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 1.268 2018/02/23 07:38:09 jmc Exp $
38 .Dd $Mdocdate: February 23 2018 $
43 .Nd OpenSSH SSH client configuration files
46 obtains configuration data from the following sources in
49 .Bl -enum -offset indent -compact
53 user's configuration file
56 system-wide configuration file
57 .Pq Pa /etc/ssh/ssh_config
60 For each parameter, the first obtained value
62 The configuration files contain sections separated by
64 specifications, and that section is only applied for hosts that
65 match one of the patterns given in the specification.
66 The matched host name is usually the one given on the command line
68 .Cm CanonicalizeHostname
69 option for exceptions).
71 Since the first obtained value for each parameter is used, more
72 host-specific declarations should be given near the beginning of the
73 file, and general defaults at the end.
75 The file contains keyword-argument pairs, one per line.
78 and empty lines are interpreted as comments.
79 Arguments may optionally be enclosed in double quotes
81 in order to represent arguments containing spaces.
82 Configuration options may be separated by whitespace or
83 optional whitespace and exactly one
85 the latter format is useful to avoid the need to quote whitespace
86 when specifying configuration options using the
95 keywords and their meanings are as follows (note that
96 keywords are case-insensitive and arguments are case-sensitive):
99 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.
110 The host is usually the
112 argument given on the command line
114 .Cm CanonicalizeHostname
115 keyword for exceptions).
117 A pattern entry may be negated by prefixing it with an exclamation mark
119 If a negated entry is matched, then the
121 entry is ignored, regardless of whether any other patterns on the line
123 Negated matches are therefore useful to provide exceptions for wildcard
128 for more information on patterns.
130 Restricts the following declarations (up to the next
134 keyword) to be used only when the conditions following the
136 keyword are satisfied.
137 Match conditions are specified using one or more criteria
140 which always matches.
141 The available criteria keywords are:
151 criteria must appear alone or immediately after
153 Other criteria may be combined arbitrarily.
159 Criteria may be negated by prepending an exclamation mark
164 keyword matches only when the configuration file is being re-parsed
165 after hostname canonicalization (see the
166 .Cm CanonicalizeHostname
168 This may be useful to specify conditions that work with canonical host
172 keyword executes the specified command under the user's shell.
173 If the command returns a zero exit status then the condition is considered true.
174 Commands containing whitespace characters must be quoted.
177 accept the tokens described in the
181 The other keywords' criteria must be single entries or comma-separated
182 lists and may use the wildcard and negation operators described in the
187 keyword are matched against the target hostname, after any substitution
191 .Cm CanonicalizeHostname
195 keyword matches against the hostname as it was specified on the command-line.
198 keyword matches against the target username on the remote host.
201 keyword matches against the name of the local user running
203 (this keyword may be useful in system-wide
206 .It Cm AddKeysToAgent
207 Specifies whether keys should be automatically added to a running
209 If this option is set to
211 and a key is loaded from a file, the key and its passphrase are added to
212 the agent with the default lifetime, as if by
214 If this option is set to
217 will require confirmation using the
219 program before adding a key (see
222 If this option is set to
224 each use of the key must be confirmed, as if the
226 option was specified to
228 If this option is set to
230 no keys are added to the agent.
239 Specifies which address family to use when connecting.
250 passphrase/password querying will be disabled.
251 This option is useful in scripts and other batch jobs where no user
252 is present to supply the password.
259 Use the specified address on the local machine as the source address of
261 Only useful on systems with more than one address.
262 Note that this option does not work if
263 .Cm UsePrivilegedPort
267 Use the address of the specified interface on the local machine as the
268 source address of the connection.
269 Note that this option does not work if
270 .Cm UsePrivilegedPort
273 .It Cm CanonicalDomains
275 .Cm CanonicalizeHostname
276 is enabled, this option specifies the list of domain suffixes in which to
277 search for the specified destination host.
278 .It Cm CanonicalizeFallbackLocal
279 Specifies whether to fail with an error when hostname canonicalization fails.
282 will attempt to look up the unqualified hostname using the system resolver's
289 .Cm CanonicalizeHostname
290 is enabled and the target hostname cannot be found in any of the domains
292 .Cm CanonicalDomains .
293 .It Cm CanonicalizeHostname
294 Controls whether explicit hostname canonicalization is performed.
297 is not to perform any name rewriting and let the system resolver handle all
301 then, for connections that do not use a
304 will attempt to canonicalize the hostname specified on the command line
308 .Cm CanonicalizePermittedCNAMEs
311 .Cm CanonicalizeHostname
314 then canonicalization is applied to proxied connections too.
