Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.315
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
18: .\" are met:
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.
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
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
35: .\"
1.315 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.314 2020/01/21 12:40:04 naddy Exp $
! 37: .Dd $Mdocdate: January 21 2020 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
1.310 jmc 42: .Nd OpenSSH client configuration file
1.1 stevesk 43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.287 djm 142: .Cm final ,
1.176 djm 143: .Cm exec ,
1.169 djm 144: .Cm host ,
145: .Cm originalhost ,
146: .Cm user ,
147: and
148: .Cm localuser .
1.193 djm 149: The
150: .Cm all
151: criteria must appear alone or immediately after
1.287 djm 152: .Cm canonical
153: or
154: .Cm final .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
1.288 jmc 157: .Cm all ,
158: .Cm canonical ,
1.193 djm 159: and
1.287 djm 160: .Cm final
1.193 djm 161: require an argument.
162: Criteria may be negated by prepending an exclamation mark
163: .Pq Sq !\& .
1.169 djm 164: .Pp
1.177 jmc 165: The
1.193 djm 166: .Cm canonical
1.210 dtucker 167: keyword matches only when the configuration file is being re-parsed
1.193 djm 168: after hostname canonicalization (see the
169: .Cm CanonicalizeHostname
1.288 jmc 170: option).
1.193 djm 171: This may be useful to specify conditions that work with canonical host
172: names only.
1.287 djm 173: .Pp
174: The
175: .Cm final
176: keyword requests that the configuration be re-parsed (regardless of whether
177: .Cm CanonicalizeHostname
178: is enabled), and matches only during this final pass.
179: If
180: .Cm CanonicalizeHostname
181: is enabled, then
182: .Cm canonical
183: and
184: .Cm final
185: match during the same pass.
186: .Pp
1.193 djm 187: The
1.176 djm 188: .Cm exec
1.177 jmc 189: keyword executes the specified command under the user's shell.
1.169 djm 190: If the command returns a zero exit status then the condition is considered true.
191: Commands containing whitespace characters must be quoted.
1.239 jmc 192: Arguments to
193: .Cm exec
194: accept the tokens described in the
195: .Sx TOKENS
196: section.
1.169 djm 197: .Pp
198: The other keywords' criteria must be single entries or comma-separated
199: lists and may use the wildcard and negation operators described in the
200: .Sx PATTERNS
201: section.
202: The criteria for the
203: .Cm host
204: keyword are matched against the target hostname, after any substitution
205: by the
1.295 jmc 206: .Cm Hostname
1.193 djm 207: or
208: .Cm CanonicalizeHostname
209: options.
1.169 djm 210: The
211: .Cm originalhost
212: keyword matches against the hostname as it was specified on the command-line.
213: The
214: .Cm user
215: keyword matches against the target username on the remote host.
216: The
217: .Cm localuser
218: keyword matches against the name of the local user running
219: .Xr ssh 1
220: (this keyword may be useful in system-wide
221: .Nm
222: files).
1.222 jcs 223: .It Cm AddKeysToAgent
224: Specifies whether keys should be automatically added to a running
1.223 jmc 225: .Xr ssh-agent 1 .
1.222 jcs 226: If this option is set to
1.240 jmc 227: .Cm yes
1.222 jcs 228: and a key is loaded from a file, the key and its passphrase are added to
229: the agent with the default lifetime, as if by
230: .Xr ssh-add 1 .
231: If this option is set to
1.240 jmc 232: .Cm ask ,
233: .Xr ssh 1
1.222 jcs 234: will require confirmation using the
235: .Ev SSH_ASKPASS
236: program before adding a key (see
237: .Xr ssh-add 1
238: for details).
239: If this option is set to
1.240 jmc 240: .Cm confirm ,
1.222 jcs 241: each use of the key must be confirmed, as if the
242: .Fl c
243: option was specified to
244: .Xr ssh-add 1 .
245: If this option is set to
1.240 jmc 246: .Cm no ,
1.222 jcs 247: no keys are added to the agent.
248: The argument must be
1.240 jmc 249: .Cm yes ,
250: .Cm confirm ,
251: .Cm ask ,
1.222 jcs 252: or
1.240 jmc 253: .Cm no
254: (the default).
1.10 djm 255: .It Cm AddressFamily
1.11 jmc 256: Specifies which address family to use when connecting.
257: Valid arguments are
1.240 jmc 258: .Cm any
259: (the default),
260: .Cm inet
1.84 jmc 261: (use IPv4 only), or
1.240 jmc 262: .Cm inet6
1.40 jmc 263: (use IPv6 only).
1.1 stevesk 264: .It Cm BatchMode
265: If set to
1.240 jmc 266: .Cm yes ,
1.1 stevesk 267: passphrase/password querying will be disabled.
268: This option is useful in scripts and other batch jobs where no user
269: is present to supply the password.
270: The argument must be
1.240 jmc 271: .Cm yes
1.1 stevesk 272: or
1.240 jmc 273: .Cm no
274: (the default).
1.268 jmc 275: .It Cm BindAddress
276: Use the specified address on the local machine as the source address of
277: the connection.
278: Only useful on systems with more than one address.
279: .It Cm BindInterface
280: Use the address of the specified interface on the local machine as the
281: source address of the connection.
1.171 djm 282: .It Cm CanonicalDomains
1.172 jmc 283: When
1.173 djm 284: .Cm CanonicalizeHostname
1.171 djm 285: is enabled, this option specifies the list of domain suffixes in which to
286: search for the specified destination host.
1.173 djm 287: .It Cm CanonicalizeFallbackLocal
1.174 djm 288: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 289: The default,
1.240 jmc 290: .Cm yes ,
1.172 jmc 291: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 292: search rules.
293: A value of
1.240 jmc 294: .Cm no
1.171 djm 295: will cause
296: .Xr ssh 1
297: to fail instantly if
1.173 djm 298: .Cm CanonicalizeHostname
1.171 djm 299: is enabled and the target hostname cannot be found in any of the domains
300: specified by
301: .Cm CanonicalDomains .
1.173 djm 302: .It Cm CanonicalizeHostname
1.174 djm 303: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 304: The default,
1.240 jmc 305: .Cm no ,
1.171 djm 306: is not to perform any name rewriting and let the system resolver handle all
307: hostname lookups.
308: If set to
1.240 jmc 309: .Cm yes
1.171 djm 310: then, for connections that do not use a
1.284 djm 311: .Cm ProxyCommand
312: or
313: .Cm ProxyJump ,
1.171 djm 314: .Xr ssh 1
1.173 djm 315: will attempt to canonicalize the hostname specified on the command line
1.171 djm 316: using the
317: .Cm CanonicalDomains
318: suffixes and
1.173 djm 319: .Cm CanonicalizePermittedCNAMEs
1.171 djm 320: rules.
321: If
1.173 djm 322: .Cm CanonicalizeHostname
1.171 djm 323: is set to
1.240 jmc 324: .Cm always ,
1.174 djm 325: then canonicalization is applied to proxied connections too.
1.185 djm 326: .Pp
1.193 djm 327: If this option is enabled, then the configuration files are processed
328: again using the new target name to pick up any new configuration in matching
1.185 djm 329: .Cm Host
1.193 djm 330: and
331: .Cm Match
1.185 djm 332: stanzas.
1.173 djm 333: .It Cm CanonicalizeMaxDots
1.172 jmc 334: Specifies the maximum number of dot characters in a hostname before
1.174 djm 335: canonicalization is disabled.
1.240 jmc 336: The default, 1,
1.172 jmc 337: allows a single dot (i.e. hostname.subdomain).
1.173 djm 338: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 339: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 340: canonicalizing hostnames.
1.171 djm 341: The rules consist of one or more arguments of
1.172 jmc 342: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 343: where
344: .Ar source_domain_list
1.174 djm 345: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 346: and
347: .Ar target_domain_list
1.172 jmc 348: is a pattern-list of domains that they may resolve to.
1.171 djm 349: .Pp
350: For example,
1.240 jmc 351: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 352: will allow hostnames matching
1.240 jmc 353: .Qq *.a.example.com
1.173 djm 354: to be canonicalized to names in the
1.240 jmc 355: .Qq *.b.example.com
1.171 djm 356: or
1.240 jmc 357: .Qq *.c.example.com
1.171 djm 358: domains.
1.283 jmc 359: .It Cm CASignatureAlgorithms
360: Specifies which algorithms are allowed for signing of certificates
361: by certificate authorities (CAs).
362: The default is:
363: .Bd -literal -offset indent
1.297 djm 364: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.283 jmc 365: ssh-ed25519,rsa-sha2-512,rsa-sha2-256,ssh-rsa
366: .Ed
367: .Pp
368: .Xr ssh 1
369: will not accept host certificates signed using algorithms other than those
370: specified.
