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 1.379 2023/03/10 02:32:04 djm Exp $
37 .Dd $Mdocdate: March 10 2023 $
42 .Nd OpenSSH client configuration file
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 Unless noted otherwise, 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:
151 criteria must appear alone or immediately after
155 Other criteria may be combined arbitrarily.
162 Criteria may be negated by prepending an exclamation mark
167 keyword matches only when the configuration file is being re-parsed
168 after hostname canonicalization (see the
169 .Cm CanonicalizeHostname
171 This may be useful to specify conditions that work with canonical host
176 keyword requests that the configuration be re-parsed (regardless of whether
177 .Cm CanonicalizeHostname
178 is enabled), and matches only during this final pass.
180 .Cm CanonicalizeHostname
185 match during the same pass.
189 keyword executes the specified command under the user's shell.
190 If the command returns a zero exit status then the condition is considered true.
191 Commands containing whitespace characters must be quoted.
194 accept the tokens described in the
198 The other keywords' criteria must be single entries or comma-separated
199 lists and may use the wildcard and negation operators described in the
204 keyword are matched against the target hostname, after any substitution
208 .Cm CanonicalizeHostname
212 keyword matches against the hostname as it was specified on the command-line.
215 keyword matches against the target username on the remote host.
218 keyword matches against the name of the local user running
220 (this keyword may be useful in system-wide
223 .It Cm AddKeysToAgent
224 Specifies whether keys should be automatically added to a running
226 If this option is set to
228 and a key is loaded from a file, the key and its passphrase are added to
229 the agent with the default lifetime, as if by
231 If this option is set to
234 will require confirmation using the
236 program before adding a key (see
239 If this option is set to
241 each use of the key must be confirmed, as if the
243 option was specified to
245 If this option is set to
247 no keys are added to the agent.
248 Alternately, this option may be specified as a time interval
249 using the format described in the
253 to specify the key's lifetime in
255 after which it will automatically be removed.
261 (optionally followed by a time interval),
265 Specifies which address family to use when connecting.
276 user interaction such as password prompts and host key confirmation requests
278 This option is useful in scripts and other batch jobs where no user
279 is present to interact with
287 Use the specified address on the local machine as the source address of
289 Only useful on systems with more than one address.
291 Use the address of the specified interface on the local machine as the
292 source address of the connection.
293 .It Cm CanonicalDomains
295 .Cm CanonicalizeHostname
296 is enabled, this option specifies the list of domain suffixes in which to
297 search for the specified destination host.
298 .It Cm CanonicalizeFallbackLocal
299 Specifies whether to fail with an error when hostname canonicalization fails.
302 will attempt to look up the unqualified hostname using the system resolver's
309 .Cm CanonicalizeHostname
310 is enabled and the target hostname cannot be found in any of the domains
312 .Cm CanonicalDomains .
313 .It Cm CanonicalizeHostname
314 Controls whether explicit hostname canonicalization is performed.
317 is not to perform any name rewriting and let the system resolver handle all
321 then, for connections that do not use a
326 will attempt to canonicalize the hostname specified on the command line
330 .Cm CanonicalizePermittedCNAMEs
333 .Cm CanonicalizeHostname
336 then canonicalization is applied to proxied connections too.
338 If this option is enabled, then the configuration files are processed
339 again using the new target name to pick up any new configuration in matching
346 disables the use of a
349 .It Cm CanonicalizeMaxDots
350 Specifies the maximum number of dot characters in a hostname before
351 canonicalization is disabled.
353 allows a single dot (i.e. hostname.subdomain).
354 .It Cm CanonicalizePermittedCNAMEs
355 Specifies rules to determine whether CNAMEs should be followed when
356 canonicalizing hostnames.
357 The rules consist of one or more arguments of
358 .Ar source_domain_list : Ns Ar target_domain_list ,
360 .Ar source_domain_list
361 is a pattern-list of domains that may follow CNAMEs in canonicalization,
363 .Ar target_domain_list
364 is a pattern-list of domains that they may resolve to.
367 .Qq *.a.example.com:*.b.example.com,*.c.example.com
368 will allow hostnames matching
370 to be canonicalized to names in the
378 causes no CNAMEs to be considered for canonicalization.
379 This is the default behaviour.
380 .It Cm CASignatureAlgorithms
381 Specifies which algorithms are allowed for signing of certificates
382 by certificate authorities (CAs).
384 .Bd -literal -offset indent
385 ssh-ed25519,ecdsa-sha2-nistp256,
386 ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
387 sk-ssh-ed25519@openssh.com,
388 sk-ecdsa-sha2-nistp256@openssh.com,
389 rsa-sha2-512,rsa-sha2-256
392 If the specified list begins with a
394 character, then the specified algorithms will be appended to the default set
395 instead of replacing them.
396 If the specified list begins with a
398 character, then the specified algorithms (including wildcards) will be removed
399 from the default set instead of replacing them.
402 will not accept host certificates signed using algorithms other than those
404 .It Cm CertificateFile
405 Specifies a file from which the user's certificate is read.
406 A corresponding private key must be provided separately in order
407 to use this certificate either
419 .Cm SecurityKeyProvider .
423 may use the tilde syntax to refer to a user's home directory,
424 the tokens described in the
426 section and environment variables as described in the
427 .Sx ENVIRONMENT VARIABLES
430 It is possible to have multiple certificate files specified in
431 configuration files; these certificates will be tried in sequence.
434 directives will add to the list of certificates used for
440 will additionally check the host IP address in the
443 This allows it to detect if a host key changed due to DNS spoofing
444 and will add addresses of destination hosts to
445 .Pa ~/.ssh/known_hosts
446 in the process, regardless of the setting of
447 .Cm StrictHostKeyChecking .
448 If the option is set to
451 the check will not be executed.
