Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.312
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
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".
11: .\"
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.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
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.
24: .\"
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,
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1.312 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.311 2019/12/19 15:09:30 naddy Exp $
! 37: .Dd $Mdocdate: December 19 2019 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
1.310 jmc 42: .Nd OpenSSH client configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
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.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.287 djm 142: .Cm final ,
1.176 djm 143: .Cm exec ,
1.169 djm 144: .Cm host ,
145: .Cm originalhost ,
146: .Cm user ,
147: and
148: .Cm localuser .
1.193 djm 149: The
150: .Cm all
151: criteria must appear alone or immediately after
1.287 djm 152: .Cm canonical
153: or
154: .Cm final .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
1.288 jmc 157: .Cm all ,
158: .Cm canonical ,
1.193 djm 159: and
1.287 djm 160: .Cm final
1.193 djm 161: require an argument.
162: Criteria may be negated by prepending an exclamation mark
163: .Pq Sq !\& .
1.169 djm 164: .Pp
1.177 jmc 165: The
1.193 djm 166: .Cm canonical
1.210 dtucker 167: keyword matches only when the configuration file is being re-parsed
1.193 djm 168: after hostname canonicalization (see the
169: .Cm CanonicalizeHostname
1.288 jmc 170: option).
1.193 djm 171: This may be useful to specify conditions that work with canonical host
172: names only.
1.287 djm 173: .Pp
174: The
175: .Cm final
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.
179: If
180: .Cm CanonicalizeHostname
181: is enabled, then
182: .Cm canonical
183: and
184: .Cm final
185: match during the same pass.
186: .Pp
1.193 djm 187: The
1.176 djm 188: .Cm exec
1.177 jmc 189: keyword executes the specified command under the user's shell.
1.169 djm 190: If the command returns a zero exit status then the condition is considered true.
191: Commands containing whitespace characters must be quoted.
1.239 jmc 192: Arguments to
193: .Cm exec
194: accept the tokens described in the
195: .Sx TOKENS
196: section.
1.169 djm 197: .Pp
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
200: .Sx PATTERNS
201: section.
202: The criteria for the
203: .Cm host
204: keyword are matched against the target hostname, after any substitution
205: by the
1.295 jmc 206: .Cm Hostname
1.193 djm 207: or
208: .Cm CanonicalizeHostname
209: options.
1.169 djm 210: The
211: .Cm originalhost
212: keyword matches against the hostname as it was specified on the command-line.
213: The
214: .Cm user
215: keyword matches against the target username on the remote host.
216: The
217: .Cm localuser
218: keyword matches against the name of the local user running
219: .Xr ssh 1
220: (this keyword may be useful in system-wide
221: .Nm
222: files).
1.222 jcs 223: .It Cm AddKeysToAgent
224: Specifies whether keys should be automatically added to a running
1.223 jmc 225: .Xr ssh-agent 1 .
1.222 jcs 226: If this option is set to
1.240 jmc 227: .Cm yes
1.222 jcs 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
230: .Xr ssh-add 1 .
231: If this option is set to
1.240 jmc 232: .Cm ask ,
233: .Xr ssh 1
1.222 jcs 234: will require confirmation using the
235: .Ev SSH_ASKPASS
236: program before adding a key (see
237: .Xr ssh-add 1
238: for details).
239: If this option is set to
1.240 jmc 240: .Cm confirm ,
1.222 jcs 241: each use of the key must be confirmed, as if the
242: .Fl c
243: option was specified to
244: .Xr ssh-add 1 .
245: If this option is set to
1.240 jmc 246: .Cm no ,
1.222 jcs 247: no keys are added to the agent.
248: The argument must be
1.240 jmc 249: .Cm yes ,
250: .Cm confirm ,
251: .Cm ask ,
1.222 jcs 252: or
1.240 jmc 253: .Cm no
254: (the default).
1.10 djm 255: .It Cm AddressFamily
1.11 jmc 256: Specifies which address family to use when connecting.
257: Valid arguments are
1.240 jmc 258: .Cm any
259: (the default),
260: .Cm inet
1.84 jmc 261: (use IPv4 only), or
1.240 jmc 262: .Cm inet6
1.40 jmc 263: (use IPv6 only).
1.1 stevesk 264: .It Cm BatchMode
265: If set to
1.240 jmc 266: .Cm yes ,
1.1 stevesk 267: passphrase/password querying will be disabled.
268: This option is useful in scripts and other batch jobs where no user
269: is present to supply the password.
270: The argument must be
1.240 jmc 271: .Cm yes
1.1 stevesk 272: or
1.240 jmc 273: .Cm no
274: (the default).
1.268 jmc 275: .It Cm BindAddress
276: Use the specified address on the local machine as the source address of
277: the connection.
278: Only useful on systems with more than one address.
279: .It Cm BindInterface
280: Use the address of the specified interface on the local machine as the
281: source address of the connection.
1.171 djm 282: .It Cm CanonicalDomains
1.172 jmc 283: When
1.173 djm 284: .Cm CanonicalizeHostname
1.171 djm 285: is enabled, this option specifies the list of domain suffixes in which to
286: search for the specified destination host.
1.173 djm 287: .It Cm CanonicalizeFallbackLocal
1.174 djm 288: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 289: The default,
1.240 jmc 290: .Cm yes ,
1.172 jmc 291: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 292: search rules.
293: A value of
1.240 jmc 294: .Cm no
1.171 djm 295: will cause
296: .Xr ssh 1
297: to fail instantly if
1.173 djm 298: .Cm CanonicalizeHostname
1.171 djm 299: is enabled and the target hostname cannot be found in any of the domains
300: specified by
301: .Cm CanonicalDomains .
1.173 djm 302: .It Cm CanonicalizeHostname
1.174 djm 303: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 304: The default,
1.240 jmc 305: .Cm no ,
1.171 djm 306: is not to perform any name rewriting and let the system resolver handle all
307: hostname lookups.
308: If set to
1.240 jmc 309: .Cm yes
1.171 djm 310: then, for connections that do not use a
1.284 djm 311: .Cm ProxyCommand
312: or
313: .Cm ProxyJump ,
1.171 djm 314: .Xr ssh 1
1.173 djm 315: will attempt to canonicalize the hostname specified on the command line
1.171 djm 316: using the
317: .Cm CanonicalDomains
318: suffixes and
1.173 djm 319: .Cm CanonicalizePermittedCNAMEs
1.171 djm 320: rules.
321: If
1.173 djm 322: .Cm CanonicalizeHostname
1.171 djm 323: is set to
1.240 jmc 324: .Cm always ,
1.174 djm 325: then canonicalization is applied to proxied connections too.
1.185 djm 326: .Pp
1.193 djm 327: If this option is enabled, then the configuration files are processed
328: again using the new target name to pick up any new configuration in matching
1.185 djm 329: .Cm Host
1.193 djm 330: and
331: .Cm Match
1.185 djm 332: stanzas.
1.173 djm 333: .It Cm CanonicalizeMaxDots
1.172 jmc 334: Specifies the maximum number of dot characters in a hostname before
1.174 djm 335: canonicalization is disabled.
1.240 jmc 336: The default, 1,
1.172 jmc 337: allows a single dot (i.e. hostname.subdomain).
1.173 djm 338: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 339: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 340: canonicalizing hostnames.
1.171 djm 341: The rules consist of one or more arguments of
1.172 jmc 342: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 343: where
344: .Ar source_domain_list
1.174 djm 345: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 346: and
347: .Ar target_domain_list
1.172 jmc 348: is a pattern-list of domains that they may resolve to.
1.171 djm 349: .Pp
350: For example,
1.240 jmc 351: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 352: will allow hostnames matching
1.240 jmc 353: .Qq *.a.example.com
1.173 djm 354: to be canonicalized to names in the
1.240 jmc 355: .Qq *.b.example.com
1.171 djm 356: or
1.240 jmc 357: .Qq *.c.example.com
1.171 djm 358: domains.
1.283 jmc 359: .It Cm CASignatureAlgorithms
360: Specifies which algorithms are allowed for signing of certificates
361: by certificate authorities (CAs).
362: The default is:
363: .Bd -literal -offset indent
1.297 djm 364: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.283 jmc 365: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
366: .Ed
367: .Pp
368: .Xr ssh 1
369: will not accept host certificates signed using algorithms other than those
370: specified.
1.221 djm 371: .It Cm CertificateFile
372: Specifies a file from which the user's certificate is read.