1.221 djm 371: .It Cm CertificateFile
372: Specifies a file from which the user's certificate is read.
373: A corresponding private key must be provided separately in order
374: to use this certificate either
375: from an
376: .Cm IdentityFile
377: directive or
378: .Fl i
379: flag to
380: .Xr ssh 1 ,
381: via
382: .Xr ssh-agent 1 ,
383: or via a
1.305 naddy 384: .Cm PKCS11Provider
385: or
386: .Cm SecurityKeyProvider .
1.221 djm 387: .Pp
1.239 jmc 388: Arguments to
389: .Cm CertificateFile
390: may use the tilde syntax to refer to a user's home directory
391: or the tokens described in the
392: .Sx TOKENS
393: section.
1.221 djm 394: .Pp
395: It is possible to have multiple certificate files specified in
396: configuration files; these certificates will be tried in sequence.
397: Multiple
398: .Cm CertificateFile
399: directives will add to the list of certificates used for
400: authentication.
1.1 stevesk 401: .It Cm ChallengeResponseAuthentication
1.82 jmc 402: Specifies whether to use challenge-response authentication.
1.1 stevesk 403: The argument to this keyword must be
1.240 jmc 404: .Cm yes
405: (the default)
1.1 stevesk 406: or
1.240 jmc 407: .Cm no .
1.1 stevesk 408: .It Cm CheckHostIP
1.240 jmc 409: If set to
410: .Cm yes
411: (the default),
1.84 jmc 412: .Xr ssh 1
413: will additionally check the host IP address in the
1.1 stevesk 414: .Pa known_hosts
415: file.
1.240 jmc 416: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 417: and will add addresses of destination hosts to
418: .Pa ~/.ssh/known_hosts
419: in the process, regardless of the setting of
420: .Cm StrictHostKeyChecking .
1.107 grunk 421: If the option is set to
1.240 jmc 422: .Cm no ,
1.1 stevesk 423: the check will not be executed.
424: .It Cm Ciphers
1.245 djm 425: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 426: Multiple ciphers must be comma-separated.
1.299 kn 427: If the specified list begins with a
1.214 djm 428: .Sq +
429: character, then the specified ciphers will be appended to the default set
430: instead of replacing them.
1.299 kn 431: If the specified list begins with a
1.241 djm 432: .Sq -
433: character, then the specified ciphers (including wildcards) will be removed
434: from the default set instead of replacing them.
1.301 naddy 435: If the specified list begins with a
436: .Sq ^
437: character, then the specified ciphers will be placed at the head of the
438: default set.
1.214 djm 439: .Pp
1.180 djm 440: The supported ciphers are:
1.240 jmc 441: .Bd -literal -offset indent
1.186 naddy 442: 3des-cbc
443: aes128-cbc
444: aes192-cbc
445: aes256-cbc
446: aes128-ctr
447: aes192-ctr
448: aes256-ctr
449: aes128-gcm@openssh.com
450: aes256-gcm@openssh.com
451: chacha20-poly1305@openssh.com
1.240 jmc 452: .Ed
1.180 djm 453: .Pp
1.84 jmc 454: The default is:
1.186 naddy 455: .Bd -literal -offset indent
1.215 jmc 456: chacha20-poly1305@openssh.com,
1.186 naddy 457: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 458: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 459: .Ed
1.180 djm 460: .Pp
1.240 jmc 461: The list of available ciphers may also be obtained using
462: .Qq ssh -Q cipher .
1.1 stevesk 463: .It Cm ClearAllForwardings
1.84 jmc 464: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 465: specified in the configuration files or on the command line be
1.7 jmc 466: cleared.
467: This option is primarily useful when used from the
1.84 jmc 468: .Xr ssh 1
1.1 stevesk 469: command line to clear port forwardings set in
470: configuration files, and is automatically set by
471: .Xr scp 1
472: and
473: .Xr sftp 1 .
474: The argument must be
1.240 jmc 475: .Cm yes
1.1 stevesk 476: or
1.240 jmc 477: .Cm no
478: (the default).
1.1 stevesk 479: .It Cm Compression
480: Specifies whether to use compression.
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).
1.247 naddy 486: .It Cm ConnectionAttempts
487: Specifies the number of tries (one per second) to make before exiting.
488: The argument must be an integer.
489: This may be useful in scripts if the connection sometimes fails.
490: The default is 1.
1.9 djm 491: .It Cm ConnectTimeout
1.84 jmc 492: Specifies the timeout (in seconds) used when connecting to the
493: SSH server, instead of using the default system TCP timeout.
1.302 djm 494: This timeout is applied both to establishing the connection and to performing
495: the initial SSH protocol handshake and key exchange.
1.36 djm 496: .It Cm ControlMaster
497: Enables the sharing of multiple sessions over a single network connection.
498: When set to
1.240 jmc 499: .Cm yes ,
1.84 jmc 500: .Xr ssh 1
1.36 djm 501: will listen for connections on a control socket specified using the
502: .Cm ControlPath
503: argument.
504: Additional sessions can connect to this socket using the same
505: .Cm ControlPath
506: with
507: .Cm ControlMaster
508: set to
1.240 jmc 509: .Cm no
1.38 jmc 510: (the default).
1.64 jmc 511: These sessions will try to reuse the master instance's network connection
1.63 djm 512: rather than initiating new ones, but will fall back to connecting normally
513: if the control socket does not exist, or is not listening.
514: .Pp
1.37 djm 515: Setting this to
1.240 jmc 516: .Cm ask
517: will cause
518: .Xr ssh 1
1.206 jmc 519: to listen for control connections, but require confirmation using
520: .Xr ssh-askpass 1 .
1.51 jakob 521: If the
522: .Cm ControlPath
1.84 jmc 523: cannot be opened,
1.240 jmc 524: .Xr ssh 1
525: will continue without connecting to a master instance.
1.58 djm 526: .Pp
527: X11 and
1.59 jmc 528: .Xr ssh-agent 1
1.58 djm 529: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 530: display and agent forwarded will be the one belonging to the master
1.59 jmc 531: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 532: .Pp
533: Two additional options allow for opportunistic multiplexing: try to use a
534: master connection but fall back to creating a new one if one does not already
535: exist.
536: These options are:
1.240 jmc 537: .Cm auto
1.56 djm 538: and
1.240 jmc 539: .Cm autoask .
1.56 djm 540: The latter requires confirmation like the
1.240 jmc 541: .Cm ask
1.56 djm 542: option.
1.36 djm 543: .It Cm ControlPath
1.55 djm 544: Specify the path to the control socket used for connection sharing as described
545: in the
1.36 djm 546: .Cm ControlMaster
1.57 djm 547: section above or the string
1.240 jmc 548: .Cm none
1.57 djm 549: to disable connection sharing.
1.239 jmc 550: Arguments to
551: .Cm ControlPath
552: may use the tilde syntax to refer to a user's home directory
553: or the tokens described in the
554: .Sx TOKENS
555: section.
1.56 djm 556: It is recommended that any
557: .Cm ControlPath
558: used for opportunistic connection sharing include
1.195 djm 559: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
560: that is not writable by other users.
1.56 djm 561: This ensures that shared connections are uniquely identified.
1.137 djm 562: .It Cm ControlPersist
563: When used in conjunction with
564: .Cm ControlMaster ,
565: specifies that the master connection should remain open
566: in the background (waiting for future client connections)
567: after the initial client connection has been closed.
568: If set to
1.314 naddy 569: .Cm no
570: (the default),
1.137 djm 571: then the master connection will not be placed into the background,
572: and will close as soon as the initial client connection is closed.
573: If set to
1.240 jmc 574: .Cm yes
575: or 0,
1.137 djm 576: then the master connection will remain in the background indefinitely
577: (until killed or closed via a mechanism such as the
1.240 jmc 578: .Qq ssh -O exit ) .
1.137 djm 579: If set to a time in seconds, or a time in any of the formats documented in
580: .Xr sshd_config 5 ,
581: then the backgrounded master connection will automatically terminate
582: after it has remained idle (with no client connections) for the
583: specified time.
1.38 jmc 584: .It Cm DynamicForward
1.74 jmc 585: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 586: over the secure channel, and the application
587: protocol is then used to determine where to connect to from the
588: remote machine.
1.62 djm 589: .Pp
590: The argument must be
591: .Sm off
592: .Oo Ar bind_address : Oc Ar port .
593: .Sm on
1.138 djm 594: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 595: By default, the local port is bound in accordance with the
596: .Cm GatewayPorts
597: setting.
598: However, an explicit
599: .Ar bind_address
600: may be used to bind the connection to a specific address.
