Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.326
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
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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
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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
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1.326 ! dtucker 36: .\" $OpenBSD: ssh_config.5,v 1.325 2020/04/11 20:20:09 jmc Exp $
! 37: .Dd $Mdocdate: April 11 2020 $
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 ,
1.318 djm 267: user interaction such as password prompts and host key confirmation requests
268: will be disabled.
1.1 stevesk 269: This option is useful in scripts and other batch jobs where no user
1.318 djm 270: is present to interact with
271: .Xr ssh 1 .
1.1 stevesk 272: The argument must be
1.240 jmc 273: .Cm yes
1.1 stevesk 274: or
1.240 jmc 275: .Cm no
276: (the default).
1.268 jmc 277: .It Cm BindAddress
278: Use the specified address on the local machine as the source address of
279: the connection.
280: Only useful on systems with more than one address.
281: .It Cm BindInterface
282: Use the address of the specified interface on the local machine as the
283: source address of the connection.
1.171 djm 284: .It Cm CanonicalDomains
1.172 jmc 285: When
1.173 djm 286: .Cm CanonicalizeHostname
1.171 djm 287: is enabled, this option specifies the list of domain suffixes in which to
288: search for the specified destination host.
1.173 djm 289: .It Cm CanonicalizeFallbackLocal
1.174 djm 290: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 291: The default,
1.240 jmc 292: .Cm yes ,
1.172 jmc 293: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 294: search rules.
295: A value of
1.240 jmc 296: .Cm no
1.171 djm 297: will cause
298: .Xr ssh 1
299: to fail instantly if
1.173 djm 300: .Cm CanonicalizeHostname
1.171 djm 301: is enabled and the target hostname cannot be found in any of the domains
302: specified by
303: .Cm CanonicalDomains .
1.173 djm 304: .It Cm CanonicalizeHostname
1.174 djm 305: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 306: The default,
1.240 jmc 307: .Cm no ,
1.171 djm 308: is not to perform any name rewriting and let the system resolver handle all
309: hostname lookups.
310: If set to
1.240 jmc 311: .Cm yes
1.171 djm 312: then, for connections that do not use a
1.284 djm 313: .Cm ProxyCommand
314: or
315: .Cm ProxyJump ,
1.171 djm 316: .Xr ssh 1
1.173 djm 317: will attempt to canonicalize the hostname specified on the command line
1.171 djm 318: using the
319: .Cm CanonicalDomains
320: suffixes and
1.173 djm 321: .Cm CanonicalizePermittedCNAMEs
1.171 djm 322: rules.
323: If
1.173 djm 324: .Cm CanonicalizeHostname
1.171 djm 325: is set to
1.240 jmc 326: .Cm always ,
1.174 djm 327: then canonicalization is applied to proxied connections too.
1.185 djm 328: .Pp
1.193 djm 329: If this option is enabled, then the configuration files are processed
330: again using the new target name to pick up any new configuration in matching
1.185 djm 331: .Cm Host
1.193 djm 332: and
333: .Cm Match
1.185 djm 334: stanzas.
1.173 djm 335: .It Cm CanonicalizeMaxDots
1.172 jmc 336: Specifies the maximum number of dot characters in a hostname before
1.174 djm 337: canonicalization is disabled.
1.240 jmc 338: The default, 1,
1.172 jmc 339: allows a single dot (i.e. hostname.subdomain).
1.173 djm 340: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 341: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 342: canonicalizing hostnames.
1.171 djm 343: The rules consist of one or more arguments of
1.172 jmc 344: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 345: where
346: .Ar source_domain_list
1.174 djm 347: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 348: and
349: .Ar target_domain_list
1.172 jmc 350: is a pattern-list of domains that they may resolve to.
1.171 djm 351: .Pp
352: For example,
1.240 jmc 353: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 354: will allow hostnames matching
1.240 jmc 355: .Qq *.a.example.com
1.173 djm 356: to be canonicalized to names in the
1.240 jmc 357: .Qq *.b.example.com
1.171 djm 358: or
1.240 jmc 359: .Qq *.c.example.com
1.171 djm 360: domains.
1.283 jmc 361: .It Cm CASignatureAlgorithms
362: Specifies which algorithms are allowed for signing of certificates
363: by certificate authorities (CAs).
364: The default is:
365: .Bd -literal -offset indent
1.297 djm 366: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.283 jmc 367: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
368: .Ed
369: .Pp
370: .Xr ssh 1
371: will not accept host certificates signed using algorithms other than those
372: specified.
1.221 djm 373: .It Cm CertificateFile
374: Specifies a file from which the user's certificate is read.
375: A corresponding private key must be provided separately in order
376: to use this certificate either
377: from an
378: .Cm IdentityFile
379: directive or
380: .Fl i
381: flag to
382: .Xr ssh 1 ,
383: via
384: .Xr ssh-agent 1 ,
385: or via a
1.305 naddy 386: .Cm PKCS11Provider
387: or
388: .Cm SecurityKeyProvider .
1.221 djm 389: .Pp
1.239 jmc 390: Arguments to
391: .Cm CertificateFile
1.326 ! dtucker 392: may use the tilde syntax to refer to a user's home directory,
! 393: the tokens described in the
1.239 jmc 394: .Sx TOKENS
1.326 ! dtucker 395: section and environment variables as described in the
! 396: .Sx ENVIRONMENT VARIABLES
1.239 jmc 397: section.
1.221 djm 398: .Pp
399: It is possible to have multiple certificate files specified in
400: configuration files; these certificates will be tried in sequence.
401: Multiple
402: .Cm CertificateFile
403: directives will add to the list of certificates used for
404: authentication.
1.1 stevesk 405: .It Cm ChallengeResponseAuthentication
1.82 jmc 406: Specifies whether to use challenge-response authentication.
1.1 stevesk 407: The argument to this keyword must be
1.240 jmc 408: .Cm yes
409: (the default)
1.1 stevesk 410: or
1.240 jmc 411: .Cm no .
1.1 stevesk 412: .It Cm CheckHostIP
1.240 jmc 413: If set to
414: .Cm yes
415: (the default),
1.84 jmc 416: .Xr ssh 1
417: will additionally check the host IP address in the
1.1 stevesk 418: .Pa known_hosts
419: file.
1.240 jmc 420: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 421: and will add addresses of destination hosts to
422: .Pa ~/.ssh/known_hosts
423: in the process, regardless of the setting of
424: .Cm StrictHostKeyChecking .
1.107 grunk 425: If the option is set to
1.240 jmc 426: .Cm no ,
1.1 stevesk 427: the check will not be executed.
428: .It Cm Ciphers
1.245 djm 429: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 430: Multiple ciphers must be comma-separated.
1.299 kn 431: If the specified list begins with a
1.214 djm 432: .Sq +
433: character, then the specified ciphers will be appended to the default set
434: instead of replacing them.
1.299 kn 435: If the specified list begins with a
1.241 djm 436: .Sq -
437: character, then the specified ciphers (including wildcards) will be removed
438: from the default set instead of replacing them.
1.301 naddy 439: If the specified list begins with a
440: .Sq ^
441: character, then the specified ciphers will be placed at the head of the
442: default set.
1.214 djm 443: .Pp
1.180 djm 444: The supported ciphers are:
1.240 jmc 445: .Bd -literal -offset indent
1.186 naddy 446: 3des-cbc
447: aes128-cbc
448: aes192-cbc
449: aes256-cbc
450: aes128-ctr
451: aes192-ctr
452: aes256-ctr
453: aes128-gcm@openssh.com
454: aes256-gcm@openssh.com
455: chacha20-poly1305@openssh.com
1.240 jmc 456: .Ed
1.180 djm 457: .Pp
1.84 jmc 458: The default is:
1.186 naddy 459: .Bd -literal -offset indent
1.215 jmc 460: chacha20-poly1305@openssh.com,
1.186 naddy 461: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 462: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 463: .Ed
1.180 djm 464: .Pp
1.240 jmc 465: The list of available ciphers may also be obtained using
466: .Qq ssh -Q cipher .
1.1 stevesk 467: .It Cm ClearAllForwardings
1.84 jmc 468: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 469: specified in the configuration files or on the command line be
1.7 jmc 470: cleared.
471: This option is primarily useful when used from the
1.84 jmc 472: .Xr ssh 1
1.1 stevesk 473: command line to clear port forwardings set in
474: configuration files, and is automatically set by
475: .Xr scp 1
476: and
477: .Xr sftp 1 .
