Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.359
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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24: .\"
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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1.359 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.358 2021/07/23 04:00:59 djm Exp $
! 37: .Dd $Mdocdate: July 23 2021 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
1.310 jmc 42: .Nd OpenSSH client configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.287 djm 142: .Cm final ,
1.176 djm 143: .Cm exec ,
1.169 djm 144: .Cm host ,
145: .Cm originalhost ,
146: .Cm user ,
147: and
148: .Cm localuser .
1.193 djm 149: The
150: .Cm all
151: criteria must appear alone or immediately after
1.287 djm 152: .Cm canonical
153: or
154: .Cm final .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
1.288 jmc 157: .Cm all ,
158: .Cm canonical ,
1.193 djm 159: and
1.287 djm 160: .Cm final
1.193 djm 161: require an argument.
162: Criteria may be negated by prepending an exclamation mark
163: .Pq Sq !\& .
1.169 djm 164: .Pp
1.177 jmc 165: The
1.193 djm 166: .Cm canonical
1.210 dtucker 167: keyword matches only when the configuration file is being re-parsed
1.193 djm 168: after hostname canonicalization (see the
169: .Cm CanonicalizeHostname
1.288 jmc 170: option).
1.193 djm 171: This may be useful to specify conditions that work with canonical host
172: names only.
1.287 djm 173: .Pp
174: The
175: .Cm final
176: keyword requests that the configuration be re-parsed (regardless of whether
177: .Cm CanonicalizeHostname
178: is enabled), and matches only during this final pass.
179: If
180: .Cm CanonicalizeHostname
181: is enabled, then
182: .Cm canonical
183: and
184: .Cm final
185: match during the same pass.
186: .Pp
1.193 djm 187: The
1.176 djm 188: .Cm exec
1.177 jmc 189: keyword executes the specified command under the user's shell.
1.169 djm 190: If the command returns a zero exit status then the condition is considered true.
191: Commands containing whitespace characters must be quoted.
1.239 jmc 192: Arguments to
193: .Cm exec
194: accept the tokens described in the
195: .Sx TOKENS
196: section.
1.169 djm 197: .Pp
198: The other keywords' criteria must be single entries or comma-separated
199: lists and may use the wildcard and negation operators described in the
200: .Sx PATTERNS
201: section.
202: The criteria for the
203: .Cm host
204: keyword are matched against the target hostname, after any substitution
205: by the
1.295 jmc 206: .Cm Hostname
1.193 djm 207: or
208: .Cm CanonicalizeHostname
209: options.
1.169 djm 210: The
211: .Cm originalhost
212: keyword matches against the hostname as it was specified on the command-line.
213: The
214: .Cm user
215: keyword matches against the target username on the remote host.
216: The
217: .Cm localuser
218: keyword matches against the name of the local user running
219: .Xr ssh 1
220: (this keyword may be useful in system-wide
221: .Nm
222: files).
1.222 jcs 223: .It Cm AddKeysToAgent
224: Specifies whether keys should be automatically added to a running
1.223 jmc 225: .Xr ssh-agent 1 .
1.222 jcs 226: If this option is set to
1.240 jmc 227: .Cm yes
1.222 jcs 228: and a key is loaded from a file, the key and its passphrase are added to
229: the agent with the default lifetime, as if by
230: .Xr ssh-add 1 .
231: If this option is set to
1.240 jmc 232: .Cm ask ,
233: .Xr ssh 1
1.222 jcs 234: will require confirmation using the
235: .Ev SSH_ASKPASS
236: program before adding a key (see
237: .Xr ssh-add 1
238: for details).
239: If this option is set to
1.240 jmc 240: .Cm confirm ,
1.222 jcs 241: each use of the key must be confirmed, as if the
242: .Fl c
243: option was specified to
244: .Xr ssh-add 1 .
245: If this option is set to
1.240 jmc 246: .Cm no ,
1.222 jcs 247: no keys are added to the agent.
1.332 djm 248: Alternately, this option may be specified as a time interval
249: using the format described in the
250: .Sx TIME FORMATS
251: section of
252: .Xr sshd_config 5
253: to specify the key's lifetime in
254: .Xr ssh-agent 1 ,
255: after which it will automatically be removed.
1.222 jcs 256: The argument must be
1.332 djm 257: .Cm no
258: (the default),
1.240 jmc 259: .Cm yes ,
1.332 djm 260: .Cm confirm
261: (optionally followed by a time interval),
262: .Cm ask
263: or a time interval.
1.10 djm 264: .It Cm AddressFamily
1.11 jmc 265: Specifies which address family to use when connecting.
266: Valid arguments are
1.240 jmc 267: .Cm any
268: (the default),
269: .Cm inet
1.84 jmc 270: (use IPv4 only), or
1.240 jmc 271: .Cm inet6
1.40 jmc 272: (use IPv6 only).
1.1 stevesk 273: .It Cm BatchMode
274: If set to
1.240 jmc 275: .Cm yes ,
1.318 djm 276: user interaction such as password prompts and host key confirmation requests
277: will be disabled.
1.1 stevesk 278: This option is useful in scripts and other batch jobs where no user
1.318 djm 279: is present to interact with
280: .Xr ssh 1 .
1.1 stevesk 281: The argument must be
1.240 jmc 282: .Cm yes
1.1 stevesk 283: or
1.240 jmc 284: .Cm no
285: (the default).
1.268 jmc 286: .It Cm BindAddress
287: Use the specified address on the local machine as the source address of
288: the connection.
289: Only useful on systems with more than one address.
290: .It Cm BindInterface
291: Use the address of the specified interface on the local machine as the
292: source address of the connection.
1.171 djm 293: .It Cm CanonicalDomains
1.172 jmc 294: When
1.173 djm 295: .Cm CanonicalizeHostname
1.171 djm 296: is enabled, this option specifies the list of domain suffixes in which to
297: search for the specified destination host.
1.173 djm 298: .It Cm CanonicalizeFallbackLocal
1.174 djm 299: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 300: The default,
1.240 jmc 301: .Cm yes ,
1.172 jmc 302: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 303: search rules.
304: A value of
1.240 jmc 305: .Cm no
1.171 djm 306: will cause
307: .Xr ssh 1
308: to fail instantly if
1.173 djm 309: .Cm CanonicalizeHostname
1.171 djm 310: is enabled and the target hostname cannot be found in any of the domains
311: specified by
312: .Cm CanonicalDomains .
1.173 djm 313: .It Cm CanonicalizeHostname
1.174 djm 314: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 315: The default,
1.240 jmc 316: .Cm no ,
1.171 djm 317: is not to perform any name rewriting and let the system resolver handle all
318: hostname lookups.
319: If set to
1.240 jmc 320: .Cm yes
1.171 djm 321: then, for connections that do not use a
1.284 djm 322: .Cm ProxyCommand
323: or
324: .Cm ProxyJump ,
1.171 djm 325: .Xr ssh 1
1.173 djm 326: will attempt to canonicalize the hostname specified on the command line
1.171 djm 327: using the
328: .Cm CanonicalDomains
329: suffixes and
1.173 djm 330: .Cm CanonicalizePermittedCNAMEs
1.171 djm 331: rules.
332: If
1.173 djm 333: .Cm CanonicalizeHostname
1.171 djm 334: is set to
1.240 jmc 335: .Cm always ,
1.174 djm 336: then canonicalization is applied to proxied connections too.
1.185 djm 337: .Pp
1.193 djm 338: If this option is enabled, then the configuration files are processed
339: again using the new target name to pick up any new configuration in matching
1.185 djm 340: .Cm Host
1.193 djm 341: and
342: .Cm Match
1.185 djm 343: stanzas.
1.173 djm 344: .It Cm CanonicalizeMaxDots
1.172 jmc 345: Specifies the maximum number of dot characters in a hostname before
1.174 djm 346: canonicalization is disabled.
1.240 jmc 347: The default, 1,
1.172 jmc 348: allows a single dot (i.e. hostname.subdomain).
1.173 djm 349: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 350: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 351: canonicalizing hostnames.
1.171 djm 352: The rules consist of one or more arguments of
1.172 jmc 353: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 354: where
355: .Ar source_domain_list
1.174 djm 356: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 357: and
358: .Ar target_domain_list
1.172 jmc 359: is a pattern-list of domains that they may resolve to.
1.171 djm 360: .Pp
361: For example,
1.240 jmc 362: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 363: will allow hostnames matching
1.240 jmc 364: .Qq *.a.example.com
1.173 djm 365: to be canonicalized to names in the
1.240 jmc 366: .Qq *.b.example.com
1.171 djm 367: or
1.240 jmc 368: .Qq *.c.example.com
1.171 djm 369: domains.
1.283 jmc 370: .It Cm CASignatureAlgorithms
371: Specifies which algorithms are allowed for signing of certificates
372: by certificate authorities (CAs).
373: The default is:
374: .Bd -literal -offset indent
1.351 djm 375: ssh-ed25519,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.353 jmc 376: sk-ssh-ed25519@openssh.com,sk-ecdsa-sha2-nistp256@openssh.com,
1.351 djm 377: rsa-sha2-512,rsa-sha2-256
1.283 jmc 378: .Ed
379: .Pp
380: .Xr ssh 1
381: will not accept host certificates signed using algorithms other than those
382: specified.
1.221 djm 383: .It Cm CertificateFile
384: Specifies a file from which the user's certificate is read.
385: A corresponding private key must be provided separately in order
386: to use this certificate either
387: from an
388: .Cm IdentityFile
389: directive or
390: .Fl i
391: flag to
392: .Xr ssh 1 ,
393: via
394: .Xr ssh-agent 1 ,
395: or via a
1.305 naddy 396: .Cm PKCS11Provider
397: or
398: .Cm SecurityKeyProvider .
1.221 djm 399: .Pp
1.239 jmc 400: Arguments to
401: .Cm CertificateFile
1.326 dtucker 402: may use the tilde syntax to refer to a user's home directory,
403: the tokens described in the
1.239 jmc 404: .Sx TOKENS
1.326 dtucker 405: section and environment variables as described in the
406: .Sx ENVIRONMENT VARIABLES
1.239 jmc 407: section.