316 If this option is enabled, then the configuration files are processed
317 again using the new target name to pick up any new configuration in matching
322 .It Cm CanonicalizeMaxDots
323 Specifies the maximum number of dot characters in a hostname before
324 canonicalization is disabled.
326 allows a single dot (i.e. hostname.subdomain).
327 .It Cm CanonicalizePermittedCNAMEs
328 Specifies rules to determine whether CNAMEs should be followed when
329 canonicalizing hostnames.
330 The rules consist of one or more arguments of
331 .Ar source_domain_list : Ns Ar target_domain_list ,
333 .Ar source_domain_list
334 is a pattern-list of domains that may follow CNAMEs in canonicalization,
336 .Ar target_domain_list
337 is a pattern-list of domains that they may resolve to.
340 .Qq *.a.example.com:*.b.example.com,*.c.example.com
341 will allow hostnames matching
343 to be canonicalized to names in the
348 .It Cm CertificateFile
349 Specifies a file from which the user's certificate is read.
350 A corresponding private key must be provided separately in order
351 to use this certificate either
365 may use the tilde syntax to refer to a user's home directory
366 or the tokens described in the
370 It is possible to have multiple certificate files specified in
371 configuration files; these certificates will be tried in sequence.
374 directives will add to the list of certificates used for
376 .It Cm ChallengeResponseAuthentication
377 Specifies whether to use challenge-response authentication.
378 The argument to this keyword must be
387 will additionally check the host IP address in the
390 This allows it to detect if a host key changed due to DNS spoofing
391 and will add addresses of destination hosts to
392 .Pa ~/.ssh/known_hosts
393 in the process, regardless of the setting of
394 .Cm StrictHostKeyChecking .
395 If the option is set to
397 the check will not be executed.
401 Specifies the ciphers allowed and their order of preference.
402 Multiple ciphers must be comma-separated.
403 If the specified value begins with a
405 character, then the specified ciphers will be appended to the default set
406 instead of replacing them.
407 If the specified value begins with a
409 character, then the specified ciphers (including wildcards) will be removed
410 from the default set instead of replacing them.
412 The supported ciphers are:
413 .Bd -literal -offset indent
421 aes128-gcm@openssh.com
422 aes256-gcm@openssh.com
423 chacha20-poly1305@openssh.com
427 .Bd -literal -offset indent
428 chacha20-poly1305@openssh.com,
429 aes128-ctr,aes192-ctr,aes256-ctr,
430 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
431 aes128-cbc,aes192-cbc,aes256-cbc
434 The list of available ciphers may also be obtained using
436 .It Cm ClearAllForwardings
437 Specifies that all local, remote, and dynamic port forwardings
438 specified in the configuration files or on the command line be
440 This option is primarily useful when used from the
442 command line to clear port forwardings set in
443 configuration files, and is automatically set by
453 Specifies whether to use compression.
459 .It Cm ConnectionAttempts
460 Specifies the number of tries (one per second) to make before exiting.
461 The argument must be an integer.
462 This may be useful in scripts if the connection sometimes fails.
464 .It Cm ConnectTimeout
465 Specifies the timeout (in seconds) used when connecting to the
466 SSH server, instead of using the default system TCP timeout.
467 This value is used only when the target is down or really unreachable,
468 not when it refuses the connection.
470 Enables the sharing of multiple sessions over a single network connection.
474 will listen for connections on a control socket specified using the
477 Additional sessions can connect to this socket using the same
484 These sessions will try to reuse the master instance's network connection
485 rather than initiating new ones, but will fall back to connecting normally
486 if the control socket does not exist, or is not listening.
492 to listen for control connections, but require confirmation using
498 will continue without connecting to a master instance.
502 forwarding is supported over these multiplexed connections, however the
503 display and agent forwarded will be the one belonging to the master
504 connection i.e. it is not possible to forward multiple displays or agents.
506 Two additional options allow for opportunistic multiplexing: try to use a
507 master connection but fall back to creating a new one if one does not already
513 The latter requires confirmation like the
517 Specify the path to the control socket used for connection sharing as described
520 section above or the string
522 to disable connection sharing.
525 may use the tilde syntax to refer to a user's home directory
526 or the tokens described in the
529 It is recommended that any
531 used for opportunistic connection sharing include
532 at least %h, %p, and %r (or alternatively %C) and be placed in a directory
533 that is not writable by other users.
534 This ensures that shared connections are uniquely identified.
535 .It Cm ControlPersist
536 When used in conjunction with
538 specifies that the master connection should remain open
539 in the background (waiting for future client connections)
540 after the initial client connection has been closed.
543 then the master connection will not be placed into the background,
544 and will close as soon as the initial client connection is closed.
