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 1.211 2015/06/02 09:10:40 djm Exp $
38 .Dd $Mdocdate: June 2 2015 $
43 .Nd OpenSSH SSH client configuration files
46 .Nm /etc/ssh/ssh_config
49 obtains configuration data from the following sources in
52 .Bl -enum -offset indent -compact
56 user's configuration file
59 system-wide configuration file
60 .Pq Pa /etc/ssh/ssh_config
63 For each parameter, the first obtained value
65 The configuration files contain sections separated by
67 specifications, and that section is only applied for hosts that
68 match one of the patterns given in the specification.
69 The matched host name is usually the one given on the command line
71 .Cm CanonicalizeHostname
72 option for exceptions.)
74 Since the first obtained value for each parameter is used, more
75 host-specific declarations should be given near the beginning of the
76 file, and general defaults at the end.
78 The configuration file has the following format:
80 Empty lines and lines starting with
83 Otherwise a line is of the format
84 .Dq keyword arguments .
85 Configuration options may be separated by whitespace or
86 optional whitespace and exactly one
88 the latter format is useful to avoid the need to quote whitespace
89 when specifying configuration options using the
96 Arguments may optionally be enclosed in double quotes
98 in order to represent arguments containing spaces.
101 keywords and their meanings are as follows (note that
102 keywords are case-insensitive and arguments are case-sensitive):
105 Restricts the following declarations (up to the next
109 keyword) to be only for those hosts that match one of the patterns
110 given after the keyword.
111 If more than one pattern is provided, they should be separated by whitespace.
114 as a pattern can be used to provide global
115 defaults for all hosts.
116 The host is usually the
118 argument given on the command line
120 .Cm CanonicalizeHostname
121 option for exceptions.)
123 A pattern entry may be negated by prefixing it with an exclamation mark
125 If a negated entry is matched, then the
127 entry is ignored, regardless of whether any other patterns on the line
129 Negated matches are therefore useful to provide exceptions for wildcard
134 for more information on patterns.
136 Restricts the following declarations (up to the next
140 keyword) to be used only when the conditions following the
142 keyword are satisfied.
143 Match conditions are specified using one or more critera
146 which always matches.
147 The available criteria keywords are:
157 criteria must appear alone or immediately after
159 Other criteria may be combined arbitrarily.
165 Criteria may be negated by prepending an exclamation mark
170 keyword matches only when the configuration file is being re-parsed
171 after hostname canonicalization (see the
172 .Cm CanonicalizeHostname
174 This may be useful to specify conditions that work with canonical host
178 keyword executes the specified command under the user's shell.
179 If the command returns a zero exit status then the condition is considered true.
180 Commands containing whitespace characters must be quoted.
181 The following character sequences in the command will be expanded prior to
184 will be substituted by the first component of the local host name,
186 will be substituted by the local host name (including any domain name),
188 will be substituted by the target host name,
190 will be substituted by the original target host name
191 specified on the command-line,
193 the destination port,
195 by the remote login username, and
197 by the username of the user running
200 The other keywords' criteria must be single entries or comma-separated
201 lists and may use the wildcard and negation operators described in the
206 keyword are matched against the target hostname, after any substitution
210 .Cm CanonicalizeHostname
214 keyword matches against the hostname as it was specified on the command-line.
217 keyword matches against the target username on the remote host.
220 keyword matches against the name of the local user running
222 (this keyword may be useful in system-wide
226 Specifies which address family to use when connecting.
236 passphrase/password querying will be disabled.
237 This option is useful in scripts and other batch jobs where no user
238 is present to supply the password.
246 Use the specified address on the local machine as the source address of
248 Only useful on systems with more than one address.
249 Note that this option does not work if
250 .Cm UsePrivilegedPort
253 .It Cm CanonicalDomains
255 .Cm CanonicalizeHostname
256 is enabled, this option specifies the list of domain suffixes in which to
257 search for the specified destination host.
258 .It Cm CanonicalizeFallbackLocal
259 Specifies whether to fail with an error when hostname canonicalization fails.
262 will attempt to look up the unqualified hostname using the system resolver's
269 .Cm CanonicalizeHostname
270 is enabled and the target hostname cannot be found in any of the domains
272 .Cm CanonicalDomains .