373: A corresponding private key must be provided separately in order
374: to use this certificate either
375: from an
376: .Cm IdentityFile
377: directive or
378: .Fl i
379: flag to
380: .Xr ssh 1 ,
381: via
382: .Xr ssh-agent 1 ,
383: or via a
1.305 naddy 384: .Cm PKCS11Provider
385: or
386: .Cm SecurityKeyProvider .
1.221 djm 387: .Pp
1.239 jmc 388: Arguments to
389: .Cm CertificateFile
390: may use the tilde syntax to refer to a user's home directory
391: or the tokens described in the
392: .Sx TOKENS
393: section.
1.221 djm 394: .Pp
395: It is possible to have multiple certificate files specified in
396: configuration files; these certificates will be tried in sequence.
397: Multiple
398: .Cm CertificateFile
399: directives will add to the list of certificates used for
400: authentication.
1.1 stevesk 401: .It Cm ChallengeResponseAuthentication
1.82 jmc 402: Specifies whether to use challenge-response authentication.
1.1 stevesk 403: The argument to this keyword must be
1.240 jmc 404: .Cm yes
405: (the default)
1.1 stevesk 406: or
1.240 jmc 407: .Cm no .
1.1 stevesk 408: .It Cm CheckHostIP
1.240 jmc 409: If set to
410: .Cm yes
411: (the default),
1.84 jmc 412: .Xr ssh 1
413: will additionally check the host IP address in the
1.1 stevesk 414: .Pa known_hosts
415: file.
1.240 jmc 416: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 417: and will add addresses of destination hosts to
418: .Pa ~/.ssh/known_hosts
419: in the process, regardless of the setting of
420: .Cm StrictHostKeyChecking .
1.107 grunk 421: If the option is set to
1.240 jmc 422: .Cm no ,
1.1 stevesk 423: the check will not be executed.
424: .It Cm Ciphers
1.245 djm 425: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 426: Multiple ciphers must be comma-separated.
1.299 kn 427: If the specified list begins with a
1.214 djm 428: .Sq +
429: character, then the specified ciphers will be appended to the default set
430: instead of replacing them.
1.299 kn 431: If the specified list begins with a
1.241 djm 432: .Sq -
433: character, then the specified ciphers (including wildcards) will be removed
434: from the default set instead of replacing them.
1.301 naddy 435: If the specified list begins with a
436: .Sq ^
437: character, then the specified ciphers will be placed at the head of the
438: default set.
1.214 djm 439: .Pp
1.180 djm 440: The supported ciphers are:
1.240 jmc 441: .Bd -literal -offset indent
1.186 naddy 442: 3des-cbc
443: aes128-cbc
444: aes192-cbc
445: aes256-cbc
446: aes128-ctr
447: aes192-ctr
448: aes256-ctr
449: aes128-gcm@openssh.com
450: aes256-gcm@openssh.com
451: chacha20-poly1305@openssh.com
1.240 jmc 452: .Ed
1.180 djm 453: .Pp
1.84 jmc 454: The default is:
1.186 naddy 455: .Bd -literal -offset indent
1.215 jmc 456: chacha20-poly1305@openssh.com,
1.186 naddy 457: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 458: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 459: .Ed
1.180 djm 460: .Pp
1.240 jmc 461: The list of available ciphers may also be obtained using
462: .Qq ssh -Q cipher .
1.1 stevesk 463: .It Cm ClearAllForwardings
1.84 jmc 464: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 465: specified in the configuration files or on the command line be
1.7 jmc 466: cleared.
467: This option is primarily useful when used from the
1.84 jmc 468: .Xr ssh 1
1.1 stevesk 469: command line to clear port forwardings set in
470: configuration files, and is automatically set by
471: .Xr scp 1
472: and
473: .Xr sftp 1 .
474: The argument must be
1.240 jmc 475: .Cm yes
1.1 stevesk 476: or
1.240 jmc 477: .Cm no
478: (the default).
1.1 stevesk 479: .It Cm Compression
480: Specifies whether to use compression.
481: The argument must be
1.240 jmc 482: .Cm yes
1.1 stevesk 483: or
1.240 jmc 484: .Cm no
485: (the default).
1.247 naddy 486: .It Cm ConnectionAttempts
487: Specifies the number of tries (one per second) to make before exiting.
488: The argument must be an integer.
489: This may be useful in scripts if the connection sometimes fails.
490: The default is 1.
1.9 djm 491: .It Cm ConnectTimeout
1.84 jmc 492: Specifies the timeout (in seconds) used when connecting to the
493: SSH server, instead of using the default system TCP timeout.
1.302 djm 494: This timeout is applied both to establishing the connection and to performing
495: the initial SSH protocol handshake and key exchange.
1.36 djm 496: .It Cm ControlMaster
497: Enables the sharing of multiple sessions over a single network connection.
498: When set to
1.240 jmc 499: .Cm yes ,
1.84 jmc 500: .Xr ssh 1
1.36 djm 501: will listen for connections on a control socket specified using the
502: .Cm ControlPath
503: argument.
504: Additional sessions can connect to this socket using the same
505: .Cm ControlPath
506: with
507: .Cm ControlMaster
508: set to
1.240 jmc 509: .Cm no
1.38 jmc 510: (the default).
1.64 jmc 511: These sessions will try to reuse the master instance's network connection
1.63 djm 512: rather than initiating new ones, but will fall back to connecting normally
513: if the control socket does not exist, or is not listening.
514: .Pp
1.37 djm 515: Setting this to
1.240 jmc 516: .Cm ask
517: will cause
518: .Xr ssh 1
1.206 jmc 519: to listen for control connections, but require confirmation using
520: .Xr ssh-askpass 1 .
1.51 jakob 521: If the
522: .Cm ControlPath
1.84 jmc 523: cannot be opened,
1.240 jmc 524: .Xr ssh 1
525: will continue without connecting to a master instance.
1.58 djm 526: .Pp
527: X11 and
1.59 jmc 528: .Xr ssh-agent 1
1.58 djm 529: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 530: display and agent forwarded will be the one belonging to the master
1.59 jmc 531: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 532: .Pp
533: Two additional options allow for opportunistic multiplexing: try to use a
534: master connection but fall back to creating a new one if one does not already
535: exist.
536: These options are:
1.240 jmc 537: .Cm auto
1.56 djm 538: and
1.240 jmc 539: .Cm autoask .
1.56 djm 540: The latter requires confirmation like the
1.240 jmc 541: .Cm ask
1.56 djm 542: option.
1.36 djm 543: .It Cm ControlPath
1.55 djm 544: Specify the path to the control socket used for connection sharing as described
545: in the
1.36 djm 546: .Cm ControlMaster
1.57 djm 547: section above or the string
1.240 jmc 548: .Cm none
1.57 djm 549: to disable connection sharing.
1.239 jmc 550: Arguments to
551: .Cm ControlPath
552: may use the tilde syntax to refer to a user's home directory
553: or the tokens described in the
554: .Sx TOKENS
555: section.
1.56 djm 556: It is recommended that any
557: .Cm ControlPath
558: used for opportunistic connection sharing include
1.195 djm 559: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
560: that is not writable by other users.
1.56 djm 561: This ensures that shared connections are uniquely identified.
1.137 djm 562: .It Cm ControlPersist
563: When used in conjunction with
564: .Cm ControlMaster ,
565: specifies that the master connection should remain open
566: in the background (waiting for future client connections)
567: after the initial client connection has been closed.
568: If set to
1.240 jmc 569: .Cm no ,
1.137 djm 570: then the master connection will not be placed into the background,
571: and will close as soon as the initial client connection is closed.
572: If set to
1.240 jmc 573: .Cm yes
574: or 0,
1.137 djm 575: then the master connection will remain in the background indefinitely
576: (until killed or closed via a mechanism such as the
1.240 jmc 577: .Qq ssh -O exit ) .
1.137 djm 578: If set to a time in seconds, or a time in any of the formats documented in
579: .Xr sshd_config 5 ,
580: then the backgrounded master connection will automatically terminate
581: after it has remained idle (with no client connections) for the
582: specified time.
1.38 jmc 583: .It Cm DynamicForward
1.74 jmc 584: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 585: over the secure channel, and the application
586: protocol is then used to determine where to connect to from the
587: remote machine.
1.62 djm 588: .Pp
589: The argument must be
590: .Sm off
591: .Oo Ar bind_address : Oc Ar port .
592: .Sm on
1.138 djm 593: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 594: By default, the local port is bound in accordance with the
595: .Cm GatewayPorts
596: setting.
597: However, an explicit
598: .Ar bind_address
599: may be used to bind the connection to a specific address.