548 then the master connection will remain in the background indefinitely
549 (until killed or closed via a mechanism such as the
551 If set to a time in seconds, or a time in any of the formats documented in
553 then the backgrounded master connection will automatically terminate
554 after it has remained idle (with no client connections) for the
556 .It Cm DynamicForward
557 Specifies that a TCP port on the local machine be forwarded
558 over the secure channel, and the application
559 protocol is then used to determine where to connect to from the
564 .Oo Ar bind_address : Oc Ar port .
566 IPv6 addresses can be specified by enclosing addresses in square brackets.
567 By default, the local port is bound in accordance with the
572 may be used to bind the connection to a specific address.
577 indicates that the listening port be bound for local use only, while an
580 indicates that the port should be available from all interfaces.
582 Currently the SOCKS4 and SOCKS5 protocols are supported, and
584 will act as a SOCKS server.
585 Multiple forwardings may be specified, and
586 additional forwardings can be given on the command line.
587 Only the superuser can forward privileged ports.
588 .It Cm EnableSSHKeysign
589 Setting this option to
591 in the global client configuration file
592 .Pa /etc/ssh/ssh_config
593 enables the use of the helper program
596 .Cm HostbasedAuthentication .
602 This option should be placed in the non-hostspecific section.
605 for more information.
607 Sets the escape character (default:
609 The escape character can also
610 be set on the command line.
611 The argument should be a single character,
613 followed by a letter, or
615 to disable the escape
616 character entirely (making the connection transparent for binary
618 .It Cm ExitOnForwardFailure
621 should terminate the connection if it cannot set up all requested
622 dynamic, tunnel, local, and remote port forwardings, (e.g.\&
623 if either end is unable to bind and listen on a specified port).
625 .Cm ExitOnForwardFailure
626 does not apply to connections made over port forwardings and will not,
629 to exit if TCP connections to the ultimate forwarding destination fail.
635 .It Cm FingerprintHash
636 Specifies the hash algorithm used when displaying key fingerprints.
643 Specifies whether the connection to the authentication agent (if any)
644 will be forwarded to the remote machine.
651 Agent forwarding should be enabled with caution.
652 Users with the ability to bypass file permissions on the remote host
653 (for the agent's Unix-domain socket)
654 can access the local agent through the forwarded connection.
655 An attacker cannot obtain key material from the agent,
656 however they can perform operations on the keys that enable them to
657 authenticate using the identities loaded into the agent.
659 Specifies whether X11 connections will be automatically redirected
660 over the secure channel and
669 X11 forwarding should be enabled with caution.
670 Users with the ability to bypass file permissions on the remote host
671 (for the user's X11 authorization database)
672 can access the local X11 display through the forwarded connection.
673 An attacker may then be able to perform activities such as keystroke monitoring
675 .Cm ForwardX11Trusted
676 option is also enabled.
677 .It Cm ForwardX11Timeout
678 Specify a timeout for untrusted X11 forwarding
679 using the format described in the
683 X11 connections received by
685 after this time will be refused.
686 The default is to disable untrusted X11 forwarding after twenty minutes has
688 .It Cm ForwardX11Trusted
689 If this option is set to
691 remote X11 clients will have full access to the original X11 display.
693 If this option is set to
696 remote X11 clients will be considered untrusted and prevented
697 from stealing or tampering with data belonging to trusted X11
701 token used for the session will be set to expire after 20 minutes.
702 Remote clients will be refused access after this time.
704 See the X11 SECURITY extension specification for full details on
705 the restrictions imposed on untrusted clients.
707 Specifies whether remote hosts are allowed to connect to local
711 binds local port forwardings to the loopback address.
712 This prevents other remote hosts from connecting to forwarded ports.
714 can be used to specify that ssh
715 should bind local port forwardings to the wildcard address,
716 thus allowing remote hosts to connect to forwarded ports.
722 .It Cm GlobalKnownHostsFile
723 Specifies one or more files to use for the global
724 host key database, separated by whitespace.
726 .Pa /etc/ssh/ssh_known_hosts ,
727 .Pa /etc/ssh/ssh_known_hosts2 .
728 .It Cm GSSAPIAuthentication
729 Specifies whether user authentication based on GSSAPI is allowed.
732 .It Cm GSSAPIDelegateCredentials
733 Forward (delegate) credentials to the server.
736 .It Cm HashKnownHosts
739 should hash host names and addresses when they are added to
740 .Pa ~/.ssh/known_hosts .
741 These hashed names may be used normally by
745 but they do not reveal identifying information should the file's contents
749 Note that existing names and addresses in known hosts files
750 will not be converted automatically,
751 but may be manually hashed using
753 .It Cm HostbasedAuthentication
754 Specifies whether to try rhosts based authentication with public key
761 .It Cm HostbasedKeyTypes
762 Specifies the key types that will be used for hostbased authentication
763 as a comma-separated pattern list.
