Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.361
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
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19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
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25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.361 ! dtucker 36: .\" $OpenBSD: ssh_config.5,v 1.360 2021/07/30 14:25:01 jmc Exp $
! 37: .Dd $Mdocdate: July 30 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.
1.361 ! dtucker 344: A value of
! 345: .Cm none
! 346: disables the use of a
! 347: .Cm ProxyJump
! 348: host.
1.173 djm 349: .It Cm CanonicalizeMaxDots
1.172 jmc 350: Specifies the maximum number of dot characters in a hostname before
1.174 djm 351: canonicalization is disabled.
1.240 jmc 352: The default, 1,
1.172 jmc 353: allows a single dot (i.e. hostname.subdomain).
1.173 djm 354: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 355: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 356: canonicalizing hostnames.
1.171 djm 357: The rules consist of one or more arguments of
1.172 jmc 358: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 359: where
360: .Ar source_domain_list
1.174 djm 361: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 362: and
363: .Ar target_domain_list
1.172 jmc 364: is a pattern-list of domains that they may resolve to.
1.171 djm 365: .Pp
366: For example,
1.240 jmc 367: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 368: will allow hostnames matching
1.240 jmc 369: .Qq *.a.example.com
1.173 djm 370: to be canonicalized to names in the
1.240 jmc 371: .Qq *.b.example.com
1.171 djm 372: or
1.240 jmc 373: .Qq *.c.example.com
1.171 djm 374: domains.
1.283 jmc 375: .It Cm CASignatureAlgorithms
376: Specifies which algorithms are allowed for signing of certificates
377: by certificate authorities (CAs).
378: The default is:
379: .Bd -literal -offset indent
1.351 djm 380: ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.353 jmc 381: sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,
1.351 djm 382: rsa-sha2-512,rsa-sha2-256
1.283 jmc 383: .Ed
384: .Pp
385: .Xr ssh 1
386: will not accept host certificates signed using algorithms other than those
387: specified.
1.221 djm 388: .It Cm CertificateFile
389: Specifies a file from which the user's certificate is read.
390: A corresponding private key must be provided separately in order
391: to use this certificate either
392: from an
393: .Cm IdentityFile
394: directive or
395: .Fl i
396: flag to
397: .Xr ssh 1 ,
398: via
399: .Xr ssh-agent 1 ,
400: or via a
1.305 naddy 401: .Cm PKCS11Provider
402: or
403: .Cm SecurityKeyProvider .
1.221 djm 404: .Pp
1.239 jmc 405: Arguments to
406: .Cm CertificateFile
1.326 dtucker 407: may use the tilde syntax to refer to a user's home directory,
408: the tokens described in the
1.239 jmc 409: .Sx TOKENS
1.326 dtucker 410: section and environment variables as described in the
411: .Sx ENVIRONMENT VARIABLES
1.239 jmc 412: section.
1.221 djm 413: .Pp
414: It is possible to have multiple certificate files specified in
415: configuration files; these certificates will be tried in sequence.
416: Multiple
417: .Cm CertificateFile
418: directives will add to the list of certificates used for
419: authentication.
1.1 stevesk 420: .It Cm CheckHostIP
1.240 jmc 421: If set to
422: .Cm yes
1.84 jmc 423: .Xr ssh 1
424: will additionally check the host IP address in the
1.1 stevesk 425: .Pa known_hosts
426: file.
1.240 jmc 427: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 428: and will add addresses of destination hosts to
429: .Pa ~/.ssh/known_hosts
430: in the process, regardless of the setting of
431: .Cm StrictHostKeyChecking .
1.107 grunk 432: If the option is set to
1.341 djm 433: .Cm no
434: (the default),
1.1 stevesk 435: the check will not be executed.
436: .It Cm Ciphers
1.245 djm 437: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 438: Multiple ciphers must be comma-separated.
1.299 kn 439: If the specified list begins with a
1.214 djm 440: .Sq +
441: character, then the specified ciphers will be appended to the default set
442: instead of replacing them.
1.299 kn 443: If the specified list begins with a
1.241 djm 444: .Sq -
445: character, then the specified ciphers (including wildcards) will be removed
446: from the default set instead of replacing them.
1.301 naddy 447: If the specified list begins with a
448: .Sq ^
449: character, then the specified ciphers will be placed at the head of the
450: default set.
1.214 djm 451: .Pp
1.180 djm 452: The supported ciphers are:
1.240 jmc 453: .Bd -literal -offset indent
1.186 naddy 454: 3des-cbc
455: aes128-cbc
456: aes192-cbc
457: aes256-cbc
458: aes128-ctr
459: aes192-ctr
460: aes256-ctr
461: aes128-gcm@openssh.com
462: aes256-gcm@openssh.com
463: chacha20-poly1305@openssh.com
1.240 jmc 464: .Ed
1.180 djm 465: .Pp
1.84 jmc 466: The default is:
1.186 naddy 467: .Bd -literal -offset indent
1.215 jmc 468: chacha20-poly1305@openssh.com,
1.186 naddy 469: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 470: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 471: .Ed
1.180 djm 472: .Pp
1.240 jmc 473: The list of available ciphers may also be obtained using
474: .Qq ssh -Q cipher .
1.1 stevesk 475: .It Cm ClearAllForwardings
1.84 jmc 476: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 477: specified in the configuration files or on the command line be
1.7 jmc 478: cleared.
479: This option is primarily useful when used from the
1.84 jmc 480: .Xr ssh 1
1.1 stevesk 481: command line to clear port forwardings set in
482: configuration files, and is automatically set by
483: .Xr scp 1
484: and
485: .Xr sftp 1 .
486: The argument must be
1.240 jmc 487: .Cm yes
1.1 stevesk 488: or
1.240 jmc 489: .Cm no
490: (the default).
1.1 stevesk 491: .It Cm Compression
492: Specifies whether to use compression.
493: The argument must be
1.240 jmc 494: .Cm yes
1.1 stevesk 495: or
1.240 jmc 496: .Cm no
497: (the default).
1.247 naddy 498: .It Cm ConnectionAttempts
499: Specifies the number of tries (one per second) to make before exiting.
500: The argument must be an integer.
501: This may be useful in scripts if the connection sometimes fails.
502: The default is 1.
1.9 djm 503: .It Cm ConnectTimeout
1.84 jmc 504: Specifies the timeout (in seconds) used when connecting to the
505: SSH server, instead of using the default system TCP timeout.
1.302 djm 506: This timeout is applied both to establishing the connection and to performing
507: the initial SSH protocol handshake and key exchange.
1.36 djm 508: .It Cm ControlMaster
509: Enables the sharing of multiple sessions over a single network connection.
510: When set to
1.240 jmc 511: .Cm yes ,
1.84 jmc 512: .Xr ssh 1
1.36 djm 513: will listen for connections on a control socket specified using the
514: .Cm ControlPath
515: argument.
516: Additional sessions can connect to this socket using the same
517: .Cm ControlPath
518: with
519: .Cm ControlMaster
520: set to
1.240 jmc 521: .Cm no
1.38 jmc 522: (the default).
1.64 jmc 523: These sessions will try to reuse the master instance's network connection
1.63 djm 524: rather than initiating new ones, but will fall back to connecting normally
525: if the control socket does not exist, or is not listening.
526: .Pp
1.37 djm 527: Setting this to
1.240 jmc 528: .Cm ask
529: will cause
530: .Xr ssh 1
1.206 jmc 531: to listen for control connections, but require confirmation using
532: .Xr ssh-askpass 1 .
1.51 jakob 533: If the
534: .Cm ControlPath
1.84 jmc 535: cannot be opened,
1.240 jmc 536: .Xr ssh 1
537: will continue without connecting to a master instance.
1.58 djm 538: .Pp
539: X11 and
1.59 jmc 540: .Xr ssh-agent 1
1.58 djm 541: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 542: display and agent forwarded will be the one belonging to the master
1.59 jmc 543: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 544: .Pp
545: Two additional options allow for opportunistic multiplexing: try to use a
546: master connection but fall back to creating a new one if one does not already
547: exist.
548: These options are:
1.240 jmc 549: .Cm auto
1.56 djm 550: and
1.240 jmc 551: .Cm autoask .
1.56 djm 552: The latter requires confirmation like the
1.240 jmc 553: .Cm ask
1.56 djm 554: option.
1.36 djm 555: .It Cm ControlPath
1.55 djm 556: Specify the path to the control socket used for connection sharing as described
557: in the
1.36 djm 558: .Cm ControlMaster
1.57 djm 559: section above or the string
1.240 jmc 560: .Cm none
1.57 djm 561: to disable connection sharing.
1.239 jmc 562: Arguments to
563: .Cm ControlPath
1.326 dtucker 564: may use the tilde syntax to refer to a user's home directory,
565: the tokens described in the
1.239 jmc 566: .Sx TOKENS
1.326 dtucker 567: section and environment variables as described in the
568: .Sx ENVIRONMENT VARIABLES
1.239 jmc 569: section.
