Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.356
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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1.356 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.355 2021/07/02 05:11:21 dtucker Exp $
! 37: .Dd $Mdocdate: July 2 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,
1.353 jmc 376: sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,
1.351 djm 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 CheckHostIP
1.240 jmc 416: If set to
417: .Cm yes
1.84 jmc 418: .Xr ssh 1
419: will additionally check the host IP address in the
1.1 stevesk 420: .Pa known_hosts
421: file.
1.240 jmc 422: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 423: and will add addresses of destination hosts to
424: .Pa ~/.ssh/known_hosts
425: in the process, regardless of the setting of
426: .Cm StrictHostKeyChecking .
1.107 grunk 427: If the option is set to
1.341 djm 428: .Cm no
429: (the default),
1.1 stevesk 430: the check will not be executed.
431: .It Cm Ciphers
1.245 djm 432: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 433: Multiple ciphers must be comma-separated.
1.299 kn 434: If the specified list begins with a
1.214 djm 435: .Sq +
436: character, then the specified ciphers will be appended to the default set
437: instead of replacing them.
1.299 kn 438: If the specified list begins with a
1.241 djm 439: .Sq -
440: character, then the specified ciphers (including wildcards) will be removed
441: from the default set instead of replacing them.
1.301 naddy 442: If the specified list begins with a
443: .Sq ^
444: character, then the specified ciphers will be placed at the head of the
445: default set.
1.214 djm 446: .Pp
1.180 djm 447: The supported ciphers are:
1.240 jmc 448: .Bd -literal -offset indent
1.186 naddy 449: 3des-cbc
450: aes128-cbc
451: aes192-cbc
452: aes256-cbc
453: aes128-ctr
454: aes192-ctr
455: aes256-ctr
456: aes128-gcm@openssh.com
457: aes256-gcm@openssh.com
458: chacha20-poly1305@openssh.com
1.240 jmc 459: .Ed
1.180 djm 460: .Pp
1.84 jmc 461: The default is:
1.186 naddy 462: .Bd -literal -offset indent
1.215 jmc 463: chacha20-poly1305@openssh.com,
1.186 naddy 464: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 465: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 466: .Ed
1.180 djm 467: .Pp
1.240 jmc 468: The list of available ciphers may also be obtained using
469: .Qq ssh -Q cipher .
1.1 stevesk 470: .It Cm ClearAllForwardings
1.84 jmc 471: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 472: specified in the configuration files or on the command line be
1.7 jmc 473: cleared.
474: This option is primarily useful when used from the
1.84 jmc 475: .Xr ssh 1
1.1 stevesk 476: command line to clear port forwardings set in
477: configuration files, and is automatically set by
478: .Xr scp 1
479: and
480: .Xr sftp 1 .
481: The argument must be
1.240 jmc 482: .Cm yes
1.1 stevesk 483: or
1.240 jmc 484: .Cm no
485: (the default).
1.1 stevesk 486: .It Cm Compression
487: Specifies whether to use compression.
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).
1.247 naddy 493: .It Cm ConnectionAttempts
494: Specifies the number of tries (one per second) to make before exiting.
495: The argument must be an integer.
496: This may be useful in scripts if the connection sometimes fails.
497: The default is 1.
1.9 djm 498: .It Cm ConnectTimeout
1.84 jmc 499: Specifies the timeout (in seconds) used when connecting to the
500: SSH server, instead of using the default system TCP timeout.
1.302 djm 501: This timeout is applied both to establishing the connection and to performing
502: the initial SSH protocol handshake and key exchange.
1.36 djm 503: .It Cm ControlMaster
504: Enables the sharing of multiple sessions over a single network connection.
505: When set to
1.240 jmc 506: .Cm yes ,
1.84 jmc 507: .Xr ssh 1
1.36 djm 508: will listen for connections on a control socket specified using the
509: .Cm ControlPath
510: argument.
511: Additional sessions can connect to this socket using the same
512: .Cm ControlPath
513: with
514: .Cm ControlMaster
515: set to
1.240 jmc 516: .Cm no
1.38 jmc 517: (the default).
1.64 jmc 518: These sessions will try to reuse the master instance's network connection
1.63 djm 519: rather than initiating new ones, but will fall back to connecting normally
520: if the control socket does not exist, or is not listening.
521: .Pp
1.37 djm 522: Setting this to
1.240 jmc 523: .Cm ask
524: will cause
525: .Xr ssh 1
1.206 jmc 526: to listen for control connections, but require confirmation using
527: .Xr ssh-askpass 1 .
1.51 jakob 528: If the
529: .Cm ControlPath
1.84 jmc 530: cannot be opened,
1.240 jmc 531: .Xr ssh 1
532: will continue without connecting to a master instance.
1.58 djm 533: .Pp
534: X11 and
1.59 jmc 535: .Xr ssh-agent 1
1.58 djm 536: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 537: display and agent forwarded will be the one belonging to the master
1.59 jmc 538: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 539: .Pp
540: Two additional options allow for opportunistic multiplexing: try to use a
541: master connection but fall back to creating a new one if one does not already
542: exist.
543: These options are:
1.240 jmc 544: .Cm auto
1.56 djm 545: and
1.240 jmc 546: .Cm autoask .
1.56 djm 547: The latter requires confirmation like the
1.240 jmc 548: .Cm ask
1.56 djm 549: option.
1.36 djm 550: .It Cm ControlPath
1.55 djm 551: Specify the path to the control socket used for connection sharing as described
552: in the
1.36 djm 553: .Cm ControlMaster
1.57 djm 554: section above or the string
1.240 jmc 555: .Cm none
1.57 djm 556: to disable connection sharing.
1.239 jmc 557: Arguments to
558: .Cm ControlPath
1.326 dtucker 559: may use the tilde syntax to refer to a user's home directory,
560: the tokens described in the
1.239 jmc 561: .Sx TOKENS
1.326 dtucker 562: section and environment variables as described in the
563: .Sx ENVIRONMENT VARIABLES
1.239 jmc 564: section.
1.56 djm 565: It is recommended that any
566: .Cm ControlPath
567: used for opportunistic connection sharing include
1.195 djm 568: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
569: that is not writable by other users.
1.56 djm 570: This ensures that shared connections are uniquely identified.
1.137 djm 571: .It Cm ControlPersist
572: When used in conjunction with
573: .Cm ControlMaster ,
574: specifies that the master connection should remain open
575: in the background (waiting for future client connections)
576: after the initial client connection has been closed.
577: If set to
1.314 naddy 578: .Cm no
579: (the default),
1.137 djm 580: then the master connection will not be placed into the background,
581: and will close as soon as the initial client connection is closed.
582: If set to
1.240 jmc 583: .Cm yes
584: or 0,
1.137 djm 585: then the master connection will remain in the background indefinitely
586: (until killed or closed via a mechanism such as the
1.240 jmc 587: .Qq ssh -O exit ) .
1.137 djm 588: If set to a time in seconds, or a time in any of the formats documented in
589: .Xr sshd_config 5 ,
590: then the backgrounded master connection will automatically terminate
591: after it has remained idle (with no client connections) for the
592: specified time.
1.38 jmc 593: .It Cm DynamicForward
1.74 jmc 594: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 595: over the secure channel, and the application
596: protocol is then used to determine where to connect to from the
597: remote machine.
1.62 djm 598: .Pp
599: The argument must be
600: .Sm off
601: .Oo Ar bind_address : Oc Ar port .
602: .Sm on
1.138 djm 603: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 604: By default, the local port is bound in accordance with the
605: .Cm GatewayPorts
606: setting.
607: However, an explicit
608: .Ar bind_address
609: may be used to bind the connection to a specific address.
610: The
611: .Ar bind_address
612: of
1.240 jmc 613: .Cm localhost
1.62 djm 614: indicates that the listening port be bound for local use only, while an
615: empty address or
616: .Sq *
617: indicates that the port should be available from all interfaces.
618: .Pp
1.38 jmc 619: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 620: .Xr ssh 1
1.38 jmc 621: will act as a SOCKS server.
622: Multiple forwardings may be specified, and
623: additional forwardings can be given on the command line.
624: Only the superuser can forward privileged ports.
1.14 markus 625: .It Cm EnableSSHKeysign
626: Setting this option to
1.240 jmc 627: .Cm yes
1.14 markus 628: in the global client configuration file
629: .Pa /etc/ssh/ssh_config
630: enables the use of the helper program
631: .Xr ssh-keysign 8
632: during
633: .Cm HostbasedAuthentication .
