing as described
313 section above or the string
315 to disable connection sharing.
318 will be substituted by the first component of the local host name,
320 will be substituted by the local host name (including any domain name),
322 will be substituted by the target host name,
324 will be substituted by the original target host name
325 specified on the command line,
329 by the remote login username, and
331 by the username of the user running
333 It is recommended that any
335 used for opportunistic connection sharing include
336 at least %h, %p, and %r.
337 This ensures that shared connections are uniquely identified.
338 .It Cm ControlPersist
339 When used in conjunction with
341 specifies that the master connection should remain open
342 in the background (waiting for future client connections)
343 after the initial client connection has been closed.
346 then the master connection will not be placed into the background,
347 and will close as soon as the initial client connection is closed.
350 then the master connection will remain in the background indefinitely
351 (until killed or closed via a mechanism such as the
355 If set to a time in seconds, or a time in any of the formats documented in
357 then the backgrounded master connection will automatically terminate
358 after it has remained idle (with no client connections) for the
360 .It Cm DynamicForward
361 Specifies that a TCP port on the local machine be forwarded
362 over the secure channel, and the application
363 protocol is then used to determine where to connect to from the
368 .Oo Ar bind_address : Oc Ar port .
370 IPv6 addresses can be specified by enclosing addresses in square brackets.
371 By default, the local port is bound in accordance with the
376 may be used to bind the connection to a specific address.
381 indicates that the listening port be bound for local use only, while an
384 indicates that the port should be available from all interfaces.
386 Currently the SOCKS4 and SOCKS5 protocols are supported, and
388 will act as a SOCKS server.
389 Multiple forwardings may be specified, and
390 additional forwardings can be given on the command line.
391 Only the superuser can forward privileged ports.
392 .It Cm EnableSSHKeysign
393 Setting this option to
395 in the global client configuration file
396 .Pa /etc/ssh/ssh_config
397 enables the use of the helper program
400 .Cm HostbasedAuthentication .
407 This option should be placed in the non-hostspecific section.
410 for more information.
412 Sets the escape character (default:
414 The escape character can also
415 be set on the command line.
416 The argument should be a single character,
418 followed by a letter, or
420 to disable the escape
421 character entirely (making the connection transparent for binary
423 .It Cm ExitOnForwardFailure
426 should terminate the connection if it cannot set up all requested
427 dynamic, tunnel, local, and remote port forwardings.
435 Specifies whether the connection to the authentication agent (if any)
436 will be forwarded to the remote machine.
444 Agent forwarding should be enabled with caution.
445 Users with the ability to bypass file permissions on the remote host
446 (for the agent's Unix-domain socket)
447 can access the local agent through the forwarded connection.
448 An attacker cannot obtain key material from the agent,
449 however they can perform operations on the keys that enable them to
450 authenticate using the identities loaded into the agent.
452 Specifies whether X11 connections will be automatically redirected
453 over the secure channel and
463 X11 forwarding should be enabled with caution.
464 Users with the ability to bypass file permissions on the remote host
465 (for the user's X11 authorization database)
466 can access the local X11 display through the forwarded connection.
467 An attacker may then be able to perform activities such as keystroke monitoring
469 .Cm ForwardX11Trusted
470 option is also enabled.
471 .It Cm ForwardX11Timeout
472 Specify a timeout for untrusted X11 forwarding
473 using the format described in the
477 X11 connections received by
479 after this time will be refused.
480 The default is to disable untrusted X11 forwarding after twenty minutes has
482 .It Cm ForwardX11Trusted
483 If this option is set to
485 remote X11 clients will have full access to the original X11 display.
487 If this option is set to
489 remote X11 clients will be considered untrusted and prevented
490 from stealing or tampering with data belonging to trusted X11
494 token used for the session will be set to expire after 20 minutes.
495 Remote clients will be refused access after this time.
500 See the X11 SECURITY extension specification for full details on
501 the restrictions imposed on untrusted clients.
503 Specifies whether remote hosts are allowed to connect to local
507 binds local port forwardings to the loopback address.
508 This prevents other remote hosts from connecting to forwarded ports.
510 can be used to specify that ssh
511 should bind local port forwardings to the wildcard address,
512 thus allowing remote hosts to connect to forwarded ports.