1.221 djm 408: .Pp
409: It is possible to have multiple certificate files specified in
410: configuration files; these certificates will be tried in sequence.
411: Multiple
412: .Cm CertificateFile
413: directives will add to the list of certificates used for
414: authentication.
1.1 stevesk 415: .It Cm CheckHostIP
1.240 jmc 416: If set to
417: .Cm yes
1.84 jmc 418: .Xr ssh 1
419: will additionally check the host IP address in the
1.1 stevesk 420: .Pa known_hosts
421: file.
1.240 jmc 422: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 423: and will add addresses of destination hosts to
424: .Pa ~/.ssh/known_hosts
425: in the process, regardless of the setting of
426: .Cm StrictHostKeyChecking .
1.107 grunk 427: If the option is set to
1.341 djm 428: .Cm no
429: (the default),
1.1 stevesk 430: the check will not be executed.
431: .It Cm Ciphers
1.245 djm 432: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 433: Multiple ciphers must be comma-separated.
1.299 kn 434: If the specified list begins with a
1.214 djm 435: .Sq +
436: character, then the specified ciphers will be appended to the default set
437: instead of replacing them.
1.299 kn 438: If the specified list begins with a
1.241 djm 439: .Sq -
440: character, then the specified ciphers (including wildcards) will be removed
441: from the default set instead of replacing them.
1.301 naddy 442: If the specified list begins with a
443: .Sq ^
444: character, then the specified ciphers will be placed at the head of the
445: default set.
1.214 djm 446: .Pp
1.180 djm 447: The supported ciphers are:
1.240 jmc 448: .Bd -literal -offset indent
1.186 naddy 449: 3des-cbc
450: aes128-cbc
451: aes192-cbc
452: aes256-cbc
453: aes128-ctr
454: aes192-ctr
455: aes256-ctr
456: aes128-gcm@openssh.com
457: aes256-gcm@openssh.com
458: chacha20-poly1305@openssh.com
1.240 jmc 459: .Ed
1.180 djm 460: .Pp
1.84 jmc 461: The default is:
1.186 naddy 462: .Bd -literal -offset indent
1.215 jmc 463: chacha20-poly1305@openssh.com,
1.186 naddy 464: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 465: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 466: .Ed
1.180 djm 467: .Pp
1.240 jmc 468: The list of available ciphers may also be obtained using
469: .Qq ssh -Q cipher .
1.1 stevesk 470: .It Cm ClearAllForwardings
1.84 jmc 471: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 472: specified in the configuration files or on the command line be
1.7 jmc 473: cleared.
474: This option is primarily useful when used from the
1.84 jmc 475: .Xr ssh 1
1.1 stevesk 476: command line to clear port forwardings set in
477: configuration files, and is automatically set by
478: .Xr scp 1
479: and
480: .Xr sftp 1 .
481: The argument must be
1.240 jmc 482: .Cm yes
1.1 stevesk 483: or
1.240 jmc 484: .Cm no
485: (the default).
1.1 stevesk 486: .It Cm Compression
487: Specifies whether to use compression.
488: The argument must be
1.240 jmc 489: .Cm yes
1.1 stevesk 490: or
1.240 jmc 491: .Cm no
492: (the default).
1.247 naddy 493: .It Cm ConnectionAttempts
494: Specifies the number of tries (one per second) to make before exiting.
495: The argument must be an integer.
496: This may be useful in scripts if the connection sometimes fails.
497: The default is 1.
1.9 djm 498: .It Cm ConnectTimeout
1.84 jmc 499: Specifies the timeout (in seconds) used when connecting to the
500: SSH server, instead of using the default system TCP timeout.
1.302 djm 501: This timeout is applied both to establishing the connection and to performing
502: the initial SSH protocol handshake and key exchange.
1.36 djm 503: .It Cm ControlMaster
504: Enables the sharing of multiple sessions over a single network connection.
505: When set to
1.240 jmc 506: .Cm yes ,
1.84 jmc 507: .Xr ssh 1
1.36 djm 508: will listen for connections on a control socket specified using the
509: .Cm ControlPath
510: argument.
511: Additional sessions can connect to this socket using the same
512: .Cm ControlPath
513: with
514: .Cm ControlMaster
515: set to
1.240 jmc 516: .Cm no
1.38 jmc 517: (the default).
1.64 jmc 518: These sessions will try to reuse the master instance's network connection
1.63 djm 519: rather than initiating new ones, but will fall back to connecting normally
520: if the control socket does not exist, or is not listening.
521: .Pp
1.37 djm 522: Setting this to
1.240 jmc 523: .Cm ask
524: will cause
525: .Xr ssh 1
1.206 jmc 526: to listen for control connections, but require confirmation using
527: .Xr ssh-askpass 1 .
1.51 jakob 528: If the
529: .Cm ControlPath
1.84 jmc 530: cannot be opened,
1.240 jmc 531: .Xr ssh 1
532: will continue without connecting to a master instance.
1.58 djm 533: .Pp
534: X11 and
1.59 jmc 535: .Xr ssh-agent 1
1.58 djm 536: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 537: display and agent forwarded will be the one belonging to the master
1.59 jmc 538: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 539: .Pp
540: Two additional options allow for opportunistic multiplexing: try to use a
541: master connection but fall back to creating a new one if one does not already
542: exist.
543: These options are:
1.240 jmc 544: .Cm auto
1.56 djm 545: and
1.240 jmc 546: .Cm autoask .
1.56 djm 547: The latter requires confirmation like the
1.240 jmc 548: .Cm ask
1.56 djm 549: option.
1.36 djm 550: .It Cm ControlPath
1.55 djm 551: Specify the path to the control socket used for connection sharing as described
552: in the
1.36 djm 553: .Cm ControlMaster
1.57 djm 554: section above or the string
1.240 jmc 555: .Cm none
1.57 djm 556: to disable connection sharing.
1.239 jmc 557: Arguments to
558: .Cm ControlPath
1.326 dtucker 559: may use the tilde syntax to refer to a user's home directory,
560: the tokens described in the
1.239 jmc 561: .Sx TOKENS
1.326 dtucker 562: section and environment variables as described in the
563: .Sx ENVIRONMENT VARIABLES
1.239 jmc 564: section.
1.56 djm 565: It is recommended that any
566: .Cm ControlPath
567: used for opportunistic connection sharing include
1.195 djm 568: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
569: that is not writable by other users.
1.56 djm 570: This ensures that shared connections are uniquely identified.
1.137 djm 571: .It Cm ControlPersist
572: When used in conjunction with
573: .Cm ControlMaster ,
574: specifies that the master connection should remain open
575: in the background (waiting for future client connections)
576: after the initial client connection has been closed.
577: If set to
1.314 naddy 578: .Cm no
579: (the default),
1.137 djm 580: then the master connection will not be placed into the background,
581: and will close as soon as the initial client connection is closed.
582: If set to
1.240 jmc 583: .Cm yes
584: or 0,
1.137 djm 585: then the master connection will remain in the background indefinitely
586: (until killed or closed via a mechanism such as the
1.240 jmc 587: .Qq ssh -O exit ) .
1.137 djm 588: If set to a time in seconds, or a time in any of the formats documented in
589: .Xr sshd_config 5 ,
590: then the backgrounded master connection will automatically terminate
591: after it has remained idle (with no client connections) for the
592: specified time.
1.38 jmc 593: .It Cm DynamicForward
1.74 jmc 594: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 595: over the secure channel, and the application
596: protocol is then used to determine where to connect to from the
597: remote machine.
1.62 djm 598: .Pp
599: The argument must be
600: .Sm off
601: .Oo Ar bind_address : Oc Ar port .
602: .Sm on
1.138 djm 603: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 604: By default, the local port is bound in accordance with the
605: .Cm GatewayPorts
606: setting.
607: However, an explicit
608: .Ar bind_address
609: may be used to bind the connection to a specific address.
610: The
611: .Ar bind_address
612: of
1.240 jmc 613: .Cm localhost
1.62 djm 614: indicates that the listening port be bound for local use only, while an
615: empty address or
616: .Sq *
617: indicates that the port should be available from all interfaces.
618: .Pp
1.38 jmc 619: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 620: .Xr ssh 1
1.38 jmc 621: will act as a SOCKS server.
622: Multiple forwardings may be specified, and
623: additional forwardings can be given on the command line.
624: Only the superuser can forward privileged ports.
1.14 markus 625: .It Cm EnableSSHKeysign
626: Setting this option to
1.240 jmc 627: .Cm yes
1.14 markus 628: in the global client configuration file
629: .Pa /etc/ssh/ssh_config
630: enables the use of the helper program
631: .Xr ssh-keysign 8
632: during
633: .Cm HostbasedAuthentication .
634: The argument must be
1.240 jmc 635: .Cm yes
1.14 markus 636: or
1.240 jmc 637: .Cm no
638: (the default).
1.23 jmc 639: This option should be placed in the non-hostspecific section.
1.14 markus 640: See
641: .Xr ssh-keysign 8
642: for more information.
1.1 stevesk 643: .It Cm EscapeChar
644: Sets the escape character (default:
645: .Ql ~ ) .
646: The escape character can also
647: be set on the command line.
648: The argument should be a single character,
649: .Ql ^
650: followed by a letter, or
1.240 jmc 651: .Cm none
1.1 stevesk 652: to disable the escape
653: character entirely (making the connection transparent for binary
654: data).
1.96 markus 655: .It Cm ExitOnForwardFailure
656: Specifies whether
657: .Xr ssh 1
658: should terminate the connection if it cannot set up all requested
1.216 djm 659: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 660: if either end is unable to bind and listen on a specified port).
1.216 djm 661: Note that
662: .Cm ExitOnForwardFailure
663: does not apply to connections made over port forwardings and will not,
664: for example, cause
665: .Xr ssh 1
666: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 667: The argument must be
1.240 jmc 668: .Cm yes
1.96 markus 669: or
1.240 jmc 670: .Cm no
671: (the default).