455 Specifies the ciphers allowed and their order of preference.
456 Multiple ciphers must be comma-separated.
457 If the specified list begins with a
459 character, then the specified ciphers will be appended to the default set
460 instead of replacing them.
461 If the specified list begins with a
463 character, then the specified ciphers (including wildcards) will be removed
464 from the default set instead of replacing them.
465 If the specified list begins with a
467 character, then the specified ciphers will be placed at the head of the
470 The supported ciphers are:
471 .Bd -literal -offset indent
479 aes128-gcm@openssh.com
480 aes256-gcm@openssh.com
481 chacha20-poly1305@openssh.com
485 .Bd -literal -offset indent
486 chacha20-poly1305@openssh.com,
487 aes128-ctr,aes192-ctr,aes256-ctr,
488 aes128-gcm@openssh.com,aes256-gcm@openssh.com
491 The list of available ciphers may also be obtained using
493 .It Cm ClearAllForwardings
494 Specifies that all local, remote, and dynamic port forwardings
495 specified in the configuration files or on the command line be
497 This option is primarily useful when used from the
499 command line to clear port forwardings set in
500 configuration files, and is automatically set by
510 Specifies whether to use compression.
516 .It Cm ConnectionAttempts
517 Specifies the number of tries (one per second) to make before exiting.
518 The argument must be an integer.
519 This may be useful in scripts if the connection sometimes fails.
521 .It Cm ConnectTimeout
522 Specifies the timeout (in seconds) used when connecting to the
523 SSH server, instead of using the default system TCP timeout.
524 This timeout is applied both to establishing the connection and to performing
525 the initial SSH protocol handshake and key exchange.
527 Enables the sharing of multiple sessions over a single network connection.
531 will listen for connections on a control socket specified using the
534 Additional sessions can connect to this socket using the same
541 These sessions will try to reuse the master instance's network connection
542 rather than initiating new ones, but will fall back to connecting normally
543 if the control socket does not exist, or is not listening.
549 to listen for control connections, but require confirmation using
555 will continue without connecting to a master instance.
559 forwarding is supported over these multiplexed connections, however the
560 display and agent forwarded will be the one belonging to the master
561 connection i.e. it is not possible to forward multiple displays or agents.
563 Two additional options allow for opportunistic multiplexing: try to use a
564 master connection but fall back to creating a new one if one does not already
570 The latter requires confirmation like the
574 Specify the path to the control socket used for connection sharing as described
577 section above or the string
579 to disable connection sharing.
582 may use the tilde syntax to refer to a user's home directory,
583 the tokens described in the
585 section and environment variables as described in the
586 .Sx ENVIRONMENT VARIABLES
588 It is recommended that any
590 used for opportunistic connection sharing include
591 at least %h, %p, and %r (or alternatively %C) and be placed in a directory
592 that is not writable by other users.
593 This ensures that shared connections are uniquely identified.
594 .It Cm ControlPersist
595 When used in conjunction with
597 specifies that the master connection should remain open
598 in the background (waiting for future client connections)
599 after the initial client connection has been closed.
603 then the master connection will not be placed into the background,
604 and will close as soon as the initial client connection is closed.
608 then the master connection will remain in the background indefinitely
609 (until killed or closed via a mechanism such as the
611 If set to a time in seconds, or a time in any of the formats documented in
613 then the backgrounded master connection will automatically terminate
614 after it has remained idle (with no client connections) for the
616 .It Cm DynamicForward
617 Specifies that a TCP port on the local machine be forwarded
618 over the secure channel, and the application
619 protocol is then used to determine where to connect to from the
624 .Oo Ar bind_address : Oc Ar port .
626 IPv6 addresses can be specified by enclosing addresses in square brackets.
627 By default, the local port is bound in accordance with the
632 may be used to bind the connection to a specific address.
637 indicates that the listening port be bound for local use only, while an
640 indicates that the port should be available from all interfaces.
642 Currently the SOCKS4 and SOCKS5 protocols are supported, and
644 will act as a SOCKS server.
645 Multiple forwardings may be specified, and
646 additional forwardings can be given on the command line.
647 Only the superuser can forward privileged ports.
648 .It Cm EnableEscapeCommandline
649 Enables the command line option in the
651 menu for interactive sessions (default
653 By default, the command line is disabled.
654 .It Cm EnableSSHKeysign
655 Setting this option to
657 in the global client configuration file
658 .Pa /etc/ssh/ssh_config
659 enables the use of the helper program
662 .Cm HostbasedAuthentication .
668 This option should be placed in the non-hostspecific section.
671 for more information.
673 Sets the escape character (default:
675 The escape character can also
676 be set on the command line.
677 The argument should be a single character,
679 followed by a letter, or
681 to disable the escape
682 character entirely (making the connection transparent for binary
684 .It Cm ExitOnForwardFailure
687 should terminate the connection if it cannot set up all requested
688 dynamic, tunnel, local, and remote port forwardings, (e.g.\&
689 if either end is unable to bind and listen on a specified port).
691 .Cm ExitOnForwardFailure
692 does not apply to connections made over port forwardings and will not,
695 to exit if TCP connections to the ultimate forwarding destination fail.
701 .It Cm FingerprintHash
702 Specifies the hash algorithm used when displaying key fingerprints.
708 .It Cm ForkAfterAuthentication
711 to go to background just before command execution.
714 is going to ask for passwords or passphrases, but the user
715 wants it in the background.
718 configuration option being set to
720 The recommended way to start X11 programs at a remote site is with
722 .Ic ssh -f host xterm ,
726 .Cm ForkAfterAuthentication
727 configuration option is set to
731 .Cm ExitOnForwardFailure
732 configuration option is set to
734 then a client started with the
735 .Cm ForkAfterAuthentication
736 configuration option being set to
738 will wait for all remote port forwards to be successfully established
739 before placing itself in the background.