478: The argument must be
1.240 jmc 479: .Cm yes
1.1 stevesk 480: or
1.240 jmc 481: .Cm no
482: (the default).
1.1 stevesk 483: .It Cm Compression
484: Specifies whether to use compression.
485: The argument must be
1.240 jmc 486: .Cm yes
1.1 stevesk 487: or
1.240 jmc 488: .Cm no
489: (the default).
1.247 naddy 490: .It Cm ConnectionAttempts
491: Specifies the number of tries (one per second) to make before exiting.
492: The argument must be an integer.
493: This may be useful in scripts if the connection sometimes fails.
494: The default is 1.
1.9 djm 495: .It Cm ConnectTimeout
1.84 jmc 496: Specifies the timeout (in seconds) used when connecting to the
497: SSH server, instead of using the default system TCP timeout.
1.302 djm 498: This timeout is applied both to establishing the connection and to performing
499: the initial SSH protocol handshake and key exchange.
1.36 djm 500: .It Cm ControlMaster
501: Enables the sharing of multiple sessions over a single network connection.
502: When set to
1.240 jmc 503: .Cm yes ,
1.84 jmc 504: .Xr ssh 1
1.36 djm 505: will listen for connections on a control socket specified using the
506: .Cm ControlPath
507: argument.
508: Additional sessions can connect to this socket using the same
509: .Cm ControlPath
510: with
511: .Cm ControlMaster
512: set to
1.240 jmc 513: .Cm no
1.38 jmc 514: (the default).
1.64 jmc 515: These sessions will try to reuse the master instance's network connection
1.63 djm 516: rather than initiating new ones, but will fall back to connecting normally
517: if the control socket does not exist, or is not listening.
518: .Pp
1.37 djm 519: Setting this to
1.240 jmc 520: .Cm ask
521: will cause
522: .Xr ssh 1
1.206 jmc 523: to listen for control connections, but require confirmation using
524: .Xr ssh-askpass 1 .
1.51 jakob 525: If the
526: .Cm ControlPath
1.84 jmc 527: cannot be opened,
1.240 jmc 528: .Xr ssh 1
529: will continue without connecting to a master instance.
1.58 djm 530: .Pp
531: X11 and
1.59 jmc 532: .Xr ssh-agent 1
1.58 djm 533: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 534: display and agent forwarded will be the one belonging to the master
1.59 jmc 535: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 536: .Pp
537: Two additional options allow for opportunistic multiplexing: try to use a
538: master connection but fall back to creating a new one if one does not already
539: exist.
540: These options are:
1.240 jmc 541: .Cm auto
1.56 djm 542: and
1.240 jmc 543: .Cm autoask .
1.56 djm 544: The latter requires confirmation like the
1.240 jmc 545: .Cm ask
1.56 djm 546: option.
1.36 djm 547: .It Cm ControlPath
1.55 djm 548: Specify the path to the control socket used for connection sharing as described
549: in the
1.36 djm 550: .Cm ControlMaster
1.57 djm 551: section above or the string
1.240 jmc 552: .Cm none
1.57 djm 553: to disable connection sharing.
1.239 jmc 554: Arguments to
555: .Cm ControlPath
1.326 ! dtucker 556: may use the tilde syntax to refer to a user's home directory,
! 557: the tokens described in the
1.239 jmc 558: .Sx TOKENS
1.326 ! dtucker 559: section and environment variables as described in the
! 560: .Sx ENVIRONMENT VARIABLES
1.239 jmc 561: section.
1.56 djm 562: It is recommended that any
563: .Cm ControlPath
564: used for opportunistic connection sharing include
1.195 djm 565: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
566: that is not writable by other users.
1.56 djm 567: This ensures that shared connections are uniquely identified.
1.137 djm 568: .It Cm ControlPersist
569: When used in conjunction with
570: .Cm ControlMaster ,
571: specifies that the master connection should remain open
572: in the background (waiting for future client connections)
573: after the initial client connection has been closed.
574: If set to
1.314 naddy 575: .Cm no
576: (the default),
1.137 djm 577: then the master connection will not be placed into the background,
578: and will close as soon as the initial client connection is closed.
579: If set to
1.240 jmc 580: .Cm yes
581: or 0,
1.137 djm 582: then the master connection will remain in the background indefinitely
583: (until killed or closed via a mechanism such as the
1.240 jmc 584: .Qq ssh -O exit ) .
1.137 djm 585: If set to a time in seconds, or a time in any of the formats documented in
586: .Xr sshd_config 5 ,
587: then the backgrounded master connection will automatically terminate
588: after it has remained idle (with no client connections) for the
589: specified time.
1.38 jmc 590: .It Cm DynamicForward
1.74 jmc 591: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 592: over the secure channel, and the application
593: protocol is then used to determine where to connect to from the
594: remote machine.
1.62 djm 595: .Pp
596: The argument must be
597: .Sm off
598: .Oo Ar bind_address : Oc Ar port .
599: .Sm on
1.138 djm 600: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 601: By default, the local port is bound in accordance with the
602: .Cm GatewayPorts
603: setting.
604: However, an explicit
605: .Ar bind_address
606: may be used to bind the connection to a specific address.
607: The
608: .Ar bind_address
609: of
1.240 jmc 610: .Cm localhost
1.62 djm 611: indicates that the listening port be bound for local use only, while an
612: empty address or
613: .Sq *
614: indicates that the port should be available from all interfaces.
615: .Pp
1.38 jmc 616: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 617: .Xr ssh 1
1.38 jmc 618: will act as a SOCKS server.
619: Multiple forwardings may be specified, and
620: additional forwardings can be given on the command line.
621: Only the superuser can forward privileged ports.
1.14 markus 622: .It Cm EnableSSHKeysign
623: Setting this option to
1.240 jmc 624: .Cm yes
1.14 markus 625: in the global client configuration file
626: .Pa /etc/ssh/ssh_config
627: enables the use of the helper program
628: .Xr ssh-keysign 8
629: during
630: .Cm HostbasedAuthentication .
631: The argument must be
1.240 jmc 632: .Cm yes
1.14 markus 633: or
1.240 jmc 634: .Cm no
635: (the default).
1.23 jmc 636: This option should be placed in the non-hostspecific section.
1.14 markus 637: See
638: .Xr ssh-keysign 8
639: for more information.
1.1 stevesk 640: .It Cm EscapeChar
641: Sets the escape character (default:
642: .Ql ~ ) .
643: The escape character can also
644: be set on the command line.
645: The argument should be a single character,
646: .Ql ^
647: followed by a letter, or
1.240 jmc 648: .Cm none
1.1 stevesk 649: to disable the escape
650: character entirely (making the connection transparent for binary
651: data).
1.96 markus 652: .It Cm ExitOnForwardFailure
653: Specifies whether
654: .Xr ssh 1
655: should terminate the connection if it cannot set up all requested
1.216 djm 656: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 657: if either end is unable to bind and listen on a specified port).
1.216 djm 658: Note that
659: .Cm ExitOnForwardFailure
660: does not apply to connections made over port forwardings and will not,
661: for example, cause
662: .Xr ssh 1
663: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 664: The argument must be
1.240 jmc 665: .Cm yes
1.96 markus 666: or
1.240 jmc 667: .Cm no
668: (the default).
1.197 djm 669: .It Cm FingerprintHash
670: Specifies the hash algorithm used when displaying key fingerprints.
671: Valid options are:
1.240 jmc 672: .Cm md5
1.197 djm 673: and
1.240 jmc 674: .Cm sha256
675: (the default).
1.1 stevesk 676: .It Cm ForwardAgent
677: Specifies whether the connection to the authentication agent (if any)
678: will be forwarded to the remote machine.
1.312 djm 679: The argument may be
680: .Cm yes ,
1.240 jmc 681: .Cm no
1.312 djm 682: (the default),
683: an explicit path to an agent socket or the name of an environment variable
684: (beginning with
685: .Sq $ )
686: in which to find the path.
1.3 stevesk 687: .Pp
1.7 jmc 688: Agent forwarding should be enabled with caution.
689: Users with the ability to bypass file permissions on the remote host
690: (for the agent's Unix-domain socket)
691: can access the local agent through the forwarded connection.