519 .It Cm GlobalKnownHostsFile
520 Specifies one or more files to use for the global
521 host key database, separated by whitespace.
523 .Pa /etc/ssh/ssh_known_hosts ,
524 .Pa /etc/ssh/ssh_known_hosts2 .
525 .It Cm GSSAPIAuthentication
526 Specifies whether user authentication based on GSSAPI is allowed.
529 Note that this option applies to protocol version 2 only.
530 .It Cm GSSAPIDelegateCredentials
531 Forward (delegate) credentials to the server.
534 Note that this option applies to protocol version 2 only.
535 .It Cm HashKnownHosts
538 should hash host names and addresses when they are added to
539 .Pa ~/.ssh/known_hosts .
540 These hashed names may be used normally by
544 but they do not reveal identifying information should the file's contents
548 Note that existing names and addresses in known hosts files
549 will not be converted automatically,
550 but may be manually hashed using
552 .It Cm HostbasedAuthentication
553 Specifies whether to try rhosts based authentication with public key
561 This option applies to protocol version 2 only and
563 .Cm RhostsRSAAuthentication .
564 .It Cm HostKeyAlgorithms
565 Specifies the protocol version 2 host key algorithms
566 that the client wants to use in order of preference.
567 The default for this option is:
568 .Bd -literal -offset 3n
569 ecdsa-sha2-nistp256-cert-v01@openssh.com,
570 ecdsa-sha2-nistp384-cert-v01@openssh.com,
571 ecdsa-sha2-nistp521-cert-v01@openssh.com,
572 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
573 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
574 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
578 If hostkeys are known for the destination host then this default is modified
579 to prefer their algorithms.
581 Specifies an alias that should be used instead of the
582 real host name when looking up or saving the host key
583 in the host key database files.
584 This option is useful for tunneling SSH connections
585 or for multiple servers running on a single host.
587 Specifies the real host name to log into.
588 This can be used to specify nicknames or abbreviations for hosts.
589 If the hostname contains the character sequence
591 then this will be replaced with the host name specified on the command line
592 (this is useful for manipulating unqualified names).
593 The default is the name given on the command line.
594 Numeric IP addresses are also permitted (both on the command line and in
597 .It Cm IdentitiesOnly
600 should only use the authentication identity files configured in the
605 offers more identities.
606 The argument to this keyword must be
610 This option is intended for situations where ssh-agent
611 offers many different identities.
615 Specifies a file from which the user's DSA, ECDSA or DSA authentication
619 for protocol version 1, and
624 for protocol version 2.
625 Additionally, any identities represented by the authentication agent
626 will be used for authentication.
628 will try to load certificate information from the filename obtained by
631 to the path of a specified
634 The file name may use the tilde
635 syntax to refer to a user's home directory or one of the following
638 (local user's home directory),
644 (remote host name) or
648 It is possible to have
649 multiple identity files specified in configuration files; all these
650 identities will be tried in sequence.
653 directives will add to the list of identities tried (this behaviour
654 differs from that of other configuration directives).
656 Specifies the IPv4 type-of-service or DSCP class for connections.
683 This option may take one or two arguments, separated by whitespace.
684 If one argument is specified, it is used as the packet class unconditionally.
685 If two values are specified, the first is automatically selected for
686 interactive sessions and the second for non-interactive sessions.
689 for interactive sessions and
691 for non-interactive sessions.
692 .It Cm KbdInteractiveAuthentication
693 Specifies whether to use keyboard-interactive authentication.
694 The argument to this keyword must be
700 .It Cm KbdInteractiveDevices
701 Specifies the list of methods to use in keyboard-interactive authentication.
702 Multiple method names must be comma-separated.
703 The default is to use the server specified list.
704 The methods available vary depending on what the server supports.
705 For an OpenSSH server,
706 it may be zero or more of:
712 Specifies the available KEX (Key Exchange) algorithms.
713 Multiple algorithms must be comma-separated.
715 .Bd -literal -offset indent
716 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
717 diffie-hellman-group-exchange-sha256,
718 diffie-hellman-group-exchange-sha1,
719 diffie-hellman-group14-sha1,
720 diffie-hellman-group1-sha1
723 Specifies a command to execute on the local machine after successfully
724 connecting to the server.