273 .It Cm CanonicalizeHostname
274 Controls whether explicit hostname canonicalization is performed.
277 is not to perform any name rewriting and let the system resolver handle all
281 then, for connections that do not use a
284 will attempt to canonicalize the hostname specified on the command line
288 .Cm CanonicalizePermittedCNAMEs
291 .Cm CanonicalizeHostname
294 then canonicalization is applied to proxied connections too.
296 If this option is enabled, then the configuration files are processed
297 again using the new target name to pick up any new configuration in matching
302 .It Cm CanonicalizeMaxDots
303 Specifies the maximum number of dot characters in a hostname before
304 canonicalization is disabled.
307 allows a single dot (i.e. hostname.subdomain).
308 .It Cm CanonicalizePermittedCNAMEs
309 Specifies rules to determine whether CNAMEs should be followed when
310 canonicalizing hostnames.
311 The rules consist of one or more arguments of
312 .Ar source_domain_list : Ns Ar target_domain_list ,
314 .Ar source_domain_list
315 is a pattern-list of domains that may follow CNAMEs in canonicalization,
317 .Ar target_domain_list
318 is a pattern-list of domains that they may resolve to.
321 .Dq *.a.example.com:*.b.example.com,*.c.example.com
322 will allow hostnames matching
324 to be canonicalized to names in the
329 .It Cm ChallengeResponseAuthentication
330 Specifies whether to use challenge-response authentication.
331 The argument to this keyword must be
338 If this flag is set to
341 will additionally check the host IP address in the
344 This allows ssh to detect if a host key changed due to DNS spoofing
345 and will add addresses of destination hosts to
346 .Pa ~/.ssh/known_hosts
347 in the process, regardless of the setting of
348 .Cm StrictHostKeyChecking .
349 If the option is set to
351 the check will not be executed.
355 Specifies the cipher to use for encrypting the session
356 in protocol version 1.
364 is only supported in the
366 client for interoperability with legacy protocol 1 implementations
367 that do not support the
370 Its use is strongly discouraged due to cryptographic weaknesses.
374 Specifies the ciphers allowed for protocol version 2
375 in order of preference.
376 Multiple ciphers must be comma-separated.
377 The supported ciphers are:
379 .Bl -item -compact -offset indent
395 aes128-gcm@openssh.com
397 aes256-gcm@openssh.com
409 chacha20-poly1305@openssh.com
413 .Bd -literal -offset indent
414 aes128-ctr,aes192-ctr,aes256-ctr,
415 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
416 chacha20-poly1305@openssh.com,
417 arcfour256,arcfour128,
418 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,
419 aes192-cbc,aes256-cbc,arcfour
422 The list of available ciphers may also be obtained using the
428 .It Cm ClearAllForwardings
429 Specifies that all local, remote, and dynamic port forwardings
430 specified in the configuration files or on the command line be
432 This option is primarily useful when used from the
434 command line to clear port forwardings set in
435 configuration files, and is automatically set by
446 Specifies whether to use compression.
453 .It Cm CompressionLevel
454 Specifies the compression level to use if compression is enabled.
455 The argument must be an integer from 1 (fast) to 9 (slow, best).
456 The default level is 6, which is good for most applications.
457 The meaning of the values is the same as in
459 Note that this option applies to protocol version 1 only.
460 .It Cm ConnectionAttempts
461 Specifies the number of tries (one per second) to make before exiting.
462 The argument must be an integer.
463 This may be useful in scripts if the connection sometimes fails.
465 .It Cm ConnectTimeout
466 Specifies the timeout (in seconds) used when connecting to the
467 SSH server, instead of using the default system TCP timeout.
468 This value is used only when the target is down or really unreachable,
469 not when it refuses the connection.
471 Enables the sharing of multiple sessions over a single network connection.
475 will listen for connections on a control socket specified using the
478 Additional sessions can connect to this socket using the same
485 These sessions will try to reuse the master instance's network connection
486 rather than initiating new ones, but will fall back to connecting normally
487 if the control socket does not exist, or is not listening.
492 to listen for control connections, but require confirmation using
497 ssh will continue without connecting to a master instance.
501 forwarding is supported over these multiplexed connections, however the
502 display and agent forwarded will be the one belonging to the master
503 connection i.e. it is not possible to forward multiple displays or agents.
