Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.351
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
23: .\" documentation and/or other materials provided with the distribution.
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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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1.351 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.350 2021/03/12 05:18:01 jsg Exp $
! 37: .Dd $Mdocdate: March 12 2021 $
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.
1.332 djm 248: Alternately, this option may be specified as a time interval
249: using the format described in the
250: .Sx TIME FORMATS
251: section of
252: .Xr sshd_config 5
253: to specify the key's lifetime in
254: .Xr ssh-agent 1 ,
255: after which it will automatically be removed.
1.222 jcs 256: The argument must be
1.332 djm 257: .Cm no
258: (the default),
1.240 jmc 259: .Cm yes ,
1.332 djm 260: .Cm confirm
261: (optionally followed by a time interval),
262: .Cm ask
263: or a time interval.
1.10 djm 264: .It Cm AddressFamily
1.11 jmc 265: Specifies which address family to use when connecting.
266: Valid arguments are
1.240 jmc 267: .Cm any
268: (the default),
269: .Cm inet
1.84 jmc 270: (use IPv4 only), or
1.240 jmc 271: .Cm inet6
1.40 jmc 272: (use IPv6 only).
1.1 stevesk 273: .It Cm BatchMode
274: If set to
1.240 jmc 275: .Cm yes ,
1.318 djm 276: user interaction such as password prompts and host key confirmation requests
277: will be disabled.
1.1 stevesk 278: This option is useful in scripts and other batch jobs where no user
1.318 djm 279: is present to interact with
280: .Xr ssh 1 .
1.1 stevesk 281: The argument must be
1.240 jmc 282: .Cm yes
1.1 stevesk 283: or
1.240 jmc 284: .Cm no
285: (the default).
1.268 jmc 286: .It Cm BindAddress
287: Use the specified address on the local machine as the source address of
288: the connection.
289: Only useful on systems with more than one address.
290: .It Cm BindInterface
291: Use the address of the specified interface on the local machine as the
292: source address of the connection.
1.171 djm 293: .It Cm CanonicalDomains
1.172 jmc 294: When
1.173 djm 295: .Cm CanonicalizeHostname
1.171 djm 296: is enabled, this option specifies the list of domain suffixes in which to
297: search for the specified destination host.
1.173 djm 298: .It Cm CanonicalizeFallbackLocal
1.174 djm 299: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 300: The default,
1.240 jmc 301: .Cm yes ,
1.172 jmc 302: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 303: search rules.
304: A value of
1.240 jmc 305: .Cm no
1.171 djm 306: will cause
307: .Xr ssh 1
308: to fail instantly if
1.173 djm 309: .Cm CanonicalizeHostname
1.171 djm 310: is enabled and the target hostname cannot be found in any of the domains
311: specified by
312: .Cm CanonicalDomains .
1.173 djm 313: .It Cm CanonicalizeHostname
1.174 djm 314: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 315: The default,
1.240 jmc 316: .Cm no ,
1.171 djm 317: is not to perform any name rewriting and let the system resolver handle all
318: hostname lookups.
319: If set to
1.240 jmc 320: .Cm yes
1.171 djm 321: then, for connections that do not use a
1.284 djm 322: .Cm ProxyCommand
323: or
324: .Cm ProxyJump ,
1.171 djm 325: .Xr ssh 1
1.173 djm 326: will attempt to canonicalize the hostname specified on the command line
1.171 djm 327: using the
328: .Cm CanonicalDomains
329: suffixes and
1.173 djm 330: .Cm CanonicalizePermittedCNAMEs
1.171 djm 331: rules.
332: If
1.173 djm 333: .Cm CanonicalizeHostname
1.171 djm 334: is set to
1.240 jmc 335: .Cm always ,
1.174 djm 336: then canonicalization is applied to proxied connections too.
1.185 djm 337: .Pp
1.193 djm 338: If this option is enabled, then the configuration files are processed
339: again using the new target name to pick up any new configuration in matching
1.185 djm 340: .Cm Host
1.193 djm 341: and
342: .Cm Match
1.185 djm 343: stanzas.
1.173 djm 344: .It Cm CanonicalizeMaxDots
1.172 jmc 345: Specifies the maximum number of dot characters in a hostname before
1.174 djm 346: canonicalization is disabled.
1.240 jmc 347: The default, 1,
1.172 jmc 348: allows a single dot (i.e. hostname.subdomain).
1.173 djm 349: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 350: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 351: canonicalizing hostnames.
1.171 djm 352: The rules consist of one or more arguments of
1.172 jmc 353: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 354: where
355: .Ar source_domain_list
1.174 djm 356: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 357: and
358: .Ar target_domain_list
1.172 jmc 359: is a pattern-list of domains that they may resolve to.
1.171 djm 360: .Pp
361: For example,
1.240 jmc 362: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 363: will allow hostnames matching
1.240 jmc 364: .Qq *.a.example.com
1.173 djm 365: to be canonicalized to names in the
1.240 jmc 366: .Qq *.b.example.com
1.171 djm 367: or
1.240 jmc 368: .Qq *.c.example.com
1.171 djm 369: domains.
1.283 jmc 370: .It Cm CASignatureAlgorithms
371: Specifies which algorithms are allowed for signing of certificates
372: by certificate authorities (CAs).
373: The default is:
374: .Bd -literal -offset indent
1.351 ! djm 375: ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
! 376: sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,i
! 377: rsa-sha2-512,rsa-sha2-256
1.283 jmc 378: .Ed
379: .Pp
380: .Xr ssh 1
381: will not accept host certificates signed using algorithms other than those
382: specified.
1.221 djm 383: .It Cm CertificateFile
384: Specifies a file from which the user's certificate is read.
385: A corresponding private key must be provided separately in order
386: to use this certificate either
387: from an
388: .Cm IdentityFile
389: directive or
390: .Fl i
391: flag to
392: .Xr ssh 1 ,
393: via
394: .Xr ssh-agent 1 ,
395: or via a
1.305 naddy 396: .Cm PKCS11Provider
397: or
398: .Cm SecurityKeyProvider .
1.221 djm 399: .Pp
1.239 jmc 400: Arguments to
401: .Cm CertificateFile
1.326 dtucker 402: may use the tilde syntax to refer to a user's home directory,
403: the tokens described in the
1.239 jmc 404: .Sx TOKENS
1.326 dtucker 405: section and environment variables as described in the
406: .Sx ENVIRONMENT VARIABLES
1.239 jmc 407: section.
1.221 djm 408: .Pp
409: It is possible to have multiple certificate files specified in
410: configuration files; these certificates will be tried in sequence.
411: Multiple
412: .Cm CertificateFile
413: directives will add to the list of certificates used for
414: authentication.
1.1 stevesk 415: .It Cm ChallengeResponseAuthentication
1.82 jmc 416: Specifies whether to use challenge-response authentication.
1.1 stevesk 417: The argument to this keyword must be
1.240 jmc 418: .Cm yes
419: (the default)
1.1 stevesk 420: or
1.240 jmc 421: .Cm no .
1.1 stevesk 422: .It Cm CheckHostIP
1.240 jmc 423: If set to
424: .Cm yes
1.84 jmc 425: .Xr ssh 1
426: will additionally check the host IP address in the
1.1 stevesk 427: .Pa known_hosts
428: file.
1.240 jmc 429: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 430: and will add addresses of destination hosts to
431: .Pa ~/.ssh/known_hosts
432: in the process, regardless of the setting of
433: .Cm StrictHostKeyChecking .
1.107 grunk 434: If the option is set to
1.341 djm 435: .Cm no
436: (the default),
1.1 stevesk 437: the check will not be executed.
438: .It Cm Ciphers
1.245 djm 439: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 440: Multiple ciphers must be comma-separated.
1.299 kn 441: If the specified list begins with a
1.214 djm 442: .Sq +
443: character, then the specified ciphers will be appended to the default set
444: instead of replacing them.
1.299 kn 445: If the specified list begins with a
1.241 djm 446: .Sq -
447: character, then the specified ciphers (including wildcards) will be removed
448: from the default set instead of replacing them.
1.301 naddy 449: If the specified list begins with a
450: .Sq ^
451: character, then the specified ciphers will be placed at the head of the
452: default set.
1.214 djm 453: .Pp
1.180 djm 454: The supported ciphers are:
1.240 jmc 455: .Bd -literal -offset indent
1.186 naddy 456: 3des-cbc
457: aes128-cbc
458: aes192-cbc
459: aes256-cbc
460: aes128-ctr
461: aes192-ctr
462: aes256-ctr
463: aes128-gcm@openssh.com
464: aes256-gcm@openssh.com
465: chacha20-poly1305@openssh.com
1.240 jmc 466: .Ed
1.180 djm 467: .Pp
1.84 jmc 468: The default is:
1.186 naddy 469: .Bd -literal -offset indent
1.215 jmc 470: chacha20-poly1305@openssh.com,
1.186 naddy 471: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 472: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 473: .Ed
1.180 djm 474: .Pp
1.240 jmc 475: The list of available ciphers may also be obtained using
476: .Qq ssh -Q cipher .