601: The
602: .Ar bind_address
603: of
1.240 jmc 604: .Cm localhost
1.62 djm 605: indicates that the listening port be bound for local use only, while an
606: empty address or
607: .Sq *
608: indicates that the port should be available from all interfaces.
609: .Pp
1.38 jmc 610: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 611: .Xr ssh 1
1.38 jmc 612: will act as a SOCKS server.
613: Multiple forwardings may be specified, and
614: additional forwardings can be given on the command line.
615: Only the superuser can forward privileged ports.
1.14 markus 616: .It Cm EnableSSHKeysign
617: Setting this option to
1.240 jmc 618: .Cm yes
1.14 markus 619: in the global client configuration file
620: .Pa /etc/ssh/ssh_config
621: enables the use of the helper program
622: .Xr ssh-keysign 8
623: during
624: .Cm HostbasedAuthentication .
625: The argument must be
1.240 jmc 626: .Cm yes
1.14 markus 627: or
1.240 jmc 628: .Cm no
629: (the default).
1.23 jmc 630: This option should be placed in the non-hostspecific section.
1.14 markus 631: See
632: .Xr ssh-keysign 8
633: for more information.
1.1 stevesk 634: .It Cm EscapeChar
635: Sets the escape character (default:
636: .Ql ~ ) .
637: The escape character can also
638: be set on the command line.
639: The argument should be a single character,
640: .Ql ^
641: followed by a letter, or
1.240 jmc 642: .Cm none
1.1 stevesk 643: to disable the escape
644: character entirely (making the connection transparent for binary
645: data).
1.96 markus 646: .It Cm ExitOnForwardFailure
647: Specifies whether
648: .Xr ssh 1
649: should terminate the connection if it cannot set up all requested
1.216 djm 650: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 651: if either end is unable to bind and listen on a specified port).
1.216 djm 652: Note that
653: .Cm ExitOnForwardFailure
654: does not apply to connections made over port forwardings and will not,
655: for example, cause
656: .Xr ssh 1
657: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 658: The argument must be
1.240 jmc 659: .Cm yes
1.96 markus 660: or
1.240 jmc 661: .Cm no
662: (the default).
1.197 djm 663: .It Cm FingerprintHash
664: Specifies the hash algorithm used when displaying key fingerprints.
665: Valid options are:
1.240 jmc 666: .Cm md5
1.197 djm 667: and
1.240 jmc 668: .Cm sha256
669: (the default).
1.1 stevesk 670: .It Cm ForwardAgent
671: Specifies whether the connection to the authentication agent (if any)
672: will be forwarded to the remote machine.
1.312 djm 673: The argument may be
674: .Cm yes ,
1.240 jmc 675: .Cm no
1.312 djm 676: (the default),
677: an explicit path to an agent socket or the name of an environment variable
678: (beginning with
679: .Sq $ )
680: in which to find the path.
1.3 stevesk 681: .Pp
1.7 jmc 682: Agent forwarding should be enabled with caution.
683: Users with the ability to bypass file permissions on the remote host
684: (for the agent's Unix-domain socket)
685: can access the local agent through the forwarded connection.
686: An attacker cannot obtain key material from the agent,
1.3 stevesk 687: however they can perform operations on the keys that enable them to
688: authenticate using the identities loaded into the agent.
1.1 stevesk 689: .It Cm ForwardX11
690: Specifies whether X11 connections will be automatically redirected
691: over the secure channel and
692: .Ev DISPLAY
693: set.
694: The argument must be
1.240 jmc 695: .Cm yes
1.1 stevesk 696: or
1.240 jmc 697: .Cm no
698: (the default).
1.3 stevesk 699: .Pp
1.7 jmc 700: X11 forwarding should be enabled with caution.
701: Users with the ability to bypass file permissions on the remote host
1.22 markus 702: (for the user's X11 authorization database)
1.7 jmc 703: can access the local X11 display through the forwarded connection.
1.22 markus 704: An attacker may then be able to perform activities such as keystroke monitoring
705: if the
706: .Cm ForwardX11Trusted
707: option is also enabled.
1.134 djm 708: .It Cm ForwardX11Timeout
1.135 jmc 709: Specify a timeout for untrusted X11 forwarding
710: using the format described in the
1.240 jmc 711: .Sx TIME FORMATS
712: section of
1.134 djm 713: .Xr sshd_config 5 .
714: X11 connections received by
715: .Xr ssh 1
716: after this time will be refused.
1.285 djm 717: Setting
718: .Cm ForwardX11Timeout
719: to zero will disable the timeout and permit X11 forwarding for the life
720: of the connection.
1.134 djm 721: The default is to disable untrusted X11 forwarding after twenty minutes has
722: elapsed.
1.22 markus 723: .It Cm ForwardX11Trusted
1.34 jmc 724: If this option is set to
1.240 jmc 725: .Cm yes ,
1.84 jmc 726: remote X11 clients will have full access to the original X11 display.
1.42 djm 727: .Pp
1.22 markus 728: If this option is set to
1.240 jmc 729: .Cm no
730: (the default),
1.84 jmc 731: remote X11 clients will be considered untrusted and prevented
1.22 markus 732: from stealing or tampering with data belonging to trusted X11
733: clients.
1.42 djm 734: Furthermore, the
735: .Xr xauth 1
736: token used for the session will be set to expire after 20 minutes.
737: Remote clients will be refused access after this time.
1.22 markus 738: .Pp
739: See the X11 SECURITY extension specification for full details on
740: the restrictions imposed on untrusted clients.
1.1 stevesk 741: .It Cm GatewayPorts
742: Specifies whether remote hosts are allowed to connect to local
743: forwarded ports.
744: By default,
1.84 jmc 745: .Xr ssh 1
1.7 jmc 746: binds local port forwardings to the loopback address.
747: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 748: .Cm GatewayPorts
1.84 jmc 749: can be used to specify that ssh
1.1 stevesk 750: should bind local port forwardings to the wildcard address,
751: thus allowing remote hosts to connect to forwarded ports.
752: The argument must be
1.240 jmc 753: .Cm yes
1.1 stevesk 754: or
1.240 jmc 755: .Cm no
756: (the default).
1.1 stevesk 757: .It Cm GlobalKnownHostsFile
1.151 djm 758: Specifies one or more files to use for the global
759: host key database, separated by whitespace.
760: The default is
761: .Pa /etc/ssh/ssh_known_hosts ,
762: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 763: .It Cm GSSAPIAuthentication
1.27 markus 764: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 765: The default is
1.240 jmc 766: .Cm no .
1.18 markus 767: .It Cm GSSAPIDelegateCredentials
768: Forward (delegate) credentials to the server.
769: The default is
1.240 jmc 770: .Cm no .
1.44 djm 771: .It Cm HashKnownHosts
772: Indicates that
1.84 jmc 773: .Xr ssh 1
1.44 djm 774: should hash host names and addresses when they are added to
1.50 djm 775: .Pa ~/.ssh/known_hosts .
1.44 djm 776: These hashed names may be used normally by
1.84 jmc 777: .Xr ssh 1
1.44 djm 778: and
1.84 jmc 779: .Xr sshd 8 ,
1.315 ! djm 780: but they do not visually reveal identifying information should the
! 781: file's contents be disclosed.
1.44 djm 782: The default is
1.240 jmc 783: .Cm no .
1.97 jmc 784: Note that existing names and addresses in known hosts files
785: will not be converted automatically,
786: but may be manually hashed using
1.45 djm 787: .Xr ssh-keygen 1 .
1.1 stevesk 788: .It Cm HostbasedAuthentication
789: Specifies whether to try rhosts based authentication with public key
790: authentication.
791: The argument must be
1.240 jmc 792: .Cm yes
1.1 stevesk 793: or
1.240 jmc 794: .Cm no
795: (the default).
1.202 djm 796: .It Cm HostbasedKeyTypes
797: Specifies the key types that will be used for hostbased authentication
1.279 djm 798: as a comma-separated list of patterns.
1.300 naddy 799: Alternately if the specified list begins with a
1.214 djm 800: .Sq +
801: character, then the specified key types will be appended to the default set
802: instead of replacing them.
1.300 naddy 803: If the specified list begins with a
1.241 djm 804: .Sq -
805: character, then the specified key types (including wildcards) will be removed
806: from the default set instead of replacing them.
1.301 naddy 807: If the specified list begins with a
808: .Sq ^
809: character, then the specified key types will be placed at the head of the
810: default set.
1.213 markus 811: The default for this option is:
812: .Bd -literal -offset 3n
813: ecdsa-sha2-nistp256-cert-v01@openssh.com,
814: ecdsa-sha2-nistp384-cert-v01@openssh.com,
815: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 816: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.213 markus 817: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 818: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 819: rsa-sha2-512-cert-v01@openssh.com,
820: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 821: ssh-rsa-cert-v01@openssh.com,
822: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 823: sk-ecdsa-sha2-nistp256@openssh.com,
824: ssh-ed25519,sk-ssh-ed25519@openssh.com,
825: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 826: .Ed
827: .Pp
1.202 djm 828: The
829: .Fl Q
830: option of
831: .Xr ssh 1
832: may be used to list supported key types.