1.56 djm 570: It is recommended that any
571: .Cm ControlPath
572: used for opportunistic connection sharing include
1.195 djm 573: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
574: that is not writable by other users.
1.56 djm 575: This ensures that shared connections are uniquely identified.
1.137 djm 576: .It Cm ControlPersist
577: When used in conjunction with
578: .Cm ControlMaster ,
579: specifies that the master connection should remain open
580: in the background (waiting for future client connections)
581: after the initial client connection has been closed.
582: If set to
1.314 naddy 583: .Cm no
584: (the default),
1.137 djm 585: then the master connection will not be placed into the background,
586: and will close as soon as the initial client connection is closed.
587: If set to
1.240 jmc 588: .Cm yes
589: or 0,
1.137 djm 590: then the master connection will remain in the background indefinitely
591: (until killed or closed via a mechanism such as the
1.240 jmc 592: .Qq ssh -O exit ) .
1.137 djm 593: If set to a time in seconds, or a time in any of the formats documented in
594: .Xr sshd_config 5 ,
595: then the backgrounded master connection will automatically terminate
596: after it has remained idle (with no client connections) for the
597: specified time.
1.38 jmc 598: .It Cm DynamicForward
1.74 jmc 599: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 600: over the secure channel, and the application
601: protocol is then used to determine where to connect to from the
602: remote machine.
1.62 djm 603: .Pp
604: The argument must be
605: .Sm off
606: .Oo Ar bind_address : Oc Ar port .
607: .Sm on
1.138 djm 608: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 609: By default, the local port is bound in accordance with the
610: .Cm GatewayPorts
611: setting.
612: However, an explicit
613: .Ar bind_address
614: may be used to bind the connection to a specific address.
615: The
616: .Ar bind_address
617: of
1.240 jmc 618: .Cm localhost
1.62 djm 619: indicates that the listening port be bound for local use only, while an
620: empty address or
621: .Sq *
622: indicates that the port should be available from all interfaces.
623: .Pp
1.38 jmc 624: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 625: .Xr ssh 1
1.38 jmc 626: will act as a SOCKS server.
627: Multiple forwardings may be specified, and
628: additional forwardings can be given on the command line.
629: Only the superuser can forward privileged ports.
1.14 markus 630: .It Cm EnableSSHKeysign
631: Setting this option to
1.240 jmc 632: .Cm yes
1.14 markus 633: in the global client configuration file
634: .Pa /etc/ssh/ssh_config
635: enables the use of the helper program
636: .Xr ssh-keysign 8
637: during
638: .Cm HostbasedAuthentication .
639: The argument must be
1.240 jmc 640: .Cm yes
1.14 markus 641: or
1.240 jmc 642: .Cm no
643: (the default).
1.23 jmc 644: This option should be placed in the non-hostspecific section.
1.14 markus 645: See
646: .Xr ssh-keysign 8
647: for more information.
1.1 stevesk 648: .It Cm EscapeChar
649: Sets the escape character (default:
650: .Ql ~ ) .
651: The escape character can also
652: be set on the command line.
653: The argument should be a single character,
654: .Ql ^
655: followed by a letter, or
1.240 jmc 656: .Cm none
1.1 stevesk 657: to disable the escape
658: character entirely (making the connection transparent for binary
659: data).
1.96 markus 660: .It Cm ExitOnForwardFailure
661: Specifies whether
662: .Xr ssh 1
663: should terminate the connection if it cannot set up all requested
1.216 djm 664: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 665: if either end is unable to bind and listen on a specified port).
1.216 djm 666: Note that
667: .Cm ExitOnForwardFailure
668: does not apply to connections made over port forwardings and will not,
669: for example, cause
670: .Xr ssh 1
671: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 672: The argument must be
1.240 jmc 673: .Cm yes
1.96 markus 674: or
1.240 jmc 675: .Cm no
676: (the default).
1.197 djm 677: .It Cm FingerprintHash
678: Specifies the hash algorithm used when displaying key fingerprints.
679: Valid options are:
1.240 jmc 680: .Cm md5
1.197 djm 681: and
1.240 jmc 682: .Cm sha256
1.359 djm 683: (the default).
684: .It Cm ForkAfterAuthentication
685: Requests
686: .Nm ssh
687: to go to background just before command execution.
688: This is useful if
689: .Nm ssh
690: is going to ask for passwords or passphrases, but the user
691: wants it in the background.
692: This implies the
693: .Cm StdinNull
694: configuration option being set to
695: .Dq yes .
696: The recommended way to start X11 programs at a remote site is with
697: something like
698: .Ic ssh -f host xterm ,
699: which is the same as
700: .Ic ssh host xterm
701: if the
702: .Cm ForkAfterAuthentication
703: configuration option is set to
704: .Dq yes .
705: .Pp
706: If the
707: .Cm ExitOnForwardFailure
708: configuration option is set to
709: .Dq yes ,
710: then a client started with the
711: .Cm ForkAfterAuthentication
712: configuration option being set to
713: .Dq yes
714: will wait for all remote port forwards to be successfully established
715: before placing itself in the background.
716: The argument to this keyword must be
717: .Cm yes
718: (same as the
719: .Fl f
720: option) or
721: .Cm no
1.240 jmc 722: (the default).
1.1 stevesk 723: .It Cm ForwardAgent
724: Specifies whether the connection to the authentication agent (if any)
725: will be forwarded to the remote machine.
1.312 djm 726: The argument may be
727: .Cm yes ,
1.240 jmc 728: .Cm no
1.312 djm 729: (the default),
730: an explicit path to an agent socket or the name of an environment variable
731: (beginning with
732: .Sq $ )
733: in which to find the path.
1.3 stevesk 734: .Pp
1.7 jmc 735: Agent forwarding should be enabled with caution.
736: Users with the ability to bypass file permissions on the remote host
737: (for the agent's Unix-domain socket)
738: can access the local agent through the forwarded connection.
739: An attacker cannot obtain key material from the agent,
1.3 stevesk 740: however they can perform operations on the keys that enable them to
741: authenticate using the identities loaded into the agent.
1.1 stevesk 742: .It Cm ForwardX11
743: Specifies whether X11 connections will be automatically redirected
744: over the secure channel and
745: .Ev DISPLAY
746: set.
747: The argument must be
1.240 jmc 748: .Cm yes
1.1 stevesk 749: or
1.240 jmc 750: .Cm no
751: (the default).
1.3 stevesk 752: .Pp
1.7 jmc 753: X11 forwarding should be enabled with caution.
754: Users with the ability to bypass file permissions on the remote host
1.22 markus 755: (for the user's X11 authorization database)
1.7 jmc 756: can access the local X11 display through the forwarded connection.
1.22 markus 757: An attacker may then be able to perform activities such as keystroke monitoring
758: if the
759: .Cm ForwardX11Trusted
760: option is also enabled.
1.134 djm 761: .It Cm ForwardX11Timeout
1.135 jmc 762: Specify a timeout for untrusted X11 forwarding
763: using the format described in the
1.240 jmc 764: .Sx TIME FORMATS
765: section of
1.134 djm 766: .Xr sshd_config 5 .
767: X11 connections received by
768: .Xr ssh 1
769: after this time will be refused.
1.285 djm 770: Setting
771: .Cm ForwardX11Timeout
772: to zero will disable the timeout and permit X11 forwarding for the life
773: of the connection.
1.134 djm 774: The default is to disable untrusted X11 forwarding after twenty minutes has
775: elapsed.
1.22 markus 776: .It Cm ForwardX11Trusted
1.34 jmc 777: If this option is set to
1.240 jmc 778: .Cm yes ,
1.84 jmc 779: remote X11 clients will have full access to the original X11 display.
1.42 djm 780: .Pp
1.22 markus 781: If this option is set to
1.240 jmc 782: .Cm no
783: (the default),
1.84 jmc 784: remote X11 clients will be considered untrusted and prevented
1.22 markus 785: from stealing or tampering with data belonging to trusted X11
786: clients.
1.42 djm 787: Furthermore, the
788: .Xr xauth 1
789: token used for the session will be set to expire after 20 minutes.
790: Remote clients will be refused access after this time.
1.22 markus 791: .Pp
792: See the X11 SECURITY extension specification for full details on
793: the restrictions imposed on untrusted clients.
1.1 stevesk 794: .It Cm GatewayPorts
795: Specifies whether remote hosts are allowed to connect to local
796: forwarded ports.
797: By default,
1.84 jmc 798: .Xr ssh 1
1.7 jmc 799: binds local port forwardings to the loopback address.
800: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 801: .Cm GatewayPorts
1.84 jmc 802: can be used to specify that ssh
1.1 stevesk 803: should bind local port forwardings to the wildcard address,
804: thus allowing remote hosts to connect to forwarded ports.
805: The argument must be
1.240 jmc 806: .Cm yes
1.1 stevesk 807: or
1.240 jmc 808: .Cm no
809: (the default).
