Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.322
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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1.322 ! dtucker 36: .\" $OpenBSD: ssh_config.5,v 1.321 2020/01/31 22:25:59 jmc Exp $
! 37: .Dd $Mdocdate: January 31 2020 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
1.310 jmc 42: .Nd OpenSSH client configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.287 djm 142: .Cm final ,
1.176 djm 143: .Cm exec ,
1.169 djm 144: .Cm host ,
145: .Cm originalhost ,
146: .Cm user ,
147: and
148: .Cm localuser .
1.193 djm 149: The
150: .Cm all
151: criteria must appear alone or immediately after
1.287 djm 152: .Cm canonical
153: or
154: .Cm final .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
1.288 jmc 157: .Cm all ,
158: .Cm canonical ,
1.193 djm 159: and
1.287 djm 160: .Cm final
1.193 djm 161: require an argument.
162: Criteria may be negated by prepending an exclamation mark
163: .Pq Sq !\& .
1.169 djm 164: .Pp
1.177 jmc 165: The
1.193 djm 166: .Cm canonical
1.210 dtucker 167: keyword matches only when the configuration file is being re-parsed
1.193 djm 168: after hostname canonicalization (see the
169: .Cm CanonicalizeHostname
1.288 jmc 170: option).
1.193 djm 171: This may be useful to specify conditions that work with canonical host
172: names only.
1.287 djm 173: .Pp
174: The
175: .Cm final
176: keyword requests that the configuration be re-parsed (regardless of whether
177: .Cm CanonicalizeHostname
178: is enabled), and matches only during this final pass.
179: If
180: .Cm CanonicalizeHostname
181: is enabled, then
182: .Cm canonical
183: and
184: .Cm final
185: match during the same pass.
186: .Pp
1.193 djm 187: The
1.176 djm 188: .Cm exec
1.177 jmc 189: keyword executes the specified command under the user's shell.
1.169 djm 190: If the command returns a zero exit status then the condition is considered true.
191: Commands containing whitespace characters must be quoted.
1.239 jmc 192: Arguments to
193: .Cm exec
194: accept the tokens described in the
195: .Sx TOKENS
196: section.
1.169 djm 197: .Pp
198: The other keywords' criteria must be single entries or comma-separated
199: lists and may use the wildcard and negation operators described in the
200: .Sx PATTERNS
201: section.
202: The criteria for the
203: .Cm host
204: keyword are matched against the target hostname, after any substitution
205: by the
1.295 jmc 206: .Cm Hostname
1.193 djm 207: or
208: .Cm CanonicalizeHostname
209: options.
1.169 djm 210: The
211: .Cm originalhost
212: keyword matches against the hostname as it was specified on the command-line.
213: The
214: .Cm user
215: keyword matches against the target username on the remote host.
216: The
217: .Cm localuser
218: keyword matches against the name of the local user running
219: .Xr ssh 1
220: (this keyword may be useful in system-wide
221: .Nm
222: files).
1.222 jcs 223: .It Cm AddKeysToAgent
224: Specifies whether keys should be automatically added to a running
1.223 jmc 225: .Xr ssh-agent 1 .
1.222 jcs 226: If this option is set to
1.240 jmc 227: .Cm yes
1.222 jcs 228: and a key is loaded from a file, the key and its passphrase are added to
229: the agent with the default lifetime, as if by
230: .Xr ssh-add 1 .
231: If this option is set to
1.240 jmc 232: .Cm ask ,
233: .Xr ssh 1
1.222 jcs 234: will require confirmation using the
235: .Ev SSH_ASKPASS
236: program before adding a key (see
237: .Xr ssh-add 1
238: for details).
239: If this option is set to
1.240 jmc 240: .Cm confirm ,
1.222 jcs 241: each use of the key must be confirmed, as if the
242: .Fl c
243: option was specified to
244: .Xr ssh-add 1 .
245: If this option is set to
1.240 jmc 246: .Cm no ,
1.222 jcs 247: no keys are added to the agent.
248: The argument must be
1.240 jmc 249: .Cm yes ,
250: .Cm confirm ,
251: .Cm ask ,
1.222 jcs 252: or
1.240 jmc 253: .Cm no
254: (the default).
1.10 djm 255: .It Cm AddressFamily
1.11 jmc 256: Specifies which address family to use when connecting.
257: Valid arguments are
1.240 jmc 258: .Cm any
259: (the default),
260: .Cm inet
1.84 jmc 261: (use IPv4 only), or
1.240 jmc 262: .Cm inet6
1.40 jmc 263: (use IPv6 only).
1.1 stevesk 264: .It Cm BatchMode
265: If set to
1.240 jmc 266: .Cm yes ,
1.318 djm 267: user interaction such as password prompts and host key confirmation requests
268: will be disabled.
1.1 stevesk 269: This option is useful in scripts and other batch jobs where no user
1.318 djm 270: is present to interact with
271: .Xr ssh 1 .
1.1 stevesk 272: The argument must be
1.240 jmc 273: .Cm yes
1.1 stevesk 274: or
1.240 jmc 275: .Cm no
276: (the default).
1.268 jmc 277: .It Cm BindAddress
278: Use the specified address on the local machine as the source address of
279: the connection.
280: Only useful on systems with more than one address.
281: .It Cm BindInterface
282: Use the address of the specified interface on the local machine as the
283: source address of the connection.
1.171 djm 284: .It Cm CanonicalDomains
1.172 jmc 285: When
1.173 djm 286: .Cm CanonicalizeHostname
1.171 djm 287: is enabled, this option specifies the list of domain suffixes in which to
288: search for the specified destination host.
1.173 djm 289: .It Cm CanonicalizeFallbackLocal
1.174 djm 290: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 291: The default,
1.240 jmc 292: .Cm yes ,
1.172 jmc 293: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 294: search rules.
295: A value of
1.240 jmc 296: .Cm no
1.171 djm 297: will cause
298: .Xr ssh 1
299: to fail instantly if
1.173 djm 300: .Cm CanonicalizeHostname
1.171 djm 301: is enabled and the target hostname cannot be found in any of the domains
302: specified by
303: .Cm CanonicalDomains .
1.173 djm 304: .It Cm CanonicalizeHostname
1.174 djm 305: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 306: The default,
1.240 jmc 307: .Cm no ,
1.171 djm 308: is not to perform any name rewriting and let the system resolver handle all
309: hostname lookups.
310: If set to
1.240 jmc 311: .Cm yes
1.171 djm 312: then, for connections that do not use a
1.284 djm 313: .Cm ProxyCommand
314: or
315: .Cm ProxyJump ,
1.171 djm 316: .Xr ssh 1
1.173 djm 317: will attempt to canonicalize the hostname specified on the command line
1.171 djm 318: using the
319: .Cm CanonicalDomains
320: suffixes and
1.173 djm 321: .Cm CanonicalizePermittedCNAMEs
1.171 djm 322: rules.
323: If
1.173 djm 324: .Cm CanonicalizeHostname
1.171 djm 325: is set to
1.240 jmc 326: .Cm always ,
1.174 djm 327: then canonicalization is applied to proxied connections too.
1.185 djm 328: .Pp
1.193 djm 329: If this option is enabled, then the configuration files are processed
330: again using the new target name to pick up any new configuration in matching
1.185 djm 331: .Cm Host
1.193 djm 332: and
333: .Cm Match
1.185 djm 334: stanzas.
1.173 djm 335: .It Cm CanonicalizeMaxDots
1.172 jmc 336: Specifies the maximum number of dot characters in a hostname before
1.174 djm 337: canonicalization is disabled.
1.240 jmc 338: The default, 1,
1.172 jmc 339: allows a single dot (i.e. hostname.subdomain).
1.173 djm 340: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 341: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 342: canonicalizing hostnames.
1.171 djm 343: The rules consist of one or more arguments of
1.172 jmc 344: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 345: where
346: .Ar source_domain_list
1.174 djm 347: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 348: and
349: .Ar target_domain_list
1.172 jmc 350: is a pattern-list of domains that they may resolve to.
1.171 djm 351: .Pp
352: For example,
1.240 jmc 353: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 354: will allow hostnames matching
1.240 jmc 355: .Qq *.a.example.com
1.173 djm 356: to be canonicalized to names in the
1.240 jmc 357: .Qq *.b.example.com
1.171 djm 358: or
1.240 jmc 359: .Qq *.c.example.com
1.171 djm 360: domains.
1.283 jmc 361: .It Cm CASignatureAlgorithms
362: Specifies which algorithms are allowed for signing of certificates
363: by certificate authorities (CAs).