1.1 stevesk 477: .It Cm ClearAllForwardings
1.84 jmc 478: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 479: specified in the configuration files or on the command line be
1.7 jmc 480: cleared.
481: This option is primarily useful when used from the
1.84 jmc 482: .Xr ssh 1
1.1 stevesk 483: command line to clear port forwardings set in
484: configuration files, and is automatically set by
485: .Xr scp 1
486: and
487: .Xr sftp 1 .
488: The argument must be
1.240 jmc 489: .Cm yes
1.1 stevesk 490: or
1.240 jmc 491: .Cm no
492: (the default).
1.1 stevesk 493: .It Cm Compression
494: Specifies whether to use compression.
495: The argument must be
1.240 jmc 496: .Cm yes
1.1 stevesk 497: or
1.240 jmc 498: .Cm no
499: (the default).
1.247 naddy 500: .It Cm ConnectionAttempts
501: Specifies the number of tries (one per second) to make before exiting.
502: The argument must be an integer.
503: This may be useful in scripts if the connection sometimes fails.
504: The default is 1.
1.9 djm 505: .It Cm ConnectTimeout
1.84 jmc 506: Specifies the timeout (in seconds) used when connecting to the
507: SSH server, instead of using the default system TCP timeout.
1.302 djm 508: This timeout is applied both to establishing the connection and to performing
509: the initial SSH protocol handshake and key exchange.
1.36 djm 510: .It Cm ControlMaster
511: Enables the sharing of multiple sessions over a single network connection.
512: When set to
1.240 jmc 513: .Cm yes ,
1.84 jmc 514: .Xr ssh 1
1.36 djm 515: will listen for connections on a control socket specified using the
516: .Cm ControlPath
517: argument.
518: Additional sessions can connect to this socket using the same
519: .Cm ControlPath
520: with
521: .Cm ControlMaster
522: set to
1.240 jmc 523: .Cm no
1.38 jmc 524: (the default).
1.64 jmc 525: These sessions will try to reuse the master instance's network connection
1.63 djm 526: rather than initiating new ones, but will fall back to connecting normally
527: if the control socket does not exist, or is not listening.
528: .Pp
1.37 djm 529: Setting this to
1.240 jmc 530: .Cm ask
531: will cause
532: .Xr ssh 1
1.206 jmc 533: to listen for control connections, but require confirmation using
534: .Xr ssh-askpass 1 .
1.51 jakob 535: If the
536: .Cm ControlPath
1.84 jmc 537: cannot be opened,
1.240 jmc 538: .Xr ssh 1
539: will continue without connecting to a master instance.
1.58 djm 540: .Pp
541: X11 and
1.59 jmc 542: .Xr ssh-agent 1
1.58 djm 543: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 544: display and agent forwarded will be the one belonging to the master
1.59 jmc 545: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 546: .Pp
547: Two additional options allow for opportunistic multiplexing: try to use a
548: master connection but fall back to creating a new one if one does not already
549: exist.
550: These options are:
1.240 jmc 551: .Cm auto
1.56 djm 552: and
1.240 jmc 553: .Cm autoask .
1.56 djm 554: The latter requires confirmation like the
1.240 jmc 555: .Cm ask
1.56 djm 556: option.
1.36 djm 557: .It Cm ControlPath
1.55 djm 558: Specify the path to the control socket used for connection sharing as described
559: in the
1.36 djm 560: .Cm ControlMaster
1.57 djm 561: section above or the string
1.240 jmc 562: .Cm none
1.57 djm 563: to disable connection sharing.
1.239 jmc 564: Arguments to
565: .Cm ControlPath
1.326 dtucker 566: may use the tilde syntax to refer to a user's home directory,
567: the tokens described in the
1.239 jmc 568: .Sx TOKENS
1.326 dtucker 569: section and environment variables as described in the
570: .Sx ENVIRONMENT VARIABLES
1.239 jmc 571: section.
1.56 djm 572: It is recommended that any
573: .Cm ControlPath
574: used for opportunistic connection sharing include
1.195 djm 575: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
576: that is not writable by other users.
1.56 djm 577: This ensures that shared connections are uniquely identified.
1.137 djm 578: .It Cm ControlPersist
579: When used in conjunction with
580: .Cm ControlMaster ,
581: specifies that the master connection should remain open
582: in the background (waiting for future client connections)
583: after the initial client connection has been closed.
584: If set to
1.314 naddy 585: .Cm no
586: (the default),
1.137 djm 587: then the master connection will not be placed into the background,
588: and will close as soon as the initial client connection is closed.
589: If set to
1.240 jmc 590: .Cm yes
591: or 0,
1.137 djm 592: then the master connection will remain in the background indefinitely
593: (until killed or closed via a mechanism such as the
1.240 jmc 594: .Qq ssh -O exit ) .
1.137 djm 595: If set to a time in seconds, or a time in any of the formats documented in
596: .Xr sshd_config 5 ,
597: then the backgrounded master connection will automatically terminate
598: after it has remained idle (with no client connections) for the
599: specified time.
1.38 jmc 600: .It Cm DynamicForward
1.74 jmc 601: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 602: over the secure channel, and the application
603: protocol is then used to determine where to connect to from the
604: remote machine.
1.62 djm 605: .Pp
606: The argument must be
607: .Sm off
608: .Oo Ar bind_address : Oc Ar port .
609: .Sm on
1.138 djm 610: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 611: By default, the local port is bound in accordance with the
612: .Cm GatewayPorts
613: setting.
614: However, an explicit
615: .Ar bind_address
616: may be used to bind the connection to a specific address.
617: The
618: .Ar bind_address
619: of
1.240 jmc 620: .Cm localhost
1.62 djm 621: indicates that the listening port be bound for local use only, while an
622: empty address or
623: .Sq *
624: indicates that the port should be available from all interfaces.
625: .Pp
1.38 jmc 626: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 627: .Xr ssh 1
1.38 jmc 628: will act as a SOCKS server.
629: Multiple forwardings may be specified, and
630: additional forwardings can be given on the command line.
631: Only the superuser can forward privileged ports.
1.14 markus 632: .It Cm EnableSSHKeysign
633: Setting this option to
1.240 jmc 634: .Cm yes
1.14 markus 635: in the global client configuration file
636: .Pa /etc/ssh/ssh_config
637: enables the use of the helper program
638: .Xr ssh-keysign 8
639: during
640: .Cm HostbasedAuthentication .
641: The argument must be
1.240 jmc 642: .Cm yes
1.14 markus 643: or
1.240 jmc 644: .Cm no
645: (the default).
1.23 jmc 646: This option should be placed in the non-hostspecific section.
1.14 markus 647: See
648: .Xr ssh-keysign 8
649: for more information.
1.1 stevesk 650: .It Cm EscapeChar
651: Sets the escape character (default:
652: .Ql ~ ) .
653: The escape character can also
654: be set on the command line.
655: The argument should be a single character,
656: .Ql ^
657: followed by a letter, or
1.240 jmc 658: .Cm none
1.1 stevesk 659: to disable the escape
660: character entirely (making the connection transparent for binary
661: data).
1.96 markus 662: .It Cm ExitOnForwardFailure
663: Specifies whether
664: .Xr ssh 1
665: should terminate the connection if it cannot set up all requested
1.216 djm 666: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 667: if either end is unable to bind and listen on a specified port).
1.216 djm 668: Note that
669: .Cm ExitOnForwardFailure
670: does not apply to connections made over port forwardings and will not,
671: for example, cause
672: .Xr ssh 1
673: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 674: The argument must be
1.240 jmc 675: .Cm yes
1.96 markus 676: or
1.240 jmc 677: .Cm no
678: (the default).
1.197 djm 679: .It Cm FingerprintHash
680: Specifies the hash algorithm used when displaying key fingerprints.
681: Valid options are:
1.240 jmc 682: .Cm md5
1.197 djm 683: and
1.240 jmc 684: .Cm sha256
685: (the default).
1.1 stevesk 686: .It Cm ForwardAgent
687: Specifies whether the connection to the authentication agent (if any)
688: will be forwarded to the remote machine.
1.312 djm 689: The argument may be
690: .Cm yes ,
1.240 jmc 691: .Cm no
1.312 djm 692: (the default),
693: an explicit path to an agent socket or the name of an environment variable
694: (beginning with
695: .Sq $ )
696: in which to find the path.
1.3 stevesk 697: .Pp
1.7 jmc 698: Agent forwarding should be enabled with caution.
699: Users with the ability to bypass file permissions on the remote host
700: (for the agent's Unix-domain socket)
701: can access the local agent through the forwarded connection.
702: An attacker cannot obtain key material from the agent,
1.3 stevesk 703: however they can perform operations on the keys that enable them to
704: authenticate using the identities loaded into the agent.
1.1 stevesk 705: .It Cm ForwardX11
706: Specifies whether X11 connections will be automatically redirected
707: over the secure channel and
708: .Ev DISPLAY
709: set.
710: The argument must be
1.240 jmc 711: .Cm yes
1.1 stevesk 712: or
1.240 jmc 713: .Cm no
714: (the default).
1.3 stevesk 715: .Pp
1.7 jmc 716: X11 forwarding should be enabled with caution.