1.1 stevesk 833: .It Cm HostKeyAlgorithms
1.226 jmc 834: Specifies the host key algorithms
1.1 stevesk 835: that the client wants to use in order of preference.
1.300 naddy 836: Alternately if the specified list begins with a
1.214 djm 837: .Sq +
838: character, then the specified key types will be appended to the default set
839: instead of replacing them.
1.300 naddy 840: If the specified list begins with a
1.241 djm 841: .Sq -
842: character, then the specified key types (including wildcards) will be removed
843: from the default set instead of replacing them.
1.301 naddy 844: If the specified list begins with a
845: .Sq ^
846: character, then the specified key types will be placed at the head of the
847: default set.
1.1 stevesk 848: The default for this option is:
1.139 djm 849: .Bd -literal -offset 3n
850: ecdsa-sha2-nistp256-cert-v01@openssh.com,
851: ecdsa-sha2-nistp384-cert-v01@openssh.com,
852: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 853: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1.183 naddy 854: ssh-ed25519-cert-v01@openssh.com,
1.311 naddy 855: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 856: rsa-sha2-512-cert-v01@openssh.com,
857: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 858: ssh-rsa-cert-v01@openssh.com,
1.139 djm 859: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.311 naddy 860: sk-ecdsa-sha2-nistp256@openssh.com,
861: ssh-ed25519,sk-ssh-ed25519@openssh.com,
862: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.139 djm 863: .Ed
1.145 djm 864: .Pp
865: If hostkeys are known for the destination host then this default is modified
866: to prefer their algorithms.
1.198 djm 867: .Pp
1.240 jmc 868: The list of available key types may also be obtained using
869: .Qq ssh -Q key .
1.1 stevesk 870: .It Cm HostKeyAlias
871: Specifies an alias that should be used instead of the
872: real host name when looking up or saving the host key
1.251 djm 873: in the host key database files and when validating host certificates.
1.84 jmc 874: This option is useful for tunneling SSH connections
1.1 stevesk 875: or for multiple servers running on a single host.
1.295 jmc 876: .It Cm Hostname
1.1 stevesk 877: Specifies the real host name to log into.
878: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 879: Arguments to
1.295 jmc 880: .Cm Hostname
1.239 jmc 881: accept the tokens described in the
882: .Sx TOKENS
883: section.
1.1 stevesk 884: Numeric IP addresses are also permitted (both on the command line and in
1.295 jmc 885: .Cm Hostname
1.1 stevesk 886: specifications).
1.239 jmc 887: The default is the name given on the command line.
1.29 markus 888: .It Cm IdentitiesOnly
889: Specifies that
1.84 jmc 890: .Xr ssh 1
1.304 djm 891: should only use the configured authentication identity and certificate files
892: (either the default files, or those explicitly configured in the
1.31 jmc 893: .Nm
1.221 djm 894: files
895: or passed on the
896: .Xr ssh 1
1.304 djm 897: command-line),
1.84 jmc 898: even if
899: .Xr ssh-agent 1
1.159 djm 900: or a
901: .Cm PKCS11Provider
1.305 naddy 902: or
903: .Cm SecurityKeyProvider
1.29 markus 904: offers more identities.
905: The argument to this keyword must be
1.240 jmc 906: .Cm yes
1.29 markus 907: or
1.240 jmc 908: .Cm no
909: (the default).
1.84 jmc 910: This option is intended for situations where ssh-agent
1.29 markus 911: offers many different identities.
1.231 markus 912: .It Cm IdentityAgent
913: Specifies the
914: .Ux Ns -domain
915: socket used to communicate with the authentication agent.
916: .Pp
917: This option overrides the
1.240 jmc 918: .Ev SSH_AUTH_SOCK
1.231 markus 919: environment variable and can be used to select a specific agent.
920: Setting the socket name to
1.240 jmc 921: .Cm none
1.231 markus 922: disables the use of an authentication agent.
1.232 markus 923: If the string
1.240 jmc 924: .Qq SSH_AUTH_SOCK
1.232 markus 925: is specified, the location of the socket will be read from the
926: .Ev SSH_AUTH_SOCK
927: environment variable.
1.286 djm 928: Otherwise if the specified value begins with a
929: .Sq $
930: character, then it will be treated as an environment variable containing
931: the location of the socket.
1.231 markus 932: .Pp
1.239 jmc 933: Arguments to
934: .Cm IdentityAgent
935: may use the tilde syntax to refer to a user's home directory
936: or the tokens described in the
937: .Sx TOKENS
938: section.
1.67 jmc 939: .It Cm IdentityFile
1.313 naddy 940: Specifies a file from which the user's DSA, ECDSA, authenticator-hosted ECDSA,
941: Ed25519, authenticator-hosted Ed25519 or RSA authentication identity is read.
1.67 jmc 942: The default is
1.139 djm 943: .Pa ~/.ssh/id_dsa ,
1.183 naddy 944: .Pa ~/.ssh/id_ecdsa ,
1.305 naddy 945: .Pa ~/.ssh/id_ecdsa_sk ,
1.308 naddy 946: .Pa ~/.ssh/id_ed25519 ,
947: .Pa ~/.ssh/id_ed25519_sk
1.139 djm 948: and
1.245 djm 949: .Pa ~/.ssh/id_rsa .
1.67 jmc 950: Additionally, any identities represented by the authentication agent
1.165 djm 951: will be used for authentication unless
952: .Cm IdentitiesOnly
953: is set.
1.221 djm 954: If no certificates have been explicitly specified by
955: .Cm CertificateFile ,
1.129 djm 956: .Xr ssh 1
957: will try to load certificate information from the filename obtained by
958: appending
959: .Pa -cert.pub
960: to the path of a specified
961: .Cm IdentityFile .
1.90 djm 962: .Pp
1.239 jmc 963: Arguments to
964: .Cm IdentityFile
965: may use the tilde syntax to refer to a user's home directory
966: or the tokens described in the
967: .Sx TOKENS
968: section.
1.90 djm 969: .Pp
1.67 jmc 970: It is possible to have
971: multiple identity files specified in configuration files; all these
972: identities will be tried in sequence.
1.152 djm 973: Multiple
974: .Cm IdentityFile
975: directives will add to the list of identities tried (this behaviour
976: differs from that of other configuration directives).
1.165 djm 977: .Pp
978: .Cm IdentityFile
979: may be used in conjunction with
980: .Cm IdentitiesOnly
981: to select which identities in an agent are offered during authentication.
1.221 djm 982: .Cm IdentityFile
983: may also be used in conjunction with
984: .Cm CertificateFile
985: in order to provide any certificate also needed for authentication with
986: the identity.
1.164 jmc 987: .It Cm IgnoreUnknown
988: Specifies a pattern-list of unknown options to be ignored if they are
989: encountered in configuration parsing.
990: This may be used to suppress errors if
991: .Nm
992: contains options that are unrecognised by
993: .Xr ssh 1 .
994: It is recommended that
995: .Cm IgnoreUnknown
996: be listed early in the configuration file as it will not be applied
997: to unknown options that appear before it.
1.229 djm 998: .It Cm Include
999: Include the specified configuration file(s).
1.230 jmc 1000: Multiple pathnames may be specified and each pathname may contain
1.281 kn 1001: .Xr glob 7
1.229 djm 1002: wildcards and, for user configurations, shell-like
1.240 jmc 1003: .Sq ~
1.229 djm 1004: references to user home directories.
1005: Files without absolute paths are assumed to be in
1006: .Pa ~/.ssh
1.230 jmc 1007: if included in a user configuration file or
1.229 djm 1008: .Pa /etc/ssh
1009: if included from the system configuration file.
1010: .Cm Include
1011: directive may appear inside a
1012: .Cm Match
1013: or
1014: .Cm Host
1015: block
1016: to perform conditional inclusion.
1.143 djm 1017: .It Cm IPQoS
1018: Specifies the IPv4 type-of-service or DSCP class for connections.
1019: Accepted values are
1.240 jmc 1020: .Cm af11 ,
1021: .Cm af12 ,
1022: .Cm af13 ,
1023: .Cm af21 ,
1024: .Cm af22 ,
1025: .Cm af23 ,
1026: .Cm af31 ,
1027: .Cm af32 ,
1028: .Cm af33 ,
1029: .Cm af41 ,
1030: .Cm af42 ,
1031: .Cm af43 ,
1032: .Cm cs0 ,
1033: .Cm cs1 ,
1034: .Cm cs2 ,
1035: .Cm cs3 ,
1036: .Cm cs4 ,
1037: .Cm cs5 ,
1038: .Cm cs6 ,
1039: .Cm cs7 ,
1040: .Cm ef ,
1041: .Cm lowdelay ,
1042: .Cm throughput ,
1043: .Cm reliability ,
1.253 djm 1044: a numeric value, or
1045: .Cm none
1046: to use the operating system default.