505 Two additional options allow for opportunistic multiplexing: try to use a
506 master connection but fall back to creating a new one if one does not already
512 The latter requires confirmation like the
516 Specify the path to the control socket used for connection sharing as described
519 section above or the string
521 to disable connection sharing.
524 will be substituted by the first component of the local host name,
526 will be substituted by the local host name (including any domain name),
528 will be substituted by the target host name,
530 will be substituted by the original target host name
531 specified on the command line,
533 the destination port,
535 by the remote login username,
537 by the username of the user running
540 by a hash of the concatenation: %l%h%p%r.
541 It is recommended that any
543 used for opportunistic connection sharing include
544 at least %h, %p, and %r (or alternatively %C) and be placed in a directory
545 that is not writable by other users.
546 This ensures that shared connections are uniquely identified.
547 .It Cm ControlPersist
548 When used in conjunction with
550 specifies that the master connection should remain open
551 in the background (waiting for future client connections)
552 after the initial client connection has been closed.
555 then the master connection will not be placed into the background,
556 and will close as soon as the initial client connection is closed.
561 then the master connection will remain in the background indefinitely
562 (until killed or closed via a mechanism such as the
566 If set to a time in seconds, or a time in any of the formats documented in
568 then the backgrounded master connection will automatically terminate
569 after it has remained idle (with no client connections) for the
571 .It Cm DynamicForward
572 Specifies that a TCP port on the local machine be forwarded
573 over the secure channel, and the application
574 protocol is then used to determine where to connect to from the
579 .Oo Ar bind_address : Oc Ar port .
581 IPv6 addresses can be specified by enclosing addresses in square brackets.
582 By default, the local port is bound in accordance with the
587 may be used to bind the connection to a specific address.
592 indicates that the listening port be bound for local use only, while an
595 indicates that the port should be available from all interfaces.
597 Currently the SOCKS4 and SOCKS5 protocols are supported, and
599 will act as a SOCKS server.
600 Multiple forwardings may be specified, and
601 additional forwardings can be given on the command line.
602 Only the superuser can forward privileged ports.
603 .It Cm EnableSSHKeysign
604 Setting this option to
606 in the global client configuration file
607 .Pa /etc/ssh/ssh_config
608 enables the use of the helper program
611 .Cm HostbasedAuthentication .
618 This option should be placed in the non-hostspecific section.
621 for more information.
623 Sets the escape character (default:
625 The escape character can also
626 be set on the command line.
627 The argument should be a single character,
629 followed by a letter, or
631 to disable the escape
632 character entirely (making the connection transparent for binary
634 .It Cm ExitOnForwardFailure
637 should terminate the connection if it cannot set up all requested
638 dynamic, tunnel, local, and remote port forwardings.
645 .It Cm FingerprintHash
646 Specifies the hash algorithm used when displaying key fingerprints.
654 Specifies whether the connection to the authentication agent (if any)
655 will be forwarded to the remote machine.
663 Agent forwarding should be enabled with caution.
664 Users with the ability to bypass file permissions on the remote host
665 (for the agent's Unix-domain socket)
666 can access the local agent through the forwarded connection.
667 An attacker cannot obtain key material from the agent,
668 however they can perform operations on the keys that enable them to
669 authenticate using the identities loaded into the agent.
671 Specifies whether X11 connections will be automatically redirected
672 over the secure channel and
682 X11 forwarding should be enabled with caution.
683 Users with the ability to bypass file permissions on the remote host
684 (for the user's X11 authorization database)
685 can access the local X11 display through the forwarded connection.
686 An attacker may then be able to perform activities such as keystroke monitoring
688 .Cm ForwardX11Trusted
689 option is also enabled.
690 .It Cm ForwardX11Timeout
691 Specify a timeout for untrusted X11 forwarding
692 using the format described in the
693 TIME FORMATS section of
695 X11 connections received by
697 after this time will be refused.
698 The default is to disable untrusted X11 forwarding after twenty minutes has
700 .It Cm ForwardX11Trusted
701 If this option is set to
703 remote X11 clients will have full access to the original X11 display.
705 If this option is set to
707 remote X11 clients will be considered untrusted and prevented
708 from stealing or tampering with data belonging to trusted X11
712 token used for the session will be set to expire after 20 minutes.
713 Remote clients will be refused access after this time.
718 See the X11 SECURITY extension specification for full details on
719 the restrictions imposed on untrusted clients.