692: An attacker cannot obtain key material from the agent,
1.3 stevesk 693: however they can perform operations on the keys that enable them to
694: authenticate using the identities loaded into the agent.
1.1 stevesk 695: .It Cm ForwardX11
696: Specifies whether X11 connections will be automatically redirected
697: over the secure channel and
698: .Ev DISPLAY
699: set.
700: The argument must be
1.240 jmc 701: .Cm yes
1.1 stevesk 702: or
1.240 jmc 703: .Cm no
704: (the default).
1.3 stevesk 705: .Pp
1.7 jmc 706: X11 forwarding should be enabled with caution.
707: Users with the ability to bypass file permissions on the remote host
1.22 markus 708: (for the user's X11 authorization database)
1.7 jmc 709: can access the local X11 display through the forwarded connection.
1.22 markus 710: An attacker may then be able to perform activities such as keystroke monitoring
711: if the
712: .Cm ForwardX11Trusted
713: option is also enabled.
1.134 djm 714: .It Cm ForwardX11Timeout
1.135 jmc 715: Specify a timeout for untrusted X11 forwarding
716: using the format described in the
1.240 jmc 717: .Sx TIME FORMATS
718: section of
1.134 djm 719: .Xr sshd_config 5 .
720: X11 connections received by
721: .Xr ssh 1
722: after this time will be refused.
1.285 djm 723: Setting
724: .Cm ForwardX11Timeout
725: to zero will disable the timeout and permit X11 forwarding for the life
726: of the connection.
1.134 djm 727: The default is to disable untrusted X11 forwarding after twenty minutes has
728: elapsed.
1.22 markus 729: .It Cm ForwardX11Trusted
1.34 jmc 730: If this option is set to
1.240 jmc 731: .Cm yes ,
1.84 jmc 732: remote X11 clients will have full access to the original X11 display.
1.42 djm 733: .Pp
1.22 markus 734: If this option is set to
1.240 jmc 735: .Cm no
736: (the default),
1.84 jmc 737: remote X11 clients will be considered untrusted and prevented
1.22 markus 738: from stealing or tampering with data belonging to trusted X11
739: clients.
1.42 djm 740: Furthermore, the
741: .Xr xauth 1
742: token used for the session will be set to expire after 20 minutes.
743: Remote clients will be refused access after this time.
1.22 markus 744: .Pp
745: See the X11 SECURITY extension specification for full details on
746: the restrictions imposed on untrusted clients.
1.1 stevesk 747: .It Cm GatewayPorts
748: Specifies whether remote hosts are allowed to connect to local
749: forwarded ports.
750: By default,
1.84 jmc 751: .Xr ssh 1
1.7 jmc 752: binds local port forwardings to the loopback address.
753: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 754: .Cm GatewayPorts
1.84 jmc 755: can be used to specify that ssh
1.1 stevesk 756: should bind local port forwardings to the wildcard address,
757: thus allowing remote hosts to connect to forwarded ports.
758: The argument must be
1.240 jmc 759: .Cm yes
1.1 stevesk 760: or
1.240 jmc 761: .Cm no
762: (the default).
1.1 stevesk 763: .It Cm GlobalKnownHostsFile
1.151 djm 764: Specifies one or more files to use for the global
765: host key database, separated by whitespace.
766: The default is
767: .Pa /etc/ssh/ssh_known_hosts ,
768: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 769: .It Cm GSSAPIAuthentication
1.27 markus 770: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 771: The default is
1.240 jmc 772: .Cm no .
1.18 markus 773: .It Cm GSSAPIDelegateCredentials
774: Forward (delegate) credentials to the server.
775: The default is
1.240 jmc 776: .Cm no .
1.44 djm 777: .It Cm HashKnownHosts
778: Indicates that
1.84 jmc 779: .Xr ssh 1
1.44 djm 780: should hash host names and addresses when they are added to
1.50 djm 781: .Pa ~/.ssh/known_hosts .
1.44 djm 782: These hashed names may be used normally by
1.84 jmc 783: .Xr ssh 1
1.44 djm 784: and
1.84 jmc 785: .Xr sshd 8 ,
1.316 djm 786: but they do not visually reveal identifying information if the
787: file's contents are disclosed.
1.44 djm 788: The default is
1.240 jmc 789: .Cm no .
1.97 jmc 790: Note that existing names and addresses in known hosts files
791: will not be converted automatically,
792: but may be manually hashed using
1.45 djm 793: .Xr ssh-keygen 1 .
1.1 stevesk 794: .It Cm HostbasedAuthentication
795: Specifies whether to try rhosts based authentication with public key
796: authentication.
797: The argument must be
1.240 jmc 798: .Cm yes
1.1 stevesk 799: or
1.240 jmc 800: .Cm no
801: (the default).
1.202 djm 802: .It Cm HostbasedKeyTypes
803: Specifies the key types that will be used for hostbased authentication
1.279 djm 804: as a comma-separated list of patterns.
1.300 naddy 805: Alternately if the specified list begins with a
1.214 djm 806: .Sq +
807: character, then the specified key types will be appended to the default set
808: instead of replacing them.
1.300 naddy 809: If the specified list begins with a
1.241 djm 810: .Sq -
811: character, then the specified key types (including wildcards) will be removed
812: from the default set instead of replacing them.
1.301 naddy 813: If the specified list begins with a
814: .Sq ^
815: character, then the specified key types will be placed at the head of the
816: default set.
1.213 markus 817: The default for this option is:
818: .Bd -literal -offset 3n
819: ecdsa-sha2-nistp256-cert-v01@openssh.com,
820: ecdsa-sha2-nistp384-cert-v01@openssh.com,
821: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 822: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.213 markus 823: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 824: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 825: rsa-sha2-512-cert-v01@openssh.com,
826: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 827: ssh-rsa-cert-v01@openssh.com,
828: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 829: sk-ecdsa-sha2-nistp256@openssh.com,
830: ssh-ed25519,sk-ssh-ed25519@openssh.com,
831: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 832: .Ed
833: .Pp
1.202 djm 834: The
835: .Fl Q
836: option of
837: .Xr ssh 1
838: may be used to list supported key types.
1.1 stevesk 839: .It Cm HostKeyAlgorithms
1.226 jmc 840: Specifies the host key algorithms
1.1 stevesk 841: that the client wants to use in order of preference.
1.300 naddy 842: Alternately if the specified list begins with a
1.214 djm 843: .Sq +
844: character, then the specified key types will be appended to the default set
845: instead of replacing them.
1.300 naddy 846: If the specified list begins with a
1.241 djm 847: .Sq -
848: character, then the specified key types (including wildcards) will be removed
849: from the default set instead of replacing them.
1.301 naddy 850: If the specified list begins with a
851: .Sq ^
852: character, then the specified key types will be placed at the head of the
853: default set.
1.1 stevesk 854: The default for this option is:
1.139 djm 855: .Bd -literal -offset 3n
856: ecdsa-sha2-nistp256-cert-v01@openssh.com,
857: ecdsa-sha2-nistp384-cert-v01@openssh.com,
858: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 859: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.183 naddy 860: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 861: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 862: rsa-sha2-512-cert-v01@openssh.com,
863: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 864: ssh-rsa-cert-v01@openssh.com,
1.139 djm 865: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 866: sk-ecdsa-sha2-nistp256@openssh.com,
867: ssh-ed25519,sk-ssh-ed25519@openssh.com,
868: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 869: .Ed
1.145 djm 870: .Pp
871: If hostkeys are known for the destination host then this default is modified
872: to prefer their algorithms.
1.198 djm 873: .Pp
1.240 jmc 874: The list of available key types may also be obtained using
1.322 dtucker 875: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 876: .It Cm HostKeyAlias
877: Specifies an alias that should be used instead of the
878: real host name when looking up or saving the host key
1.251 djm 879: in the host key database files and when validating host certificates.
1.84 jmc 880: This option is useful for tunneling SSH connections
1.1 stevesk 881: or for multiple servers running on a single host.
1.295 jmc 882: .It Cm Hostname
1.1 stevesk 883: Specifies the real host name to log into.
884: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 885: Arguments to
1.295 jmc 886: .Cm Hostname
1.239 jmc 887: accept the tokens described in the
888: .Sx TOKENS
889: section.
1.1 stevesk 890: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 891: .Cm Hostname
1.1 stevesk 892: specifications).