764 Alternately if the specified value begins with a
766 character, then the specified key types will be appended to the default set
767 instead of replacing them.
768 If the specified value begins with a
770 character, then the specified key types (including wildcards) will be removed
771 from the default set instead of replacing them.
772 The default for this option is:
773 .Bd -literal -offset 3n
774 ecdsa-sha2-nistp256-cert-v01@openssh.com,
775 ecdsa-sha2-nistp384-cert-v01@openssh.com,
776 ecdsa-sha2-nistp521-cert-v01@openssh.com,
777 ssh-ed25519-cert-v01@openssh.com,
778 ssh-rsa-cert-v01@openssh.com,
779 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
787 may be used to list supported key types.
788 .It Cm HostKeyAlgorithms
789 Specifies the host key algorithms
790 that the client wants to use in order of preference.
791 Alternately if the specified value begins with a
793 character, then the specified key types will be appended to the default set
794 instead of replacing them.
795 If the specified value begins with a
797 character, then the specified key types (including wildcards) will be removed
798 from the default set instead of replacing them.
799 The default for this option is:
800 .Bd -literal -offset 3n
801 ecdsa-sha2-nistp256-cert-v01@openssh.com,
802 ecdsa-sha2-nistp384-cert-v01@openssh.com,
803 ecdsa-sha2-nistp521-cert-v01@openssh.com,
804 ssh-ed25519-cert-v01@openssh.com,
805 ssh-rsa-cert-v01@openssh.com,
806 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
810 If hostkeys are known for the destination host then this default is modified
811 to prefer their algorithms.
813 The list of available key types may also be obtained using
816 Specifies an alias that should be used instead of the
817 real host name when looking up or saving the host key
818 in the host key database files and when validating host certificates.
819 This option is useful for tunneling SSH connections
820 or for multiple servers running on a single host.
822 Specifies the real host name to log into.
823 This can be used to specify nicknames or abbreviations for hosts.
826 accept the tokens described in the
829 Numeric IP addresses are also permitted (both on the command line and in
832 The default is the name given on the command line.
833 .It Cm IdentitiesOnly
836 should only use the authentication identity and certificate files explicitly
847 offers more identities.
848 The argument to this keyword must be
853 This option is intended for situations where ssh-agent
854 offers many different identities.
858 socket used to communicate with the authentication agent.
860 This option overrides the
862 environment variable and can be used to select a specific agent.
863 Setting the socket name to
865 disables the use of an authentication agent.
868 is specified, the location of the socket will be read from the
870 environment variable.
874 may use the tilde syntax to refer to a user's home directory
875 or the tokens described in the
879 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
883 .Pa ~/.ssh/id_ecdsa ,
884 .Pa ~/.ssh/id_ed25519
887 Additionally, any identities represented by the authentication agent
888 will be used for authentication unless
891 If no certificates have been explicitly specified by
892 .Cm CertificateFile ,
894 will try to load certificate information from the filename obtained by
897 to the path of a specified
902 may use the tilde syntax to refer to a user's home directory
903 or the tokens described in the
907 It is possible to have
908 multiple identity files specified in configuration files; all these
909 identities will be tried in sequence.
912 directives will add to the list of identities tried (this behaviour
913 differs from that of other configuration directives).
916 may be used in conjunction with
918 to select which identities in an agent are offered during authentication.
920 may also be used in conjunction with
922 in order to provide any certificate also needed for authentication with
925 Specifies a pattern-list of unknown options to be ignored if they are
926 encountered in configuration parsing.
927 This may be used to suppress errors if
929 contains options that are unrecognised by
931 It is recommended that
933 be listed early in the configuration file as it will not be applied
934 to unknown options that appear before it.
936 Include the specified configuration file(s).
937 Multiple pathnames may be specified and each pathname may contain
939 wildcards and, for user configurations, shell-like
941 references to user home directories.
942 Files without absolute paths are assumed to be in
944 if included in a user configuration file or
946 if included from the system configuration file.
948 directive may appear inside a
953 to perform conditional inclusion.
955 Specifies the IPv4 type-of-service or DSCP class for connections.
983 to use the operating system default.
984 This option may take one or two arguments, separated by whitespace.
985 If one argument is specified, it is used as the packet class unconditionally.
986 If two values are specified, the first is automatically selected for
987 interactive sessions and the second for non-interactive sessions.
990 for interactive sessions and
992 for non-interactive sessions.