721 Specifies whether remote hosts are allowed to connect to local
725 binds local port forwardings to the loopback address.
726 This prevents other remote hosts from connecting to forwarded ports.
728 can be used to specify that ssh
729 should bind local port forwardings to the wildcard address,
730 thus allowing remote hosts to connect to forwarded ports.
737 .It Cm GlobalKnownHostsFile
738 Specifies one or more files to use for the global
739 host key database, separated by whitespace.
741 .Pa /etc/ssh/ssh_known_hosts ,
742 .Pa /etc/ssh/ssh_known_hosts2 .
743 .It Cm GSSAPIAuthentication
744 Specifies whether user authentication based on GSSAPI is allowed.
747 Note that this option applies to protocol version 2 only.
748 .It Cm GSSAPIDelegateCredentials
749 Forward (delegate) credentials to the server.
752 Note that this option applies to protocol version 2 only.
753 .It Cm HashKnownHosts
756 should hash host names and addresses when they are added to
757 .Pa ~/.ssh/known_hosts .
758 These hashed names may be used normally by
762 but they do not reveal identifying information should the file's contents
766 Note that existing names and addresses in known hosts files
767 will not be converted automatically,
768 but may be manually hashed using
770 .It Cm HostbasedAuthentication
771 Specifies whether to try rhosts based authentication with public key
779 This option applies to protocol version 2 only and
781 .Cm RhostsRSAAuthentication .
782 .It Cm HostbasedKeyTypes
783 Specifies the key types that will be used for hostbased authentication
784 as a comma-separated pattern list.
787 will allow all key types.
792 may be used to list supported key types.
793 .It Cm HostKeyAlgorithms
794 Specifies the protocol version 2 host key algorithms
795 that the client wants to use in order of preference.
796 The default for this option is:
797 .Bd -literal -offset 3n
798 ecdsa-sha2-nistp256-cert-v01@openssh.com,
799 ecdsa-sha2-nistp384-cert-v01@openssh.com,
800 ecdsa-sha2-nistp521-cert-v01@openssh.com,
801 ssh-ed25519-cert-v01@openssh.com,
802 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
803 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
804 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
805 ssh-ed25519,ssh-rsa,ssh-dss
808 If hostkeys are known for the destination host then this default is modified
809 to prefer their algorithms.
811 The list of available key types may also be obtained using the
818 Specifies an alias that should be used instead of the
819 real host name when looking up or saving the host key
820 in the host key database files.
821 This option is useful for tunneling SSH connections
822 or for multiple servers running on a single host.
824 Specifies the real host name to log into.
825 This can be used to specify nicknames or abbreviations for hosts.
826 If the hostname contains the character sequence
828 then this will be replaced with the host name specified on the command line
829 (this is useful for manipulating unqualified names).
830 The character sequence
832 will be replaced by a single
834 character, which may be used when specifying IPv6 link-local addresses.
836 The default is the name given on the command line.
837 Numeric IP addresses are also permitted (both on the command line and in
840 .It Cm IdentitiesOnly
843 should only use the authentication identity files configured in the
850 offers more identities.
851 The argument to this keyword must be
855 This option is intended for situations where ssh-agent
856 offers many different identities.
860 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
864 for protocol version 1, and
866 .Pa ~/.ssh/id_ecdsa ,
867 .Pa ~/.ssh/id_ed25519
870 for protocol version 2.
871 Additionally, any identities represented by the authentication agent
872 will be used for authentication unless
876 will try to load certificate information from the filename obtained by
879 to the path of a specified
882 The file name may use the tilde
883 syntax to refer to a user's home directory or one of the following
886 (local user's home directory),
892 (remote host name) or
896 It is possible to have
897 multiple identity files specified in configuration files; all these
898 identities will be tried in sequence.
901 directives will add to the list of identities tried (this behaviour
902 differs from that of other configuration directives).
905 may be used in conjunction with
907 to select which identities in an agent are offered during authentication.
909 Specifies a pattern-list of unknown options to be ignored if they are
910 encountered in configuration parsing.
911 This may be used to suppress errors if
913 contains options that are unrecognised by
915 It is recommended that
917 be listed early in the configuration file as it will not be applied
918 to unknown options that appear before it.