634: The argument must be
1.240 jmc 635: .Cm yes
1.14 markus 636: or
1.240 jmc 637: .Cm no
638: (the default).
1.23 jmc 639: This option should be placed in the non-hostspecific section.
1.14 markus 640: See
641: .Xr ssh-keysign 8
642: for more information.
1.1 stevesk 643: .It Cm EscapeChar
644: Sets the escape character (default:
645: .Ql ~ ) .
646: The escape character can also
647: be set on the command line.
648: The argument should be a single character,
649: .Ql ^
650: followed by a letter, or
1.240 jmc 651: .Cm none
1.1 stevesk 652: to disable the escape
653: character entirely (making the connection transparent for binary
654: data).
1.96 markus 655: .It Cm ExitOnForwardFailure
656: Specifies whether
657: .Xr ssh 1
658: should terminate the connection if it cannot set up all requested
1.216 djm 659: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 660: if either end is unable to bind and listen on a specified port).
1.216 djm 661: Note that
662: .Cm ExitOnForwardFailure
663: does not apply to connections made over port forwardings and will not,
664: for example, cause
665: .Xr ssh 1
666: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 667: The argument must be
1.240 jmc 668: .Cm yes
1.96 markus 669: or
1.240 jmc 670: .Cm no
671: (the default).
1.197 djm 672: .It Cm FingerprintHash
673: Specifies the hash algorithm used when displaying key fingerprints.
674: Valid options are:
1.240 jmc 675: .Cm md5
1.197 djm 676: and
1.240 jmc 677: .Cm sha256
678: (the default).
1.1 stevesk 679: .It Cm ForwardAgent
680: Specifies whether the connection to the authentication agent (if any)
681: will be forwarded to the remote machine.
1.312 djm 682: The argument may be
683: .Cm yes ,
1.240 jmc 684: .Cm no
1.312 djm 685: (the default),
686: an explicit path to an agent socket or the name of an environment variable
687: (beginning with
688: .Sq $ )
689: in which to find the path.
1.3 stevesk 690: .Pp
1.7 jmc 691: Agent forwarding should be enabled with caution.
692: Users with the ability to bypass file permissions on the remote host
693: (for the agent's Unix-domain socket)
694: can access the local agent through the forwarded connection.
695: An attacker cannot obtain key material from the agent,
1.3 stevesk 696: however they can perform operations on the keys that enable them to
697: authenticate using the identities loaded into the agent.
1.1 stevesk 698: .It Cm ForwardX11
699: Specifies whether X11 connections will be automatically redirected
700: over the secure channel and
701: .Ev DISPLAY
702: set.
703: The argument must be
1.240 jmc 704: .Cm yes
1.1 stevesk 705: or
1.240 jmc 706: .Cm no
707: (the default).
1.3 stevesk 708: .Pp
1.7 jmc 709: X11 forwarding should be enabled with caution.
710: Users with the ability to bypass file permissions on the remote host
1.22 markus 711: (for the user's X11 authorization database)
1.7 jmc 712: can access the local X11 display through the forwarded connection.
1.22 markus 713: An attacker may then be able to perform activities such as keystroke monitoring
714: if the
715: .Cm ForwardX11Trusted
716: option is also enabled.
1.134 djm 717: .It Cm ForwardX11Timeout
1.135 jmc 718: Specify a timeout for untrusted X11 forwarding
719: using the format described in the
1.240 jmc 720: .Sx TIME FORMATS
721: section of
1.134 djm 722: .Xr sshd_config 5 .
723: X11 connections received by
724: .Xr ssh 1
725: after this time will be refused.
1.285 djm 726: Setting
727: .Cm ForwardX11Timeout
728: to zero will disable the timeout and permit X11 forwarding for the life
729: of the connection.
1.134 djm 730: The default is to disable untrusted X11 forwarding after twenty minutes has
731: elapsed.
1.22 markus 732: .It Cm ForwardX11Trusted
1.34 jmc 733: If this option is set to
1.240 jmc 734: .Cm yes ,
1.84 jmc 735: remote X11 clients will have full access to the original X11 display.
1.42 djm 736: .Pp
1.22 markus 737: If this option is set to
1.240 jmc 738: .Cm no
739: (the default),
1.84 jmc 740: remote X11 clients will be considered untrusted and prevented
1.22 markus 741: from stealing or tampering with data belonging to trusted X11
742: clients.
1.42 djm 743: Furthermore, the
744: .Xr xauth 1
745: token used for the session will be set to expire after 20 minutes.
746: Remote clients will be refused access after this time.
1.22 markus 747: .Pp
748: See the X11 SECURITY extension specification for full details on
749: the restrictions imposed on untrusted clients.
1.1 stevesk 750: .It Cm GatewayPorts
751: Specifies whether remote hosts are allowed to connect to local
752: forwarded ports.
753: By default,
1.84 jmc 754: .Xr ssh 1
1.7 jmc 755: binds local port forwardings to the loopback address.
756: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 757: .Cm GatewayPorts
1.84 jmc 758: can be used to specify that ssh
1.1 stevesk 759: should bind local port forwardings to the wildcard address,
760: thus allowing remote hosts to connect to forwarded ports.
761: The argument must be
1.240 jmc 762: .Cm yes
1.1 stevesk 763: or
1.240 jmc 764: .Cm no
765: (the default).
1.1 stevesk 766: .It Cm GlobalKnownHostsFile
1.151 djm 767: Specifies one or more files to use for the global
768: host key database, separated by whitespace.
769: The default is
770: .Pa /etc/ssh/ssh_known_hosts ,
771: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 772: .It Cm GSSAPIAuthentication
1.27 markus 773: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 774: The default is
1.240 jmc 775: .Cm no .
1.18 markus 776: .It Cm GSSAPIDelegateCredentials
777: Forward (delegate) credentials to the server.
778: The default is
1.240 jmc 779: .Cm no .
1.44 djm 780: .It Cm HashKnownHosts
781: Indicates that
1.84 jmc 782: .Xr ssh 1
1.44 djm 783: should hash host names and addresses when they are added to
1.50 djm 784: .Pa ~/.ssh/known_hosts .
1.44 djm 785: These hashed names may be used normally by
1.84 jmc 786: .Xr ssh 1
1.44 djm 787: and
1.84 jmc 788: .Xr sshd 8 ,
1.316 djm 789: but they do not visually reveal identifying information if the
790: file's contents are disclosed.
1.44 djm 791: The default is
1.240 jmc 792: .Cm no .
1.97 jmc 793: Note that existing names and addresses in known hosts files
794: will not be converted automatically,
795: but may be manually hashed using
1.45 djm 796: .Xr ssh-keygen 1 .
1.344 dtucker 797: .It Cm HostbasedAcceptedAlgorithms
1.348 djm 798: Specifies the signature algorithms that will be used for hostbased
799: authentication as a comma-separated list of patterns.
1.300 naddy 800: Alternately if the specified list begins with a
1.214 djm 801: .Sq +
1.348 djm 802: character, then the specified signature algorithms will be appended
803: to the default set instead of replacing them.
1.300 naddy 804: If the specified list begins with a
1.241 djm 805: .Sq -
1.348 djm 806: character, then the specified signature algorithms (including wildcards)
807: will be removed from the default set instead of replacing them.
1.301 naddy 808: If the specified list begins with a
809: .Sq ^
1.348 djm 810: character, then the specified signature algorithms will be placed
811: at the head of the default set.
1.213 markus 812: The default for this option is:
813: .Bd -literal -offset 3n
1.333 djm 814: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 815: ecdsa-sha2-nistp256-cert-v01@openssh.com,
816: ecdsa-sha2-nistp384-cert-v01@openssh.com,
817: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 818: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 819: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 820: rsa-sha2-512-cert-v01@openssh.com,
821: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 822: ssh-rsa-cert-v01@openssh.com,
1.333 djm 823: ssh-ed25519,
1.213 markus 824: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 825: sk-ssh-ed25519@openssh.com,
1.311 naddy 826: sk-ecdsa-sha2-nistp256@openssh.com,
827: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 828: .Ed
829: .Pp
1.202 djm 830: The
831: .Fl Q
832: option of
833: .Xr ssh 1
1.348 djm 834: may be used to list supported signature algorithms.