600: The
601: .Ar bind_address
602: of
1.240 jmc 603: .Cm localhost
1.62 djm 604: indicates that the listening port be bound for local use only, while an
605: empty address or
606: .Sq *
607: indicates that the port should be available from all interfaces.
608: .Pp
1.38 jmc 609: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 610: .Xr ssh 1
1.38 jmc 611: will act as a SOCKS server.
612: Multiple forwardings may be specified, and
613: additional forwardings can be given on the command line.
614: Only the superuser can forward privileged ports.
1.14 markus 615: .It Cm EnableSSHKeysign
616: Setting this option to
1.240 jmc 617: .Cm yes
1.14 markus 618: in the global client configuration file
619: .Pa /etc/ssh/ssh_config
620: enables the use of the helper program
621: .Xr ssh-keysign 8
622: during
623: .Cm HostbasedAuthentication .
624: The argument must be
1.240 jmc 625: .Cm yes
1.14 markus 626: or
1.240 jmc 627: .Cm no
628: (the default).
1.23 jmc 629: This option should be placed in the non-hostspecific section.
1.14 markus 630: See
631: .Xr ssh-keysign 8
632: for more information.
1.1 stevesk 633: .It Cm EscapeChar
634: Sets the escape character (default:
635: .Ql ~ ) .
636: The escape character can also
637: be set on the command line.
638: The argument should be a single character,
639: .Ql ^
640: followed by a letter, or
1.240 jmc 641: .Cm none
1.1 stevesk 642: to disable the escape
643: character entirely (making the connection transparent for binary
644: data).
1.96 markus 645: .It Cm ExitOnForwardFailure
646: Specifies whether
647: .Xr ssh 1
648: should terminate the connection if it cannot set up all requested
1.216 djm 649: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 650: if either end is unable to bind and listen on a specified port).
1.216 djm 651: Note that
652: .Cm ExitOnForwardFailure
653: does not apply to connections made over port forwardings and will not,
654: for example, cause
655: .Xr ssh 1
656: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 657: The argument must be
1.240 jmc 658: .Cm yes
1.96 markus 659: or
1.240 jmc 660: .Cm no
661: (the default).
1.197 djm 662: .It Cm FingerprintHash
663: Specifies the hash algorithm used when displaying key fingerprints.
664: Valid options are:
1.240 jmc 665: .Cm md5
1.197 djm 666: and
1.240 jmc 667: .Cm sha256
668: (the default).
1.1 stevesk 669: .It Cm ForwardAgent
670: Specifies whether the connection to the authentication agent (if any)
671: will be forwarded to the remote machine.
1.312 ! djm 672: The argument may be
! 673: .Cm yes ,
1.240 jmc 674: .Cm no
1.312 ! djm 675: (the default),
! 676: an explicit path to an agent socket or the name of an environment variable
! 677: (beginning with
! 678: .Sq $ )
! 679: in which to find the path.
1.3 stevesk 680: .Pp
1.7 jmc 681: Agent forwarding should be enabled with caution.
682: Users with the ability to bypass file permissions on the remote host
683: (for the agent's Unix-domain socket)
684: can access the local agent through the forwarded connection.
685: An attacker cannot obtain key material from the agent,
1.3 stevesk 686: however they can perform operations on the keys that enable them to
687: authenticate using the identities loaded into the agent.
1.1 stevesk 688: .It Cm ForwardX11
689: Specifies whether X11 connections will be automatically redirected
690: over the secure channel and
691: .Ev DISPLAY
692: set.
693: The argument must be
1.240 jmc 694: .Cm yes
1.1 stevesk 695: or
1.240 jmc 696: .Cm no
697: (the default).
1.3 stevesk 698: .Pp
1.7 jmc 699: X11 forwarding should be enabled with caution.
700: Users with the ability to bypass file permissions on the remote host
1.22 markus 701: (for the user's X11 authorization database)
1.7 jmc 702: can access the local X11 display through the forwarded connection.
1.22 markus 703: An attacker may then be able to perform activities such as keystroke monitoring
704: if the
705: .Cm ForwardX11Trusted
706: option is also enabled.
1.134 djm 707: .It Cm ForwardX11Timeout
1.135 jmc 708: Specify a timeout for untrusted X11 forwarding
709: using the format described in the
1.240 jmc 710: .Sx TIME FORMATS
711: section of
1.134 djm 712: .Xr sshd_config 5 .
713: X11 connections received by
714: .Xr ssh 1
715: after this time will be refused.
1.285 djm 716: Setting
717: .Cm ForwardX11Timeout
718: to zero will disable the timeout and permit X11 forwarding for the life
719: of the connection.
1.134 djm 720: The default is to disable untrusted X11 forwarding after twenty minutes has
721: elapsed.
1.22 markus 722: .It Cm ForwardX11Trusted
1.34 jmc 723: If this option is set to
1.240 jmc 724: .Cm yes ,
1.84 jmc 725: remote X11 clients will have full access to the original X11 display.
1.42 djm 726: .Pp
1.22 markus 727: If this option is set to
1.240 jmc 728: .Cm no
729: (the default),
1.84 jmc 730: remote X11 clients will be considered untrusted and prevented
1.22 markus 731: from stealing or tampering with data belonging to trusted X11
732: clients.
1.42 djm 733: Furthermore, the
734: .Xr xauth 1
735: token used for the session will be set to expire after 20 minutes.
736: Remote clients will be refused access after this time.
1.22 markus 737: .Pp
738: See the X11 SECURITY extension specification for full details on
739: the restrictions imposed on untrusted clients.
1.1 stevesk 740: .It Cm GatewayPorts
741: Specifies whether remote hosts are allowed to connect to local
742: forwarded ports.
743: By default,
1.84 jmc 744: .Xr ssh 1
1.7 jmc 745: binds local port forwardings to the loopback address.
746: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 747: .Cm GatewayPorts
1.84 jmc 748: can be used to specify that ssh
1.1 stevesk 749: should bind local port forwardings to the wildcard address,
750: thus allowing remote hosts to connect to forwarded ports.
751: The argument must be
1.240 jmc 752: .Cm yes
1.1 stevesk 753: or
1.240 jmc 754: .Cm no
755: (the default).
1.1 stevesk 756: .It Cm GlobalKnownHostsFile
1.151 djm 757: Specifies one or more files to use for the global
758: host key database, separated by whitespace.
759: The default is
760: .Pa /etc/ssh/ssh_known_hosts ,
761: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 762: .It Cm GSSAPIAuthentication
1.27 markus 763: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 764: The default is
1.240 jmc 765: .Cm no .
1.18 markus 766: .It Cm GSSAPIDelegateCredentials
767: Forward (delegate) credentials to the server.
768: The default is
1.240 jmc 769: .Cm no .
1.44 djm 770: .It Cm HashKnownHosts
771: Indicates that
1.84 jmc 772: .Xr ssh 1
1.44 djm 773: should hash host names and addresses when they are added to
1.50 djm 774: .Pa ~/.ssh/known_hosts .
1.44 djm 775: These hashed names may be used normally by
1.84 jmc 776: .Xr ssh 1
1.44 djm 777: and
1.84 jmc 778: .Xr sshd 8 ,
1.44 djm 779: but they do not reveal identifying information should the file's contents
780: be disclosed.
781: The default is
1.240 jmc 782: .Cm no .
1.97 jmc 783: Note that existing names and addresses in known hosts files
784: will not be converted automatically,
785: but may be manually hashed using
1.45 djm 786: .Xr ssh-keygen 1 .
1.1 stevesk 787: .It Cm HostbasedAuthentication
788: Specifies whether to try rhosts based authentication with public key
789: authentication.
790: The argument must be
1.240 jmc 791: .Cm yes
1.1 stevesk 792: or
1.240 jmc 793: .Cm no
794: (the default).
1.202 djm 795: .It Cm HostbasedKeyTypes
796: Specifies the key types that will be used for hostbased authentication
1.279 djm 797: as a comma-separated list of patterns.
1.300 naddy 798: Alternately if the specified list begins with a
1.214 djm 799: .Sq +
800: character, then the specified key types will be appended to the default set
801: instead of replacing them.
1.300 naddy 802: If the specified list begins with a
1.241 djm 803: .Sq -
804: character, then the specified key types (including wildcards) will be removed
805: from the default set instead of replacing them.
1.301 naddy 806: If the specified list begins with a
807: .Sq ^
808: character, then the specified key types will be placed at the head of the
809: default set.