1.1 stevesk 810: .It Cm GlobalKnownHostsFile
1.151 djm 811: Specifies one or more files to use for the global
812: host key database, separated by whitespace.
813: The default is
814: .Pa /etc/ssh/ssh_known_hosts ,
815: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 816: .It Cm GSSAPIAuthentication
1.27 markus 817: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 818: The default is
1.240 jmc 819: .Cm no .
1.18 markus 820: .It Cm GSSAPIDelegateCredentials
821: Forward (delegate) credentials to the server.
822: The default is
1.240 jmc 823: .Cm no .
1.44 djm 824: .It Cm HashKnownHosts
825: Indicates that
1.84 jmc 826: .Xr ssh 1
1.44 djm 827: should hash host names and addresses when they are added to
1.50 djm 828: .Pa ~/.ssh/known_hosts .
1.44 djm 829: These hashed names may be used normally by
1.84 jmc 830: .Xr ssh 1
1.44 djm 831: and
1.84 jmc 832: .Xr sshd 8 ,
1.316 djm 833: but they do not visually reveal identifying information if the
834: file's contents are disclosed.
1.44 djm 835: The default is
1.240 jmc 836: .Cm no .
1.97 jmc 837: Note that existing names and addresses in known hosts files
838: will not be converted automatically,
839: but may be manually hashed using
1.45 djm 840: .Xr ssh-keygen 1 .
1.344 dtucker 841: .It Cm HostbasedAcceptedAlgorithms
1.348 djm 842: Specifies the signature algorithms that will be used for hostbased
843: authentication as a comma-separated list of patterns.
1.300 naddy 844: Alternately if the specified list begins with a
1.214 djm 845: .Sq +
1.348 djm 846: character, then the specified signature algorithms will be appended
847: to the default set instead of replacing them.
1.300 naddy 848: If the specified list begins with a
1.241 djm 849: .Sq -
1.348 djm 850: character, then the specified signature algorithms (including wildcards)
851: will be removed from the default set instead of replacing them.
1.301 naddy 852: If the specified list begins with a
853: .Sq ^
1.348 djm 854: character, then the specified signature algorithms will be placed
855: at the head of the default set.
1.213 markus 856: The default for this option is:
857: .Bd -literal -offset 3n
1.333 djm 858: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 859: ecdsa-sha2-nistp256-cert-v01@openssh.com,
860: ecdsa-sha2-nistp384-cert-v01@openssh.com,
861: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 862: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 863: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 864: rsa-sha2-512-cert-v01@openssh.com,
865: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 866: ssh-rsa-cert-v01@openssh.com,
1.333 djm 867: ssh-ed25519,
1.213 markus 868: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 869: sk-ssh-ed25519@openssh.com,
1.311 naddy 870: sk-ecdsa-sha2-nistp256@openssh.com,
871: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 872: .Ed
873: .Pp
1.202 djm 874: The
875: .Fl Q
876: option of
877: .Xr ssh 1
1.348 djm 878: may be used to list supported signature algorithms.
1.344 dtucker 879: This was formerly named HostbasedKeyTypes.
1.345 naddy 880: .It Cm HostbasedAuthentication
881: Specifies whether to try rhosts based authentication with public key
882: authentication.
883: The argument must be
884: .Cm yes
885: or
886: .Cm no
887: (the default).
1.1 stevesk 888: .It Cm HostKeyAlgorithms
1.348 djm 889: Specifies the host key signature algorithms
1.1 stevesk 890: that the client wants to use in order of preference.
1.300 naddy 891: Alternately if the specified list begins with a
1.214 djm 892: .Sq +
1.348 djm 893: character, then the specified signature algorithms will be appended to
894: the default set instead of replacing them.
1.300 naddy 895: If the specified list begins with a
1.241 djm 896: .Sq -
1.348 djm 897: character, then the specified signature algorithms (including wildcards)
898: will be removed from the default set instead of replacing them.
1.301 naddy 899: If the specified list begins with a
900: .Sq ^
1.348 djm 901: character, then the specified signature algorithms will be placed
902: at the head of the default set.
1.1 stevesk 903: The default for this option is:
1.139 djm 904: .Bd -literal -offset 3n
1.333 djm 905: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 906: ecdsa-sha2-nistp256-cert-v01@openssh.com,
907: ecdsa-sha2-nistp384-cert-v01@openssh.com,
908: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 909: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 910: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 911: rsa-sha2-512-cert-v01@openssh.com,
912: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 913: ssh-rsa-cert-v01@openssh.com,
1.333 djm 914: ssh-ed25519,
1.139 djm 915: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 916: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 917: sk-ssh-ed25519@openssh.com,
1.311 naddy 918: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 919: .Ed
1.145 djm 920: .Pp
921: If hostkeys are known for the destination host then this default is modified
922: to prefer their algorithms.
1.198 djm 923: .Pp
1.348 djm 924: The list of available signature algorithms may also be obtained using
1.322 dtucker 925: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 926: .It Cm HostKeyAlias
927: Specifies an alias that should be used instead of the
928: real host name when looking up or saving the host key
1.251 djm 929: in the host key database files and when validating host certificates.
1.84 jmc 930: This option is useful for tunneling SSH connections
1.1 stevesk 931: or for multiple servers running on a single host.
1.295 jmc 932: .It Cm Hostname
1.1 stevesk 933: Specifies the real host name to log into.
934: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 935: Arguments to
1.295 jmc 936: .Cm Hostname
1.239 jmc 937: accept the tokens described in the
938: .Sx TOKENS
939: section.
1.1 stevesk 940: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 941: .Cm Hostname
1.1 stevesk 942: specifications).
1.239 jmc 943: The default is the name given on the command line.
1.29 markus 944: .It Cm IdentitiesOnly
945: Specifies that
1.84 jmc 946: .Xr ssh 1
1.304 djm 947: should only use the configured authentication identity and certificate files
948: (either the default files, or those explicitly configured in the
1.31 jmc 949: .Nm
1.221 djm 950: files
951: or passed on the
952: .Xr ssh 1
1.304 djm 953: command-line),
1.84 jmc 954: even if
955: .Xr ssh-agent 1
1.159 djm 956: or a
957: .Cm PKCS11Provider
1.305 naddy 958: or
959: .Cm SecurityKeyProvider
1.29 markus 960: offers more identities.
961: The argument to this keyword must be
1.240 jmc 962: .Cm yes
1.29 markus 963: or
1.240 jmc 964: .Cm no
965: (the default).
1.84 jmc 966: This option is intended for situations where ssh-agent
1.29 markus 967: offers many different identities.
1.231 markus 968: .It Cm IdentityAgent
969: Specifies the
970: .Ux Ns -domain
971: socket used to communicate with the authentication agent.
972: .Pp
973: This option overrides the
1.240 jmc 974: .Ev SSH_AUTH_SOCK
1.231 markus 975: environment variable and can be used to select a specific agent.
976: Setting the socket name to
1.240 jmc 977: .Cm none
1.231 markus 978: disables the use of an authentication agent.
1.232 markus 979: If the string
1.240 jmc 980: .Qq SSH_AUTH_SOCK
1.232 markus 981: is specified, the location of the socket will be read from the
982: .Ev SSH_AUTH_SOCK
983: environment variable.
1.286 djm 984: Otherwise if the specified value begins with a
985: .Sq $
986: character, then it will be treated as an environment variable containing
987: the location of the socket.
1.231 markus 988: .Pp
1.239 jmc 989: Arguments to
990: .Cm IdentityAgent
1.326 dtucker 991: may use the tilde syntax to refer to a user's home directory,
992: the tokens described in the
1.239 jmc 993: .Sx TOKENS
1.326 dtucker 994: section and environment variables as described in the
995: .Sx ENVIRONMENT VARIABLES
1.239 jmc 996: section.
1.67 jmc 997: .It Cm IdentityFile
1.313 naddy 998: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
999: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 1000: The default is
1.139 djm 1001: .Pa ~/.ssh/id_dsa ,
1.183 naddy 1002: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 1003: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 1004: .Pa ~/.ssh/id_ed25519 ,
1005: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 1006: and
1.245 djm 1007: .Pa ~/.ssh/id_rsa .
1.67 jmc 1008: Additionally, any identities represented by the authentication agent
1.165 djm 1009: will be used for authentication unless
1010: .Cm IdentitiesOnly
1011: is set.
1.221 djm 1012: If no certificates have been explicitly specified by
1013: .Cm CertificateFile ,
1.129 djm 1014: .Xr ssh 1
1015: will try to load certificate information from the filename obtained by
1016: appending
1017: .Pa -cert.pub
1018: to the path of a specified
1019: .Cm IdentityFile .
1.90 djm 1020: .Pp
1.239 jmc 1021: Arguments to
1022: .Cm IdentityFile
1023: may use the tilde syntax to refer to a user's home directory
1024: or the tokens described in the
1025: .Sx TOKENS
1026: section.
1.90 djm 1027: .Pp
1.67 jmc 1028: It is possible to have
1029: multiple identity files specified in configuration files; all these
1030: identities will be tried in sequence.