1.344 dtucker 835: This was formerly named HostbasedKeyTypes.
1.345 naddy 836: .It Cm HostbasedAuthentication
837: Specifies whether to try rhosts based authentication with public key
838: authentication.
839: The argument must be
840: .Cm yes
841: or
842: .Cm no
843: (the default).
1.1 stevesk 844: .It Cm HostKeyAlgorithms
1.348 djm 845: Specifies the host key signature algorithms
1.1 stevesk 846: that the client wants to use in order of preference.
1.300 naddy 847: Alternately if the specified list begins with a
1.214 djm 848: .Sq +
1.348 djm 849: character, then the specified signature algorithms will be appended to
850: the default set instead of replacing them.
1.300 naddy 851: If the specified list begins with a
1.241 djm 852: .Sq -
1.348 djm 853: character, then the specified signature algorithms (including wildcards)
854: will be removed from the default set instead of replacing them.
1.301 naddy 855: If the specified list begins with a
856: .Sq ^
1.348 djm 857: character, then the specified signature algorithms will be placed
858: at the head of the default set.
1.1 stevesk 859: The default for this option is:
1.139 djm 860: .Bd -literal -offset 3n
1.333 djm 861: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 862: ecdsa-sha2-nistp256-cert-v01@openssh.com,
863: ecdsa-sha2-nistp384-cert-v01@openssh.com,
864: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 865: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 866: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 867: rsa-sha2-512-cert-v01@openssh.com,
868: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 869: ssh-rsa-cert-v01@openssh.com,
1.333 djm 870: ssh-ed25519,
1.139 djm 871: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 872: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 873: sk-ssh-ed25519@openssh.com,
1.311 naddy 874: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 875: .Ed
1.145 djm 876: .Pp
877: If hostkeys are known for the destination host then this default is modified
878: to prefer their algorithms.
1.198 djm 879: .Pp
1.348 djm 880: The list of available signature algorithms may also be obtained using
1.322 dtucker 881: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 882: .It Cm HostKeyAlias
883: Specifies an alias that should be used instead of the
884: real host name when looking up or saving the host key
1.251 djm 885: in the host key database files and when validating host certificates.
1.84 jmc 886: This option is useful for tunneling SSH connections
1.1 stevesk 887: or for multiple servers running on a single host.
1.295 jmc 888: .It Cm Hostname
1.1 stevesk 889: Specifies the real host name to log into.
890: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 891: Arguments to
1.295 jmc 892: .Cm Hostname
1.239 jmc 893: accept the tokens described in the
894: .Sx TOKENS
895: section.
1.1 stevesk 896: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 897: .Cm Hostname
1.1 stevesk 898: specifications).
1.239 jmc 899: The default is the name given on the command line.
1.29 markus 900: .It Cm IdentitiesOnly
901: Specifies that
1.84 jmc 902: .Xr ssh 1
1.304 djm 903: should only use the configured authentication identity and certificate files
904: (either the default files, or those explicitly configured in the
1.31 jmc 905: .Nm
1.221 djm 906: files
907: or passed on the
908: .Xr ssh 1
1.304 djm 909: command-line),
1.84 jmc 910: even if
911: .Xr ssh-agent 1
1.159 djm 912: or a
913: .Cm PKCS11Provider
1.305 naddy 914: or
915: .Cm SecurityKeyProvider
1.29 markus 916: offers more identities.
917: The argument to this keyword must be
1.240 jmc 918: .Cm yes
1.29 markus 919: or
1.240 jmc 920: .Cm no
921: (the default).
1.84 jmc 922: This option is intended for situations where ssh-agent
1.29 markus 923: offers many different identities.
1.231 markus 924: .It Cm IdentityAgent
925: Specifies the
926: .Ux Ns -domain
927: socket used to communicate with the authentication agent.
928: .Pp
929: This option overrides the
1.240 jmc 930: .Ev SSH_AUTH_SOCK
1.231 markus 931: environment variable and can be used to select a specific agent.
932: Setting the socket name to
1.240 jmc 933: .Cm none
1.231 markus 934: disables the use of an authentication agent.
1.232 markus 935: If the string
1.240 jmc 936: .Qq SSH_AUTH_SOCK
1.232 markus 937: is specified, the location of the socket will be read from the
938: .Ev SSH_AUTH_SOCK
939: environment variable.
1.286 djm 940: Otherwise if the specified value begins with a
941: .Sq $
942: character, then it will be treated as an environment variable containing
943: the location of the socket.
1.231 markus 944: .Pp
1.239 jmc 945: Arguments to
946: .Cm IdentityAgent
1.326 dtucker 947: may use the tilde syntax to refer to a user's home directory,
948: the tokens described in the
1.239 jmc 949: .Sx TOKENS
1.326 dtucker 950: section and environment variables as described in the
951: .Sx ENVIRONMENT VARIABLES
1.239 jmc 952: section.
1.67 jmc 953: .It Cm IdentityFile
1.313 naddy 954: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
955: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 956: The default is
1.139 djm 957: .Pa ~/.ssh/id_dsa ,
1.183 naddy 958: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 959: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 960: .Pa ~/.ssh/id_ed25519 ,
961: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 962: and
1.245 djm 963: .Pa ~/.ssh/id_rsa .
1.67 jmc 964: Additionally, any identities represented by the authentication agent
1.165 djm 965: will be used for authentication unless
966: .Cm IdentitiesOnly
967: is set.
1.221 djm 968: If no certificates have been explicitly specified by
969: .Cm CertificateFile ,
1.129 djm 970: .Xr ssh 1
971: will try to load certificate information from the filename obtained by
972: appending
973: .Pa -cert.pub
974: to the path of a specified
975: .Cm IdentityFile .
1.90 djm 976: .Pp
1.239 jmc 977: Arguments to
978: .Cm IdentityFile
979: may use the tilde syntax to refer to a user's home directory
980: or the tokens described in the
981: .Sx TOKENS
982: section.
1.90 djm 983: .Pp
1.67 jmc 984: It is possible to have
985: multiple identity files specified in configuration files; all these
986: identities will be tried in sequence.
1.152 djm 987: Multiple
988: .Cm IdentityFile
989: directives will add to the list of identities tried (this behaviour
990: differs from that of other configuration directives).
1.165 djm 991: .Pp
992: .Cm IdentityFile
993: may be used in conjunction with
994: .Cm IdentitiesOnly
995: to select which identities in an agent are offered during authentication.
1.221 djm 996: .Cm IdentityFile
997: may also be used in conjunction with
998: .Cm CertificateFile
999: in order to provide any certificate also needed for authentication with
1000: the identity.
1.164 jmc 1001: .It Cm IgnoreUnknown
1002: Specifies a pattern-list of unknown options to be ignored if they are
1003: encountered in configuration parsing.
1004: This may be used to suppress errors if
1005: .Nm
1006: contains options that are unrecognised by
1007: .Xr ssh 1 .
1008: It is recommended that
1009: .Cm IgnoreUnknown
1010: be listed early in the configuration file as it will not be applied
1011: to unknown options that appear before it.
1.229 djm 1012: .It Cm Include
1013: Include the specified configuration file(s).
1.230 jmc 1014: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1015: .Xr glob 7
1.229 djm 1016: wildcards and, for user configurations, shell-like
1.240 jmc 1017: .Sq ~
1.229 djm 1018: references to user home directories.
1.327 djm 1019: Wildcards will be expanded and processed in lexical order.
1.229 djm 1020: Files without absolute paths are assumed to be in
1021: .Pa ~/.ssh
1.230 jmc 1022: if included in a user configuration file or
1.229 djm 1023: .Pa /etc/ssh
1024: if included from the system configuration file.
1025: .Cm Include
1026: directive may appear inside a
1027: .Cm Match
1028: or
1029: .Cm Host
1030: block
1031: to perform conditional inclusion.
1.143 djm 1032: .It Cm IPQoS
1033: Specifies the IPv4 type-of-service or DSCP class for connections.