1.213 markus 810: The default for this option is:
811: .Bd -literal -offset 3n
812: ecdsa-sha2-nistp256-cert-v01@openssh.com,
813: ecdsa-sha2-nistp384-cert-v01@openssh.com,
814: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 815: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.213 markus 816: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 817: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 818: rsa-sha2-512-cert-v01@openssh.com,
819: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 820: ssh-rsa-cert-v01@openssh.com,
821: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 822: sk-ecdsa-sha2-nistp256@openssh.com,
823: ssh-ed25519,sk-ssh-ed25519@openssh.com,
824: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 825: .Ed
826: .Pp
1.202 djm 827: The
828: .Fl Q
829: option of
830: .Xr ssh 1
831: may be used to list supported key types.
1.1 stevesk 832: .It Cm HostKeyAlgorithms
1.226 jmc 833: Specifies the host key algorithms
1.1 stevesk 834: that the client wants to use in order of preference.
1.300 naddy 835: Alternately if the specified list begins with a
1.214 djm 836: .Sq +
837: character, then the specified key types will be appended to the default set
838: instead of replacing them.
1.300 naddy 839: If the specified list begins with a
1.241 djm 840: .Sq -
841: character, then the specified key types (including wildcards) will be removed
842: from the default set instead of replacing them.
1.301 naddy 843: If the specified list begins with a
844: .Sq ^
845: character, then the specified key types will be placed at the head of the
846: default set.
1.1 stevesk 847: The default for this option is:
1.139 djm 848: .Bd -literal -offset 3n
849: ecdsa-sha2-nistp256-cert-v01@openssh.com,
850: ecdsa-sha2-nistp384-cert-v01@openssh.com,
851: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 852: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.183 naddy 853: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 854: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 855: rsa-sha2-512-cert-v01@openssh.com,
856: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 857: ssh-rsa-cert-v01@openssh.com,
1.139 djm 858: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 859: sk-ecdsa-sha2-nistp256@openssh.com,
860: ssh-ed25519,sk-ssh-ed25519@openssh.com,
861: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 862: .Ed
1.145 djm 863: .Pp
864: If hostkeys are known for the destination host then this default is modified
865: to prefer their algorithms.
1.198 djm 866: .Pp
1.240 jmc 867: The list of available key types may also be obtained using
868: .Qq ssh -Q key .
1.1 stevesk 869: .It Cm HostKeyAlias
870: Specifies an alias that should be used instead of the
871: real host name when looking up or saving the host key
1.251 djm 872: in the host key database files and when validating host certificates.
1.84 jmc 873: This option is useful for tunneling SSH connections
1.1 stevesk 874: or for multiple servers running on a single host.
1.295 jmc 875: .It Cm Hostname
1.1 stevesk 876: Specifies the real host name to log into.
877: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 878: Arguments to
1.295 jmc 879: .Cm Hostname
1.239 jmc 880: accept the tokens described in the
881: .Sx TOKENS
882: section.
1.1 stevesk 883: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 884: .Cm Hostname
1.1 stevesk 885: specifications).
1.239 jmc 886: The default is the name given on the command line.
1.29 markus 887: .It Cm IdentitiesOnly
888: Specifies that
1.84 jmc 889: .Xr ssh 1
1.304 djm 890: should only use the configured authentication identity and certificate files
891: (either the default files, or those explicitly configured in the
1.31 jmc 892: .Nm
1.221 djm 893: files
894: or passed on the
895: .Xr ssh 1
1.304 djm 896: command-line),
1.84 jmc 897: even if
898: .Xr ssh-agent 1
1.159 djm 899: or a
900: .Cm PKCS11Provider
1.305 naddy 901: or
902: .Cm SecurityKeyProvider
1.29 markus 903: offers more identities.
904: The argument to this keyword must be
1.240 jmc 905: .Cm yes
1.29 markus 906: or
1.240 jmc 907: .Cm no
908: (the default).
1.84 jmc 909: This option is intended for situations where ssh-agent
1.29 markus 910: offers many different identities.
1.231 markus 911: .It Cm IdentityAgent
912: Specifies the
913: .Ux Ns -domain
914: socket used to communicate with the authentication agent.
915: .Pp
916: This option overrides the
1.240 jmc 917: .Ev SSH_AUTH_SOCK
1.231 markus 918: environment variable and can be used to select a specific agent.
919: Setting the socket name to
1.240 jmc 920: .Cm none
1.231 markus 921: disables the use of an authentication agent.
1.232 markus 922: If the string
1.240 jmc 923: .Qq SSH_AUTH_SOCK
1.232 markus 924: is specified, the location of the socket will be read from the
925: .Ev SSH_AUTH_SOCK
926: environment variable.
1.286 djm 927: Otherwise if the specified value begins with a
928: .Sq $
929: character, then it will be treated as an environment variable containing
930: the location of the socket.
1.231 markus 931: .Pp
1.239 jmc 932: Arguments to
933: .Cm IdentityAgent
934: may use the tilde syntax to refer to a user's home directory
935: or the tokens described in the
936: .Sx TOKENS
937: section.
1.67 jmc 938: .It Cm IdentityFile
1.305 naddy 939: Specifies a file from which the user's DSA, ECDSA, security key-hosted ECDSA,
940: Ed25519 or RSA authentication identity is read.
1.67 jmc 941: The default is
1.139 djm 942: .Pa ~/.ssh/id_dsa ,
1.183 naddy 943: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 944: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 945: .Pa ~/.ssh/id_ed25519 ,
946: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 947: and
1.245 djm 948: .Pa ~/.ssh/id_rsa .
1.67 jmc 949: Additionally, any identities represented by the authentication agent
1.165 djm 950: will be used for authentication unless
951: .Cm IdentitiesOnly
952: is set.
1.221 djm 953: If no certificates have been explicitly specified by
954: .Cm CertificateFile ,
1.129 djm 955: .Xr ssh 1
956: will try to load certificate information from the filename obtained by
957: appending
958: .Pa -cert.pub
959: to the path of a specified
960: .Cm IdentityFile .
1.90 djm 961: .Pp
1.239 jmc 962: Arguments to
963: .Cm IdentityFile
964: may use the tilde syntax to refer to a user's home directory
965: or the tokens described in the
966: .Sx TOKENS
967: section.
1.90 djm 968: .Pp
1.67 jmc 969: It is possible to have
970: multiple identity files specified in configuration files; all these
971: identities will be tried in sequence.
1.152 djm 972: Multiple
973: .Cm IdentityFile
974: directives will add to the list of identities tried (this behaviour
975: differs from that of other configuration directives).
1.165 djm 976: .Pp
977: .Cm IdentityFile
978: may be used in conjunction with
979: .Cm IdentitiesOnly
980: to select which identities in an agent are offered during authentication.
1.221 djm 981: .Cm IdentityFile
982: may also be used in conjunction with
983: .Cm CertificateFile
984: in order to provide any certificate also needed for authentication with
985: the identity.
1.164 jmc 986: .It Cm IgnoreUnknown
987: Specifies a pattern-list of unknown options to be ignored if they are
988: encountered in configuration parsing.
989: This may be used to suppress errors if
990: .Nm
991: contains options that are unrecognised by
992: .Xr ssh 1 .
993: It is recommended that
994: .Cm IgnoreUnknown
995: be listed early in the configuration file as it will not be applied
996: to unknown options that appear before it.
1.229 djm 997: .It Cm Include
998: Include the specified configuration file(s).
1.230 jmc 999: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1000: .Xr glob 7
1.229 djm 1001: wildcards and, for user configurations, shell-like
1.240 jmc 1002: .Sq ~
1.229 djm 1003: references to user home directories.
1004: Files without absolute paths are assumed to be in
1005: .Pa ~/.ssh
1.230 jmc 1006: if included in a user configuration file or
1.229 djm 1007: .Pa /etc/ssh
1008: if included from the system configuration file.
1009: .Cm Include
1010: directive may appear inside a
1011: .Cm Match
1012: or
1013: .Cm Host
1014: block
1015: to perform conditional inclusion.
1.143 djm 1016: .It Cm IPQoS
1017: Specifies the IPv4 type-of-service or DSCP class for connections.