717: Users with the ability to bypass file permissions on the remote host
1.22 markus 718: (for the user's X11 authorization database)
1.7 jmc 719: can access the local X11 display through the forwarded connection.
1.22 markus 720: An attacker may then be able to perform activities such as keystroke monitoring
721: if the
722: .Cm ForwardX11Trusted
723: option is also enabled.
1.134 djm 724: .It Cm ForwardX11Timeout
1.135 jmc 725: Specify a timeout for untrusted X11 forwarding
726: using the format described in the
1.240 jmc 727: .Sx TIME FORMATS
728: section of
1.134 djm 729: .Xr sshd_config 5 .
730: X11 connections received by
731: .Xr ssh 1
732: after this time will be refused.
1.285 djm 733: Setting
734: .Cm ForwardX11Timeout
735: to zero will disable the timeout and permit X11 forwarding for the life
736: of the connection.
1.134 djm 737: The default is to disable untrusted X11 forwarding after twenty minutes has
738: elapsed.
1.22 markus 739: .It Cm ForwardX11Trusted
1.34 jmc 740: If this option is set to
1.240 jmc 741: .Cm yes ,
1.84 jmc 742: remote X11 clients will have full access to the original X11 display.
1.42 djm 743: .Pp
1.22 markus 744: If this option is set to
1.240 jmc 745: .Cm no
746: (the default),
1.84 jmc 747: remote X11 clients will be considered untrusted and prevented
1.22 markus 748: from stealing or tampering with data belonging to trusted X11
749: clients.
1.42 djm 750: Furthermore, the
751: .Xr xauth 1
752: token used for the session will be set to expire after 20 minutes.
753: Remote clients will be refused access after this time.
1.22 markus 754: .Pp
755: See the X11 SECURITY extension specification for full details on
756: the restrictions imposed on untrusted clients.
1.1 stevesk 757: .It Cm GatewayPorts
758: Specifies whether remote hosts are allowed to connect to local
759: forwarded ports.
760: By default,
1.84 jmc 761: .Xr ssh 1
1.7 jmc 762: binds local port forwardings to the loopback address.
763: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 764: .Cm GatewayPorts
1.84 jmc 765: can be used to specify that ssh
1.1 stevesk 766: should bind local port forwardings to the wildcard address,
767: thus allowing remote hosts to connect to forwarded ports.
768: The argument must be
1.240 jmc 769: .Cm yes
1.1 stevesk 770: or
1.240 jmc 771: .Cm no
772: (the default).
1.1 stevesk 773: .It Cm GlobalKnownHostsFile
1.151 djm 774: Specifies one or more files to use for the global
775: host key database, separated by whitespace.
776: The default is
777: .Pa /etc/ssh/ssh_known_hosts ,
778: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 779: .It Cm GSSAPIAuthentication
1.27 markus 780: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 781: The default is
1.240 jmc 782: .Cm no .
1.18 markus 783: .It Cm GSSAPIDelegateCredentials
784: Forward (delegate) credentials to the server.
785: The default is
1.240 jmc 786: .Cm no .
1.44 djm 787: .It Cm HashKnownHosts
788: Indicates that
1.84 jmc 789: .Xr ssh 1
1.44 djm 790: should hash host names and addresses when they are added to
1.50 djm 791: .Pa ~/.ssh/known_hosts .
1.44 djm 792: These hashed names may be used normally by
1.84 jmc 793: .Xr ssh 1
1.44 djm 794: and
1.84 jmc 795: .Xr sshd 8 ,
1.316 djm 796: but they do not visually reveal identifying information if the
797: file's contents are disclosed.
1.44 djm 798: The default is
1.240 jmc 799: .Cm no .
1.97 jmc 800: Note that existing names and addresses in known hosts files
801: will not be converted automatically,
802: but may be manually hashed using
1.45 djm 803: .Xr ssh-keygen 1 .
1.344 dtucker 804: .It Cm HostbasedAcceptedAlgorithms
1.348 djm 805: Specifies the signature algorithms that will be used for hostbased
806: authentication as a comma-separated list of patterns.
1.300 naddy 807: Alternately if the specified list begins with a
1.214 djm 808: .Sq +
1.348 djm 809: character, then the specified signature algorithms will be appended
810: to the default set instead of replacing them.
1.300 naddy 811: If the specified list begins with a
1.241 djm 812: .Sq -
1.348 djm 813: character, then the specified signature algorithms (including wildcards)
814: will be removed from the default set instead of replacing them.
1.301 naddy 815: If the specified list begins with a
816: .Sq ^
1.348 djm 817: character, then the specified signature algorithms will be placed
818: at the head of the default set.
1.213 markus 819: The default for this option is:
820: .Bd -literal -offset 3n
1.333 djm 821: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 822: ecdsa-sha2-nistp256-cert-v01@openssh.com,
823: ecdsa-sha2-nistp384-cert-v01@openssh.com,
824: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 825: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 826: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 827: rsa-sha2-512-cert-v01@openssh.com,
828: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 829: ssh-rsa-cert-v01@openssh.com,
1.333 djm 830: ssh-ed25519,
1.213 markus 831: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 832: sk-ssh-ed25519@openssh.com,
1.311 naddy 833: sk-ecdsa-sha2-nistp256@openssh.com,
834: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 835: .Ed
836: .Pp
1.202 djm 837: The
838: .Fl Q
839: option of
840: .Xr ssh 1
1.348 djm 841: may be used to list supported signature algorithms.
1.344 dtucker 842: This was formerly named HostbasedKeyTypes.
1.345 naddy 843: .It Cm HostbasedAuthentication
844: Specifies whether to try rhosts based authentication with public key
845: authentication.
846: The argument must be
847: .Cm yes
848: or
849: .Cm no
850: (the default).
1.1 stevesk 851: .It Cm HostKeyAlgorithms
1.348 djm 852: Specifies the host key signature algorithms
1.1 stevesk 853: that the client wants to use in order of preference.
1.300 naddy 854: Alternately if the specified list begins with a
1.214 djm 855: .Sq +
1.348 djm 856: character, then the specified signature algorithms will be appended to
857: the default set instead of replacing them.
1.300 naddy 858: If the specified list begins with a
1.241 djm 859: .Sq -
1.348 djm 860: character, then the specified signature algorithms (including wildcards)
861: will be removed from the default set instead of replacing them.
1.301 naddy 862: If the specified list begins with a
863: .Sq ^
1.348 djm 864: character, then the specified signature algorithms will be placed
865: at the head of the default set.
1.1 stevesk 866: The default for this option is:
1.139 djm 867: .Bd -literal -offset 3n
1.333 djm 868: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 869: ecdsa-sha2-nistp256-cert-v01@openssh.com,
870: ecdsa-sha2-nistp384-cert-v01@openssh.com,
871: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 872: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 873: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 874: rsa-sha2-512-cert-v01@openssh.com,
875: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 876: ssh-rsa-cert-v01@openssh.com,
1.333 djm 877: ssh-ed25519,
1.139 djm 878: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 879: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 880: sk-ssh-ed25519@openssh.com,
1.311 naddy 881: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 882: .Ed
1.145 djm 883: .Pp
884: If hostkeys are known for the destination host then this default is modified
885: to prefer their algorithms.
1.198 djm 886: .Pp
1.348 djm 887: The list of available signature algorithms may also be obtained using
1.322 dtucker 888: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 889: .It Cm HostKeyAlias
890: Specifies an alias that should be used instead of the
891: real host name when looking up or saving the host key
1.251 djm 892: in the host key database files and when validating host certificates.
1.84 jmc 893: This option is useful for tunneling SSH connections
1.1 stevesk 894: or for multiple servers running on a single host.
1.295 jmc 895: .It Cm Hostname
1.1 stevesk 896: Specifies the real host name to log into.
897: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 898: Arguments to
1.295 jmc 899: .Cm Hostname
1.239 jmc 900: accept the tokens described in the
901: .Sx TOKENS
902: section.
1.1 stevesk 903: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 904: .Cm Hostname
1.1 stevesk 905: specifications).
1.239 jmc 906: The default is the name given on the command line.
1.29 markus 907: .It Cm IdentitiesOnly
908: Specifies that
1.84 jmc 909: .Xr ssh 1
1.304 djm 910: should only use the configured authentication identity and certificate files
911: (either the default files, or those explicitly configured in the
1.31 jmc 912: .Nm
1.221 djm 913: files
914: or passed on the
915: .Xr ssh 1
1.304 djm 916: command-line),
1.84 jmc 917: even if
918: .Xr ssh-agent 1
1.159 djm 919: or a
920: .Cm PKCS11Provider
1.305 naddy 921: or
922: .Cm SecurityKeyProvider
1.29 markus 923: offers more identities.
924: The argument to this keyword must be
1.240 jmc 925: .Cm yes
1.29 markus 926: or
1.240 jmc 927: .Cm no
928: (the default).
1.84 jmc 929: This option is intended for situations where ssh-agent
1.29 markus 930: offers many different identities.
1.231 markus 931: .It Cm IdentityAgent
932: Specifies the
933: .Ux Ns -domain
934: socket used to communicate with the authentication agent.