1034: Accepted values are
1.240 jmc 1035: .Cm af11 ,
1036: .Cm af12 ,
1037: .Cm af13 ,
1038: .Cm af21 ,
1039: .Cm af22 ,
1040: .Cm af23 ,
1041: .Cm af31 ,
1042: .Cm af32 ,
1043: .Cm af33 ,
1044: .Cm af41 ,
1045: .Cm af42 ,
1046: .Cm af43 ,
1047: .Cm cs0 ,
1048: .Cm cs1 ,
1049: .Cm cs2 ,
1050: .Cm cs3 ,
1051: .Cm cs4 ,
1052: .Cm cs5 ,
1053: .Cm cs6 ,
1054: .Cm cs7 ,
1055: .Cm ef ,
1.319 djm 1056: .Cm le ,
1.240 jmc 1057: .Cm lowdelay ,
1058: .Cm throughput ,
1059: .Cm reliability ,
1.253 djm 1060: a numeric value, or
1061: .Cm none
1062: to use the operating system default.
1.146 djm 1063: This option may take one or two arguments, separated by whitespace.
1.143 djm 1064: If one argument is specified, it is used as the packet class unconditionally.
1065: If two values are specified, the first is automatically selected for
1066: interactive sessions and the second for non-interactive sessions.
1067: The default is
1.269 job 1068: .Cm af21
1.272 jmc 1069: (Low-Latency Data)
1.143 djm 1070: for interactive sessions and
1.269 job 1071: .Cm cs1
1.272 jmc 1072: (Lower Effort)
1.143 djm 1073: for non-interactive sessions.
1.103 djm 1074: .It Cm KbdInteractiveAuthentication
1075: Specifies whether to use keyboard-interactive authentication.
1076: The argument to this keyword must be
1.240 jmc 1077: .Cm yes
1078: (the default)
1.103 djm 1079: or
1.240 jmc 1080: .Cm no .
1.355 dtucker 1081: .Cm ChallengeResponseAuthentication
1082: is a deprecated alias for this.
1.39 djm 1083: .It Cm KbdInteractiveDevices
1084: Specifies the list of methods to use in keyboard-interactive authentication.
1085: Multiple method names must be comma-separated.
1086: The default is to use the server specified list.
1.85 jmc 1087: The methods available vary depending on what the server supports.
1088: For an OpenSSH server,
1089: it may be zero or more of:
1.240 jmc 1090: .Cm bsdauth ,
1091: .Cm pam ,
1.85 jmc 1092: and
1.240 jmc 1093: .Cm skey .
1.140 djm 1094: .It Cm KexAlgorithms
1095: Specifies the available KEX (Key Exchange) algorithms.
1096: Multiple algorithms must be comma-separated.
1.299 kn 1097: If the specified list begins with a
1.214 djm 1098: .Sq +
1099: character, then the specified methods will be appended to the default set
1100: instead of replacing them.
1.299 kn 1101: If the specified list begins with a
1.241 djm 1102: .Sq -
1103: character, then the specified methods (including wildcards) will be removed
1104: from the default set instead of replacing them.
1.301 naddy 1105: If the specified list begins with a
1106: .Sq ^
1107: character, then the specified methods will be placed at the head of the
1108: default set.
1.141 jmc 1109: The default is:
1110: .Bd -literal -offset indent
1.238 djm 1111: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1112: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1113: diffie-hellman-group-exchange-sha256,
1.266 djm 1114: diffie-hellman-group16-sha512,
1115: diffie-hellman-group18-sha512,
1.317 tedu 1116: diffie-hellman-group14-sha256
1.141 jmc 1117: .Ed
1.198 djm 1118: .Pp
1.240 jmc 1119: The list of available key exchange algorithms may also be obtained using
1120: .Qq ssh -Q kex .
1.339 djm 1121: .It Cm KnownHostsCommand
1.340 jmc 1122: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1123: those listed in
1124: .Cm UserKnownHostsFile
1125: and
1126: .Cm GlobalKnownHostsFile .
1127: This command is executed after the files have been read.
1.340 jmc 1128: It may write host key lines to standard output in identical format to the
1.339 djm 1129: usual files (described in the
1130: .Sx VERIFYING HOST KEYS
1131: section in
1132: .Xr ssh 1 ) .
1133: Arguments to
1134: .Cm KnownHostsCommand
1135: accept the tokens described in the
1136: .Sx TOKENS
1137: section.
1.340 jmc 1138: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1139: the preference list of host key algorithms to use, again to obtain the
1140: host key for the requested host name and, if
1141: .Cm CheckHostIP
1142: is enabled, one more time to obtain the host key matching the server's
1143: address.
1144: If the command exits abnormally or returns a non-zero exit status then the
1145: connection is terminated.
1.65 reyk 1146: .It Cm LocalCommand
1147: Specifies a command to execute on the local machine after successfully
1148: connecting to the server.
1149: The command string extends to the end of the line, and is executed with
1.105 jmc 1150: the user's shell.
1.239 jmc 1151: Arguments to
1152: .Cm LocalCommand
1153: accept the tokens described in the
1154: .Sx TOKENS
1155: section.
1.123 djm 1156: .Pp
1157: The command is run synchronously and does not have access to the
1158: session of the
1159: .Xr ssh 1
1160: that spawned it.
1161: It should not be used for interactive commands.
1162: .Pp
1.65 reyk 1163: This directive is ignored unless
1164: .Cm PermitLocalCommand
1165: has been enabled.
1.1 stevesk 1166: .It Cm LocalForward
1.74 jmc 1167: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1168: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1169: The first argument specifies the listener and may be
1.43 djm 1170: .Sm off
1.49 jmc 1171: .Oo Ar bind_address : Oc Ar port
1.43 djm 1172: .Sm on
1.324 dtucker 1173: or a Unix domain socket path.
1174: The second argument is the destination and may be
1175: .Ar host : Ns Ar hostport
1176: or a Unix domain socket path if the remote host supports it.
1177: .Pp
1.138 djm 1178: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1179: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1180: given on the command line.
1.1 stevesk 1181: Only the superuser can forward privileged ports.
1.43 djm 1182: By default, the local port is bound in accordance with the
1183: .Cm GatewayPorts
1184: setting.
1185: However, an explicit
1186: .Ar bind_address
1187: may be used to bind the connection to a specific address.
1188: The
1189: .Ar bind_address
1190: of
1.240 jmc 1191: .Cm localhost
1.46 jmc 1192: indicates that the listening port be bound for local use only, while an
1193: empty address or
1194: .Sq *
1.43 djm 1195: indicates that the port should be available from all interfaces.
1.326 dtucker 1196: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1197: .Sx TOKENS
1.326 dtucker 1198: section and environment variables as described in the
1199: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1200: section.
1.1 stevesk 1201: .It Cm LogLevel
1202: Gives the verbosity level that is used when logging messages from
1.84 jmc 1203: .Xr ssh 1 .
1.1 stevesk 1204: The possible values are:
1.84 jmc 1205: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1206: The default is INFO.
1207: DEBUG and DEBUG1 are equivalent.
1208: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1209: .It Cm LogVerbose
1210: Specify one or more overrides to LogLevel.
1211: An override consists of a pattern lists that matches the source file, function
1212: and line number to force detailed logging for.
1213: For example, an override pattern of:
1214: .Bd -literal -offset indent
1215: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1216: .Ed
1217: .Pp
1218: would enable detailed logging for line 1000 of
1.338 jmc 1219: .Pa kex.c ,
1.337 djm 1220: everything in the
1221: .Fn kex_exchange_identification
1222: function, and all code in the
1223: .Pa packet.c
1224: file.
1225: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1226: .It Cm MACs
1227: Specifies the MAC (message authentication code) algorithms
1228: in order of preference.
1.226 jmc 1229: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1230: Multiple algorithms must be comma-separated.
1.299 kn 1231: If the specified list begins with a
1.214 djm 1232: .Sq +
1233: character, then the specified algorithms will be appended to the default set
1234: instead of replacing them.
1.299 kn 1235: If the specified list begins with a
1.241 djm 1236: .Sq -
1237: character, then the specified algorithms (including wildcards) will be removed
1238: from the default set instead of replacing them.
1.301 naddy 1239: If the specified list begins with a
1240: .Sq ^
1241: character, then the specified algorithms will be placed at the head of the
1242: default set.
1.214 djm 1243: .Pp
1.160 markus 1244: The algorithms that contain
1.240 jmc 1245: .Qq -etm
1.160 markus 1246: calculate the MAC after encryption (encrypt-then-mac).
1247: These are considered safer and their use recommended.
1.214 djm 1248: .Pp
1.84 jmc 1249: The default is:
1.101 jmc 1250: .Bd -literal -offset indent
1.160 markus 1251: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1252: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1253: hmac-sha1-etm@openssh.com,
1.186 naddy 1254: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1255: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1256: .Ed
1.198 djm 1257: .Pp
1.240 jmc 1258: The list of available MAC algorithms may also be obtained using
1259: .Qq ssh -Q mac .