1018: Accepted values are
1.240 jmc 1019: .Cm af11 ,
1020: .Cm af12 ,
1021: .Cm af13 ,
1022: .Cm af21 ,
1023: .Cm af22 ,
1024: .Cm af23 ,
1025: .Cm af31 ,
1026: .Cm af32 ,
1027: .Cm af33 ,
1028: .Cm af41 ,
1029: .Cm af42 ,
1030: .Cm af43 ,
1031: .Cm cs0 ,
1032: .Cm cs1 ,
1033: .Cm cs2 ,
1034: .Cm cs3 ,
1035: .Cm cs4 ,
1036: .Cm cs5 ,
1037: .Cm cs6 ,
1038: .Cm cs7 ,
1039: .Cm ef ,
1040: .Cm lowdelay ,
1041: .Cm throughput ,
1042: .Cm reliability ,
1.253 djm 1043: a numeric value, or
1044: .Cm none
1045: to use the operating system default.
1.146 djm 1046: This option may take one or two arguments, separated by whitespace.
1.143 djm 1047: If one argument is specified, it is used as the packet class unconditionally.
1048: If two values are specified, the first is automatically selected for
1049: interactive sessions and the second for non-interactive sessions.
1050: The default is
1.269 job 1051: .Cm af21
1.272 jmc 1052: (Low-Latency Data)
1.143 djm 1053: for interactive sessions and
1.269 job 1054: .Cm cs1
1.272 jmc 1055: (Lower Effort)
1.143 djm 1056: for non-interactive sessions.
1.103 djm 1057: .It Cm KbdInteractiveAuthentication
1058: Specifies whether to use keyboard-interactive authentication.
1059: The argument to this keyword must be
1.240 jmc 1060: .Cm yes
1061: (the default)
1.103 djm 1062: or
1.240 jmc 1063: .Cm no .
1.39 djm 1064: .It Cm KbdInteractiveDevices
1065: Specifies the list of methods to use in keyboard-interactive authentication.
1066: Multiple method names must be comma-separated.
1067: The default is to use the server specified list.
1.85 jmc 1068: The methods available vary depending on what the server supports.
1069: For an OpenSSH server,
1070: it may be zero or more of:
1.240 jmc 1071: .Cm bsdauth ,
1072: .Cm pam ,
1.85 jmc 1073: and
1.240 jmc 1074: .Cm skey .
1.140 djm 1075: .It Cm KexAlgorithms
1076: Specifies the available KEX (Key Exchange) algorithms.
1077: Multiple algorithms must be comma-separated.
1.299 kn 1078: If the specified list begins with a
1.214 djm 1079: .Sq +
1080: character, then the specified methods will be appended to the default set
1081: instead of replacing them.
1.299 kn 1082: If the specified list begins with a
1.241 djm 1083: .Sq -
1084: character, then the specified methods (including wildcards) will be removed
1085: from the default set instead of replacing them.
1.301 naddy 1086: If the specified list begins with a
1087: .Sq ^
1088: character, then the specified methods will be placed at the head of the
1089: default set.
1.141 jmc 1090: The default is:
1091: .Bd -literal -offset indent
1.238 djm 1092: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1093: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1094: diffie-hellman-group-exchange-sha256,
1.266 djm 1095: diffie-hellman-group16-sha512,
1096: diffie-hellman-group18-sha512,
1097: diffie-hellman-group14-sha256,
1.212 djm 1098: diffie-hellman-group14-sha1
1.141 jmc 1099: .Ed
1.198 djm 1100: .Pp
1.240 jmc 1101: The list of available key exchange algorithms may also be obtained using
1102: .Qq ssh -Q kex .
1.65 reyk 1103: .It Cm LocalCommand
1104: Specifies a command to execute on the local machine after successfully
1105: connecting to the server.
1106: The command string extends to the end of the line, and is executed with
1.105 jmc 1107: the user's shell.
1.239 jmc 1108: Arguments to
1109: .Cm LocalCommand
1110: accept the tokens described in the
1111: .Sx TOKENS
1112: section.
1.123 djm 1113: .Pp
1114: The command is run synchronously and does not have access to the
1115: session of the
1116: .Xr ssh 1
1117: that spawned it.
1118: It should not be used for interactive commands.
1119: .Pp
1.65 reyk 1120: This directive is ignored unless
1121: .Cm PermitLocalCommand
1122: has been enabled.
1.1 stevesk 1123: .It Cm LocalForward
1.74 jmc 1124: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1125: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1126: The first argument must be
1.43 djm 1127: .Sm off
1.49 jmc 1128: .Oo Ar bind_address : Oc Ar port
1.43 djm 1129: .Sm on
1.49 jmc 1130: and the second argument must be
1131: .Ar host : Ns Ar hostport .
1.138 djm 1132: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1133: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1134: given on the command line.
1.1 stevesk 1135: Only the superuser can forward privileged ports.
1.43 djm 1136: By default, the local port is bound in accordance with the
1137: .Cm GatewayPorts
1138: setting.
1139: However, an explicit
1140: .Ar bind_address
1141: may be used to bind the connection to a specific address.
1142: The
1143: .Ar bind_address
1144: of
1.240 jmc 1145: .Cm localhost
1.46 jmc 1146: indicates that the listening port be bound for local use only, while an
1147: empty address or
1148: .Sq *
1.43 djm 1149: indicates that the port should be available from all interfaces.
1.1 stevesk 1150: .It Cm LogLevel
1151: Gives the verbosity level that is used when logging messages from
1.84 jmc 1152: .Xr ssh 1 .
1.1 stevesk 1153: The possible values are:
1.84 jmc 1154: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1155: The default is INFO.
1156: DEBUG and DEBUG1 are equivalent.
1157: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1158: .It Cm MACs
1159: Specifies the MAC (message authentication code) algorithms
1160: in order of preference.
1.226 jmc 1161: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1162: Multiple algorithms must be comma-separated.
1.299 kn 1163: If the specified list begins with a
1.214 djm 1164: .Sq +
1165: character, then the specified algorithms will be appended to the default set
1166: instead of replacing them.
1.299 kn 1167: If the specified list begins with a
1.241 djm 1168: .Sq -
1169: character, then the specified algorithms (including wildcards) will be removed
1170: from the default set instead of replacing them.
1.301 naddy 1171: If the specified list begins with a
1172: .Sq ^
1173: character, then the specified algorithms will be placed at the head of the
1174: default set.
1.214 djm 1175: .Pp
1.160 markus 1176: The algorithms that contain
1.240 jmc 1177: .Qq -etm
1.160 markus 1178: calculate the MAC after encryption (encrypt-then-mac).
1179: These are considered safer and their use recommended.
1.214 djm 1180: .Pp
1.84 jmc 1181: The default is:
1.101 jmc 1182: .Bd -literal -offset indent
1.160 markus 1183: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1184: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1185: hmac-sha1-etm@openssh.com,
1.186 naddy 1186: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1187: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1188: .Ed
1.198 djm 1189: .Pp
1.240 jmc 1190: The list of available MAC algorithms may also be obtained using
1191: .Qq ssh -Q mac .
1.1 stevesk 1192: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1193: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1194: The argument to this keyword must be
1.240 jmc 1195: .Cm yes
1.1 stevesk 1196: or
1.242 jmc 1197: .Cm no
1.240 jmc 1198: (the default).
1.1 stevesk 1199: .It Cm NumberOfPasswordPrompts
1200: Specifies the number of password prompts before giving up.
1201: The argument to this keyword must be an integer.
1.84 jmc 1202: The default is 3.
1.1 stevesk 1203: .It Cm PasswordAuthentication
1204: Specifies whether to use password authentication.
1205: The argument to this keyword must be
1.240 jmc 1206: .Cm yes
1207: (the default)
1.1 stevesk 1208: or
1.240 jmc 1209: .Cm no .
1.65 reyk 1210: .It Cm PermitLocalCommand
1211: Allow local command execution via the
1212: .Ic LocalCommand
1213: option or using the
1.66 jmc 1214: .Ic !\& Ns Ar command
1.65 reyk 1215: escape sequence in
1216: .Xr ssh 1 .
1217: The argument must be
1.240 jmc 1218: .Cm yes
1.65 reyk 1219: or
1.240 jmc 1220: .Cm no
1221: (the default).
1.127 markus 1222: .It Cm PKCS11Provider
1.292 djm 1223: Specifies which PKCS#11 provider to use or
1224: .Cm none
1225: to indicate that no provider should be used (the default).
1226: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1227: .Xr ssh 1
1.292 djm 1228: should use to communicate with a PKCS#11 token providing keys for user
1229: authentication.
1.67 jmc 1230: .It Cm Port
1231: Specifies the port number to connect on the remote host.
1.84 jmc 1232: The default is 22.
1.1 stevesk 1233: .It Cm PreferredAuthentications
1.226 jmc 1234: Specifies the order in which the client should try authentication methods.