935: .Pp
936: This option overrides the
1.240 jmc 937: .Ev SSH_AUTH_SOCK
1.231 markus 938: environment variable and can be used to select a specific agent.
939: Setting the socket name to
1.240 jmc 940: .Cm none
1.231 markus 941: disables the use of an authentication agent.
1.232 markus 942: If the string
1.240 jmc 943: .Qq SSH_AUTH_SOCK
1.232 markus 944: is specified, the location of the socket will be read from the
945: .Ev SSH_AUTH_SOCK
946: environment variable.
1.286 djm 947: Otherwise if the specified value begins with a
948: .Sq $
949: character, then it will be treated as an environment variable containing
950: the location of the socket.
1.231 markus 951: .Pp
1.239 jmc 952: Arguments to
953: .Cm IdentityAgent
1.326 dtucker 954: may use the tilde syntax to refer to a user's home directory,
955: the tokens described in the
1.239 jmc 956: .Sx TOKENS
1.326 dtucker 957: section and environment variables as described in the
958: .Sx ENVIRONMENT VARIABLES
1.239 jmc 959: section.
1.67 jmc 960: .It Cm IdentityFile
1.313 naddy 961: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
962: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 963: The default is
1.139 djm 964: .Pa ~/.ssh/id_dsa ,
1.183 naddy 965: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 966: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 967: .Pa ~/.ssh/id_ed25519 ,
968: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 969: and
1.245 djm 970: .Pa ~/.ssh/id_rsa .
1.67 jmc 971: Additionally, any identities represented by the authentication agent
1.165 djm 972: will be used for authentication unless
973: .Cm IdentitiesOnly
974: is set.
1.221 djm 975: If no certificates have been explicitly specified by
976: .Cm CertificateFile ,
1.129 djm 977: .Xr ssh 1
978: will try to load certificate information from the filename obtained by
979: appending
980: .Pa -cert.pub
981: to the path of a specified
982: .Cm IdentityFile .
1.90 djm 983: .Pp
1.239 jmc 984: Arguments to
985: .Cm IdentityFile
986: may use the tilde syntax to refer to a user's home directory
987: or the tokens described in the
988: .Sx TOKENS
989: section.
1.90 djm 990: .Pp
1.67 jmc 991: It is possible to have
992: multiple identity files specified in configuration files; all these
993: identities will be tried in sequence.
1.152 djm 994: Multiple
995: .Cm IdentityFile
996: directives will add to the list of identities tried (this behaviour
997: differs from that of other configuration directives).
1.165 djm 998: .Pp
999: .Cm IdentityFile
1000: may be used in conjunction with
1001: .Cm IdentitiesOnly
1002: to select which identities in an agent are offered during authentication.
1.221 djm 1003: .Cm IdentityFile
1004: may also be used in conjunction with
1005: .Cm CertificateFile
1006: in order to provide any certificate also needed for authentication with
1007: the identity.
1.164 jmc 1008: .It Cm IgnoreUnknown
1009: Specifies a pattern-list of unknown options to be ignored if they are
1010: encountered in configuration parsing.
1011: This may be used to suppress errors if
1012: .Nm
1013: contains options that are unrecognised by
1014: .Xr ssh 1 .
1015: It is recommended that
1016: .Cm IgnoreUnknown
1017: be listed early in the configuration file as it will not be applied
1018: to unknown options that appear before it.
1.229 djm 1019: .It Cm Include
1020: Include the specified configuration file(s).
1.230 jmc 1021: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1022: .Xr glob 7
1.229 djm 1023: wildcards and, for user configurations, shell-like
1.240 jmc 1024: .Sq ~
1.229 djm 1025: references to user home directories.
1.327 djm 1026: Wildcards will be expanded and processed in lexical order.
1.229 djm 1027: Files without absolute paths are assumed to be in
1028: .Pa ~/.ssh
1.230 jmc 1029: if included in a user configuration file or
1.229 djm 1030: .Pa /etc/ssh
1031: if included from the system configuration file.
1032: .Cm Include
1033: directive may appear inside a
1034: .Cm Match
1035: or
1036: .Cm Host
1037: block
1038: to perform conditional inclusion.
1.143 djm 1039: .It Cm IPQoS
1040: Specifies the IPv4 type-of-service or DSCP class for connections.
1041: Accepted values are
1.240 jmc 1042: .Cm af11 ,
1043: .Cm af12 ,
1044: .Cm af13 ,
1045: .Cm af21 ,
1046: .Cm af22 ,
1047: .Cm af23 ,
1048: .Cm af31 ,
1049: .Cm af32 ,
1050: .Cm af33 ,
1051: .Cm af41 ,
1052: .Cm af42 ,
1053: .Cm af43 ,
1054: .Cm cs0 ,
1055: .Cm cs1 ,
1056: .Cm cs2 ,
1057: .Cm cs3 ,
1058: .Cm cs4 ,
1059: .Cm cs5 ,
1060: .Cm cs6 ,
1061: .Cm cs7 ,
1062: .Cm ef ,
1.319 djm 1063: .Cm le ,
1.240 jmc 1064: .Cm lowdelay ,
1065: .Cm throughput ,
1066: .Cm reliability ,
1.253 djm 1067: a numeric value, or
1068: .Cm none
1069: to use the operating system default.
1.146 djm 1070: This option may take one or two arguments, separated by whitespace.
1.143 djm 1071: If one argument is specified, it is used as the packet class unconditionally.
1072: If two values are specified, the first is automatically selected for
1073: interactive sessions and the second for non-interactive sessions.
1074: The default is
1.269 job 1075: .Cm af21
1.272 jmc 1076: (Low-Latency Data)
1.143 djm 1077: for interactive sessions and
1.269 job 1078: .Cm cs1
1.272 jmc 1079: (Lower Effort)
1.143 djm 1080: for non-interactive sessions.
1.103 djm 1081: .It Cm KbdInteractiveAuthentication
1082: Specifies whether to use keyboard-interactive authentication.
1083: The argument to this keyword must be
1.240 jmc 1084: .Cm yes
1085: (the default)
1.103 djm 1086: or
1.240 jmc 1087: .Cm no .
1.39 djm 1088: .It Cm KbdInteractiveDevices
1089: Specifies the list of methods to use in keyboard-interactive authentication.
1090: Multiple method names must be comma-separated.
1091: The default is to use the server specified list.
1.85 jmc 1092: The methods available vary depending on what the server supports.
1093: For an OpenSSH server,
1094: it may be zero or more of:
1.240 jmc 1095: .Cm bsdauth ,
1096: .Cm pam ,
1.85 jmc 1097: and
1.240 jmc 1098: .Cm skey .
1.140 djm 1099: .It Cm KexAlgorithms
1100: Specifies the available KEX (Key Exchange) algorithms.
1101: Multiple algorithms must be comma-separated.
1.299 kn 1102: If the specified list begins with a
1.214 djm 1103: .Sq +
1104: character, then the specified methods will be appended to the default set
1105: instead of replacing them.
1.299 kn 1106: If the specified list begins with a
1.241 djm 1107: .Sq -
1108: character, then the specified methods (including wildcards) will be removed
1109: from the default set instead of replacing them.
1.301 naddy 1110: If the specified list begins with a
1111: .Sq ^
1112: character, then the specified methods will be placed at the head of the
1113: default set.
1.141 jmc 1114: The default is:
1115: .Bd -literal -offset indent
1.238 djm 1116: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1117: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1118: diffie-hellman-group-exchange-sha256,
1.266 djm 1119: diffie-hellman-group16-sha512,
1120: diffie-hellman-group18-sha512,
1.317 tedu 1121: diffie-hellman-group14-sha256
1.141 jmc 1122: .Ed
1.198 djm 1123: .Pp
1.240 jmc 1124: The list of available key exchange algorithms may also be obtained using
1125: .Qq ssh -Q kex .
1.339 djm 1126: .It Cm KnownHostsCommand
1.340 jmc 1127: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1128: those listed in
1129: .Cm UserKnownHostsFile
1130: and
1131: .Cm GlobalKnownHostsFile .
1132: This command is executed after the files have been read.
1.340 jmc 1133: It may write host key lines to standard output in identical format to the
1.339 djm 1134: usual files (described in the
1135: .Sx VERIFYING HOST KEYS
1136: section in
1137: .Xr ssh 1 ) .
1138: Arguments to
1139: .Cm KnownHostsCommand
1140: accept the tokens described in the
1141: .Sx TOKENS
1142: section.
1.340 jmc 1143: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1144: the preference list of host key algorithms to use, again to obtain the
1145: host key for the requested host name and, if
1146: .Cm CheckHostIP
1147: is enabled, one more time to obtain the host key matching the server's
1148: address.
1149: If the command exits abnormally or returns a non-zero exit status then the
1150: connection is terminated.
1.65 reyk 1151: .It Cm LocalCommand
1152: Specifies a command to execute on the local machine after successfully
1153: connecting to the server.
1154: The command string extends to the end of the line, and is executed with
1.105 jmc 1155: the user's shell.
1.239 jmc 1156: Arguments to
1157: .Cm LocalCommand
1158: accept the tokens described in the
1159: .Sx TOKENS
1160: section.