364: The default is:
365: .Bd -literal -offset indent
1.297 djm 366: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.283 jmc 367: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
368: .Ed
369: .Pp
370: .Xr ssh 1
371: will not accept host certificates signed using algorithms other than those
372: specified.
1.221 djm 373: .It Cm CertificateFile
374: Specifies a file from which the user's certificate is read.
375: A corresponding private key must be provided separately in order
376: to use this certificate either
377: from an
378: .Cm IdentityFile
379: directive or
380: .Fl i
381: flag to
382: .Xr ssh 1 ,
383: via
384: .Xr ssh-agent 1 ,
385: or via a
1.305 naddy 386: .Cm PKCS11Provider
387: or
388: .Cm SecurityKeyProvider .
1.221 djm 389: .Pp
1.239 jmc 390: Arguments to
391: .Cm CertificateFile
392: may use the tilde syntax to refer to a user's home directory
393: or the tokens described in the
394: .Sx TOKENS
395: section.
1.221 djm 396: .Pp
397: It is possible to have multiple certificate files specified in
398: configuration files; these certificates will be tried in sequence.
399: Multiple
400: .Cm CertificateFile
401: directives will add to the list of certificates used for
402: authentication.
1.1 stevesk 403: .It Cm ChallengeResponseAuthentication
1.82 jmc 404: Specifies whether to use challenge-response authentication.
1.1 stevesk 405: The argument to this keyword must be
1.240 jmc 406: .Cm yes
407: (the default)
1.1 stevesk 408: or
1.240 jmc 409: .Cm no .
1.1 stevesk 410: .It Cm CheckHostIP
1.240 jmc 411: If set to
412: .Cm yes
413: (the default),
1.84 jmc 414: .Xr ssh 1
415: will additionally check the host IP address in the
1.1 stevesk 416: .Pa known_hosts
417: file.
1.240 jmc 418: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 419: and will add addresses of destination hosts to
420: .Pa ~/.ssh/known_hosts
421: in the process, regardless of the setting of
422: .Cm StrictHostKeyChecking .
1.107 grunk 423: If the option is set to
1.240 jmc 424: .Cm no ,
1.1 stevesk 425: the check will not be executed.
426: .It Cm Ciphers
1.245 djm 427: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 428: Multiple ciphers must be comma-separated.
1.299 kn 429: If the specified list begins with a
1.214 djm 430: .Sq +
431: character, then the specified ciphers will be appended to the default set
432: instead of replacing them.
1.299 kn 433: If the specified list begins with a
1.241 djm 434: .Sq -
435: character, then the specified ciphers (including wildcards) will be removed
436: from the default set instead of replacing them.
1.301 naddy 437: If the specified list begins with a
438: .Sq ^
439: character, then the specified ciphers will be placed at the head of the
440: default set.
1.214 djm 441: .Pp
1.180 djm 442: The supported ciphers are:
1.240 jmc 443: .Bd -literal -offset indent
1.186 naddy 444: 3des-cbc
445: aes128-cbc
446: aes192-cbc
447: aes256-cbc
448: aes128-ctr
449: aes192-ctr
450: aes256-ctr
451: aes128-gcm@openssh.com
452: aes256-gcm@openssh.com
453: chacha20-poly1305@openssh.com
1.240 jmc 454: .Ed
1.180 djm 455: .Pp
1.84 jmc 456: The default is:
1.186 naddy 457: .Bd -literal -offset indent
1.215 jmc 458: chacha20-poly1305@openssh.com,
1.186 naddy 459: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 460: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 461: .Ed
1.180 djm 462: .Pp
1.240 jmc 463: The list of available ciphers may also be obtained using
464: .Qq ssh -Q cipher .
1.1 stevesk 465: .It Cm ClearAllForwardings
1.84 jmc 466: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 467: specified in the configuration files or on the command line be
1.7 jmc 468: cleared.
469: This option is primarily useful when used from the
1.84 jmc 470: .Xr ssh 1
1.1 stevesk 471: command line to clear port forwardings set in
472: configuration files, and is automatically set by
473: .Xr scp 1
474: and
475: .Xr sftp 1 .
476: The argument must be
1.240 jmc 477: .Cm yes
1.1 stevesk 478: or
1.240 jmc 479: .Cm no
480: (the default).
1.1 stevesk 481: .It Cm Compression
482: Specifies whether to use compression.
483: The argument must be
1.240 jmc 484: .Cm yes
1.1 stevesk 485: or
1.240 jmc 486: .Cm no
487: (the default).
1.247 naddy 488: .It Cm ConnectionAttempts
489: Specifies the number of tries (one per second) to make before exiting.
490: The argument must be an integer.
491: This may be useful in scripts if the connection sometimes fails.
492: The default is 1.
1.9 djm 493: .It Cm ConnectTimeout
1.84 jmc 494: Specifies the timeout (in seconds) used when connecting to the
495: SSH server, instead of using the default system TCP timeout.
1.302 djm 496: This timeout is applied both to establishing the connection and to performing
497: the initial SSH protocol handshake and key exchange.
1.36 djm 498: .It Cm ControlMaster
499: Enables the sharing of multiple sessions over a single network connection.
500: When set to
1.240 jmc 501: .Cm yes ,
1.84 jmc 502: .Xr ssh 1
1.36 djm 503: will listen for connections on a control socket specified using the
504: .Cm ControlPath
505: argument.
506: Additional sessions can connect to this socket using the same
507: .Cm ControlPath
508: with
509: .Cm ControlMaster
510: set to
1.240 jmc 511: .Cm no
1.38 jmc 512: (the default).
1.64 jmc 513: These sessions will try to reuse the master instance's network connection
1.63 djm 514: rather than initiating new ones, but will fall back to connecting normally
515: if the control socket does not exist, or is not listening.
516: .Pp
1.37 djm 517: Setting this to
1.240 jmc 518: .Cm ask
519: will cause
520: .Xr ssh 1
1.206 jmc 521: to listen for control connections, but require confirmation using
522: .Xr ssh-askpass 1 .
1.51 jakob 523: If the
524: .Cm ControlPath
1.84 jmc 525: cannot be opened,
1.240 jmc 526: .Xr ssh 1
527: will continue without connecting to a master instance.
1.58 djm 528: .Pp
529: X11 and
1.59 jmc 530: .Xr ssh-agent 1
1.58 djm 531: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 532: display and agent forwarded will be the one belonging to the master
1.59 jmc 533: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 534: .Pp
535: Two additional options allow for opportunistic multiplexing: try to use a
536: master connection but fall back to creating a new one if one does not already
537: exist.
538: These options are:
1.240 jmc 539: .Cm auto
1.56 djm 540: and
1.240 jmc 541: .Cm autoask .
1.56 djm 542: The latter requires confirmation like the
1.240 jmc 543: .Cm ask
1.56 djm 544: option.
1.36 djm 545: .It Cm ControlPath
1.55 djm 546: Specify the path to the control socket used for connection sharing as described
547: in the
1.36 djm 548: .Cm ControlMaster
1.57 djm 549: section above or the string
1.240 jmc 550: .Cm none
1.57 djm 551: to disable connection sharing.
1.239 jmc 552: Arguments to
553: .Cm ControlPath
554: may use the tilde syntax to refer to a user's home directory
555: or the tokens described in the
556: .Sx TOKENS
557: section.
1.56 djm 558: It is recommended that any
559: .Cm ControlPath
560: used for opportunistic connection sharing include
1.195 djm 561: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
562: that is not writable by other users.
1.56 djm 563: This ensures that shared connections are uniquely identified.
1.137 djm 564: .It Cm ControlPersist
565: When used in conjunction with
566: .Cm ControlMaster ,
567: specifies that the master connection should remain open
568: in the background (waiting for future client connections)
569: after the initial client connection has been closed.
570: If set to
1.314 naddy 571: .Cm no
572: (the default),
1.137 djm 573: then the master connection will not be placed into the background,
574: and will close as soon as the initial client connection is closed.
575: If set to
1.240 jmc 576: .Cm yes
577: or 0,
1.137 djm 578: then the master connection will remain in the background indefinitely
579: (until killed or closed via a mechanism such as the
1.240 jmc 580: .Qq ssh -O exit ) .
1.137 djm 581: If set to a time in seconds, or a time in any of the formats documented in
582: .Xr sshd_config 5 ,
583: then the backgrounded master connection will automatically terminate
584: after it has remained idle (with no client connections) for the
585: specified time.
1.38 jmc 586: .It Cm DynamicForward
1.74 jmc 587: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 588: over the secure channel, and the application
589: protocol is then used to determine where to connect to from the
590: remote machine.