1.152 djm 1031: Multiple
1032: .Cm IdentityFile
1033: directives will add to the list of identities tried (this behaviour
1034: differs from that of other configuration directives).
1.165 djm 1035: .Pp
1036: .Cm IdentityFile
1037: may be used in conjunction with
1038: .Cm IdentitiesOnly
1039: to select which identities in an agent are offered during authentication.
1.221 djm 1040: .Cm IdentityFile
1041: may also be used in conjunction with
1042: .Cm CertificateFile
1043: in order to provide any certificate also needed for authentication with
1044: the identity.
1.164 jmc 1045: .It Cm IgnoreUnknown
1046: Specifies a pattern-list of unknown options to be ignored if they are
1047: encountered in configuration parsing.
1048: This may be used to suppress errors if
1049: .Nm
1050: contains options that are unrecognised by
1051: .Xr ssh 1 .
1052: It is recommended that
1053: .Cm IgnoreUnknown
1054: be listed early in the configuration file as it will not be applied
1055: to unknown options that appear before it.
1.229 djm 1056: .It Cm Include
1057: Include the specified configuration file(s).
1.230 jmc 1058: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1059: .Xr glob 7
1.229 djm 1060: wildcards and, for user configurations, shell-like
1.240 jmc 1061: .Sq ~
1.229 djm 1062: references to user home directories.
1.327 djm 1063: Wildcards will be expanded and processed in lexical order.
1.229 djm 1064: Files without absolute paths are assumed to be in
1065: .Pa ~/.ssh
1.230 jmc 1066: if included in a user configuration file or
1.229 djm 1067: .Pa /etc/ssh
1068: if included from the system configuration file.
1069: .Cm Include
1070: directive may appear inside a
1071: .Cm Match
1072: or
1073: .Cm Host
1074: block
1075: to perform conditional inclusion.
1.143 djm 1076: .It Cm IPQoS
1077: Specifies the IPv4 type-of-service or DSCP class for connections.
1078: Accepted values are
1.240 jmc 1079: .Cm af11 ,
1080: .Cm af12 ,
1081: .Cm af13 ,
1082: .Cm af21 ,
1083: .Cm af22 ,
1084: .Cm af23 ,
1085: .Cm af31 ,
1086: .Cm af32 ,
1087: .Cm af33 ,
1088: .Cm af41 ,
1089: .Cm af42 ,
1090: .Cm af43 ,
1091: .Cm cs0 ,
1092: .Cm cs1 ,
1093: .Cm cs2 ,
1094: .Cm cs3 ,
1095: .Cm cs4 ,
1096: .Cm cs5 ,
1097: .Cm cs6 ,
1098: .Cm cs7 ,
1099: .Cm ef ,
1.319 djm 1100: .Cm le ,
1.240 jmc 1101: .Cm lowdelay ,
1102: .Cm throughput ,
1103: .Cm reliability ,
1.253 djm 1104: a numeric value, or
1105: .Cm none
1106: to use the operating system default.
1.146 djm 1107: This option may take one or two arguments, separated by whitespace.
1.143 djm 1108: If one argument is specified, it is used as the packet class unconditionally.
1109: If two values are specified, the first is automatically selected for
1110: interactive sessions and the second for non-interactive sessions.
1111: The default is
1.269 job 1112: .Cm af21
1.272 jmc 1113: (Low-Latency Data)
1.143 djm 1114: for interactive sessions and
1.269 job 1115: .Cm cs1
1.272 jmc 1116: (Lower Effort)
1.143 djm 1117: for non-interactive sessions.
1.103 djm 1118: .It Cm KbdInteractiveAuthentication
1119: Specifies whether to use keyboard-interactive authentication.
1120: The argument to this keyword must be
1.240 jmc 1121: .Cm yes
1122: (the default)
1.103 djm 1123: or
1.240 jmc 1124: .Cm no .
1.355 dtucker 1125: .Cm ChallengeResponseAuthentication
1126: is a deprecated alias for this.
1.39 djm 1127: .It Cm KbdInteractiveDevices
1128: Specifies the list of methods to use in keyboard-interactive authentication.
1129: Multiple method names must be comma-separated.
1130: The default is to use the server specified list.
1.85 jmc 1131: The methods available vary depending on what the server supports.
1132: For an OpenSSH server,
1133: it may be zero or more of:
1.240 jmc 1134: .Cm bsdauth ,
1135: .Cm pam ,
1.85 jmc 1136: and
1.240 jmc 1137: .Cm skey .
1.140 djm 1138: .It Cm KexAlgorithms
1139: Specifies the available KEX (Key Exchange) algorithms.
1140: Multiple algorithms must be comma-separated.
1.299 kn 1141: If the specified list begins with a
1.214 djm 1142: .Sq +
1143: character, then the specified methods will be appended to the default set
1144: instead of replacing them.
1.299 kn 1145: If the specified list begins with a
1.241 djm 1146: .Sq -
1147: character, then the specified methods (including wildcards) will be removed
1148: from the default set instead of replacing them.
1.301 naddy 1149: If the specified list begins with a
1150: .Sq ^
1151: character, then the specified methods will be placed at the head of the
1152: default set.
1.141 jmc 1153: The default is:
1154: .Bd -literal -offset indent
1.238 djm 1155: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1156: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1157: diffie-hellman-group-exchange-sha256,
1.266 djm 1158: diffie-hellman-group16-sha512,
1159: diffie-hellman-group18-sha512,
1.317 tedu 1160: diffie-hellman-group14-sha256
1.141 jmc 1161: .Ed
1.198 djm 1162: .Pp
1.240 jmc 1163: The list of available key exchange algorithms may also be obtained using
1164: .Qq ssh -Q kex .
1.339 djm 1165: .It Cm KnownHostsCommand
1.340 jmc 1166: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1167: those listed in
1168: .Cm UserKnownHostsFile
1169: and
1170: .Cm GlobalKnownHostsFile .
1171: This command is executed after the files have been read.
1.340 jmc 1172: It may write host key lines to standard output in identical format to the
1.339 djm 1173: usual files (described in the
1174: .Sx VERIFYING HOST KEYS
1175: section in
1176: .Xr ssh 1 ) .
1177: Arguments to
1178: .Cm KnownHostsCommand
1179: accept the tokens described in the
1180: .Sx TOKENS
1181: section.
1.340 jmc 1182: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1183: the preference list of host key algorithms to use, again to obtain the
1184: host key for the requested host name and, if
1185: .Cm CheckHostIP
1186: is enabled, one more time to obtain the host key matching the server's
1187: address.
1188: If the command exits abnormally or returns a non-zero exit status then the
1189: connection is terminated.
1.65 reyk 1190: .It Cm LocalCommand
1191: Specifies a command to execute on the local machine after successfully
1192: connecting to the server.
1193: The command string extends to the end of the line, and is executed with
1.105 jmc 1194: the user's shell.
1.239 jmc 1195: Arguments to
1196: .Cm LocalCommand
1197: accept the tokens described in the
1198: .Sx TOKENS
1199: section.
1.123 djm 1200: .Pp
1201: The command is run synchronously and does not have access to the
1202: session of the
1203: .Xr ssh 1
1204: that spawned it.
1205: It should not be used for interactive commands.
1206: .Pp
1.65 reyk 1207: This directive is ignored unless
1208: .Cm PermitLocalCommand
1209: has been enabled.
1.1 stevesk 1210: .It Cm LocalForward
1.74 jmc 1211: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1212: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1213: The first argument specifies the listener and may be
1.43 djm 1214: .Sm off
1.49 jmc 1215: .Oo Ar bind_address : Oc Ar port
1.43 djm 1216: .Sm on
1.324 dtucker 1217: or a Unix domain socket path.
1218: The second argument is the destination and may be
1219: .Ar host : Ns Ar hostport
1220: or a Unix domain socket path if the remote host supports it.
1221: .Pp
1.138 djm 1222: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1223: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1224: given on the command line.
1.1 stevesk 1225: Only the superuser can forward privileged ports.
1.43 djm 1226: By default, the local port is bound in accordance with the
1227: .Cm GatewayPorts
1228: setting.
1229: However, an explicit
1230: .Ar bind_address
1231: may be used to bind the connection to a specific address.
1232: The
1233: .Ar bind_address
1234: of
1.240 jmc 1235: .Cm localhost
1.46 jmc 1236: indicates that the listening port be bound for local use only, while an
1237: empty address or
1238: .Sq *
1.43 djm 1239: indicates that the port should be available from all interfaces.
1.326 dtucker 1240: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1241: .Sx TOKENS
1.326 dtucker 1242: section and environment variables as described in the
1243: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1244: section.
1.1 stevesk 1245: .It Cm LogLevel
1246: Gives the verbosity level that is used when logging messages from
1.84 jmc 1247: .Xr ssh 1 .
1.1 stevesk 1248: The possible values are:
1.84 jmc 1249: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1250: The default is INFO.