725 The command string extends to the end of the line, and is executed with
727 The following escape character substitutions will be performed:
729 (local user's home directory),
735 (host name as provided on the command line),
739 (remote user name) or
743 The command is run synchronously and does not have access to the
747 It should not be used for interactive commands.
749 This directive is ignored unless
750 .Cm PermitLocalCommand
753 Specifies that a TCP port on the local machine be forwarded over
754 the secure channel to the specified host and port from the remote machine.
755 The first argument must be
757 .Oo Ar bind_address : Oc Ar port
759 and the second argument must be
760 .Ar host : Ns Ar hostport .
761 IPv6 addresses can be specified by enclosing addresses in square brackets.
762 Multiple forwardings may be specified, and additional forwardings can be
763 given on the command line.
764 Only the superuser can forward privileged ports.
765 By default, the local port is bound in accordance with the
770 may be used to bind the connection to a specific address.
775 indicates that the listening port be bound for local use only, while an
778 indicates that the port should be available from all interfaces.
780 Gives the verbosity level that is used when logging messages from
782 The possible values are:
783 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
785 DEBUG and DEBUG1 are equivalent.
786 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
788 Specifies the MAC (message authentication code) algorithms
789 in order of preference.
790 The MAC algorithm is used in protocol version 2
791 for data integrity protection.
792 Multiple algorithms must be comma-separated.
794 .Bd -literal -offset indent
795 hmac-md5,hmac-sha1,umac-64@openssh.com,
796 hmac-ripemd160,hmac-sha1-96,hmac-md5-96,
797 hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,
800 .It Cm NoHostAuthenticationForLocalhost
801 This option can be used if the home directory is shared across machines.
802 In this case localhost will refer to a different machine on each of
803 the machines and the user will get many warnings about changed host keys.
804 However, this option disables host authentication for localhost.
805 The argument to this keyword must be
809 The default is to check the host key for localhost.
810 .It Cm NumberOfPasswordPrompts
811 Specifies the number of password prompts before giving up.
812 The argument to this keyword must be an integer.
814 .It Cm PasswordAuthentication
815 Specifies whether to use password authentication.
816 The argument to this keyword must be
822 .It Cm PermitLocalCommand
823 Allow local command execution via the
826 .Ic !\& Ns Ar command
835 .It Cm PKCS11Provider
836 Specifies which PKCS#11 provider to use.
837 The argument to this keyword is the PKCS#11 shared library
839 should use to communicate with a PKCS#11 token providing the user's
842 Specifies the port number to connect on the remote host.
844 .It Cm PreferredAuthentications
845 Specifies the order in which the client should try protocol 2
846 authentication methods.
847 This allows a client to prefer one method (e.g.\&
848 .Cm keyboard-interactive )
849 over another method (e.g.\&
852 .Bd -literal -offset indent
853 gssapi-with-mic,hostbased,publickey,
854 keyboard-interactive,password
857 Specifies the protocol versions
859 should support in order of preference.
860 The possible values are
864 Multiple versions must be comma-separated.
865 When this option is set to
868 will try version 2 and fall back to version 1
869 if version 2 is not available.
873 Specifies the command to use to connect to the server.
875 string extends to the end of the line, and is executed with
877 In the command string, any occurrence of
879 will be substituted by the host name to
884 by the remote user name.
885 The command can be basically anything,
886 and should read from its standard input and write to its standard output.
887 It should eventually connect an
889 server running on some machine, or execute
892 Host key management will be done using the
893 HostName of the host being connected (defaulting to the name typed by
895 Setting the command to
897 disables this option entirely.
900 is not available for connects with a proxy command.
902 This directive is useful in conjunction with
904 and its proxy support.
905 For example, the following directive would connect via an HTTP proxy at
907 .Bd -literal -offset 3n
908 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
910 .It Cm PubkeyAuthentication
911 Specifies whether to try public key authentication.
912 The argument to this keyword must be
918 This option applies to protocol version 2 only.
920 Specifies the maximum amount of data that may be transmitted before the
921 session key is renegotiated.