1.62 djm 591: .Pp
592: The argument must be
593: .Sm off
594: .Oo Ar bind_address : Oc Ar port .
595: .Sm on
1.138 djm 596: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 597: By default, the local port is bound in accordance with the
598: .Cm GatewayPorts
599: setting.
600: However, an explicit
601: .Ar bind_address
602: may be used to bind the connection to a specific address.
603: The
604: .Ar bind_address
605: of
1.240 jmc 606: .Cm localhost
1.62 djm 607: indicates that the listening port be bound for local use only, while an
608: empty address or
609: .Sq *
610: indicates that the port should be available from all interfaces.
611: .Pp
1.38 jmc 612: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 613: .Xr ssh 1
1.38 jmc 614: will act as a SOCKS server.
615: Multiple forwardings may be specified, and
616: additional forwardings can be given on the command line.
617: Only the superuser can forward privileged ports.
1.14 markus 618: .It Cm EnableSSHKeysign
619: Setting this option to
1.240 jmc 620: .Cm yes
1.14 markus 621: in the global client configuration file
622: .Pa /etc/ssh/ssh_config
623: enables the use of the helper program
624: .Xr ssh-keysign 8
625: during
626: .Cm HostbasedAuthentication .
627: The argument must be
1.240 jmc 628: .Cm yes
1.14 markus 629: or
1.240 jmc 630: .Cm no
631: (the default).
1.23 jmc 632: This option should be placed in the non-hostspecific section.
1.14 markus 633: See
634: .Xr ssh-keysign 8
635: for more information.
1.1 stevesk 636: .It Cm EscapeChar
637: Sets the escape character (default:
638: .Ql ~ ) .
639: The escape character can also
640: be set on the command line.
641: The argument should be a single character,
642: .Ql ^
643: followed by a letter, or
1.240 jmc 644: .Cm none
1.1 stevesk 645: to disable the escape
646: character entirely (making the connection transparent for binary
647: data).
1.96 markus 648: .It Cm ExitOnForwardFailure
649: Specifies whether
650: .Xr ssh 1
651: should terminate the connection if it cannot set up all requested
1.216 djm 652: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 653: if either end is unable to bind and listen on a specified port).
1.216 djm 654: Note that
655: .Cm ExitOnForwardFailure
656: does not apply to connections made over port forwardings and will not,
657: for example, cause
658: .Xr ssh 1
659: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 660: The argument must be
1.240 jmc 661: .Cm yes
1.96 markus 662: or
1.240 jmc 663: .Cm no
664: (the default).
1.197 djm 665: .It Cm FingerprintHash
666: Specifies the hash algorithm used when displaying key fingerprints.
667: Valid options are:
1.240 jmc 668: .Cm md5
1.197 djm 669: and
1.240 jmc 670: .Cm sha256
671: (the default).
1.1 stevesk 672: .It Cm ForwardAgent
673: Specifies whether the connection to the authentication agent (if any)
674: will be forwarded to the remote machine.
1.312 djm 675: The argument may be
676: .Cm yes ,
1.240 jmc 677: .Cm no
1.312 djm 678: (the default),
679: an explicit path to an agent socket or the name of an environment variable
680: (beginning with
681: .Sq $ )
682: in which to find the path.
1.3 stevesk 683: .Pp
1.7 jmc 684: Agent forwarding should be enabled with caution.
685: Users with the ability to bypass file permissions on the remote host
686: (for the agent's Unix-domain socket)
687: can access the local agent through the forwarded connection.
688: An attacker cannot obtain key material from the agent,
1.3 stevesk 689: however they can perform operations on the keys that enable them to
690: authenticate using the identities loaded into the agent.
1.1 stevesk 691: .It Cm ForwardX11
692: Specifies whether X11 connections will be automatically redirected
693: over the secure channel and
694: .Ev DISPLAY
695: set.
696: The argument must be
1.240 jmc 697: .Cm yes
1.1 stevesk 698: or
1.240 jmc 699: .Cm no
700: (the default).
1.3 stevesk 701: .Pp
1.7 jmc 702: X11 forwarding should be enabled with caution.
703: Users with the ability to bypass file permissions on the remote host
1.22 markus 704: (for the user's X11 authorization database)
1.7 jmc 705: can access the local X11 display through the forwarded connection.
1.22 markus 706: An attacker may then be able to perform activities such as keystroke monitoring
707: if the
708: .Cm ForwardX11Trusted
709: option is also enabled.
1.134 djm 710: .It Cm ForwardX11Timeout
1.135 jmc 711: Specify a timeout for untrusted X11 forwarding
712: using the format described in the
1.240 jmc 713: .Sx TIME FORMATS
714: section of
1.134 djm 715: .Xr sshd_config 5 .
716: X11 connections received by
717: .Xr ssh 1
718: after this time will be refused.
1.285 djm 719: Setting
720: .Cm ForwardX11Timeout
721: to zero will disable the timeout and permit X11 forwarding for the life
722: of the connection.
1.134 djm 723: The default is to disable untrusted X11 forwarding after twenty minutes has
724: elapsed.
1.22 markus 725: .It Cm ForwardX11Trusted
1.34 jmc 726: If this option is set to
1.240 jmc 727: .Cm yes ,
1.84 jmc 728: remote X11 clients will have full access to the original X11 display.
1.42 djm 729: .Pp
1.22 markus 730: If this option is set to
1.240 jmc 731: .Cm no
732: (the default),
1.84 jmc 733: remote X11 clients will be considered untrusted and prevented
1.22 markus 734: from stealing or tampering with data belonging to trusted X11
735: clients.
1.42 djm 736: Furthermore, the
737: .Xr xauth 1
738: token used for the session will be set to expire after 20 minutes.
739: Remote clients will be refused access after this time.
1.22 markus 740: .Pp
741: See the X11 SECURITY extension specification for full details on
742: the restrictions imposed on untrusted clients.
1.1 stevesk 743: .It Cm GatewayPorts
744: Specifies whether remote hosts are allowed to connect to local
745: forwarded ports.
746: By default,
1.84 jmc 747: .Xr ssh 1
1.7 jmc 748: binds local port forwardings to the loopback address.
749: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 750: .Cm GatewayPorts
1.84 jmc 751: can be used to specify that ssh
1.1 stevesk 752: should bind local port forwardings to the wildcard address,
753: thus allowing remote hosts to connect to forwarded ports.
754: The argument must be
1.240 jmc 755: .Cm yes
1.1 stevesk 756: or
1.240 jmc 757: .Cm no
758: (the default).
1.1 stevesk 759: .It Cm GlobalKnownHostsFile
1.151 djm 760: Specifies one or more files to use for the global
761: host key database, separated by whitespace.
762: The default is
763: .Pa /etc/ssh/ssh_known_hosts ,
764: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 765: .It Cm GSSAPIAuthentication
1.27 markus 766: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 767: The default is
1.240 jmc 768: .Cm no .
1.18 markus 769: .It Cm GSSAPIDelegateCredentials
770: Forward (delegate) credentials to the server.
771: The default is
1.240 jmc 772: .Cm no .
1.44 djm 773: .It Cm HashKnownHosts
774: Indicates that
1.84 jmc 775: .Xr ssh 1
1.44 djm 776: should hash host names and addresses when they are added to
1.50 djm 777: .Pa ~/.ssh/known_hosts .
1.44 djm 778: These hashed names may be used normally by
1.84 jmc 779: .Xr ssh 1
1.44 djm 780: and
1.84 jmc 781: .Xr sshd 8 ,
1.316 djm 782: but they do not visually reveal identifying information if the
783: file's contents are disclosed.
1.44 djm 784: The default is
1.240 jmc 785: .Cm no .
1.97 jmc 786: Note that existing names and addresses in known hosts files
787: will not be converted automatically,
788: but may be manually hashed using
1.45 djm 789: .Xr ssh-keygen 1 .
1.1 stevesk 790: .It Cm HostbasedAuthentication
791: Specifies whether to try rhosts based authentication with public key
792: authentication.
793: The argument must be
1.240 jmc 794: .Cm yes
1.1 stevesk 795: or
1.240 jmc 796: .Cm no
797: (the default).
1.202 djm 798: .It Cm HostbasedKeyTypes
799: Specifies the key types that will be used for hostbased authentication
1.279 djm 800: as a comma-separated list of patterns.
1.300 naddy 801: Alternately if the specified list begins with a
1.214 djm 802: .Sq +
803: character, then the specified key types will be appended to the default set
804: instead of replacing them.
1.300 naddy 805: If the specified list begins with a
1.241 djm 806: .Sq -
807: character, then the specified key types (including wildcards) will be removed
808: from the default set instead of replacing them.