993 .It Cm KbdInteractiveAuthentication
994 Specifies whether to use keyboard-interactive authentication.
995 The argument to this keyword must be
1000 .It Cm KbdInteractiveDevices
1001 Specifies the list of methods to use in keyboard-interactive authentication.
1002 Multiple method names must be comma-separated.
1003 The default is to use the server specified list.
1004 The methods available vary depending on what the server supports.
1005 For an OpenSSH server,
1006 it may be zero or more of:
1011 .It Cm KexAlgorithms
1012 Specifies the available KEX (Key Exchange) algorithms.
1013 Multiple algorithms must be comma-separated.
1014 Alternately if the specified value begins with a
1016 character, then the specified methods will be appended to the default set
1017 instead of replacing them.
1018 If the specified value begins with a
1020 character, then the specified methods (including wildcards) will be removed
1021 from the default set instead of replacing them.
1023 .Bd -literal -offset indent
1024 curve25519-sha256,curve25519-sha256@libssh.org,
1025 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1026 diffie-hellman-group-exchange-sha256,
1027 diffie-hellman-group16-sha512,
1028 diffie-hellman-group18-sha512,
1029 diffie-hellman-group-exchange-sha1,
1030 diffie-hellman-group14-sha256,
1031 diffie-hellman-group14-sha1
1034 The list of available key exchange algorithms may also be obtained using
1037 Specifies a command to execute on the local machine after successfully
1038 connecting to the server.
1039 The command string extends to the end of the line, and is executed with
1043 accept the tokens described in the
1047 The command is run synchronously and does not have access to the
1051 It should not be used for interactive commands.
1053 This directive is ignored unless
1054 .Cm PermitLocalCommand
1057 Specifies that a TCP port on the local machine be forwarded over
1058 the secure channel to the specified host and port from the remote machine.
1059 The first argument must be
1061 .Oo Ar bind_address : Oc Ar port
1063 and the second argument must be
1064 .Ar host : Ns Ar hostport .
1065 IPv6 addresses can be specified by enclosing addresses in square brackets.
1066 Multiple forwardings may be specified, and additional forwardings can be
1067 given on the command line.
1068 Only the superuser can forward privileged ports.
1069 By default, the local port is bound in accordance with the
1072 However, an explicit
1074 may be used to bind the connection to a specific address.
1079 indicates that the listening port be bound for local use only, while an
1082 indicates that the port should be available from all interfaces.
1084 Gives the verbosity level that is used when logging messages from
1086 The possible values are:
1087 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1088 The default is INFO.
1089 DEBUG and DEBUG1 are equivalent.
1090 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1092 Specifies the MAC (message authentication code) algorithms
1093 in order of preference.
1094 The MAC algorithm is used for data integrity protection.
1095 Multiple algorithms must be comma-separated.
1096 If the specified value begins with a
1098 character, then the specified algorithms will be appended to the default set
1099 instead of replacing them.
1100 If the specified value begins with a
1102 character, then the specified algorithms (including wildcards) will be removed
1103 from the default set instead of replacing them.
1105 The algorithms that contain
1107 calculate the MAC after encryption (encrypt-then-mac).
1108 These are considered safer and their use recommended.
1111 .Bd -literal -offset indent
1112 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1113 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1114 hmac-sha1-etm@openssh.com,
1115 umac-64@openssh.com,umac-128@openssh.com,
1116 hmac-sha2-256,hmac-sha2-512,hmac-sha1
1119 The list of available MAC algorithms may also be obtained using
1121 .It Cm NoHostAuthenticationForLocalhost
1122 Disable host authentication for localhost (loopback addresses).
1123 The argument to this keyword must be
1128 .It Cm NumberOfPasswordPrompts
1129 Specifies the number of password prompts before giving up.
1130 The argument to this keyword must be an integer.
1132 .It Cm PasswordAuthentication
1133 Specifies whether to use password authentication.
1134 The argument to this keyword must be
1139 .It Cm PermitLocalCommand
1140 Allow local command execution via the
1143 .Ic !\& Ns Ar command
1146 The argument must be
1151 .It Cm PKCS11Provider
1152 Specifies which PKCS#11 provider to use.
1153 The argument to this keyword is the PKCS#11 shared library
1155 should use to communicate with a PKCS#11 token providing the user's
1158 Specifies the port number to connect on the remote host.
1160 .It Cm PreferredAuthentications
1161 Specifies the order in which the client should try authentication methods.
1162 This allows a client to prefer one method (e.g.\&
1163 .Cm keyboard-interactive )
1164 over another method (e.g.\&
1167 .Bd -literal -offset indent
1168 gssapi-with-mic,hostbased,publickey,
1169 keyboard-interactive,password
1172 Specifies the command to use to connect to the server.
1174 string extends to the end of the line, and is executed
1175 using the user's shell
1177 directive to avoid a lingering shell process.
1181 accept the tokens described in the
1184 The command can be basically anything,
1185 and should read from its standard input and write to its standard output.