1.123 djm 1161: .Pp
1162: The command is run synchronously and does not have access to the
1163: session of the
1164: .Xr ssh 1
1165: that spawned it.
1166: It should not be used for interactive commands.
1167: .Pp
1.65 reyk 1168: This directive is ignored unless
1169: .Cm PermitLocalCommand
1170: has been enabled.
1.1 stevesk 1171: .It Cm LocalForward
1.74 jmc 1172: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1173: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1174: The first argument specifies the listener and may be
1.43 djm 1175: .Sm off
1.49 jmc 1176: .Oo Ar bind_address : Oc Ar port
1.43 djm 1177: .Sm on
1.324 dtucker 1178: or a Unix domain socket path.
1179: The second argument is the destination and may be
1180: .Ar host : Ns Ar hostport
1181: or a Unix domain socket path if the remote host supports it.
1182: .Pp
1.138 djm 1183: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1184: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1185: given on the command line.
1.1 stevesk 1186: Only the superuser can forward privileged ports.
1.43 djm 1187: By default, the local port is bound in accordance with the
1188: .Cm GatewayPorts
1189: setting.
1190: However, an explicit
1191: .Ar bind_address
1192: may be used to bind the connection to a specific address.
1193: The
1194: .Ar bind_address
1195: of
1.240 jmc 1196: .Cm localhost
1.46 jmc 1197: indicates that the listening port be bound for local use only, while an
1198: empty address or
1199: .Sq *
1.43 djm 1200: indicates that the port should be available from all interfaces.
1.326 dtucker 1201: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1202: .Sx TOKENS
1.326 dtucker 1203: section and environment variables as described in the
1204: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1205: section.
1.1 stevesk 1206: .It Cm LogLevel
1207: Gives the verbosity level that is used when logging messages from
1.84 jmc 1208: .Xr ssh 1 .
1.1 stevesk 1209: The possible values are:
1.84 jmc 1210: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1211: The default is INFO.
1212: DEBUG and DEBUG1 are equivalent.
1213: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1214: .It Cm LogVerbose
1215: Specify one or more overrides to LogLevel.
1216: An override consists of a pattern lists that matches the source file, function
1217: and line number to force detailed logging for.
1218: For example, an override pattern of:
1219: .Bd -literal -offset indent
1220: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1221: .Ed
1222: .Pp
1223: would enable detailed logging for line 1000 of
1.338 jmc 1224: .Pa kex.c ,
1.337 djm 1225: everything in the
1226: .Fn kex_exchange_identification
1227: function, and all code in the
1228: .Pa packet.c
1229: file.
1230: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1231: .It Cm MACs
1232: Specifies the MAC (message authentication code) algorithms
1233: in order of preference.
1.226 jmc 1234: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1235: Multiple algorithms must be comma-separated.
1.299 kn 1236: If the specified list begins with a
1.214 djm 1237: .Sq +
1238: character, then the specified algorithms will be appended to the default set
1239: instead of replacing them.
1.299 kn 1240: If the specified list begins with a
1.241 djm 1241: .Sq -
1242: character, then the specified algorithms (including wildcards) will be removed
1243: from the default set instead of replacing them.
1.301 naddy 1244: If the specified list begins with a
1245: .Sq ^
1246: character, then the specified algorithms will be placed at the head of the
1247: default set.
1.214 djm 1248: .Pp
1.160 markus 1249: The algorithms that contain
1.240 jmc 1250: .Qq -etm
1.160 markus 1251: calculate the MAC after encryption (encrypt-then-mac).
1252: These are considered safer and their use recommended.
1.214 djm 1253: .Pp
1.84 jmc 1254: The default is:
1.101 jmc 1255: .Bd -literal -offset indent
1.160 markus 1256: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1257: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1258: hmac-sha1-etm@openssh.com,
1.186 naddy 1259: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1260: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1261: .Ed
1.198 djm 1262: .Pp
1.240 jmc 1263: The list of available MAC algorithms may also be obtained using
1264: .Qq ssh -Q mac .
1.1 stevesk 1265: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1266: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1267: The argument to this keyword must be
1.240 jmc 1268: .Cm yes
1.1 stevesk 1269: or
1.242 jmc 1270: .Cm no
1.240 jmc 1271: (the default).
1.1 stevesk 1272: .It Cm NumberOfPasswordPrompts
1273: Specifies the number of password prompts before giving up.
1274: The argument to this keyword must be an integer.
1.84 jmc 1275: The default is 3.
1.1 stevesk 1276: .It Cm PasswordAuthentication
1277: Specifies whether to use password authentication.
1278: The argument to this keyword must be
1.240 jmc 1279: .Cm yes
1280: (the default)
1.1 stevesk 1281: or
1.240 jmc 1282: .Cm no .
1.65 reyk 1283: .It Cm PermitLocalCommand
1284: Allow local command execution via the
1285: .Ic LocalCommand
1286: option or using the
1.66 jmc 1287: .Ic !\& Ns Ar command
1.65 reyk 1288: escape sequence in
1289: .Xr ssh 1 .
1290: The argument must be
1.240 jmc 1291: .Cm yes
1.65 reyk 1292: or
1.240 jmc 1293: .Cm no
1294: (the default).
1.347 markus 1295: .It Cm PermitRemoteOpen
1296: Specifies the destinations to which remote TCP port forwarding is permitted when
1297: .Cm RemoteForward
1298: is used as a SOCKS proxy.
1299: The forwarding specification must be one of the following forms:
1300: .Pp
1301: .Bl -item -offset indent -compact
1302: .It
1303: .Cm PermitRemoteOpen
1304: .Sm off
1305: .Ar host : port
1306: .Sm on
1307: .It
1308: .Cm PermitRemoteOpen
1309: .Sm off
1310: .Ar IPv4_addr : port
1311: .Sm on
1312: .It
1313: .Cm PermitRemoteOpen
1314: .Sm off
1315: .Ar \&[ IPv6_addr \&] : port
1316: .Sm on
1317: .El
1318: .Pp
1319: Multiple forwards may be specified by separating them with whitespace.
1320: An argument of
1321: .Cm any
1322: can be used to remove all restrictions and permit any forwarding requests.
1323: An argument of
1324: .Cm none
1325: can be used to prohibit all forwarding requests.
1326: The wildcard
1327: .Sq *
1328: can be used for host or port to allow all hosts or ports respectively.
1329: Otherwise, no pattern matching or address lookups are performed on supplied
1330: names.
1.127 markus 1331: .It Cm PKCS11Provider
1.292 djm 1332: Specifies which PKCS#11 provider to use or
1333: .Cm none
1334: to indicate that no provider should be used (the default).
1335: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1336: .Xr ssh 1
1.292 djm 1337: should use to communicate with a PKCS#11 token providing keys for user
1338: authentication.
1.67 jmc 1339: .It Cm Port
1340: Specifies the port number to connect on the remote host.
1.84 jmc 1341: The default is 22.
1.1 stevesk 1342: .It Cm PreferredAuthentications
1.226 jmc 1343: Specifies the order in which the client should try authentication methods.
1.48 jmc 1344: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1345: .Cm keyboard-interactive )
1.48 jmc 1346: over another method (e.g.\&
1.131 jmc 1347: .Cm password ) .
1348: The default is:
1349: .Bd -literal -offset indent
1350: gssapi-with-mic,hostbased,publickey,
1351: keyboard-interactive,password
1352: .Ed
1.1 stevesk 1353: .It Cm ProxyCommand
1354: Specifies the command to use to connect to the server.
1355: The command
1.190 djm 1356: string extends to the end of the line, and is executed
1357: using the user's shell
1358: .Ql exec
1359: directive to avoid a lingering shell process.
1360: .Pp
1.239 jmc 1361: Arguments to
1362: .Cm ProxyCommand
1363: accept the tokens described in the
1364: .Sx TOKENS
1365: section.
1.1 stevesk 1366: The command can be basically anything,
1367: and should read from its standard input and write to its standard output.
1368: It should eventually connect an
1369: .Xr sshd 8
1370: server running on some machine, or execute
1371: .Ic sshd -i
1372: somewhere.
1373: Host key management will be done using the
1.296 jmc 1374: .Cm Hostname
1375: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1376: Setting the command to
1.240 jmc 1377: .Cm none
1.6 markus 1378: disables this option entirely.
1.1 stevesk 1379: Note that
1380: .Cm CheckHostIP
1381: is not available for connects with a proxy command.
1.52 djm 1382: .Pp
1383: This directive is useful in conjunction with
1384: .Xr nc 1
1385: and its proxy support.
1.53 jmc 1386: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1387: 192.0.2.0:
1388: .Bd -literal -offset 3n
1389: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1390: .Ed
1.233 djm 1391: .It Cm ProxyJump
1.260 millert 1392: Specifies one or more jump proxies as either
1.233 djm 1393: .Xo
1394: .Sm off
1.234 jmc 1395: .Op Ar user No @
1.233 djm 1396: .Ar host
1.234 jmc 1397: .Op : Ns Ar port
1.233 djm 1398: .Sm on
1.260 millert 1399: or an ssh URI
1.233 djm 1400: .Xc .
1.235 djm 1401: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1402: sequentially.