920 Specifies the IPv4 type-of-service or DSCP class for connections.
947 This option may take one or two arguments, separated by whitespace.
948 If one argument is specified, it is used as the packet class unconditionally.
949 If two values are specified, the first is automatically selected for
950 interactive sessions and the second for non-interactive sessions.
953 for interactive sessions and
955 for non-interactive sessions.
956 .It Cm KbdInteractiveAuthentication
957 Specifies whether to use keyboard-interactive authentication.
958 The argument to this keyword must be
964 .It Cm KbdInteractiveDevices
965 Specifies the list of methods to use in keyboard-interactive authentication.
966 Multiple method names must be comma-separated.
967 The default is to use the server specified list.
968 The methods available vary depending on what the server supports.
969 For an OpenSSH server,
970 it may be zero or more of:
976 Specifies the available KEX (Key Exchange) algorithms.
977 Multiple algorithms must be comma-separated.
979 .Bd -literal -offset indent
980 curve25519-sha256@libssh.org,
981 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
982 diffie-hellman-group-exchange-sha256,
983 diffie-hellman-group-exchange-sha1,
984 diffie-hellman-group14-sha1,
985 diffie-hellman-group1-sha1
988 The list of available key exchange algorithms may also be obtained using the
995 Specifies a command to execute on the local machine after successfully
996 connecting to the server.
997 The command string extends to the end of the line, and is executed with
999 The following escape character substitutions will be performed:
1001 (local user's home directory),
1007 (host name as provided on the command line),
1011 (remote user name) or
1013 (local user name) or
1015 by a hash of the concatenation: %l%h%p%r.
1017 The command is run synchronously and does not have access to the
1021 It should not be used for interactive commands.
1023 This directive is ignored unless
1024 .Cm PermitLocalCommand
1027 Specifies that a TCP port on the local machine be forwarded over
1028 the secure channel to the specified host and port from the remote machine.
1029 The first argument must be
1031 .Oo Ar bind_address : Oc Ar port
1033 and the second argument must be
1034 .Ar host : Ns Ar hostport .
1035 IPv6 addresses can be specified by enclosing addresses in square brackets.
1036 Multiple forwardings may be specified, and additional forwardings can be
1037 given on the command line.
1038 Only the superuser can forward privileged ports.
1039 By default, the local port is bound in accordance with the
1042 However, an explicit
1044 may be used to bind the connection to a specific address.
1049 indicates that the listening port be bound for local use only, while an
1052 indicates that the port should be available from all interfaces.
1054 Gives the verbosity level that is used when logging messages from
1056 The possible values are:
1057 QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1058 The default is INFO.
1059 DEBUG and DEBUG1 are equivalent.
1060 DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1062 Specifies the MAC (message authentication code) algorithms
1063 in order of preference.
1064 The MAC algorithm is used in protocol version 2
1065 for data integrity protection.
1066 Multiple algorithms must be comma-separated.
1067 The algorithms that contain
1069 calculate the MAC after encryption (encrypt-then-mac).
1070 These are considered safer and their use recommended.
1072 .Bd -literal -offset indent
1073 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1074 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1075 umac-64@openssh.com,umac-128@openssh.com,
1076 hmac-sha2-256,hmac-sha2-512,
1077 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
1078 hmac-ripemd160-etm@openssh.com,
1079 hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,
1080 hmac-md5,hmac-sha1,hmac-ripemd160,
1081 hmac-sha1-96,hmac-md5-96
1084 The list of available MAC algorithms may also be obtained using the
1090 .It Cm NoHostAuthenticationForLocalhost
1091 This option can be used if the home directory is shared across machines.
1092 In this case localhost will refer to a different machine on each of
1093 the machines and the user will get many warnings about changed host keys.
1094 However, this option disables host authentication for localhost.
1095 The argument to this keyword must be
1099 The default is to check the host key for localhost.
1100 .It Cm NumberOfPasswordPrompts
1101 Specifies the number of password prompts before giving up.
1102 The argument to this keyword must be an integer.
1104 .It Cm PasswordAuthentication
1105 Specifies whether to use password authentication.
1106 The argument to this keyword must be
1112 .It Cm PermitLocalCommand
1113 Allow local command execution via the
1116 .Ic !\& Ns Ar command
1119 The argument must be
1125 .It Cm PKCS11Provider
1126 Specifies which PKCS#11 provider to use.
1127 The argument to this keyword is the PKCS#11 shared library
1129 should use to communicate with a PKCS#11 token providing the user's
1132 Specifies the port number to connect on the remote host.
1134 .It Cm PreferredAuthentications
1135 Specifies the order in which the client should try protocol 2
1136 authentication methods.
