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 1.256 2017/09/21 19:16:53 markus Exp $
37 .Dd $Mdocdate: September 21 2017 $
42 .Nd OpenSSH SSH client configuration files
45 obtains configuration data from the following sources in
48 .Bl -enum -offset indent -compact
52 user's configuration file
55 system-wide configuration file
56 .Pq Pa /etc/ssh/ssh_config
59 For each parameter, the first obtained value
61 The configuration files contain sections separated by
63 specifications, and that section is only applied for hosts that
64 match one of the patterns given in the specification.
65 The matched host name is usually the one given on the command line
67 .Cm CanonicalizeHostname
68 option for exceptions).
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 file contains keyword-argument pairs, one per line.
77 and empty lines are interpreted as comments.
78 Arguments may optionally be enclosed in double quotes
80 in order to represent arguments containing spaces.
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
94 keywords and their meanings are as follows (note that
95 keywords are case-insensitive and arguments are case-sensitive):
98 Restricts the following declarations (up to the next
102 keyword) to be only for those hosts that match one of the patterns
103 given after the keyword.
104 If more than one pattern is provided, they should be separated by whitespace.
107 as a pattern can be used to provide global
108 defaults for all hosts.
109 The host is usually the
111 argument given on the command line
113 .Cm CanonicalizeHostname
114 keyword for exceptions).
116 A pattern entry may be negated by prefixing it with an exclamation mark
118 If a negated entry is matched, then the
120 entry is ignored, regardless of whether any other patterns on the line
122 Negated matches are therefore useful to provide exceptions for wildcard
127 for more information on patterns.
129 Restricts the following declarations (up to the next
133 keyword) to be used only when the conditions following the
135 keyword are satisfied.
136 Match conditions are specified using one or more criteria
139 which always matches.
140 The available criteria keywords are:
150 criteria must appear alone or immediately after
152 Other criteria may be combined arbitrarily.
158 Criteria may be negated by prepending an exclamation mark
163 keyword matches only when the configuration file is being re-parsed
164 after hostname canonicalization (see the
165 .Cm CanonicalizeHostname
167 This may be useful to specify conditions that work with canonical host
171 keyword executes the specified command under the user's shell.
172 If the command returns a zero exit status then the condition is considered true.
173 Commands containing whitespace characters must be quoted.
176 accept the tokens described in the
180 The other keywords' criteria must be single entries or comma-separated
181 lists and may use the wildcard and negation operators described in the
186 keyword are matched against the target hostname, after any substitution
190 .Cm CanonicalizeHostname
194 keyword matches against the hostname as it was specified on the command-line.
197 keyword matches against the target username on the remote host.
200 keyword matches against the name of the local user running
202 (this keyword may be useful in system-wide
205 .It Cm AddKeysToAgent
206 Specifies whether keys should be automatically added to a running
208 If this option is set to
210 and a key is loaded from a file, the key and its passphrase are added to
211 the agent with the default lifetime, as if by
213 If this option is set to
216 will require confirmation using the
218 program before adding a key (see
221 If this option is set to
223 each use of the key must be confirmed, as if the
225 option was specified to
227 If this option is set to
229 no keys are added to the agent.
238 Specifies which address family to use when connecting.
249 passphrase/password querying will be disabled.
250 This option is useful in scripts and other batch jobs where no user
251 is present to supply the password.
258 Use the specified address on the local machine as the source address of
260 Only useful on systems with more than one address.
261 Note that this option does not work if
262 .Cm UsePrivilegedPort
265 .It Cm CanonicalDomains
267 .Cm CanonicalizeHostname
268 is enabled, this option specifies the list of domain suffixes in which to
269 search for the specified destination host.
270 .It Cm CanonicalizeFallbackLocal
271 Specifies whether to fail with an error when hostname canonicalization fails.
274 will attempt to look up the unqualified hostname using the system resolver's
281 .Cm CanonicalizeHostname
282 is enabled and the target hostname cannot be found in any of the domains
284 .Cm CanonicalDomains .
285 .It Cm CanonicalizeHostname
286 Controls whether explicit hostname canonicalization is performed.
289 is not to perform any name rewriting and let the system resolver handle all
293 then, for connections that do not use a
296 will attempt to canonicalize the hostname specified on the command line
300 .Cm CanonicalizePermittedCNAMEs
303 .Cm CanonicalizeHostname
306 then canonicalization is applied to proxied connections too.
308 If this option is enabled, then the configuration files are processed
309 again using the new target name to pick up any new configuration in matching
314 .It Cm CanonicalizeMaxDots
315 Specifies the maximum number of dot characters in a hostname before
316 canonicalization is disabled.