1.233 djm 1403: Setting this option will cause
1404: .Xr ssh 1
1405: to connect to the target host by first making a
1406: .Xr ssh 1
1407: connection to the specified
1408: .Cm ProxyJump
1409: host and then establishing a
1.234 jmc 1410: TCP forwarding to the ultimate target from there.
1.346 dlg 1411: Setting the host to
1412: .Cm none
1413: disables this option entirely.
1.233 djm 1414: .Pp
1415: Note that this option will compete with the
1416: .Cm ProxyCommand
1417: option - whichever is specified first will prevent later instances of the
1418: other from taking effect.
1.289 djm 1419: .Pp
1420: Note also that the configuration for the destination host (either supplied
1421: via the command-line or the configuration file) is not generally applied
1422: to jump hosts.
1423: .Pa ~/.ssh/config
1424: should be used if specific configuration is required for jump hosts.
1.167 djm 1425: .It Cm ProxyUseFdpass
1.168 jmc 1426: Specifies that
1.167 djm 1427: .Cm ProxyCommand
1428: will pass a connected file descriptor back to
1.168 jmc 1429: .Xr ssh 1
1.167 djm 1430: instead of continuing to execute and pass data.
1431: The default is
1.240 jmc 1432: .Cm no .
1.343 dtucker 1433: .It Cm PubkeyAcceptedAlgorithms
1434: Specifies the signature algorithms that will be used for public key
1435: authentication as a comma-separated list of patterns.
1.299 kn 1436: If the specified list begins with a
1.214 djm 1437: .Sq +
1.343 dtucker 1438: character, then the algorithms after it will be appended to the default
1.214 djm 1439: instead of replacing it.
1.299 kn 1440: If the specified list begins with a
1.241 djm 1441: .Sq -
1.343 dtucker 1442: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1443: from the default set instead of replacing them.
1.301 naddy 1444: If the specified list begins with a
1445: .Sq ^
1.343 dtucker 1446: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1447: default set.
1.213 markus 1448: The default for this option is:
1449: .Bd -literal -offset 3n
1.333 djm 1450: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1451: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1452: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1453: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1454: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1455: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1456: rsa-sha2-512-cert-v01@openssh.com,
1457: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1458: ssh-rsa-cert-v01@openssh.com,
1.333 djm 1459: ssh-ed25519,
1.311 naddy 1460: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1461: sk-ssh-ed25519@openssh.com,
1.305 naddy 1462: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1463: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1464: .Ed
1465: .Pp
1.348 djm 1466: The list of available signature algorithms may also be obtained using
1.343 dtucker 1467: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.1 stevesk 1468: .It Cm PubkeyAuthentication
1469: Specifies whether to try public key authentication.
1470: The argument to this keyword must be
1.240 jmc 1471: .Cm yes
1472: (the default)
1.1 stevesk 1473: or
1.240 jmc 1474: .Cm no .
1.75 dtucker 1475: .It Cm RekeyLimit
1476: Specifies the maximum amount of data that may be transmitted before the
1.342 rob 1477: session key is renegotiated, optionally followed by a maximum amount of
1.162 dtucker 1478: time that may pass before the session key is renegotiated.
1479: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1480: .Sq K ,
1481: .Sq M ,
1.75 dtucker 1482: or
1.76 jmc 1483: .Sq G
1.75 dtucker 1484: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1485: The default is between
1.84 jmc 1486: .Sq 1G
1.75 dtucker 1487: and
1.84 jmc 1488: .Sq 4G ,
1.75 dtucker 1489: depending on the cipher.
1.162 dtucker 1490: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1491: units documented in the TIME FORMATS section of
1.162 dtucker 1492: .Xr sshd_config 5 .
1493: The default value for
1494: .Cm RekeyLimit
1495: is
1.240 jmc 1496: .Cm default none ,
1.162 dtucker 1497: which means that rekeying is performed after the cipher's default amount
1498: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1499: .It Cm RemoteCommand
1500: Specifies a command to execute on the remote machine after successfully
1501: connecting to the server.
1502: The command string extends to the end of the line, and is executed with
1503: the user's shell.
1.250 jmc 1504: Arguments to
1505: .Cm RemoteCommand
1506: accept the tokens described in the
1507: .Sx TOKENS
1508: section.
1.1 stevesk 1509: .It Cm RemoteForward
1.74 jmc 1510: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1511: the secure channel.
1.273 djm 1512: The remote port may either be forwarded to a specified host and port
1.256 markus 1513: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1514: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1515: The first argument is the listening specification and may be
1.43 djm 1516: .Sm off
1.49 jmc 1517: .Oo Ar bind_address : Oc Ar port
1.43 djm 1518: .Sm on
1.324 dtucker 1519: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1520: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1521: .Ar host : Ns Ar hostport
1522: or a Unix domain socket path,
1.256 markus 1523: otherwise if no destination argument is specified then the remote forwarding
1524: will be established as a SOCKS proxy.
1.347 markus 1525: When acting as a SOCKS proxy the destination of the connection can be
1526: restricted by
1527: .Cm PermitRemoteOpen .
1.256 markus 1528: .Pp
1.138 djm 1529: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1530: Multiple forwardings may be specified, and additional
1531: forwardings can be given on the command line.
1.113 stevesk 1532: Privileged ports can be forwarded only when
1533: logging in as root on the remote machine.
1.326 dtucker 1534: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1535: .Sx TOKENS
1.326 dtucker 1536: section and environment variables as described in the
1537: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1538: section.
1.118 jmc 1539: .Pp
1.117 djm 1540: If the
1541: .Ar port
1.240 jmc 1542: argument is 0,
1.117 djm 1543: the listen port will be dynamically allocated on the server and reported
1544: to the client at run time.
1.43 djm 1545: .Pp
1546: If the
1547: .Ar bind_address
1548: is not specified, the default is to only bind to loopback addresses.
1549: If the
1550: .Ar bind_address
1551: is
1552: .Ql *
1553: or an empty string, then the forwarding is requested to listen on all
1554: interfaces.
1555: Specifying a remote
1556: .Ar bind_address
1.46 jmc 1557: will only succeed if the server's
1558: .Cm GatewayPorts
1.43 djm 1559: option is enabled (see
1.46 jmc 1560: .Xr sshd_config 5 ) .
1.149 djm 1561: .It Cm RequestTTY
1562: Specifies whether to request a pseudo-tty for the session.
1563: The argument may be one of:
1.240 jmc 1564: .Cm no
1.149 djm 1565: (never request a TTY),
1.240 jmc 1566: .Cm yes
1.149 djm 1567: (always request a TTY when standard input is a TTY),
1.240 jmc 1568: .Cm force
1.149 djm 1569: (always request a TTY) or
1.240 jmc 1570: .Cm auto
1.149 djm 1571: (request a TTY when opening a login session).
1572: This option mirrors the
1573: .Fl t
1574: and
1575: .Fl T
1576: flags for
1577: .Xr ssh 1 .
1.196 djm 1578: .It Cm RevokedHostKeys
1579: Specifies revoked host public keys.
1580: Keys listed in this file will be refused for host authentication.
1581: Note that if this file does not exist or is not readable,
1582: then host authentication will be refused for all hosts.
1583: Keys may be specified as a text file, listing one public key per line, or as
1584: an OpenSSH Key Revocation List (KRL) as generated by
1585: .Xr ssh-keygen 1 .
1586: For more information on KRLs, see the KEY REVOCATION LISTS section in
1587: .Xr ssh-keygen 1 .
1.305 naddy 1588: .It Cm SecurityKeyProvider
1.313 naddy 1589: Specifies a path to a library that will be used when loading any
1590: FIDO authenticator-hosted keys, overriding the default of using
1591: the built-in USB HID support.
1.309 naddy 1592: .Pp
1593: If the specified value begins with a
1594: .Sq $
1595: character, then it will be treated as an environment variable containing
1596: the path to the library.
1.32 djm 1597: .It Cm SendEnv
1598: Specifies what variables from the local
1599: .Xr environ 7
1600: should be sent to the server.
1.84 jmc 1601: The server must also support it, and the server must be configured to
1.33 djm 1602: accept these environment variables.
1.207 dtucker 1603: Note that the
1604: .Ev TERM
1.208 jmc 1605: environment variable is always sent whenever a
1.207 dtucker 1606: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1607: Refer to
1608: .Cm AcceptEnv
1609: in
1610: .Xr sshd_config 5
1611: for how to configure the server.
1.80 jmc 1612: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1613: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1614: across multiple
1615: .Cm SendEnv
1616: directives.
1.81 jmc 1617: .Pp
1618: See
1619: .Sx PATTERNS
1620: for more information on patterns.
1.271 djm 1621: .Pp
1.272 jmc 1622: It is possible to clear previously set
1.271 djm 1623: .Cm SendEnv
1624: variable names by prefixing patterns with
1625: .Pa - .
1626: The default is not to send any environment variables.
1.28 markus 1627: .It Cm ServerAliveCountMax
1.73 jmc 1628: Sets the number of server alive messages (see below) which may be
1.28 markus 1629: sent without
1.84 jmc 1630: .Xr ssh 1
1.28 markus 1631: receiving any messages back from the server.