1.197 djm 672: .It Cm FingerprintHash
673: Specifies the hash algorithm used when displaying key fingerprints.
674: Valid options are:
1.240 jmc 675: .Cm md5
1.197 djm 676: and
1.240 jmc 677: .Cm sha256
1.359 ! djm 678: (the default).
! 679: .It Cm ForkAfterAuthentication
! 680: Requests
! 681: .Nm ssh
! 682: to go to background just before command execution.
! 683: This is useful if
! 684: .Nm ssh
! 685: is going to ask for passwords or passphrases, but the user
! 686: wants it in the background.
! 687: This implies the
! 688: .Cm StdinNull
! 689: configuration option being set to
! 690: .Dq yes .
! 691: The recommended way to start X11 programs at a remote site is with
! 692: something like
! 693: .Ic ssh -f host xterm ,
! 694: which is the same as
! 695: .Ic ssh host xterm
! 696: if the
! 697: .Cm ForkAfterAuthentication
! 698: configuration option is set to
! 699: .Dq yes .
! 700: .Pp
! 701: If the
! 702: .Cm ExitOnForwardFailure
! 703: configuration option is set to
! 704: .Dq yes ,
! 705: then a client started with the
! 706: .Cm ForkAfterAuthentication
! 707: configuration option being set to
! 708: .Dq yes
! 709: will wait for all remote port forwards to be successfully established
! 710: before placing itself in the background.
! 711: The argument to this keyword must be
! 712: .Cm yes
! 713: (same as the
! 714: .Fl f
! 715: option) or
! 716: .Cm no
1.240 jmc 717: (the default).
1.1 stevesk 718: .It Cm ForwardAgent
719: Specifies whether the connection to the authentication agent (if any)
720: will be forwarded to the remote machine.
1.312 djm 721: The argument may be
722: .Cm yes ,
1.240 jmc 723: .Cm no
1.312 djm 724: (the default),
725: an explicit path to an agent socket or the name of an environment variable
726: (beginning with
727: .Sq $ )
728: in which to find the path.
1.3 stevesk 729: .Pp
1.7 jmc 730: Agent forwarding should be enabled with caution.
731: Users with the ability to bypass file permissions on the remote host
732: (for the agent's Unix-domain socket)
733: can access the local agent through the forwarded connection.
734: An attacker cannot obtain key material from the agent,
1.3 stevesk 735: however they can perform operations on the keys that enable them to
736: authenticate using the identities loaded into the agent.
1.1 stevesk 737: .It Cm ForwardX11
738: Specifies whether X11 connections will be automatically redirected
739: over the secure channel and
740: .Ev DISPLAY
741: set.
742: The argument must be
1.240 jmc 743: .Cm yes
1.1 stevesk 744: or
1.240 jmc 745: .Cm no
746: (the default).
1.3 stevesk 747: .Pp
1.7 jmc 748: X11 forwarding should be enabled with caution.
749: Users with the ability to bypass file permissions on the remote host
1.22 markus 750: (for the user's X11 authorization database)
1.7 jmc 751: can access the local X11 display through the forwarded connection.
1.22 markus 752: An attacker may then be able to perform activities such as keystroke monitoring
753: if the
754: .Cm ForwardX11Trusted
755: option is also enabled.
1.134 djm 756: .It Cm ForwardX11Timeout
1.135 jmc 757: Specify a timeout for untrusted X11 forwarding
758: using the format described in the
1.240 jmc 759: .Sx TIME FORMATS
760: section of
1.134 djm 761: .Xr sshd_config 5 .
762: X11 connections received by
763: .Xr ssh 1
764: after this time will be refused.
1.285 djm 765: Setting
766: .Cm ForwardX11Timeout
767: to zero will disable the timeout and permit X11 forwarding for the life
768: of the connection.
1.134 djm 769: The default is to disable untrusted X11 forwarding after twenty minutes has
770: elapsed.
1.22 markus 771: .It Cm ForwardX11Trusted
1.34 jmc 772: If this option is set to
1.240 jmc 773: .Cm yes ,
1.84 jmc 774: remote X11 clients will have full access to the original X11 display.
1.42 djm 775: .Pp
1.22 markus 776: If this option is set to
1.240 jmc 777: .Cm no
778: (the default),
1.84 jmc 779: remote X11 clients will be considered untrusted and prevented
1.22 markus 780: from stealing or tampering with data belonging to trusted X11
781: clients.
1.42 djm 782: Furthermore, the
783: .Xr xauth 1
784: token used for the session will be set to expire after 20 minutes.
785: Remote clients will be refused access after this time.
1.22 markus 786: .Pp
787: See the X11 SECURITY extension specification for full details on
788: the restrictions imposed on untrusted clients.
1.1 stevesk 789: .It Cm GatewayPorts
790: Specifies whether remote hosts are allowed to connect to local
791: forwarded ports.
792: By default,
1.84 jmc 793: .Xr ssh 1
1.7 jmc 794: binds local port forwardings to the loopback address.
795: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 796: .Cm GatewayPorts
1.84 jmc 797: can be used to specify that ssh
1.1 stevesk 798: should bind local port forwardings to the wildcard address,
799: thus allowing remote hosts to connect to forwarded ports.
800: The argument must be
1.240 jmc 801: .Cm yes
1.1 stevesk 802: or
1.240 jmc 803: .Cm no
804: (the default).
1.1 stevesk 805: .It Cm GlobalKnownHostsFile
1.151 djm 806: Specifies one or more files to use for the global
807: host key database, separated by whitespace.
808: The default is
809: .Pa /etc/ssh/ssh_known_hosts ,
810: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 811: .It Cm GSSAPIAuthentication
1.27 markus 812: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 813: The default is
1.240 jmc 814: .Cm no .
1.18 markus 815: .It Cm GSSAPIDelegateCredentials
816: Forward (delegate) credentials to the server.
817: The default is
1.240 jmc 818: .Cm no .
1.44 djm 819: .It Cm HashKnownHosts
820: Indicates that
1.84 jmc 821: .Xr ssh 1
1.44 djm 822: should hash host names and addresses when they are added to
1.50 djm 823: .Pa ~/.ssh/known_hosts .
1.44 djm 824: These hashed names may be used normally by
1.84 jmc 825: .Xr ssh 1
1.44 djm 826: and
1.84 jmc 827: .Xr sshd 8 ,
1.316 djm 828: but they do not visually reveal identifying information if the
829: file's contents are disclosed.
1.44 djm 830: The default is
1.240 jmc 831: .Cm no .
1.97 jmc 832: Note that existing names and addresses in known hosts files
833: will not be converted automatically,
834: but may be manually hashed using
1.45 djm 835: .Xr ssh-keygen 1 .
1.344 dtucker 836: .It Cm HostbasedAcceptedAlgorithms
1.348 djm 837: Specifies the signature algorithms that will be used for hostbased
838: authentication as a comma-separated list of patterns.
1.300 naddy 839: Alternately if the specified list begins with a
1.214 djm 840: .Sq +
1.348 djm 841: character, then the specified signature algorithms will be appended
842: to the default set instead of replacing them.
1.300 naddy 843: If the specified list begins with a
1.241 djm 844: .Sq -
1.348 djm 845: character, then the specified signature algorithms (including wildcards)
846: will be removed from the default set instead of replacing them.
1.301 naddy 847: If the specified list begins with a
848: .Sq ^
1.348 djm 849: character, then the specified signature algorithms will be placed
850: at the head of the default set.
1.213 markus 851: The default for this option is:
852: .Bd -literal -offset 3n
1.333 djm 853: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 854: ecdsa-sha2-nistp256-cert-v01@openssh.com,
855: ecdsa-sha2-nistp384-cert-v01@openssh.com,
856: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 857: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 858: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 859: rsa-sha2-512-cert-v01@openssh.com,
860: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 861: ssh-rsa-cert-v01@openssh.com,
1.333 djm 862: ssh-ed25519,
1.213 markus 863: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 864: sk-ssh-ed25519@openssh.com,
1.311 naddy 865: sk-ecdsa-sha2-nistp256@openssh.com,
866: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 867: .Ed
868: .Pp
1.202 djm 869: The
870: .Fl Q
871: option of
872: .Xr ssh 1
1.348 djm 873: may be used to list supported signature algorithms.
1.344 dtucker 874: This was formerly named HostbasedKeyTypes.
1.345 naddy 875: .It Cm HostbasedAuthentication
876: Specifies whether to try rhosts based authentication with public key
877: authentication.
878: The argument must be
879: .Cm yes
880: or
881: .Cm no
882: (the default).
1.1 stevesk 883: .It Cm HostKeyAlgorithms
1.348 djm 884: Specifies the host key signature algorithms
1.1 stevesk 885: that the client wants to use in order of preference.
1.300 naddy 886: Alternately if the specified list begins with a
1.214 djm 887: .Sq +
1.348 djm 888: character, then the specified signature algorithms will be appended to
889: the default set instead of replacing them.
1.300 naddy 890: If the specified list begins with a
1.241 djm 891: .Sq -
1.348 djm 892: character, then the specified signature algorithms (including wildcards)
893: will be removed from the default set instead of replacing them.
1.301 naddy 894: If the specified list begins with a
895: .Sq ^
1.348 djm 896: character, then the specified signature algorithms will be placed
897: at the head of the default set.
1.1 stevesk 898: The default for this option is:
1.139 djm 899: .Bd -literal -offset 3n
1.333 djm 900: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 901: ecdsa-sha2-nistp256-cert-v01@openssh.com,
902: ecdsa-sha2-nistp384-cert-v01@openssh.com,
903: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 904: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 905: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 906: rsa-sha2-512-cert-v01@openssh.com,
907: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 908: ssh-rsa-cert-v01@openssh.com,
1.333 djm 909: ssh-ed25519,
1.139 djm 910: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 911: sk-ecdsa-sha2-nistp256@openssh.com,
1.333 djm 912: sk-ssh-ed25519@openssh.com,
1.311 naddy 913: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 914: .Ed
1.145 djm 915: .Pp
916: If hostkeys are known for the destination host then this default is modified
917: to prefer their algorithms.