1.239 jmc 893: The default is the name given on the command line.
1.29 markus 894: .It Cm IdentitiesOnly
895: Specifies that
1.84 jmc 896: .Xr ssh 1
1.304 djm 897: should only use the configured authentication identity and certificate files
898: (either the default files, or those explicitly configured in the
1.31 jmc 899: .Nm
1.221 djm 900: files
901: or passed on the
902: .Xr ssh 1
1.304 djm 903: command-line),
1.84 jmc 904: even if
905: .Xr ssh-agent 1
1.159 djm 906: or a
907: .Cm PKCS11Provider
1.305 naddy 908: or
909: .Cm SecurityKeyProvider
1.29 markus 910: offers more identities.
911: The argument to this keyword must be
1.240 jmc 912: .Cm yes
1.29 markus 913: or
1.240 jmc 914: .Cm no
915: (the default).
1.84 jmc 916: This option is intended for situations where ssh-agent
1.29 markus 917: offers many different identities.
1.231 markus 918: .It Cm IdentityAgent
919: Specifies the
920: .Ux Ns -domain
921: socket used to communicate with the authentication agent.
922: .Pp
923: This option overrides the
1.240 jmc 924: .Ev SSH_AUTH_SOCK
1.231 markus 925: environment variable and can be used to select a specific agent.
926: Setting the socket name to
1.240 jmc 927: .Cm none
1.231 markus 928: disables the use of an authentication agent.
1.232 markus 929: If the string
1.240 jmc 930: .Qq SSH_AUTH_SOCK
1.232 markus 931: is specified, the location of the socket will be read from the
932: .Ev SSH_AUTH_SOCK
933: environment variable.
1.286 djm 934: Otherwise if the specified value begins with a
935: .Sq $
936: character, then it will be treated as an environment variable containing
937: the location of the socket.
1.231 markus 938: .Pp
1.239 jmc 939: Arguments to
940: .Cm IdentityAgent
1.326 ! dtucker 941: may use the tilde syntax to refer to a user's home directory,
! 942: the tokens described in the
1.239 jmc 943: .Sx TOKENS
1.326 ! dtucker 944: section and environment variables as described in the
! 945: .Sx ENVIRONMENT VARIABLES
1.239 jmc 946: section.
1.67 jmc 947: .It Cm IdentityFile
1.313 naddy 948: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
949: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 950: The default is
1.139 djm 951: .Pa ~/.ssh/id_dsa ,
1.183 naddy 952: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 953: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 954: .Pa ~/.ssh/id_ed25519 ,
955: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 956: and
1.245 djm 957: .Pa ~/.ssh/id_rsa .
1.67 jmc 958: Additionally, any identities represented by the authentication agent
1.165 djm 959: will be used for authentication unless
960: .Cm IdentitiesOnly
961: is set.
1.221 djm 962: If no certificates have been explicitly specified by
963: .Cm CertificateFile ,
1.129 djm 964: .Xr ssh 1
965: will try to load certificate information from the filename obtained by
966: appending
967: .Pa -cert.pub
968: to the path of a specified
969: .Cm IdentityFile .
1.90 djm 970: .Pp
1.239 jmc 971: Arguments to
972: .Cm IdentityFile
973: may use the tilde syntax to refer to a user's home directory
974: or the tokens described in the
975: .Sx TOKENS
976: section.
1.90 djm 977: .Pp
1.67 jmc 978: It is possible to have
979: multiple identity files specified in configuration files; all these
980: identities will be tried in sequence.
1.152 djm 981: Multiple
982: .Cm IdentityFile
983: directives will add to the list of identities tried (this behaviour
984: differs from that of other configuration directives).
1.165 djm 985: .Pp
986: .Cm IdentityFile
987: may be used in conjunction with
988: .Cm IdentitiesOnly
989: to select which identities in an agent are offered during authentication.
1.221 djm 990: .Cm IdentityFile
991: may also be used in conjunction with
992: .Cm CertificateFile
993: in order to provide any certificate also needed for authentication with
994: the identity.
1.164 jmc 995: .It Cm IgnoreUnknown
996: Specifies a pattern-list of unknown options to be ignored if they are
997: encountered in configuration parsing.
998: This may be used to suppress errors if
999: .Nm
1000: contains options that are unrecognised by
1001: .Xr ssh 1 .
1002: It is recommended that
1003: .Cm IgnoreUnknown
1004: be listed early in the configuration file as it will not be applied
1005: to unknown options that appear before it.
1.229 djm 1006: .It Cm Include
1007: Include the specified configuration file(s).
1.230 jmc 1008: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1009: .Xr glob 7
1.229 djm 1010: wildcards and, for user configurations, shell-like
1.240 jmc 1011: .Sq ~
1.229 djm 1012: references to user home directories.
1013: Files without absolute paths are assumed to be in
1014: .Pa ~/.ssh
1.230 jmc 1015: if included in a user configuration file or
1.229 djm 1016: .Pa /etc/ssh
1017: if included from the system configuration file.
1018: .Cm Include
1019: directive may appear inside a
1020: .Cm Match
1021: or
1022: .Cm Host
1023: block
1024: to perform conditional inclusion.
1.143 djm 1025: .It Cm IPQoS
1026: Specifies the IPv4 type-of-service or DSCP class for connections.
1027: Accepted values are
1.240 jmc 1028: .Cm af11 ,
1029: .Cm af12 ,
1030: .Cm af13 ,
1031: .Cm af21 ,
1032: .Cm af22 ,
1033: .Cm af23 ,
1034: .Cm af31 ,
1035: .Cm af32 ,
1036: .Cm af33 ,
1037: .Cm af41 ,
1038: .Cm af42 ,
1039: .Cm af43 ,
1040: .Cm cs0 ,
1041: .Cm cs1 ,
1042: .Cm cs2 ,
1043: .Cm cs3 ,
1044: .Cm cs4 ,
1045: .Cm cs5 ,
1046: .Cm cs6 ,
1047: .Cm cs7 ,
1048: .Cm ef ,
1.319 djm 1049: .Cm le ,
1.240 jmc 1050: .Cm lowdelay ,
1051: .Cm throughput ,
1052: .Cm reliability ,
1.253 djm 1053: a numeric value, or
1054: .Cm none
1055: to use the operating system default.
1.146 djm 1056: This option may take one or two arguments, separated by whitespace.
1.143 djm 1057: If one argument is specified, it is used as the packet class unconditionally.
1058: If two values are specified, the first is automatically selected for
1059: interactive sessions and the second for non-interactive sessions.
1060: The default is
1.269 job 1061: .Cm af21
1.272 jmc 1062: (Low-Latency Data)
1.143 djm 1063: for interactive sessions and
1.269 job 1064: .Cm cs1
1.272 jmc 1065: (Lower Effort)
1.143 djm 1066: for non-interactive sessions.
1.103 djm 1067: .It Cm KbdInteractiveAuthentication
1068: Specifies whether to use keyboard-interactive authentication.
1069: The argument to this keyword must be
1.240 jmc 1070: .Cm yes
1071: (the default)
1.103 djm 1072: or
1.240 jmc 1073: .Cm no .
1.39 djm 1074: .It Cm KbdInteractiveDevices
1075: Specifies the list of methods to use in keyboard-interactive authentication.
1076: Multiple method names must be comma-separated.
1077: The default is to use the server specified list.
1.85 jmc 1078: The methods available vary depending on what the server supports.
1079: For an OpenSSH server,
1080: it may be zero or more of:
1.240 jmc 1081: .Cm bsdauth ,
1082: .Cm pam ,
1.85 jmc 1083: and
1.240 jmc 1084: .Cm skey .
1.140 djm 1085: .It Cm KexAlgorithms
1086: Specifies the available KEX (Key Exchange) algorithms.
1087: Multiple algorithms must be comma-separated.
1.299 kn 1088: If the specified list begins with a
1.214 djm 1089: .Sq +
1090: character, then the specified methods will be appended to the default set
1091: instead of replacing them.
1.299 kn 1092: If the specified list begins with a
1.241 djm 1093: .Sq -
1094: character, then the specified methods (including wildcards) will be removed
1095: from the default set instead of replacing them.
1.301 naddy 1096: If the specified list begins with a
1097: .Sq ^
1098: character, then the specified methods will be placed at the head of the
1099: default set.