740 The argument to this keyword must be
748 Specifies whether the connection to the authentication agent (if any)
749 will be forwarded to the remote machine.
754 an explicit path to an agent socket or the name of an environment variable
757 in which to find the path.
759 Agent forwarding should be enabled with caution.
760 Users with the ability to bypass file permissions on the remote host
761 (for the agent's Unix-domain socket)
762 can access the local agent through the forwarded connection.
763 An attacker cannot obtain key material from the agent,
764 however they can perform operations on the keys that enable them to
765 authenticate using the identities loaded into the agent.
767 Specifies whether X11 connections will be automatically redirected
768 over the secure channel and
777 X11 forwarding should be enabled with caution.
778 Users with the ability to bypass file permissions on the remote host
779 (for the user's X11 authorization database)
780 can access the local X11 display through the forwarded connection.
781 An attacker may then be able to perform activities such as keystroke monitoring
783 .Cm ForwardX11Trusted
784 option is also enabled.
785 .It Cm ForwardX11Timeout
786 Specify a timeout for untrusted X11 forwarding
787 using the format described in the
791 X11 connections received by
793 after this time will be refused.
795 .Cm ForwardX11Timeout
796 to zero will disable the timeout and permit X11 forwarding for the life
798 The default is to disable untrusted X11 forwarding after twenty minutes has
800 .It Cm ForwardX11Trusted
801 If this option is set to
803 remote X11 clients will have full access to the original X11 display.
805 If this option is set to
808 remote X11 clients will be considered untrusted and prevented
809 from stealing or tampering with data belonging to trusted X11
813 token used for the session will be set to expire after 20 minutes.
814 Remote clients will be refused access after this time.
816 See the X11 SECURITY extension specification for full details on
817 the restrictions imposed on untrusted clients.
819 Specifies whether remote hosts are allowed to connect to local
823 binds local port forwardings to the loopback address.
824 This prevents other remote hosts from connecting to forwarded ports.
826 can be used to specify that ssh
827 should bind local port forwardings to the wildcard address,
828 thus allowing remote hosts to connect to forwarded ports.
834 .It Cm GlobalKnownHostsFile
835 Specifies one or more files to use for the global
836 host key database, separated by whitespace.
838 .Pa /etc/ssh/ssh_known_hosts ,
839 .Pa /etc/ssh/ssh_known_hosts2 .
840 .It Cm GSSAPIAuthentication
841 Specifies whether user authentication based on GSSAPI is allowed.
844 .It Cm GSSAPIDelegateCredentials
845 Forward (delegate) credentials to the server.
848 .It Cm HashKnownHosts
851 should hash host names and addresses when they are added to
852 .Pa ~/.ssh/known_hosts .
853 These hashed names may be used normally by
857 but they do not visually reveal identifying information if the
858 file's contents are disclosed.
861 Note that existing names and addresses in known hosts files
862 will not be converted automatically,
863 but may be manually hashed using
865 .It Cm HostbasedAcceptedAlgorithms
866 Specifies the signature algorithms that will be used for hostbased
867 authentication as a comma-separated list of patterns.
868 Alternately if the specified list begins with a
870 character, then the specified signature algorithms will be appended
871 to the default set instead of replacing them.
872 If the specified list begins with a
874 character, then the specified signature algorithms (including wildcards)
875 will be removed from the default set instead of replacing them.
876 If the specified list begins with a
878 character, then the specified signature algorithms will be placed
879 at the head of the default set.
880 The default for this option is:
881 .Bd -literal -offset 3n
882 ssh-ed25519-cert-v01@openssh.com,
883 ecdsa-sha2-nistp256-cert-v01@openssh.com,
884 ecdsa-sha2-nistp384-cert-v01@openssh.com,
885 ecdsa-sha2-nistp521-cert-v01@openssh.com,
886 sk-ssh-ed25519-cert-v01@openssh.com,
887 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
888 rsa-sha2-512-cert-v01@openssh.com,
889 rsa-sha2-256-cert-v01@openssh.com,
891 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
892 sk-ssh-ed25519@openssh.com,
893 sk-ecdsa-sha2-nistp256@openssh.com,
894 rsa-sha2-512,rsa-sha2-256
901 may be used to list supported signature algorithms.
902 This was formerly named HostbasedKeyTypes.
903 .It Cm HostbasedAuthentication
904 Specifies whether to try rhosts based authentication with public key
911 .It Cm HostKeyAlgorithms
912 Specifies the host key signature algorithms
913 that the client wants to use in order of preference.
914 Alternately if the specified list begins with a
916 character, then the specified signature algorithms will be appended to
917 the default set instead of replacing them.
918 If the specified list begins with a
920 character, then the specified signature algorithms (including wildcards)
921 will be removed from the default set instead of replacing them.
922 If the specified list begins with a
924 character, then the specified signature algorithms will be placed
925 at the head of the default set.
926 The default for this option is:
927 .Bd -literal -offset 3n
928 ssh-ed25519-cert-v01@openssh.com,
929 ecdsa-sha2-nistp256-cert-v01@openssh.com,
930 ecdsa-sha2-nistp384-cert-v01@openssh.com,
931 ecdsa-sha2-nistp521-cert-v01@openssh.com,
932 sk-ssh-ed25519-cert-v01@openssh.com,
933 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
934 rsa-sha2-512-cert-v01@openssh.com,
935 rsa-sha2-256-cert-v01@openssh.com,
937 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
938 sk-ecdsa-sha2-nistp256@openssh.com,
939 sk-ssh-ed25519@openssh.com,
940 rsa-sha2-512,rsa-sha2-256
943 If hostkeys are known for the destination host then this default is modified
944 to prefer their algorithms.
946 The list of available signature algorithms may also be obtained using
947 .Qq ssh -Q HostKeyAlgorithms .