1.301 naddy 809: If the specified list begins with a
810: .Sq ^
811: character, then the specified key types will be placed at the head of the
812: default set.
1.213 markus 813: The default for this option is:
814: .Bd -literal -offset 3n
815: ecdsa-sha2-nistp256-cert-v01@openssh.com,
816: ecdsa-sha2-nistp384-cert-v01@openssh.com,
817: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 818: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.213 markus 819: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 820: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 821: rsa-sha2-512-cert-v01@openssh.com,
822: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 823: ssh-rsa-cert-v01@openssh.com,
824: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 825: sk-ecdsa-sha2-nistp256@openssh.com,
826: ssh-ed25519,sk-ssh-ed25519@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
834: may be used to list supported key types.
1.1 stevesk 835: .It Cm HostKeyAlgorithms
1.226 jmc 836: Specifies the host key algorithms
1.1 stevesk 837: that the client wants to use in order of preference.
1.300 naddy 838: Alternately if the specified list begins with a
1.214 djm 839: .Sq +
840: character, then the specified key types will be appended to the default set
841: instead of replacing them.
1.300 naddy 842: If the specified list begins with a
1.241 djm 843: .Sq -
844: character, then the specified key types (including wildcards) will be removed
845: from the default set instead of replacing them.
1.301 naddy 846: If the specified list begins with a
847: .Sq ^
848: character, then the specified key types will be placed at the head of the
849: default set.
1.1 stevesk 850: The default for this option is:
1.139 djm 851: .Bd -literal -offset 3n
852: ecdsa-sha2-nistp256-cert-v01@openssh.com,
853: ecdsa-sha2-nistp384-cert-v01@openssh.com,
854: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 855: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.183 naddy 856: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 857: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 858: rsa-sha2-512-cert-v01@openssh.com,
859: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 860: ssh-rsa-cert-v01@openssh.com,
1.139 djm 861: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 862: sk-ecdsa-sha2-nistp256@openssh.com,
863: ssh-ed25519,sk-ssh-ed25519@openssh.com,
864: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 865: .Ed
1.145 djm 866: .Pp
867: If hostkeys are known for the destination host then this default is modified
868: to prefer their algorithms.
1.198 djm 869: .Pp
1.240 jmc 870: The list of available key types may also be obtained using
1.322 ! dtucker 871: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 872: .It Cm HostKeyAlias
873: Specifies an alias that should be used instead of the
874: real host name when looking up or saving the host key
1.251 djm 875: in the host key database files and when validating host certificates.
1.84 jmc 876: This option is useful for tunneling SSH connections
1.1 stevesk 877: or for multiple servers running on a single host.
1.295 jmc 878: .It Cm Hostname
1.1 stevesk 879: Specifies the real host name to log into.
880: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 881: Arguments to
1.295 jmc 882: .Cm Hostname
1.239 jmc 883: accept the tokens described in the
884: .Sx TOKENS
885: section.
1.1 stevesk 886: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 887: .Cm Hostname
1.1 stevesk 888: specifications).
1.239 jmc 889: The default is the name given on the command line.
1.29 markus 890: .It Cm IdentitiesOnly
891: Specifies that
1.84 jmc 892: .Xr ssh 1
1.304 djm 893: should only use the configured authentication identity and certificate files
894: (either the default files, or those explicitly configured in the
1.31 jmc 895: .Nm
1.221 djm 896: files
897: or passed on the
898: .Xr ssh 1
1.304 djm 899: command-line),
1.84 jmc 900: even if
901: .Xr ssh-agent 1
1.159 djm 902: or a
903: .Cm PKCS11Provider
1.305 naddy 904: or
905: .Cm SecurityKeyProvider
1.29 markus 906: offers more identities.
907: The argument to this keyword must be
1.240 jmc 908: .Cm yes
1.29 markus 909: or
1.240 jmc 910: .Cm no
911: (the default).
1.84 jmc 912: This option is intended for situations where ssh-agent
1.29 markus 913: offers many different identities.
1.231 markus 914: .It Cm IdentityAgent
915: Specifies the
916: .Ux Ns -domain
917: socket used to communicate with the authentication agent.
918: .Pp
919: This option overrides the
1.240 jmc 920: .Ev SSH_AUTH_SOCK
1.231 markus 921: environment variable and can be used to select a specific agent.
922: Setting the socket name to
1.240 jmc 923: .Cm none
1.231 markus 924: disables the use of an authentication agent.
1.232 markus 925: If the string
1.240 jmc 926: .Qq SSH_AUTH_SOCK
1.232 markus 927: is specified, the location of the socket will be read from the
928: .Ev SSH_AUTH_SOCK
929: environment variable.
1.286 djm 930: Otherwise if the specified value begins with a
931: .Sq $
932: character, then it will be treated as an environment variable containing
933: the location of the socket.
1.231 markus 934: .Pp
1.239 jmc 935: Arguments to
936: .Cm IdentityAgent
937: may use the tilde syntax to refer to a user's home directory
938: or the tokens described in the
939: .Sx TOKENS
940: section.
1.67 jmc 941: .It Cm IdentityFile
1.313 naddy 942: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
943: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 944: The default is
1.139 djm 945: .Pa ~/.ssh/id_dsa ,
1.183 naddy 946: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 947: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 948: .Pa ~/.ssh/id_ed25519 ,
949: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 950: and
1.245 djm 951: .Pa ~/.ssh/id_rsa .
1.67 jmc 952: Additionally, any identities represented by the authentication agent
1.165 djm 953: will be used for authentication unless
954: .Cm IdentitiesOnly
955: is set.
1.221 djm 956: If no certificates have been explicitly specified by
957: .Cm CertificateFile ,
1.129 djm 958: .Xr ssh 1
959: will try to load certificate information from the filename obtained by
960: appending
961: .Pa -cert.pub
962: to the path of a specified
963: .Cm IdentityFile .
1.90 djm 964: .Pp
1.239 jmc 965: Arguments to
966: .Cm IdentityFile
967: may use the tilde syntax to refer to a user's home directory
968: or the tokens described in the
969: .Sx TOKENS
970: section.
1.90 djm 971: .Pp
1.67 jmc 972: It is possible to have
973: multiple identity files specified in configuration files; all these
974: identities will be tried in sequence.
1.152 djm 975: Multiple
976: .Cm IdentityFile
977: directives will add to the list of identities tried (this behaviour
978: differs from that of other configuration directives).
1.165 djm 979: .Pp
980: .Cm IdentityFile
981: may be used in conjunction with
982: .Cm IdentitiesOnly
983: to select which identities in an agent are offered during authentication.
1.221 djm 984: .Cm IdentityFile
985: may also be used in conjunction with
986: .Cm CertificateFile
987: in order to provide any certificate also needed for authentication with
988: the identity.
1.164 jmc 989: .It Cm IgnoreUnknown
990: Specifies a pattern-list of unknown options to be ignored if they are
991: encountered in configuration parsing.
992: This may be used to suppress errors if
993: .Nm
994: contains options that are unrecognised by
995: .Xr ssh 1 .
996: It is recommended that
997: .Cm IgnoreUnknown
998: be listed early in the configuration file as it will not be applied
999: to unknown options that appear before it.
1.229 djm 1000: .It Cm Include
1001: Include the specified configuration file(s).
1.230 jmc 1002: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1003: .Xr glob 7
1.229 djm 1004: wildcards and, for user configurations, shell-like
1.240 jmc 1005: .Sq ~
1.229 djm 1006: references to user home directories.
1007: Files without absolute paths are assumed to be in
1008: .Pa ~/.ssh
1.230 jmc 1009: if included in a user configuration file or
1.229 djm 1010: .Pa /etc/ssh
1011: if included from the system configuration file.
1012: .Cm Include
1013: directive may appear inside a
1014: .Cm Match
1015: or
1016: .Cm Host
1017: block
1018: to perform conditional inclusion.
1.143 djm 1019: .It Cm IPQoS
1020: Specifies the IPv4 type-of-service or DSCP class for connections.
1021: Accepted values are
1.240 jmc 1022: .Cm af11 ,
1023: .Cm af12 ,
1024: .Cm af13 ,
1025: .Cm af21 ,
1026: .Cm af22 ,
1027: .Cm af23 ,
1028: .Cm af31 ,
1029: .Cm af32 ,
1030: .Cm af33 ,
1031: .Cm af41 ,
1032: .Cm af42 ,
1033: .Cm af43 ,
1034: .Cm cs0 ,
1035: .Cm cs1 ,
1036: .Cm cs2 ,
1037: .Cm cs3 ,
1038: .Cm cs4 ,
1039: .Cm cs5 ,
1040: .Cm cs6 ,
1041: .Cm cs7 ,
1042: .Cm ef ,
1.319 djm 1043: .Cm le ,
1.240 jmc 1044: .Cm lowdelay ,
1045: .Cm throughput ,
1046: .Cm reliability ,
1.253 djm 1047: a numeric value, or
1048: .Cm none
1049: to use the operating system default.