1.146 djm 1047: This option may take one or two arguments, separated by whitespace.
1.143 djm 1048: If one argument is specified, it is used as the packet class unconditionally.
1049: If two values are specified, the first is automatically selected for
1050: interactive sessions and the second for non-interactive sessions.
1051: The default is
1.269 job 1052: .Cm af21
1.272 jmc 1053: (Low-Latency Data)
1.143 djm 1054: for interactive sessions and
1.269 job 1055: .Cm cs1
1.272 jmc 1056: (Lower Effort)
1.143 djm 1057: for non-interactive sessions.
1.103 djm 1058: .It Cm KbdInteractiveAuthentication
1059: Specifies whether to use keyboard-interactive authentication.
1060: The argument to this keyword must be
1.240 jmc 1061: .Cm yes
1062: (the default)
1.103 djm 1063: or
1.240 jmc 1064: .Cm no .
1.39 djm 1065: .It Cm KbdInteractiveDevices
1066: Specifies the list of methods to use in keyboard-interactive authentication.
1067: Multiple method names must be comma-separated.
1068: The default is to use the server specified list.
1.85 jmc 1069: The methods available vary depending on what the server supports.
1070: For an OpenSSH server,
1071: it may be zero or more of:
1.240 jmc 1072: .Cm bsdauth ,
1073: .Cm pam ,
1.85 jmc 1074: and
1.240 jmc 1075: .Cm skey .
1.140 djm 1076: .It Cm KexAlgorithms
1077: Specifies the available KEX (Key Exchange) algorithms.
1078: Multiple algorithms must be comma-separated.
1.299 kn 1079: If the specified list begins with a
1.214 djm 1080: .Sq +
1081: character, then the specified methods will be appended to the default set
1082: instead of replacing them.
1.299 kn 1083: If the specified list begins with a
1.241 djm 1084: .Sq -
1085: character, then the specified methods (including wildcards) will be removed
1086: from the default set instead of replacing them.
1.301 naddy 1087: If the specified list begins with a
1088: .Sq ^
1089: character, then the specified methods will be placed at the head of the
1090: default set.
1.141 jmc 1091: The default is:
1092: .Bd -literal -offset indent
1.238 djm 1093: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1094: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1095: diffie-hellman-group-exchange-sha256,
1.266 djm 1096: diffie-hellman-group16-sha512,
1097: diffie-hellman-group18-sha512,
1098: diffie-hellman-group14-sha256,
1.212 djm 1099: diffie-hellman-group14-sha1
1.141 jmc 1100: .Ed
1.198 djm 1101: .Pp
1.240 jmc 1102: The list of available key exchange algorithms may also be obtained using
1103: .Qq ssh -Q kex .
1.65 reyk 1104: .It Cm LocalCommand
1105: Specifies a command to execute on the local machine after successfully
1106: connecting to the server.
1107: The command string extends to the end of the line, and is executed with
1.105 jmc 1108: the user's shell.
1.239 jmc 1109: Arguments to
1110: .Cm LocalCommand
1111: accept the tokens described in the
1112: .Sx TOKENS
1113: section.
1.123 djm 1114: .Pp
1115: The command is run synchronously and does not have access to the
1116: session of the
1117: .Xr ssh 1
1118: that spawned it.
1119: It should not be used for interactive commands.
1120: .Pp
1.65 reyk 1121: This directive is ignored unless
1122: .Cm PermitLocalCommand
1123: has been enabled.
1.1 stevesk 1124: .It Cm LocalForward
1.74 jmc 1125: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1126: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1127: The first argument must be
1.43 djm 1128: .Sm off
1.49 jmc 1129: .Oo Ar bind_address : Oc Ar port
1.43 djm 1130: .Sm on
1.49 jmc 1131: and the second argument must be
1132: .Ar host : Ns Ar hostport .
1.138 djm 1133: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1134: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1135: given on the command line.
1.1 stevesk 1136: Only the superuser can forward privileged ports.
1.43 djm 1137: By default, the local port is bound in accordance with the
1138: .Cm GatewayPorts
1139: setting.
1140: However, an explicit
1141: .Ar bind_address
1142: may be used to bind the connection to a specific address.
1143: The
1144: .Ar bind_address
1145: of
1.240 jmc 1146: .Cm localhost
1.46 jmc 1147: indicates that the listening port be bound for local use only, while an
1148: empty address or
1149: .Sq *
1.43 djm 1150: indicates that the port should be available from all interfaces.
1.1 stevesk 1151: .It Cm LogLevel
1152: Gives the verbosity level that is used when logging messages from
1.84 jmc 1153: .Xr ssh 1 .
1.1 stevesk 1154: The possible values are:
1.84 jmc 1155: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1156: The default is INFO.
1157: DEBUG and DEBUG1 are equivalent.
1158: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1159: .It Cm MACs
1160: Specifies the MAC (message authentication code) algorithms
1161: in order of preference.
1.226 jmc 1162: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1163: Multiple algorithms must be comma-separated.
1.299 kn 1164: If the specified list begins with a
1.214 djm 1165: .Sq +
1166: character, then the specified algorithms will be appended to the default set
1167: instead of replacing them.
1.299 kn 1168: If the specified list begins with a
1.241 djm 1169: .Sq -
1170: character, then the specified algorithms (including wildcards) will be removed
1171: from the default set instead of replacing them.
1.301 naddy 1172: If the specified list begins with a
1173: .Sq ^
1174: character, then the specified algorithms will be placed at the head of the
1175: default set.
1.214 djm 1176: .Pp
1.160 markus 1177: The algorithms that contain
1.240 jmc 1178: .Qq -etm
1.160 markus 1179: calculate the MAC after encryption (encrypt-then-mac).
1180: These are considered safer and their use recommended.
1.214 djm 1181: .Pp
1.84 jmc 1182: The default is:
1.101 jmc 1183: .Bd -literal -offset indent
1.160 markus 1184: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1185: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1186: hmac-sha1-etm@openssh.com,
1.186 naddy 1187: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1188: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1189: .Ed
1.198 djm 1190: .Pp
1.240 jmc 1191: The list of available MAC algorithms may also be obtained using
1192: .Qq ssh -Q mac .
1.1 stevesk 1193: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1194: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1195: The argument to this keyword must be
1.240 jmc 1196: .Cm yes
1.1 stevesk 1197: or
1.242 jmc 1198: .Cm no
1.240 jmc 1199: (the default).
1.1 stevesk 1200: .It Cm NumberOfPasswordPrompts
1201: Specifies the number of password prompts before giving up.
1202: The argument to this keyword must be an integer.
1.84 jmc 1203: The default is 3.
1.1 stevesk 1204: .It Cm PasswordAuthentication
1205: Specifies whether to use password authentication.
1206: The argument to this keyword must be
1.240 jmc 1207: .Cm yes
1208: (the default)
1.1 stevesk 1209: or
1.240 jmc 1210: .Cm no .
1.65 reyk 1211: .It Cm PermitLocalCommand
1212: Allow local command execution via the
1213: .Ic LocalCommand
1214: option or using the
1.66 jmc 1215: .Ic !\& Ns Ar command
1.65 reyk 1216: escape sequence in
1217: .Xr ssh 1 .
1218: The argument must be
1.240 jmc 1219: .Cm yes
1.65 reyk 1220: or
1.240 jmc 1221: .Cm no
1222: (the default).
1.127 markus 1223: .It Cm PKCS11Provider
1.292 djm 1224: Specifies which PKCS#11 provider to use or
1225: .Cm none
1226: to indicate that no provider should be used (the default).
1227: The argument to this keyword is a path to the PKCS#11 shared library
1.127 markus 1228: .Xr ssh 1
1.292 djm 1229: should use to communicate with a PKCS#11 token providing keys for user
1230: authentication.
1.67 jmc 1231: .It Cm Port
1232: Specifies the port number to connect on the remote host.
1.84 jmc 1233: The default is 22.
1.1 stevesk 1234: .It Cm PreferredAuthentications
1.226 jmc 1235: Specifies the order in which the client should try authentication methods.
1.48 jmc 1236: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1237: .Cm keyboard-interactive )
1.48 jmc 1238: over another method (e.g.\&
1.131 jmc 1239: .Cm password ) .