1137 This allows a client to prefer one method (e.g.\&
1138 .Cm keyboard-interactive )
1139 over another method (e.g.\&
1142 .Bd -literal -offset indent
1143 gssapi-with-mic,hostbased,publickey,
1144 keyboard-interactive,password
1147 Specifies the protocol versions
1149 should support in order of preference.
1150 The possible values are
1154 Multiple versions must be comma-separated.
1155 When this option is set to
1158 will try version 2 and fall back to version 1
1159 if version 2 is not available.
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.
1170 In the command string, any occurrence of
1172 will be substituted by the host name to
1177 by the remote user name.
1178 The command can be basically anything,
1179 and should read from its standard input and write to its standard output.
1180 It should eventually connect an
1182 server running on some machine, or execute
1185 Host key management will be done using the
1186 HostName of the host being connected (defaulting to the name typed by
1188 Setting the command to
1190 disables this option entirely.
1193 is not available for connects with a proxy command.
1195 This directive is useful in conjunction with
1197 and its proxy support.
1198 For example, the following directive would connect via an HTTP proxy at
1200 .Bd -literal -offset 3n
1201 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1203 .It Cm ProxyUseFdpass
1206 will pass a connected file descriptor back to
1208 instead of continuing to execute and pass data.
1211 .It Cm PubkeyAuthentication
1212 Specifies whether to try public key authentication.
1213 The argument to this keyword must be
1219 This option applies to protocol version 2 only.
1221 Specifies the maximum amount of data that may be transmitted before the
1222 session key is renegotiated, optionally followed a maximum amount of
1223 time that may pass before the session key is renegotiated.
1224 The first argument is specified in bytes and may have a suffix of
1229 to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1230 The default is between
1234 depending on the cipher.
1235 The optional second value is specified in seconds and may use any of the
1236 units documented in the
1237 TIME FORMATS section of
1239 The default value for
1243 which means that rekeying is performed after the cipher's default amount
1244 of data has been sent or received and no time based rekeying is done.
1245 This option applies to protocol version 2 only.
1246 .It Cm RemoteForward
1247 Specifies that a TCP port on the remote machine be forwarded over
1248 the secure channel to the specified host and port from the local machine.
1249 The first argument must be
1251 .Oo Ar bind_address : Oc Ar port
1253 and the second argument must be
1254 .Ar host : Ns Ar hostport .
1255 IPv6 addresses can be specified by enclosing addresses in square brackets.
1256 Multiple forwardings may be specified, and additional
1257 forwardings can be given on the command line.
1258 Privileged ports can be forwarded only when
1259 logging in as root on the remote machine.
1265 the listen port will be dynamically allocated on the server and reported
1266 to the client at run time.
1270 is not specified, the default is to only bind to loopback addresses.
1275 or an empty string, then the forwarding is requested to listen on all
1279 will only succeed if the server's
1281 option is enabled (see
1282 .Xr sshd_config 5 ) .
1284 Specifies whether to request a pseudo-tty for the session.
1285 The argument may be one of:
1287 (never request a TTY),
1289 (always request a TTY when standard input is a TTY),
1291 (always request a TTY) or
1293 (request a TTY when opening a login session).
1294 This option mirrors the
1300 .It Cm RevokedHostKeys
1301 Specifies revoked host public keys.
1302 Keys listed in this file will be refused for host authentication.
1303 Note that if this file does not exist or is not readable,
1304 then host authentication will be refused for all hosts.
1305 Keys may be specified as a text file, listing one public key per line, or as
1306 an OpenSSH Key Revocation List (KRL) as generated by
1308 For more information on KRLs, see the KEY REVOCATION LISTS section in
1310 .It Cm RhostsRSAAuthentication
1311 Specifies whether to try rhosts based authentication with RSA host
1313 The argument must be
1319 This option applies to protocol version 1 only and requires
1322 .It Cm RSAAuthentication
1323 Specifies whether to try RSA authentication.
1324 The argument to this keyword must be
1328 RSA authentication will only be
1329 attempted if the identity file exists, or an authentication agent is
1333 Note that this option applies to protocol version 1 only.
1335 Specifies what variables from the local
1337 should be sent to the server.