1.141 jmc 1100: The default is:
1101: .Bd -literal -offset indent
1.238 djm 1102: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1103: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1104: diffie-hellman-group-exchange-sha256,
1.266 djm 1105: diffie-hellman-group16-sha512,
1106: diffie-hellman-group18-sha512,
1.317 tedu 1107: diffie-hellman-group14-sha256
1.141 jmc 1108: .Ed
1.198 djm 1109: .Pp
1.240 jmc 1110: The list of available key exchange algorithms may also be obtained using
1111: .Qq ssh -Q kex .
1.65 reyk 1112: .It Cm LocalCommand
1113: Specifies a command to execute on the local machine after successfully
1114: connecting to the server.
1115: The command string extends to the end of the line, and is executed with
1.105 jmc 1116: the user's shell.
1.239 jmc 1117: Arguments to
1118: .Cm LocalCommand
1119: accept the tokens described in the
1120: .Sx TOKENS
1121: section.
1.123 djm 1122: .Pp
1123: The command is run synchronously and does not have access to the
1124: session of the
1125: .Xr ssh 1
1126: that spawned it.
1127: It should not be used for interactive commands.
1128: .Pp
1.65 reyk 1129: This directive is ignored unless
1130: .Cm PermitLocalCommand
1131: has been enabled.
1.1 stevesk 1132: .It Cm LocalForward
1.74 jmc 1133: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1134: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1135: The first argument specifies the listener and may be
1.43 djm 1136: .Sm off
1.49 jmc 1137: .Oo Ar bind_address : Oc Ar port
1.43 djm 1138: .Sm on
1.324 dtucker 1139: or a Unix domain socket path.
1140: The second argument is the destination and may be
1141: .Ar host : Ns Ar hostport
1142: or a Unix domain socket path if the remote host supports it.
1143: .Pp
1.138 djm 1144: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1145: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1146: given on the command line.
1.1 stevesk 1147: Only the superuser can forward privileged ports.
1.43 djm 1148: By default, the local port is bound in accordance with the
1149: .Cm GatewayPorts
1150: setting.
1151: However, an explicit
1152: .Ar bind_address
1153: may be used to bind the connection to a specific address.
1154: The
1155: .Ar bind_address
1156: of
1.240 jmc 1157: .Cm localhost
1.46 jmc 1158: indicates that the listening port be bound for local use only, while an
1159: empty address or
1160: .Sq *
1.43 djm 1161: indicates that the port should be available from all interfaces.
1.326 ! dtucker 1162: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1163: .Sx TOKENS
1.326 ! dtucker 1164: section and environment variables as described in the
! 1165: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1166: section.
1.1 stevesk 1167: .It Cm LogLevel
1168: Gives the verbosity level that is used when logging messages from
1.84 jmc 1169: .Xr ssh 1 .
1.1 stevesk 1170: The possible values are:
1.84 jmc 1171: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1172: The default is INFO.
1173: DEBUG and DEBUG1 are equivalent.
1174: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1175: .It Cm MACs
1176: Specifies the MAC (message authentication code) algorithms
1177: in order of preference.
1.226 jmc 1178: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1179: Multiple algorithms must be comma-separated.
1.299 kn 1180: If the specified list begins with a
1.214 djm 1181: .Sq +
1182: character, then the specified algorithms will be appended to the default set
1183: instead of replacing them.
1.299 kn 1184: If the specified list begins with a
1.241 djm 1185: .Sq -
1186: character, then the specified algorithms (including wildcards) will be removed
1187: from the default set instead of replacing them.
1.301 naddy 1188: If the specified list begins with a
1189: .Sq ^
1190: character, then the specified algorithms will be placed at the head of the
1191: default set.
1.214 djm 1192: .Pp
1.160 markus 1193: The algorithms that contain
1.240 jmc 1194: .Qq -etm
1.160 markus 1195: calculate the MAC after encryption (encrypt-then-mac).
1196: These are considered safer and their use recommended.
1.214 djm 1197: .Pp
1.84 jmc 1198: The default is:
1.101 jmc 1199: .Bd -literal -offset indent
1.160 markus 1200: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1201: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1202: hmac-sha1-etm@openssh.com,
1.186 naddy 1203: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1204: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1205: .Ed
1.198 djm 1206: .Pp
1.240 jmc 1207: The list of available MAC algorithms may also be obtained using
1208: .Qq ssh -Q mac .
1.1 stevesk 1209: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1210: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1211: The argument to this keyword must be
1.240 jmc 1212: .Cm yes
1.1 stevesk 1213: or
1.242 jmc 1214: .Cm no
1.240 jmc 1215: (the default).
1.1 stevesk 1216: .It Cm NumberOfPasswordPrompts
1217: Specifies the number of password prompts before giving up.
1218: The argument to this keyword must be an integer.
1.84 jmc 1219: The default is 3.
1.1 stevesk 1220: .It Cm PasswordAuthentication
1221: Specifies whether to use password authentication.
1222: The argument to this keyword must be
1.240 jmc 1223: .Cm yes
1224: (the default)
1.1 stevesk 1225: or
1.240 jmc 1226: .Cm no .
1.65 reyk 1227: .It Cm PermitLocalCommand
1228: Allow local command execution via the
1229: .Ic LocalCommand
1230: option or using the
1.66 jmc 1231: .Ic !\& Ns Ar command
1.65 reyk 1232: escape sequence in
1233: .Xr ssh 1 .
1234: The argument must be
1.240 jmc 1235: .Cm yes
1.65 reyk 1236: or
1.240 jmc 1237: .Cm no
1238: (the default).
1.127 markus 1239: .It Cm PKCS11Provider
1.292 djm 1240: Specifies which PKCS#11 provider to use or
1241: .Cm none
1242: to indicate that no provider should be used (the default).
1243: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1244: .Xr ssh 1
1.292 djm 1245: should use to communicate with a PKCS#11 token providing keys for user
1246: authentication.
1.67 jmc 1247: .It Cm Port
1248: Specifies the port number to connect on the remote host.
1.84 jmc 1249: The default is 22.
1.1 stevesk 1250: .It Cm PreferredAuthentications
1.226 jmc 1251: Specifies the order in which the client should try authentication methods.
1.48 jmc 1252: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1253: .Cm keyboard-interactive )
1.48 jmc 1254: over another method (e.g.\&
1.131 jmc 1255: .Cm password ) .
1256: The default is:
1257: .Bd -literal -offset indent
1258: gssapi-with-mic,hostbased,publickey,
1259: keyboard-interactive,password
1260: .Ed
1.1 stevesk 1261: .It Cm ProxyCommand
1262: Specifies the command to use to connect to the server.
1263: The command
1.190 djm 1264: string extends to the end of the line, and is executed
1265: using the user's shell
1266: .Ql exec
1267: directive to avoid a lingering shell process.
1268: .Pp
1.239 jmc 1269: Arguments to
1270: .Cm ProxyCommand
1271: accept the tokens described in the
1272: .Sx TOKENS
1273: section.
1.1 stevesk 1274: The command can be basically anything,
1275: and should read from its standard input and write to its standard output.
1276: It should eventually connect an
1277: .Xr sshd 8
1278: server running on some machine, or execute
1279: .Ic sshd -i
1280: somewhere.
1281: Host key management will be done using the
1.296 jmc 1282: .Cm Hostname
1283: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1284: Setting the command to
1.240 jmc 1285: .Cm none
1.6 markus 1286: disables this option entirely.
1.1 stevesk 1287: Note that
1288: .Cm CheckHostIP
1289: is not available for connects with a proxy command.
1.52 djm 1290: .Pp
1291: This directive is useful in conjunction with
1292: .Xr nc 1
1293: and its proxy support.
1.53 jmc 1294: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1295: 192.0.2.0:
1296: .Bd -literal -offset 3n
1297: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1298: .Ed
1.233 djm 1299: .It Cm ProxyJump
1.260 millert 1300: Specifies one or more jump proxies as either
1.233 djm 1301: .Xo
1302: .Sm off
1.234 jmc 1303: .Op Ar user No @
1.233 djm 1304: .Ar host
1.234 jmc 1305: .Op : Ns Ar port
1.233 djm 1306: .Sm on
1.260 millert 1307: or an ssh URI
1.233 djm 1308: .Xc .
1.235 djm 1309: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1310: sequentially.