1632: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1633: ssh will disconnect from the server, terminating the session.
1.28 markus 1634: It is important to note that the use of server alive messages is very
1635: different from
1636: .Cm TCPKeepAlive
1637: (below).
1638: The server alive messages are sent through the encrypted channel
1639: and therefore will not be spoofable.
1640: The TCP keepalive option enabled by
1641: .Cm TCPKeepAlive
1642: is spoofable.
1643: The server alive mechanism is valuable when the client or
1.298 dtucker 1644: server depend on knowing when a connection has become unresponsive.
1.28 markus 1645: .Pp
1646: The default value is 3.
1647: If, for example,
1648: .Cm ServerAliveInterval
1.84 jmc 1649: (see below) is set to 15 and
1.28 markus 1650: .Cm ServerAliveCountMax
1.84 jmc 1651: is left at the default, if the server becomes unresponsive,
1652: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1653: .It Cm ServerAliveInterval
1654: Sets a timeout interval in seconds after which if no data has been received
1655: from the server,
1.84 jmc 1656: .Xr ssh 1
1.67 jmc 1657: will send a message through the encrypted
1658: channel to request a response from the server.
1659: The default
1660: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1661: .It Cm SetEnv
1662: Directly specify one or more environment variables and their contents to
1663: be sent to the server.
1664: Similarly to
1665: .Cm SendEnv ,
1666: the server must be prepared to accept the environment variable.
1.191 millert 1667: .It Cm StreamLocalBindMask
1668: Sets the octal file creation mode mask
1669: .Pq umask
1670: used when creating a Unix-domain socket file for local or remote
1671: port forwarding.
1672: This option is only used for port forwarding to a Unix-domain socket file.
1673: .Pp
1674: The default value is 0177, which creates a Unix-domain socket file that is
1675: readable and writable only by the owner.
1676: Note that not all operating systems honor the file mode on Unix-domain
1677: socket files.
1678: .It Cm StreamLocalBindUnlink
1679: Specifies whether to remove an existing Unix-domain socket file for local
1680: or remote port forwarding before creating a new one.
1681: If the socket file already exists and
1682: .Cm StreamLocalBindUnlink
1683: is not enabled,
1684: .Nm ssh
1685: will be unable to forward the port to the Unix-domain socket file.
1686: This option is only used for port forwarding to a Unix-domain socket file.
1687: .Pp
1688: The argument must be
1.240 jmc 1689: .Cm yes
1.191 millert 1690: or
1.240 jmc 1691: .Cm no
1692: (the default).
1.1 stevesk 1693: .It Cm StrictHostKeyChecking
1694: If this flag is set to
1.240 jmc 1695: .Cm yes ,
1.84 jmc 1696: .Xr ssh 1
1.1 stevesk 1697: will never automatically add host keys to the
1.50 djm 1698: .Pa ~/.ssh/known_hosts
1.1 stevesk 1699: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1700: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1701: though it can be annoying when the
1.1 stevesk 1702: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1703: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1704: frequently made.
1705: This option forces the user to manually
1706: add all new hosts.
1.255 jmc 1707: .Pp
1.1 stevesk 1708: If this flag is set to
1.254 djm 1709: .Dq accept-new
1.255 jmc 1710: then ssh will automatically add new host keys to the user
1.254 djm 1711: known hosts files, but will not permit connections to hosts with
1712: changed host keys.
1713: If this flag is set to
1714: .Dq no
1715: or
1716: .Dq off ,
1.255 jmc 1717: ssh will automatically add new host keys to the user known hosts files
1718: and allow connections to hosts with changed hostkeys to proceed,
1719: subject to some restrictions.
1.1 stevesk 1720: If this flag is set to
1.240 jmc 1721: .Cm ask
1722: (the default),
1.1 stevesk 1723: new host keys
1724: will be added to the user known host files only after the user
1725: has confirmed that is what they really want to do, and
1.84 jmc 1726: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1727: The host keys of
1728: known hosts will be verified automatically in all cases.
1.244 jmc 1729: .It Cm SyslogFacility
1730: Gives the facility code that is used when logging messages from
1731: .Xr ssh 1 .
1732: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1733: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1734: The default is USER.
1.26 markus 1735: .It Cm TCPKeepAlive
1736: Specifies whether the system should send TCP keepalive messages to the
1737: other side.
1738: If they are sent, death of the connection or crash of one
1739: of the machines will be properly noticed.
1740: However, this means that
1741: connections will die if the route is down temporarily, and some people
1742: find it annoying.
1743: .Pp
1744: The default is
1.240 jmc 1745: .Cm yes
1.26 markus 1746: (to send TCP keepalive messages), and the client will notice
1747: if the network goes down or the remote host dies.
1748: This is important in scripts, and many users want it too.
1749: .Pp
1750: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1751: .Cm no .
1.265 djm 1752: See also
1753: .Cm ServerAliveInterval
1754: for protocol-level keepalives.
1.65 reyk 1755: .It Cm Tunnel
1.95 stevesk 1756: Request
1.65 reyk 1757: .Xr tun 4
1.69 jmc 1758: device forwarding between the client and the server.
1.65 reyk 1759: The argument must be
1.240 jmc 1760: .Cm yes ,
1761: .Cm point-to-point
1.95 stevesk 1762: (layer 3),
1.240 jmc 1763: .Cm ethernet
1.95 stevesk 1764: (layer 2),
1.65 reyk 1765: or
1.240 jmc 1766: .Cm no
1767: (the default).
1.95 stevesk 1768: Specifying
1.240 jmc 1769: .Cm yes
1.95 stevesk 1770: requests the default tunnel mode, which is
1.240 jmc 1771: .Cm point-to-point .
1.65 reyk 1772: .It Cm TunnelDevice
1.95 stevesk 1773: Specifies the
1.65 reyk 1774: .Xr tun 4
1.95 stevesk 1775: devices to open on the client
1776: .Pq Ar local_tun
1777: and the server
1778: .Pq Ar remote_tun .
1779: .Pp
1780: The argument must be
1781: .Sm off
1782: .Ar local_tun Op : Ar remote_tun .
1783: .Sm on
1784: The devices may be specified by numerical ID or the keyword
1.240 jmc 1785: .Cm any ,
1.95 stevesk 1786: which uses the next available tunnel device.
1787: If
1788: .Ar remote_tun
1789: is not specified, it defaults to
1.240 jmc 1790: .Cm any .
1.95 stevesk 1791: The default is
1.240 jmc 1792: .Cm any:any .
1.201 djm 1793: .It Cm UpdateHostKeys
1.200 djm 1794: Specifies whether
1795: .Xr ssh 1
1796: should accept notifications of additional hostkeys from the server sent
1797: after authentication has completed and add them to
1798: .Cm UserKnownHostsFile .
1799: The argument must be
1.240 jmc 1800: .Cm yes ,
1801: .Cm no
1.320 djm 1802: or
1.240 jmc 1803: .Cm ask .
1.320 djm 1804: This option allows learning alternate hostkeys for a server
1.201 djm 1805: and supports graceful key rotation by allowing a server to send replacement
1806: public keys before old ones are removed.
1.336 djm 1807: .Pp
1.200 djm 1808: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 1809: host was already trusted or explicitly accepted by the user, the host was
1810: authenticated via
1811: .Cm UserKnownHostsFile
1812: (i.e. not
1813: .Cm GlobalKnownHostsFile )
1814: and the host was authenticated using a plain key and not a certificate.
1.320 djm 1815: .Pp
1816: .Cm UpdateHostKeys
1.321 jmc 1817: is enabled by default if the user has not overridden the default
1.320 djm 1818: .Cm UserKnownHostsFile
1.335 djm 1819: setting and has not enabled
1820: .Cm VerifyHostKeyDNS ,
1821: otherwise
1.320 djm 1822: .Cm UpdateHostKeys
1823: will be set to
1.334 djm 1824: .Cm no .
1.320 djm 1825: .Pp
1.204 djm 1826: If
1827: .Cm UpdateHostKeys
1828: is set to
1.240 jmc 1829: .Cm ask ,
1.204 djm 1830: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1831: Confirmation is currently incompatible with
1832: .Cm ControlPersist ,
1833: and will be disabled if it is enabled.
1.200 djm 1834: .Pp
1835: Presently, only
1836: .Xr sshd 8
1837: from OpenSSH 6.8 and greater support the
1.240 jmc 1838: .Qq hostkeys@openssh.com
1.200 djm 1839: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1840: .It Cm User
1841: Specifies the user to log in as.
1842: This can be useful when a different user name is used on different machines.
1843: This saves the trouble of
1844: having to remember to give the user name on the command line.
1845: .It Cm UserKnownHostsFile
1.151 djm 1846: Specifies one or more files to use for the user
1847: host key database, separated by whitespace.
1.329 dtucker 1848: Each filename may use tilde notation to refer to the user's home directory,
1849: the tokens described in the
1850: .Sx TOKENS
1851: section and environment variables as described in the
1852: .Sx ENVIRONMENT VARIABLES
1853: section.