949 Specifies an alias that should be used instead of the
950 real host name when looking up or saving the host key
951 in the host key database files and when validating host certificates.
952 This option is useful for tunneling SSH connections
953 or for multiple servers running on a single host.
955 Specifies the real host name to log into.
956 This can be used to specify nicknames or abbreviations for hosts.
959 accept the tokens described in the
962 Numeric IP addresses are also permitted (both on the command line and in
965 The default is the name given on the command line.
966 .It Cm IdentitiesOnly
969 should only use the configured authentication identity and certificate files
970 (either the default files, or those explicitly configured in the
981 .Cm SecurityKeyProvider
982 offers more identities.
983 The argument to this keyword must be
988 This option is intended for situations where ssh-agent
989 offers many different identities.
993 socket used to communicate with the authentication agent.
995 This option overrides the
997 environment variable and can be used to select a specific agent.
998 Setting the socket name to
1000 disables the use of an authentication agent.
1003 is specified, the location of the socket will be read from the
1005 environment variable.
1006 Otherwise if the specified value begins with a
1008 character, then it will be treated as an environment variable containing
1009 the location of the socket.
1013 may use the tilde syntax to refer to a user's home directory,
1014 the tokens described in the
1016 section and environment variables as described in the
1017 .Sx ENVIRONMENT VARIABLES
1020 Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
1021 Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1022 You can also specify a public key file to use the corresponding
1023 private key that is loaded in
1025 when the private key file is not present locally.
1028 .Pa ~/.ssh/id_ecdsa ,
1029 .Pa ~/.ssh/id_ecdsa_sk ,
1030 .Pa ~/.ssh/id_ed25519 ,
1031 .Pa ~/.ssh/id_ed25519_sk
1034 Additionally, any identities represented by the authentication agent
1035 will be used for authentication unless
1038 If no certificates have been explicitly specified by
1039 .Cm CertificateFile ,
1041 will try to load certificate information from the filename obtained by
1044 to the path of a specified
1049 may use the tilde syntax to refer to a user's home directory
1050 or the tokens described in the
1054 It is possible to have
1055 multiple identity files specified in configuration files; all these
1056 identities will be tried in sequence.
1059 directives will add to the list of identities tried (this behaviour
1060 differs from that of other configuration directives).
1063 may be used in conjunction with
1065 to select which identities in an agent are offered during authentication.
1067 may also be used in conjunction with
1069 in order to provide any certificate also needed for authentication with
1071 .It Cm IgnoreUnknown
1072 Specifies a pattern-list of unknown options to be ignored if they are
1073 encountered in configuration parsing.
1074 This may be used to suppress errors if
1076 contains options that are unrecognised by
1078 It is recommended that
1080 be listed early in the configuration file as it will not be applied
1081 to unknown options that appear before it.
1083 Include the specified configuration file(s).
1084 Multiple pathnames may be specified and each pathname may contain
1086 wildcards and, for user configurations, shell-like
1088 references to user home directories.
1089 Wildcards will be expanded and processed in lexical order.
1090 Files without absolute paths are assumed to be in
1092 if included in a user configuration file or
1094 if included from the system configuration file.
1096 directive may appear inside a
1101 to perform conditional inclusion.
1103 Specifies the IPv4 type-of-service or DSCP class for connections.
1132 to use the operating system default.
1133 This option may take one or two arguments, separated by whitespace.
1134 If one argument is specified, it is used as the packet class unconditionally.
1135 If two values are specified, the first is automatically selected for
1136 interactive sessions and the second for non-interactive sessions.
1140 for interactive sessions and
1143 for non-interactive sessions.
1144 .It Cm KbdInteractiveAuthentication
1145 Specifies whether to use keyboard-interactive authentication.
1146 The argument to this keyword must be
1151 .Cm ChallengeResponseAuthentication
1152 is a deprecated alias for this.
1153 .It Cm KbdInteractiveDevices
1154 Specifies the list of methods to use in keyboard-interactive authentication.
1155 Multiple method names must be comma-separated.
1156 The default is to use the server specified list.
1157 The methods available vary depending on what the server supports.
1158 For an OpenSSH server,
1159 it may be zero or more of:
1163 .It Cm KexAlgorithms
1164 Specifies the available KEX (Key Exchange) algorithms.
1165 Multiple algorithms must be comma-separated.
1166 If the specified list begins with a
1168 character, then the specified algorithms will be appended to the default set
1169 instead of replacing them.
1170 If the specified list begins with a
1172 character, then the specified algorithms (including wildcards) will be removed
1173 from the default set instead of replacing them.
1174 If the specified list begins with a
1176 character, then the specified algorithms will be placed at the head of the
1179 .Bd -literal -offset indent
1180 sntrup761x25519-sha512@openssh.com,
1181 curve25519-sha256,curve25519-sha256@libssh.org,
1182 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1183 diffie-hellman-group-exchange-sha256,
1184 diffie-hellman-group16-sha512,
1185 diffie-hellman-group18-sha512,
1186 diffie-hellman-group14-sha256
1189 The list of available key exchange algorithms may also be obtained using
1191 .It Cm KnownHostsCommand
1192 Specifies a command to use to obtain a list of host keys, in addition to
1194 .Cm UserKnownHostsFile
1196 .Cm GlobalKnownHostsFile .
1197 This command is executed after the files have been read.
1198 It may write host key lines to standard output in identical format to the
1199 usual files (described in the
1200 .Sx VERIFYING HOST KEYS
1204 .Cm KnownHostsCommand
1205 accept the tokens described in the
1208 The command may be invoked multiple times per connection: once when preparing
1209 the preference list of host key algorithms to use, again to obtain the
1210 host key for the requested host name and, if
1212 is enabled, one more time to obtain the host key matching the server's
1214 If the command exits abnormally or returns a non-zero exit status then the
1215 connection is terminated.