1338 Note that environment passing is only supported for protocol 2.
1339 The server must also support it, and the server must be configured to
1340 accept these environment variables.
1343 environment variable is always sent whenever a
1344 pseudo-terminal is requested as it is required by the protocol.
1349 for how to configure the server.
1350 Variables are specified by name, which may contain wildcard characters.
1351 Multiple environment variables may be separated by whitespace or spread
1355 The default is not to send any environment variables.
1359 for more information on patterns.
1360 .It Cm ServerAliveCountMax
1361 Sets the number of server alive messages (see below) which may be
1364 receiving any messages back from the server.
1365 If this threshold is reached while server alive messages are being sent,
1366 ssh will disconnect from the server, terminating the session.
1367 It is important to note that the use of server alive messages is very
1371 The server alive messages are sent through the encrypted channel
1372 and therefore will not be spoofable.
1373 The TCP keepalive option enabled by
1376 The server alive mechanism is valuable when the client or
1377 server depend on knowing when a connection has become inactive.
1379 The default value is 3.
1381 .Cm ServerAliveInterval
1382 (see below) is set to 15 and
1383 .Cm ServerAliveCountMax
1384 is left at the default, if the server becomes unresponsive,
1385 ssh will disconnect after approximately 45 seconds.
1386 This option applies to protocol version 2 only.
1387 .It Cm ServerAliveInterval
1388 Sets a timeout interval in seconds after which if no data has been received
1391 will send a message through the encrypted
1392 channel to request a response from the server.
1394 is 0, indicating that these messages will not be sent to the server.
1395 This option applies to protocol version 2 only.
1396 .It Cm StreamLocalBindMask
1397 Sets the octal file creation mode mask
1399 used when creating a Unix-domain socket file for local or remote
1401 This option is only used for port forwarding to a Unix-domain socket file.
1403 The default value is 0177, which creates a Unix-domain socket file that is
1404 readable and writable only by the owner.
1405 Note that not all operating systems honor the file mode on Unix-domain
1407 .It Cm StreamLocalBindUnlink
1408 Specifies whether to remove an existing Unix-domain socket file for local
1409 or remote port forwarding before creating a new one.
1410 If the socket file already exists and
1411 .Cm StreamLocalBindUnlink
1414 will be unable to forward the port to the Unix-domain socket file.
1415 This option is only used for port forwarding to a Unix-domain socket file.
1417 The argument must be
1423 .It Cm StrictHostKeyChecking
1424 If this flag is set to
1427 will never automatically add host keys to the
1428 .Pa ~/.ssh/known_hosts
1429 file, and refuses to connect to hosts whose host key has changed.
1430 This provides maximum protection against trojan horse attacks,
1431 though it can be annoying when the
1432 .Pa /etc/ssh/ssh_known_hosts
1433 file is poorly maintained or when connections to new hosts are
1435 This option forces the user to manually
1437 If this flag is set to
1439 ssh will automatically add new host keys to the
1440 user known hosts files.
1441 If this flag is set to
1444 will be added to the user known host files only after the user
1445 has confirmed that is what they really want to do, and
1446 ssh will refuse to connect to hosts whose host key has changed.
1448 known hosts will be verified automatically in all cases.
1449 The argument must be
1457 Specifies whether the system should send TCP keepalive messages to the
1459 If they are sent, death of the connection or crash of one
1460 of the machines will be properly noticed.
1461 However, this means that
1462 connections will die if the route is down temporarily, and some people
1467 (to send TCP keepalive messages), and the client will notice
1468 if the network goes down or the remote host dies.
1469 This is important in scripts, and many users want it too.
1471 To disable TCP keepalive messages, the value should be set to
1476 device forwarding between the client and the server.
1477 The argument must be
1487 requests the default tunnel mode, which is
1488 .Dq point-to-point .
1494 devices to open on the client
1499 The argument must be
1501 .Ar local_tun Op : Ar remote_tun .
1503 The devices may be specified by numerical ID or the keyword
1505 which uses the next available tunnel device.