1251: DEBUG and DEBUG1 are equivalent.
1252: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1253: .It Cm LogVerbose
1254: Specify one or more overrides to LogLevel.
1255: An override consists of a pattern lists that matches the source file, function
1256: and line number to force detailed logging for.
1257: For example, an override pattern of:
1258: .Bd -literal -offset indent
1259: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1260: .Ed
1261: .Pp
1262: would enable detailed logging for line 1000 of
1.338 jmc 1263: .Pa kex.c ,
1.337 djm 1264: everything in the
1265: .Fn kex_exchange_identification
1266: function, and all code in the
1267: .Pa packet.c
1268: file.
1269: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1270: .It Cm MACs
1271: Specifies the MAC (message authentication code) algorithms
1272: in order of preference.
1.226 jmc 1273: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1274: Multiple algorithms must be comma-separated.
1.299 kn 1275: If the specified list begins with a
1.214 djm 1276: .Sq +
1277: character, then the specified algorithms will be appended to the default set
1278: instead of replacing them.
1.299 kn 1279: If the specified list begins with a
1.241 djm 1280: .Sq -
1281: character, then the specified algorithms (including wildcards) will be removed
1282: from the default set instead of replacing them.
1.301 naddy 1283: If the specified list begins with a
1284: .Sq ^
1285: character, then the specified algorithms will be placed at the head of the
1286: default set.
1.214 djm 1287: .Pp
1.160 markus 1288: The algorithms that contain
1.240 jmc 1289: .Qq -etm
1.160 markus 1290: calculate the MAC after encryption (encrypt-then-mac).
1291: These are considered safer and their use recommended.
1.214 djm 1292: .Pp
1.84 jmc 1293: The default is:
1.101 jmc 1294: .Bd -literal -offset indent
1.160 markus 1295: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1296: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1297: hmac-sha1-etm@openssh.com,
1.186 naddy 1298: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1299: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1300: .Ed
1.198 djm 1301: .Pp
1.240 jmc 1302: The list of available MAC algorithms may also be obtained using
1303: .Qq ssh -Q mac .
1.1 stevesk 1304: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1305: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1306: The argument to this keyword must be
1.240 jmc 1307: .Cm yes
1.1 stevesk 1308: or
1.242 jmc 1309: .Cm no
1.240 jmc 1310: (the default).
1.1 stevesk 1311: .It Cm NumberOfPasswordPrompts
1312: Specifies the number of password prompts before giving up.
1313: The argument to this keyword must be an integer.
1.84 jmc 1314: The default is 3.
1.1 stevesk 1315: .It Cm PasswordAuthentication
1316: Specifies whether to use password authentication.
1317: The argument to this keyword must be
1.240 jmc 1318: .Cm yes
1319: (the default)
1.1 stevesk 1320: or
1.240 jmc 1321: .Cm no .
1.65 reyk 1322: .It Cm PermitLocalCommand
1323: Allow local command execution via the
1324: .Ic LocalCommand
1325: option or using the
1.66 jmc 1326: .Ic !\& Ns Ar command
1.65 reyk 1327: escape sequence in
1328: .Xr ssh 1 .
1329: The argument must be
1.240 jmc 1330: .Cm yes
1.65 reyk 1331: or
1.240 jmc 1332: .Cm no
1333: (the default).
1.347 markus 1334: .It Cm PermitRemoteOpen
1335: Specifies the destinations to which remote TCP port forwarding is permitted when
1336: .Cm RemoteForward
1337: is used as a SOCKS proxy.
1338: The forwarding specification must be one of the following forms:
1339: .Pp
1340: .Bl -item -offset indent -compact
1341: .It
1342: .Cm PermitRemoteOpen
1343: .Sm off
1344: .Ar host : port
1345: .Sm on
1346: .It
1347: .Cm PermitRemoteOpen
1348: .Sm off
1349: .Ar IPv4_addr : port
1350: .Sm on
1351: .It
1352: .Cm PermitRemoteOpen
1353: .Sm off
1354: .Ar \&[ IPv6_addr \&] : port
1355: .Sm on
1356: .El
1357: .Pp
1358: Multiple forwards may be specified by separating them with whitespace.
1359: An argument of
1360: .Cm any
1361: can be used to remove all restrictions and permit any forwarding requests.
1362: An argument of
1363: .Cm none
1364: can be used to prohibit all forwarding requests.
1365: The wildcard
1366: .Sq *
1367: can be used for host or port to allow all hosts or ports respectively.
1368: Otherwise, no pattern matching or address lookups are performed on supplied
1369: names.
1.127 markus 1370: .It Cm PKCS11Provider
1.292 djm 1371: Specifies which PKCS#11 provider to use or
1372: .Cm none
1373: to indicate that no provider should be used (the default).
1374: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1375: .Xr ssh 1
1.292 djm 1376: should use to communicate with a PKCS#11 token providing keys for user
1377: authentication.
1.67 jmc 1378: .It Cm Port
1379: Specifies the port number to connect on the remote host.
1.84 jmc 1380: The default is 22.
1.1 stevesk 1381: .It Cm PreferredAuthentications
1.226 jmc 1382: Specifies the order in which the client should try authentication methods.
1.48 jmc 1383: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1384: .Cm keyboard-interactive )
1.48 jmc 1385: over another method (e.g.\&
1.131 jmc 1386: .Cm password ) .
1387: The default is:
1388: .Bd -literal -offset indent
1389: gssapi-with-mic,hostbased,publickey,
1390: keyboard-interactive,password
1391: .Ed
1.1 stevesk 1392: .It Cm ProxyCommand
1393: Specifies the command to use to connect to the server.
1394: The command
1.190 djm 1395: string extends to the end of the line, and is executed
1396: using the user's shell
1397: .Ql exec
1398: directive to avoid a lingering shell process.
1399: .Pp
1.239 jmc 1400: Arguments to
1401: .Cm ProxyCommand
1402: accept the tokens described in the
1403: .Sx TOKENS
1404: section.
1.1 stevesk 1405: The command can be basically anything,
1406: and should read from its standard input and write to its standard output.
1407: It should eventually connect an
1408: .Xr sshd 8
1409: server running on some machine, or execute
1410: .Ic sshd -i
1411: somewhere.
1412: Host key management will be done using the
1.296 jmc 1413: .Cm Hostname
1414: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1415: Setting the command to
1.240 jmc 1416: .Cm none
1.6 markus 1417: disables this option entirely.
1.1 stevesk 1418: Note that
1419: .Cm CheckHostIP
1420: is not available for connects with a proxy command.
1.52 djm 1421: .Pp
1422: This directive is useful in conjunction with
1423: .Xr nc 1
1424: and its proxy support.
1.53 jmc 1425: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1426: 192.0.2.0:
1427: .Bd -literal -offset 3n
1428: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1429: .Ed
1.233 djm 1430: .It Cm ProxyJump
1.260 millert 1431: Specifies one or more jump proxies as either
1.233 djm 1432: .Xo
1433: .Sm off
1.234 jmc 1434: .Op Ar user No @
1.233 djm 1435: .Ar host
1.234 jmc 1436: .Op : Ns Ar port
1.233 djm 1437: .Sm on
1.260 millert 1438: or an ssh URI
1.233 djm 1439: .Xc .
1.235 djm 1440: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1441: sequentially.
1.233 djm 1442: Setting this option will cause
1443: .Xr ssh 1
1444: to connect to the target host by first making a
1445: .Xr ssh 1
1446: connection to the specified
1447: .Cm ProxyJump
1448: host and then establishing a
1.234 jmc 1449: TCP forwarding to the ultimate target from there.
1.346 dlg 1450: Setting the host to
1451: .Cm none
1452: disables this option entirely.
1.233 djm 1453: .Pp
1454: Note that this option will compete with the
1455: .Cm ProxyCommand
1456: option - whichever is specified first will prevent later instances of the
1457: other from taking effect.
1.289 djm 1458: .Pp
1459: Note also that the configuration for the destination host (either supplied
1460: via the command-line or the configuration file) is not generally applied
1461: to jump hosts.
1462: .Pa ~/.ssh/config
1463: should be used if specific configuration is required for jump hosts.
1.167 djm 1464: .It Cm ProxyUseFdpass
1.168 jmc 1465: Specifies that
1.167 djm 1466: .Cm ProxyCommand
1467: will pass a connected file descriptor back to
1.168 jmc 1468: .Xr ssh 1
1.167 djm 1469: instead of continuing to execute and pass data.
1470: The default is
1.240 jmc 1471: .Cm no .
1.343 dtucker 1472: .It Cm PubkeyAcceptedAlgorithms
1473: Specifies the signature algorithms that will be used for public key
1474: authentication as a comma-separated list of patterns.
1.299 kn 1475: If the specified list begins with a
1.214 djm 1476: .Sq +
1.343 dtucker 1477: character, then the algorithms after it will be appended to the default
1.214 djm 1478: instead of replacing it.