1.198 djm 918: .Pp
1.348 djm 919: The list of available signature algorithms may also be obtained using
1.322 dtucker 920: .Qq ssh -Q HostKeyAlgorithms .
1.1 stevesk 921: .It Cm HostKeyAlias
922: Specifies an alias that should be used instead of the
923: real host name when looking up or saving the host key
1.251 djm 924: in the host key database files and when validating host certificates.
1.84 jmc 925: This option is useful for tunneling SSH connections
1.1 stevesk 926: or for multiple servers running on a single host.
1.295 jmc 927: .It Cm Hostname
1.1 stevesk 928: Specifies the real host name to log into.
929: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 930: Arguments to
1.295 jmc 931: .Cm Hostname
1.239 jmc 932: accept the tokens described in the
933: .Sx TOKENS
934: section.
1.1 stevesk 935: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 936: .Cm Hostname
1.1 stevesk 937: specifications).
1.239 jmc 938: The default is the name given on the command line.
1.29 markus 939: .It Cm IdentitiesOnly
940: Specifies that
1.84 jmc 941: .Xr ssh 1
1.304 djm 942: should only use the configured authentication identity and certificate files
943: (either the default files, or those explicitly configured in the
1.31 jmc 944: .Nm
1.221 djm 945: files
946: or passed on the
947: .Xr ssh 1
1.304 djm 948: command-line),
1.84 jmc 949: even if
950: .Xr ssh-agent 1
1.159 djm 951: or a
952: .Cm PKCS11Provider
1.305 naddy 953: or
954: .Cm SecurityKeyProvider
1.29 markus 955: offers more identities.
956: The argument to this keyword must be
1.240 jmc 957: .Cm yes
1.29 markus 958: or
1.240 jmc 959: .Cm no
960: (the default).
1.84 jmc 961: This option is intended for situations where ssh-agent
1.29 markus 962: offers many different identities.
1.231 markus 963: .It Cm IdentityAgent
964: Specifies the
965: .Ux Ns -domain
966: socket used to communicate with the authentication agent.
967: .Pp
968: This option overrides the
1.240 jmc 969: .Ev SSH_AUTH_SOCK
1.231 markus 970: environment variable and can be used to select a specific agent.
971: Setting the socket name to
1.240 jmc 972: .Cm none
1.231 markus 973: disables the use of an authentication agent.
1.232 markus 974: If the string
1.240 jmc 975: .Qq SSH_AUTH_SOCK
1.232 markus 976: is specified, the location of the socket will be read from the
977: .Ev SSH_AUTH_SOCK
978: environment variable.
1.286 djm 979: Otherwise if the specified value begins with a
980: .Sq $
981: character, then it will be treated as an environment variable containing
982: the location of the socket.
1.231 markus 983: .Pp
1.239 jmc 984: Arguments to
985: .Cm IdentityAgent
1.326 dtucker 986: may use the tilde syntax to refer to a user's home directory,
987: the tokens described in the
1.239 jmc 988: .Sx TOKENS
1.326 dtucker 989: section and environment variables as described in the
990: .Sx ENVIRONMENT VARIABLES
1.239 jmc 991: section.
1.67 jmc 992: .It Cm IdentityFile
1.313 naddy 993: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
994: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 995: The default is
1.139 djm 996: .Pa ~/.ssh/id_dsa ,
1.183 naddy 997: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 998: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 999: .Pa ~/.ssh/id_ed25519 ,
1000: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 1001: and
1.245 djm 1002: .Pa ~/.ssh/id_rsa .
1.67 jmc 1003: Additionally, any identities represented by the authentication agent
1.165 djm 1004: will be used for authentication unless
1005: .Cm IdentitiesOnly
1006: is set.
1.221 djm 1007: If no certificates have been explicitly specified by
1008: .Cm CertificateFile ,
1.129 djm 1009: .Xr ssh 1
1010: will try to load certificate information from the filename obtained by
1011: appending
1012: .Pa -cert.pub
1013: to the path of a specified
1014: .Cm IdentityFile .
1.90 djm 1015: .Pp
1.239 jmc 1016: Arguments to
1017: .Cm IdentityFile
1018: may use the tilde syntax to refer to a user's home directory
1019: or the tokens described in the
1020: .Sx TOKENS
1021: section.
1.90 djm 1022: .Pp
1.67 jmc 1023: It is possible to have
1024: multiple identity files specified in configuration files; all these
1025: identities will be tried in sequence.
1.152 djm 1026: Multiple
1027: .Cm IdentityFile
1028: directives will add to the list of identities tried (this behaviour
1029: differs from that of other configuration directives).
1.165 djm 1030: .Pp
1031: .Cm IdentityFile
1032: may be used in conjunction with
1033: .Cm IdentitiesOnly
1034: to select which identities in an agent are offered during authentication.
1.221 djm 1035: .Cm IdentityFile
1036: may also be used in conjunction with
1037: .Cm CertificateFile
1038: in order to provide any certificate also needed for authentication with
1039: the identity.
1.164 jmc 1040: .It Cm IgnoreUnknown
1041: Specifies a pattern-list of unknown options to be ignored if they are
1042: encountered in configuration parsing.
1043: This may be used to suppress errors if
1044: .Nm
1045: contains options that are unrecognised by
1046: .Xr ssh 1 .
1047: It is recommended that
1048: .Cm IgnoreUnknown
1049: be listed early in the configuration file as it will not be applied
1050: to unknown options that appear before it.
1.229 djm 1051: .It Cm Include
1052: Include the specified configuration file(s).
1.230 jmc 1053: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1054: .Xr glob 7
1.229 djm 1055: wildcards and, for user configurations, shell-like
1.240 jmc 1056: .Sq ~
1.229 djm 1057: references to user home directories.
1.327 djm 1058: Wildcards will be expanded and processed in lexical order.
1.229 djm 1059: Files without absolute paths are assumed to be in
1060: .Pa ~/.ssh
1.230 jmc 1061: if included in a user configuration file or
1.229 djm 1062: .Pa /etc/ssh
1063: if included from the system configuration file.
1064: .Cm Include
1065: directive may appear inside a
1066: .Cm Match
1067: or
1068: .Cm Host
1069: block
1070: to perform conditional inclusion.
1.143 djm 1071: .It Cm IPQoS
1072: Specifies the IPv4 type-of-service or DSCP class for connections.
1073: Accepted values are
1.240 jmc 1074: .Cm af11 ,
1075: .Cm af12 ,
1076: .Cm af13 ,
1077: .Cm af21 ,
1078: .Cm af22 ,
1079: .Cm af23 ,
1080: .Cm af31 ,
1081: .Cm af32 ,
1082: .Cm af33 ,
1083: .Cm af41 ,
1084: .Cm af42 ,
1085: .Cm af43 ,
1086: .Cm cs0 ,
1087: .Cm cs1 ,
1088: .Cm cs2 ,
1089: .Cm cs3 ,
1090: .Cm cs4 ,
1091: .Cm cs5 ,
1092: .Cm cs6 ,
1093: .Cm cs7 ,
1094: .Cm ef ,
1.319 djm 1095: .Cm le ,
1.240 jmc 1096: .Cm lowdelay ,
1097: .Cm throughput ,
1098: .Cm reliability ,
1.253 djm 1099: a numeric value, or
1100: .Cm none
1101: to use the operating system default.
1.146 djm 1102: This option may take one or two arguments, separated by whitespace.
1.143 djm 1103: If one argument is specified, it is used as the packet class unconditionally.
1104: If two values are specified, the first is automatically selected for
1105: interactive sessions and the second for non-interactive sessions.
1106: The default is
1.269 job 1107: .Cm af21
1.272 jmc 1108: (Low-Latency Data)
1.143 djm 1109: for interactive sessions and
1.269 job 1110: .Cm cs1
1.272 jmc 1111: (Lower Effort)
1.143 djm 1112: for non-interactive sessions.
1.103 djm 1113: .It Cm KbdInteractiveAuthentication
1114: Specifies whether to use keyboard-interactive authentication.
1115: The argument to this keyword must be
1.240 jmc 1116: .Cm yes
1117: (the default)
1.103 djm 1118: or
1.240 jmc 1119: .Cm no .
1.355 dtucker 1120: .Cm ChallengeResponseAuthentication
1121: is a deprecated alias for this.
1.39 djm 1122: .It Cm KbdInteractiveDevices
1123: Specifies the list of methods to use in keyboard-interactive authentication.
1124: Multiple method names must be comma-separated.
1125: The default is to use the server specified list.
1.85 jmc 1126: The methods available vary depending on what the server supports.
1127: For an OpenSSH server,
1128: it may be zero or more of:
1.240 jmc 1129: .Cm bsdauth ,
1130: .Cm pam ,
1.85 jmc 1131: and
1.240 jmc 1132: .Cm skey .
1.140 djm 1133: .It Cm KexAlgorithms
1134: Specifies the available KEX (Key Exchange) algorithms.
1135: Multiple algorithms must be comma-separated.
1.299 kn 1136: If the specified list begins with a
1.214 djm 1137: .Sq +
1138: character, then the specified methods will be appended to the default set
1139: instead of replacing them.
1.299 kn 1140: If the specified list begins with a
1.241 djm 1141: .Sq -
1142: character, then the specified methods (including wildcards) will be removed
1143: from the default set instead of replacing them.
1.301 naddy 1144: If the specified list begins with a
1145: .Sq ^
1146: character, then the specified methods will be placed at the head of the
1147: default set.
1.141 jmc 1148: The default is:
1149: .Bd -literal -offset indent
1.238 djm 1150: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1151: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1152: diffie-hellman-group-exchange-sha256,
1.266 djm 1153: diffie-hellman-group16-sha512,
1154: diffie-hellman-group18-sha512,
1.317 tedu 1155: diffie-hellman-group14-sha256
1.141 jmc 1156: .Ed
1.198 djm 1157: .Pp
1.240 jmc 1158: The list of available key exchange algorithms may also be obtained using
1159: .Qq ssh -Q kex .