922 The argument is the number of bytes, with an optional suffix of
927 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
928 The default is between
932 depending on the cipher.
933 This option applies to protocol version 2 only.
935 Specifies that a TCP port on the remote machine be forwarded over
936 the secure channel to the specified host and port from the local machine.
937 The first argument must be
939 .Oo Ar bind_address : Oc Ar port
941 and the second argument must be
942 .Ar host : Ns Ar hostport .
943 IPv6 addresses can be specified by enclosing addresses in square brackets.
944 Multiple forwardings may be specified, and additional
945 forwardings can be given on the command line.
946 Privileged ports can be forwarded only when
947 logging in as root on the remote machine.
953 the listen port will be dynamically allocated on the server and reported
954 to the client at run time.
958 is not specified, the default is to only bind to loopback addresses.
963 or an empty string, then the forwarding is requested to listen on all
967 will only succeed if the server's
969 option is enabled (see
970 .Xr sshd_config 5 ) .
972 Specifies whether to request a pseudo-tty for the session.
973 The argument may be one of:
975 (never request a TTY),
977 (always request a TTY when standard input is a TTY),
979 (always request a TTY) or
981 (request a TTY when opening a login session).
982 This option mirrors the
988 .It Cm RhostsRSAAuthentication
989 Specifies whether to try rhosts based authentication with RSA host
997 This option applies to protocol version 1 only and requires
1000 .It Cm RSAAuthentication
1001 Specifies whether to try RSA authentication.
1002 The argument to this keyword must be
1006 RSA authentication will only be
1007 attempted if the identity file exists, or an authentication agent is
1011 Note that this option applies to protocol version 1 only.
1013 Specifies what variables from the local
1015 should be sent to the server.
1016 Note that environment passing is only supported for protocol 2.
1017 The server must also support it, and the server must be configured to
1018 accept these environment variables.
1023 for how to configure the server.
1024 Variables are specified by name, which may contain wildcard characters.
1025 Multiple environment variables may be separated by whitespace or spread
1029 The default is not to send any environment variables.
1033 for more information on patterns.
1034 .It Cm ServerAliveCountMax
1035 Sets the number of server alive messages (see below) which may be
1038 receiving any messages back from the server.
1039 If this threshold is reached while server alive messages are being sent,
1040 ssh will disconnect from the server, terminating the session.
1041 It is important to note that the use of server alive messages is very
1045 The server alive messages are sent through the encrypted channel
1046 and therefore will not be spoofable.
1047 The TCP keepalive option enabled by
1050 The server alive mechanism is valuable when the client or
1051 server depend on knowing when a connection has become inactive.
1053 The default value is 3.
1055 .Cm ServerAliveInterval
1056 (see below) is set to 15 and
1057 .Cm ServerAliveCountMax
1058 is left at the default, if the server becomes unresponsive,
1059 ssh will disconnect after approximately 45 seconds.
1060 This option applies to protocol version 2 only.
1061 .It Cm ServerAliveInterval
1062 Sets a timeout interval in seconds after which if no data has been received
1065 will send a message through the encrypted
1066 channel to request a response from the server.
1068 is 0, indicating that these messages will not be sent to the server.
1069 This option applies to protocol version 2 only.
1070 .It Cm StrictHostKeyChecking
1071 If this flag is set to
1074 will never automatically add host keys to the
1075 .Pa ~/.ssh/known_hosts
1076 file, and refuses to connect to hosts whose host key has changed.
1077 This provides maximum protection against trojan horse attacks,
1078 though it can be annoying when the
1079 .Pa /etc/ssh/ssh_known_hosts
1080 file is poorly maintained or when connections to new hosts are
1082 This option forces the user to manually
1084 If this flag is set to
1086 ssh will automatically add new host keys to the
1087 user known hosts files.
1088 If this flag is set to
1091 will be added to the user known host files only after the user
1092 has confirmed that is what they really want to do, and
1093 ssh will refuse to connect to hosts whose host key has changed.
1095 known hosts will be verified automatically in all cases.