1.146 djm 1050: This option may take one or two arguments, separated by whitespace.
1.143 djm 1051: If one argument is specified, it is used as the packet class unconditionally.
1052: If two values are specified, the first is automatically selected for
1053: interactive sessions and the second for non-interactive sessions.
1054: The default is
1.269 job 1055: .Cm af21
1.272 jmc 1056: (Low-Latency Data)
1.143 djm 1057: for interactive sessions and
1.269 job 1058: .Cm cs1
1.272 jmc 1059: (Lower Effort)
1.143 djm 1060: for non-interactive sessions.
1.103 djm 1061: .It Cm KbdInteractiveAuthentication
1062: Specifies whether to use keyboard-interactive authentication.
1063: The argument to this keyword must be
1.240 jmc 1064: .Cm yes
1065: (the default)
1.103 djm 1066: or
1.240 jmc 1067: .Cm no .
1.39 djm 1068: .It Cm KbdInteractiveDevices
1069: Specifies the list of methods to use in keyboard-interactive authentication.
1070: Multiple method names must be comma-separated.
1071: The default is to use the server specified list.
1.85 jmc 1072: The methods available vary depending on what the server supports.
1073: For an OpenSSH server,
1074: it may be zero or more of:
1.240 jmc 1075: .Cm bsdauth ,
1076: .Cm pam ,
1.85 jmc 1077: and
1.240 jmc 1078: .Cm skey .
1.140 djm 1079: .It Cm KexAlgorithms
1080: Specifies the available KEX (Key Exchange) algorithms.
1081: Multiple algorithms must be comma-separated.
1.299 kn 1082: If the specified list begins with a
1.214 djm 1083: .Sq +
1084: character, then the specified methods will be appended to the default set
1085: instead of replacing them.
1.299 kn 1086: If the specified list begins with a
1.241 djm 1087: .Sq -
1088: character, then the specified methods (including wildcards) will be removed
1089: from the default set instead of replacing them.
1.301 naddy 1090: If the specified list begins with a
1091: .Sq ^
1092: character, then the specified methods will be placed at the head of the
1093: default set.
1.141 jmc 1094: The default is:
1095: .Bd -literal -offset indent
1.238 djm 1096: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1097: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1098: diffie-hellman-group-exchange-sha256,
1.266 djm 1099: diffie-hellman-group16-sha512,
1100: diffie-hellman-group18-sha512,
1.317 tedu 1101: diffie-hellman-group14-sha256
1.141 jmc 1102: .Ed
1.198 djm 1103: .Pp
1.240 jmc 1104: The list of available key exchange algorithms may also be obtained using
1105: .Qq ssh -Q kex .
1.65 reyk 1106: .It Cm LocalCommand
1107: Specifies a command to execute on the local machine after successfully
1108: connecting to the server.
1109: The command string extends to the end of the line, and is executed with
1.105 jmc 1110: the user's shell.
1.239 jmc 1111: Arguments to
1112: .Cm LocalCommand
1113: accept the tokens described in the
1114: .Sx TOKENS
1115: section.
1.123 djm 1116: .Pp
1117: The command is run synchronously and does not have access to the
1118: session of the
1119: .Xr ssh 1
1120: that spawned it.
1121: It should not be used for interactive commands.
1122: .Pp
1.65 reyk 1123: This directive is ignored unless
1124: .Cm PermitLocalCommand
1125: has been enabled.
1.1 stevesk 1126: .It Cm LocalForward
1.74 jmc 1127: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1128: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1129: The first argument must be
1.43 djm 1130: .Sm off
1.49 jmc 1131: .Oo Ar bind_address : Oc Ar port
1.43 djm 1132: .Sm on
1.49 jmc 1133: and the second argument must be
1134: .Ar host : Ns Ar hostport .
1.138 djm 1135: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1136: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1137: given on the command line.
1.1 stevesk 1138: Only the superuser can forward privileged ports.
1.43 djm 1139: By default, the local port is bound in accordance with the
1140: .Cm GatewayPorts
1141: setting.
1142: However, an explicit
1143: .Ar bind_address
1144: may be used to bind the connection to a specific address.
1145: The
1146: .Ar bind_address
1147: of
1.240 jmc 1148: .Cm localhost
1.46 jmc 1149: indicates that the listening port be bound for local use only, while an
1150: empty address or
1151: .Sq *
1.43 djm 1152: indicates that the port should be available from all interfaces.
1.1 stevesk 1153: .It Cm LogLevel
1154: Gives the verbosity level that is used when logging messages from
1.84 jmc 1155: .Xr ssh 1 .
1.1 stevesk 1156: The possible values are:
1.84 jmc 1157: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1158: The default is INFO.
1159: DEBUG and DEBUG1 are equivalent.
1160: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1161: .It Cm MACs
1162: Specifies the MAC (message authentication code) algorithms
1163: in order of preference.
1.226 jmc 1164: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1165: Multiple algorithms must be comma-separated.
1.299 kn 1166: If the specified list begins with a
1.214 djm 1167: .Sq +
1168: character, then the specified algorithms will be appended to the default set
1169: instead of replacing them.
1.299 kn 1170: If the specified list begins with a
1.241 djm 1171: .Sq -
1172: character, then the specified algorithms (including wildcards) will be removed
1173: from the default set instead of replacing them.
1.301 naddy 1174: If the specified list begins with a
1175: .Sq ^
1176: character, then the specified algorithms will be placed at the head of the
1177: default set.
1.214 djm 1178: .Pp
1.160 markus 1179: The algorithms that contain
1.240 jmc 1180: .Qq -etm
1.160 markus 1181: calculate the MAC after encryption (encrypt-then-mac).
1182: These are considered safer and their use recommended.
1.214 djm 1183: .Pp
1.84 jmc 1184: The default is:
1.101 jmc 1185: .Bd -literal -offset indent
1.160 markus 1186: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1187: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1188: hmac-sha1-etm@openssh.com,
1.186 naddy 1189: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1190: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1191: .Ed
1.198 djm 1192: .Pp
1.240 jmc 1193: The list of available MAC algorithms may also be obtained using
1194: .Qq ssh -Q mac .
1.1 stevesk 1195: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1196: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1197: The argument to this keyword must be
1.240 jmc 1198: .Cm yes
1.1 stevesk 1199: or
1.242 jmc 1200: .Cm no
1.240 jmc 1201: (the default).
1.1 stevesk 1202: .It Cm NumberOfPasswordPrompts
1203: Specifies the number of password prompts before giving up.
1204: The argument to this keyword must be an integer.
1.84 jmc 1205: The default is 3.
1.1 stevesk 1206: .It Cm PasswordAuthentication
1207: Specifies whether to use password authentication.
1208: The argument to this keyword must be
1.240 jmc 1209: .Cm yes
1210: (the default)
1.1 stevesk 1211: or
1.240 jmc 1212: .Cm no .
1.65 reyk 1213: .It Cm PermitLocalCommand
1214: Allow local command execution via the
1215: .Ic LocalCommand
1216: option or using the
1.66 jmc 1217: .Ic !\& Ns Ar command
1.65 reyk 1218: escape sequence in
1219: .Xr ssh 1 .
1220: The argument must be
1.240 jmc 1221: .Cm yes
1.65 reyk 1222: or
1.240 jmc 1223: .Cm no
1224: (the default).
1.127 markus 1225: .It Cm PKCS11Provider
1.292 djm 1226: Specifies which PKCS#11 provider to use or
1227: .Cm none
1228: to indicate that no provider should be used (the default).
1229: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1230: .Xr ssh 1
1.292 djm 1231: should use to communicate with a PKCS#11 token providing keys for user
1232: authentication.
1.67 jmc 1233: .It Cm Port
1234: Specifies the port number to connect on the remote host.
1.84 jmc 1235: The default is 22.
1.1 stevesk 1236: .It Cm PreferredAuthentications
1.226 jmc 1237: Specifies the order in which the client should try authentication methods.
1.48 jmc 1238: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1239: .Cm keyboard-interactive )
1.48 jmc 1240: over another method (e.g.\&
1.131 jmc 1241: .Cm password ) .