1217 Specifies a command to execute on the local machine after successfully
1218 connecting to the server.
1219 The command string extends to the end of the line, and is executed with
1223 accept the tokens described in the
1227 The command is run synchronously and does not have access to the
1231 It should not be used for interactive commands.
1233 This directive is ignored unless
1234 .Cm PermitLocalCommand
1237 Specifies that a TCP port on the local machine be forwarded over
1238 the secure channel to the specified host and port from the remote machine.
1239 The first argument specifies the listener and may be
1241 .Oo Ar bind_address : Oc Ar port
1243 or a Unix domain socket path.
1244 The second argument is the destination and may be
1245 .Ar host : Ns Ar hostport
1246 or a Unix domain socket path if the remote host supports it.
1248 IPv6 addresses can be specified by enclosing addresses in square brackets.
1249 Multiple forwardings may be specified, and additional forwardings can be
1250 given on the command line.
1251 Only the superuser can forward privileged ports.
1252 By default, the local port is bound in accordance with the
1255 However, an explicit
1257 may be used to bind the connection to a specific address.
1262 indicates that the listening port be bound for local use only, while an
1265 indicates that the port should be available from all interfaces.
1266 Unix domain socket paths may use the tokens described in the
1268 section and environment variables as described in the
1269 .Sx ENVIRONMENT VARIABLES
1272 Gives the verbosity level that is used when logging messages from
1274 The possible values are:
1275 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1276 The default is INFO.
1277 DEBUG and DEBUG1 are equivalent.
1278 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1280 Specify one or more overrides to LogLevel.
1281 An override consists of a pattern lists that matches the source file, function
1282 and line number to force detailed logging for.
1283 For example, an override pattern of:
1284 .Bd -literal -offset indent
1285 kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1288 would enable detailed logging for line 1000 of
1291 .Fn kex_exchange_identification
1292 function, and all code in the
1295 This option is intended for debugging and no overrides are enabled by default.
1297 Specifies the MAC (message authentication code) algorithms
1298 in order of preference.
1299 The MAC algorithm is used for data integrity protection.
1300 Multiple algorithms must be comma-separated.
1301 If the specified list begins with a
1303 character, then the specified algorithms will be appended to the default set
1304 instead of replacing them.
1305 If the specified list begins with a
1307 character, then the specified algorithms (including wildcards) will be removed
1308 from the default set instead of replacing them.
1309 If the specified list begins with a
1311 character, then the specified algorithms will be placed at the head of the
1314 The algorithms that contain
1316 calculate the MAC after encryption (encrypt-then-mac).
1317 These are considered safer and their use recommended.
1320 .Bd -literal -offset indent
1321 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1322 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1323 hmac-sha1-etm@openssh.com,
1324 umac-64@openssh.com,umac-128@openssh.com,
1325 hmac-sha2-256,hmac-sha2-512,hmac-sha1
1328 The list of available MAC algorithms may also be obtained using
1330 .It Cm NoHostAuthenticationForLocalhost
1331 Disable host authentication for localhost (loopback addresses).
1332 The argument to this keyword must be
1337 .It Cm NumberOfPasswordPrompts
1338 Specifies the number of password prompts before giving up.
1339 The argument to this keyword must be an integer.
1341 .It Cm PasswordAuthentication
1342 Specifies whether to use password authentication.
1343 The argument to this keyword must be
1348 .It Cm PermitLocalCommand
1349 Allow local command execution via the
1352 .Ic !\& Ns Ar command
1355 The argument must be
1360 .It Cm PermitRemoteOpen
1361 Specifies the destinations to which remote TCP port forwarding is permitted when
1363 is used as a SOCKS proxy.
1364 The forwarding specification must be one of the following forms:
1366 .Bl -item -offset indent -compact
1368 .Cm PermitRemoteOpen
1373 .Cm PermitRemoteOpen
1375 .Ar IPv4_addr : port
1378 .Cm PermitRemoteOpen
1380 .Ar \&[ IPv6_addr \&] : port
1384 Multiple forwards may be specified by separating them with whitespace.
1387 can be used to remove all restrictions and permit any forwarding requests.
1390 can be used to prohibit all forwarding requests.
1393 can be used for host or port to allow all hosts or ports respectively.
1394 Otherwise, no pattern matching or address lookups are performed on supplied
1396 .It Cm PKCS11Provider
1397 Specifies which PKCS#11 provider to use or
1399 to indicate that no provider should be used (the default).
1400 The argument to this keyword is a path to the PKCS#11 shared library
1402 should use to communicate with a PKCS#11 token providing keys for user
1405 Specifies the port number to connect on the remote host.
1407 .It Cm PreferredAuthentications
1408 Specifies the order in which the client should try authentication methods.
1409 This allows a client to prefer one method (e.g.\&
1410 .Cm keyboard-interactive )
1411 over another method (e.g.\&
1414 .Bd -literal -offset indent
1415 gssapi-with-mic,hostbased,publickey,
1416 keyboard-interactive,password
1419 Specifies the command to use to connect to the server.
1421 string extends to the end of the line, and is executed
1422 using the user's shell
1424 directive to avoid a lingering shell process.
1428 accept the tokens described in the
1431 The command can be basically anything,
1432 and should read from its standard input and write to its standard output.
1433 It should eventually connect an
1435 server running on some machine, or execute
1438 Host key management will be done using the
1440 of the host being connected (defaulting to the name typed by the user).
1441 Setting the command to
1443 disables this option entirely.
1446 is not available for connects with a proxy command.
1448 This directive is useful in conjunction with
1450 and its proxy support.