318 allows a single dot (i.e. hostname.subdomain).
319 .It Cm CanonicalizePermittedCNAMEs
320 Specifies rules to determine whether CNAMEs should be followed when
321 canonicalizing hostnames.
322 The rules consist of one or more arguments of
323 .Ar source_domain_list : Ns Ar target_domain_list ,
325 .Ar source_domain_list
326 is a pattern-list of domains that may follow CNAMEs in canonicalization,
328 .Ar target_domain_list
329 is a pattern-list of domains that they may resolve to.
332 .Qq *.a.example.com:*.b.example.com,*.c.example.com
333 will allow hostnames matching
335 to be canonicalized to names in the
340 .It Cm CertificateFile
341 Specifies a file from which the user's certificate is read.
342 A corresponding private key must be provided separately in order
343 to use this certificate either
357 may use the tilde syntax to refer to a user's home directory
358 or the tokens described in the
362 It is possible to have multiple certificate files specified in
363 configuration files; these certificates will be tried in sequence.
366 directives will add to the list of certificates used for
368 .It Cm ChallengeResponseAuthentication
369 Specifies whether to use challenge-response authentication.
370 The argument to this keyword must be
380 will additionally check the host IP address in the
383 This allows it to detect if a host key changed due to DNS spoofing
384 and will add addresses of destination hosts to
385 .Pa ~/.ssh/known_hosts
386 in the process, regardless of the setting of
387 .Cm StrictHostKeyChecking .
388 If the option is set to
390 the check will not be executed.
392 Specifies the ciphers allowed and their order of preference.
393 Multiple ciphers must be comma-separated.
394 If the specified value begins with a
396 character, then the specified ciphers will be appended to the default set
397 instead of replacing them.
398 If the specified value begins with a
400 character, then the specified ciphers (including wildcards) will be removed
401 from the default set instead of replacing them.
403 The supported ciphers are:
404 .Bd -literal -offset indent
412 aes128-gcm@openssh.com
413 aes256-gcm@openssh.com
414 chacha20-poly1305@openssh.com
418 .Bd -literal -offset indent
419 chacha20-poly1305@openssh.com,
420 aes128-ctr,aes192-ctr,aes256-ctr,
421 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
422 aes128-cbc,aes192-cbc,aes256-cbc
425 The list of available ciphers may also be obtained using
427 .It Cm ClearAllForwardings
428 Specifies that all local, remote, and dynamic port forwardings
429 specified in the configuration files or on the command line be
431 This option is primarily useful when used from the
433 command line to clear port forwardings set in
434 configuration files, and is automatically set by
444 Specifies whether to use compression.
450 .It Cm ConnectionAttempts
451 Specifies the number of tries (one per second) to make before exiting.
452 The argument must be an integer.
453 This may be useful in scripts if the connection sometimes fails.
455 .It Cm ConnectTimeout
456 Specifies the timeout (in seconds) used when connecting to the
457 SSH server, instead of using the default system TCP timeout.
458 This value is used only when the target is down or really unreachable,
459 not when it refuses the connection.
461 Enables the sharing of multiple sessions over a single network connection.
465 will listen for connections on a control socket specified using the
468 Additional sessions can connect to this socket using the same
475 These sessions will try to reuse the master instance's network connection
476 rather than initiating new ones, but will fall back to connecting normally
477 if the control socket does not exist, or is not listening.
483 to listen for control connections, but require confirmation using
489 will continue without connecting to a master instance.
493 forwarding is supported over these multiplexed connections, however the
494 display and agent forwarded will be the one belonging to the master
495 connection i.e. it is not possible to forward multiple displays or agents.
497 Two additional options allow for opportunistic multiplexing: try to use a
498 master connection but fall back to creating a new one if one does not already
504 The latter requires confirmation like the
508 Specify the path to the control socket used for connection sharing as described
511 section above or the string
513 to disable connection sharing.
516 may use the tilde syntax to refer to a user's home directory
517 or the tokens described in the
520 It is recommended that any
522 used for opportunistic connection sharing include
523 at least %h, %p, and %r (or alternatively %C) and be placed in a directory
524 that is not writable by other users.
525 This ensures that shared connections are uniquely identified.
526 .It Cm ControlPersist
527 When used in conjunction with
529 specifies that the master connection should remain open
530 in the background (waiting for future client connections)
531 after the initial client connection has been closed.
534 then the master connection will not be placed into the background,
535 and will close as soon as the initial client connection is closed.