1.48 jmc 1235: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1236: .Cm keyboard-interactive )
1.48 jmc 1237: over another method (e.g.\&
1.131 jmc 1238: .Cm password ) .
1239: The default is:
1240: .Bd -literal -offset indent
1241: gssapi-with-mic,hostbased,publickey,
1242: keyboard-interactive,password
1243: .Ed
1.1 stevesk 1244: .It Cm ProxyCommand
1245: Specifies the command to use to connect to the server.
1246: The command
1.190 djm 1247: string extends to the end of the line, and is executed
1248: using the user's shell
1249: .Ql exec
1250: directive to avoid a lingering shell process.
1251: .Pp
1.239 jmc 1252: Arguments to
1253: .Cm ProxyCommand
1254: accept the tokens described in the
1255: .Sx TOKENS
1256: section.
1.1 stevesk 1257: The command can be basically anything,
1258: and should read from its standard input and write to its standard output.
1259: It should eventually connect an
1260: .Xr sshd 8
1261: server running on some machine, or execute
1262: .Ic sshd -i
1263: somewhere.
1264: Host key management will be done using the
1.296 jmc 1265: .Cm Hostname
1266: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1267: Setting the command to
1.240 jmc 1268: .Cm none
1.6 markus 1269: disables this option entirely.
1.1 stevesk 1270: Note that
1271: .Cm CheckHostIP
1272: is not available for connects with a proxy command.
1.52 djm 1273: .Pp
1274: This directive is useful in conjunction with
1275: .Xr nc 1
1276: and its proxy support.
1.53 jmc 1277: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1278: 192.0.2.0:
1279: .Bd -literal -offset 3n
1280: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1281: .Ed
1.233 djm 1282: .It Cm ProxyJump
1.260 millert 1283: Specifies one or more jump proxies as either
1.233 djm 1284: .Xo
1285: .Sm off
1.234 jmc 1286: .Op Ar user No @
1.233 djm 1287: .Ar host
1.234 jmc 1288: .Op : Ns Ar port
1.233 djm 1289: .Sm on
1.260 millert 1290: or an ssh URI
1.233 djm 1291: .Xc .
1.235 djm 1292: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1293: sequentially.
1.233 djm 1294: Setting this option will cause
1295: .Xr ssh 1
1296: to connect to the target host by first making a
1297: .Xr ssh 1
1298: connection to the specified
1299: .Cm ProxyJump
1300: host and then establishing a
1.234 jmc 1301: TCP forwarding to the ultimate target from there.
1.233 djm 1302: .Pp
1303: Note that this option will compete with the
1304: .Cm ProxyCommand
1305: option - whichever is specified first will prevent later instances of the
1306: other from taking effect.
1.289 djm 1307: .Pp
1308: Note also that the configuration for the destination host (either supplied
1309: via the command-line or the configuration file) is not generally applied
1310: to jump hosts.
1311: .Pa ~/.ssh/config
1312: should be used if specific configuration is required for jump hosts.
1.167 djm 1313: .It Cm ProxyUseFdpass
1.168 jmc 1314: Specifies that
1.167 djm 1315: .Cm ProxyCommand
1316: will pass a connected file descriptor back to
1.168 jmc 1317: .Xr ssh 1
1.167 djm 1318: instead of continuing to execute and pass data.
1319: The default is
1.240 jmc 1320: .Cm no .
1.213 markus 1321: .It Cm PubkeyAcceptedKeyTypes
1322: Specifies the key types that will be used for public key authentication
1.279 djm 1323: as a comma-separated list of patterns.
1.299 kn 1324: If the specified list begins with a
1.214 djm 1325: .Sq +
1326: character, then the key types after it will be appended to the default
1327: instead of replacing it.
1.299 kn 1328: If the specified list begins with a
1.241 djm 1329: .Sq -
1330: character, then the specified key types (including wildcards) will be removed
1331: from the default set instead of replacing them.
1.301 naddy 1332: If the specified list begins with a
1333: .Sq ^
1334: character, then the specified key types will be placed at the head of the
1335: default set.
1.213 markus 1336: The default for this option is:
1337: .Bd -literal -offset 3n
1338: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1339: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1340: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 1341: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1342: ssh-ed25519-cert-v01@openssh.com,
1.307 djm 1343: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 1344: rsa-sha2-512-cert-v01@openssh.com,
1345: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1346: ssh-rsa-cert-v01@openssh.com,
1.311 naddy 1347: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.305 naddy 1348: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1349: ssh-ed25519,sk-ssh-ed25519@openssh.com,
1350: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1351: .Ed
1352: .Pp
1.240 jmc 1353: The list of available key types may also be obtained using
1354: .Qq ssh -Q key .
1.1 stevesk 1355: .It Cm PubkeyAuthentication
1356: Specifies whether to try public key authentication.
1357: The argument to this keyword must be
1.240 jmc 1358: .Cm yes
1359: (the default)
1.1 stevesk 1360: or
1.240 jmc 1361: .Cm no .
1.75 dtucker 1362: .It Cm RekeyLimit
1363: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1364: session key is renegotiated, optionally followed a maximum amount of
1365: time that may pass before the session key is renegotiated.
1366: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1367: .Sq K ,
1368: .Sq M ,
1.75 dtucker 1369: or
1.76 jmc 1370: .Sq G
1.75 dtucker 1371: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1372: The default is between
1.84 jmc 1373: .Sq 1G
1.75 dtucker 1374: and
1.84 jmc 1375: .Sq 4G ,
1.75 dtucker 1376: depending on the cipher.
1.162 dtucker 1377: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1378: units documented in the TIME FORMATS section of
1.162 dtucker 1379: .Xr sshd_config 5 .
1380: The default value for
1381: .Cm RekeyLimit
1382: is
1.240 jmc 1383: .Cm default none ,
1.162 dtucker 1384: which means that rekeying is performed after the cipher's default amount
1385: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1386: .It Cm RemoteCommand
1387: Specifies a command to execute on the remote machine after successfully
1388: connecting to the server.
1389: The command string extends to the end of the line, and is executed with
1390: the user's shell.
1.250 jmc 1391: Arguments to
1392: .Cm RemoteCommand
1393: accept the tokens described in the
1394: .Sx TOKENS
1395: section.
1.1 stevesk 1396: .It Cm RemoteForward
1.74 jmc 1397: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1398: the secure channel.
1.273 djm 1399: The remote port may either be forwarded to a specified host and port
1.256 markus 1400: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1401: client to connect to arbitrary destinations from the local machine.
1.49 jmc 1402: The first argument must be
1.43 djm 1403: .Sm off
1.49 jmc 1404: .Oo Ar bind_address : Oc Ar port
1.43 djm 1405: .Sm on
1.256 markus 1406: If forwarding to a specific destination then the second argument must be
1407: .Ar host : Ns Ar hostport ,
1408: otherwise if no destination argument is specified then the remote forwarding
1409: will be established as a SOCKS proxy.
1410: .Pp
1.138 djm 1411: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1412: Multiple forwardings may be specified, and additional
1413: forwardings can be given on the command line.
1.113 stevesk 1414: Privileged ports can be forwarded only when
1415: logging in as root on the remote machine.
1.118 jmc 1416: .Pp
1.117 djm 1417: If the
1418: .Ar port
1.240 jmc 1419: argument is 0,
1.117 djm 1420: the listen port will be dynamically allocated on the server and reported
1421: to the client at run time.
1.43 djm 1422: .Pp
1423: If the
1424: .Ar bind_address
1425: is not specified, the default is to only bind to loopback addresses.
1426: If the
1427: .Ar bind_address
1428: is
1429: .Ql *
1430: or an empty string, then the forwarding is requested to listen on all
1431: interfaces.
1432: Specifying a remote
1433: .Ar bind_address
1.46 jmc 1434: will only succeed if the server's
1435: .Cm GatewayPorts
1.43 djm 1436: option is enabled (see
1.46 jmc 1437: .Xr sshd_config 5 ) .
1.149 djm 1438: .It Cm RequestTTY
1439: Specifies whether to request a pseudo-tty for the session.
1440: The argument may be one of:
1.240 jmc 1441: .Cm no
1.149 djm 1442: (never request a TTY),
1.240 jmc 1443: .Cm yes
1.149 djm 1444: (always request a TTY when standard input is a TTY),
1.240 jmc 1445: .Cm force
1.149 djm 1446: (always request a TTY) or
1.240 jmc 1447: .Cm auto
1.149 djm 1448: (request a TTY when opening a login session).