1451 For example, the following directive would connect via an HTTP proxy at
1453 .Bd -literal -offset 3n
1454 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1457 Specifies one or more jump proxies as either
1466 Multiple proxies may be separated by comma characters and will be visited
1468 Setting this option will cause
1470 to connect to the target host by first making a
1472 connection to the specified
1474 host and then establishing a
1475 TCP forwarding to the ultimate target from there.
1478 disables this option entirely.
1480 Note that this option will compete with the
1482 option - whichever is specified first will prevent later instances of the
1483 other from taking effect.
1485 Note also that the configuration for the destination host (either supplied
1486 via the command-line or the configuration file) is not generally applied
1489 should be used if specific configuration is required for jump hosts.
1490 .It Cm ProxyUseFdpass
1493 will pass a connected file descriptor back to
1495 instead of continuing to execute and pass data.
1498 .It Cm PubkeyAcceptedAlgorithms
1499 Specifies the signature algorithms that will be used for public key
1500 authentication as a comma-separated list of patterns.
1501 If the specified list begins with a
1503 character, then the algorithms after it will be appended to the default
1504 instead of replacing it.
1505 If the specified list begins with a
1507 character, then the specified algorithms (including wildcards) will be removed
1508 from the default set instead of replacing them.
1509 If the specified list begins with a
1511 character, then the specified algorithms will be placed at the head of the
1513 The default for this option is:
1514 .Bd -literal -offset 3n
1515 ssh-ed25519-cert-v01@openssh.com,
1516 ecdsa-sha2-nistp256-cert-v01@openssh.com,
1517 ecdsa-sha2-nistp384-cert-v01@openssh.com,
1518 ecdsa-sha2-nistp521-cert-v01@openssh.com,
1519 sk-ssh-ed25519-cert-v01@openssh.com,
1520 sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1521 rsa-sha2-512-cert-v01@openssh.com,
1522 rsa-sha2-256-cert-v01@openssh.com,
1524 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1525 sk-ssh-ed25519@openssh.com,
1526 sk-ecdsa-sha2-nistp256@openssh.com,
1527 rsa-sha2-512,rsa-sha2-256
1530 The list of available signature algorithms may also be obtained using
1531 .Qq ssh -Q PubkeyAcceptedAlgorithms .
1532 .It Cm PubkeyAuthentication
1533 Specifies whether to try public key authentication.
1534 The argument to this keyword must be
1541 The final two options enable public key authentication while respectively
1542 disabling or enabling the OpenSSH host-bound authentication protocol
1543 extension required for restricted
1547 Specifies the maximum amount of data that may be transmitted or received
1548 before the session key is renegotiated, optionally followed by a maximum
1549 amount of time that may pass before the session key is renegotiated.
1550 The first argument is specified in bytes and may have a suffix of
1555 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1556 The default is between
1560 depending on the cipher.
1561 The optional second value is specified in seconds and may use any of the
1562 units documented in the TIME FORMATS section of
1564 The default value for
1568 which means that rekeying is performed after the cipher's default amount
1569 of data has been sent or received and no time based rekeying is done.
1570 .It Cm RemoteCommand
1571 Specifies a command to execute on the remote machine after successfully
1572 connecting to the server.
1573 The command string extends to the end of the line, and is executed with
1577 accept the tokens described in the
1580 .It Cm RemoteForward
1581 Specifies that a TCP port on the remote machine be forwarded over
1583 The remote port may either be forwarded to a specified host and port
1584 from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1585 client to connect to arbitrary destinations from the local machine.
1586 The first argument is the listening specification and may be
1588 .Oo Ar bind_address : Oc Ar port
1590 or, if the remote host supports it, a Unix domain socket path.
1591 If forwarding to a specific destination then the second argument must be
1592 .Ar host : Ns Ar hostport
1593 or a Unix domain socket path,
1594 otherwise if no destination argument is specified then the remote forwarding
1595 will be established as a SOCKS proxy.
1596 When acting as a SOCKS proxy, the destination of the connection can be
1598 .Cm PermitRemoteOpen .
1600 IPv6 addresses can be specified by enclosing addresses in square brackets.
1601 Multiple forwardings may be specified, and additional
1602 forwardings can be given on the command line.
1603 Privileged ports can be forwarded only when
1604 logging in as root on the remote machine.
1605 Unix domain socket paths may use the tokens described in the
1607 section and environment variables as described in the
1608 .Sx ENVIRONMENT VARIABLES
1614 the listen port will be dynamically allocated on the server and reported
1615 to the client at run time.
1619 is not specified, the default is to only bind to loopback addresses.
1624 or an empty string, then the forwarding is requested to listen on all
1628 will only succeed if the server's
1630 option is enabled (see
1631 .Xr sshd_config 5 ) .
1633 Specifies whether to request a pseudo-tty for the session.
1634 The argument may be one of:
1636 (never request a TTY),
1638 (always request a TTY when standard input is a TTY),
1640 (always request a TTY) or
1642 (request a TTY when opening a login session).
1643 This option mirrors the
1649 .It Cm RequiredRSASize
1650 Specifies the minimum RSA key size (in bits) that
1653 User authentication keys smaller than this limit will be ignored.
1654 Servers that present host keys smaller than this limit will cause the
1655 connection to be terminated.
1659 Note that this limit may only be raised from the default.
1660 .It Cm RevokedHostKeys
1661 Specifies revoked host public keys.
1662 Keys listed in this file will be refused for host authentication.
1663 Note that if this file does not exist or is not readable,
1664 then host authentication will be refused for all hosts.
1665 Keys may be specified as a text file, listing one public key per line, or as
1666 an OpenSSH Key Revocation List (KRL) as generated by
1668 For more information on KRLs, see the KEY REVOCATION LISTS section in
1670 .It Cm SecurityKeyProvider
1671 Specifies a path to a library that will be used when loading any
1672 FIDO authenticator-hosted keys, overriding the default of using
1673 the built-in USB HID support.