539 then the master connection will remain in the background indefinitely
540 (until killed or closed via a mechanism such as the
542 If set to a time in seconds, or a time in any of the formats documented in
544 then the backgrounded master connection will automatically terminate
545 after it has remained idle (with no client connections) for the
547 .It Cm DynamicForward
548 Specifies that a TCP port on the local machine be forwarded
549 over the secure channel, and the application
550 protocol is then used to determine where to connect to from the
555 .Oo Ar bind_address : Oc Ar port .
557 IPv6 addresses can be specified by enclosing addresses in square brackets.
558 By default, the local port is bound in accordance with the
563 may be used to bind the connection to a specific address.
568 indicates that the listening port be bound for local use only, while an
571 indicates that the port should be available from all interfaces.
573 Currently the SOCKS4 and SOCKS5 protocols are supported, and
575 will act as a SOCKS server.
576 Multiple forwardings may be specified, and
577 additional forwardings can be given on the command line.
578 Only the superuser can forward privileged ports.
579 .It Cm EnableSSHKeysign
580 Setting this option to
582 in the global client configuration file
583 .Pa /etc/ssh/ssh_config
584 enables the use of the helper program
587 .Cm HostbasedAuthentication .
593 This option should be placed in the non-hostspecific section.
596 for more information.
598 Sets the escape character (default:
600 The escape character can also
601 be set on the command line.
602 The argument should be a single character,
604 followed by a letter, or
606 to disable the escape
607 character entirely (making the connection transparent for binary
609 .It Cm ExitOnForwardFailure
612 should terminate the connection if it cannot set up all requested
613 dynamic, tunnel, local, and remote port forwardings, (e.g.\&
614 if either end is unable to bind and listen on a specified port).
616 .Cm ExitOnForwardFailure
617 does not apply to connections made over port forwardings and will not,
620 to exit if TCP connections to the ultimate forwarding destination fail.
626 .It Cm FingerprintHash
627 Specifies the hash algorithm used when displaying key fingerprints.
634 Specifies whether the connection to the authentication agent (if any)
635 will be forwarded to the remote machine.
642 Agent forwarding should be enabled with caution.
643 Users with the ability to bypass file permissions on the remote host
644 (for the agent's Unix-domain socket)
645 can access the local agent through the forwarded connection.
646 An attacker cannot obtain key material from the agent,
647 however they can perform operations on the keys that enable them to
648 authenticate using the identities loaded into the agent.
650 Specifies whether X11 connections will be automatically redirected
651 over the secure channel and
660 X11 forwarding should be enabled with caution.
661 Users with the ability to bypass file permissions on the remote host
662 (for the user's X11 authorization database)
663 can access the local X11 display through the forwarded connection.
664 An attacker may then be able to perform activities such as keystroke monitoring
666 .Cm ForwardX11Trusted
667 option is also enabled.
668 .It Cm ForwardX11Timeout
669 Specify a timeout for untrusted X11 forwarding
670 using the format described in the
674 X11 connections received by
676 after this time will be refused.
677 The default is to disable untrusted X11 forwarding after twenty minutes has
679 .It Cm ForwardX11Trusted
680 If this option is set to
682 remote X11 clients will have full access to the original X11 display.
684 If this option is set to
687 remote X11 clients will be considered untrusted and prevented
688 from stealing or tampering with data belonging to trusted X11
692 token used for the session will be set to expire after 20 minutes.
693 Remote clients will be refused access after this time.
695 See the X11 SECURITY extension specification for full details on
696 the restrictions imposed on untrusted clients.
698 Specifies whether remote hosts are allowed to connect to local
702 binds local port forwardings to the loopback address.
703 This prevents other remote hosts from connecting to forwarded ports.
705 can be used to specify that ssh
706 should bind local port forwardings to the wildcard address,
707 thus allowing remote hosts to connect to forwarded ports.
713 .It Cm GlobalKnownHostsFile
714 Specifies one or more files to use for the global
715 host key database, separated by whitespace.
717 .Pa /etc/ssh/ssh_known_hosts ,
718 .Pa /etc/ssh/ssh_known_hosts2 .
719 .It Cm GSSAPIAuthentication
720 Specifies whether user authentication based on GSSAPI is allowed.
723 .It Cm GSSAPIDelegateCredentials
724 Forward (delegate) credentials to the server.
727 .It Cm HashKnownHosts
730 should hash host names and addresses when they are added to
731 .Pa ~/.ssh/known_hosts .
732 These hashed names may be used normally by
736 but they do not reveal identifying information should the file's contents
740 Note that existing names and addresses in known hosts files
741 will not be converted automatically,
742 but may be manually hashed using
744 .It Cm HostbasedAuthentication
745 Specifies whether to try rhosts based authentication with public key
752 .It Cm HostbasedKeyTypes
753 Specifies the key types that will be used for hostbased authentication
754 as a comma-separated pattern list.