1096 The argument must be
1104 Specifies whether the system should send TCP keepalive messages to the
1106 If they are sent, death of the connection or crash of one
1107 of the machines will be properly noticed.
1108 However, this means that
1109 connections will die if the route is down temporarily, and some people
1114 (to send TCP keepalive messages), and the client will notice
1115 if the network goes down or the remote host dies.
1116 This is important in scripts, and many users want it too.
1118 To disable TCP keepalive messages, the value should be set to
1123 device forwarding between the client and the server.
1124 The argument must be
1134 requests the default tunnel mode, which is
1135 .Dq point-to-point .
1141 devices to open on the client
1146 The argument must be
1148 .Ar local_tun Op : Ar remote_tun .
1150 The devices may be specified by numerical ID or the keyword
1152 which uses the next available tunnel device.
1155 is not specified, it defaults to
1159 .It Cm UsePrivilegedPort
1160 Specifies whether to use a privileged port for outgoing connections.
1161 The argument must be
1170 must be setuid root.
1171 Note that this option must be set to
1174 .Cm RhostsRSAAuthentication
1177 Specifies the user to log in as.
1178 This can be useful when a different user name is used on different machines.
1179 This saves the trouble of
1180 having to remember to give the user name on the command line.
1181 .It Cm UserKnownHostsFile
1182 Specifies one or more files to use for the user
1183 host key database, separated by whitespace.
1185 .Pa ~/.ssh/known_hosts ,
1186 .Pa ~/.ssh/known_hosts2 .
1187 .It Cm VerifyHostKeyDNS
1188 Specifies whether to verify the remote key using DNS and SSHFP resource
1190 If this option is set to
1192 the client will implicitly trust keys that match a secure fingerprint
1194 Insecure fingerprints will be handled as if this option was set to
1196 If this option is set to
1198 information on fingerprint match will be displayed, but the user will still
1199 need to confirm new host keys according to the
1200 .Cm StrictHostKeyChecking
1202 The argument must be
1209 Note that this option applies to protocol version 2 only.
1212 .Sx VERIFYING HOST KEYS
1215 .It Cm VersionAddendum
1216 Specifies a string to append to the regular version string to identify
1217 OS- or site-specific modifications.
1219 .Dq DragonFly-20110920 .
1220 .It Cm VisualHostKey
1221 If this flag is set to
1223 an ASCII art representation of the remote host key fingerprint is
1224 printed in addition to the hex fingerprint string at login and
1225 for unknown host keys.
1226 If this flag is set to
1228 no fingerprint strings are printed at login and
1229 only the hex fingerprint string will be printed for unknown host keys.
1232 .It Cm XAuthLocation
1233 Specifies the full pathname of the
1237 .Pa /usr/X11R6/bin/xauth .
1242 consists of zero or more non-whitespace characters,
1244 (a wildcard that matches zero or more characters),
1247 (a wildcard that matches exactly one character).
1248 For example, to specify a set of declarations for any host in the
1251 the following pattern could be used:
1255 The following pattern
1256 would match any host in the 192.168.0.[0-9] network range:
1258 .Dl Host 192.168.0.?
1262 is a comma-separated list of patterns.
1263 Patterns within pattern-lists may be negated
1264 by preceding them with an exclamation mark
1267 to allow a key to be used from anywhere within an organisation
1271 the following entry (in authorized_keys) could be used:
1273 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1276 .It Pa ~/.ssh/config
1277 This is the per-user configuration file.
1278 The format of this file is described above.
1279 This file is used by the SSH client.
1280 Because of the potential for abuse, this file must have strict permissions:
1281 read/write for the user, and not accessible by others.
1282 .It Pa /etc/ssh/ssh_config
1283 Systemwide configuration file.
1284 This file provides defaults for those
1285 values that are not specified in the user's configuration file, and
1286 for those users who do not have a configuration file.
1287 This file must be world-readable.
1292 OpenSSH is a derivative of the original and free
1293 ssh 1.2.12 release by Tatu Ylonen.
1294 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1295 Theo de Raadt and Dug Song
1296 removed many bugs, re-added newer features and
1298 Markus Friedl contributed the support for SSH
1299 protocol versions 1.5 and 2.0.