1.339 djm 1160: .It Cm KnownHostsCommand
1.340 jmc 1161: Specifies a command to use to obtain a list of host keys, in addition to
1.339 djm 1162: those listed in
1163: .Cm UserKnownHostsFile
1164: and
1165: .Cm GlobalKnownHostsFile .
1166: This command is executed after the files have been read.
1.340 jmc 1167: It may write host key lines to standard output in identical format to the
1.339 djm 1168: usual files (described in the
1169: .Sx VERIFYING HOST KEYS
1170: section in
1171: .Xr ssh 1 ) .
1172: Arguments to
1173: .Cm KnownHostsCommand
1174: accept the tokens described in the
1175: .Sx TOKENS
1176: section.
1.340 jmc 1177: The command may be invoked multiple times per connection: once when preparing
1.339 djm 1178: the preference list of host key algorithms to use, again to obtain the
1179: host key for the requested host name and, if
1180: .Cm CheckHostIP
1181: is enabled, one more time to obtain the host key matching the server's
1182: address.
1183: If the command exits abnormally or returns a non-zero exit status then the
1184: connection is terminated.
1.65 reyk 1185: .It Cm LocalCommand
1186: Specifies a command to execute on the local machine after successfully
1187: connecting to the server.
1188: The command string extends to the end of the line, and is executed with
1.105 jmc 1189: the user's shell.
1.239 jmc 1190: Arguments to
1191: .Cm LocalCommand
1192: accept the tokens described in the
1193: .Sx TOKENS
1194: section.
1.123 djm 1195: .Pp
1196: The command is run synchronously and does not have access to the
1197: session of the
1198: .Xr ssh 1
1199: that spawned it.
1200: It should not be used for interactive commands.
1201: .Pp
1.65 reyk 1202: This directive is ignored unless
1203: .Cm PermitLocalCommand
1204: has been enabled.
1.1 stevesk 1205: .It Cm LocalForward
1.74 jmc 1206: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1207: the secure channel to the specified host and port from the remote machine.
1.324 dtucker 1208: The first argument specifies the listener and may be
1.43 djm 1209: .Sm off
1.49 jmc 1210: .Oo Ar bind_address : Oc Ar port
1.43 djm 1211: .Sm on
1.324 dtucker 1212: or a Unix domain socket path.
1213: The second argument is the destination and may be
1214: .Ar host : Ns Ar hostport
1215: or a Unix domain socket path if the remote host supports it.
1216: .Pp
1.138 djm 1217: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1218: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1219: given on the command line.
1.1 stevesk 1220: Only the superuser can forward privileged ports.
1.43 djm 1221: By default, the local port is bound in accordance with the
1222: .Cm GatewayPorts
1223: setting.
1224: However, an explicit
1225: .Ar bind_address
1226: may be used to bind the connection to a specific address.
1227: The
1228: .Ar bind_address
1229: of
1.240 jmc 1230: .Cm localhost
1.46 jmc 1231: indicates that the listening port be bound for local use only, while an
1232: empty address or
1233: .Sq *
1.43 djm 1234: indicates that the port should be available from all interfaces.
1.326 dtucker 1235: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1236: .Sx TOKENS
1.326 dtucker 1237: section and environment variables as described in the
1238: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1239: section.
1.1 stevesk 1240: .It Cm LogLevel
1241: Gives the verbosity level that is used when logging messages from
1.84 jmc 1242: .Xr ssh 1 .
1.1 stevesk 1243: The possible values are:
1.84 jmc 1244: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1245: The default is INFO.
1246: DEBUG and DEBUG1 are equivalent.
1247: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.337 djm 1248: .It Cm LogVerbose
1249: Specify one or more overrides to LogLevel.
1250: An override consists of a pattern lists that matches the source file, function
1251: and line number to force detailed logging for.
1252: For example, an override pattern of:
1253: .Bd -literal -offset indent
1254: kex.c:*:1000,*:kex_exchange_identification():*,packet.c:*
1255: .Ed
1256: .Pp
1257: would enable detailed logging for line 1000 of
1.338 jmc 1258: .Pa kex.c ,
1.337 djm 1259: everything in the
1260: .Fn kex_exchange_identification
1261: function, and all code in the
1262: .Pa packet.c
1263: file.
1264: This option is intended for debugging and no overrides are enabled by default.
1.1 stevesk 1265: .It Cm MACs
1266: Specifies the MAC (message authentication code) algorithms
1267: in order of preference.
1.226 jmc 1268: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1269: Multiple algorithms must be comma-separated.
1.299 kn 1270: If the specified list begins with a
1.214 djm 1271: .Sq +
1272: character, then the specified algorithms will be appended to the default set
1273: instead of replacing them.
1.299 kn 1274: If the specified list begins with a
1.241 djm 1275: .Sq -
1276: character, then the specified algorithms (including wildcards) will be removed
1277: from the default set instead of replacing them.
1.301 naddy 1278: If the specified list begins with a
1279: .Sq ^
1280: character, then the specified algorithms will be placed at the head of the
1281: default set.
1.214 djm 1282: .Pp
1.160 markus 1283: The algorithms that contain
1.240 jmc 1284: .Qq -etm
1.160 markus 1285: calculate the MAC after encryption (encrypt-then-mac).
1286: These are considered safer and their use recommended.
1.214 djm 1287: .Pp
1.84 jmc 1288: The default is:
1.101 jmc 1289: .Bd -literal -offset indent
1.160 markus 1290: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1291: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1292: hmac-sha1-etm@openssh.com,
1.186 naddy 1293: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1294: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1295: .Ed
1.198 djm 1296: .Pp
1.240 jmc 1297: The list of available MAC algorithms may also be obtained using
1298: .Qq ssh -Q mac .
1.1 stevesk 1299: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1300: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1301: The argument to this keyword must be
1.240 jmc 1302: .Cm yes
1.1 stevesk 1303: or
1.242 jmc 1304: .Cm no
1.240 jmc 1305: (the default).
1.1 stevesk 1306: .It Cm NumberOfPasswordPrompts
1307: Specifies the number of password prompts before giving up.
1308: The argument to this keyword must be an integer.
1.84 jmc 1309: The default is 3.
1.1 stevesk 1310: .It Cm PasswordAuthentication
1311: Specifies whether to use password authentication.
1312: The argument to this keyword must be
1.240 jmc 1313: .Cm yes
1314: (the default)
1.1 stevesk 1315: or
1.240 jmc 1316: .Cm no .
1.65 reyk 1317: .It Cm PermitLocalCommand
1318: Allow local command execution via the
1319: .Ic LocalCommand
1320: option or using the
1.66 jmc 1321: .Ic !\& Ns Ar command
1.65 reyk 1322: escape sequence in
1323: .Xr ssh 1 .
1324: The argument must be
1.240 jmc 1325: .Cm yes
1.65 reyk 1326: or
1.240 jmc 1327: .Cm no
1328: (the default).
1.347 markus 1329: .It Cm PermitRemoteOpen
1330: Specifies the destinations to which remote TCP port forwarding is permitted when
1331: .Cm RemoteForward
1332: is used as a SOCKS proxy.
1333: The forwarding specification must be one of the following forms:
1334: .Pp
1335: .Bl -item -offset indent -compact
1336: .It
1337: .Cm PermitRemoteOpen
1338: .Sm off
1339: .Ar host : port
1340: .Sm on
1341: .It
1342: .Cm PermitRemoteOpen
1343: .Sm off
1344: .Ar IPv4_addr : port
1345: .Sm on
1346: .It
1347: .Cm PermitRemoteOpen
1348: .Sm off
1349: .Ar \&[ IPv6_addr \&] : port
1350: .Sm on
1351: .El
1352: .Pp
1353: Multiple forwards may be specified by separating them with whitespace.
1354: An argument of
1355: .Cm any
1356: can be used to remove all restrictions and permit any forwarding requests.
1357: An argument of
1358: .Cm none
1359: can be used to prohibit all forwarding requests.
1360: The wildcard
1361: .Sq *
1362: can be used for host or port to allow all hosts or ports respectively.
1363: Otherwise, no pattern matching or address lookups are performed on supplied
1364: names.
1.127 markus 1365: .It Cm PKCS11Provider
1.292 djm 1366: Specifies which PKCS#11 provider to use or
1367: .Cm none
1368: to indicate that no provider should be used (the default).
1369: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1370: .Xr ssh 1
1.292 djm 1371: should use to communicate with a PKCS#11 token providing keys for user
1372: authentication.
1.67 jmc 1373: .It Cm Port
1374: Specifies the port number to connect on the remote host.
1.84 jmc 1375: The default is 22.
1.1 stevesk 1376: .It Cm PreferredAuthentications
1.226 jmc 1377: Specifies the order in which the client should try authentication methods.
1.48 jmc 1378: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1379: .Cm keyboard-interactive )
1.48 jmc 1380: over another method (e.g.\&
1.131 jmc 1381: .Cm password ) .
1382: The default is:
1383: .Bd -literal -offset indent
1384: gssapi-with-mic,hostbased,publickey,
1385: keyboard-interactive,password
1386: .Ed
1.1 stevesk 1387: .It Cm ProxyCommand
1388: Specifies the command to use to connect to the server.
1389: The command
1.190 djm 1390: string extends to the end of the line, and is executed
1391: using the user's shell
1392: .Ql exec
1393: directive to avoid a lingering shell process.
1394: .Pp
1.239 jmc 1395: Arguments to
1396: .Cm ProxyCommand
1397: accept the tokens described in the
1398: .Sx TOKENS
1399: section.
1.1 stevesk 1400: The command can be basically anything,
1401: and should read from its standard input and write to its standard output.
1402: It should eventually connect an
1403: .Xr sshd 8
1404: server running on some machine, or execute
1405: .Ic sshd -i
1406: somewhere.
1407: Host key management will be done using the
1.296 jmc 1408: .Cm Hostname
1409: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1410: Setting the command to
1.240 jmc 1411: .Cm none
1.6 markus 1412: disables this option entirely.