755 Alternately if the specified value begins with a
757 character, then the specified key types will be appended to the default set
758 instead of replacing them.
759 If the specified value begins with a
761 character, then the specified key types (including wildcards) will be removed
762 from the default set instead of replacing them.
763 The default for this option is:
764 .Bd -literal -offset 3n
765 ecdsa-sha2-nistp256-cert-v01@openssh.com,
766 ecdsa-sha2-nistp384-cert-v01@openssh.com,
767 ecdsa-sha2-nistp521-cert-v01@openssh.com,
768 ssh-ed25519-cert-v01@openssh.com,
769 ssh-rsa-cert-v01@openssh.com,
770 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
778 may be used to list supported key types.
779 .It Cm HostKeyAlgorithms
780 Specifies the host key algorithms
781 that the client wants to use in order of preference.
782 Alternately if the specified value begins with a
784 character, then the specified key types will be appended to the default set
785 instead of replacing them.
786 If the specified value begins with a
788 character, then the specified key types (including wildcards) will be removed
789 from the default set instead of replacing them.
790 The default for this option is:
791 .Bd -literal -offset 3n
792 ecdsa-sha2-nistp256-cert-v01@openssh.com,
793 ecdsa-sha2-nistp384-cert-v01@openssh.com,
794 ecdsa-sha2-nistp521-cert-v01@openssh.com,
795 ssh-ed25519-cert-v01@openssh.com,
796 ssh-rsa-cert-v01@openssh.com,
797 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
801 If hostkeys are known for the destination host then this default is modified
802 to prefer their algorithms.
804 The list of available key types may also be obtained using
807 Specifies an alias that should be used instead of the
808 real host name when looking up or saving the host key
809 in the host key database files and when validating host certificates.
810 This option is useful for tunneling SSH connections
811 or for multiple servers running on a single host.
813 Specifies the real host name to log into.
814 This can be used to specify nicknames or abbreviations for hosts.
817 accept the tokens described in the
820 Numeric IP addresses are also permitted (both on the command line and in
823 The default is the name given on the command line.
824 .It Cm IdentitiesOnly
827 should only use the authentication identity and certificate files explicitly
838 offers more identities.
839 The argument to this keyword must be
844 This option is intended for situations where ssh-agent
845 offers many different identities.
849 socket used to communicate with the authentication agent.
851 This option overrides the
853 environment variable and can be used to select a specific agent.
854 Setting the socket name to
856 disables the use of an authentication agent.
859 is specified, the location of the socket will be read from the
861 environment variable.
865 may use the tilde syntax to refer to a user's home directory
866 or the tokens described in the
870 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
874 .Pa ~/.ssh/id_ecdsa ,
875 .Pa ~/.ssh/id_ed25519
878 Additionally, any identities represented by the authentication agent
879 will be used for authentication unless
882 If no certificates have been explicitly specified by
883 .Cm CertificateFile ,
885 will try to load certificate information from the filename obtained by
888 to the path of a specified
893 may use the tilde syntax to refer to a user's home directory
894 or the tokens described in the
898 It is possible to have
899 multiple identity files specified in configuration files; all these
900 identities will be tried in sequence.
903 directives will add to the list of identities tried (this behaviour
904 differs from that of other configuration directives).
907 may be used in conjunction with
909 to select which identities in an agent are offered during authentication.
911 may also be used in conjunction with
913 in order to provide any certificate also needed for authentication with
916 Specifies a pattern-list of unknown options to be ignored if they are
917 encountered in configuration parsing.
918 This may be used to suppress errors if
920 contains options that are unrecognised by
922 It is recommended that
924 be listed early in the configuration file as it will not be applied
925 to unknown options that appear before it.
927 Include the specified configuration file(s).
928 Multiple pathnames may be specified and each pathname may contain
930 wildcards and, for user configurations, shell-like
932 references to user home directories.
933 Files without absolute paths are assumed to be in
935 if included in a user configuration file or
937 if included from the system configuration file.
939 directive may appear inside a
944 to perform conditional inclusion.
946 Specifies the IPv4 type-of-service or DSCP class for connections.
974 to use the operating system default.
975 This option may take one or two arguments, separated by whitespace.
976 If one argument is specified, it is used as the packet class unconditionally.
977 If two values are specified, the first is automatically selected for
978 interactive sessions and the second for non-interactive sessions.
981 for interactive sessions and
983 for non-interactive sessions.