1675 If the specified value begins with a
1677 character, then it will be treated as an environment variable containing
1678 the path to the library.
1680 Specifies what variables from the local
1682 should be sent to the server.
1683 The server must also support it, and the server must be configured to
1684 accept these environment variables.
1687 environment variable is always sent whenever a
1688 pseudo-terminal is requested as it is required by the protocol.
1693 for how to configure the server.
1694 Variables are specified by name, which may contain wildcard characters.
1695 Multiple environment variables may be separated by whitespace or spread
1702 for more information on patterns.
1704 It is possible to clear previously set
1706 variable names by prefixing patterns with
1708 The default is not to send any environment variables.
1709 .It Cm ServerAliveCountMax
1710 Sets the number of server alive messages (see below) which may be
1713 receiving any messages back from the server.
1714 If this threshold is reached while server alive messages are being sent,
1715 ssh will disconnect from the server, terminating the session.
1716 It is important to note that the use of server alive messages is very
1720 The server alive messages are sent through the encrypted channel
1721 and therefore will not be spoofable.
1722 The TCP keepalive option enabled by
1725 The server alive mechanism is valuable when the client or
1726 server depend on knowing when a connection has become unresponsive.
1728 The default value is 3.
1730 .Cm ServerAliveInterval
1731 (see below) is set to 15 and
1732 .Cm ServerAliveCountMax
1733 is left at the default, if the server becomes unresponsive,
1734 ssh will disconnect after approximately 45 seconds.
1735 .It Cm ServerAliveInterval
1736 Sets a timeout interval in seconds after which if no data has been received
1739 will send a message through the encrypted
1740 channel to request a response from the server.
1742 is 0, indicating that these messages will not be sent to the server.
1744 May be used to either request invocation of a subsystem on the remote system,
1745 or to prevent the execution of a remote command at all.
1746 The latter is useful for just forwarding ports.
1747 The argument to this keyword must be
1757 (shell or command execution).
1759 Directly specify one or more environment variables and their contents to
1760 be sent to the server.
1763 with the exception of the
1765 variable, the server must be prepared to accept the environment variable.
1767 Redirects stdin from
1769 (actually, prevents reading from stdin).
1770 Either this or the equivalent
1772 option must be used when
1774 is run in the background.
1775 The argument to this keyword must be
1782 .It Cm StreamLocalBindMask
1783 Sets the octal file creation mode mask
1785 used when creating a Unix-domain socket file for local or remote
1787 This option is only used for port forwarding to a Unix-domain socket file.
1789 The default value is 0177, which creates a Unix-domain socket file that is
1790 readable and writable only by the owner.
1791 Note that not all operating systems honor the file mode on Unix-domain
1793 .It Cm StreamLocalBindUnlink
1794 Specifies whether to remove an existing Unix-domain socket file for local
1795 or remote port forwarding before creating a new one.
1796 If the socket file already exists and
1797 .Cm StreamLocalBindUnlink
1800 will be unable to forward the port to the Unix-domain socket file.
1801 This option is only used for port forwarding to a Unix-domain socket file.
1803 The argument must be
1808 .It Cm StrictHostKeyChecking
1809 If this flag is set to
1812 will never automatically add host keys to the
1813 .Pa ~/.ssh/known_hosts
1814 file, and refuses to connect to hosts whose host key has changed.
1815 This provides maximum protection against man-in-the-middle (MITM) attacks,
1816 though it can be annoying when the
1817 .Pa /etc/ssh/ssh_known_hosts
1818 file is poorly maintained or when connections to new hosts are
1820 This option forces the user to manually
1823 If this flag is set to
1825 then ssh will automatically add new host keys to the user's
1827 file, but will not permit connections to hosts with
1829 If this flag is set to
1833 ssh will automatically add new host keys to the user known hosts files
1834 and allow connections to hosts with changed hostkeys to proceed,
1835 subject to some restrictions.
1836 If this flag is set to
1840 will be added to the user known host files only after the user
1841 has confirmed that is what they really want to do, and
1842 ssh will refuse to connect to hosts whose host key has changed.
1844 known hosts will be verified automatically in all cases.
1845 .It Cm SyslogFacility
1846 Gives the facility code that is used when logging messages from
1848 The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1849 LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1850 The default is USER.
1852 Specifies whether the system should send TCP keepalive messages to the
1854 If they are sent, death of the connection or crash of one
1855 of the machines will be properly noticed.
1856 However, this means that
1857 connections will die if the route is down temporarily, and some people
1862 (to send TCP keepalive messages), and the client will notice
1863 if the network goes down or the remote host dies.
1864 This is important in scripts, and many users want it too.
1866 To disable TCP keepalive messages, the value should be set to
1869 .Cm ServerAliveInterval
1870 for protocol-level keepalives.
1874 device forwarding between the client and the server.
1875 The argument must be
1886 requests the default tunnel mode, which is
1887 .Cm point-to-point .
1891 devices to open on the client
1896 The argument must be
1898 .Ar local_tun Op : Ar remote_tun .
1900 The devices may be specified by numerical ID or the keyword
1902 which uses the next available tunnel device.
1905 is not specified, it defaults to
1909 .It Cm UpdateHostKeys
1912 should accept notifications of additional hostkeys from the server sent
1913 after authentication has completed and add them to
1914 .Cm UserKnownHostsFile .
1915 The argument must be
1920 This option allows learning alternate hostkeys for a server
1921 and supports graceful key rotation by allowing a server to send replacement
1922 public keys before old ones are removed.
1924 Additional hostkeys are only accepted if the key used to authenticate the
1925 host was already trusted or explicitly accepted by the user, the host was
1927 .Cm UserKnownHostsFile
1929 .Cm GlobalKnownHostsFile )
1930 and the host was authenticated using a plain key and not a certificate.