1186 It should eventually connect an
1188 server running on some machine, or execute
1191 Host key management will be done using the
1192 HostName of the host being connected (defaulting to the name typed by
1194 Setting the command to
1196 disables this option entirely.
1199 is not available for connects with a proxy command.
1201 This directive is useful in conjunction with
1203 and its proxy support.
1204 For example, the following directive would connect via an HTTP proxy at
1206 .Bd -literal -offset 3n
1207 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1210 Specifies one or more jump proxies as either
1219 Multiple proxies may be separated by comma characters and will be visited
1221 Setting this option will cause
1223 to connect to the target host by first making a
1225 connection to the specified
1227 host and then establishing a
1228 TCP forwarding to the ultimate target from there.
1230 Note that this option will compete with the
1232 option - whichever is specified first will prevent later instances of the
1233 other from taking effect.
1234 .It Cm ProxyUseFdpass
1237 will pass a connected file descriptor back to
1239 instead of continuing to execute and pass data.
1242 .It Cm PubkeyAcceptedKeyTypes
1243 Specifies the key types that will be used for public key authentication
1244 as a comma-separated pattern list.
1245 Alternately if the specified value begins with a
1247 character, then the key types after it will be appended to the default
1248 instead of replacing it.
1249 If the specified value begins with a
1251 character, then the specified key types (including wildcards) will be removed
1252 from the default set instead of replacing them.
1253 The default for this option is:
1254 .Bd -literal -offset 3n
1255 ecdsa-sha2-nistp256-cert-v01@openssh.com,
1256 ecdsa-sha2-nistp384-cert-v01@openssh.com,
1257 ecdsa-sha2-nistp521-cert-v01@openssh.com,
1258 ssh-ed25519-cert-v01@openssh.com,
1259 ssh-rsa-cert-v01@openssh.com,
1260 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1264 The list of available key types may also be obtained using
1266 .It Cm PubkeyAuthentication
1267 Specifies whether to try public key authentication.
1268 The argument to this keyword must be
1274 Specifies the maximum amount of data that may be transmitted before the
1275 session key is renegotiated, optionally followed a maximum amount of
1276 time that may pass before the session key is renegotiated.
1277 The first argument is specified in bytes and may have a suffix of
1282 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1283 The default is between
1287 depending on the cipher.
1288 The optional second value is specified in seconds and may use any of the
1289 units documented in the
1293 The default value for
1297 which means that rekeying is performed after the cipher's default amount
1298 of data has been sent or received and no time based rekeying is done.
1299 .It Cm RemoteCommand
1300 Specifies a command to execute on the remote machine after successfully
1301 connecting to the server.
1302 The command string extends to the end of the line, and is executed with
1306 accept the tokens described in the
1309 .It Cm RemoteForward
1310 Specifies that a TCP port on the remote machine be forwarded over
1312 The remote port may either be fowarded to a specified host and port
1313 from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1314 client to connect to arbitrary destinations from the local machine.
1315 The first argument must be
1317 .Oo Ar bind_address : Oc Ar port
1319 If forwarding to a specific destination then the second argument must be
1320 .Ar host : Ns Ar hostport ,
1321 otherwise if no destination argument is specified then the remote forwarding
1322 will be established as a SOCKS proxy.
1324 IPv6 addresses can be specified by enclosing addresses in square brackets.
1325 Multiple forwardings may be specified, and additional
1326 forwardings can be given on the command line.
1327 Privileged ports can be forwarded only when
1328 logging in as root on the remote machine.
1333 the listen port will be dynamically allocated on the server and reported
1334 to the client at run time.
1338 is not specified, the default is to only bind to loopback addresses.
1343 or an empty string, then the forwarding is requested to listen on all
1347 will only succeed if the server's
1349 option is enabled (see
1350 .Xr sshd_config 5 ) .
1352 Specifies whether to request a pseudo-tty for the session.
1353 The argument may be one of:
1355 (never request a TTY),
1357 (always request a TTY when standard input is a TTY),
1359 (always request a TTY) or
1361 (request a TTY when opening a login session).
1362 This option mirrors the
1368 .It Cm RevokedHostKeys
1369 Specifies revoked host public keys.
1370 Keys listed in this file will be refused for host authentication.
1371 Note that if this file does not exist or is not readable,
1372 then host authentication will be refused for all hosts.
1373 Keys may be specified as a text file, listing one public key per line, or as
1374 an OpenSSH Key Revocation List (KRL) as generated by
1376 For more information on KRLs, see the KEY REVOCATION LISTS section in
1379 Specifies what variables from the local
1381 should be sent to the server.
1382 The server must also support it, and the server must be configured to
1383 accept these environment variables.