984 .It Cm KbdInteractiveAuthentication
985 Specifies whether to use keyboard-interactive authentication.
986 The argument to this keyword must be
991 .It Cm KbdInteractiveDevices
992 Specifies the list of methods to use in keyboard-interactive authentication.
993 Multiple method names must be comma-separated.
994 The default is to use the server specified list.
995 The methods available vary depending on what the server supports.
996 For an OpenSSH server,
997 it may be zero or more of:
1002 .It Cm KexAlgorithms
1003 Specifies the available KEX (Key Exchange) algorithms.
1004 Multiple algorithms must be comma-separated.
1005 Alternately if the specified value begins with a
1007 character, then the specified methods will be appended to the default set
1008 instead of replacing them.
1009 If the specified value begins with a
1011 character, then the specified methods (including wildcards) will be removed
1012 from the default set instead of replacing them.
1014 .Bd -literal -offset indent
1015 curve25519-sha256,curve25519-sha256@libssh.org,
1016 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1017 diffie-hellman-group-exchange-sha256,
1018 diffie-hellman-group-exchange-sha1,
1019 diffie-hellman-group14-sha1
1022 The list of available key exchange algorithms may also be obtained using
1025 Specifies a command to execute on the local machine after successfully
1026 connecting to the server.
1027 The command string extends to the end of the line, and is executed with
1031 accept the tokens described in the
1035 The command is run synchronously and does not have access to the
1039 It should not be used for interactive commands.
1041 This directive is ignored unless
1042 .Cm PermitLocalCommand
1045 Specifies that a TCP port on the local machine be forwarded over
1046 the secure channel to the specified host and port from the remote machine.
1047 The first argument must be
1049 .Oo Ar bind_address : Oc Ar port
1051 and the second argument must be
1052 .Ar host : Ns Ar hostport .
1053 IPv6 addresses can be specified by enclosing addresses in square brackets.
1054 Multiple forwardings may be specified, and additional forwardings can be
1055 given on the command line.
1056 Only the superuser can forward privileged ports.
1057 By default, the local port is bound in accordance with the
1060 However, an explicit
1062 may be used to bind the connection to a specific address.
1067 indicates that the listening port be bound for local use only, while an
1070 indicates that the port should be available from all interfaces.
1072 Gives the verbosity level that is used when logging messages from
1074 The possible values are:
1075 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1076 The default is INFO.
1077 DEBUG and DEBUG1 are equivalent.
1078 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1080 Specifies the MAC (message authentication code) algorithms
1081 in order of preference.
1082 The MAC algorithm is used for data integrity protection.
1083 Multiple algorithms must be comma-separated.
1084 If the specified value begins with a
1086 character, then the specified algorithms will be appended to the default set
1087 instead of replacing them.
1088 If the specified value begins with a
1090 character, then the specified algorithms (including wildcards) will be removed
1091 from the default set instead of replacing them.
1093 The algorithms that contain
1095 calculate the MAC after encryption (encrypt-then-mac).
1096 These are considered safer and their use recommended.
1099 .Bd -literal -offset indent
1100 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1101 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1102 hmac-sha1-etm@openssh.com,
1103 umac-64@openssh.com,umac-128@openssh.com,
1104 hmac-sha2-256,hmac-sha2-512,hmac-sha1
1107 The list of available MAC algorithms may also be obtained using
1109 .It Cm NoHostAuthenticationForLocalhost
1110 This option can be used if the home directory is shared across machines.
1111 In this case localhost will refer to a different machine on each of
1112 the machines and the user will get many warnings about changed host keys.
1113 However, this option disables host authentication for localhost.
1114 The argument to this keyword must be
1119 .It Cm NumberOfPasswordPrompts
1120 Specifies the number of password prompts before giving up.
1121 The argument to this keyword must be an integer.
1123 .It Cm PasswordAuthentication
1124 Specifies whether to use password authentication.
1125 The argument to this keyword must be
1130 .It Cm PermitLocalCommand
1131 Allow local command execution via the
1134 .Ic !\& Ns Ar command
1137 The argument must be
1142 .It Cm PKCS11Provider
1143 Specifies which PKCS#11 provider to use.
1144 The argument to this keyword is the PKCS#11 shared library
1146 should use to communicate with a PKCS#11 token providing the user's
1149 Specifies the port number to connect on the remote host.
1151 .It Cm PreferredAuthentications
1152 Specifies the order in which the client should try authentication methods.
1153 This allows a client to prefer one method (e.g.\&
1154 .Cm keyboard-interactive )
1155 over another method (e.g.\&
1158 .Bd -literal -offset indent
1159 gssapi-with-mic,hostbased,publickey,
1160 keyboard-interactive,password
1163 Specifies the command to use to connect to the server.
1165 string extends to the end of the line, and is executed
1166 using the user's shell
1168 directive to avoid a lingering shell process.