1.299 kn 1479: If the specified list begins with a
1.241 djm 1480: .Sq -
1.343 dtucker 1481: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1482: from the default set instead of replacing them.
1.301 naddy 1483: If the specified list begins with a
1484: .Sq ^
1.343 dtucker 1485: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1486: default set.
1.213 markus 1487: The default for this option is:
1488: .Bd -literal -offset 3n
1.333 djm 1489: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1490: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1491: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1492: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1493: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1494: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1495: rsa-sha2-512-cert-v01@openssh.com,
1496: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1497: ssh-rsa-cert-v01@openssh.com,
1.333 djm 1498: ssh-ed25519,
1.311 naddy 1499: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1500: sk-ssh-ed25519@openssh.com,
1.305 naddy 1501: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1502: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1503: .Ed
1504: .Pp
1.348 djm 1505: The list of available signature algorithms may also be obtained using
1.343 dtucker 1506: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.1 stevesk 1507: .It Cm PubkeyAuthentication
1508: Specifies whether to try public key authentication.
1509: The argument to this keyword must be
1.240 jmc 1510: .Cm yes
1511: (the default)
1.1 stevesk 1512: or
1.240 jmc 1513: .Cm no .
1.75 dtucker 1514: .It Cm RekeyLimit
1515: Specifies the maximum amount of data that may be transmitted before the
1.342 rob 1516: session key is renegotiated, optionally followed by a maximum amount of
1.162 dtucker 1517: time that may pass before the session key is renegotiated.
1518: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1519: .Sq K ,
1520: .Sq M ,
1.75 dtucker 1521: or
1.76 jmc 1522: .Sq G
1.75 dtucker 1523: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1524: The default is between
1.84 jmc 1525: .Sq 1G
1.75 dtucker 1526: and
1.84 jmc 1527: .Sq 4G ,
1.75 dtucker 1528: depending on the cipher.
1.162 dtucker 1529: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1530: units documented in the TIME FORMATS section of
1.162 dtucker 1531: .Xr sshd_config 5 .
1532: The default value for
1533: .Cm RekeyLimit
1534: is
1.240 jmc 1535: .Cm default none ,
1.162 dtucker 1536: which means that rekeying is performed after the cipher's default amount
1537: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1538: .It Cm RemoteCommand
1539: Specifies a command to execute on the remote machine after successfully
1540: connecting to the server.
1541: The command string extends to the end of the line, and is executed with
1542: the user's shell.
1.250 jmc 1543: Arguments to
1544: .Cm RemoteCommand
1545: accept the tokens described in the
1546: .Sx TOKENS
1547: section.
1.1 stevesk 1548: .It Cm RemoteForward
1.74 jmc 1549: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1550: the secure channel.
1.273 djm 1551: The remote port may either be forwarded to a specified host and port
1.256 markus 1552: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1553: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1554: The first argument is the listening specification and may be
1.43 djm 1555: .Sm off
1.49 jmc 1556: .Oo Ar bind_address : Oc Ar port
1.43 djm 1557: .Sm on
1.324 dtucker 1558: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1559: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1560: .Ar host : Ns Ar hostport
1561: or a Unix domain socket path,
1.256 markus 1562: otherwise if no destination argument is specified then the remote forwarding
1563: will be established as a SOCKS proxy.
1.347 markus 1564: When acting as a SOCKS proxy the destination of the connection can be
1565: restricted by
1566: .Cm PermitRemoteOpen .
1.256 markus 1567: .Pp
1.138 djm 1568: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1569: Multiple forwardings may be specified, and additional
1570: forwardings can be given on the command line.
1.113 stevesk 1571: Privileged ports can be forwarded only when
1572: logging in as root on the remote machine.
1.326 dtucker 1573: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1574: .Sx TOKENS
1.326 dtucker 1575: section and environment variables as described in the
1576: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1577: section.
1.118 jmc 1578: .Pp
1.117 djm 1579: If the
1580: .Ar port
1.240 jmc 1581: argument is 0,
1.117 djm 1582: the listen port will be dynamically allocated on the server and reported
1583: to the client at run time.
1.43 djm 1584: .Pp
1585: If the
1586: .Ar bind_address
1587: is not specified, the default is to only bind to loopback addresses.
1588: If the
1589: .Ar bind_address
1590: is
1591: .Ql *
1592: or an empty string, then the forwarding is requested to listen on all
1593: interfaces.
1594: Specifying a remote
1595: .Ar bind_address
1.46 jmc 1596: will only succeed if the server's
1597: .Cm GatewayPorts
1.43 djm 1598: option is enabled (see
1.46 jmc 1599: .Xr sshd_config 5 ) .
1.149 djm 1600: .It Cm RequestTTY
1601: Specifies whether to request a pseudo-tty for the session.
1602: The argument may be one of:
1.240 jmc 1603: .Cm no
1.149 djm 1604: (never request a TTY),
1.240 jmc 1605: .Cm yes
1.149 djm 1606: (always request a TTY when standard input is a TTY),
1.240 jmc 1607: .Cm force
1.149 djm 1608: (always request a TTY) or
1.240 jmc 1609: .Cm auto
1.149 djm 1610: (request a TTY when opening a login session).
1611: This option mirrors the
1612: .Fl t
1613: and
1614: .Fl T
1615: flags for
1616: .Xr ssh 1 .
1.196 djm 1617: .It Cm RevokedHostKeys
1618: Specifies revoked host public keys.
1619: Keys listed in this file will be refused for host authentication.
1620: Note that if this file does not exist or is not readable,
1621: then host authentication will be refused for all hosts.
1622: Keys may be specified as a text file, listing one public key per line, or as
1623: an OpenSSH Key Revocation List (KRL) as generated by
1624: .Xr ssh-keygen 1 .
1625: For more information on KRLs, see the KEY REVOCATION LISTS section in
1626: .Xr ssh-keygen 1 .
1.305 naddy 1627: .It Cm SecurityKeyProvider
1.313 naddy 1628: Specifies a path to a library that will be used when loading any
1629: FIDO authenticator-hosted keys, overriding the default of using
1630: the built-in USB HID support.
1.309 naddy 1631: .Pp
1632: If the specified value begins with a
1633: .Sq $
1634: character, then it will be treated as an environment variable containing
1635: the path to the library.
1.32 djm 1636: .It Cm SendEnv
1637: Specifies what variables from the local
1638: .Xr environ 7
1639: should be sent to the server.
1.84 jmc 1640: The server must also support it, and the server must be configured to
1.33 djm 1641: accept these environment variables.
1.207 dtucker 1642: Note that the
1643: .Ev TERM
1.208 jmc 1644: environment variable is always sent whenever a
1.207 dtucker 1645: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1646: Refer to
1647: .Cm AcceptEnv
1648: in
1649: .Xr sshd_config 5
1650: for how to configure the server.
1.80 jmc 1651: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1652: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1653: across multiple
1654: .Cm SendEnv
1655: directives.
1.81 jmc 1656: .Pp
1657: See
1658: .Sx PATTERNS
1659: for more information on patterns.
1.271 djm 1660: .Pp
1.272 jmc 1661: It is possible to clear previously set
1.271 djm 1662: .Cm SendEnv
1663: variable names by prefixing patterns with
1664: .Pa - .
1665: The default is not to send any environment variables.
1.28 markus 1666: .It Cm ServerAliveCountMax
1.73 jmc 1667: Sets the number of server alive messages (see below) which may be
1.28 markus 1668: sent without
1.84 jmc 1669: .Xr ssh 1
1.28 markus 1670: receiving any messages back from the server.
1671: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1672: ssh will disconnect from the server, terminating the session.
1.28 markus 1673: It is important to note that the use of server alive messages is very
1674: different from
1675: .Cm TCPKeepAlive
1676: (below).
1677: The server alive messages are sent through the encrypted channel
1678: and therefore will not be spoofable.
1679: The TCP keepalive option enabled by
1680: .Cm TCPKeepAlive
1681: is spoofable.
1682: The server alive mechanism is valuable when the client or
1.298 dtucker 1683: server depend on knowing when a connection has become unresponsive.
1.28 markus 1684: .Pp
1685: The default value is 3.
1686: If, for example,
1687: .Cm ServerAliveInterval
1.84 jmc 1688: (see below) is set to 15 and
1.28 markus 1689: .Cm ServerAliveCountMax
1.84 jmc 1690: is left at the default, if the server becomes unresponsive,
1691: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1692: .It Cm ServerAliveInterval
1693: Sets a timeout interval in seconds after which if no data has been received
1694: from the server,
1.84 jmc 1695: .Xr ssh 1
1.67 jmc 1696: will send a message through the encrypted
1697: channel to request a response from the server.
1698: The default
1699: is 0, indicating that these messages will not be sent to the server.
1.357 jmc 1700: .It Cm SessionType
1701: May be used to either request invocation of a subsystem on the remote system,
1702: or to prevent the execution of a remote command at all.
1703: The latter is useful for just forwarding ports.