1.1 stevesk 1260: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1261: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1262: The argument to this keyword must be
1.240 jmc 1263: .Cm yes
1.1 stevesk 1264: or
1.242 jmc 1265: .Cm no
1.240 jmc 1266: (the default).
1.356 ! djm 1267: .It Cm SessionType
! 1268: May be used to either request invocation of a subsystem on the remote system,
! 1269: or to prevent the execution of a remote command at all.
! 1270: The latter is useful for just forwarding ports.
! 1271: The argument to this keyword must be
! 1272: .Cm none
! 1273: (same as the
! 1274: .Fl N
! 1275: option),
! 1276: .Cm subsystem
! 1277: (same as the
! 1278: .Fl s
! 1279: option) or
! 1280: .Cm default
! 1281: (shell or command execution).
1.1 stevesk 1282: .It Cm NumberOfPasswordPrompts
1283: Specifies the number of password prompts before giving up.
1284: The argument to this keyword must be an integer.
1.84 jmc 1285: The default is 3.
1.1 stevesk 1286: .It Cm PasswordAuthentication
1287: Specifies whether to use password authentication.
1288: The argument to this keyword must be
1.240 jmc 1289: .Cm yes
1290: (the default)
1.1 stevesk 1291: or
1.240 jmc 1292: .Cm no .
1.65 reyk 1293: .It Cm PermitLocalCommand
1294: Allow local command execution via the
1295: .Ic LocalCommand
1296: option or using the
1.66 jmc 1297: .Ic !\& Ns Ar command
1.65 reyk 1298: escape sequence in
1299: .Xr ssh 1 .
1300: The argument must be
1.240 jmc 1301: .Cm yes
1.65 reyk 1302: or
1.240 jmc 1303: .Cm no
1304: (the default).
1.347 markus 1305: .It Cm PermitRemoteOpen
1306: Specifies the destinations to which remote TCP port forwarding is permitted when
1307: .Cm RemoteForward
1308: is used as a SOCKS proxy.
1309: The forwarding specification must be one of the following forms:
1310: .Pp
1311: .Bl -item -offset indent -compact
1312: .It
1313: .Cm PermitRemoteOpen
1314: .Sm off
1315: .Ar host : port
1316: .Sm on
1317: .It
1318: .Cm PermitRemoteOpen
1319: .Sm off
1320: .Ar IPv4_addr : port
1321: .Sm on
1322: .It
1323: .Cm PermitRemoteOpen
1324: .Sm off
1325: .Ar \&[ IPv6_addr \&] : port
1326: .Sm on
1327: .El
1328: .Pp
1329: Multiple forwards may be specified by separating them with whitespace.
1330: An argument of
1331: .Cm any
1332: can be used to remove all restrictions and permit any forwarding requests.
1333: An argument of
1334: .Cm none
1335: can be used to prohibit all forwarding requests.
1336: The wildcard
1337: .Sq *
1338: can be used for host or port to allow all hosts or ports respectively.
1339: Otherwise, no pattern matching or address lookups are performed on supplied
1340: names.
1.127 markus 1341: .It Cm PKCS11Provider
1.292 djm 1342: Specifies which PKCS#11 provider to use or
1343: .Cm none
1344: to indicate that no provider should be used (the default).
1345: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1346: .Xr ssh 1
1.292 djm 1347: should use to communicate with a PKCS#11 token providing keys for user
1348: authentication.
1.67 jmc 1349: .It Cm Port
1350: Specifies the port number to connect on the remote host.
1.84 jmc 1351: The default is 22.
1.1 stevesk 1352: .It Cm PreferredAuthentications
1.226 jmc 1353: Specifies the order in which the client should try authentication methods.
1.48 jmc 1354: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1355: .Cm keyboard-interactive )
1.48 jmc 1356: over another method (e.g.\&
1.131 jmc 1357: .Cm password ) .
1358: The default is:
1359: .Bd -literal -offset indent
1360: gssapi-with-mic,hostbased,publickey,
1361: keyboard-interactive,password
1362: .Ed
1.1 stevesk 1363: .It Cm ProxyCommand
1364: Specifies the command to use to connect to the server.
1365: The command
1.190 djm 1366: string extends to the end of the line, and is executed
1367: using the user's shell
1368: .Ql exec
1369: directive to avoid a lingering shell process.
1370: .Pp
1.239 jmc 1371: Arguments to
1372: .Cm ProxyCommand
1373: accept the tokens described in the
1374: .Sx TOKENS
1375: section.
1.1 stevesk 1376: The command can be basically anything,
1377: and should read from its standard input and write to its standard output.
1378: It should eventually connect an
1379: .Xr sshd 8
1380: server running on some machine, or execute
1381: .Ic sshd -i
1382: somewhere.
1383: Host key management will be done using the
1.296 jmc 1384: .Cm Hostname
1385: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1386: Setting the command to
1.240 jmc 1387: .Cm none
1.6 markus 1388: disables this option entirely.
1.1 stevesk 1389: Note that
1390: .Cm CheckHostIP
1391: is not available for connects with a proxy command.
1.52 djm 1392: .Pp
1393: This directive is useful in conjunction with
1394: .Xr nc 1
1395: and its proxy support.
1.53 jmc 1396: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1397: 192.0.2.0:
1398: .Bd -literal -offset 3n
1399: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1400: .Ed
1.233 djm 1401: .It Cm ProxyJump
1.260 millert 1402: Specifies one or more jump proxies as either
1.233 djm 1403: .Xo
1404: .Sm off
1.234 jmc 1405: .Op Ar user No @
1.233 djm 1406: .Ar host
1.234 jmc 1407: .Op : Ns Ar port
1.233 djm 1408: .Sm on
1.260 millert 1409: or an ssh URI
1.233 djm 1410: .Xc .
1.235 djm 1411: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1412: sequentially.
1.233 djm 1413: Setting this option will cause
1414: .Xr ssh 1
1415: to connect to the target host by first making a
1416: .Xr ssh 1
1417: connection to the specified
1418: .Cm ProxyJump
1419: host and then establishing a
1.234 jmc 1420: TCP forwarding to the ultimate target from there.
1.346 dlg 1421: Setting the host to
1422: .Cm none
1423: disables this option entirely.
1.233 djm 1424: .Pp
1425: Note that this option will compete with the
1426: .Cm ProxyCommand
1427: option - whichever is specified first will prevent later instances of the
1428: other from taking effect.
1.289 djm 1429: .Pp
1430: Note also that the configuration for the destination host (either supplied
1431: via the command-line or the configuration file) is not generally applied
1432: to jump hosts.
1433: .Pa ~/.ssh/config
1434: should be used if specific configuration is required for jump hosts.
1.167 djm 1435: .It Cm ProxyUseFdpass
1.168 jmc 1436: Specifies that
1.167 djm 1437: .Cm ProxyCommand
1438: will pass a connected file descriptor back to
1.168 jmc 1439: .Xr ssh 1
1.167 djm 1440: instead of continuing to execute and pass data.
1441: The default is
1.240 jmc 1442: .Cm no .
1.343 dtucker 1443: .It Cm PubkeyAcceptedAlgorithms
1444: Specifies the signature algorithms that will be used for public key
1445: authentication as a comma-separated list of patterns.
1.299 kn 1446: If the specified list begins with a
1.214 djm 1447: .Sq +
1.343 dtucker 1448: character, then the algorithms after it will be appended to the default
1.214 djm 1449: instead of replacing it.
1.299 kn 1450: If the specified list begins with a
1.241 djm 1451: .Sq -
1.343 dtucker 1452: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1453: from the default set instead of replacing them.
1.301 naddy 1454: If the specified list begins with a
1455: .Sq ^
1.343 dtucker 1456: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1457: default set.
1.213 markus 1458: The default for this option is:
1459: .Bd -literal -offset 3n
1.333 djm 1460: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1461: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1462: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1463: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1464: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1465: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1466: rsa-sha2-512-cert-v01@openssh.com,
1467: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1468: ssh-rsa-cert-v01@openssh.com,
1.333 djm 1469: ssh-ed25519,
1.311 naddy 1470: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1471: sk-ssh-ed25519@openssh.com,
1.305 naddy 1472: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1473: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1474: .Ed
1475: .Pp
1.348 djm 1476: The list of available signature algorithms may also be obtained using
1.343 dtucker 1477: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.1 stevesk 1478: .It Cm PubkeyAuthentication
1479: Specifies whether to try public key authentication.