1172 accept the tokens described in the
1175 The command can be basically anything,
1176 and should read from its standard input and write to its standard output.
1177 It should eventually connect an
1179 server running on some machine, or execute
1182 Host key management will be done using the
1183 HostName of the host being connected (defaulting to the name typed by
1185 Setting the command to
1187 disables this option entirely.
1190 is not available for connects with a proxy command.
1192 This directive is useful in conjunction with
1194 and its proxy support.
1195 For example, the following directive would connect via an HTTP proxy at
1197 .Bd -literal -offset 3n
1198 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1201 Specifies one or more jump proxies as
1209 Multiple proxies may be separated by comma characters and will be visited
1211 Setting this option will cause
1213 to connect to the target host by first making a
1215 connection to the specified
1217 host and then establishing a
1218 TCP forwarding to the ultimate target from there.
1220 Note that this option will compete with the
1222 option - whichever is specified first will prevent later instances of the
1223 other from taking effect.
1224 .It Cm ProxyUseFdpass
1227 will pass a connected file descriptor back to
1229 instead of continuing to execute and pass data.
1232 .It Cm PubkeyAcceptedKeyTypes
1233 Specifies the key types that will be used for public key authentication
1234 as a comma-separated pattern list.
1235 Alternately if the specified value begins with a
1237 character, then the key types after it will be appended to the default
1238 instead of replacing it.
1239 If the specified value begins with a
1241 character, then the specified key types (including wildcards) will be removed
1242 from the default set instead of replacing them.
1243 The default for this option is:
1244 .Bd -literal -offset 3n
1245 ecdsa-sha2-nistp256-cert-v01@openssh.com,
1246 ecdsa-sha2-nistp384-cert-v01@openssh.com,
1247 ecdsa-sha2-nistp521-cert-v01@openssh.com,
1248 ssh-ed25519-cert-v01@openssh.com,
1249 ssh-rsa-cert-v01@openssh.com,
1250 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1254 The list of available key types may also be obtained using
1256 .It Cm PubkeyAuthentication
1257 Specifies whether to try public key authentication.
1258 The argument to this keyword must be
1264 Specifies the maximum amount of data that may be transmitted before the
1265 session key is renegotiated, optionally followed a maximum amount of
1266 time that may pass before the session key is renegotiated.
1267 The first argument is specified in bytes and may have a suffix of
1272 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1273 The default is between
1277 depending on the cipher.
1278 The optional second value is specified in seconds and may use any of the
1279 units documented in the
1283 The default value for
1287 which means that rekeying is performed after the cipher's default amount
1288 of data has been sent or received and no time based rekeying is done.
1289 .It Cm RemoteCommand
1290 Specifies a command to execute on the remote machine after successfully
1291 connecting to the server.
1292 The command string extends to the end of the line, and is executed with
1296 accept the tokens described in the
1299 .It Cm RemoteForward
1300 Specifies that a TCP port on the remote machine be forwarded over
1302 The remote port may either be fowarded to a specified host and port
1303 from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1304 client to connect to arbitrary destinations from the local machine.
1305 The first argument must be
1307 .Oo Ar bind_address : Oc Ar port
1309 If forwarding to a specific destination then the second argument must be
1310 .Ar host : Ns Ar hostport ,
1311 otherwise if no destination argument is specified then the remote forwarding
1312 will be established as a SOCKS proxy.
1314 IPv6 addresses can be specified by enclosing addresses in square brackets.
1315 Multiple forwardings may be specified, and additional
1316 forwardings can be given on the command line.
1317 Privileged ports can be forwarded only when
1318 logging in as root on the remote machine.
1323 the listen port will be dynamically allocated on the server and reported
1324 to the client at run time.
1328 is not specified, the default is to only bind to loopback addresses.
1333 or an empty string, then the forwarding is requested to listen on all
1337 will only succeed if the server's
1339 option is enabled (see
1340 .Xr sshd_config 5 ) .
1342 Specifies whether to request a pseudo-tty for the session.
1343 The argument may be one of:
1345 (never request a TTY),
1347 (always request a TTY when standard input is a TTY),
1349 (always request a TTY) or
1351 (request a TTY when opening a login session).
1352 This option mirrors the
1358 .It Cm RevokedHostKeys
1359 Specifies revoked host public keys.
1360 Keys listed in this file will be refused for host authentication.
1361 Note that if this file does not exist or is not readable,
1362 then host authentication will be refused for all hosts.