1449: This option mirrors the
1450: .Fl t
1451: and
1452: .Fl T
1453: flags for
1454: .Xr ssh 1 .
1.196 djm 1455: .It Cm RevokedHostKeys
1456: Specifies revoked host public keys.
1457: Keys listed in this file will be refused for host authentication.
1458: Note that if this file does not exist or is not readable,
1459: then host authentication will be refused for all hosts.
1460: Keys may be specified as a text file, listing one public key per line, or as
1461: an OpenSSH Key Revocation List (KRL) as generated by
1462: .Xr ssh-keygen 1 .
1463: For more information on KRLs, see the KEY REVOCATION LISTS section in
1464: .Xr ssh-keygen 1 .
1.305 naddy 1465: .It Cm SecurityKeyProvider
1466: Specifies a path to a security key provider library that will be used when
1.306 djm 1467: loading any security key-hosted keys, overriding the default of using
1.309 naddy 1468: the built-in support for USB HID keys.
1469: .Pp
1470: If the specified value begins with a
1471: .Sq $
1472: character, then it will be treated as an environment variable containing
1473: the path to the library.
1.32 djm 1474: .It Cm SendEnv
1475: Specifies what variables from the local
1476: .Xr environ 7
1477: should be sent to the server.
1.84 jmc 1478: The server must also support it, and the server must be configured to
1.33 djm 1479: accept these environment variables.
1.207 dtucker 1480: Note that the
1481: .Ev TERM
1.208 jmc 1482: environment variable is always sent whenever a
1.207 dtucker 1483: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1484: Refer to
1485: .Cm AcceptEnv
1486: in
1487: .Xr sshd_config 5
1488: for how to configure the server.
1.80 jmc 1489: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1490: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1491: across multiple
1492: .Cm SendEnv
1493: directives.
1.81 jmc 1494: .Pp
1495: See
1496: .Sx PATTERNS
1497: for more information on patterns.
1.271 djm 1498: .Pp
1.272 jmc 1499: It is possible to clear previously set
1.271 djm 1500: .Cm SendEnv
1501: variable names by prefixing patterns with
1502: .Pa - .
1503: The default is not to send any environment variables.
1.28 markus 1504: .It Cm ServerAliveCountMax
1.73 jmc 1505: Sets the number of server alive messages (see below) which may be
1.28 markus 1506: sent without
1.84 jmc 1507: .Xr ssh 1
1.28 markus 1508: receiving any messages back from the server.
1509: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1510: ssh will disconnect from the server, terminating the session.
1.28 markus 1511: It is important to note that the use of server alive messages is very
1512: different from
1513: .Cm TCPKeepAlive
1514: (below).
1515: The server alive messages are sent through the encrypted channel
1516: and therefore will not be spoofable.
1517: The TCP keepalive option enabled by
1518: .Cm TCPKeepAlive
1519: is spoofable.
1520: The server alive mechanism is valuable when the client or
1.298 dtucker 1521: server depend on knowing when a connection has become unresponsive.
1.28 markus 1522: .Pp
1523: The default value is 3.
1524: If, for example,
1525: .Cm ServerAliveInterval
1.84 jmc 1526: (see below) is set to 15 and
1.28 markus 1527: .Cm ServerAliveCountMax
1.84 jmc 1528: is left at the default, if the server becomes unresponsive,
1529: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1530: .It Cm ServerAliveInterval
1531: Sets a timeout interval in seconds after which if no data has been received
1532: from the server,
1.84 jmc 1533: .Xr ssh 1
1.67 jmc 1534: will send a message through the encrypted
1535: channel to request a response from the server.
1536: The default
1537: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1538: .It Cm SetEnv
1539: Directly specify one or more environment variables and their contents to
1540: be sent to the server.
1541: Similarly to
1542: .Cm SendEnv ,
1543: the server must be prepared to accept the environment variable.
1.191 millert 1544: .It Cm StreamLocalBindMask
1545: Sets the octal file creation mode mask
1546: .Pq umask
1547: used when creating a Unix-domain socket file for local or remote
1548: port forwarding.
1549: This option is only used for port forwarding to a Unix-domain socket file.
1550: .Pp
1551: The default value is 0177, which creates a Unix-domain socket file that is
1552: readable and writable only by the owner.
1553: Note that not all operating systems honor the file mode on Unix-domain
1554: socket files.
1555: .It Cm StreamLocalBindUnlink
1556: Specifies whether to remove an existing Unix-domain socket file for local
1557: or remote port forwarding before creating a new one.
1558: If the socket file already exists and
1559: .Cm StreamLocalBindUnlink
1560: is not enabled,
1561: .Nm ssh
1562: will be unable to forward the port to the Unix-domain socket file.
1563: This option is only used for port forwarding to a Unix-domain socket file.
1564: .Pp
1565: The argument must be
1.240 jmc 1566: .Cm yes
1.191 millert 1567: or
1.240 jmc 1568: .Cm no
1569: (the default).
1.1 stevesk 1570: .It Cm StrictHostKeyChecking
1571: If this flag is set to
1.240 jmc 1572: .Cm yes ,
1.84 jmc 1573: .Xr ssh 1
1.1 stevesk 1574: will never automatically add host keys to the
1.50 djm 1575: .Pa ~/.ssh/known_hosts
1.1 stevesk 1576: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1577: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1578: though it can be annoying when the
1.1 stevesk 1579: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1580: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1581: frequently made.
1582: This option forces the user to manually
1583: add all new hosts.
1.255 jmc 1584: .Pp
1.1 stevesk 1585: If this flag is set to
1.254 djm 1586: .Dq accept-new
1.255 jmc 1587: then ssh will automatically add new host keys to the user
1.254 djm 1588: known hosts files, but will not permit connections to hosts with
1589: changed host keys.
1590: If this flag is set to
1591: .Dq no
1592: or
1593: .Dq off ,
1.255 jmc 1594: ssh will automatically add new host keys to the user known hosts files
1595: and allow connections to hosts with changed hostkeys to proceed,
1596: subject to some restrictions.
1.1 stevesk 1597: If this flag is set to
1.240 jmc 1598: .Cm ask
1599: (the default),
1.1 stevesk 1600: new host keys
1601: will be added to the user known host files only after the user
1602: has confirmed that is what they really want to do, and
1.84 jmc 1603: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1604: The host keys of
1605: known hosts will be verified automatically in all cases.
1.244 jmc 1606: .It Cm SyslogFacility
1607: Gives the facility code that is used when logging messages from
1608: .Xr ssh 1 .
1609: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1610: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1611: The default is USER.
1.26 markus 1612: .It Cm TCPKeepAlive
1613: Specifies whether the system should send TCP keepalive messages to the
1614: other side.
1615: If they are sent, death of the connection or crash of one
1616: of the machines will be properly noticed.
1617: However, this means that
1618: connections will die if the route is down temporarily, and some people
1619: find it annoying.
1620: .Pp
1621: The default is
1.240 jmc 1622: .Cm yes
1.26 markus 1623: (to send TCP keepalive messages), and the client will notice
1624: if the network goes down or the remote host dies.
1625: This is important in scripts, and many users want it too.
1626: .Pp
1627: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1628: .Cm no .
1.265 djm 1629: See also
1630: .Cm ServerAliveInterval
1631: for protocol-level keepalives.
1.65 reyk 1632: .It Cm Tunnel
1.95 stevesk 1633: Request
1.65 reyk 1634: .Xr tun 4
1.69 jmc 1635: device forwarding between the client and the server.
1.65 reyk 1636: The argument must be
1.240 jmc 1637: .Cm yes ,
1638: .Cm point-to-point
1.95 stevesk 1639: (layer 3),
1.240 jmc 1640: .Cm ethernet
1.95 stevesk 1641: (layer 2),
1.65 reyk 1642: or
1.240 jmc 1643: .Cm no
1644: (the default).
1.95 stevesk 1645: Specifying
1.240 jmc 1646: .Cm yes
1.95 stevesk 1647: requests the default tunnel mode, which is
1.240 jmc 1648: .Cm point-to-point .
1.65 reyk 1649: .It Cm TunnelDevice
1.95 stevesk 1650: Specifies the
1.65 reyk 1651: .Xr tun 4
1.95 stevesk 1652: devices to open on the client
1653: .Pq Ar local_tun
1654: and the server
1655: .Pq Ar remote_tun .
1656: .Pp
1657: The argument must be
1658: .Sm off
1659: .Ar local_tun Op : Ar remote_tun .