1242: The default is:
1243: .Bd -literal -offset indent
1244: gssapi-with-mic,hostbased,publickey,
1245: keyboard-interactive,password
1246: .Ed
1.1 stevesk 1247: .It Cm ProxyCommand
1248: Specifies the command to use to connect to the server.
1249: The command
1.190 djm 1250: string extends to the end of the line, and is executed
1251: using the user's shell
1252: .Ql exec
1253: directive to avoid a lingering shell process.
1254: .Pp
1.239 jmc 1255: Arguments to
1256: .Cm ProxyCommand
1257: accept the tokens described in the
1258: .Sx TOKENS
1259: section.
1.1 stevesk 1260: The command can be basically anything,
1261: and should read from its standard input and write to its standard output.
1262: It should eventually connect an
1263: .Xr sshd 8
1264: server running on some machine, or execute
1265: .Ic sshd -i
1266: somewhere.
1267: Host key management will be done using the
1.296 jmc 1268: .Cm Hostname
1269: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1270: Setting the command to
1.240 jmc 1271: .Cm none
1.6 markus 1272: disables this option entirely.
1.1 stevesk 1273: Note that
1274: .Cm CheckHostIP
1275: is not available for connects with a proxy command.
1.52 djm 1276: .Pp
1277: This directive is useful in conjunction with
1278: .Xr nc 1
1279: and its proxy support.
1.53 jmc 1280: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1281: 192.0.2.0:
1282: .Bd -literal -offset 3n
1283: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1284: .Ed
1.233 djm 1285: .It Cm ProxyJump
1.260 millert 1286: Specifies one or more jump proxies as either
1.233 djm 1287: .Xo
1288: .Sm off
1.234 jmc 1289: .Op Ar user No @
1.233 djm 1290: .Ar host
1.234 jmc 1291: .Op : Ns Ar port
1.233 djm 1292: .Sm on
1.260 millert 1293: or an ssh URI
1.233 djm 1294: .Xc .
1.235 djm 1295: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1296: sequentially.
1.233 djm 1297: Setting this option will cause
1298: .Xr ssh 1
1299: to connect to the target host by first making a
1300: .Xr ssh 1
1301: connection to the specified
1302: .Cm ProxyJump
1303: host and then establishing a
1.234 jmc 1304: TCP forwarding to the ultimate target from there.
1.233 djm 1305: .Pp
1306: Note that this option will compete with the
1307: .Cm ProxyCommand
1308: option - whichever is specified first will prevent later instances of the
1309: other from taking effect.
1.289 djm 1310: .Pp
1311: Note also that the configuration for the destination host (either supplied
1312: via the command-line or the configuration file) is not generally applied
1313: to jump hosts.
1314: .Pa ~/.ssh/config
1315: should be used if specific configuration is required for jump hosts.
1.167 djm 1316: .It Cm ProxyUseFdpass
1.168 jmc 1317: Specifies that
1.167 djm 1318: .Cm ProxyCommand
1319: will pass a connected file descriptor back to
1.168 jmc 1320: .Xr ssh 1
1.167 djm 1321: instead of continuing to execute and pass data.
1322: The default is
1.240 jmc 1323: .Cm no .
1.213 markus 1324: .It Cm PubkeyAcceptedKeyTypes
1325: Specifies the key types that will be used for public key authentication
1.279 djm 1326: as a comma-separated list of patterns.
1.299 kn 1327: If the specified list begins with a
1.214 djm 1328: .Sq +
1329: character, then the key types after it will be appended to the default
1330: instead of replacing it.
1.299 kn 1331: If the specified list begins with a
1.241 djm 1332: .Sq -
1333: character, then the specified key types (including wildcards) will be removed
1334: from the default set instead of replacing them.
1.301 naddy 1335: If the specified list begins with a
1336: .Sq ^
1337: character, then the specified key types will be placed at the head of the
1338: default set.
1.213 markus 1339: The default for this option is:
1340: .Bd -literal -offset 3n
1341: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1342: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1343: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 1344: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1345: ssh-ed25519-cert-v01@openssh.com,
1.307 djm 1346: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 1347: rsa-sha2-512-cert-v01@openssh.com,
1348: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1349: ssh-rsa-cert-v01@openssh.com,
1.311 naddy 1350: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.305 naddy 1351: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1352: ssh-ed25519,sk-ssh-ed25519@openssh.com,
1353: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1354: .Ed
1355: .Pp
1.240 jmc 1356: The list of available key types may also be obtained using
1.322 ! dtucker 1357: .Qq ssh -Q PubkeyAcceptedKeyTypes .
1.1 stevesk 1358: .It Cm PubkeyAuthentication
1359: Specifies whether to try public key authentication.
1360: The argument to this keyword must be
1.240 jmc 1361: .Cm yes
1362: (the default)
1.1 stevesk 1363: or
1.240 jmc 1364: .Cm no .
1.75 dtucker 1365: .It Cm RekeyLimit
1366: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1367: session key is renegotiated, optionally followed a maximum amount of
1368: time that may pass before the session key is renegotiated.
1369: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1370: .Sq K ,
1371: .Sq M ,
1.75 dtucker 1372: or
1.76 jmc 1373: .Sq G
1.75 dtucker 1374: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1375: The default is between
1.84 jmc 1376: .Sq 1G
1.75 dtucker 1377: and
1.84 jmc 1378: .Sq 4G ,
1.75 dtucker 1379: depending on the cipher.
1.162 dtucker 1380: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1381: units documented in the TIME FORMATS section of
1.162 dtucker 1382: .Xr sshd_config 5 .
1383: The default value for
1384: .Cm RekeyLimit
1385: is
1.240 jmc 1386: .Cm default none ,
1.162 dtucker 1387: which means that rekeying is performed after the cipher's default amount
1388: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1389: .It Cm RemoteCommand
1390: Specifies a command to execute on the remote machine after successfully
1391: connecting to the server.
1392: The command string extends to the end of the line, and is executed with
1393: the user's shell.
1.250 jmc 1394: Arguments to
1395: .Cm RemoteCommand
1396: accept the tokens described in the
1397: .Sx TOKENS
1398: section.
1.1 stevesk 1399: .It Cm RemoteForward
1.74 jmc 1400: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1401: the secure channel.
1.273 djm 1402: The remote port may either be forwarded to a specified host and port
1.256 markus 1403: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1404: client to connect to arbitrary destinations from the local machine.
1.49 jmc 1405: The first argument must be
1.43 djm 1406: .Sm off
1.49 jmc 1407: .Oo Ar bind_address : Oc Ar port
1.43 djm 1408: .Sm on
1.256 markus 1409: If forwarding to a specific destination then the second argument must be
1410: .Ar host : Ns Ar hostport ,
1411: otherwise if no destination argument is specified then the remote forwarding
1412: will be established as a SOCKS proxy.
1413: .Pp
1.138 djm 1414: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1415: Multiple forwardings may be specified, and additional
1416: forwardings can be given on the command line.
1.113 stevesk 1417: Privileged ports can be forwarded only when
1418: logging in as root on the remote machine.
1.118 jmc 1419: .Pp
1.117 djm 1420: If the
1421: .Ar port
1.240 jmc 1422: argument is 0,
1.117 djm 1423: the listen port will be dynamically allocated on the server and reported
1424: to the client at run time.
1.43 djm 1425: .Pp
1426: If the
1427: .Ar bind_address
1428: is not specified, the default is to only bind to loopback addresses.
1429: If the
1430: .Ar bind_address
1431: is
1432: .Ql *
1433: or an empty string, then the forwarding is requested to listen on all
1434: interfaces.
1435: Specifying a remote
1436: .Ar bind_address
1.46 jmc 1437: will only succeed if the server's
1438: .Cm GatewayPorts
1.43 djm 1439: option is enabled (see
1.46 jmc 1440: .Xr sshd_config 5 ) .
1.149 djm 1441: .It Cm RequestTTY
1442: Specifies whether to request a pseudo-tty for the session.
1443: The argument may be one of:
1.240 jmc 1444: .Cm no
1.149 djm 1445: (never request a TTY),
1.240 jmc 1446: .Cm yes
1.149 djm 1447: (always request a TTY when standard input is a TTY),
1.240 jmc 1448: .Cm force
1.149 djm 1449: (always request a TTY) or
1.240 jmc 1450: .Cm auto
1.149 djm 1451: (request a TTY when opening a login session).
1452: This option mirrors the
1453: .Fl t
1454: and
1455: .Fl T
1456: flags for
1457: .Xr ssh 1 .
1.196 djm 1458: .It Cm RevokedHostKeys
1459: Specifies revoked host public keys.
1460: Keys listed in this file will be refused for host authentication.