1.233 djm 1311: Setting this option will cause
1312: .Xr ssh 1
1313: to connect to the target host by first making a
1314: .Xr ssh 1
1315: connection to the specified
1316: .Cm ProxyJump
1317: host and then establishing a
1.234 jmc 1318: TCP forwarding to the ultimate target from there.
1.233 djm 1319: .Pp
1320: Note that this option will compete with the
1321: .Cm ProxyCommand
1322: option - whichever is specified first will prevent later instances of the
1323: other from taking effect.
1.289 djm 1324: .Pp
1325: Note also that the configuration for the destination host (either supplied
1326: via the command-line or the configuration file) is not generally applied
1327: to jump hosts.
1328: .Pa ~/.ssh/config
1329: should be used if specific configuration is required for jump hosts.
1.167 djm 1330: .It Cm ProxyUseFdpass
1.168 jmc 1331: Specifies that
1.167 djm 1332: .Cm ProxyCommand
1333: will pass a connected file descriptor back to
1.168 jmc 1334: .Xr ssh 1
1.167 djm 1335: instead of continuing to execute and pass data.
1336: The default is
1.240 jmc 1337: .Cm no .
1.213 markus 1338: .It Cm PubkeyAcceptedKeyTypes
1339: Specifies the key types that will be used for public key authentication
1.279 djm 1340: as a comma-separated list of patterns.
1.299 kn 1341: If the specified list begins with a
1.214 djm 1342: .Sq +
1343: character, then the key types after it will be appended to the default
1344: instead of replacing it.
1.299 kn 1345: If the specified list begins with a
1.241 djm 1346: .Sq -
1347: character, then the specified key types (including wildcards) will be removed
1348: from the default set instead of replacing them.
1.301 naddy 1349: If the specified list begins with a
1350: .Sq ^
1351: character, then the specified key types will be placed at the head of the
1352: default set.
1.213 markus 1353: The default for this option is:
1354: .Bd -literal -offset 3n
1355: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1356: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1357: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 1358: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1359: ssh-ed25519-cert-v01@openssh.com,
1.307 djm 1360: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 1361: rsa-sha2-512-cert-v01@openssh.com,
1362: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1363: ssh-rsa-cert-v01@openssh.com,
1.311 naddy 1364: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.305 naddy 1365: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1366: ssh-ed25519,sk-ssh-ed25519@openssh.com,
1367: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1368: .Ed
1369: .Pp
1.240 jmc 1370: The list of available key types may also be obtained using
1.322 dtucker 1371: .Qq ssh -Q PubkeyAcceptedKeyTypes .
1.1 stevesk 1372: .It Cm PubkeyAuthentication
1373: Specifies whether to try public key authentication.
1374: The argument to this keyword must be
1.240 jmc 1375: .Cm yes
1376: (the default)
1.1 stevesk 1377: or
1.240 jmc 1378: .Cm no .
1.75 dtucker 1379: .It Cm RekeyLimit
1380: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1381: session key is renegotiated, optionally followed a maximum amount of
1382: time that may pass before the session key is renegotiated.
1383: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1384: .Sq K ,
1385: .Sq M ,
1.75 dtucker 1386: or
1.76 jmc 1387: .Sq G
1.75 dtucker 1388: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1389: The default is between
1.84 jmc 1390: .Sq 1G
1.75 dtucker 1391: and
1.84 jmc 1392: .Sq 4G ,
1.75 dtucker 1393: depending on the cipher.
1.162 dtucker 1394: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1395: units documented in the TIME FORMATS section of
1.162 dtucker 1396: .Xr sshd_config 5 .
1397: The default value for
1398: .Cm RekeyLimit
1399: is
1.240 jmc 1400: .Cm default none ,
1.162 dtucker 1401: which means that rekeying is performed after the cipher's default amount
1402: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1403: .It Cm RemoteCommand
1404: Specifies a command to execute on the remote machine after successfully
1405: connecting to the server.
1406: The command string extends to the end of the line, and is executed with
1407: the user's shell.
1.250 jmc 1408: Arguments to
1409: .Cm RemoteCommand
1410: accept the tokens described in the
1411: .Sx TOKENS
1412: section.
1.1 stevesk 1413: .It Cm RemoteForward
1.74 jmc 1414: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1415: the secure channel.
1.273 djm 1416: The remote port may either be forwarded to a specified host and port
1.256 markus 1417: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1418: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1419: The first argument is the listening specification and may be
1.43 djm 1420: .Sm off
1.49 jmc 1421: .Oo Ar bind_address : Oc Ar port
1.43 djm 1422: .Sm on
1.324 dtucker 1423: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1424: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1425: .Ar host : Ns Ar hostport
1426: or a Unix domain socket path,
1.256 markus 1427: otherwise if no destination argument is specified then the remote forwarding
1428: will be established as a SOCKS proxy.
1429: .Pp
1.138 djm 1430: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1431: Multiple forwardings may be specified, and additional
1432: forwardings can be given on the command line.
1.113 stevesk 1433: Privileged ports can be forwarded only when
1434: logging in as root on the remote machine.
1.326 ! dtucker 1435: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1436: .Sx TOKENS
1.326 ! dtucker 1437: section and environment variables as described in the
! 1438: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1439: section.
1.118 jmc 1440: .Pp
1.117 djm 1441: If the
1442: .Ar port
1.240 jmc 1443: argument is 0,
1.117 djm 1444: the listen port will be dynamically allocated on the server and reported
1445: to the client at run time.
1.43 djm 1446: .Pp
1447: If the
1448: .Ar bind_address
1449: is not specified, the default is to only bind to loopback addresses.
1450: If the
1451: .Ar bind_address
1452: is
1453: .Ql *
1454: or an empty string, then the forwarding is requested to listen on all
1455: interfaces.
1456: Specifying a remote
1457: .Ar bind_address
1.46 jmc 1458: will only succeed if the server's
1459: .Cm GatewayPorts
1.43 djm 1460: option is enabled (see
1.46 jmc 1461: .Xr sshd_config 5 ) .
1.149 djm 1462: .It Cm RequestTTY
1463: Specifies whether to request a pseudo-tty for the session.
1464: The argument may be one of:
1.240 jmc 1465: .Cm no
1.149 djm 1466: (never request a TTY),
1.240 jmc 1467: .Cm yes
1.149 djm 1468: (always request a TTY when standard input is a TTY),
1.240 jmc 1469: .Cm force
1.149 djm 1470: (always request a TTY) or
1.240 jmc 1471: .Cm auto
1.149 djm 1472: (request a TTY when opening a login session).
1473: This option mirrors the
1474: .Fl t
1475: and
1476: .Fl T
1477: flags for
1478: .Xr ssh 1 .
1.196 djm 1479: .It Cm RevokedHostKeys
1480: Specifies revoked host public keys.
1481: Keys listed in this file will be refused for host authentication.
1482: Note that if this file does not exist or is not readable,
1483: then host authentication will be refused for all hosts.
1484: Keys may be specified as a text file, listing one public key per line, or as
1485: an OpenSSH Key Revocation List (KRL) as generated by
1486: .Xr ssh-keygen 1 .
1487: For more information on KRLs, see the KEY REVOCATION LISTS section in
1488: .Xr ssh-keygen 1 .
1.305 naddy 1489: .It Cm SecurityKeyProvider
1.313 naddy 1490: Specifies a path to a library that will be used when loading any
1491: FIDO authenticator-hosted keys, overriding the default of using
1492: the built-in USB HID support.
1.309 naddy 1493: .Pp
1494: If the specified value begins with a
1495: .Sq $
1496: character, then it will be treated as an environment variable containing
1497: the path to the library.
1.32 djm 1498: .It Cm SendEnv
1499: Specifies what variables from the local
1500: .Xr environ 7
1501: should be sent to the server.
1.84 jmc 1502: The server must also support it, and the server must be configured to
1.33 djm 1503: accept these environment variables.
1.207 dtucker 1504: Note that the
1505: .Ev TERM
1.208 jmc 1506: environment variable is always sent whenever a
1.207 dtucker 1507: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1508: Refer to
1509: .Cm AcceptEnv
1510: in
1511: .Xr sshd_config 5
1512: for how to configure the server.
1.80 jmc 1513: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1514: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1515: across multiple
1516: .Cm SendEnv
1517: directives.
1.81 jmc 1518: .Pp
1519: See
1520: .Sx PATTERNS
1521: for more information on patterns.