1386 environment variable is always sent whenever a
1387 pseudo-terminal is requested as it is required by the protocol.
1392 for how to configure the server.
1393 Variables are specified by name, which may contain wildcard characters.
1394 Multiple environment variables may be separated by whitespace or spread
1398 The default is not to send any environment variables.
1402 for more information on patterns.
1403 .It Cm ServerAliveCountMax
1404 Sets the number of server alive messages (see below) which may be
1407 receiving any messages back from the server.
1408 If this threshold is reached while server alive messages are being sent,
1409 ssh will disconnect from the server, terminating the session.
1410 It is important to note that the use of server alive messages is very
1414 The server alive messages are sent through the encrypted channel
1415 and therefore will not be spoofable.
1416 The TCP keepalive option enabled by
1419 The server alive mechanism is valuable when the client or
1420 server depend on knowing when a connection has become inactive.
1422 The default value is 3.
1424 .Cm ServerAliveInterval
1425 (see below) is set to 15 and
1426 .Cm ServerAliveCountMax
1427 is left at the default, if the server becomes unresponsive,
1428 ssh will disconnect after approximately 45 seconds.
1429 .It Cm ServerAliveInterval
1430 Sets a timeout interval in seconds after which if no data has been received
1433 will send a message through the encrypted
1434 channel to request a response from the server.
1436 is 0, indicating that these messages will not be sent to the server.
1437 .It Cm StreamLocalBindMask
1438 Sets the octal file creation mode mask
1440 used when creating a Unix-domain socket file for local or remote
1442 This option is only used for port forwarding to a Unix-domain socket file.
1444 The default value is 0177, which creates a Unix-domain socket file that is
1445 readable and writable only by the owner.
1446 Note that not all operating systems honor the file mode on Unix-domain
1448 .It Cm StreamLocalBindUnlink
1449 Specifies whether to remove an existing Unix-domain socket file for local
1450 or remote port forwarding before creating a new one.
1451 If the socket file already exists and
1452 .Cm StreamLocalBindUnlink
1455 will be unable to forward the port to the Unix-domain socket file.
1456 This option is only used for port forwarding to a Unix-domain socket file.
1458 The argument must be
1463 .It Cm StrictHostKeyChecking
1464 If this flag is set to
1467 will never automatically add host keys to the
1468 .Pa ~/.ssh/known_hosts
1469 file, and refuses to connect to hosts whose host key has changed.
1470 This provides maximum protection against man-in-the-middle (MITM) attacks,
1471 though it can be annoying when the
1472 .Pa /etc/ssh/ssh_known_hosts
1473 file is poorly maintained or when connections to new hosts are
1475 This option forces the user to manually
1478 If this flag is set to
1480 then ssh will automatically add new host keys to the user
1481 known hosts files, but will not permit connections to hosts with
1483 If this flag is set to
1487 ssh will automatically add new host keys to the user known hosts files
1488 and allow connections to hosts with changed hostkeys to proceed,
1489 subject to some restrictions.
1490 If this flag is set to
1494 will be added to the user known host files only after the user
1495 has confirmed that is what they really want to do, and
1496 ssh will refuse to connect to hosts whose host key has changed.
1498 known hosts will be verified automatically in all cases.
1499 .It Cm SyslogFacility
1500 Gives the facility code that is used when logging messages from
1502 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1503 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1504 The default is USER.
1506 Specifies whether the system should send TCP keepalive messages to the
1508 If they are sent, death of the connection or crash of one
1509 of the machines will be properly noticed.
1510 However, this means that
1511 connections will die if the route is down temporarily, and some people
1516 (to send TCP keepalive messages), and the client will notice
1517 if the network goes down or the remote host dies.
1518 This is important in scripts, and many users want it too.
1520 To disable TCP keepalive messages, the value should be set to
1523 .Cm ServerAliveInterval
1524 for protocol-level keepalives.
1528 device forwarding between the client and the server.
1529 The argument must be
1540 requests the default tunnel mode, which is
1541 .Cm point-to-point .
1545 devices to open on the client
1550 The argument must be
1552 .Ar local_tun Op : Ar remote_tun .
1554 The devices may be specified by numerical ID or the keyword
1556 which uses the next available tunnel device.
1559 is not specified, it defaults to
1563 .It Cm UpdateHostKeys
1566 should accept notifications of additional hostkeys from the server sent
1567 after authentication has completed and add them to
1568 .Cm UserKnownHostsFile .
1569 The argument must be
1574 Enabling this option allows learning alternate hostkeys for a server
1575 and supports graceful key rotation by allowing a server to send replacement
1576 public keys before old ones are removed.
1577 Additional hostkeys are only accepted if the key used to authenticate the
1578 host was already trusted or explicitly accepted by the user.