1363 Keys may be specified as a text file, listing one public key per line, or as
1364 an OpenSSH Key Revocation List (KRL) as generated by
1366 For more information on KRLs, see the KEY REVOCATION LISTS section in
1369 Specifies what variables from the local
1371 should be sent to the server.
1372 The server must also support it, and the server must be configured to
1373 accept these environment variables.
1376 environment variable is always sent whenever a
1377 pseudo-terminal is requested as it is required by the protocol.
1382 for how to configure the server.
1383 Variables are specified by name, which may contain wildcard characters.
1384 Multiple environment variables may be separated by whitespace or spread
1388 The default is not to send any environment variables.
1392 for more information on patterns.
1393 .It Cm ServerAliveCountMax
1394 Sets the number of server alive messages (see below) which may be
1397 receiving any messages back from the server.
1398 If this threshold is reached while server alive messages are being sent,
1399 ssh will disconnect from the server, terminating the session.
1400 It is important to note that the use of server alive messages is very
1404 The server alive messages are sent through the encrypted channel
1405 and therefore will not be spoofable.
1406 The TCP keepalive option enabled by
1409 The server alive mechanism is valuable when the client or
1410 server depend on knowing when a connection has become inactive.
1412 The default value is 3.
1414 .Cm ServerAliveInterval
1415 (see below) is set to 15 and
1416 .Cm ServerAliveCountMax
1417 is left at the default, if the server becomes unresponsive,
1418 ssh will disconnect after approximately 45 seconds.
1419 .It Cm ServerAliveInterval
1420 Sets a timeout interval in seconds after which if no data has been received
1423 will send a message through the encrypted
1424 channel to request a response from the server.
1426 is 0, indicating that these messages will not be sent to the server.
1427 .It Cm StreamLocalBindMask
1428 Sets the octal file creation mode mask
1430 used when creating a Unix-domain socket file for local or remote
1432 This option is only used for port forwarding to a Unix-domain socket file.
1434 The default value is 0177, which creates a Unix-domain socket file that is
1435 readable and writable only by the owner.
1436 Note that not all operating systems honor the file mode on Unix-domain
1438 .It Cm StreamLocalBindUnlink
1439 Specifies whether to remove an existing Unix-domain socket file for local
1440 or remote port forwarding before creating a new one.
1441 If the socket file already exists and
1442 .Cm StreamLocalBindUnlink
1445 will be unable to forward the port to the Unix-domain socket file.
1446 This option is only used for port forwarding to a Unix-domain socket file.
1448 The argument must be
1453 .It Cm StrictHostKeyChecking
1454 If this flag is set to
1457 will never automatically add host keys to the
1458 .Pa ~/.ssh/known_hosts
1459 file, and refuses to connect to hosts whose host key has changed.
1460 This provides maximum protection against trojan horse attacks,
1461 though it can be annoying when the
1462 .Pa /etc/ssh/ssh_known_hosts
1463 file is poorly maintained or when connections to new hosts are
1465 This option forces the user to manually
1468 If this flag is set to
1470 then ssh will automatically add new host keys to the user
1471 known hosts files, but will not permit connections to hosts with
1473 If this flag is set to
1477 ssh will automatically add new host keys to the user known hosts files
1478 and allow connections to hosts with changed hostkeys to proceed,
1479 subject to some restrictions.
1480 If this flag is set to
1484 will be added to the user known host files only after the user
1485 has confirmed that is what they really want to do, and
1486 ssh will refuse to connect to hosts whose host key has changed.
1488 known hosts will be verified automatically in all cases.
1489 .It Cm SyslogFacility
1490 Gives the facility code that is used when logging messages from
1492 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1493 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1494 The default is USER.
1496 Specifies whether the system should send TCP keepalive messages to the
1498 If they are sent, death of the connection or crash of one
1499 of the machines will be properly noticed.
1500 However, this means that
1501 connections will die if the route is down temporarily, and some people
1506 (to send TCP keepalive messages), and the client will notice
1507 if the network goes down or the remote host dies.
1508 This is important in scripts, and many users want it too.
1510 To disable TCP keepalive messages, the value should be set to
1515 device forwarding between the client and the server.
1516 The argument must be
1527 requests the default tunnel mode, which is
1528 .Cm point-to-point .
1532 devices to open on the client
1537 The argument must be
1539 .Ar local_tun Op : Ar remote_tun .
1541 The devices may be specified by numerical ID or the keyword
1543 which uses the next available tunnel device.