1.271 djm 1522: .Pp
1.272 jmc 1523: It is possible to clear previously set
1.271 djm 1524: .Cm SendEnv
1525: variable names by prefixing patterns with
1526: .Pa - .
1527: The default is not to send any environment variables.
1.28 markus 1528: .It Cm ServerAliveCountMax
1.73 jmc 1529: Sets the number of server alive messages (see below) which may be
1.28 markus 1530: sent without
1.84 jmc 1531: .Xr ssh 1
1.28 markus 1532: receiving any messages back from the server.
1533: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1534: ssh will disconnect from the server, terminating the session.
1.28 markus 1535: It is important to note that the use of server alive messages is very
1536: different from
1537: .Cm TCPKeepAlive
1538: (below).
1539: The server alive messages are sent through the encrypted channel
1540: and therefore will not be spoofable.
1541: The TCP keepalive option enabled by
1542: .Cm TCPKeepAlive
1543: is spoofable.
1544: The server alive mechanism is valuable when the client or
1.298 dtucker 1545: server depend on knowing when a connection has become unresponsive.
1.28 markus 1546: .Pp
1547: The default value is 3.
1548: If, for example,
1549: .Cm ServerAliveInterval
1.84 jmc 1550: (see below) is set to 15 and
1.28 markus 1551: .Cm ServerAliveCountMax
1.84 jmc 1552: is left at the default, if the server becomes unresponsive,
1553: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1554: .It Cm ServerAliveInterval
1555: Sets a timeout interval in seconds after which if no data has been received
1556: from the server,
1.84 jmc 1557: .Xr ssh 1
1.67 jmc 1558: will send a message through the encrypted
1559: channel to request a response from the server.
1560: The default
1561: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1562: .It Cm SetEnv
1563: Directly specify one or more environment variables and their contents to
1564: be sent to the server.
1565: Similarly to
1566: .Cm SendEnv ,
1567: the server must be prepared to accept the environment variable.
1.191 millert 1568: .It Cm StreamLocalBindMask
1569: Sets the octal file creation mode mask
1570: .Pq umask
1571: used when creating a Unix-domain socket file for local or remote
1572: port forwarding.
1573: This option is only used for port forwarding to a Unix-domain socket file.
1574: .Pp
1575: The default value is 0177, which creates a Unix-domain socket file that is
1576: readable and writable only by the owner.
1577: Note that not all operating systems honor the file mode on Unix-domain
1578: socket files.
1579: .It Cm StreamLocalBindUnlink
1580: Specifies whether to remove an existing Unix-domain socket file for local
1581: or remote port forwarding before creating a new one.
1582: If the socket file already exists and
1583: .Cm StreamLocalBindUnlink
1584: is not enabled,
1585: .Nm ssh
1586: will be unable to forward the port to the Unix-domain socket file.
1587: This option is only used for port forwarding to a Unix-domain socket file.
1588: .Pp
1589: The argument must be
1.240 jmc 1590: .Cm yes
1.191 millert 1591: or
1.240 jmc 1592: .Cm no
1593: (the default).
1.1 stevesk 1594: .It Cm StrictHostKeyChecking
1595: If this flag is set to
1.240 jmc 1596: .Cm yes ,
1.84 jmc 1597: .Xr ssh 1
1.1 stevesk 1598: will never automatically add host keys to the
1.50 djm 1599: .Pa ~/.ssh/known_hosts
1.1 stevesk 1600: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1601: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1602: though it can be annoying when the
1.1 stevesk 1603: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1604: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1605: frequently made.
1606: This option forces the user to manually
1607: add all new hosts.
1.255 jmc 1608: .Pp
1.1 stevesk 1609: If this flag is set to
1.254 djm 1610: .Dq accept-new
1.255 jmc 1611: then ssh will automatically add new host keys to the user
1.254 djm 1612: known hosts files, but will not permit connections to hosts with
1613: changed host keys.
1614: If this flag is set to
1615: .Dq no
1616: or
1617: .Dq off ,
1.255 jmc 1618: ssh will automatically add new host keys to the user known hosts files
1619: and allow connections to hosts with changed hostkeys to proceed,
1620: subject to some restrictions.
1.1 stevesk 1621: If this flag is set to
1.240 jmc 1622: .Cm ask
1623: (the default),
1.1 stevesk 1624: new host keys
1625: will be added to the user known host files only after the user
1626: has confirmed that is what they really want to do, and
1.84 jmc 1627: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1628: The host keys of
1629: known hosts will be verified automatically in all cases.
1.244 jmc 1630: .It Cm SyslogFacility
1631: Gives the facility code that is used when logging messages from
1632: .Xr ssh 1 .
1633: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1634: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1635: The default is USER.
1.26 markus 1636: .It Cm TCPKeepAlive
1637: Specifies whether the system should send TCP keepalive messages to the
1638: other side.
1639: If they are sent, death of the connection or crash of one
1640: of the machines will be properly noticed.
1641: However, this means that
1642: connections will die if the route is down temporarily, and some people
1643: find it annoying.
1644: .Pp
1645: The default is
1.240 jmc 1646: .Cm yes
1.26 markus 1647: (to send TCP keepalive messages), and the client will notice
1648: if the network goes down or the remote host dies.
1649: This is important in scripts, and many users want it too.
1650: .Pp
1651: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1652: .Cm no .
1.265 djm 1653: See also
1654: .Cm ServerAliveInterval
1655: for protocol-level keepalives.
1.65 reyk 1656: .It Cm Tunnel
1.95 stevesk 1657: Request
1.65 reyk 1658: .Xr tun 4
1.69 jmc 1659: device forwarding between the client and the server.
1.65 reyk 1660: The argument must be
1.240 jmc 1661: .Cm yes ,
1662: .Cm point-to-point
1.95 stevesk 1663: (layer 3),
1.240 jmc 1664: .Cm ethernet
1.95 stevesk 1665: (layer 2),
1.65 reyk 1666: or
1.240 jmc 1667: .Cm no
1668: (the default).
1.95 stevesk 1669: Specifying
1.240 jmc 1670: .Cm yes
1.95 stevesk 1671: requests the default tunnel mode, which is
1.240 jmc 1672: .Cm point-to-point .
1.65 reyk 1673: .It Cm TunnelDevice
1.95 stevesk 1674: Specifies the
1.65 reyk 1675: .Xr tun 4
1.95 stevesk 1676: devices to open on the client
1677: .Pq Ar local_tun
1678: and the server
1679: .Pq Ar remote_tun .
1680: .Pp
1681: The argument must be
1682: .Sm off
1683: .Ar local_tun Op : Ar remote_tun .
1684: .Sm on
1685: The devices may be specified by numerical ID or the keyword
1.240 jmc 1686: .Cm any ,
1.95 stevesk 1687: which uses the next available tunnel device.
1688: If
1689: .Ar remote_tun
1690: is not specified, it defaults to
1.240 jmc 1691: .Cm any .
1.95 stevesk 1692: The default is
1.240 jmc 1693: .Cm any:any .
1.201 djm 1694: .It Cm UpdateHostKeys
1.200 djm 1695: Specifies whether
1696: .Xr ssh 1
1697: should accept notifications of additional hostkeys from the server sent
1698: after authentication has completed and add them to
1699: .Cm UserKnownHostsFile .
1700: The argument must be
1.240 jmc 1701: .Cm yes ,
1702: .Cm no
1.320 djm 1703: or
1.240 jmc 1704: .Cm ask .
1.320 djm 1705: This option allows learning alternate hostkeys for a server
1.201 djm 1706: and supports graceful key rotation by allowing a server to send replacement
1707: public keys before old ones are removed.
1.200 djm 1708: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1709: host was already trusted or explicitly accepted by the user.
1.320 djm 1710: .Pp
1711: .Cm UpdateHostKeys
1.321 jmc 1712: is enabled by default if the user has not overridden the default
1.320 djm 1713: .Cm UserKnownHostsFile
1714: setting, otherwise
1715: .Cm UpdateHostKeys
1716: will be set to
1717: .Cm ask .
1718: .Pp
1.204 djm 1719: If
1720: .Cm UpdateHostKeys
1721: is set to
1.240 jmc 1722: .Cm ask ,
1.204 djm 1723: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1724: Confirmation is currently incompatible with
1725: .Cm ControlPersist ,
1726: and will be disabled if it is enabled.