1704: The argument to this keyword must be
1705: .Cm none
1706: (same as the
1707: .Fl N
1708: option),
1709: .Cm subsystem
1710: (same as the
1711: .Fl s
1712: option) or
1713: .Cm default
1714: (shell or command execution).
1.277 jmc 1715: .It Cm SetEnv
1716: Directly specify one or more environment variables and their contents to
1717: be sent to the server.
1718: Similarly to
1719: .Cm SendEnv ,
1.354 djm 1720: with the exception of the
1721: .Ev TERM
1722: variable, the server must be prepared to accept the environment variable.
1.358 djm 1723: .It Cm StdinNull
1724: Redirects stdin from
1725: .Pa /dev/null
1726: (actually, prevents reading from stdin).
1727: Either this or the equivalent
1728: .Fl n
1729: option must be used when
1730: .Nm ssh
1731: is run in the background.
1732: The argument to this keyword must be
1733: .Cm yes
1734: (same as the
1735: .Fl n
1736: option) or
1737: .Cm no
1738: (the default).
1.191 millert 1739: .It Cm StreamLocalBindMask
1740: Sets the octal file creation mode mask
1741: .Pq umask
1742: used when creating a Unix-domain socket file for local or remote
1743: port forwarding.
1744: This option is only used for port forwarding to a Unix-domain socket file.
1745: .Pp
1746: The default value is 0177, which creates a Unix-domain socket file that is
1747: readable and writable only by the owner.
1748: Note that not all operating systems honor the file mode on Unix-domain
1749: socket files.
1750: .It Cm StreamLocalBindUnlink
1751: Specifies whether to remove an existing Unix-domain socket file for local
1752: or remote port forwarding before creating a new one.
1753: If the socket file already exists and
1754: .Cm StreamLocalBindUnlink
1755: is not enabled,
1756: .Nm ssh
1757: will be unable to forward the port to the Unix-domain socket file.
1758: This option is only used for port forwarding to a Unix-domain socket file.
1759: .Pp
1760: The argument must be
1.240 jmc 1761: .Cm yes
1.191 millert 1762: or
1.240 jmc 1763: .Cm no
1764: (the default).
1.1 stevesk 1765: .It Cm StrictHostKeyChecking
1766: If this flag is set to
1.240 jmc 1767: .Cm yes ,
1.84 jmc 1768: .Xr ssh 1
1.1 stevesk 1769: will never automatically add host keys to the
1.50 djm 1770: .Pa ~/.ssh/known_hosts
1.1 stevesk 1771: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1772: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1773: though it can be annoying when the
1.1 stevesk 1774: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1775: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1776: frequently made.
1777: This option forces the user to manually
1778: add all new hosts.
1.255 jmc 1779: .Pp
1.1 stevesk 1780: If this flag is set to
1.254 djm 1781: .Dq accept-new
1.360 jmc 1782: then ssh will automatically add new host keys to the user's
1783: .Pa known_hosts
1784: file, but will not permit connections to hosts with
1.254 djm 1785: changed host keys.
1786: If this flag is set to
1787: .Dq no
1788: or
1789: .Dq off ,
1.255 jmc 1790: ssh will automatically add new host keys to the user known hosts files
1791: and allow connections to hosts with changed hostkeys to proceed,
1792: subject to some restrictions.
1.1 stevesk 1793: If this flag is set to
1.240 jmc 1794: .Cm ask
1795: (the default),
1.1 stevesk 1796: new host keys
1797: will be added to the user known host files only after the user
1798: has confirmed that is what they really want to do, and
1.84 jmc 1799: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1800: The host keys of
1801: known hosts will be verified automatically in all cases.
1.244 jmc 1802: .It Cm SyslogFacility
1803: Gives the facility code that is used when logging messages from
1804: .Xr ssh 1 .
1805: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1806: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1807: The default is USER.
1.26 markus 1808: .It Cm TCPKeepAlive
1809: Specifies whether the system should send TCP keepalive messages to the
1810: other side.
1811: If they are sent, death of the connection or crash of one
1812: of the machines will be properly noticed.
1813: However, this means that
1814: connections will die if the route is down temporarily, and some people
1815: find it annoying.
1816: .Pp
1817: The default is
1.240 jmc 1818: .Cm yes
1.26 markus 1819: (to send TCP keepalive messages), and the client will notice
1820: if the network goes down or the remote host dies.
1821: This is important in scripts, and many users want it too.
1822: .Pp
1823: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1824: .Cm no .
1.265 djm 1825: See also
1826: .Cm ServerAliveInterval
1827: for protocol-level keepalives.
1.65 reyk 1828: .It Cm Tunnel
1.95 stevesk 1829: Request
1.65 reyk 1830: .Xr tun 4
1.69 jmc 1831: device forwarding between the client and the server.
1.65 reyk 1832: The argument must be
1.240 jmc 1833: .Cm yes ,
1834: .Cm point-to-point
1.95 stevesk 1835: (layer 3),
1.240 jmc 1836: .Cm ethernet
1.95 stevesk 1837: (layer 2),
1.65 reyk 1838: or
1.240 jmc 1839: .Cm no
1840: (the default).
1.95 stevesk 1841: Specifying
1.240 jmc 1842: .Cm yes
1.95 stevesk 1843: requests the default tunnel mode, which is
1.240 jmc 1844: .Cm point-to-point .
1.65 reyk 1845: .It Cm TunnelDevice
1.95 stevesk 1846: Specifies the
1.65 reyk 1847: .Xr tun 4
1.95 stevesk 1848: devices to open on the client
1849: .Pq Ar local_tun
1850: and the server
1851: .Pq Ar remote_tun .
1852: .Pp
1853: The argument must be
1854: .Sm off
1855: .Ar local_tun Op : Ar remote_tun .
1856: .Sm on
1857: The devices may be specified by numerical ID or the keyword
1.240 jmc 1858: .Cm any ,
1.95 stevesk 1859: which uses the next available tunnel device.
1860: If
1861: .Ar remote_tun
1862: is not specified, it defaults to
1.240 jmc 1863: .Cm any .
1.95 stevesk 1864: The default is
1.240 jmc 1865: .Cm any:any .
1.201 djm 1866: .It Cm UpdateHostKeys
1.200 djm 1867: Specifies whether
1868: .Xr ssh 1
1869: should accept notifications of additional hostkeys from the server sent
1870: after authentication has completed and add them to
1871: .Cm UserKnownHostsFile .
1872: The argument must be
1.240 jmc 1873: .Cm yes ,
1874: .Cm no
1.320 djm 1875: or
1.240 jmc 1876: .Cm ask .
1.320 djm 1877: This option allows learning alternate hostkeys for a server
1.201 djm 1878: and supports graceful key rotation by allowing a server to send replacement
1879: public keys before old ones are removed.
1.336 djm 1880: .Pp
1.200 djm 1881: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 1882: host was already trusted or explicitly accepted by the user, the host was
1883: authenticated via
1884: .Cm UserKnownHostsFile
1885: (i.e. not
1886: .Cm GlobalKnownHostsFile )
1887: and the host was authenticated using a plain key and not a certificate.
1.320 djm 1888: .Pp
1889: .Cm UpdateHostKeys
1.321 jmc 1890: is enabled by default if the user has not overridden the default
1.320 djm 1891: .Cm UserKnownHostsFile
1.335 djm 1892: setting and has not enabled
1893: .Cm VerifyHostKeyDNS ,
1894: otherwise
1.320 djm 1895: .Cm UpdateHostKeys
1896: will be set to
1.334 djm 1897: .Cm no .
1.320 djm 1898: .Pp
1.204 djm 1899: If
1900: .Cm UpdateHostKeys
1901: is set to
1.240 jmc 1902: .Cm ask ,
1.204 djm 1903: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1904: Confirmation is currently incompatible with
1905: .Cm ControlPersist ,
1906: and will be disabled if it is enabled.
1.200 djm 1907: .Pp
1908: Presently, only
1909: .Xr sshd 8
1910: from OpenSSH 6.8 and greater support the
1.240 jmc 1911: .Qq hostkeys@openssh.com
1.200 djm 1912: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1913: .It Cm User
1914: Specifies the user to log in as.
1915: This can be useful when a different user name is used on different machines.
1916: This saves the trouble of
1917: having to remember to give the user name on the command line.
1918: .It Cm UserKnownHostsFile
1.151 djm 1919: Specifies one or more files to use for the user
1920: host key database, separated by whitespace.
1.329 dtucker 1921: Each filename may use tilde notation to refer to the user's home directory,
1922: the tokens described in the
1923: .Sx TOKENS
1924: section and environment variables as described in the
1925: .Sx ENVIRONMENT VARIABLES
1926: section.
1.151 djm 1927: The default is
1928: .Pa ~/.ssh/known_hosts ,
1929: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1930: .It Cm VerifyHostKeyDNS
1931: Specifies whether to verify the remote key using DNS and SSHFP resource
1932: records.