1480: The argument to this keyword must be
1.240 jmc 1481: .Cm yes
1482: (the default)
1.1 stevesk 1483: or
1.240 jmc 1484: .Cm no .
1.75 dtucker 1485: .It Cm RekeyLimit
1486: Specifies the maximum amount of data that may be transmitted before the
1.342 rob 1487: session key is renegotiated, optionally followed by a maximum amount of
1.162 dtucker 1488: time that may pass before the session key is renegotiated.
1489: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1490: .Sq K ,
1491: .Sq M ,
1.75 dtucker 1492: or
1.76 jmc 1493: .Sq G
1.75 dtucker 1494: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1495: The default is between
1.84 jmc 1496: .Sq 1G
1.75 dtucker 1497: and
1.84 jmc 1498: .Sq 4G ,
1.75 dtucker 1499: depending on the cipher.
1.162 dtucker 1500: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1501: units documented in the TIME FORMATS section of
1.162 dtucker 1502: .Xr sshd_config 5 .
1503: The default value for
1504: .Cm RekeyLimit
1505: is
1.240 jmc 1506: .Cm default none ,
1.162 dtucker 1507: which means that rekeying is performed after the cipher's default amount
1508: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1509: .It Cm RemoteCommand
1510: Specifies a command to execute on the remote machine after successfully
1511: connecting to the server.
1512: The command string extends to the end of the line, and is executed with
1513: the user's shell.
1.250 jmc 1514: Arguments to
1515: .Cm RemoteCommand
1516: accept the tokens described in the
1517: .Sx TOKENS
1518: section.
1.1 stevesk 1519: .It Cm RemoteForward
1.74 jmc 1520: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1521: the secure channel.
1.273 djm 1522: The remote port may either be forwarded to a specified host and port
1.256 markus 1523: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1524: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1525: The first argument is the listening specification and may be
1.43 djm 1526: .Sm off
1.49 jmc 1527: .Oo Ar bind_address : Oc Ar port
1.43 djm 1528: .Sm on
1.324 dtucker 1529: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1530: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1531: .Ar host : Ns Ar hostport
1532: or a Unix domain socket path,
1.256 markus 1533: otherwise if no destination argument is specified then the remote forwarding
1534: will be established as a SOCKS proxy.
1.347 markus 1535: When acting as a SOCKS proxy the destination of the connection can be
1536: restricted by
1537: .Cm PermitRemoteOpen .
1.256 markus 1538: .Pp
1.138 djm 1539: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1540: Multiple forwardings may be specified, and additional
1541: forwardings can be given on the command line.
1.113 stevesk 1542: Privileged ports can be forwarded only when
1543: logging in as root on the remote machine.
1.326 dtucker 1544: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1545: .Sx TOKENS
1.326 dtucker 1546: section and environment variables as described in the
1547: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1548: section.
1.118 jmc 1549: .Pp
1.117 djm 1550: If the
1551: .Ar port
1.240 jmc 1552: argument is 0,
1.117 djm 1553: the listen port will be dynamically allocated on the server and reported
1554: to the client at run time.
1.43 djm 1555: .Pp
1556: If the
1557: .Ar bind_address
1558: is not specified, the default is to only bind to loopback addresses.
1559: If the
1560: .Ar bind_address
1561: is
1562: .Ql *
1563: or an empty string, then the forwarding is requested to listen on all
1564: interfaces.
1565: Specifying a remote
1566: .Ar bind_address
1.46 jmc 1567: will only succeed if the server's
1568: .Cm GatewayPorts
1.43 djm 1569: option is enabled (see
1.46 jmc 1570: .Xr sshd_config 5 ) .
1.149 djm 1571: .It Cm RequestTTY
1572: Specifies whether to request a pseudo-tty for the session.
1573: The argument may be one of:
1.240 jmc 1574: .Cm no
1.149 djm 1575: (never request a TTY),
1.240 jmc 1576: .Cm yes
1.149 djm 1577: (always request a TTY when standard input is a TTY),
1.240 jmc 1578: .Cm force
1.149 djm 1579: (always request a TTY) or
1.240 jmc 1580: .Cm auto
1.149 djm 1581: (request a TTY when opening a login session).
1582: This option mirrors the
1583: .Fl t
1584: and
1585: .Fl T
1586: flags for
1587: .Xr ssh 1 .
1.196 djm 1588: .It Cm RevokedHostKeys
1589: Specifies revoked host public keys.
1590: Keys listed in this file will be refused for host authentication.
1591: Note that if this file does not exist or is not readable,
1592: then host authentication will be refused for all hosts.
1593: Keys may be specified as a text file, listing one public key per line, or as
1594: an OpenSSH Key Revocation List (KRL) as generated by
1595: .Xr ssh-keygen 1 .
1596: For more information on KRLs, see the KEY REVOCATION LISTS section in
1597: .Xr ssh-keygen 1 .
1.305 naddy 1598: .It Cm SecurityKeyProvider
1.313 naddy 1599: Specifies a path to a library that will be used when loading any
1600: FIDO authenticator-hosted keys, overriding the default of using
1601: the built-in USB HID support.
1.309 naddy 1602: .Pp
1603: If the specified value begins with a
1604: .Sq $
1605: character, then it will be treated as an environment variable containing
1606: the path to the library.
1.32 djm 1607: .It Cm SendEnv
1608: Specifies what variables from the local
1609: .Xr environ 7
1610: should be sent to the server.
1.84 jmc 1611: The server must also support it, and the server must be configured to
1.33 djm 1612: accept these environment variables.
1.207 dtucker 1613: Note that the
1614: .Ev TERM
1.208 jmc 1615: environment variable is always sent whenever a
1.207 dtucker 1616: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1617: Refer to
1618: .Cm AcceptEnv
1619: in
1620: .Xr sshd_config 5
1621: for how to configure the server.
1.80 jmc 1622: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1623: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1624: across multiple
1625: .Cm SendEnv
1626: directives.
1.81 jmc 1627: .Pp
1628: See
1629: .Sx PATTERNS
1630: for more information on patterns.
1.271 djm 1631: .Pp
1.272 jmc 1632: It is possible to clear previously set
1.271 djm 1633: .Cm SendEnv
1634: variable names by prefixing patterns with
1635: .Pa - .
1636: The default is not to send any environment variables.
1.28 markus 1637: .It Cm ServerAliveCountMax
1.73 jmc 1638: Sets the number of server alive messages (see below) which may be
1.28 markus 1639: sent without
1.84 jmc 1640: .Xr ssh 1
1.28 markus 1641: receiving any messages back from the server.
1642: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1643: ssh will disconnect from the server, terminating the session.
1.28 markus 1644: It is important to note that the use of server alive messages is very
1645: different from
1646: .Cm TCPKeepAlive
1647: (below).
1648: The server alive messages are sent through the encrypted channel
1649: and therefore will not be spoofable.
1650: The TCP keepalive option enabled by
1651: .Cm TCPKeepAlive
1652: is spoofable.
1653: The server alive mechanism is valuable when the client or
1.298 dtucker 1654: server depend on knowing when a connection has become unresponsive.
1.28 markus 1655: .Pp
1656: The default value is 3.
1657: If, for example,
1658: .Cm ServerAliveInterval
1.84 jmc 1659: (see below) is set to 15 and
1.28 markus 1660: .Cm ServerAliveCountMax
1.84 jmc 1661: is left at the default, if the server becomes unresponsive,
1662: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1663: .It Cm ServerAliveInterval
1664: Sets a timeout interval in seconds after which if no data has been received
1665: from the server,
1.84 jmc 1666: .Xr ssh 1
1.67 jmc 1667: will send a message through the encrypted
1668: channel to request a response from the server.
1669: The default
1670: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1671: .It Cm SetEnv
1672: Directly specify one or more environment variables and their contents to
1673: be sent to the server.
1674: Similarly to
1675: .Cm SendEnv ,
1.354 djm 1676: with the exception of the
1677: .Ev TERM
1678: variable, the server must be prepared to accept the environment variable.
1.191 millert 1679: .It Cm StreamLocalBindMask
1680: Sets the octal file creation mode mask
1681: .Pq umask
1682: used when creating a Unix-domain socket file for local or remote
1683: port forwarding.