1.200 djm 1727: .Pp
1728: Presently, only
1729: .Xr sshd 8
1730: from OpenSSH 6.8 and greater support the
1.240 jmc 1731: .Qq hostkeys@openssh.com
1.200 djm 1732: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1733: .It Cm User
1734: Specifies the user to log in as.
1735: This can be useful when a different user name is used on different machines.
1736: This saves the trouble of
1737: having to remember to give the user name on the command line.
1738: .It Cm UserKnownHostsFile
1.151 djm 1739: Specifies one or more files to use for the user
1740: host key database, separated by whitespace.
1741: The default is
1742: .Pa ~/.ssh/known_hosts ,
1743: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1744: .It Cm VerifyHostKeyDNS
1745: Specifies whether to verify the remote key using DNS and SSHFP resource
1746: records.
1.24 jakob 1747: If this option is set to
1.240 jmc 1748: .Cm yes ,
1.25 jmc 1749: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1750: from DNS.
1751: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1752: .Cm ask .
1.24 jakob 1753: If this option is set to
1.240 jmc 1754: .Cm ask ,
1.24 jakob 1755: information on fingerprint match will be displayed, but the user will still
1756: need to confirm new host keys according to the
1757: .Cm StrictHostKeyChecking
1758: option.
1.8 jakob 1759: The default is
1.240 jmc 1760: .Cm no .
1.84 jmc 1761: .Pp
1.240 jmc 1762: See also
1763: .Sx VERIFYING HOST KEYS
1764: in
1.84 jmc 1765: .Xr ssh 1 .
1.111 grunk 1766: .It Cm VisualHostKey
1767: If this flag is set to
1.240 jmc 1768: .Cm yes ,
1.111 grunk 1769: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1770: printed in addition to the fingerprint string at login and
1.114 stevesk 1771: for unknown host keys.
1.111 grunk 1772: If this flag is set to
1.240 jmc 1773: .Cm no
1774: (the default),
1.114 stevesk 1775: no fingerprint strings are printed at login and
1.197 djm 1776: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1777: .It Cm XAuthLocation
1.5 stevesk 1778: Specifies the full pathname of the
1.1 stevesk 1779: .Xr xauth 1
1780: program.
1781: The default is
1782: .Pa /usr/X11R6/bin/xauth .
1783: .El
1.86 jmc 1784: .Sh PATTERNS
1785: A
1786: .Em pattern
1787: consists of zero or more non-whitespace characters,
1788: .Sq *
1789: (a wildcard that matches zero or more characters),
1790: or
1791: .Sq ?\&
1792: (a wildcard that matches exactly one character).
1793: For example, to specify a set of declarations for any host in the
1.240 jmc 1794: .Qq .co.uk
1.86 jmc 1795: set of domains,
1796: the following pattern could be used:
1797: .Pp
1798: .Dl Host *.co.uk
1799: .Pp
1800: The following pattern
1801: would match any host in the 192.168.0.[0-9] network range:
1802: .Pp
1803: .Dl Host 192.168.0.?
1804: .Pp
1805: A
1806: .Em pattern-list
1807: is a comma-separated list of patterns.
1808: Patterns within pattern-lists may be negated
1809: by preceding them with an exclamation mark
1810: .Pq Sq !\& .
1811: For example,
1.174 djm 1812: to allow a key to be used from anywhere within an organization
1.86 jmc 1813: except from the
1.240 jmc 1814: .Qq dialup
1.86 jmc 1815: pool,
1816: the following entry (in authorized_keys) could be used:
1817: .Pp
1818: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1819: .Pp
1820: Note that a negated match will never produce a positive result by itself.
1821: For example, attempting to match
1822: .Qq host3
1823: against the following pattern-list will fail:
1824: .Pp
1825: .Dl from=\&"!host1,!host2\&"
1826: .Pp
1827: The solution here is to include a term that will yield a positive match,
1828: such as a wildcard:
1829: .Pp
1830: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1831: .Sh TOKENS
1832: Arguments to some keywords can make use of tokens,
1833: which are expanded at runtime:
1834: .Pp
1835: .Bl -tag -width XXXX -offset indent -compact
1836: .It %%
1837: A literal
1838: .Sq % .
1839: .It \&%C
1.257 jmc 1840: Hash of %l%h%p%r.
1.239 jmc 1841: .It %d
1842: Local user's home directory.
1843: .It %h
1844: The remote hostname.
1845: .It %i
1846: The local user ID.
1847: .It %L
1848: The local hostname.
1849: .It %l
1850: The local hostname, including the domain name.
1851: .It %n
1852: The original remote hostname, as given on the command line.
1853: .It %p
1854: The remote port.
1855: .It %r
1856: The remote username.
1.261 djm 1857: .It \&%T
1858: The local
1859: .Xr tun 4
1860: or
1861: .Xr tap 4
1862: network interface assigned if
1.262 jmc 1863: tunnel forwarding was requested, or
1864: .Qq NONE
1.261 djm 1865: otherwise.
1.239 jmc 1866: .It %u
1867: The local username.
1868: .El
1869: .Pp
1.323 dtucker 1870: .Cm CertificateFile ,
1871: .Cm ControlPath ,
1872: .Cm IdentityAgent ,
1873: .Cm IdentityFile ,
1.325 jmc 1874: .Cm LocalForward ,
1.324 dtucker 1875: .Cm Match exec ,
1876: .Cm RemoteCommand ,
1.323 dtucker 1877: and
1.324 dtucker 1878: .Cm RemoteForward
1.323 dtucker 1879: accept the tokens %%, %C, %d, %h, %i, %L, %l, %n, %p, %r, and %u.
1.239 jmc 1880: .Pp
1.295 jmc 1881: .Cm Hostname
1.239 jmc 1882: accepts the tokens %% and %h.
1883: .Pp
1884: .Cm LocalCommand
1.323 dtucker 1885: accepts all tokens.
1.239 jmc 1886: .Pp
1887: .Cm ProxyCommand
1.303 djm 1888: accepts the tokens %%, %h, %n, %p, and %r.
1.326 ! dtucker 1889: .Sh ENVIRONMENT VARIABLES
! 1890: Arguments to some keywords can be expanded at runtime from environment
! 1891: variables on the client by enclosing them in
! 1892: .Ic ${} ,
! 1893: for example
! 1894: .Ic ${HOME}/.ssh
! 1895: would refer to the user's .ssh directory.
! 1896: If a specified environment variable does not exist then an error will be
! 1897: returned and the setting for that keyword will be ignored.
! 1898: .Pp
! 1899: The keywords
! 1900: .El
! 1901: .Cm CertificateFile ,
! 1902: .Cm ControlPath ,
! 1903: .Cm IdentityAgent
! 1904: and
! 1905: .Cm IdentityFile
! 1906: support environment variables.
! 1907: The keywords
! 1908: .Cm LocalForward
! 1909: and
! 1910: .Cm RemoteForward
! 1911: support environment variables only for Unix domain socket paths.
1.1 stevesk 1912: .Sh FILES
1913: .Bl -tag -width Ds
1.50 djm 1914: .It Pa ~/.ssh/config
1.1 stevesk 1915: This is the per-user configuration file.
1916: The format of this file is described above.
1.84 jmc 1917: This file is used by the SSH client.
1.30 djm 1918: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 1919: read/write for the user, and not writable by others.
1.1 stevesk 1920: .It Pa /etc/ssh/ssh_config
1921: Systemwide configuration file.
1922: This file provides defaults for those
1923: values that are not specified in the user's configuration file, and
1924: for those users who do not have a configuration file.
1925: This file must be world-readable.
1926: .El
1.13 jmc 1927: .Sh SEE ALSO
1928: .Xr ssh 1
1.1 stevesk 1929: .Sh AUTHORS
1.240 jmc 1930: .An -nosplit
1.1 stevesk 1931: OpenSSH is a derivative of the original and free
1.240 jmc 1932: ssh 1.2.12 release by
1933: .An Tatu Ylonen .
1934: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1935: .An Niels Provos , Theo de Raadt
1936: and
1937: .An Dug Song
1.1 stevesk 1938: removed many bugs, re-added newer features and
1939: created OpenSSH.
1.240 jmc 1940: .An Markus Friedl
1941: contributed the support for SSH protocol versions 1.5 and 2.0.
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