1.1 stevesk 1413: Note that
1414: .Cm CheckHostIP
1415: is not available for connects with a proxy command.
1.52 djm 1416: .Pp
1417: This directive is useful in conjunction with
1418: .Xr nc 1
1419: and its proxy support.
1.53 jmc 1420: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1421: 192.0.2.0:
1422: .Bd -literal -offset 3n
1423: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1424: .Ed
1.233 djm 1425: .It Cm ProxyJump
1.260 millert 1426: Specifies one or more jump proxies as either
1.233 djm 1427: .Xo
1428: .Sm off
1.234 jmc 1429: .Op Ar user No @
1.233 djm 1430: .Ar host
1.234 jmc 1431: .Op : Ns Ar port
1.233 djm 1432: .Sm on
1.260 millert 1433: or an ssh URI
1.233 djm 1434: .Xc .
1.235 djm 1435: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1436: sequentially.
1.233 djm 1437: Setting this option will cause
1438: .Xr ssh 1
1439: to connect to the target host by first making a
1440: .Xr ssh 1
1441: connection to the specified
1442: .Cm ProxyJump
1443: host and then establishing a
1.234 jmc 1444: TCP forwarding to the ultimate target from there.
1.346 dlg 1445: Setting the host to
1446: .Cm none
1447: disables this option entirely.
1.233 djm 1448: .Pp
1449: Note that this option will compete with the
1450: .Cm ProxyCommand
1451: option - whichever is specified first will prevent later instances of the
1452: other from taking effect.
1.289 djm 1453: .Pp
1454: Note also that the configuration for the destination host (either supplied
1455: via the command-line or the configuration file) is not generally applied
1456: to jump hosts.
1457: .Pa ~/.ssh/config
1458: should be used if specific configuration is required for jump hosts.
1.167 djm 1459: .It Cm ProxyUseFdpass
1.168 jmc 1460: Specifies that
1.167 djm 1461: .Cm ProxyCommand
1462: will pass a connected file descriptor back to
1.168 jmc 1463: .Xr ssh 1
1.167 djm 1464: instead of continuing to execute and pass data.
1465: The default is
1.240 jmc 1466: .Cm no .
1.343 dtucker 1467: .It Cm PubkeyAcceptedAlgorithms
1468: Specifies the signature algorithms that will be used for public key
1469: authentication as a comma-separated list of patterns.
1.299 kn 1470: If the specified list begins with a
1.214 djm 1471: .Sq +
1.343 dtucker 1472: character, then the algorithms after it will be appended to the default
1.214 djm 1473: instead of replacing it.
1.299 kn 1474: If the specified list begins with a
1.241 djm 1475: .Sq -
1.343 dtucker 1476: character, then the specified algorithms (including wildcards) will be removed
1.241 djm 1477: from the default set instead of replacing them.
1.301 naddy 1478: If the specified list begins with a
1479: .Sq ^
1.343 dtucker 1480: character, then the specified algorithms will be placed at the head of the
1.301 naddy 1481: default set.
1.213 markus 1482: The default for this option is:
1483: .Bd -literal -offset 3n
1.333 djm 1484: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 1485: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1486: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1487: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.333 djm 1488: sk-ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 1489: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.305 naddy 1490: rsa-sha2-512-cert-v01@openssh.com,
1491: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1492: ssh-rsa-cert-v01@openssh.com,
1.333 djm 1493: ssh-ed25519,
1.311 naddy 1494: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.333 djm 1495: sk-ssh-ed25519@openssh.com,
1.305 naddy 1496: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1497: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1498: .Ed
1499: .Pp
1.348 djm 1500: The list of available signature algorithms may also be obtained using
1.343 dtucker 1501: .Qq ssh -Q PubkeyAcceptedAlgorithms .
1.1 stevesk 1502: .It Cm PubkeyAuthentication
1503: Specifies whether to try public key authentication.
1504: The argument to this keyword must be
1.240 jmc 1505: .Cm yes
1506: (the default)
1.1 stevesk 1507: or
1.240 jmc 1508: .Cm no .
1.75 dtucker 1509: .It Cm RekeyLimit
1510: Specifies the maximum amount of data that may be transmitted before the
1.342 rob 1511: session key is renegotiated, optionally followed by a maximum amount of
1.162 dtucker 1512: time that may pass before the session key is renegotiated.
1513: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1514: .Sq K ,
1515: .Sq M ,
1.75 dtucker 1516: or
1.76 jmc 1517: .Sq G
1.75 dtucker 1518: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1519: The default is between
1.84 jmc 1520: .Sq 1G
1.75 dtucker 1521: and
1.84 jmc 1522: .Sq 4G ,
1.75 dtucker 1523: depending on the cipher.
1.162 dtucker 1524: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1525: units documented in the TIME FORMATS section of
1.162 dtucker 1526: .Xr sshd_config 5 .
1527: The default value for
1528: .Cm RekeyLimit
1529: is
1.240 jmc 1530: .Cm default none ,
1.162 dtucker 1531: which means that rekeying is performed after the cipher's default amount
1532: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1533: .It Cm RemoteCommand
1534: Specifies a command to execute on the remote machine after successfully
1535: connecting to the server.
1536: The command string extends to the end of the line, and is executed with
1537: the user's shell.
1.250 jmc 1538: Arguments to
1539: .Cm RemoteCommand
1540: accept the tokens described in the
1541: .Sx TOKENS
1542: section.
1.1 stevesk 1543: .It Cm RemoteForward
1.74 jmc 1544: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1545: the secure channel.
1.273 djm 1546: The remote port may either be forwarded to a specified host and port
1.256 markus 1547: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1548: client to connect to arbitrary destinations from the local machine.
1.324 dtucker 1549: The first argument is the listening specification and may be
1.43 djm 1550: .Sm off
1.49 jmc 1551: .Oo Ar bind_address : Oc Ar port
1.43 djm 1552: .Sm on
1.324 dtucker 1553: or, if the remote host supports it, a Unix domain socket path.
1.256 markus 1554: If forwarding to a specific destination then the second argument must be
1.324 dtucker 1555: .Ar host : Ns Ar hostport
1556: or a Unix domain socket path,
1.256 markus 1557: otherwise if no destination argument is specified then the remote forwarding
1558: will be established as a SOCKS proxy.
1.347 markus 1559: When acting as a SOCKS proxy the destination of the connection can be
1560: restricted by
1561: .Cm PermitRemoteOpen .
1.256 markus 1562: .Pp
1.138 djm 1563: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1564: Multiple forwardings may be specified, and additional
1565: forwardings can be given on the command line.
1.113 stevesk 1566: Privileged ports can be forwarded only when
1567: logging in as root on the remote machine.
1.326 dtucker 1568: Unix domain socket paths may use the tokens described in the
1.324 dtucker 1569: .Sx TOKENS
1.326 dtucker 1570: section and environment variables as described in the
1571: .Sx ENVIRONMENT VARIABLES
1.324 dtucker 1572: section.
1.118 jmc 1573: .Pp
1.117 djm 1574: If the
1575: .Ar port
1.240 jmc 1576: argument is 0,
1.117 djm 1577: the listen port will be dynamically allocated on the server and reported
1578: to the client at run time.
1.43 djm 1579: .Pp
1580: If the
1581: .Ar bind_address
1582: is not specified, the default is to only bind to loopback addresses.
1583: If the
1584: .Ar bind_address
1585: is
1586: .Ql *
1587: or an empty string, then the forwarding is requested to listen on all
1588: interfaces.
1589: Specifying a remote
1590: .Ar bind_address
1.46 jmc 1591: will only succeed if the server's
1592: .Cm GatewayPorts
1.43 djm 1593: option is enabled (see
1.46 jmc 1594: .Xr sshd_config 5 ) .
1.149 djm 1595: .It Cm RequestTTY
1596: Specifies whether to request a pseudo-tty for the session.
1597: The argument may be one of:
1.240 jmc 1598: .Cm no
1.149 djm 1599: (never request a TTY),
1.240 jmc 1600: .Cm yes
1.149 djm 1601: (always request a TTY when standard input is a TTY),
1.240 jmc 1602: .Cm force
1.149 djm 1603: (always request a TTY) or
1.240 jmc 1604: .Cm auto
1.149 djm 1605: (request a TTY when opening a login session).
1606: This option mirrors the
1607: .Fl t
1608: and
1609: .Fl T
1610: flags for
1611: .Xr ssh 1 .
1.196 djm 1612: .It Cm RevokedHostKeys
1613: Specifies revoked host public keys.
1614: Keys listed in this file will be refused for host authentication.
1615: Note that if this file does not exist or is not readable,
1616: then host authentication will be refused for all hosts.
1617: Keys may be specified as a text file, listing one public key per line, or as
1618: an OpenSSH Key Revocation List (KRL) as generated by
1619: .Xr ssh-keygen 1 .
1620: For more information on KRLs, see the KEY REVOCATION LISTS section in
1621: .Xr ssh-keygen 1 .
1.305 naddy 1622: .It Cm SecurityKeyProvider
1.313 naddy 1623: Specifies a path to a library that will be used when loading any
1624: FIDO authenticator-hosted keys, overriding the default of using
1625: the built-in USB HID support.
1.309 naddy 1626: .Pp
1627: If the specified value begins with a
1628: .Sq $
1629: character, then it will be treated as an environment variable containing
1630: the path to the library.
1.32 djm 1631: .It Cm SendEnv
1632: Specifies what variables from the local
1633: .Xr environ 7
1634: should be sent to the server.
1.84 jmc 1635: The server must also support it, and the server must be configured to
1.33 djm 1636: accept these environment variables.
1.207 dtucker 1637: Note that the
1638: .Ev TERM
1.208 jmc 1639: environment variable is always sent whenever a
1.207 dtucker 1640: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1641: Refer to
1642: .Cm AcceptEnv
1643: in
1644: .Xr sshd_config 5
1645: for how to configure the server.
1.80 jmc 1646: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1647: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1648: across multiple
1649: .Cm SendEnv
1650: directives.