1.24 jakob 1933: If this option is set to
1.240 jmc 1934: .Cm yes ,
1.25 jmc 1935: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1936: from DNS.
1937: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1938: .Cm ask .
1.24 jakob 1939: If this option is set to
1.240 jmc 1940: .Cm ask ,
1.24 jakob 1941: information on fingerprint match will be displayed, but the user will still
1942: need to confirm new host keys according to the
1943: .Cm StrictHostKeyChecking
1944: option.
1.8 jakob 1945: The default is
1.240 jmc 1946: .Cm no .
1.84 jmc 1947: .Pp
1.240 jmc 1948: See also
1949: .Sx VERIFYING HOST KEYS
1950: in
1.84 jmc 1951: .Xr ssh 1 .
1.111 grunk 1952: .It Cm VisualHostKey
1953: If this flag is set to
1.240 jmc 1954: .Cm yes ,
1.111 grunk 1955: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1956: printed in addition to the fingerprint string at login and
1.114 stevesk 1957: for unknown host keys.
1.111 grunk 1958: If this flag is set to
1.240 jmc 1959: .Cm no
1960: (the default),
1.114 stevesk 1961: no fingerprint strings are printed at login and
1.197 djm 1962: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1963: .It Cm XAuthLocation
1.5 stevesk 1964: Specifies the full pathname of the
1.1 stevesk 1965: .Xr xauth 1
1966: program.
1967: The default is
1968: .Pa /usr/X11R6/bin/xauth .
1969: .El
1.86 jmc 1970: .Sh PATTERNS
1971: A
1972: .Em pattern
1973: consists of zero or more non-whitespace characters,
1974: .Sq *
1975: (a wildcard that matches zero or more characters),
1976: or
1977: .Sq ?\&
1978: (a wildcard that matches exactly one character).
1979: For example, to specify a set of declarations for any host in the
1.240 jmc 1980: .Qq .co.uk
1.86 jmc 1981: set of domains,
1982: the following pattern could be used:
1983: .Pp
1984: .Dl Host *.co.uk
1985: .Pp
1986: The following pattern
1987: would match any host in the 192.168.0.[0-9] network range:
1988: .Pp
1989: .Dl Host 192.168.0.?
1990: .Pp
1991: A
1992: .Em pattern-list
1993: is a comma-separated list of patterns.
1994: Patterns within pattern-lists may be negated
1995: by preceding them with an exclamation mark
1996: .Pq Sq !\& .
1997: For example,
1.174 djm 1998: to allow a key to be used from anywhere within an organization
1.86 jmc 1999: except from the
1.240 jmc 2000: .Qq dialup
1.86 jmc 2001: pool,
2002: the following entry (in authorized_keys) could be used:
2003: .Pp
2004: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 2005: .Pp
2006: Note that a negated match will never produce a positive result by itself.
2007: For example, attempting to match
2008: .Qq host3
2009: against the following pattern-list will fail:
2010: .Pp
2011: .Dl from=\&"!host1,!host2\&"
2012: .Pp
2013: The solution here is to include a term that will yield a positive match,
2014: such as a wildcard:
2015: .Pp
2016: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 2017: .Sh TOKENS
2018: Arguments to some keywords can make use of tokens,
2019: which are expanded at runtime:
2020: .Pp
2021: .Bl -tag -width XXXX -offset indent -compact
2022: .It %%
2023: A literal
2024: .Sq % .
2025: .It \&%C
1.257 jmc 2026: Hash of %l%h%p%r.
1.239 jmc 2027: .It %d
2028: Local user's home directory.
1.339 djm 2029: .It %f
2030: The fingerprint of the server's host key.
2031: .It %H
2032: The
2033: .Pa known_hosts
2034: hostname or address that is being searched for.
1.239 jmc 2035: .It %h
2036: The remote hostname.
1.340 jmc 2037: .It \%%I
1.339 djm 2038: A string describing the reason for a
2039: .Cm KnownHostsCommand
1.340 jmc 2040: execution: either
2041: .Cm ADDRESS
1.339 djm 2042: when looking up a host by address (only when
2043: .Cm CheckHostIP
2044: is enabled),
1.340 jmc 2045: .Cm HOSTNAME
2046: when searching by hostname, or
2047: .Cm ORDER
1.339 djm 2048: when preparing the host key algorithm preference list to use for the
2049: destination host.
1.239 jmc 2050: .It %i
2051: The local user ID.
1.339 djm 2052: .It %K
2053: The base64 encoded host key.
1.330 dtucker 2054: .It %k
1.350 jsg 2055: The host key alias if specified, otherwise the original remote hostname given
1.330 dtucker 2056: on the command line.
1.239 jmc 2057: .It %L
2058: The local hostname.
2059: .It %l
2060: The local hostname, including the domain name.
2061: .It %n
2062: The original remote hostname, as given on the command line.
2063: .It %p
2064: The remote port.
2065: .It %r
2066: The remote username.
1.261 djm 2067: .It \&%T
2068: The local
2069: .Xr tun 4
2070: or
2071: .Xr tap 4
2072: network interface assigned if
1.262 jmc 2073: tunnel forwarding was requested, or
2074: .Qq NONE
1.261 djm 2075: otherwise.
1.339 djm 2076: .It %t
2077: The type of the server host key, e.g.
1.360 jmc 2078: .Cm ssh-ed25519 .
1.239 jmc 2079: .It %u
2080: The local username.
2081: .El
2082: .Pp
1.323 dtucker 2083: .Cm CertificateFile ,
2084: .Cm ControlPath ,
2085: .Cm IdentityAgent ,
2086: .Cm IdentityFile ,
1.339 djm 2087: .Cm KnownHostsCommand ,
1.325 jmc 2088: .Cm LocalForward ,
1.324 dtucker 2089: .Cm Match exec ,
2090: .Cm RemoteCommand ,
1.329 dtucker 2091: .Cm RemoteForward ,
1.323 dtucker 2092: and
1.331 jmc 2093: .Cm UserKnownHostsFile
1.349 dtucker 2094: accept the tokens %%, %C, %d, %h, %i, %k, %L, %l, %n, %p, %r, and %u.
1.239 jmc 2095: .Pp
1.339 djm 2096: .Cm KnownHostsCommand
2097: additionally accepts the tokens %f, %H, %I, %K and %t.
2098: .Pp
1.295 jmc 2099: .Cm Hostname
1.239 jmc 2100: accepts the tokens %% and %h.
2101: .Pp
2102: .Cm LocalCommand
1.323 dtucker 2103: accepts all tokens.
1.239 jmc 2104: .Pp
2105: .Cm ProxyCommand
1.303 djm 2106: accepts the tokens %%, %h, %n, %p, and %r.
1.326 dtucker 2107: .Sh ENVIRONMENT VARIABLES
2108: Arguments to some keywords can be expanded at runtime from environment
2109: variables on the client by enclosing them in
2110: .Ic ${} ,
2111: for example
2112: .Ic ${HOME}/.ssh
2113: would refer to the user's .ssh directory.
2114: If a specified environment variable does not exist then an error will be
2115: returned and the setting for that keyword will be ignored.
2116: .Pp
2117: The keywords
2118: .Cm CertificateFile ,
2119: .Cm ControlPath ,
1.329 dtucker 2120: .Cm IdentityAgent ,
1.352 jmc 2121: .Cm IdentityFile ,
1.339 djm 2122: .Cm KnownHostsCommand ,
1.326 dtucker 2123: and
1.329 dtucker 2124: .Cm UserKnownHostsFile
1.326 dtucker 2125: support environment variables.
2126: The keywords
2127: .Cm LocalForward
2128: and
2129: .Cm RemoteForward
2130: support environment variables only for Unix domain socket paths.
1.1 stevesk 2131: .Sh FILES
2132: .Bl -tag -width Ds
1.50 djm 2133: .It Pa ~/.ssh/config
1.1 stevesk 2134: This is the per-user configuration file.
2135: The format of this file is described above.
1.84 jmc 2136: This file is used by the SSH client.
1.30 djm 2137: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2138: read/write for the user, and not writable by others.
1.1 stevesk 2139: .It Pa /etc/ssh/ssh_config
2140: Systemwide configuration file.
2141: This file provides defaults for those
2142: values that are not specified in the user's configuration file, and
2143: for those users who do not have a configuration file.
2144: This file must be world-readable.
2145: .El
1.13 jmc 2146: .Sh SEE ALSO
2147: .Xr ssh 1
1.1 stevesk 2148: .Sh AUTHORS
1.240 jmc 2149: .An -nosplit
1.1 stevesk 2150: OpenSSH is a derivative of the original and free
1.240 jmc 2151: ssh 1.2.12 release by
2152: .An Tatu Ylonen .
2153: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2154: .An Niels Provos , Theo de Raadt
2155: and
2156: .An Dug Song
1.1 stevesk 2157: removed many bugs, re-added newer features and
2158: created OpenSSH.
1.240 jmc 2159: .An Markus Friedl
2160: contributed the support for SSH protocol versions 1.5 and 2.0.
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