1240: The default is:
1241: .Bd -literal -offset indent
1242: gssapi-with-mic,hostbased,publickey,
1243: keyboard-interactive,password
1244: .Ed
1.1 stevesk 1245: .It Cm ProxyCommand
1246: Specifies the command to use to connect to the server.
1247: The command
1.190 djm 1248: string extends to the end of the line, and is executed
1249: using the user's shell
1250: .Ql exec
1251: directive to avoid a lingering shell process.
1252: .Pp
1.239 jmc 1253: Arguments to
1254: .Cm ProxyCommand
1255: accept the tokens described in the
1256: .Sx TOKENS
1257: section.
1.1 stevesk 1258: The command can be basically anything,
1259: and should read from its standard input and write to its standard output.
1260: It should eventually connect an
1261: .Xr sshd 8
1262: server running on some machine, or execute
1263: .Ic sshd -i
1264: somewhere.
1265: Host key management will be done using the
1.296 jmc 1266: .Cm Hostname
1267: of the host being connected (defaulting to the name typed by the user).
1.7 jmc 1268: Setting the command to
1.240 jmc 1269: .Cm none
1.6 markus 1270: disables this option entirely.
1.1 stevesk 1271: Note that
1272: .Cm CheckHostIP
1273: is not available for connects with a proxy command.
1.52 djm 1274: .Pp
1275: This directive is useful in conjunction with
1276: .Xr nc 1
1277: and its proxy support.
1.53 jmc 1278: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1279: 192.0.2.0:
1280: .Bd -literal -offset 3n
1281: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1282: .Ed
1.233 djm 1283: .It Cm ProxyJump
1.260 millert 1284: Specifies one or more jump proxies as either
1.233 djm 1285: .Xo
1286: .Sm off
1.234 jmc 1287: .Op Ar user No @
1.233 djm 1288: .Ar host
1.234 jmc 1289: .Op : Ns Ar port
1.233 djm 1290: .Sm on
1.260 millert 1291: or an ssh URI
1.233 djm 1292: .Xc .
1.235 djm 1293: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1294: sequentially.
1.233 djm 1295: Setting this option will cause
1296: .Xr ssh 1
1297: to connect to the target host by first making a
1298: .Xr ssh 1
1299: connection to the specified
1300: .Cm ProxyJump
1301: host and then establishing a
1.234 jmc 1302: TCP forwarding to the ultimate target from there.
1.233 djm 1303: .Pp
1304: Note that this option will compete with the
1305: .Cm ProxyCommand
1306: option - whichever is specified first will prevent later instances of the
1307: other from taking effect.
1.289 djm 1308: .Pp
1309: Note also that the configuration for the destination host (either supplied
1310: via the command-line or the configuration file) is not generally applied
1311: to jump hosts.
1312: .Pa ~/.ssh/config
1313: should be used if specific configuration is required for jump hosts.
1.167 djm 1314: .It Cm ProxyUseFdpass
1.168 jmc 1315: Specifies that
1.167 djm 1316: .Cm ProxyCommand
1317: will pass a connected file descriptor back to
1.168 jmc 1318: .Xr ssh 1
1.167 djm 1319: instead of continuing to execute and pass data.
1320: The default is
1.240 jmc 1321: .Cm no .
1.213 markus 1322: .It Cm PubkeyAcceptedKeyTypes
1323: Specifies the key types that will be used for public key authentication
1.279 djm 1324: as a comma-separated list of patterns.
1.299 kn 1325: If the specified list begins with a
1.214 djm 1326: .Sq +
1327: character, then the key types after it will be appended to the default
1328: instead of replacing it.
1.299 kn 1329: If the specified list begins with a
1.241 djm 1330: .Sq -
1331: character, then the specified key types (including wildcards) will be removed
1332: from the default set instead of replacing them.
1.301 naddy 1333: If the specified list begins with a
1334: .Sq ^
1335: character, then the specified key types will be placed at the head of the
1336: default set.
1.213 markus 1337: The default for this option is:
1338: .Bd -literal -offset 3n
1339: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1340: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1341: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.311 naddy 1342: sk-ecdsa-sha2-nistp256-cert-v01@openssh.com,
1343: ssh-ed25519-cert-v01@openssh.com,
1.307 djm 1344: sk-ssh-ed25519-cert-v01@openssh.com,
1.305 naddy 1345: rsa-sha2-512-cert-v01@openssh.com,
1346: rsa-sha2-256-cert-v01@openssh.com,
1.213 markus 1347: ssh-rsa-cert-v01@openssh.com,
1.311 naddy 1348: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.305 naddy 1349: sk-ecdsa-sha2-nistp256@openssh.com,
1.311 naddy 1350: ssh-ed25519,sk-ssh-ed25519@openssh.com,
1351: rsa-sha2-512,rsa-sha2-256,ssh-rsa
1.213 markus 1352: .Ed
1353: .Pp
1.240 jmc 1354: The list of available key types may also be obtained using
1355: .Qq ssh -Q key .
1.1 stevesk 1356: .It Cm PubkeyAuthentication
1357: Specifies whether to try public key authentication.
1358: The argument to this keyword must be
1.240 jmc 1359: .Cm yes
1360: (the default)
1.1 stevesk 1361: or
1.240 jmc 1362: .Cm no .
1.75 dtucker 1363: .It Cm RekeyLimit
1364: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1365: session key is renegotiated, optionally followed a maximum amount of
1366: time that may pass before the session key is renegotiated.
1367: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1368: .Sq K ,
1369: .Sq M ,
1.75 dtucker 1370: or
1.76 jmc 1371: .Sq G
1.75 dtucker 1372: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1373: The default is between
1.84 jmc 1374: .Sq 1G
1.75 dtucker 1375: and
1.84 jmc 1376: .Sq 4G ,
1.75 dtucker 1377: depending on the cipher.
1.162 dtucker 1378: The optional second value is specified in seconds and may use any of the
1.293 schwarze 1379: units documented in the TIME FORMATS section of
1.162 dtucker 1380: .Xr sshd_config 5 .
1381: The default value for
1382: .Cm RekeyLimit
1383: is
1.240 jmc 1384: .Cm default none ,
1.162 dtucker 1385: which means that rekeying is performed after the cipher's default amount
1386: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1387: .It Cm RemoteCommand
1388: Specifies a command to execute on the remote machine after successfully
1389: connecting to the server.
1390: The command string extends to the end of the line, and is executed with
1391: the user's shell.
1.250 jmc 1392: Arguments to
1393: .Cm RemoteCommand
1394: accept the tokens described in the
1395: .Sx TOKENS
1396: section.
1.1 stevesk 1397: .It Cm RemoteForward
1.74 jmc 1398: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1399: the secure channel.
1.273 djm 1400: The remote port may either be forwarded to a specified host and port
1.256 markus 1401: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1402: client to connect to arbitrary destinations from the local machine.
1.49 jmc 1403: The first argument must be
1.43 djm 1404: .Sm off
1.49 jmc 1405: .Oo Ar bind_address : Oc Ar port
1.43 djm 1406: .Sm on
1.256 markus 1407: If forwarding to a specific destination then the second argument must be
1408: .Ar host : Ns Ar hostport ,
1409: otherwise if no destination argument is specified then the remote forwarding
1410: will be established as a SOCKS proxy.
1411: .Pp
1.138 djm 1412: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1413: Multiple forwardings may be specified, and additional
1414: forwardings can be given on the command line.
1.113 stevesk 1415: Privileged ports can be forwarded only when
1416: logging in as root on the remote machine.
1.118 jmc 1417: .Pp
1.117 djm 1418: If the
1419: .Ar port
1.240 jmc 1420: argument is 0,
1.117 djm 1421: the listen port will be dynamically allocated on the server and reported
1422: to the client at run time.
1.43 djm 1423: .Pp
1424: If the
1425: .Ar bind_address
1426: is not specified, the default is to only bind to loopback addresses.
1427: If the
1428: .Ar bind_address
1429: is
1430: .Ql *
1431: or an empty string, then the forwarding is requested to listen on all
1432: interfaces.
1433: Specifying a remote
1434: .Ar bind_address
1.46 jmc 1435: will only succeed if the server's
1436: .Cm GatewayPorts
1.43 djm 1437: option is enabled (see
1.46 jmc 1438: .Xr sshd_config 5 ) .
1.149 djm 1439: .It Cm RequestTTY
1440: Specifies whether to request a pseudo-tty for the session.
1441: The argument may be one of:
1.240 jmc 1442: .Cm no
1.149 djm 1443: (never request a TTY),
1.240 jmc 1444: .Cm yes
1.149 djm 1445: (always request a TTY when standard input is a TTY),
1.240 jmc 1446: .Cm force
1.149 djm 1447: (always request a TTY) or
1.240 jmc 1448: .Cm auto
1.149 djm 1449: (request a TTY when opening a login session).