1.81 jmc 1651: .Pp
1652: See
1653: .Sx PATTERNS
1654: for more information on patterns.
1.271 djm 1655: .Pp
1.272 jmc 1656: It is possible to clear previously set
1.271 djm 1657: .Cm SendEnv
1658: variable names by prefixing patterns with
1659: .Pa - .
1660: The default is not to send any environment variables.
1.28 markus 1661: .It Cm ServerAliveCountMax
1.73 jmc 1662: Sets the number of server alive messages (see below) which may be
1.28 markus 1663: sent without
1.84 jmc 1664: .Xr ssh 1
1.28 markus 1665: receiving any messages back from the server.
1666: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1667: ssh will disconnect from the server, terminating the session.
1.28 markus 1668: It is important to note that the use of server alive messages is very
1669: different from
1670: .Cm TCPKeepAlive
1671: (below).
1672: The server alive messages are sent through the encrypted channel
1673: and therefore will not be spoofable.
1674: The TCP keepalive option enabled by
1675: .Cm TCPKeepAlive
1676: is spoofable.
1677: The server alive mechanism is valuable when the client or
1.298 dtucker 1678: server depend on knowing when a connection has become unresponsive.
1.28 markus 1679: .Pp
1680: The default value is 3.
1681: If, for example,
1682: .Cm ServerAliveInterval
1.84 jmc 1683: (see below) is set to 15 and
1.28 markus 1684: .Cm ServerAliveCountMax
1.84 jmc 1685: is left at the default, if the server becomes unresponsive,
1686: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1687: .It Cm ServerAliveInterval
1688: Sets a timeout interval in seconds after which if no data has been received
1689: from the server,
1.84 jmc 1690: .Xr ssh 1
1.67 jmc 1691: will send a message through the encrypted
1692: channel to request a response from the server.
1693: The default
1694: is 0, indicating that these messages will not be sent to the server.
1.357 jmc 1695: .It Cm SessionType
1696: May be used to either request invocation of a subsystem on the remote system,
1697: or to prevent the execution of a remote command at all.
1698: The latter is useful for just forwarding ports.
1699: The argument to this keyword must be
1700: .Cm none
1701: (same as the
1702: .Fl N
1703: option),
1704: .Cm subsystem
1705: (same as the
1706: .Fl s
1707: option) or
1708: .Cm default
1709: (shell or command execution).
1.277 jmc 1710: .It Cm SetEnv
1711: Directly specify one or more environment variables and their contents to
1712: be sent to the server.
1713: Similarly to
1714: .Cm SendEnv ,
1.354 djm 1715: with the exception of the
1716: .Ev TERM
1717: variable, the server must be prepared to accept the environment variable.
1.358 djm 1718: .It Cm StdinNull
1719: Redirects stdin from
1720: .Pa /dev/null
1721: (actually, prevents reading from stdin).
1722: Either this or the equivalent
1723: .Fl n
1724: option must be used when
1725: .Nm ssh
1726: is run in the background.
1727: The argument to this keyword must be
1728: .Cm yes
1729: (same as the
1730: .Fl n
1731: option) or
1732: .Cm no
1733: (the default).
1.191 millert 1734: .It Cm StreamLocalBindMask
1735: Sets the octal file creation mode mask
1736: .Pq umask
1737: used when creating a Unix-domain socket file for local or remote
1738: port forwarding.
1739: This option is only used for port forwarding to a Unix-domain socket file.
1740: .Pp
1741: The default value is 0177, which creates a Unix-domain socket file that is
1742: readable and writable only by the owner.
1743: Note that not all operating systems honor the file mode on Unix-domain
1744: socket files.
1745: .It Cm StreamLocalBindUnlink
1746: Specifies whether to remove an existing Unix-domain socket file for local
1747: or remote port forwarding before creating a new one.
1748: If the socket file already exists and
1749: .Cm StreamLocalBindUnlink
1750: is not enabled,
1751: .Nm ssh
1752: will be unable to forward the port to the Unix-domain socket file.
1753: This option is only used for port forwarding to a Unix-domain socket file.
1754: .Pp
1755: The argument must be
1.240 jmc 1756: .Cm yes
1.191 millert 1757: or
1.240 jmc 1758: .Cm no
1759: (the default).
1.1 stevesk 1760: .It Cm StrictHostKeyChecking
1761: If this flag is set to
1.240 jmc 1762: .Cm yes ,
1.84 jmc 1763: .Xr ssh 1
1.1 stevesk 1764: will never automatically add host keys to the
1.50 djm 1765: .Pa ~/.ssh/known_hosts
1.1 stevesk 1766: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1767: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1768: though it can be annoying when the
1.1 stevesk 1769: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1770: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1771: frequently made.
1772: This option forces the user to manually
1773: add all new hosts.
1.255 jmc 1774: .Pp
1.1 stevesk 1775: If this flag is set to
1.254 djm 1776: .Dq accept-new
1.255 jmc 1777: then ssh will automatically add new host keys to the user
1.254 djm 1778: known hosts files, but will not permit connections to hosts with
1779: changed host keys.
1780: If this flag is set to
1781: .Dq no
1782: or
1783: .Dq off ,
1.255 jmc 1784: ssh will automatically add new host keys to the user known hosts files
1785: and allow connections to hosts with changed hostkeys to proceed,
1786: subject to some restrictions.
1.1 stevesk 1787: If this flag is set to
1.240 jmc 1788: .Cm ask
1789: (the default),
1.1 stevesk 1790: new host keys
1791: will be added to the user known host files only after the user
1792: has confirmed that is what they really want to do, and
1.84 jmc 1793: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1794: The host keys of
1795: known hosts will be verified automatically in all cases.
1.244 jmc 1796: .It Cm SyslogFacility
1797: Gives the facility code that is used when logging messages from
1798: .Xr ssh 1 .
1799: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1800: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1801: The default is USER.
1.26 markus 1802: .It Cm TCPKeepAlive
1803: Specifies whether the system should send TCP keepalive messages to the
1804: other side.
1805: If they are sent, death of the connection or crash of one
1806: of the machines will be properly noticed.
1807: However, this means that
1808: connections will die if the route is down temporarily, and some people
1809: find it annoying.
1810: .Pp
1811: The default is
1.240 jmc 1812: .Cm yes
1.26 markus 1813: (to send TCP keepalive messages), and the client will notice
1814: if the network goes down or the remote host dies.
1815: This is important in scripts, and many users want it too.
1816: .Pp
1817: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1818: .Cm no .
1.265 djm 1819: See also
1820: .Cm ServerAliveInterval
1821: for protocol-level keepalives.
1.65 reyk 1822: .It Cm Tunnel
1.95 stevesk 1823: Request
1.65 reyk 1824: .Xr tun 4
1.69 jmc 1825: device forwarding between the client and the server.
1.65 reyk 1826: The argument must be
1.240 jmc 1827: .Cm yes ,
1828: .Cm point-to-point
1.95 stevesk 1829: (layer 3),
1.240 jmc 1830: .Cm ethernet
1.95 stevesk 1831: (layer 2),
1.65 reyk 1832: or
1.240 jmc 1833: .Cm no
1834: (the default).
1.95 stevesk 1835: Specifying
1.240 jmc 1836: .Cm yes
1.95 stevesk 1837: requests the default tunnel mode, which is
1.240 jmc 1838: .Cm point-to-point .
1.65 reyk 1839: .It Cm TunnelDevice
1.95 stevesk 1840: Specifies the
1.65 reyk 1841: .Xr tun 4
1.95 stevesk 1842: devices to open on the client
1843: .Pq Ar local_tun
1844: and the server
1845: .Pq Ar remote_tun .
1846: .Pp
1847: The argument must be
1848: .Sm off
1849: .Ar local_tun Op : Ar remote_tun .
1850: .Sm on
1851: The devices may be specified by numerical ID or the keyword
1.240 jmc 1852: .Cm any ,
1.95 stevesk 1853: which uses the next available tunnel device.
1854: If
1855: .Ar remote_tun
1856: is not specified, it defaults to
1.240 jmc 1857: .Cm any .
1.95 stevesk 1858: The default is
1.240 jmc 1859: .Cm any:any .
1.201 djm 1860: .It Cm UpdateHostKeys
1.200 djm 1861: Specifies whether
1862: .Xr ssh 1
1863: should accept notifications of additional hostkeys from the server sent
1864: after authentication has completed and add them to
1865: .Cm UserKnownHostsFile .
1866: The argument must be
1.240 jmc 1867: .Cm yes ,
1868: .Cm no
1.320 djm 1869: or
1.240 jmc 1870: .Cm ask .
1.320 djm 1871: This option allows learning alternate hostkeys for a server
1.201 djm 1872: and supports graceful key rotation by allowing a server to send replacement
1873: public keys before old ones are removed.
1.336 djm 1874: .Pp
1.200 djm 1875: Additional hostkeys are only accepted if the key used to authenticate the
1.336 djm 1876: host was already trusted or explicitly accepted by the user, the host was
1877: authenticated via
1878: .Cm UserKnownHostsFile
1879: (i.e. not
1880: .Cm GlobalKnownHostsFile )
1881: and the host was authenticated using a plain key and not a certificate.
1.320 djm 1882: .Pp
1883: .Cm UpdateHostKeys
1.321 jmc 1884: is enabled by default if the user has not overridden the default
1.320 djm 1885: .Cm UserKnownHostsFile
1.335 djm 1886: setting and has not enabled
1887: .Cm VerifyHostKeyDNS ,
1888: otherwise
1.320 djm 1889: .Cm UpdateHostKeys
1890: will be set to
1.334 djm 1891: .Cm no .
1.320 djm 1892: .Pp
1.204 djm 1893: If
1894: .Cm UpdateHostKeys
1895: is set to
1.240 jmc 1896: .Cm ask ,
1.204 djm 1897: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1898: Confirmation is currently incompatible with
1899: .Cm ControlPersist ,
1900: and will be disabled if it is enabled.