1.151 djm 1854: The default is
1855: .Pa ~/.ssh/known_hosts ,
1856: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1857: .It Cm VerifyHostKeyDNS
1858: Specifies whether to verify the remote key using DNS and SSHFP resource
1859: records.
1.24 jakob 1860: If this option is set to
1.240 jmc 1861: .Cm yes ,
1.25 jmc 1862: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1863: from DNS.
1864: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1865: .Cm ask .
1.24 jakob 1866: If this option is set to
1.240 jmc 1867: .Cm ask ,
1.24 jakob 1868: information on fingerprint match will be displayed, but the user will still
1869: need to confirm new host keys according to the
1870: .Cm StrictHostKeyChecking
1871: option.
1.8 jakob 1872: The default is
1.240 jmc 1873: .Cm no .
1.84 jmc 1874: .Pp
1.240 jmc 1875: See also
1876: .Sx VERIFYING HOST KEYS
1877: in
1.84 jmc 1878: .Xr ssh 1 .
1.111 grunk 1879: .It Cm VisualHostKey
1880: If this flag is set to
1.240 jmc 1881: .Cm yes ,
1.111 grunk 1882: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1883: printed in addition to the fingerprint string at login and
1.114 stevesk 1884: for unknown host keys.
1.111 grunk 1885: If this flag is set to
1.240 jmc 1886: .Cm no
1887: (the default),
1.114 stevesk 1888: no fingerprint strings are printed at login and
1.197 djm 1889: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1890: .It Cm XAuthLocation
1.5 stevesk 1891: Specifies the full pathname of the
1.1 stevesk 1892: .Xr xauth 1
1893: program.
1894: The default is
1895: .Pa /usr/X11R6/bin/xauth .
1896: .El
1.86 jmc 1897: .Sh PATTERNS
1898: A
1899: .Em pattern
1900: consists of zero or more non-whitespace characters,
1901: .Sq *
1902: (a wildcard that matches zero or more characters),
1903: or
1904: .Sq ?\&
1905: (a wildcard that matches exactly one character).
1906: For example, to specify a set of declarations for any host in the
1.240 jmc 1907: .Qq .co.uk
1.86 jmc 1908: set of domains,
1909: the following pattern could be used:
1910: .Pp
1911: .Dl Host *.co.uk
1912: .Pp
1913: The following pattern
1914: would match any host in the 192.168.0.[0-9] network range:
1915: .Pp
1916: .Dl Host 192.168.0.?
1917: .Pp
1918: A
1919: .Em pattern-list
1920: is a comma-separated list of patterns.
1921: Patterns within pattern-lists may be negated
1922: by preceding them with an exclamation mark
1923: .Pq Sq !\& .
1924: For example,
1.174 djm 1925: to allow a key to be used from anywhere within an organization
1.86 jmc 1926: except from the
1.240 jmc 1927: .Qq dialup
1.86 jmc 1928: pool,
1929: the following entry (in authorized_keys) could be used:
1930: .Pp
1931: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1932: .Pp
1933: Note that a negated match will never produce a positive result by itself.
1934: For example, attempting to match
1935: .Qq host3
1936: against the following pattern-list will fail:
1937: .Pp
1938: .Dl from=\&"!host1,!host2\&"
1939: .Pp
1940: The solution here is to include a term that will yield a positive match,
1941: such as a wildcard:
1942: .Pp
1943: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1944: .Sh TOKENS
1945: Arguments to some keywords can make use of tokens,
1946: which are expanded at runtime:
1947: .Pp
1948: .Bl -tag -width XXXX -offset indent -compact
1949: .It %%
1950: A literal
1951: .Sq % .
1952: .It \&%C
1.257 jmc 1953: Hash of %l%h%p%r.
1.239 jmc 1954: .It %d
1955: Local user's home directory.
1.339 djm 1956: .It %f
1957: The fingerprint of the server's host key.
1958: .It %H
1959: The
1960: .Pa known_hosts
1961: hostname or address that is being searched for.
1.239 jmc 1962: .It %h
1963: The remote hostname.
1.340 jmc 1964: .It \%%I
1.339 djm 1965: A string describing the reason for a
1966: .Cm KnownHostsCommand
1.340 jmc 1967: execution: either
1968: .Cm ADDRESS
1.339 djm 1969: when looking up a host by address (only when
1970: .Cm CheckHostIP
1971: is enabled),
1.340 jmc 1972: .Cm HOSTNAME
1973: when searching by hostname, or
1974: .Cm ORDER
1.339 djm 1975: when preparing the host key algorithm preference list to use for the
1976: destination host.
1.239 jmc 1977: .It %i
1978: The local user ID.
1.339 djm 1979: .It %K
1980: The base64 encoded host key.
1.330 dtucker 1981: .It %k
1.350 jsg 1982: The host key alias if specified, otherwise the original remote hostname given
1.330 dtucker 1983: on the command line.
1.239 jmc 1984: .It %L
1985: The local hostname.
1986: .It %l
1987: The local hostname, including the domain name.
1988: .It %n
1989: The original remote hostname, as given on the command line.
1990: .It %p
1991: The remote port.
1992: .It %r
1993: The remote username.
1.261 djm 1994: .It \&%T
1995: The local
1996: .Xr tun 4
1997: or
1998: .Xr tap 4
1999: network interface assigned if
1.262 jmc 2000: tunnel forwarding was requested, or
2001: .Qq NONE
1.261 djm 2002: otherwise.
1.339 djm 2003: .It %t
2004: The type of the server host key, e.g.
2005: .Cm ssh-ed25519
1.239 jmc 2006: .It %u
2007: The local username.
2008: .El
2009: .Pp
1.323 dtucker 2010: .Cm CertificateFile ,
2011: .Cm ControlPath ,
2012: .Cm IdentityAgent ,
2013: .Cm IdentityFile ,
1.339 djm 2014: .Cm KnownHostsCommand ,
1.325 jmc 2015: .Cm LocalForward ,
1.324 dtucker 2016: .Cm Match exec ,
2017: .Cm RemoteCommand ,
1.329 dtucker 2018: .Cm RemoteForward ,
1.323 dtucker 2019: and
1.331 jmc 2020: .Cm UserKnownHostsFile
1.349 dtucker 2021: accept the tokens %%, %C, %d, %h, %i, %k, %L, %l, %n, %p, %r, and %u.
1.239 jmc 2022: .Pp
1.339 djm 2023: .Cm KnownHostsCommand
2024: additionally accepts the tokens %f, %H, %I, %K and %t.
2025: .Pp
1.295 jmc 2026: .Cm Hostname
1.239 jmc 2027: accepts the tokens %% and %h.
2028: .Pp
2029: .Cm LocalCommand
1.323 dtucker 2030: accepts all tokens.
1.239 jmc 2031: .Pp
2032: .Cm ProxyCommand
1.303 djm 2033: accepts the tokens %%, %h, %n, %p, and %r.
1.326 dtucker 2034: .Sh ENVIRONMENT VARIABLES
2035: Arguments to some keywords can be expanded at runtime from environment
2036: variables on the client by enclosing them in
2037: .Ic ${} ,
2038: for example
2039: .Ic ${HOME}/.ssh
2040: would refer to the user's .ssh directory.
2041: If a specified environment variable does not exist then an error will be
2042: returned and the setting for that keyword will be ignored.
2043: .Pp
2044: The keywords
2045: .Cm CertificateFile ,
2046: .Cm ControlPath ,
1.329 dtucker 2047: .Cm IdentityAgent ,
2048: .Cm IdentityFile
1.339 djm 2049: .Cm KnownHostsCommand ,
1.326 dtucker 2050: and
1.329 dtucker 2051: .Cm UserKnownHostsFile
1.326 dtucker 2052: support environment variables.
2053: The keywords
2054: .Cm LocalForward
2055: and
2056: .Cm RemoteForward
2057: support environment variables only for Unix domain socket paths.
1.1 stevesk 2058: .Sh FILES
2059: .Bl -tag -width Ds
1.50 djm 2060: .It Pa ~/.ssh/config
1.1 stevesk 2061: This is the per-user configuration file.
2062: The format of this file is described above.
1.84 jmc 2063: This file is used by the SSH client.
1.30 djm 2064: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2065: read/write for the user, and not writable by others.
1.1 stevesk 2066: .It Pa /etc/ssh/ssh_config
2067: Systemwide configuration file.
2068: This file provides defaults for those
2069: values that are not specified in the user's configuration file, and
2070: for those users who do not have a configuration file.
2071: This file must be world-readable.
2072: .El
1.13 jmc 2073: .Sh SEE ALSO
2074: .Xr ssh 1
1.1 stevesk 2075: .Sh AUTHORS
1.240 jmc 2076: .An -nosplit
1.1 stevesk 2077: OpenSSH is a derivative of the original and free
1.240 jmc 2078: ssh 1.2.12 release by
2079: .An Tatu Ylonen .
2080: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2081: .An Niels Provos , Theo de Raadt
2082: and
2083: .An Dug Song
1.1 stevesk 2084: removed many bugs, re-added newer features and
2085: created OpenSSH.
1.240 jmc 2086: .An Markus Friedl
2087: contributed the support for SSH protocol versions 1.5 and 2.0.
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