1508 is not specified, it defaults to
1512 .It Cm UpdateHostKeys
1515 should accept notifications of additional hostkeys from the server sent
1516 after authentication has completed and add them to
1517 .Cm UserKnownHostsFile .
1518 The argument must be
1523 Enabling this option allows learning alternate hostkeys for a server
1524 and supports graceful key rotation by allowing a server to send replacement
1525 public keys before old ones are removed.
1526 Additional hostkeys are only accepted if the key used to authenticate the
1527 host was already trusted or explicity accepted by the user.
1532 then the user is asked to confirm the modifications to the known_hosts file.
1533 Confirmation is currently incompatible with
1534 .Cm ControlPersist ,
1535 and will be disabled if it is enabled.
1539 from OpenSSH 6.8 and greater support the
1540 .Dq hostkeys@openssh.com
1541 protocol extension used to inform the client of all the server's hostkeys.
1542 .It Cm UsePrivilegedPort
1543 Specifies whether to use a privileged port for outgoing connections.
1544 The argument must be
1553 must be setuid root.
1554 Note that this option must be set to
1557 .Cm RhostsRSAAuthentication
1560 Specifies the user to log in as.
1561 This can be useful when a different user name is used on different machines.
1562 This saves the trouble of
1563 having to remember to give the user name on the command line.
1564 .It Cm UserKnownHostsFile
1565 Specifies one or more files to use for the user
1566 host key database, separated by whitespace.
1568 .Pa ~/.ssh/known_hosts ,
1569 .Pa ~/.ssh/known_hosts2 .
1570 .It Cm VerifyHostKeyDNS
1571 Specifies whether to verify the remote key using DNS and SSHFP resource
1573 If this option is set to
1575 the client will implicitly trust keys that match a secure fingerprint
1577 Insecure fingerprints will be handled as if this option was set to
1579 If this option is set to
1581 information on fingerprint match will be displayed, but the user will still
1582 need to confirm new host keys according to the
1583 .Cm StrictHostKeyChecking
1585 The argument must be
1592 if compiled with LDNS and
1595 Note that this option applies to protocol version 2 only.
1597 See also VERIFYING HOST KEYS in
1599 .It Cm VersionAddendum
1600 Specifies a string to append to the regular version string to identify
1601 OS- or site-specific modifications.
1603 .Dq FreeBSD-20160119 .
1606 may be used to disable this.
1607 .It Cm VisualHostKey
1608 If this flag is set to
1610 an ASCII art representation of the remote host key fingerprint is
1611 printed in addition to the fingerprint string at login and
1612 for unknown host keys.
1613 If this flag is set to
1615 no fingerprint strings are printed at login and
1616 only the fingerprint string will be printed for unknown host keys.
1619 .It Cm XAuthLocation
1620 Specifies the full pathname of the
1624 .Pa /usr/local/bin/xauth .
1629 consists of zero or more non-whitespace characters,
1631 (a wildcard that matches zero or more characters),
1634 (a wildcard that matches exactly one character).
1635 For example, to specify a set of declarations for any host in the
1638 the following pattern could be used:
1642 The following pattern
1643 would match any host in the 192.168.0.[0-9] network range:
1645 .Dl Host 192.168.0.?
1649 is a comma-separated list of patterns.
1650 Patterns within pattern-lists may be negated
1651 by preceding them with an exclamation mark
1654 to allow a key to be used from anywhere within an organization
1658 the following entry (in authorized_keys) could be used:
1660 .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1663 .It Pa ~/.ssh/config
1664 This is the per-user configuration file.
1665 The format of this file is described above.
1666 This file is used by the SSH client.
1667 Because of the potential for abuse, this file must have strict permissions:
1668 read/write for the user, and not accessible by others.
1669 .It Pa /etc/ssh/ssh_config
1670 Systemwide configuration file.
1671 This file provides defaults for those
1672 values that are not specified in the user's configuration file, and
1673 for those users who do not have a configuration file.
1674 This file must be world-readable.
1679 OpenSSH is a derivative of the original and free
1680 ssh 1.2.12 release by Tatu Ylonen.
1681 Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1682 Theo de Raadt and Dug Song
1683 removed many bugs, re-added newer features and
1685 Markus Friedl contributed the support for SSH
1686 protocol versions 1.5 and 2.0.
projects / FreeBSD / FreeBSD.git / blob