1.200 djm 1901: .Pp
1902: Presently, only
1903: .Xr sshd 8
1904: from OpenSSH 6.8 and greater support the
1.240 jmc 1905: .Qq hostkeys@openssh.com
1.200 djm 1906: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1907: .It Cm User
1908: Specifies the user to log in as.
1909: This can be useful when a different user name is used on different machines.
1910: This saves the trouble of
1911: having to remember to give the user name on the command line.
1912: .It Cm UserKnownHostsFile
1.151 djm 1913: Specifies one or more files to use for the user
1914: host key database, separated by whitespace.
1.329 dtucker 1915: Each filename may use tilde notation to refer to the user's home directory,
1916: the tokens described in the
1917: .Sx TOKENS
1918: section and environment variables as described in the
1919: .Sx ENVIRONMENT VARIABLES
1920: section.
1.151 djm 1921: The default is
1922: .Pa ~/.ssh/known_hosts ,
1923: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1924: .It Cm VerifyHostKeyDNS
1925: Specifies whether to verify the remote key using DNS and SSHFP resource
1926: records.
1.24 jakob 1927: If this option is set to
1.240 jmc 1928: .Cm yes ,
1.25 jmc 1929: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1930: from DNS.
1931: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1932: .Cm ask .
1.24 jakob 1933: If this option is set to
1.240 jmc 1934: .Cm ask ,
1.24 jakob 1935: information on fingerprint match will be displayed, but the user will still
1936: need to confirm new host keys according to the
1937: .Cm StrictHostKeyChecking
1938: option.
1.8 jakob 1939: The default is
1.240 jmc 1940: .Cm no .
1.84 jmc 1941: .Pp
1.240 jmc 1942: See also
1943: .Sx VERIFYING HOST KEYS
1944: in
1.84 jmc 1945: .Xr ssh 1 .
1.111 grunk 1946: .It Cm VisualHostKey
1947: If this flag is set to
1.240 jmc 1948: .Cm yes ,
1.111 grunk 1949: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1950: printed in addition to the fingerprint string at login and
1.114 stevesk 1951: for unknown host keys.
1.111 grunk 1952: If this flag is set to
1.240 jmc 1953: .Cm no
1954: (the default),
1.114 stevesk 1955: no fingerprint strings are printed at login and
1.197 djm 1956: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1957: .It Cm XAuthLocation
1.5 stevesk 1958: Specifies the full pathname of the
1.1 stevesk 1959: .Xr xauth 1
1960: program.
1961: The default is
1962: .Pa /usr/X11R6/bin/xauth .
1963: .El
1.86 jmc 1964: .Sh PATTERNS
1965: A
1966: .Em pattern
1967: consists of zero or more non-whitespace characters,
1968: .Sq *
1969: (a wildcard that matches zero or more characters),
1970: or
1971: .Sq ?\&
1972: (a wildcard that matches exactly one character).
1973: For example, to specify a set of declarations for any host in the
1.240 jmc 1974: .Qq .co.uk
1.86 jmc 1975: set of domains,
1976: the following pattern could be used:
1977: .Pp
1978: .Dl Host *.co.uk
1979: .Pp
1980: The following pattern
1981: would match any host in the 192.168.0.[0-9] network range:
1982: .Pp
1983: .Dl Host 192.168.0.?
1984: .Pp
1985: A
1986: .Em pattern-list
1987: is a comma-separated list of patterns.
1988: Patterns within pattern-lists may be negated
1989: by preceding them with an exclamation mark
1990: .Pq Sq !\& .
1991: For example,
1.174 djm 1992: to allow a key to be used from anywhere within an organization
1.86 jmc 1993: except from the
1.240 jmc 1994: .Qq dialup
1.86 jmc 1995: pool,
1996: the following entry (in authorized_keys) could be used:
1997: .Pp
1998: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1999: .Pp
2000: Note that a negated match will never produce a positive result by itself.
2001: For example, attempting to match
2002: .Qq host3
2003: against the following pattern-list will fail:
2004: .Pp
2005: .Dl from=\&"!host1,!host2\&"
2006: .Pp
2007: The solution here is to include a term that will yield a positive match,
2008: such as a wildcard:
2009: .Pp
2010: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 2011: .Sh TOKENS
2012: Arguments to some keywords can make use of tokens,
2013: which are expanded at runtime:
2014: .Pp
2015: .Bl -tag -width XXXX -offset indent -compact
2016: .It %%
2017: A literal
2018: .Sq % .
2019: .It \&%C
1.257 jmc 2020: Hash of %l%h%p%r.
1.239 jmc 2021: .It %d
2022: Local user's home directory.
1.339 djm 2023: .It %f
2024: The fingerprint of the server's host key.
2025: .It %H
2026: The
2027: .Pa known_hosts
2028: hostname or address that is being searched for.
1.239 jmc 2029: .It %h
2030: The remote hostname.
1.340 jmc 2031: .It \%%I
1.339 djm 2032: A string describing the reason for a
2033: .Cm KnownHostsCommand
1.340 jmc 2034: execution: either
2035: .Cm ADDRESS
1.339 djm 2036: when looking up a host by address (only when
2037: .Cm CheckHostIP
2038: is enabled),
1.340 jmc 2039: .Cm HOSTNAME
2040: when searching by hostname, or
2041: .Cm ORDER
1.339 djm 2042: when preparing the host key algorithm preference list to use for the
2043: destination host.
1.239 jmc 2044: .It %i
2045: The local user ID.
1.339 djm 2046: .It %K
2047: The base64 encoded host key.
1.330 dtucker 2048: .It %k
1.350 jsg 2049: The host key alias if specified, otherwise the original remote hostname given
1.330 dtucker 2050: on the command line.
1.239 jmc 2051: .It %L
2052: The local hostname.
2053: .It %l
2054: The local hostname, including the domain name.
2055: .It %n
2056: The original remote hostname, as given on the command line.
2057: .It %p
2058: The remote port.
2059: .It %r
2060: The remote username.
1.261 djm 2061: .It \&%T
2062: The local
2063: .Xr tun 4
2064: or
2065: .Xr tap 4
2066: network interface assigned if
1.262 jmc 2067: tunnel forwarding was requested, or
2068: .Qq NONE
1.261 djm 2069: otherwise.
1.339 djm 2070: .It %t
2071: The type of the server host key, e.g.
2072: .Cm ssh-ed25519
1.239 jmc 2073: .It %u
2074: The local username.
2075: .El
2076: .Pp
1.323 dtucker 2077: .Cm CertificateFile ,
2078: .Cm ControlPath ,
2079: .Cm IdentityAgent ,
2080: .Cm IdentityFile ,
1.339 djm 2081: .Cm KnownHostsCommand ,
1.325 jmc 2082: .Cm LocalForward ,
1.324 dtucker 2083: .Cm Match exec ,
2084: .Cm RemoteCommand ,
1.329 dtucker 2085: .Cm RemoteForward ,
1.323 dtucker 2086: and
1.331 jmc 2087: .Cm UserKnownHostsFile
1.349 dtucker 2088: accept the tokens %%, %C, %d, %h, %i, %k, %L, %l, %n, %p, %r, and %u.
1.239 jmc 2089: .Pp
1.339 djm 2090: .Cm KnownHostsCommand
2091: additionally accepts the tokens %f, %H, %I, %K and %t.
2092: .Pp
1.295 jmc 2093: .Cm Hostname
1.239 jmc 2094: accepts the tokens %% and %h.
2095: .Pp
2096: .Cm LocalCommand
1.323 dtucker 2097: accepts all tokens.
1.239 jmc 2098: .Pp
2099: .Cm ProxyCommand
1.303 djm 2100: accepts the tokens %%, %h, %n, %p, and %r.
1.326 dtucker 2101: .Sh ENVIRONMENT VARIABLES
2102: Arguments to some keywords can be expanded at runtime from environment
2103: variables on the client by enclosing them in
2104: .Ic ${} ,
2105: for example
2106: .Ic ${HOME}/.ssh
2107: would refer to the user's .ssh directory.
2108: If a specified environment variable does not exist then an error will be
2109: returned and the setting for that keyword will be ignored.
2110: .Pp
2111: The keywords
2112: .Cm CertificateFile ,
2113: .Cm ControlPath ,
1.329 dtucker 2114: .Cm IdentityAgent ,
1.352 jmc 2115: .Cm IdentityFile ,
1.339 djm 2116: .Cm KnownHostsCommand ,
1.326 dtucker 2117: and
1.329 dtucker 2118: .Cm UserKnownHostsFile
1.326 dtucker 2119: support environment variables.
2120: The keywords
2121: .Cm LocalForward
2122: and
2123: .Cm RemoteForward
2124: support environment variables only for Unix domain socket paths.
1.1 stevesk 2125: .Sh FILES
2126: .Bl -tag -width Ds
1.50 djm 2127: .It Pa ~/.ssh/config
1.1 stevesk 2128: This is the per-user configuration file.
2129: The format of this file is described above.
1.84 jmc 2130: This file is used by the SSH client.
1.30 djm 2131: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 2132: read/write for the user, and not writable by others.
1.1 stevesk 2133: .It Pa /etc/ssh/ssh_config
2134: Systemwide configuration file.
2135: This file provides defaults for those
2136: values that are not specified in the user's configuration file, and
2137: for those users who do not have a configuration file.
2138: This file must be world-readable.
2139: .El
1.13 jmc 2140: .Sh SEE ALSO
2141: .Xr ssh 1
1.1 stevesk 2142: .Sh AUTHORS
1.240 jmc 2143: .An -nosplit
1.1 stevesk 2144: OpenSSH is a derivative of the original and free
1.240 jmc 2145: ssh 1.2.12 release by
2146: .An Tatu Ylonen .
2147: .An Aaron Campbell , Bob Beck , Markus Friedl ,
2148: .An Niels Provos , Theo de Raadt
2149: and
2150: .An Dug Song
1.1 stevesk 2151: removed many bugs, re-added newer features and
2152: created OpenSSH.
1.240 jmc 2153: .An Markus Friedl
2154: contributed the support for SSH protocol versions 1.5 and 2.0.
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