1660: .Sm on
1661: The devices may be specified by numerical ID or the keyword
1.240 jmc 1662: .Cm any ,
1.95 stevesk 1663: which uses the next available tunnel device.
1664: If
1665: .Ar remote_tun
1666: is not specified, it defaults to
1.240 jmc 1667: .Cm any .
1.95 stevesk 1668: The default is
1.240 jmc 1669: .Cm any:any .
1.201 djm 1670: .It Cm UpdateHostKeys
1.200 djm 1671: Specifies whether
1672: .Xr ssh 1
1673: should accept notifications of additional hostkeys from the server sent
1674: after authentication has completed and add them to
1675: .Cm UserKnownHostsFile .
1676: The argument must be
1.240 jmc 1677: .Cm yes ,
1678: .Cm no
1.204 djm 1679: (the default) or
1.240 jmc 1680: .Cm ask .
1.200 djm 1681: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1682: and supports graceful key rotation by allowing a server to send replacement
1683: public keys before old ones are removed.
1.200 djm 1684: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1685: host was already trusted or explicitly accepted by the user.
1.204 djm 1686: If
1687: .Cm UpdateHostKeys
1688: is set to
1.240 jmc 1689: .Cm ask ,
1.204 djm 1690: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1691: Confirmation is currently incompatible with
1692: .Cm ControlPersist ,
1693: and will be disabled if it is enabled.
1.200 djm 1694: .Pp
1695: Presently, only
1696: .Xr sshd 8
1697: from OpenSSH 6.8 and greater support the
1.240 jmc 1698: .Qq hostkeys@openssh.com
1.200 djm 1699: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1700: .It Cm User
1701: Specifies the user to log in as.
1702: This can be useful when a different user name is used on different machines.
1703: This saves the trouble of
1704: having to remember to give the user name on the command line.
1705: .It Cm UserKnownHostsFile
1.151 djm 1706: Specifies one or more files to use for the user
1707: host key database, separated by whitespace.
1708: The default is
1709: .Pa ~/.ssh/known_hosts ,
1710: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1711: .It Cm VerifyHostKeyDNS
1712: Specifies whether to verify the remote key using DNS and SSHFP resource
1713: records.
1.24 jakob 1714: If this option is set to
1.240 jmc 1715: .Cm yes ,
1.25 jmc 1716: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1717: from DNS.
1718: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1719: .Cm ask .
1.24 jakob 1720: If this option is set to
1.240 jmc 1721: .Cm ask ,
1.24 jakob 1722: information on fingerprint match will be displayed, but the user will still
1723: need to confirm new host keys according to the
1724: .Cm StrictHostKeyChecking
1725: option.
1.8 jakob 1726: The default is
1.240 jmc 1727: .Cm no .
1.84 jmc 1728: .Pp
1.240 jmc 1729: See also
1730: .Sx VERIFYING HOST KEYS
1731: in
1.84 jmc 1732: .Xr ssh 1 .
1.111 grunk 1733: .It Cm VisualHostKey
1734: If this flag is set to
1.240 jmc 1735: .Cm yes ,
1.111 grunk 1736: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1737: printed in addition to the fingerprint string at login and
1.114 stevesk 1738: for unknown host keys.
1.111 grunk 1739: If this flag is set to
1.240 jmc 1740: .Cm no
1741: (the default),
1.114 stevesk 1742: no fingerprint strings are printed at login and
1.197 djm 1743: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1744: .It Cm XAuthLocation
1.5 stevesk 1745: Specifies the full pathname of the
1.1 stevesk 1746: .Xr xauth 1
1747: program.
1748: The default is
1749: .Pa /usr/X11R6/bin/xauth .
1750: .El
1.86 jmc 1751: .Sh PATTERNS
1752: A
1753: .Em pattern
1754: consists of zero or more non-whitespace characters,
1755: .Sq *
1756: (a wildcard that matches zero or more characters),
1757: or
1758: .Sq ?\&
1759: (a wildcard that matches exactly one character).
1760: For example, to specify a set of declarations for any host in the
1.240 jmc 1761: .Qq .co.uk
1.86 jmc 1762: set of domains,
1763: the following pattern could be used:
1764: .Pp
1765: .Dl Host *.co.uk
1766: .Pp
1767: The following pattern
1768: would match any host in the 192.168.0.[0-9] network range:
1769: .Pp
1770: .Dl Host 192.168.0.?
1771: .Pp
1772: A
1773: .Em pattern-list
1774: is a comma-separated list of patterns.
1775: Patterns within pattern-lists may be negated
1776: by preceding them with an exclamation mark
1777: .Pq Sq !\& .
1778: For example,
1.174 djm 1779: to allow a key to be used from anywhere within an organization
1.86 jmc 1780: except from the
1.240 jmc 1781: .Qq dialup
1.86 jmc 1782: pool,
1783: the following entry (in authorized_keys) could be used:
1784: .Pp
1785: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1786: .Pp
1787: Note that a negated match will never produce a positive result by itself.
1788: For example, attempting to match
1789: .Qq host3
1790: against the following pattern-list will fail:
1791: .Pp
1792: .Dl from=\&"!host1,!host2\&"
1793: .Pp
1794: The solution here is to include a term that will yield a positive match,
1795: such as a wildcard:
1796: .Pp
1797: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1798: .Sh TOKENS
1799: Arguments to some keywords can make use of tokens,
1800: which are expanded at runtime:
1801: .Pp
1802: .Bl -tag -width XXXX -offset indent -compact
1803: .It %%
1804: A literal
1805: .Sq % .
1806: .It \&%C
1.257 jmc 1807: Hash of %l%h%p%r.
1.239 jmc 1808: .It %d
1809: Local user's home directory.
1810: .It %h
1811: The remote hostname.
1812: .It %i
1813: The local user ID.
1814: .It %L
1815: The local hostname.
1816: .It %l
1817: The local hostname, including the domain name.
1818: .It %n
1819: The original remote hostname, as given on the command line.
1820: .It %p
1821: The remote port.
1822: .It %r
1823: The remote username.
1.261 djm 1824: .It \&%T
1825: The local
1826: .Xr tun 4
1827: or
1828: .Xr tap 4
1829: network interface assigned if
1.262 jmc 1830: tunnel forwarding was requested, or
1831: .Qq NONE
1.261 djm 1832: otherwise.
1.239 jmc 1833: .It %u
1834: The local username.
1835: .El
1836: .Pp
1837: .Cm Match exec
1.274 djm 1838: accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1.239 jmc 1839: .Pp
1840: .Cm CertificateFile
1.275 jmc 1841: accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1842: .Pp
1843: .Cm ControlPath
1844: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1845: .Pp
1.295 jmc 1846: .Cm Hostname
1.239 jmc 1847: accepts the tokens %% and %h.
1848: .Pp
1849: .Cm IdentityAgent
1850: and
1851: .Cm IdentityFile
1.275 jmc 1852: accept the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1853: .Pp
1854: .Cm LocalCommand
1.275 jmc 1855: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T, and %u.
1.239 jmc 1856: .Pp
1857: .Cm ProxyCommand
1.303 djm 1858: accepts the tokens %%, %h, %n, %p, and %r.
1.250 jmc 1859: .Pp
1860: .Cm RemoteCommand
1.274 djm 1861: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and %u.
1.1 stevesk 1862: .Sh FILES
1863: .Bl -tag -width Ds
1.50 djm 1864: .It Pa ~/.ssh/config
1.1 stevesk 1865: This is the per-user configuration file.
1866: The format of this file is described above.
1.84 jmc 1867: This file is used by the SSH client.
1.30 djm 1868: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 1869: read/write for the user, and not writable by others.
1.1 stevesk 1870: .It Pa /etc/ssh/ssh_config
1871: Systemwide configuration file.
1872: This file provides defaults for those
1873: values that are not specified in the user's configuration file, and
1874: for those users who do not have a configuration file.
1875: This file must be world-readable.
1876: .El
1.13 jmc 1877: .Sh SEE ALSO
1878: .Xr ssh 1
1.1 stevesk 1879: .Sh AUTHORS
1.240 jmc 1880: .An -nosplit
1.1 stevesk 1881: OpenSSH is a derivative of the original and free
1.240 jmc 1882: ssh 1.2.12 release by
1883: .An Tatu Ylonen .
1884: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1885: .An Niels Provos , Theo de Raadt
1886: and
1887: .An Dug Song
1.1 stevesk 1888: removed many bugs, re-added newer features and
1889: created OpenSSH.
1.240 jmc 1890: .An Markus Friedl
1891: contributed the support for SSH protocol versions 1.5 and 2.0.