1684: This option is only used for port forwarding to a Unix-domain socket file.
1685: .Pp
1686: The default value is 0177, which creates a Unix-domain socket file that is
1687: readable and writable only by the owner.
1688: Note that not all operating systems honor the file mode on Unix-domain
1689: socket files.
1690: .It Cm StreamLocalBindUnlink
1691: Specifies whether to remove an existing Unix-domain socket file for local
1692: or remote port forwarding before creating a new one.
1693: If the socket file already exists and
1694: .Cm StreamLocalBindUnlink
1695: is not enabled,
1696: .Nm ssh
1697: will be unable to forward the port to the Unix-domain socket file.
1698: This option is only used for port forwarding to a Unix-domain socket file.
1699: .Pp
1700: The argument must be
1.240 jmc 1701: .Cm yes
1.191 millert 1702: or
1.240 jmc 1703: .Cm no
1704: (the default).
1.1 stevesk 1705: .It Cm StrictHostKeyChecking
1706: If this flag is set to
1.240 jmc 1707: .Cm yes ,
1.84 jmc 1708: .Xr ssh 1
1.1 stevesk 1709: will never automatically add host keys to the
1.50 djm 1710: .Pa ~/.ssh/known_hosts
1.1 stevesk 1711: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1712: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1713: though it can be annoying when the
1.1 stevesk 1714: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1715: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1716: frequently made.
1717: This option forces the user to manually
1718: add all new hosts.
1.255 jmc 1719: .Pp
1.1 stevesk 1720: If this flag is set to
1.254 djm 1721: .Dq accept-new
1.255 jmc 1722: then ssh will automatically add new host keys to the user
1.254 djm 1723: known hosts files, but will not permit connections to hosts with
1724: changed host keys.
1725: If this flag is set to
1726: .Dq no
1727: or
1728: .Dq off ,
1.255 jmc 1729: ssh will automatically add new host keys to the user known hosts files
1730: and allow connections to hosts with changed hostkeys to proceed,
1731: subject to some restrictions.
1.1 stevesk 1732: If this flag is set to
1.240 jmc 1733: .Cm ask
1734: (the default),
1.1 stevesk 1735: new host keys
1736: will be added to the user known host files only after the user
1737: has confirmed that is what they really want to do, and
1.84 jmc 1738: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1739: The host keys of
1740: known hosts will be verified automatically in all cases.
1.244 jmc 1741: .It Cm SyslogFacility
1742: Gives the facility code that is used when logging messages from
1743: .Xr ssh 1 .
1744: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1745: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1746: The default is USER.
1.26 markus 1747: .It Cm TCPKeepAlive
1748: Specifies whether the system should send TCP keepalive messages to the
1749: other side.
1750: If they are sent, death of the connection or crash of one
1751: of the machines will be properly noticed.
1752: However, this means that
1753: connections will die if the route is down temporarily, and some people
1754: find it annoying.
1755: .Pp
1756: The default is
1.240 jmc 1757: .Cm yes
1.26 markus 1758: (to send TCP keepalive messages), and the client will notice
1759: if the network goes down or the remote host dies.
1760: This is important in scripts, and many users want it too.
1761: .Pp
1762: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1763: .Cm no .
1.265 djm 1764: See also
1765: .Cm ServerAliveInterval
1766: for protocol-level keepalives.
1.65 reyk 1767: .It Cm Tunnel
1.95 stevesk 1768: Request
1.65 reyk 1769: .Xr tun 4
1.69 jmc 1770: device forwarding between the client and the server.
1.65 reyk 1771: The argument must be
1.240 jmc 1772: .Cm yes ,
1773: .Cm point-to-point
1.95 stevesk 1774: (layer 3),
1.240 jmc 1775: .Cm ethernet
1.95 stevesk 1776: (layer 2),
1.65 reyk 1777: or
1.240 jmc 1778: .Cm no
1779: (the default).
1.95 stevesk 1780: Specifying
1.240 jmc 1781: .Cm yes
1.95 stevesk 1782: requests the default tunnel mode, which is
1.240 jmc 1783: .Cm point-to-point .
1.65 reyk 1784: .It Cm TunnelDevice
1.95 stevesk 1785: Specifies the
1.65 reyk 1786: .Xr tun 4
1.95 stevesk 1787: devices to open on the client
1788: .Pq Ar local_tun
1789: and the server
1790: .Pq Ar remote_tun .
1791: .Pp
1792: The argument must be
1793: .Sm off
1794: .Ar local_tun Op : Ar remote_tun .
1795: .Sm on
1796: The devices may be specified by numerical ID or the keyword
1.240 jmc 1797: .Cm any ,
1.95 stevesk 1798: which uses the next available tunnel device.
1799: If
1800: .Ar remote_tun
1801: is not specified, it defaults to
1.240 jmc 1802: .Cm any .
1.95 stevesk 1803: The default is
1.240 jmc 1804: .Cm any:any .
1.201 djm 1805: .It Cm UpdateHostKeys
1.200 djm 1806: Specifies whether
1807: .Xr ssh 1
1808: should accept notifications of additional hostkeys from the server sent
1809: after authentication has completed and add them to
1810: .Cm UserKnownHostsFile .
1811: The argument must be
1.240 jmc 1812: .Cm yes ,
1813: .Cm no
1.320 djm 1814: or
1.240 jmc 1815: .Cm ask .
1.320 djm 1816: This option allows learning alternate hostkeys for a server
1.201 djm 1817: and supports graceful key rotation by allowing a server to send replacement
1818: public keys before old ones are removed.
1.336 djm 1819: .Pp
1.200 djm 1820: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 1821: host was already trusted or explicitly accepted by the user, the host was
1822: authenticated via
1823: .Cm UserKnownHostsFile
1824: (i.e. not
1825: .Cm GlobalKnownHostsFile )
1826: and the host was authenticated using a plain key and not a certificate.
1.320 djm 1827: .Pp
1828: .Cm UpdateHostKeys
1.321 jmc 1829: is enabled by default if the user has not overridden the default
1.320 djm 1830: .Cm UserKnownHostsFile
1.335 djm 1831: setting and has not enabled
1832: .Cm VerifyHostKeyDNS ,
1833: otherwise
1.320 djm 1834: .Cm UpdateHostKeys
1835: will be set to
1.334 djm 1836: .Cm no .
1.320 djm 1837: .Pp
1.204 djm 1838: If
1839: .Cm UpdateHostKeys
1840: is set to
1.240 jmc 1841: .Cm ask ,
1.204 djm 1842: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1843: Confirmation is currently incompatible with
1844: .Cm ControlPersist ,
1845: and will be disabled if it is enabled.
1.200 djm 1846: .Pp
1847: Presently, only
1848: .Xr sshd 8
1849: from OpenSSH 6.8 and greater support the
1.240 jmc 1850: .Qq hostkeys@openssh.com
1.200 djm 1851: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1852: .It Cm User
1853: Specifies the user to log in as.
1854: This can be useful when a different user name is used on different machines.
1855: This saves the trouble of
1856: having to remember to give the user name on the command line.
1857: .It Cm UserKnownHostsFile
1.151 djm 1858: Specifies one or more files to use for the user
1859: host key database, separated by whitespace.
1.329 dtucker 1860: Each filename may use tilde notation to refer to the user's home directory,
1861: the tokens described in the
1862: .Sx TOKENS
1863: section and environment variables as described in the
1864: .Sx ENVIRONMENT VARIABLES
1865: section.
1.151 djm 1866: The default is
1867: .Pa ~/.ssh/known_hosts ,
1868: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1869: .It Cm VerifyHostKeyDNS
1870: Specifies whether to verify the remote key using DNS and SSHFP resource
1871: records.
1.24 jakob 1872: If this option is set to
1.240 jmc 1873: .Cm yes ,
1.25 jmc 1874: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1875: from DNS.
1876: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1877: .Cm ask .
1.24 jakob 1878: If this option is set to
1.240 jmc 1879: .Cm ask ,
1.24 jakob 1880: information on fingerprint match will be displayed, but the user will still
1881: need to confirm new host keys according to the
1882: .Cm StrictHostKeyChecking
1883: option.
1.8 jakob 1884: The default is
1.240 jmc 1885: .Cm no .