1583 then the user is asked to confirm the modifications to the known_hosts file.
1584 Confirmation is currently incompatible with
1585 .Cm ControlPersist ,
1586 and will be disabled if it is enabled.
1590 from OpenSSH 6.8 and greater support the
1591 .Qq hostkeys@openssh.com
1592 protocol extension used to inform the client of all the server's hostkeys.
1593 .It Cm UsePrivilegedPort
1594 Specifies whether to use a privileged port for outgoing connections.
1595 The argument must be
1603 must be setuid root.
1605 Specifies the user to log in as.
1606 This can be useful when a different user name is used on different machines.
1607 This saves the trouble of
1608 having to remember to give the user name on the command line.
1609 .It Cm UserKnownHostsFile
1610 Specifies one or more files to use for the user
1611 host key database, separated by whitespace.
1613 .Pa ~/.ssh/known_hosts ,
1614 .Pa ~/.ssh/known_hosts2 .
1615 .It Cm VerifyHostKeyDNS
1616 Specifies whether to verify the remote key using DNS and SSHFP resource
1618 If this option is set to
1620 the client will implicitly trust keys that match a secure fingerprint
1622 Insecure fingerprints will be handled as if this option was set to
1624 If this option is set to
1626 information on fingerprint match will be displayed, but the user will still
1627 need to confirm new host keys according to the
1628 .Cm StrictHostKeyChecking
1632 if compiled with LDNS and
1637 .Sx VERIFYING HOST KEYS
1640 .It Cm VersionAddendum
1641 Specifies a string to append to the regular version string to identify
1642 OS- or site-specific modifications.
1644 .Dq FreeBSD-20180510 .
1647 may be used to disable this.
1648 .It Cm VisualHostKey
1649 If this flag is set to
1651 an ASCII art representation of the remote host key fingerprint is
1652 printed in addition to the fingerprint string at login and
1653 for unknown host keys.
1654 If this flag is set to
1657 no fingerprint strings are printed at login and
1658 only the fingerprint string will be printed for unknown host keys.
1659 .It Cm XAuthLocation
1660 Specifies the full pathname of the
1664 .Pa /usr/local/bin/xauth .
1669 consists of zero or more non-whitespace characters,
1671 (a wildcard that matches zero or more characters),
1674 (a wildcard that matches exactly one character).
1675 For example, to specify a set of declarations for any host in the
1678 the following pattern could be used:
1682 The following pattern
1683 would match any host in the 192.168.0.[0-9] network range:
1685 .Dl Host 192.168.0.?
1689 is a comma-separated list of patterns.
1690 Patterns within pattern-lists may be negated
1691 by preceding them with an exclamation mark
1694 to allow a key to be used from anywhere within an organization
1698 the following entry (in authorized_keys) could be used:
1700 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1702 Note that a negated match will never produce a positive result by itself.
1703 For example, attempting to match
1705 against the following pattern-list will fail:
1707 .Dl from=\&"!host1,!host2\&"
1709 The solution here is to include a term that will yield a positive match,
1712 .Dl from=\&"!host1,!host2,*\&"
1714 Arguments to some keywords can make use of tokens,
1715 which are expanded at runtime:
1717 .Bl -tag -width XXXX -offset indent -compact
1724 Local user's home directory.
1726 The remote hostname.
1732 The local hostname, including the domain name.
1734 The original remote hostname, as given on the command line.
1738 The remote username.
1744 network interface assigned if
1745 tunnel forwarding was requested, or
1753 accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1756 accepts the tokens %%, %d, %h, %l, %r, and %u.
1759 accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1762 accepts the tokens %% and %h.
1767 accept the tokens %%, %d, %h, %l, %r, and %u.
1770 accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, %T, and %u.
1773 accepts the tokens %%, %h, %p, and %r.
1776 accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1779 .It Pa ~/.ssh/config
1780 This is the per-user configuration file.
1781 The format of this file is described above.
1782 This file is used by the SSH client.
1783 Because of the potential for abuse, this file must have strict permissions:
1784 read/write for the user, and not accessible by others.
1785 .It Pa /etc/ssh/ssh_config
1786 Systemwide configuration file.
1787 This file provides defaults for those
1788 values that are not specified in the user's configuration file, and
1789 for those users who do not have a configuration file.
1790 This file must be world-readable.
1796 OpenSSH is a derivative of the original and free
1797 ssh 1.2.12 release by
1799 .An Aaron Campbell , Bob Beck , Markus Friedl ,
1800 .An Niels Provos , Theo de Raadt
1803 removed many bugs, re-added newer features and
1806 contributed the support for SSH protocol versions 1.5 and 2.0.
projects / FreeBSD / FreeBSD.git / blob