1461: Note that if this file does not exist or is not readable,
1462: then host authentication will be refused for all hosts.
1463: Keys may be specified as a text file, listing one public key per line, or as
1464: an OpenSSH Key Revocation List (KRL) as generated by
1465: .Xr ssh-keygen 1 .
1466: For more information on KRLs, see the KEY REVOCATION LISTS section in
1467: .Xr ssh-keygen 1 .
1.305 naddy 1468: .It Cm SecurityKeyProvider
1.313 naddy 1469: Specifies a path to a library that will be used when loading any
1470: FIDO authenticator-hosted keys, overriding the default of using
1471: the built-in USB HID support.
1.309 naddy 1472: .Pp
1473: If the specified value begins with a
1474: .Sq $
1475: character, then it will be treated as an environment variable containing
1476: the path to the library.
1.32 djm 1477: .It Cm SendEnv
1478: Specifies what variables from the local
1479: .Xr environ 7
1480: should be sent to the server.
1.84 jmc 1481: The server must also support it, and the server must be configured to
1.33 djm 1482: accept these environment variables.
1.207 dtucker 1483: Note that the
1484: .Ev TERM
1.208 jmc 1485: environment variable is always sent whenever a
1.207 dtucker 1486: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1487: Refer to
1488: .Cm AcceptEnv
1489: in
1490: .Xr sshd_config 5
1491: for how to configure the server.
1.80 jmc 1492: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1493: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1494: across multiple
1495: .Cm SendEnv
1496: directives.
1.81 jmc 1497: .Pp
1498: See
1499: .Sx PATTERNS
1500: for more information on patterns.
1.271 djm 1501: .Pp
1.272 jmc 1502: It is possible to clear previously set
1.271 djm 1503: .Cm SendEnv
1504: variable names by prefixing patterns with
1505: .Pa - .
1506: The default is not to send any environment variables.
1.28 markus 1507: .It Cm ServerAliveCountMax
1.73 jmc 1508: Sets the number of server alive messages (see below) which may be
1.28 markus 1509: sent without
1.84 jmc 1510: .Xr ssh 1
1.28 markus 1511: receiving any messages back from the server.
1512: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1513: ssh will disconnect from the server, terminating the session.
1.28 markus 1514: It is important to note that the use of server alive messages is very
1515: different from
1516: .Cm TCPKeepAlive
1517: (below).
1518: The server alive messages are sent through the encrypted channel
1519: and therefore will not be spoofable.
1520: The TCP keepalive option enabled by
1521: .Cm TCPKeepAlive
1522: is spoofable.
1523: The server alive mechanism is valuable when the client or
1.298 dtucker 1524: server depend on knowing when a connection has become unresponsive.
1.28 markus 1525: .Pp
1526: The default value is 3.
1527: If, for example,
1528: .Cm ServerAliveInterval
1.84 jmc 1529: (see below) is set to 15 and
1.28 markus 1530: .Cm ServerAliveCountMax
1.84 jmc 1531: is left at the default, if the server becomes unresponsive,
1532: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1533: .It Cm ServerAliveInterval
1534: Sets a timeout interval in seconds after which if no data has been received
1535: from the server,
1.84 jmc 1536: .Xr ssh 1
1.67 jmc 1537: will send a message through the encrypted
1538: channel to request a response from the server.
1539: The default
1540: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1541: .It Cm SetEnv
1542: Directly specify one or more environment variables and their contents to
1543: be sent to the server.
1544: Similarly to
1545: .Cm SendEnv ,
1546: the server must be prepared to accept the environment variable.
1.191 millert 1547: .It Cm StreamLocalBindMask
1548: Sets the octal file creation mode mask
1549: .Pq umask
1550: used when creating a Unix-domain socket file for local or remote
1551: port forwarding.
1552: This option is only used for port forwarding to a Unix-domain socket file.
1553: .Pp
1554: The default value is 0177, which creates a Unix-domain socket file that is
1555: readable and writable only by the owner.
1556: Note that not all operating systems honor the file mode on Unix-domain
1557: socket files.
1558: .It Cm StreamLocalBindUnlink
1559: Specifies whether to remove an existing Unix-domain socket file for local
1560: or remote port forwarding before creating a new one.
1561: If the socket file already exists and
1562: .Cm StreamLocalBindUnlink
1563: is not enabled,
1564: .Nm ssh
1565: will be unable to forward the port to the Unix-domain socket file.
1566: This option is only used for port forwarding to a Unix-domain socket file.
1567: .Pp
1568: The argument must be
1.240 jmc 1569: .Cm yes
1.191 millert 1570: or
1.240 jmc 1571: .Cm no
1572: (the default).
1.1 stevesk 1573: .It Cm StrictHostKeyChecking
1574: If this flag is set to
1.240 jmc 1575: .Cm yes ,
1.84 jmc 1576: .Xr ssh 1
1.1 stevesk 1577: will never automatically add host keys to the
1.50 djm 1578: .Pa ~/.ssh/known_hosts
1.1 stevesk 1579: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1580: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1581: though it can be annoying when the
1.1 stevesk 1582: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1583: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1584: frequently made.
1585: This option forces the user to manually
1586: add all new hosts.
1.255 jmc 1587: .Pp
1.1 stevesk 1588: If this flag is set to
1.254 djm 1589: .Dq accept-new
1.255 jmc 1590: then ssh will automatically add new host keys to the user
1.254 djm 1591: known hosts files, but will not permit connections to hosts with
1592: changed host keys.
1593: If this flag is set to
1594: .Dq no
1595: or
1596: .Dq off ,
1.255 jmc 1597: ssh will automatically add new host keys to the user known hosts files
1598: and allow connections to hosts with changed hostkeys to proceed,
1599: subject to some restrictions.
1.1 stevesk 1600: If this flag is set to
1.240 jmc 1601: .Cm ask
1602: (the default),
1.1 stevesk 1603: new host keys
1604: will be added to the user known host files only after the user
1605: has confirmed that is what they really want to do, and
1.84 jmc 1606: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1607: The host keys of
1608: known hosts will be verified automatically in all cases.
1.244 jmc 1609: .It Cm SyslogFacility
1610: Gives the facility code that is used when logging messages from
1611: .Xr ssh 1 .
1612: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1613: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1614: The default is USER.
1.26 markus 1615: .It Cm TCPKeepAlive
1616: Specifies whether the system should send TCP keepalive messages to the
1617: other side.
1618: If they are sent, death of the connection or crash of one
1619: of the machines will be properly noticed.
1620: However, this means that
1621: connections will die if the route is down temporarily, and some people
1622: find it annoying.
1623: .Pp
1624: The default is
1.240 jmc 1625: .Cm yes
1.26 markus 1626: (to send TCP keepalive messages), and the client will notice
1627: if the network goes down or the remote host dies.
1628: This is important in scripts, and many users want it too.
1629: .Pp
1630: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1631: .Cm no .
1.265 djm 1632: See also
1633: .Cm ServerAliveInterval
1634: for protocol-level keepalives.
1.65 reyk 1635: .It Cm Tunnel
1.95 stevesk 1636: Request
1.65 reyk 1637: .Xr tun 4
1.69 jmc 1638: device forwarding between the client and the server.
1.65 reyk 1639: The argument must be
1.240 jmc 1640: .Cm yes ,
1641: .Cm point-to-point
1.95 stevesk 1642: (layer 3),
1.240 jmc 1643: .Cm ethernet
1.95 stevesk 1644: (layer 2),
1.65 reyk 1645: or
1.240 jmc 1646: .Cm no
1647: (the default).
1.95 stevesk 1648: Specifying
1.240 jmc 1649: .Cm yes
1.95 stevesk 1650: requests the default tunnel mode, which is
1.240 jmc 1651: .Cm point-to-point .
1.65 reyk 1652: .It Cm TunnelDevice
1.95 stevesk 1653: Specifies the
1.65 reyk 1654: .Xr tun 4
1.95 stevesk 1655: devices to open on the client
1656: .Pq Ar local_tun
1657: and the server
1658: .Pq Ar remote_tun .
1659: .Pp
1660: The argument must be
1661: .Sm off
1662: .Ar local_tun Op : Ar remote_tun .
1663: .Sm on
1664: The devices may be specified by numerical ID or the keyword
1.240 jmc 1665: .Cm any ,
1.95 stevesk 1666: which uses the next available tunnel device.
1667: If
1668: .Ar remote_tun
1669: is not specified, it defaults to
1.240 jmc 1670: .Cm any .
1.95 stevesk 1671: The default is
1.240 jmc 1672: .Cm any:any .