1933 is enabled by default if the user has not overridden the default
1934 .Cm UserKnownHostsFile
1935 setting and has not enabled
1936 .Cm VerifyHostKeyDNS ,
1946 then the user is asked to confirm the modifications to the known_hosts file.
1947 Confirmation is currently incompatible with
1948 .Cm ControlPersist ,
1949 and will be disabled if it is enabled.
1953 from OpenSSH 6.8 and greater support the
1954 .Qq hostkeys@openssh.com
1955 protocol extension used to inform the client of all the server's hostkeys.
1957 Specifies the user to log in as.
1958 This can be useful when a different user name is used on different machines.
1959 This saves the trouble of
1960 having to remember to give the user name on the command line.
1961 .It Cm UserKnownHostsFile
1962 Specifies one or more files to use for the user
1963 host key database, separated by whitespace.
1964 Each filename may use tilde notation to refer to the user's home directory,
1965 the tokens described in the
1967 section and environment variables as described in the
1968 .Sx ENVIRONMENT VARIABLES
1974 to ignore any user-specific known hosts files.
1976 .Pa ~/.ssh/known_hosts ,
1977 .Pa ~/.ssh/known_hosts2 .
1978 .It Cm VerifyHostKeyDNS
1979 Specifies whether to verify the remote key using DNS and SSHFP resource
1981 If this option is set to
1983 the client will implicitly trust keys that match a secure fingerprint
1985 Insecure fingerprints will be handled as if this option was set to
1987 If this option is set to
1989 information on fingerprint match will be displayed, but the user will still
1990 need to confirm new host keys according to the
1991 .Cm StrictHostKeyChecking
1997 .Sx VERIFYING HOST KEYS
2000 .It Cm VisualHostKey
2001 If this flag is set to
2003 an ASCII art representation of the remote host key fingerprint is
2004 printed in addition to the fingerprint string at login and
2005 for unknown host keys.
2006 If this flag is set to
2009 no fingerprint strings are printed at login and
2010 only the fingerprint string will be printed for unknown host keys.
2011 .It Cm XAuthLocation
2012 Specifies the full pathname of the
2016 .Pa /usr/local/bin/xauth .
2021 consists of zero or more non-whitespace characters,
2023 (a wildcard that matches zero or more characters),
2026 (a wildcard that matches exactly one character).
2027 For example, to specify a set of declarations for any host in the
2030 the following pattern could be used:
2034 The following pattern
2035 would match any host in the 192.168.0.[0-9] network range:
2037 .Dl Host 192.168.0.?
2041 is a comma-separated list of patterns.
2042 Patterns within pattern-lists may be negated
2043 by preceding them with an exclamation mark
2046 to allow a key to be used from anywhere within an organization
2050 the following entry (in authorized_keys) could be used:
2052 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
2054 Note that a negated match will never produce a positive result by itself.
2055 For example, attempting to match
2057 against the following pattern-list will fail:
2059 .Dl from=\&"!host1,!host2\&"
2061 The solution here is to include a term that will yield a positive match,
2064 .Dl from=\&"!host1,!host2,*\&"
2066 Arguments to some keywords can make use of tokens,
2067 which are expanded at runtime:
2069 .Bl -tag -width XXXX -offset indent -compact
2076 Local user's home directory.
2078 The fingerprint of the server's host key.
2082 hostname or address that is being searched for.
2084 The remote hostname.
2086 A string describing the reason for a
2087 .Cm KnownHostsCommand
2090 when looking up a host by address (only when
2094 when searching by hostname, or
2096 when preparing the host key algorithm preference list to use for the
2101 The base64 encoded host key.
2103 The host key alias if specified, otherwise the original remote hostname given
2104 on the command line.
2108 The local hostname, including the domain name.
2110 The original remote hostname, as given on the command line.
2114 The remote username.
2120 network interface assigned if
2121 tunnel forwarding was requested, or
2125 The type of the server host key, e.g.
2131 .Cm CertificateFile ,
2135 .Cm KnownHostsCommand ,
2141 .Cm UserKnownHostsFile
2142 accept the tokens %%, %C, %d, %h, %i, %k, %L, %l, %n, %p, %r, and %u.
2144 .Cm KnownHostsCommand
2145 additionally accepts the tokens %f, %H, %I, %K and %t.
2148 accepts the tokens %% and %h.
2156 accept the tokens %%, %h, %n, %p, and %r.
2157 .Sh ENVIRONMENT VARIABLES
2158 Arguments to some keywords can be expanded at runtime from environment
2159 variables on the client by enclosing them in
2163 would refer to the user's .ssh directory.
2164 If a specified environment variable does not exist then an error will be
2165 returned and the setting for that keyword will be ignored.
2168 .Cm CertificateFile ,
2172 .Cm KnownHostsCommand ,
2174 .Cm UserKnownHostsFile
2175 support environment variables.
2180 support environment variables only for Unix domain socket paths.
2183 .It Pa ~/.ssh/config
2184 This is the per-user configuration file.
2185 The format of this file is described above.
2186 This file is used by the SSH client.
2187 Because of the potential for abuse, this file must have strict permissions:
2188 read/write for the user, and not writable by others.
2189 .It Pa /etc/ssh/ssh_config
2190 Systemwide configuration file.
2191 This file provides defaults for those
2192 values that are not specified in the user's configuration file, and
2193 for those users who do not have a configuration file.
2194 This file must be world-readable.
2200 OpenSSH is a derivative of the original and free
2201 ssh 1.2.12 release by
2203 .An Aaron Campbell , Bob Beck , Markus Friedl ,
2204 .An Niels Provos , Theo de Raadt
2207 removed many bugs, re-added newer features and
2210 contributed the support for SSH protocol versions 1.5 and 2.0.
projects / FreeBSD / FreeBSD.git / blob