1546 is not specified, it defaults to
1550 .It Cm UpdateHostKeys
1553 should accept notifications of additional hostkeys from the server sent
1554 after authentication has completed and add them to
1555 .Cm UserKnownHostsFile .
1556 The argument must be
1561 Enabling this option allows learning alternate hostkeys for a server
1562 and supports graceful key rotation by allowing a server to send replacement
1563 public keys before old ones are removed.
1564 Additional hostkeys are only accepted if the key used to authenticate the
1565 host was already trusted or explicitly accepted by the user.
1570 then the user is asked to confirm the modifications to the known_hosts file.
1571 Confirmation is currently incompatible with
1572 .Cm ControlPersist ,
1573 and will be disabled if it is enabled.
1577 from OpenSSH 6.8 and greater support the
1578 .Qq hostkeys@openssh.com
1579 protocol extension used to inform the client of all the server's hostkeys.
1580 .It Cm UsePrivilegedPort
1581 Specifies whether to use a privileged port for outgoing connections.
1582 The argument must be
1590 must be setuid root.
1592 Specifies the user to log in as.
1593 This can be useful when a different user name is used on different machines.
1594 This saves the trouble of
1595 having to remember to give the user name on the command line.
1596 .It Cm UserKnownHostsFile
1597 Specifies one or more files to use for the user
1598 host key database, separated by whitespace.
1600 .Pa ~/.ssh/known_hosts ,
1601 .Pa ~/.ssh/known_hosts2 .
1602 .It Cm VerifyHostKeyDNS
1603 Specifies whether to verify the remote key using DNS and SSHFP resource
1605 If this option is set to
1607 the client will implicitly trust keys that match a secure fingerprint
1609 Insecure fingerprints will be handled as if this option was set to
1611 If this option is set to
1613 information on fingerprint match will be displayed, but the user will still
1614 need to confirm new host keys according to the
1615 .Cm StrictHostKeyChecking
1621 .Sx VERIFYING HOST KEYS
1624 .It Cm VisualHostKey
1625 If this flag is set to
1627 an ASCII art representation of the remote host key fingerprint is
1628 printed in addition to the fingerprint string at login and
1629 for unknown host keys.
1630 If this flag is set to
1633 no fingerprint strings are printed at login and
1634 only the fingerprint string will be printed for unknown host keys.
1635 .It Cm XAuthLocation
1636 Specifies the full pathname of the
1640 .Pa /usr/X11R6/bin/xauth .
1645 consists of zero or more non-whitespace characters,
1647 (a wildcard that matches zero or more characters),
1650 (a wildcard that matches exactly one character).
1651 For example, to specify a set of declarations for any host in the
1654 the following pattern could be used:
1658 The following pattern
1659 would match any host in the 192.168.0.[0-9] network range:
1661 .Dl Host 192.168.0.?
1665 is a comma-separated list of patterns.
1666 Patterns within pattern-lists may be negated
1667 by preceding them with an exclamation mark
1670 to allow a key to be used from anywhere within an organization
1674 the following entry (in authorized_keys) could be used:
1676 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1678 Arguments to some keywords can make use of tokens,
1679 which are expanded at runtime:
1681 .Bl -tag -width XXXX -offset indent -compact
1686 Shorthand for %l%h%p%r.
1688 Local user's home directory.
1690 The remote hostname.
1696 The local hostname, including the domain name.
1698 The original remote hostname, as given on the command line.
1702 The remote username.
1708 accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1711 accepts the tokens %%, %d, %h, %l, %r, and %u.
1714 accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1717 accepts the tokens %% and %h.
1722 accept the tokens %%, %d, %h, %l, %r, and %u.
1725 accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1728 accepts the tokens %%, %h, %p, and %r.
1731 accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1734 .It Pa ~/.ssh/config
1735 This is the per-user configuration file.
1736 The format of this file is described above.
1737 This file is used by the SSH client.
1738 Because of the potential for abuse, this file must have strict permissions:
1739 read/write for the user, and not accessible by others.
1740 .It Pa /etc/ssh/ssh_config
1741 Systemwide configuration file.
1742 This file provides defaults for those
1743 values that are not specified in the user's configuration file, and
1744 for those users who do not have a configuration file.
1745 This file must be world-readable.
1751 OpenSSH is a derivative of the original and free
1752 ssh 1.2.12 release by
1754 .An Aaron Campbell , Bob Beck , Markus Friedl ,
1755 .An Niels Provos , Theo de Raadt
1758 removed many bugs, re-added newer features and
1761 contributed the support for SSH protocol versions 1.5 and 2.0.
projects / dragonfly.git / blob