1450: This option mirrors the
1451: .Fl t
1452: and
1453: .Fl T
1454: flags for
1455: .Xr ssh 1 .
1.196 djm 1456: .It Cm RevokedHostKeys
1457: Specifies revoked host public keys.
1458: Keys listed in this file will be refused for host authentication.
1459: Note that if this file does not exist or is not readable,
1460: then host authentication will be refused for all hosts.
1461: Keys may be specified as a text file, listing one public key per line, or as
1462: an OpenSSH Key Revocation List (KRL) as generated by
1463: .Xr ssh-keygen 1 .
1464: For more information on KRLs, see the KEY REVOCATION LISTS section in
1465: .Xr ssh-keygen 1 .
1.305 naddy 1466: .It Cm SecurityKeyProvider
1.313 naddy 1467: Specifies a path to a library that will be used when loading any
1468: FIDO authenticator-hosted keys, overriding the default of using
1469: the built-in USB HID support.
1.309 naddy 1470: .Pp
1471: If the specified value begins with a
1472: .Sq $
1473: character, then it will be treated as an environment variable containing
1474: the path to the library.
1.32 djm 1475: .It Cm SendEnv
1476: Specifies what variables from the local
1477: .Xr environ 7
1478: should be sent to the server.
1.84 jmc 1479: The server must also support it, and the server must be configured to
1.33 djm 1480: accept these environment variables.
1.207 dtucker 1481: Note that the
1482: .Ev TERM
1.208 jmc 1483: environment variable is always sent whenever a
1.207 dtucker 1484: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1485: Refer to
1486: .Cm AcceptEnv
1487: in
1488: .Xr sshd_config 5
1489: for how to configure the server.
1.80 jmc 1490: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1491: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1492: across multiple
1493: .Cm SendEnv
1494: directives.
1.81 jmc 1495: .Pp
1496: See
1497: .Sx PATTERNS
1498: for more information on patterns.
1.271 djm 1499: .Pp
1.272 jmc 1500: It is possible to clear previously set
1.271 djm 1501: .Cm SendEnv
1502: variable names by prefixing patterns with
1503: .Pa - .
1504: The default is not to send any environment variables.
1.28 markus 1505: .It Cm ServerAliveCountMax
1.73 jmc 1506: Sets the number of server alive messages (see below) which may be
1.28 markus 1507: sent without
1.84 jmc 1508: .Xr ssh 1
1.28 markus 1509: receiving any messages back from the server.
1510: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1511: ssh will disconnect from the server, terminating the session.
1.28 markus 1512: It is important to note that the use of server alive messages is very
1513: different from
1514: .Cm TCPKeepAlive
1515: (below).
1516: The server alive messages are sent through the encrypted channel
1517: and therefore will not be spoofable.
1518: The TCP keepalive option enabled by
1519: .Cm TCPKeepAlive
1520: is spoofable.
1521: The server alive mechanism is valuable when the client or
1.298 dtucker 1522: server depend on knowing when a connection has become unresponsive.
1.28 markus 1523: .Pp
1524: The default value is 3.
1525: If, for example,
1526: .Cm ServerAliveInterval
1.84 jmc 1527: (see below) is set to 15 and
1.28 markus 1528: .Cm ServerAliveCountMax
1.84 jmc 1529: is left at the default, if the server becomes unresponsive,
1530: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1531: .It Cm ServerAliveInterval
1532: Sets a timeout interval in seconds after which if no data has been received
1533: from the server,
1.84 jmc 1534: .Xr ssh 1
1.67 jmc 1535: will send a message through the encrypted
1536: channel to request a response from the server.
1537: The default
1538: is 0, indicating that these messages will not be sent to the server.
1.277 jmc 1539: .It Cm SetEnv
1540: Directly specify one or more environment variables and their contents to
1541: be sent to the server.
1542: Similarly to
1543: .Cm SendEnv ,
1544: the server must be prepared to accept the environment variable.
1.191 millert 1545: .It Cm StreamLocalBindMask
1546: Sets the octal file creation mode mask
1547: .Pq umask
1548: used when creating a Unix-domain socket file for local or remote
1549: port forwarding.
1550: This option is only used for port forwarding to a Unix-domain socket file.
1551: .Pp
1552: The default value is 0177, which creates a Unix-domain socket file that is
1553: readable and writable only by the owner.
1554: Note that not all operating systems honor the file mode on Unix-domain
1555: socket files.
1556: .It Cm StreamLocalBindUnlink
1557: Specifies whether to remove an existing Unix-domain socket file for local
1558: or remote port forwarding before creating a new one.
1559: If the socket file already exists and
1560: .Cm StreamLocalBindUnlink
1561: is not enabled,
1562: .Nm ssh
1563: will be unable to forward the port to the Unix-domain socket file.
1564: This option is only used for port forwarding to a Unix-domain socket file.
1565: .Pp
1566: The argument must be
1.240 jmc 1567: .Cm yes
1.191 millert 1568: or
1.240 jmc 1569: .Cm no
1570: (the default).
1.1 stevesk 1571: .It Cm StrictHostKeyChecking
1572: If this flag is set to
1.240 jmc 1573: .Cm yes ,
1.84 jmc 1574: .Xr ssh 1
1.1 stevesk 1575: will never automatically add host keys to the
1.50 djm 1576: .Pa ~/.ssh/known_hosts
1.1 stevesk 1577: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1578: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1579: though it can be annoying when the
1.1 stevesk 1580: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1581: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1582: frequently made.
1583: This option forces the user to manually
1584: add all new hosts.
1.255 jmc 1585: .Pp
1.1 stevesk 1586: If this flag is set to
1.254 djm 1587: .Dq accept-new
1.255 jmc 1588: then ssh will automatically add new host keys to the user
1.254 djm 1589: known hosts files, but will not permit connections to hosts with
1590: changed host keys.
1591: If this flag is set to
1592: .Dq no
1593: or
1594: .Dq off ,
1.255 jmc 1595: ssh will automatically add new host keys to the user known hosts files
1596: and allow connections to hosts with changed hostkeys to proceed,
1597: subject to some restrictions.
1.1 stevesk 1598: If this flag is set to
1.240 jmc 1599: .Cm ask
1600: (the default),
1.1 stevesk 1601: new host keys
1602: will be added to the user known host files only after the user
1603: has confirmed that is what they really want to do, and
1.84 jmc 1604: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1605: The host keys of
1606: known hosts will be verified automatically in all cases.
1.244 jmc 1607: .It Cm SyslogFacility
1608: Gives the facility code that is used when logging messages from
1609: .Xr ssh 1 .
1610: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1611: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1612: The default is USER.
1.26 markus 1613: .It Cm TCPKeepAlive
1614: Specifies whether the system should send TCP keepalive messages to the
1615: other side.
1616: If they are sent, death of the connection or crash of one
1617: of the machines will be properly noticed.
1618: However, this means that
1619: connections will die if the route is down temporarily, and some people
1620: find it annoying.
1621: .Pp
1622: The default is
1.240 jmc 1623: .Cm yes
1.26 markus 1624: (to send TCP keepalive messages), and the client will notice
1625: if the network goes down or the remote host dies.
1626: This is important in scripts, and many users want it too.
1627: .Pp
1628: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1629: .Cm no .
1.265 djm 1630: See also
1631: .Cm ServerAliveInterval
1632: for protocol-level keepalives.
1.65 reyk 1633: .It Cm Tunnel
1.95 stevesk 1634: Request
1.65 reyk 1635: .Xr tun 4
1.69 jmc 1636: device forwarding between the client and the server.
1.65 reyk 1637: The argument must be
1.240 jmc 1638: .Cm yes ,
1639: .Cm point-to-point
1.95 stevesk 1640: (layer 3),
1.240 jmc 1641: .Cm ethernet
1.95 stevesk 1642: (layer 2),
1.65 reyk 1643: or
1.240 jmc 1644: .Cm no
1645: (the default).
1.95 stevesk 1646: Specifying
1.240 jmc 1647: .Cm yes
1.95 stevesk 1648: requests the default tunnel mode, which is
1.240 jmc 1649: .Cm point-to-point .
1.65 reyk 1650: .It Cm TunnelDevice
1.95 stevesk 1651: Specifies the
1.65 reyk 1652: .Xr tun 4
1.95 stevesk 1653: devices to open on the client
1654: .Pq Ar local_tun
1655: and the server
1656: .Pq Ar remote_tun .
1657: .Pp
1658: The argument must be
1659: .Sm off
1660: .Ar local_tun Op : Ar remote_tun .
1661: .Sm on
1662: The devices may be specified by numerical ID or the keyword
1.240 jmc 1663: .Cm any ,
1.95 stevesk 1664: which uses the next available tunnel device.