1.201 djm 1673: .It Cm UpdateHostKeys
1.200 djm 1674: Specifies whether
1675: .Xr ssh 1
1676: should accept notifications of additional hostkeys from the server sent
1677: after authentication has completed and add them to
1678: .Cm UserKnownHostsFile .
1679: The argument must be
1.240 jmc 1680: .Cm yes ,
1681: .Cm no
1.320 djm 1682: or
1.240 jmc 1683: .Cm ask .
1.320 djm 1684: This option allows learning alternate hostkeys for a server
1.201 djm 1685: and supports graceful key rotation by allowing a server to send replacement
1686: public keys before old ones are removed.
1.200 djm 1687: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1688: host was already trusted or explicitly accepted by the user.
1.320 djm 1689: .Pp
1690: .Cm UpdateHostKeys
1.321 jmc 1691: is enabled by default if the user has not overridden the default
1.320 djm 1692: .Cm UserKnownHostsFile
1693: setting, otherwise
1694: .Cm UpdateHostKeys
1695: will be set to
1696: .Cm ask .
1697: .Pp
1.204 djm 1698: If
1699: .Cm UpdateHostKeys
1700: is set to
1.240 jmc 1701: .Cm ask ,
1.204 djm 1702: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1703: Confirmation is currently incompatible with
1704: .Cm ControlPersist ,
1705: and will be disabled if it is enabled.
1.200 djm 1706: .Pp
1707: Presently, only
1708: .Xr sshd 8
1709: from OpenSSH 6.8 and greater support the
1.240 jmc 1710: .Qq hostkeys@openssh.com
1.200 djm 1711: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1712: .It Cm User
1713: Specifies the user to log in as.
1714: This can be useful when a different user name is used on different machines.
1715: This saves the trouble of
1716: having to remember to give the user name on the command line.
1717: .It Cm UserKnownHostsFile
1.151 djm 1718: Specifies one or more files to use for the user
1719: host key database, separated by whitespace.
1720: The default is
1721: .Pa ~/.ssh/known_hosts ,
1722: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1723: .It Cm VerifyHostKeyDNS
1724: Specifies whether to verify the remote key using DNS and SSHFP resource
1725: records.
1.24 jakob 1726: If this option is set to
1.240 jmc 1727: .Cm yes ,
1.25 jmc 1728: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1729: from DNS.
1730: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1731: .Cm ask .
1.24 jakob 1732: If this option is set to
1.240 jmc 1733: .Cm ask ,
1.24 jakob 1734: information on fingerprint match will be displayed, but the user will still
1735: need to confirm new host keys according to the
1736: .Cm StrictHostKeyChecking
1737: option.
1.8 jakob 1738: The default is
1.240 jmc 1739: .Cm no .
1.84 jmc 1740: .Pp
1.240 jmc 1741: See also
1742: .Sx VERIFYING HOST KEYS
1743: in
1.84 jmc 1744: .Xr ssh 1 .
1.111 grunk 1745: .It Cm VisualHostKey
1746: If this flag is set to
1.240 jmc 1747: .Cm yes ,
1.111 grunk 1748: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1749: printed in addition to the fingerprint string at login and
1.114 stevesk 1750: for unknown host keys.
1.111 grunk 1751: If this flag is set to
1.240 jmc 1752: .Cm no
1753: (the default),
1.114 stevesk 1754: no fingerprint strings are printed at login and
1.197 djm 1755: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1756: .It Cm XAuthLocation
1.5 stevesk 1757: Specifies the full pathname of the
1.1 stevesk 1758: .Xr xauth 1
1759: program.
1760: The default is
1761: .Pa /usr/X11R6/bin/xauth .
1762: .El
1.86 jmc 1763: .Sh PATTERNS
1764: A
1765: .Em pattern
1766: consists of zero or more non-whitespace characters,
1767: .Sq *
1768: (a wildcard that matches zero or more characters),
1769: or
1770: .Sq ?\&
1771: (a wildcard that matches exactly one character).
1772: For example, to specify a set of declarations for any host in the
1.240 jmc 1773: .Qq .co.uk
1.86 jmc 1774: set of domains,
1775: the following pattern could be used:
1776: .Pp
1777: .Dl Host *.co.uk
1778: .Pp
1779: The following pattern
1780: would match any host in the 192.168.0.[0-9] network range:
1781: .Pp
1782: .Dl Host 192.168.0.?
1783: .Pp
1784: A
1785: .Em pattern-list
1786: is a comma-separated list of patterns.
1787: Patterns within pattern-lists may be negated
1788: by preceding them with an exclamation mark
1789: .Pq Sq !\& .
1790: For example,
1.174 djm 1791: to allow a key to be used from anywhere within an organization
1.86 jmc 1792: except from the
1.240 jmc 1793: .Qq dialup
1.86 jmc 1794: pool,
1795: the following entry (in authorized_keys) could be used:
1796: .Pp
1797: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1798: .Pp
1799: Note that a negated match will never produce a positive result by itself.
1800: For example, attempting to match
1801: .Qq host3
1802: against the following pattern-list will fail:
1803: .Pp
1804: .Dl from=\&"!host1,!host2\&"
1805: .Pp
1806: The solution here is to include a term that will yield a positive match,
1807: such as a wildcard:
1808: .Pp
1809: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1810: .Sh TOKENS
1811: Arguments to some keywords can make use of tokens,
1812: which are expanded at runtime:
1813: .Pp
1814: .Bl -tag -width XXXX -offset indent -compact
1815: .It %%
1816: A literal
1817: .Sq % .
1818: .It \&%C
1.257 jmc 1819: Hash of %l%h%p%r.
1.239 jmc 1820: .It %d
1821: Local user's home directory.
1822: .It %h
1823: The remote hostname.
1824: .It %i
1825: The local user ID.
1826: .It %L
1827: The local hostname.
1828: .It %l
1829: The local hostname, including the domain name.
1830: .It %n
1831: The original remote hostname, as given on the command line.
1832: .It %p
1833: The remote port.
1834: .It %r
1835: The remote username.
1.261 djm 1836: .It \&%T
1837: The local
1838: .Xr tun 4
1839: or
1840: .Xr tap 4
1841: network interface assigned if
1.262 jmc 1842: tunnel forwarding was requested, or
1843: .Qq NONE
1.261 djm 1844: otherwise.
1.239 jmc 1845: .It %u
1846: The local username.
1847: .El
1848: .Pp
1849: .Cm Match exec
1.274 djm 1850: accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1.239 jmc 1851: .Pp
1852: .Cm CertificateFile
1.275 jmc 1853: accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1854: .Pp
1855: .Cm ControlPath
1856: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1857: .Pp
1.295 jmc 1858: .Cm Hostname
1.239 jmc 1859: accepts the tokens %% and %h.
1860: .Pp
1861: .Cm IdentityAgent
1862: and
1863: .Cm IdentityFile
1.275 jmc 1864: accept the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1865: .Pp
1866: .Cm LocalCommand
1.275 jmc 1867: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T, and %u.
1.239 jmc 1868: .Pp
1869: .Cm ProxyCommand
1.303 djm 1870: accepts the tokens %%, %h, %n, %p, and %r.
1.250 jmc 1871: .Pp
1872: .Cm RemoteCommand
1.274 djm 1873: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and %u.
1.1 stevesk 1874: .Sh FILES
1875: .Bl -tag -width Ds
1.50 djm 1876: .It Pa ~/.ssh/config
1.1 stevesk 1877: This is the per-user configuration file.
1878: The format of this file is described above.
1.84 jmc 1879: This file is used by the SSH client.
1.30 djm 1880: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 1881: read/write for the user, and not writable by others.
1.1 stevesk 1882: .It Pa /etc/ssh/ssh_config
1883: Systemwide configuration file.
1884: This file provides defaults for those
1885: values that are not specified in the user's configuration file, and
1886: for those users who do not have a configuration file.
1887: This file must be world-readable.
1888: .El
1.13 jmc 1889: .Sh SEE ALSO
1890: .Xr ssh 1
1.1 stevesk 1891: .Sh AUTHORS
1.240 jmc 1892: .An -nosplit
1.1 stevesk 1893: OpenSSH is a derivative of the original and free
1.240 jmc 1894: ssh 1.2.12 release by
1895: .An Tatu Ylonen .
1896: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1897: .An Niels Provos , Theo de Raadt
1898: and
1899: .An Dug Song
1.1 stevesk 1900: removed many bugs, re-added newer features and
1901: created OpenSSH.
1.240 jmc 1902: .An Markus Friedl
1903: contributed the support for SSH protocol versions 1.5 and 2.0.
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