1.84 jmc 1886: .Pp
1.240 jmc 1887: See also
1888: .Sx VERIFYING HOST KEYS
1889: in
1.84 jmc 1890: .Xr ssh 1 .
1.111 grunk 1891: .It Cm VisualHostKey
1892: If this flag is set to
1.240 jmc 1893: .Cm yes ,
1.111 grunk 1894: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1895: printed in addition to the fingerprint string at login and
1.114 stevesk 1896: for unknown host keys.
1.111 grunk 1897: If this flag is set to
1.240 jmc 1898: .Cm no
1899: (the default),
1.114 stevesk 1900: no fingerprint strings are printed at login and
1.197 djm 1901: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1902: .It Cm XAuthLocation
1.5 stevesk 1903: Specifies the full pathname of the
1.1 stevesk 1904: .Xr xauth 1
1905: program.
1906: The default is
1907: .Pa /usr/X11R6/bin/xauth .
1908: .El
1.86 jmc 1909: .Sh PATTERNS
1910: A
1911: .Em pattern
1912: consists of zero or more non-whitespace characters,
1913: .Sq *
1914: (a wildcard that matches zero or more characters),
1915: or
1916: .Sq ?\&
1917: (a wildcard that matches exactly one character).
1918: For example, to specify a set of declarations for any host in the
1.240 jmc 1919: .Qq .co.uk
1.86 jmc 1920: set of domains,
1921: the following pattern could be used:
1922: .Pp
1923: .Dl Host *.co.uk
1924: .Pp
1925: The following pattern
1926: would match any host in the 192.168.0.[0-9] network range:
1927: .Pp
1928: .Dl Host 192.168.0.?
1929: .Pp
1930: A
1931: .Em pattern-list
1932: is a comma-separated list of patterns.
1933: Patterns within pattern-lists may be negated
1934: by preceding them with an exclamation mark
1935: .Pq Sq !\& .
1936: For example,
1.174 djm 1937: to allow a key to be used from anywhere within an organization
1.86 jmc 1938: except from the
1.240 jmc 1939: .Qq dialup
1.86 jmc 1940: pool,
1941: the following entry (in authorized_keys) could be used:
1942: .Pp
1943: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1944: .Pp
1945: Note that a negated match will never produce a positive result by itself.
1946: For example, attempting to match
1947: .Qq host3
1948: against the following pattern-list will fail:
1949: .Pp
1950: .Dl from=\&"!host1,!host2\&"
1951: .Pp
1952: The solution here is to include a term that will yield a positive match,
1953: such as a wildcard:
1954: .Pp
1955: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1956: .Sh TOKENS
1957: Arguments to some keywords can make use of tokens,
1958: which are expanded at runtime:
1959: .Pp
1960: .Bl -tag -width XXXX -offset indent -compact
1961: .It %%
1962: A literal
1963: .Sq % .
1964: .It \&%C
1.257 jmc 1965: Hash of %l%h%p%r.
1.239 jmc 1966: .It %d
1967: Local user's home directory.
1.339 djm 1968: .It %f
1969: The fingerprint of the server's host key.
1970: .It %H
1971: The
1972: .Pa known_hosts
1973: hostname or address that is being searched for.
1.239 jmc 1974: .It %h
1975: The remote hostname.
1.340 jmc 1976: .It \%%I
1.339 djm 1977: A string describing the reason for a
1978: .Cm KnownHostsCommand
1.340 jmc 1979: execution: either
1980: .Cm ADDRESS
1.339 djm 1981: when looking up a host by address (only when
1982: .Cm CheckHostIP
1983: is enabled),
1.340 jmc 1984: .Cm HOSTNAME
1985: when searching by hostname, or
1986: .Cm ORDER
1.339 djm 1987: when preparing the host key algorithm preference list to use for the
1988: destination host.
1.239 jmc 1989: .It %i
1990: The local user ID.
1.339 djm 1991: .It %K
1992: The base64 encoded host key.
1.330 dtucker 1993: .It %k
1.350 jsg 1994: The host key alias if specified, otherwise the original remote hostname given
1.330 dtucker 1995: on the command line.
1.239 jmc 1996: .It %L
1997: The local hostname.
1998: .It %l
1999: The local hostname, including the domain name.
2000: .It %n
2001: The original remote hostname, as given on the command line.
2002: .It %p
2003: The remote port.
2004: .It %r
2005: The remote username.
1.261 djm 2006: .It \&%T
2007: The local
2008: .Xr tun 4
2009: or
2010: .Xr tap 4
2011: network interface assigned if
1.262 jmc 2012: tunnel forwarding was requested, or
2013: .Qq NONE
1.261 djm 2014: otherwise.
1.339 djm 2015: .It %t
2016: The type of the server host key, e.g.
2017: .Cm ssh-ed25519
1.239 jmc 2018: .It %u
2019: The local username.
2020: .El
2021: .Pp
1.323 dtucker 2022: .Cm CertificateFile ,
2023: .Cm ControlPath ,
2024: .Cm IdentityAgent ,
2025: .Cm IdentityFile ,
1.339 djm 2026: .Cm KnownHostsCommand ,
1.325 jmc 2027: .Cm LocalForward ,
1.324 dtucker 2028: .Cm Match exec ,
2029: .Cm RemoteCommand ,
1.329 dtucker 2030: .Cm RemoteForward ,
1.323 dtucker 2031: and
1.331 jmc 2032: .Cm UserKnownHostsFile
1.349 dtucker 2033: accept the tokens %%, %C, %d, %h, %i, %k, %L, %l, %n, %p, %r, and %u.
1.239 jmc 2034: .Pp
1.339 djm 2035: .Cm KnownHostsCommand
2036: additionally accepts the tokens %f, %H, %I, %K and %t.
2037: .Pp
1.295 jmc 2038: .Cm Hostname
1.239 jmc 2039: accepts the tokens %% and %h.
2040: .Pp
2041: .Cm LocalCommand
1.323 dtucker 2042: accepts all tokens.
1.239 jmc 2043: .Pp
2044: .Cm ProxyCommand
1.303 djm 2045: accepts the tokens %%, %h, %n, %p, and %r.
1.326 dtucker 2046: .Sh ENVIRONMENT VARIABLES
2047: Arguments to some keywords can be expanded at runtime from environment
2048: variables on the client by enclosing them in
2049: .Ic ${} ,
2050: for example
2051: .Ic ${HOME}/.ssh
2052: would refer to the user's .ssh directory.
2053: If a specified environment variable does not exist then an error will be
2054: returned and the setting for that keyword will be ignored.
2055: .Pp
2056: The keywords
2057: .Cm CertificateFile ,
2058: .Cm ControlPath ,
1.329 dtucker 2059: .Cm IdentityAgent ,
1.352 jmc 2060: .Cm IdentityFile ,
1.339 djm 2061: .Cm KnownHostsCommand ,
1.326 dtucker 2062: and
1.329 dtucker 2063: .Cm UserKnownHostsFile
1.326 dtucker 2064: support environment variables.
2065: The keywords
2066: .Cm LocalForward
2067: and
2068: .Cm RemoteForward
2069: support environment variables only for Unix domain socket paths.
1.1 stevesk 2070: .Sh FILES
2071: .Bl -tag -width Ds
1.50 djm 2072: .It Pa ~/.ssh/config
1.1 stevesk 2073: This is the per-user configuration file.
2074: The format of this file is described above.
1.84 jmc 2075: This file is used by the SSH client.
1.30 djm 2076: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2077: read/write for the user, and not writable by others.
1.1 stevesk 2078: .It Pa /etc/ssh/ssh_config
2079: Systemwide configuration file.
2080: This file provides defaults for those
2081: values that are not specified in the user's configuration file, and
2082: for those users who do not have a configuration file.
2083: This file must be world-readable.
2084: .El
1.13 jmc 2085: .Sh SEE ALSO
2086: .Xr ssh 1
1.1 stevesk 2087: .Sh AUTHORS
1.240 jmc 2088: .An -nosplit
1.1 stevesk 2089: OpenSSH is a derivative of the original and free
1.240 jmc 2090: ssh 1.2.12 release by
2091: .An Tatu Ylonen .
2092: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2093: .An Niels Provos , Theo de Raadt
2094: and
2095: .An Dug Song
1.1 stevesk 2096: removed many bugs, re-added newer features and
2097: created OpenSSH.
1.240 jmc 2098: .An Markus Friedl
2099: contributed the support for SSH protocol versions 1.5 and 2.0.
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