1665: If
1666: .Ar remote_tun
1667: is not specified, it defaults to
1.240 jmc 1668: .Cm any .
1.95 stevesk 1669: The default is
1.240 jmc 1670: .Cm any:any .
1.201 djm 1671: .It Cm UpdateHostKeys
1.200 djm 1672: Specifies whether
1673: .Xr ssh 1
1674: should accept notifications of additional hostkeys from the server sent
1675: after authentication has completed and add them to
1676: .Cm UserKnownHostsFile .
1677: The argument must be
1.240 jmc 1678: .Cm yes ,
1679: .Cm no
1.204 djm 1680: (the default) or
1.240 jmc 1681: .Cm ask .
1.200 djm 1682: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1683: and supports graceful key rotation by allowing a server to send replacement
1684: public keys before old ones are removed.
1.200 djm 1685: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1686: host was already trusted or explicitly accepted by the user.
1.204 djm 1687: If
1688: .Cm UpdateHostKeys
1689: is set to
1.240 jmc 1690: .Cm ask ,
1.204 djm 1691: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1692: Confirmation is currently incompatible with
1693: .Cm ControlPersist ,
1694: and will be disabled if it is enabled.
1.200 djm 1695: .Pp
1696: Presently, only
1697: .Xr sshd 8
1698: from OpenSSH 6.8 and greater support the
1.240 jmc 1699: .Qq hostkeys@openssh.com
1.200 djm 1700: protocol extension used to inform the client of all the server's hostkeys.
1.1 stevesk 1701: .It Cm User
1702: Specifies the user to log in as.
1703: This can be useful when a different user name is used on different machines.
1704: This saves the trouble of
1705: having to remember to give the user name on the command line.
1706: .It Cm UserKnownHostsFile
1.151 djm 1707: Specifies one or more files to use for the user
1708: host key database, separated by whitespace.
1709: The default is
1710: .Pa ~/.ssh/known_hosts ,
1711: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1712: .It Cm VerifyHostKeyDNS
1713: Specifies whether to verify the remote key using DNS and SSHFP resource
1714: records.
1.24 jakob 1715: If this option is set to
1.240 jmc 1716: .Cm yes ,
1.25 jmc 1717: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1718: from DNS.
1719: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1720: .Cm ask .
1.24 jakob 1721: If this option is set to
1.240 jmc 1722: .Cm ask ,
1.24 jakob 1723: information on fingerprint match will be displayed, but the user will still
1724: need to confirm new host keys according to the
1725: .Cm StrictHostKeyChecking
1726: option.
1.8 jakob 1727: The default is
1.240 jmc 1728: .Cm no .
1.84 jmc 1729: .Pp
1.240 jmc 1730: See also
1731: .Sx VERIFYING HOST KEYS
1732: in
1.84 jmc 1733: .Xr ssh 1 .
1.111 grunk 1734: .It Cm VisualHostKey
1735: If this flag is set to
1.240 jmc 1736: .Cm yes ,
1.111 grunk 1737: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1738: printed in addition to the fingerprint string at login and
1.114 stevesk 1739: for unknown host keys.
1.111 grunk 1740: If this flag is set to
1.240 jmc 1741: .Cm no
1742: (the default),
1.114 stevesk 1743: no fingerprint strings are printed at login and
1.197 djm 1744: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1745: .It Cm XAuthLocation
1.5 stevesk 1746: Specifies the full pathname of the
1.1 stevesk 1747: .Xr xauth 1
1748: program.
1749: The default is
1750: .Pa /usr/X11R6/bin/xauth .
1751: .El
1.86 jmc 1752: .Sh PATTERNS
1753: A
1754: .Em pattern
1755: consists of zero or more non-whitespace characters,
1756: .Sq *
1757: (a wildcard that matches zero or more characters),
1758: or
1759: .Sq ?\&
1760: (a wildcard that matches exactly one character).
1761: For example, to specify a set of declarations for any host in the
1.240 jmc 1762: .Qq .co.uk
1.86 jmc 1763: set of domains,
1764: the following pattern could be used:
1765: .Pp
1766: .Dl Host *.co.uk
1767: .Pp
1768: The following pattern
1769: would match any host in the 192.168.0.[0-9] network range:
1770: .Pp
1771: .Dl Host 192.168.0.?
1772: .Pp
1773: A
1774: .Em pattern-list
1775: is a comma-separated list of patterns.
1776: Patterns within pattern-lists may be negated
1777: by preceding them with an exclamation mark
1778: .Pq Sq !\& .
1779: For example,
1.174 djm 1780: to allow a key to be used from anywhere within an organization
1.86 jmc 1781: except from the
1.240 jmc 1782: .Qq dialup
1.86 jmc 1783: pool,
1784: the following entry (in authorized_keys) could be used:
1785: .Pp
1786: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1787: .Pp
1788: Note that a negated match will never produce a positive result by itself.
1789: For example, attempting to match
1790: .Qq host3
1791: against the following pattern-list will fail:
1792: .Pp
1793: .Dl from=\&"!host1,!host2\&"
1794: .Pp
1795: The solution here is to include a term that will yield a positive match,
1796: such as a wildcard:
1797: .Pp
1798: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1799: .Sh TOKENS
1800: Arguments to some keywords can make use of tokens,
1801: which are expanded at runtime:
1802: .Pp
1803: .Bl -tag -width XXXX -offset indent -compact
1804: .It %%
1805: A literal
1806: .Sq % .
1807: .It \&%C
1.257 jmc 1808: Hash of %l%h%p%r.
1.239 jmc 1809: .It %d
1810: Local user's home directory.
1811: .It %h
1812: The remote hostname.
1813: .It %i
1814: The local user ID.
1815: .It %L
1816: The local hostname.
1817: .It %l
1818: The local hostname, including the domain name.
1819: .It %n
1820: The original remote hostname, as given on the command line.
1821: .It %p
1822: The remote port.
1823: .It %r
1824: The remote username.
1.261 djm 1825: .It \&%T
1826: The local
1827: .Xr tun 4
1828: or
1829: .Xr tap 4
1830: network interface assigned if
1.262 jmc 1831: tunnel forwarding was requested, or
1832: .Qq NONE
1.261 djm 1833: otherwise.
1.239 jmc 1834: .It %u
1835: The local username.
1836: .El
1837: .Pp
1838: .Cm Match exec
1.274 djm 1839: accepts the tokens %%, %h, %i, %L, %l, %n, %p, %r, and %u.
1.239 jmc 1840: .Pp
1841: .Cm CertificateFile
1.275 jmc 1842: accepts the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1843: .Pp
1844: .Cm ControlPath
1845: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1846: .Pp
1.295 jmc 1847: .Cm Hostname
1.239 jmc 1848: accepts the tokens %% and %h.
1849: .Pp
1850: .Cm IdentityAgent
1851: and
1852: .Cm IdentityFile
1.275 jmc 1853: accept the tokens %%, %d, %h, %i, %l, %r, and %u.
1.239 jmc 1854: .Pp
1855: .Cm LocalCommand
1.275 jmc 1856: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, %T, and %u.
1.239 jmc 1857: .Pp
1858: .Cm ProxyCommand
1.303 djm 1859: accepts the tokens %%, %h, %n, %p, and %r.
1.250 jmc 1860: .Pp
1861: .Cm RemoteCommand
1.274 djm 1862: accepts the tokens %%, %C, %d, %h, %i, %l, %n, %p, %r, and %u.
1.1 stevesk 1863: .Sh FILES
1864: .Bl -tag -width Ds
1.50 djm 1865: .It Pa ~/.ssh/config
1.1 stevesk 1866: This is the per-user configuration file.
1867: The format of this file is described above.
1.84 jmc 1868: This file is used by the SSH client.
1.30 djm 1869: Because of the potential for abuse, this file must have strict permissions:
1.290 jmc 1870: read/write for the user, and not writable by others.
1.1 stevesk 1871: .It Pa /etc/ssh/ssh_config
1872: Systemwide configuration file.
1873: This file provides defaults for those
1874: values that are not specified in the user's configuration file, and
1875: for those users who do not have a configuration file.
1876: This file must be world-readable.
1877: .El
1.13 jmc 1878: .Sh SEE ALSO
1879: .Xr ssh 1
1.1 stevesk 1880: .Sh AUTHORS
1.240 jmc 1881: .An -nosplit
1.1 stevesk 1882: OpenSSH is a derivative of the original and free
1.240 jmc 1883: ssh 1.2.12 release by
1884: .An Tatu Ylonen .
1885: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1886: .An Niels Provos , Theo de Raadt
1887: and
1888: .An Dug Song
1.1 stevesk 1889: removed many bugs, re-added newer features and
1890: created OpenSSH.
1.240 jmc 1891: .An Markus Friedl
1892: contributed the support for SSH protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh