Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.253
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.
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1.253 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.252 2017/07/13 19:16:33 jmc Exp $
! 37: .Dd $Mdocdate: July 13 2017 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
42: .Nd OpenSSH SSH client configuration files
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 ,
1.176 djm 142: .Cm exec ,
1.169 djm 143: .Cm host ,
144: .Cm originalhost ,
145: .Cm user ,
146: and
147: .Cm localuser .
1.193 djm 148: The
149: .Cm all
150: criteria must appear alone or immediately after
1.194 jmc 151: .Cm canonical .
1.193 djm 152: Other criteria may be combined arbitrarily.
153: All criteria but
154: .Cm all
155: and
156: .Cm canonical
157: require an argument.
158: Criteria may be negated by prepending an exclamation mark
159: .Pq Sq !\& .
1.169 djm 160: .Pp
1.177 jmc 161: The
1.193 djm 162: .Cm canonical
1.210 dtucker 163: keyword matches only when the configuration file is being re-parsed
1.193 djm 164: after hostname canonicalization (see the
165: .Cm CanonicalizeHostname
166: option.)
167: This may be useful to specify conditions that work with canonical host
168: names only.
169: The
1.176 djm 170: .Cm exec
1.177 jmc 171: keyword executes the specified command under the user's shell.
1.169 djm 172: If the command returns a zero exit status then the condition is considered true.
173: Commands containing whitespace characters must be quoted.
1.239 jmc 174: Arguments to
175: .Cm exec
176: accept the tokens described in the
177: .Sx TOKENS
178: section.
1.169 djm 179: .Pp
180: The other keywords' criteria must be single entries or comma-separated
181: lists and may use the wildcard and negation operators described in the
182: .Sx PATTERNS
183: section.
184: The criteria for the
185: .Cm host
186: keyword are matched against the target hostname, after any substitution
187: by the
188: .Cm Hostname
1.193 djm 189: or
190: .Cm CanonicalizeHostname
191: options.
1.169 djm 192: The
193: .Cm originalhost
194: keyword matches against the hostname as it was specified on the command-line.
195: The
196: .Cm user
197: keyword matches against the target username on the remote host.
198: The
199: .Cm localuser
200: keyword matches against the name of the local user running
201: .Xr ssh 1
202: (this keyword may be useful in system-wide
203: .Nm
204: files).
1.222 jcs 205: .It Cm AddKeysToAgent
206: Specifies whether keys should be automatically added to a running
1.223 jmc 207: .Xr ssh-agent 1 .
1.222 jcs 208: If this option is set to
1.240 jmc 209: .Cm yes
1.222 jcs 210: and a key is loaded from a file, the key and its passphrase are added to
211: the agent with the default lifetime, as if by
212: .Xr ssh-add 1 .
213: If this option is set to
1.240 jmc 214: .Cm ask ,
215: .Xr ssh 1
1.222 jcs 216: will require confirmation using the
217: .Ev SSH_ASKPASS
218: program before adding a key (see
219: .Xr ssh-add 1
220: for details).
221: If this option is set to
1.240 jmc 222: .Cm confirm ,
1.222 jcs 223: each use of the key must be confirmed, as if the
224: .Fl c
225: option was specified to
226: .Xr ssh-add 1 .
227: If this option is set to
1.240 jmc 228: .Cm no ,
1.222 jcs 229: no keys are added to the agent.
230: The argument must be
1.240 jmc 231: .Cm yes ,
232: .Cm confirm ,
233: .Cm ask ,
1.222 jcs 234: or
1.240 jmc 235: .Cm no
236: (the default).
1.10 djm 237: .It Cm AddressFamily
1.11 jmc 238: Specifies which address family to use when connecting.
239: Valid arguments are
1.240 jmc 240: .Cm any
241: (the default),
242: .Cm inet
1.84 jmc 243: (use IPv4 only), or
1.240 jmc 244: .Cm inet6
1.40 jmc 245: (use IPv6 only).
1.1 stevesk 246: .It Cm BatchMode
247: If set to
1.240 jmc 248: .Cm yes ,
1.1 stevesk 249: passphrase/password querying will be disabled.
250: This option is useful in scripts and other batch jobs where no user
251: is present to supply the password.
252: The argument must be
1.240 jmc 253: .Cm yes
1.1 stevesk 254: or
1.240 jmc 255: .Cm no
256: (the default).
1.1 stevesk 257: .It Cm BindAddress
1.60 dtucker 258: Use the specified address on the local machine as the source address of
1.61 jmc 259: the connection.
260: Only useful on systems with more than one address.
1.1 stevesk 261: Note that this option does not work if
262: .Cm UsePrivilegedPort
263: is set to
1.240 jmc 264: .Cm yes .
1.171 djm 265: .It Cm CanonicalDomains
1.172 jmc 266: When
1.173 djm 267: .Cm CanonicalizeHostname
1.171 djm 268: is enabled, this option specifies the list of domain suffixes in which to
269: search for the specified destination host.
1.173 djm 270: .It Cm CanonicalizeFallbackLocal
1.174 djm 271: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 272: The default,
1.240 jmc 273: .Cm yes ,
1.172 jmc 274: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 275: search rules.
276: A value of
1.240 jmc 277: .Cm no
1.171 djm 278: will cause
279: .Xr ssh 1
280: to fail instantly if
1.173 djm 281: .Cm CanonicalizeHostname
1.171 djm 282: is enabled and the target hostname cannot be found in any of the domains
283: specified by
284: .Cm CanonicalDomains .
1.173 djm 285: .It Cm CanonicalizeHostname
1.174 djm 286: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 287: The default,
1.240 jmc 288: .Cm no ,
1.171 djm 289: is not to perform any name rewriting and let the system resolver handle all
290: hostname lookups.
291: If set to
1.240 jmc 292: .Cm yes
1.171 djm 293: then, for connections that do not use a
294: .Cm ProxyCommand ,
295: .Xr ssh 1
1.173 djm 296: will attempt to canonicalize the hostname specified on the command line
1.171 djm 297: using the
298: .Cm CanonicalDomains
299: suffixes and
1.173 djm 300: .Cm CanonicalizePermittedCNAMEs
1.171 djm 301: rules.
302: If
1.173 djm 303: .Cm CanonicalizeHostname
1.171 djm 304: is set to
1.240 jmc 305: .Cm always ,
1.174 djm 306: then canonicalization is applied to proxied connections too.
1.185 djm 307: .Pp
1.193 djm 308: If this option is enabled, then the configuration files are processed
309: again using the new target name to pick up any new configuration in matching
1.185 djm 310: .Cm Host
1.193 djm 311: and
312: .Cm Match
1.185 djm 313: stanzas.
1.173 djm 314: .It Cm CanonicalizeMaxDots
1.172 jmc 315: Specifies the maximum number of dot characters in a hostname before
1.174 djm 316: canonicalization is disabled.
1.240 jmc 317: The default, 1,
1.172 jmc 318: allows a single dot (i.e. hostname.subdomain).
1.173 djm 319: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 320: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 321: canonicalizing hostnames.
1.171 djm 322: The rules consist of one or more arguments of
1.172 jmc 323: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 324: where
325: .Ar source_domain_list
1.174 djm 326: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 327: and
328: .Ar target_domain_list
1.172 jmc 329: is a pattern-list of domains that they may resolve to.
1.171 djm 330: .Pp
331: For example,
1.240 jmc 332: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 333: will allow hostnames matching
1.240 jmc 334: .Qq *.a.example.com
1.173 djm 335: to be canonicalized to names in the
1.240 jmc 336: .Qq *.b.example.com
1.171 djm 337: or
1.240 jmc 338: .Qq *.c.example.com
1.171 djm 339: domains.
1.221 djm 340: .It Cm CertificateFile
341: Specifies a file from which the user's certificate is read.
342: A corresponding private key must be provided separately in order
343: to use this certificate either
344: from an
345: .Cm IdentityFile
346: directive or
347: .Fl i
348: flag to
349: .Xr ssh 1 ,
350: via
351: .Xr ssh-agent 1 ,
352: or via a
353: .Cm PKCS11Provider .
354: .Pp
1.239 jmc 355: Arguments to
356: .Cm CertificateFile
357: may use the tilde syntax to refer to a user's home directory
358: or the tokens described in the
359: .Sx TOKENS
360: section.
1.221 djm 361: .Pp
362: It is possible to have multiple certificate files specified in
363: configuration files; these certificates will be tried in sequence.
364: Multiple
365: .Cm CertificateFile
366: directives will add to the list of certificates used for
367: authentication.
1.1 stevesk 368: .It Cm ChallengeResponseAuthentication
1.82 jmc 369: Specifies whether to use challenge-response authentication.
1.1 stevesk 370: The argument to this keyword must be
1.240 jmc 371: .Cm yes
372: (the default)
1.1 stevesk 373: or
1.240 jmc 374: .Cm no .
1.1 stevesk 375: .It Cm CheckHostIP
1.240 jmc 376: If set to
377: .Cm yes
378: (the default),
1.84 jmc 379: .Xr ssh 1
380: will additionally check the host IP address in the
1.1 stevesk 381: .Pa known_hosts
382: file.
1.240 jmc 383: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 384: and will add addresses of destination hosts to
385: .Pa ~/.ssh/known_hosts
386: in the process, regardless of the setting of
387: .Cm StrictHostKeyChecking .
1.107 grunk 388: If the option is set to
1.240 jmc 389: .Cm no ,
1.1 stevesk 390: the check will not be executed.
391: .It Cm Ciphers
1.245 djm 392: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 393: Multiple ciphers must be comma-separated.
1.214 djm 394: If the specified value begins with a
395: .Sq +
396: character, then the specified ciphers will be appended to the default set
397: instead of replacing them.
1.241 djm 398: If the specified value begins with a
399: .Sq -
400: character, then the specified ciphers (including wildcards) will be removed
401: from the default set instead of replacing them.
1.214 djm 402: .Pp
1.180 djm 403: The supported ciphers are:
1.240 jmc 404: .Bd -literal -offset indent
1.186 naddy 405: 3des-cbc
406: aes128-cbc
407: aes192-cbc
408: aes256-cbc
409: aes128-ctr
410: aes192-ctr
411: aes256-ctr
412: aes128-gcm@openssh.com
413: aes256-gcm@openssh.com
414: chacha20-poly1305@openssh.com
1.240 jmc 415: .Ed
1.180 djm 416: .Pp
1.84 jmc 417: The default is:
1.186 naddy 418: .Bd -literal -offset indent
1.215 jmc 419: chacha20-poly1305@openssh.com,
1.186 naddy 420: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 421: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.237 djm 422: aes128-cbc,aes192-cbc,aes256-cbc
1.1 stevesk 423: .Ed
1.180 djm 424: .Pp
1.240 jmc 425: The list of available ciphers may also be obtained using
426: .Qq ssh -Q cipher .
1.1 stevesk 427: .It Cm ClearAllForwardings
1.84 jmc 428: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 429: specified in the configuration files or on the command line be
1.7 jmc 430: cleared.
431: This option is primarily useful when used from the
1.84 jmc 432: .Xr ssh 1
1.1 stevesk 433: command line to clear port forwardings set in
434: configuration files, and is automatically set by
435: .Xr scp 1
436: and
437: .Xr sftp 1 .
438: The argument must be
1.240 jmc 439: .Cm yes
1.1 stevesk 440: or
1.240 jmc 441: .Cm no
442: (the default).
1.1 stevesk 443: .It Cm Compression
444: Specifies whether to use compression.
445: The argument must be
1.240 jmc 446: .Cm yes
1.1 stevesk 447: or
1.240 jmc 448: .Cm no
449: (the default).
1.247 naddy 450: .It Cm ConnectionAttempts
451: Specifies the number of tries (one per second) to make before exiting.
452: The argument must be an integer.
453: This may be useful in scripts if the connection sometimes fails.
454: The default is 1.
1.9 djm 455: .It Cm ConnectTimeout
1.84 jmc 456: Specifies the timeout (in seconds) used when connecting to the
457: SSH server, instead of using the default system TCP timeout.
1.11 jmc 458: This value is used only when the target is down or really unreachable,
459: not when it refuses the connection.
1.36 djm 460: .It Cm ControlMaster
461: Enables the sharing of multiple sessions over a single network connection.
462: When set to
1.240 jmc 463: .Cm yes ,
1.84 jmc 464: .Xr ssh 1
1.36 djm 465: will listen for connections on a control socket specified using the
466: .Cm ControlPath
467: argument.
468: Additional sessions can connect to this socket using the same
469: .Cm ControlPath
470: with
471: .Cm ControlMaster
472: set to
1.240 jmc 473: .Cm no
1.38 jmc 474: (the default).
1.64 jmc 475: These sessions will try to reuse the master instance's network connection
1.63 djm 476: rather than initiating new ones, but will fall back to connecting normally
477: if the control socket does not exist, or is not listening.
478: .Pp
1.37 djm 479: Setting this to
1.240 jmc 480: .Cm ask
481: will cause
482: .Xr ssh 1
1.206 jmc 483: to listen for control connections, but require confirmation using
484: .Xr ssh-askpass 1 .
1.51 jakob 485: If the
486: .Cm ControlPath
1.84 jmc 487: cannot be opened,
1.240 jmc 488: .Xr ssh 1
489: will continue without connecting to a master instance.
1.58 djm 490: .Pp
491: X11 and
1.59 jmc 492: .Xr ssh-agent 1
1.58 djm 493: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 494: display and agent forwarded will be the one belonging to the master
1.59 jmc 495: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 496: .Pp
497: Two additional options allow for opportunistic multiplexing: try to use a
498: master connection but fall back to creating a new one if one does not already
499: exist.
500: These options are:
1.240 jmc 501: .Cm auto
1.56 djm 502: and
1.240 jmc 503: .Cm autoask .
1.56 djm 504: The latter requires confirmation like the
1.240 jmc 505: .Cm ask
1.56 djm 506: option.
1.36 djm 507: .It Cm ControlPath
1.55 djm 508: Specify the path to the control socket used for connection sharing as described
509: in the
1.36 djm 510: .Cm ControlMaster
1.57 djm 511: section above or the string
1.240 jmc 512: .Cm none
1.57 djm 513: to disable connection sharing.
1.239 jmc 514: Arguments to
515: .Cm ControlPath
516: may use the tilde syntax to refer to a user's home directory
517: or the tokens described in the
518: .Sx TOKENS
519: section.
1.56 djm 520: It is recommended that any
521: .Cm ControlPath
522: used for opportunistic connection sharing include
1.195 djm 523: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
524: that is not writable by other users.
1.56 djm 525: This ensures that shared connections are uniquely identified.
1.137 djm 526: .It Cm ControlPersist
527: When used in conjunction with
528: .Cm ControlMaster ,
529: specifies that the master connection should remain open
530: in the background (waiting for future client connections)
531: after the initial client connection has been closed.
532: If set to
1.240 jmc 533: .Cm no ,
1.137 djm 534: then the master connection will not be placed into the background,
535: and will close as soon as the initial client connection is closed.
536: If set to
1.240 jmc 537: .Cm yes
538: or 0,
1.137 djm 539: then the master connection will remain in the background indefinitely
540: (until killed or closed via a mechanism such as the
1.240 jmc 541: .Qq ssh -O exit ) .
1.137 djm 542: If set to a time in seconds, or a time in any of the formats documented in
543: .Xr sshd_config 5 ,
544: then the backgrounded master connection will automatically terminate
545: after it has remained idle (with no client connections) for the
546: specified time.
1.38 jmc 547: .It Cm DynamicForward
1.74 jmc 548: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 549: over the secure channel, and the application
550: protocol is then used to determine where to connect to from the
551: remote machine.
1.62 djm 552: .Pp
553: The argument must be
554: .Sm off
555: .Oo Ar bind_address : Oc Ar port .
556: .Sm on
1.138 djm 557: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 558: By default, the local port is bound in accordance with the
559: .Cm GatewayPorts
560: setting.
561: However, an explicit
562: .Ar bind_address
563: may be used to bind the connection to a specific address.
564: The
565: .Ar bind_address
566: of
1.240 jmc 567: .Cm localhost
1.62 djm 568: indicates that the listening port be bound for local use only, while an
569: empty address or
570: .Sq *
571: indicates that the port should be available from all interfaces.
572: .Pp
1.38 jmc 573: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 574: .Xr ssh 1
1.38 jmc 575: will act as a SOCKS server.
576: Multiple forwardings may be specified, and
577: additional forwardings can be given on the command line.
578: Only the superuser can forward privileged ports.
1.14 markus 579: .It Cm EnableSSHKeysign
580: Setting this option to
1.240 jmc 581: .Cm yes
1.14 markus 582: in the global client configuration file
583: .Pa /etc/ssh/ssh_config
584: enables the use of the helper program
585: .Xr ssh-keysign 8
586: during
587: .Cm HostbasedAuthentication .
588: The argument must be
1.240 jmc 589: .Cm yes
1.14 markus 590: or
1.240 jmc 591: .Cm no
592: (the default).
1.23 jmc 593: This option should be placed in the non-hostspecific section.
1.14 markus 594: See
595: .Xr ssh-keysign 8
596: for more information.
1.1 stevesk 597: .It Cm EscapeChar
598: Sets the escape character (default:
599: .Ql ~ ) .
600: The escape character can also
601: be set on the command line.
602: The argument should be a single character,
603: .Ql ^
604: followed by a letter, or
1.240 jmc 605: .Cm none
1.1 stevesk 606: to disable the escape
607: character entirely (making the connection transparent for binary
608: data).
1.96 markus 609: .It Cm ExitOnForwardFailure
610: Specifies whether
611: .Xr ssh 1
612: should terminate the connection if it cannot set up all requested
1.216 djm 613: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 614: if either end is unable to bind and listen on a specified port).
1.216 djm 615: Note that
616: .Cm ExitOnForwardFailure
617: does not apply to connections made over port forwardings and will not,
618: for example, cause
619: .Xr ssh 1
620: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 621: The argument must be
1.240 jmc 622: .Cm yes
1.96 markus 623: or
1.240 jmc 624: .Cm no
625: (the default).
1.197 djm 626: .It Cm FingerprintHash
627: Specifies the hash algorithm used when displaying key fingerprints.
628: Valid options are:
1.240 jmc 629: .Cm md5
1.197 djm 630: and
1.240 jmc 631: .Cm sha256
632: (the default).
1.1 stevesk 633: .It Cm ForwardAgent
634: Specifies whether the connection to the authentication agent (if any)
635: will be forwarded to the remote machine.
636: The argument must be
1.240 jmc 637: .Cm yes
1.1 stevesk 638: or
1.240 jmc 639: .Cm no
640: (the default).
1.3 stevesk 641: .Pp
1.7 jmc 642: Agent forwarding should be enabled with caution.
643: Users with the ability to bypass file permissions on the remote host
644: (for the agent's Unix-domain socket)
645: can access the local agent through the forwarded connection.
646: An attacker cannot obtain key material from the agent,
1.3 stevesk 647: however they can perform operations on the keys that enable them to
648: authenticate using the identities loaded into the agent.
1.1 stevesk 649: .It Cm ForwardX11
650: Specifies whether X11 connections will be automatically redirected
651: over the secure channel and
652: .Ev DISPLAY
653: set.
654: The argument must be
1.240 jmc 655: .Cm yes
1.1 stevesk 656: or
1.240 jmc 657: .Cm no
658: (the default).
1.3 stevesk 659: .Pp
1.7 jmc 660: X11 forwarding should be enabled with caution.
661: Users with the ability to bypass file permissions on the remote host
1.22 markus 662: (for the user's X11 authorization database)
1.7 jmc 663: can access the local X11 display through the forwarded connection.
1.22 markus 664: An attacker may then be able to perform activities such as keystroke monitoring
665: if the
666: .Cm ForwardX11Trusted
667: option is also enabled.
1.134 djm 668: .It Cm ForwardX11Timeout
1.135 jmc 669: Specify a timeout for untrusted X11 forwarding
670: using the format described in the
1.240 jmc 671: .Sx TIME FORMATS
672: section of
1.134 djm 673: .Xr sshd_config 5 .
674: X11 connections received by
675: .Xr ssh 1
676: after this time will be refused.
677: The default is to disable untrusted X11 forwarding after twenty minutes has
678: elapsed.
1.22 markus 679: .It Cm ForwardX11Trusted
1.34 jmc 680: If this option is set to
1.240 jmc 681: .Cm yes ,
1.84 jmc 682: remote X11 clients will have full access to the original X11 display.
1.42 djm 683: .Pp
1.22 markus 684: If this option is set to
1.240 jmc 685: .Cm no
686: (the default),
1.84 jmc 687: remote X11 clients will be considered untrusted and prevented
1.22 markus 688: from stealing or tampering with data belonging to trusted X11
689: clients.
1.42 djm 690: Furthermore, the
691: .Xr xauth 1
692: token used for the session will be set to expire after 20 minutes.
693: Remote clients will be refused access after this time.
1.22 markus 694: .Pp
695: See the X11 SECURITY extension specification for full details on
696: the restrictions imposed on untrusted clients.
1.1 stevesk 697: .It Cm GatewayPorts
698: Specifies whether remote hosts are allowed to connect to local
699: forwarded ports.
700: By default,
1.84 jmc 701: .Xr ssh 1
1.7 jmc 702: binds local port forwardings to the loopback address.
703: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 704: .Cm GatewayPorts
1.84 jmc 705: can be used to specify that ssh
1.1 stevesk 706: should bind local port forwardings to the wildcard address,
707: thus allowing remote hosts to connect to forwarded ports.
708: The argument must be
1.240 jmc 709: .Cm yes
1.1 stevesk 710: or
1.240 jmc 711: .Cm no
712: (the default).
1.1 stevesk 713: .It Cm GlobalKnownHostsFile
1.151 djm 714: Specifies one or more files to use for the global
715: host key database, separated by whitespace.
716: The default is
717: .Pa /etc/ssh/ssh_known_hosts ,
718: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 719: .It Cm GSSAPIAuthentication
1.27 markus 720: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 721: The default is
1.240 jmc 722: .Cm no .
1.18 markus 723: .It Cm GSSAPIDelegateCredentials
724: Forward (delegate) credentials to the server.
725: The default is
1.240 jmc 726: .Cm no .
1.44 djm 727: .It Cm HashKnownHosts
728: Indicates that
1.84 jmc 729: .Xr ssh 1
1.44 djm 730: should hash host names and addresses when they are added to
1.50 djm 731: .Pa ~/.ssh/known_hosts .
1.44 djm 732: These hashed names may be used normally by
1.84 jmc 733: .Xr ssh 1
1.44 djm 734: and
1.84 jmc 735: .Xr sshd 8 ,
1.44 djm 736: but they do not reveal identifying information should the file's contents
737: be disclosed.
738: The default is
1.240 jmc 739: .Cm no .
1.97 jmc 740: Note that existing names and addresses in known hosts files
741: will not be converted automatically,
742: but may be manually hashed using
1.45 djm 743: .Xr ssh-keygen 1 .
1.1 stevesk 744: .It Cm HostbasedAuthentication
745: Specifies whether to try rhosts based authentication with public key
746: authentication.
747: The argument must be
1.240 jmc 748: .Cm yes
1.1 stevesk 749: or
1.240 jmc 750: .Cm no
751: (the default).
1.202 djm 752: .It Cm HostbasedKeyTypes
753: Specifies the key types that will be used for hostbased authentication
754: as a comma-separated pattern list.
1.214 djm 755: Alternately if the specified value begins with a
756: .Sq +
757: character, then the specified key types will be appended to the default set
758: instead of replacing them.
1.241 djm 759: If the specified value begins with a
760: .Sq -
761: character, then the specified key types (including wildcards) will be removed
762: from the default set instead of replacing them.
1.213 markus 763: The default for this option is:
764: .Bd -literal -offset 3n
765: ecdsa-sha2-nistp256-cert-v01@openssh.com,
766: ecdsa-sha2-nistp384-cert-v01@openssh.com,
767: ecdsa-sha2-nistp521-cert-v01@openssh.com,
768: ssh-ed25519-cert-v01@openssh.com,
769: ssh-rsa-cert-v01@openssh.com,
770: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 771: ssh-ed25519,ssh-rsa
1.213 markus 772: .Ed
773: .Pp
1.202 djm 774: The
775: .Fl Q
776: option of
777: .Xr ssh 1
778: may be used to list supported key types.
1.1 stevesk 779: .It Cm HostKeyAlgorithms
1.226 jmc 780: Specifies the host key algorithms
1.1 stevesk 781: that the client wants to use in order of preference.
1.214 djm 782: Alternately if the specified value begins with a
783: .Sq +
784: character, then the specified key types will be appended to the default set
785: instead of replacing them.
1.241 djm 786: If the specified value begins with a
787: .Sq -
788: character, then the specified key types (including wildcards) will be removed
789: from the default set instead of replacing them.
1.1 stevesk 790: The default for this option is:
1.139 djm 791: .Bd -literal -offset 3n
792: ecdsa-sha2-nistp256-cert-v01@openssh.com,
793: ecdsa-sha2-nistp384-cert-v01@openssh.com,
794: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 795: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 796: ssh-rsa-cert-v01@openssh.com,
1.139 djm 797: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 798: ssh-ed25519,ssh-rsa
1.139 djm 799: .Ed
1.145 djm 800: .Pp
801: If hostkeys are known for the destination host then this default is modified
802: to prefer their algorithms.
1.198 djm 803: .Pp
1.240 jmc 804: The list of available key types may also be obtained using
805: .Qq ssh -Q key .
1.1 stevesk 806: .It Cm HostKeyAlias
807: Specifies an alias that should be used instead of the
808: real host name when looking up or saving the host key
1.251 djm 809: in the host key database files and when validating host certificates.
1.84 jmc 810: This option is useful for tunneling SSH connections
1.1 stevesk 811: or for multiple servers running on a single host.
812: .It Cm HostName
813: Specifies the real host name to log into.
814: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 815: Arguments to
816: .Cm HostName
817: accept the tokens described in the
818: .Sx TOKENS
819: section.
1.1 stevesk 820: Numeric IP addresses are also permitted (both on the command line and in
821: .Cm HostName
822: specifications).
1.239 jmc 823: The default is the name given on the command line.
1.29 markus 824: .It Cm IdentitiesOnly
825: Specifies that
1.84 jmc 826: .Xr ssh 1
1.221 djm 827: should only use the authentication identity and certificate files explicitly
828: configured in the
1.31 jmc 829: .Nm
1.221 djm 830: files
831: or passed on the
832: .Xr ssh 1
833: command-line,
1.84 jmc 834: even if
835: .Xr ssh-agent 1
1.159 djm 836: or a
837: .Cm PKCS11Provider
1.29 markus 838: offers more identities.
839: The argument to this keyword must be
1.240 jmc 840: .Cm yes
1.29 markus 841: or
1.240 jmc 842: .Cm no
843: (the default).
1.84 jmc 844: This option is intended for situations where ssh-agent
1.29 markus 845: offers many different identities.
1.231 markus 846: .It Cm IdentityAgent
847: Specifies the
848: .Ux Ns -domain
849: socket used to communicate with the authentication agent.
850: .Pp
851: This option overrides the
1.240 jmc 852: .Ev SSH_AUTH_SOCK
1.231 markus 853: environment variable and can be used to select a specific agent.
854: Setting the socket name to
1.240 jmc 855: .Cm none
1.231 markus 856: disables the use of an authentication agent.
1.232 markus 857: If the string
1.240 jmc 858: .Qq SSH_AUTH_SOCK
1.232 markus 859: is specified, the location of the socket will be read from the
860: .Ev SSH_AUTH_SOCK
861: environment variable.
1.231 markus 862: .Pp
1.239 jmc 863: Arguments to
864: .Cm IdentityAgent
865: may use the tilde syntax to refer to a user's home directory
866: or the tokens described in the
867: .Sx TOKENS
868: section.
1.67 jmc 869: .It Cm IdentityFile
1.192 sobrado 870: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 871: identity is read.
1.67 jmc 872: The default is
1.139 djm 873: .Pa ~/.ssh/id_dsa ,
1.183 naddy 874: .Pa ~/.ssh/id_ecdsa ,
875: .Pa ~/.ssh/id_ed25519
1.139 djm 876: and
1.245 djm 877: .Pa ~/.ssh/id_rsa .
1.67 jmc 878: Additionally, any identities represented by the authentication agent
1.165 djm 879: will be used for authentication unless
880: .Cm IdentitiesOnly
881: is set.
1.221 djm 882: If no certificates have been explicitly specified by
883: .Cm CertificateFile ,
1.129 djm 884: .Xr ssh 1
885: will try to load certificate information from the filename obtained by
886: appending
887: .Pa -cert.pub
888: to the path of a specified
889: .Cm IdentityFile .
1.90 djm 890: .Pp
1.239 jmc 891: Arguments to
892: .Cm IdentityFile
893: may use the tilde syntax to refer to a user's home directory
894: or the tokens described in the
895: .Sx TOKENS
896: section.
1.90 djm 897: .Pp
1.67 jmc 898: It is possible to have
899: multiple identity files specified in configuration files; all these
900: identities will be tried in sequence.
1.152 djm 901: Multiple
902: .Cm IdentityFile
903: directives will add to the list of identities tried (this behaviour
904: differs from that of other configuration directives).
1.165 djm 905: .Pp
906: .Cm IdentityFile
907: may be used in conjunction with
908: .Cm IdentitiesOnly
909: to select which identities in an agent are offered during authentication.
1.221 djm 910: .Cm IdentityFile
911: may also be used in conjunction with
912: .Cm CertificateFile
913: in order to provide any certificate also needed for authentication with
914: the identity.
1.164 jmc 915: .It Cm IgnoreUnknown
916: Specifies a pattern-list of unknown options to be ignored if they are
917: encountered in configuration parsing.
918: This may be used to suppress errors if
919: .Nm
920: contains options that are unrecognised by
921: .Xr ssh 1 .
922: It is recommended that
923: .Cm IgnoreUnknown
924: be listed early in the configuration file as it will not be applied
925: to unknown options that appear before it.
1.229 djm 926: .It Cm Include
927: Include the specified configuration file(s).
1.230 jmc 928: Multiple pathnames may be specified and each pathname may contain
1.229 djm 929: .Xr glob 3
930: wildcards and, for user configurations, shell-like
1.240 jmc 931: .Sq ~
1.229 djm 932: references to user home directories.
933: Files without absolute paths are assumed to be in
934: .Pa ~/.ssh
1.230 jmc 935: if included in a user configuration file or
1.229 djm 936: .Pa /etc/ssh
937: if included from the system configuration file.
938: .Cm Include
939: directive may appear inside a
940: .Cm Match
941: or
942: .Cm Host
943: block
944: to perform conditional inclusion.
1.143 djm 945: .It Cm IPQoS
946: Specifies the IPv4 type-of-service or DSCP class for connections.
947: Accepted values are
1.240 jmc 948: .Cm af11 ,
949: .Cm af12 ,
950: .Cm af13 ,
951: .Cm af21 ,
952: .Cm af22 ,
953: .Cm af23 ,
954: .Cm af31 ,
955: .Cm af32 ,
956: .Cm af33 ,
957: .Cm af41 ,
958: .Cm af42 ,
959: .Cm af43 ,
960: .Cm cs0 ,
961: .Cm cs1 ,
962: .Cm cs2 ,
963: .Cm cs3 ,
964: .Cm cs4 ,
965: .Cm cs5 ,
966: .Cm cs6 ,
967: .Cm cs7 ,
968: .Cm ef ,
969: .Cm lowdelay ,
970: .Cm throughput ,
971: .Cm reliability ,
1.253 ! djm 972: a numeric value, or
! 973: .Cm none
! 974: to use the operating system default.
1.146 djm 975: This option may take one or two arguments, separated by whitespace.
1.143 djm 976: If one argument is specified, it is used as the packet class unconditionally.
977: If two values are specified, the first is automatically selected for
978: interactive sessions and the second for non-interactive sessions.
979: The default is
1.240 jmc 980: .Cm lowdelay
1.143 djm 981: for interactive sessions and
1.240 jmc 982: .Cm throughput
1.143 djm 983: for non-interactive sessions.
1.103 djm 984: .It Cm KbdInteractiveAuthentication
985: Specifies whether to use keyboard-interactive authentication.
986: The argument to this keyword must be
1.240 jmc 987: .Cm yes
988: (the default)
1.103 djm 989: or
1.240 jmc 990: .Cm no .
1.39 djm 991: .It Cm KbdInteractiveDevices
992: Specifies the list of methods to use in keyboard-interactive authentication.
993: Multiple method names must be comma-separated.
994: The default is to use the server specified list.
1.85 jmc 995: The methods available vary depending on what the server supports.
996: For an OpenSSH server,
997: it may be zero or more of:
1.240 jmc 998: .Cm bsdauth ,
999: .Cm pam ,
1.85 jmc 1000: and
1.240 jmc 1001: .Cm skey .
1.140 djm 1002: .It Cm KexAlgorithms
1003: Specifies the available KEX (Key Exchange) algorithms.
1004: Multiple algorithms must be comma-separated.
1.214 djm 1005: Alternately if the specified value begins with a
1006: .Sq +
1007: character, then the specified methods will be appended to the default set
1008: instead of replacing them.
1.241 djm 1009: If the specified value begins with a
1010: .Sq -
1011: character, then the specified methods (including wildcards) will be removed
1012: from the default set instead of replacing them.
1.141 jmc 1013: The default is:
1014: .Bd -literal -offset indent
1.238 djm 1015: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1016: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1017: diffie-hellman-group-exchange-sha256,
1.209 dtucker 1018: diffie-hellman-group-exchange-sha1,
1.212 djm 1019: diffie-hellman-group14-sha1
1.141 jmc 1020: .Ed
1.198 djm 1021: .Pp
1.240 jmc 1022: The list of available key exchange algorithms may also be obtained using
1023: .Qq ssh -Q kex .
1.65 reyk 1024: .It Cm LocalCommand
1025: Specifies a command to execute on the local machine after successfully
1026: connecting to the server.
1027: The command string extends to the end of the line, and is executed with
1.105 jmc 1028: the user's shell.
1.239 jmc 1029: Arguments to
1030: .Cm LocalCommand
1031: accept the tokens described in the
1032: .Sx TOKENS
1033: section.
1.123 djm 1034: .Pp
1035: The command is run synchronously and does not have access to the
1036: session of the
1037: .Xr ssh 1
1038: that spawned it.
1039: It should not be used for interactive commands.
1040: .Pp
1.65 reyk 1041: This directive is ignored unless
1042: .Cm PermitLocalCommand
1043: has been enabled.
1.1 stevesk 1044: .It Cm LocalForward
1.74 jmc 1045: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1046: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1047: The first argument must be
1.43 djm 1048: .Sm off
1.49 jmc 1049: .Oo Ar bind_address : Oc Ar port
1.43 djm 1050: .Sm on
1.49 jmc 1051: and the second argument must be
1052: .Ar host : Ns Ar hostport .
1.138 djm 1053: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1054: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1055: given on the command line.
1.1 stevesk 1056: Only the superuser can forward privileged ports.
1.43 djm 1057: By default, the local port is bound in accordance with the
1058: .Cm GatewayPorts
1059: setting.
1060: However, an explicit
1061: .Ar bind_address
1062: may be used to bind the connection to a specific address.
1063: The
1064: .Ar bind_address
1065: of
1.240 jmc 1066: .Cm localhost
1.46 jmc 1067: indicates that the listening port be bound for local use only, while an
1068: empty address or
1069: .Sq *
1.43 djm 1070: indicates that the port should be available from all interfaces.
1.1 stevesk 1071: .It Cm LogLevel
1072: Gives the verbosity level that is used when logging messages from
1.84 jmc 1073: .Xr ssh 1 .
1.1 stevesk 1074: The possible values are:
1.84 jmc 1075: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1076: The default is INFO.
1077: DEBUG and DEBUG1 are equivalent.
1078: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1079: .It Cm MACs
1080: Specifies the MAC (message authentication code) algorithms
1081: in order of preference.
1.226 jmc 1082: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1083: Multiple algorithms must be comma-separated.
1.214 djm 1084: If the specified value begins with a
1085: .Sq +
1086: character, then the specified algorithms will be appended to the default set
1087: instead of replacing them.
1.241 djm 1088: If the specified value begins with a
1089: .Sq -
1090: character, then the specified algorithms (including wildcards) will be removed
1091: from the default set instead of replacing them.
1.214 djm 1092: .Pp
1.160 markus 1093: The algorithms that contain
1.240 jmc 1094: .Qq -etm
1.160 markus 1095: calculate the MAC after encryption (encrypt-then-mac).
1096: These are considered safer and their use recommended.
1.214 djm 1097: .Pp
1.84 jmc 1098: The default is:
1.101 jmc 1099: .Bd -literal -offset indent
1.160 markus 1100: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1101: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1102: hmac-sha1-etm@openssh.com,
1.186 naddy 1103: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1104: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1105: .Ed
1.198 djm 1106: .Pp
1.240 jmc 1107: The list of available MAC algorithms may also be obtained using
1108: .Qq ssh -Q mac .
1.1 stevesk 1109: .It Cm NoHostAuthenticationForLocalhost
1110: This option can be used if the home directory is shared across machines.
1111: In this case localhost will refer to a different machine on each of
1112: the machines and the user will get many warnings about changed host keys.
1113: However, this option disables host authentication for localhost.
1114: The argument to this keyword must be
1.240 jmc 1115: .Cm yes
1.1 stevesk 1116: or
1.242 jmc 1117: .Cm no
1.240 jmc 1118: (the default).
1.1 stevesk 1119: .It Cm NumberOfPasswordPrompts
1120: Specifies the number of password prompts before giving up.
1121: The argument to this keyword must be an integer.
1.84 jmc 1122: The default is 3.
1.1 stevesk 1123: .It Cm PasswordAuthentication
1124: Specifies whether to use password authentication.
1125: The argument to this keyword must be
1.240 jmc 1126: .Cm yes
1127: (the default)
1.1 stevesk 1128: or
1.240 jmc 1129: .Cm no .
1.65 reyk 1130: .It Cm PermitLocalCommand
1131: Allow local command execution via the
1132: .Ic LocalCommand
1133: option or using the
1.66 jmc 1134: .Ic !\& Ns Ar command
1.65 reyk 1135: escape sequence in
1136: .Xr ssh 1 .
1137: The argument must be
1.240 jmc 1138: .Cm yes
1.65 reyk 1139: or
1.240 jmc 1140: .Cm no
1141: (the default).
1.127 markus 1142: .It Cm PKCS11Provider
1143: Specifies which PKCS#11 provider to use.
1.144 jmc 1144: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1145: .Xr ssh 1
1.128 markus 1146: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1147: private RSA key.
1.67 jmc 1148: .It Cm Port
1149: Specifies the port number to connect on the remote host.
1.84 jmc 1150: The default is 22.
1.1 stevesk 1151: .It Cm PreferredAuthentications
1.226 jmc 1152: Specifies the order in which the client should try authentication methods.
1.48 jmc 1153: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1154: .Cm keyboard-interactive )
1.48 jmc 1155: over another method (e.g.\&
1.131 jmc 1156: .Cm password ) .
1157: The default is:
1158: .Bd -literal -offset indent
1159: gssapi-with-mic,hostbased,publickey,
1160: keyboard-interactive,password
1161: .Ed
1.1 stevesk 1162: .It Cm ProxyCommand
1163: Specifies the command to use to connect to the server.
1164: The command
1.190 djm 1165: string extends to the end of the line, and is executed
1166: using the user's shell
1167: .Ql exec
1168: directive to avoid a lingering shell process.
1169: .Pp
1.239 jmc 1170: Arguments to
1171: .Cm ProxyCommand
1172: accept the tokens described in the
1173: .Sx TOKENS
1174: section.
1.1 stevesk 1175: The command can be basically anything,
1176: and should read from its standard input and write to its standard output.
1177: It should eventually connect an
1178: .Xr sshd 8
1179: server running on some machine, or execute
1180: .Ic sshd -i
1181: somewhere.
1182: Host key management will be done using the
1183: HostName of the host being connected (defaulting to the name typed by
1184: the user).
1.7 jmc 1185: Setting the command to
1.240 jmc 1186: .Cm none
1.6 markus 1187: disables this option entirely.
1.1 stevesk 1188: Note that
1189: .Cm CheckHostIP
1190: is not available for connects with a proxy command.
1.52 djm 1191: .Pp
1192: This directive is useful in conjunction with
1193: .Xr nc 1
1194: and its proxy support.
1.53 jmc 1195: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1196: 192.0.2.0:
1197: .Bd -literal -offset 3n
1198: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1199: .Ed
1.233 djm 1200: .It Cm ProxyJump
1201: Specifies one or more jump proxies as
1202: .Xo
1203: .Sm off
1.234 jmc 1204: .Op Ar user No @
1.233 djm 1205: .Ar host
1.234 jmc 1206: .Op : Ns Ar port
1.233 djm 1207: .Sm on
1208: .Xc .
1.235 djm 1209: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1210: sequentially.
1.233 djm 1211: Setting this option will cause
1212: .Xr ssh 1
1213: to connect to the target host by first making a
1214: .Xr ssh 1
1215: connection to the specified
1216: .Cm ProxyJump
1217: host and then establishing a
1.234 jmc 1218: TCP forwarding to the ultimate target from there.
1.233 djm 1219: .Pp
1220: Note that this option will compete with the
1221: .Cm ProxyCommand
1222: option - whichever is specified first will prevent later instances of the
1223: other from taking effect.
1.167 djm 1224: .It Cm ProxyUseFdpass
1.168 jmc 1225: Specifies that
1.167 djm 1226: .Cm ProxyCommand
1227: will pass a connected file descriptor back to
1.168 jmc 1228: .Xr ssh 1
1.167 djm 1229: instead of continuing to execute and pass data.
1230: The default is
1.240 jmc 1231: .Cm no .
1.213 markus 1232: .It Cm PubkeyAcceptedKeyTypes
1233: Specifies the key types that will be used for public key authentication
1234: as a comma-separated pattern list.
1.214 djm 1235: Alternately if the specified value begins with a
1236: .Sq +
1237: character, then the key types after it will be appended to the default
1238: instead of replacing it.
1.241 djm 1239: If the specified value begins with a
1240: .Sq -
1241: character, then the specified key types (including wildcards) will be removed
1242: from the default set instead of replacing them.
1.213 markus 1243: The default for this option is:
1244: .Bd -literal -offset 3n
1245: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1246: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1247: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1248: ssh-ed25519-cert-v01@openssh.com,
1249: ssh-rsa-cert-v01@openssh.com,
1250: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 1251: ssh-ed25519,ssh-rsa
1.213 markus 1252: .Ed
1253: .Pp
1.240 jmc 1254: The list of available key types may also be obtained using
1255: .Qq ssh -Q key .
1.1 stevesk 1256: .It Cm PubkeyAuthentication
1257: Specifies whether to try public key authentication.
1258: The argument to this keyword must be
1.240 jmc 1259: .Cm yes
1260: (the default)
1.1 stevesk 1261: or
1.240 jmc 1262: .Cm no .
1.75 dtucker 1263: .It Cm RekeyLimit
1264: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1265: session key is renegotiated, optionally followed a maximum amount of
1266: time that may pass before the session key is renegotiated.
1267: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1268: .Sq K ,
1269: .Sq M ,
1.75 dtucker 1270: or
1.76 jmc 1271: .Sq G
1.75 dtucker 1272: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1273: The default is between
1.84 jmc 1274: .Sq 1G
1.75 dtucker 1275: and
1.84 jmc 1276: .Sq 4G ,
1.75 dtucker 1277: depending on the cipher.
1.162 dtucker 1278: The optional second value is specified in seconds and may use any of the
1279: units documented in the
1.240 jmc 1280: .Sx TIME FORMATS
1281: section of
1.162 dtucker 1282: .Xr sshd_config 5 .
1283: The default value for
1284: .Cm RekeyLimit
1285: is
1.240 jmc 1286: .Cm default none ,
1.162 dtucker 1287: which means that rekeying is performed after the cipher's default amount
1288: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1289: .It Cm RemoteCommand
1290: Specifies a command to execute on the remote machine after successfully
1291: connecting to the server.
1292: The command string extends to the end of the line, and is executed with
1293: the user's shell.
1.250 jmc 1294: Arguments to
1295: .Cm RemoteCommand
1296: accept the tokens described in the
1297: .Sx TOKENS
1298: section.
1.1 stevesk 1299: .It Cm RemoteForward
1.74 jmc 1300: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1301: the secure channel to the specified host and port from the local machine.
1.49 jmc 1302: The first argument must be
1.43 djm 1303: .Sm off
1.49 jmc 1304: .Oo Ar bind_address : Oc Ar port
1.43 djm 1305: .Sm on
1.49 jmc 1306: and the second argument must be
1307: .Ar host : Ns Ar hostport .
1.138 djm 1308: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1309: Multiple forwardings may be specified, and additional
1310: forwardings can be given on the command line.
1.113 stevesk 1311: Privileged ports can be forwarded only when
1312: logging in as root on the remote machine.
1.118 jmc 1313: .Pp
1.117 djm 1314: If the
1315: .Ar port
1.240 jmc 1316: argument is 0,
1.117 djm 1317: the listen port will be dynamically allocated on the server and reported
1318: to the client at run time.
1.43 djm 1319: .Pp
1320: If the
1321: .Ar bind_address
1322: is not specified, the default is to only bind to loopback addresses.
1323: If the
1324: .Ar bind_address
1325: is
1326: .Ql *
1327: or an empty string, then the forwarding is requested to listen on all
1328: interfaces.
1329: Specifying a remote
1330: .Ar bind_address
1.46 jmc 1331: will only succeed if the server's
1332: .Cm GatewayPorts
1.43 djm 1333: option is enabled (see
1.46 jmc 1334: .Xr sshd_config 5 ) .
1.149 djm 1335: .It Cm RequestTTY
1336: Specifies whether to request a pseudo-tty for the session.
1337: The argument may be one of:
1.240 jmc 1338: .Cm no
1.149 djm 1339: (never request a TTY),
1.240 jmc 1340: .Cm yes
1.149 djm 1341: (always request a TTY when standard input is a TTY),
1.240 jmc 1342: .Cm force
1.149 djm 1343: (always request a TTY) or
1.240 jmc 1344: .Cm auto
1.149 djm 1345: (request a TTY when opening a login session).
1346: This option mirrors the
1347: .Fl t
1348: and
1349: .Fl T
1350: flags for
1351: .Xr ssh 1 .
1.196 djm 1352: .It Cm RevokedHostKeys
1353: Specifies revoked host public keys.
1354: Keys listed in this file will be refused for host authentication.
1355: Note that if this file does not exist or is not readable,
1356: then host authentication will be refused for all hosts.
1357: Keys may be specified as a text file, listing one public key per line, or as
1358: an OpenSSH Key Revocation List (KRL) as generated by
1359: .Xr ssh-keygen 1 .
1360: For more information on KRLs, see the KEY REVOCATION LISTS section in
1361: .Xr ssh-keygen 1 .
1.32 djm 1362: .It Cm SendEnv
1363: Specifies what variables from the local
1364: .Xr environ 7
1365: should be sent to the server.
1.84 jmc 1366: The server must also support it, and the server must be configured to
1.33 djm 1367: accept these environment variables.
1.207 dtucker 1368: Note that the
1369: .Ev TERM
1.208 jmc 1370: environment variable is always sent whenever a
1.207 dtucker 1371: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1372: Refer to
1373: .Cm AcceptEnv
1374: in
1375: .Xr sshd_config 5
1376: for how to configure the server.
1.80 jmc 1377: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1378: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1379: across multiple
1380: .Cm SendEnv
1381: directives.
1382: The default is not to send any environment variables.
1.81 jmc 1383: .Pp
1384: See
1385: .Sx PATTERNS
1386: for more information on patterns.
1.28 markus 1387: .It Cm ServerAliveCountMax
1.73 jmc 1388: Sets the number of server alive messages (see below) which may be
1.28 markus 1389: sent without
1.84 jmc 1390: .Xr ssh 1
1.28 markus 1391: receiving any messages back from the server.
1392: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1393: ssh will disconnect from the server, terminating the session.
1.28 markus 1394: It is important to note that the use of server alive messages is very
1395: different from
1396: .Cm TCPKeepAlive
1397: (below).
1398: The server alive messages are sent through the encrypted channel
1399: and therefore will not be spoofable.
1400: The TCP keepalive option enabled by
1401: .Cm TCPKeepAlive
1402: is spoofable.
1403: The server alive mechanism is valuable when the client or
1404: server depend on knowing when a connection has become inactive.
1405: .Pp
1406: The default value is 3.
1407: If, for example,
1408: .Cm ServerAliveInterval
1.84 jmc 1409: (see below) is set to 15 and
1.28 markus 1410: .Cm ServerAliveCountMax
1.84 jmc 1411: is left at the default, if the server becomes unresponsive,
1412: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1413: .It Cm ServerAliveInterval
1414: Sets a timeout interval in seconds after which if no data has been received
1415: from the server,
1.84 jmc 1416: .Xr ssh 1
1.67 jmc 1417: will send a message through the encrypted
1418: channel to request a response from the server.
1419: The default
1420: is 0, indicating that these messages will not be sent to the server.
1.191 millert 1421: .It Cm StreamLocalBindMask
1422: Sets the octal file creation mode mask
1423: .Pq umask
1424: used when creating a Unix-domain socket file for local or remote
1425: port forwarding.
1426: This option is only used for port forwarding to a Unix-domain socket file.
1427: .Pp
1428: The default value is 0177, which creates a Unix-domain socket file that is
1429: readable and writable only by the owner.
1430: Note that not all operating systems honor the file mode on Unix-domain
1431: socket files.
1432: .It Cm StreamLocalBindUnlink
1433: Specifies whether to remove an existing Unix-domain socket file for local
1434: or remote port forwarding before creating a new one.
1435: If the socket file already exists and
1436: .Cm StreamLocalBindUnlink
1437: is not enabled,
1438: .Nm ssh
1439: will be unable to forward the port to the Unix-domain socket file.
1440: This option is only used for port forwarding to a Unix-domain socket file.
1441: .Pp
1442: The argument must be
1.240 jmc 1443: .Cm yes
1.191 millert 1444: or
1.240 jmc 1445: .Cm no
1446: (the default).
1.1 stevesk 1447: .It Cm StrictHostKeyChecking
1448: If this flag is set to
1.240 jmc 1449: .Cm yes ,
1.84 jmc 1450: .Xr ssh 1
1.1 stevesk 1451: will never automatically add host keys to the
1.50 djm 1452: .Pa ~/.ssh/known_hosts
1.1 stevesk 1453: file, and refuses to connect to hosts whose host key has changed.
1454: This provides maximum protection against trojan horse attacks,
1.84 jmc 1455: though it can be annoying when the
1.1 stevesk 1456: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1457: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1458: frequently made.
1459: This option forces the user to manually
1460: add all new hosts.
1461: If this flag is set to
1.240 jmc 1462: .Cm no ,
1.84 jmc 1463: ssh will automatically add new host keys to the
1.1 stevesk 1464: user known hosts files.
1465: If this flag is set to
1.240 jmc 1466: .Cm ask
1467: (the default),
1.1 stevesk 1468: new host keys
1469: will be added to the user known host files only after the user
1470: has confirmed that is what they really want to do, and
1.84 jmc 1471: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1472: The host keys of
1473: known hosts will be verified automatically in all cases.
1.244 jmc 1474: .It Cm SyslogFacility
1475: Gives the facility code that is used when logging messages from
1476: .Xr ssh 1 .
1477: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1478: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1479: The default is USER.
1.26 markus 1480: .It Cm TCPKeepAlive
1481: Specifies whether the system should send TCP keepalive messages to the
1482: other side.
1483: If they are sent, death of the connection or crash of one
1484: of the machines will be properly noticed.
1485: However, this means that
1486: connections will die if the route is down temporarily, and some people
1487: find it annoying.
1488: .Pp
1489: The default is
1.240 jmc 1490: .Cm yes
1.26 markus 1491: (to send TCP keepalive messages), and the client will notice
1492: if the network goes down or the remote host dies.
1493: This is important in scripts, and many users want it too.
1494: .Pp
1495: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1496: .Cm no .
1.65 reyk 1497: .It Cm Tunnel
1.95 stevesk 1498: Request
1.65 reyk 1499: .Xr tun 4
1.69 jmc 1500: device forwarding between the client and the server.
1.65 reyk 1501: The argument must be
1.240 jmc 1502: .Cm yes ,
1503: .Cm point-to-point
1.95 stevesk 1504: (layer 3),
1.240 jmc 1505: .Cm ethernet
1.95 stevesk 1506: (layer 2),
1.65 reyk 1507: or
1.240 jmc 1508: .Cm no
1509: (the default).
1.95 stevesk 1510: Specifying
1.240 jmc 1511: .Cm yes
1.95 stevesk 1512: requests the default tunnel mode, which is
1.240 jmc 1513: .Cm point-to-point .
1.65 reyk 1514: .It Cm TunnelDevice
1.95 stevesk 1515: Specifies the
1.65 reyk 1516: .Xr tun 4
1.95 stevesk 1517: devices to open on the client
1518: .Pq Ar local_tun
1519: and the server
1520: .Pq Ar remote_tun .
1521: .Pp
1522: The argument must be
1523: .Sm off
1524: .Ar local_tun Op : Ar remote_tun .
1525: .Sm on
1526: The devices may be specified by numerical ID or the keyword
1.240 jmc 1527: .Cm any ,
1.95 stevesk 1528: which uses the next available tunnel device.
1529: If
1530: .Ar remote_tun
1531: is not specified, it defaults to
1.240 jmc 1532: .Cm any .
1.95 stevesk 1533: The default is
1.240 jmc 1534: .Cm any:any .
1.201 djm 1535: .It Cm UpdateHostKeys
1.200 djm 1536: Specifies whether
1537: .Xr ssh 1
1538: should accept notifications of additional hostkeys from the server sent
1539: after authentication has completed and add them to
1540: .Cm UserKnownHostsFile .
1541: The argument must be
1.240 jmc 1542: .Cm yes ,
1543: .Cm no
1.204 djm 1544: (the default) or
1.240 jmc 1545: .Cm ask .
1.200 djm 1546: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1547: and supports graceful key rotation by allowing a server to send replacement
1548: public keys before old ones are removed.
1.200 djm 1549: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1550: host was already trusted or explicitly accepted by the user.
1.204 djm 1551: If
1552: .Cm UpdateHostKeys
1553: is set to
1.240 jmc 1554: .Cm ask ,
1.204 djm 1555: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1556: Confirmation is currently incompatible with
1557: .Cm ControlPersist ,
1558: and will be disabled if it is enabled.
1.200 djm 1559: .Pp
1560: Presently, only
1561: .Xr sshd 8
1562: from OpenSSH 6.8 and greater support the
1.240 jmc 1563: .Qq hostkeys@openssh.com
1.200 djm 1564: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1565: .It Cm UsePrivilegedPort
1566: Specifies whether to use a privileged port for outgoing connections.
1567: The argument must be
1.240 jmc 1568: .Cm yes
1.72 jmc 1569: or
1.240 jmc 1570: .Cm no
1571: (the default).
1.72 jmc 1572: If set to
1.240 jmc 1573: .Cm yes ,
1.84 jmc 1574: .Xr ssh 1
1.72 jmc 1575: must be setuid root.
1.1 stevesk 1576: .It Cm User
1577: Specifies the user to log in as.
1578: This can be useful when a different user name is used on different machines.
1579: This saves the trouble of
1580: having to remember to give the user name on the command line.
1581: .It Cm UserKnownHostsFile
1.151 djm 1582: Specifies one or more files to use for the user
1583: host key database, separated by whitespace.
1584: The default is
1585: .Pa ~/.ssh/known_hosts ,
1586: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1587: .It Cm VerifyHostKeyDNS
1588: Specifies whether to verify the remote key using DNS and SSHFP resource
1589: records.
1.24 jakob 1590: If this option is set to
1.240 jmc 1591: .Cm yes ,
1.25 jmc 1592: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1593: from DNS.
1594: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1595: .Cm ask .
1.24 jakob 1596: If this option is set to
1.240 jmc 1597: .Cm ask ,
1.24 jakob 1598: information on fingerprint match will be displayed, but the user will still
1599: need to confirm new host keys according to the
1600: .Cm StrictHostKeyChecking
1601: option.
1.8 jakob 1602: The default is
1.240 jmc 1603: .Cm no .
1.84 jmc 1604: .Pp
1.240 jmc 1605: See also
1606: .Sx VERIFYING HOST KEYS
1607: in
1.84 jmc 1608: .Xr ssh 1 .
1.111 grunk 1609: .It Cm VisualHostKey
1610: If this flag is set to
1.240 jmc 1611: .Cm yes ,
1.111 grunk 1612: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1613: printed in addition to the fingerprint string at login and
1.114 stevesk 1614: for unknown host keys.
1.111 grunk 1615: If this flag is set to
1.240 jmc 1616: .Cm no
1617: (the default),
1.114 stevesk 1618: no fingerprint strings are printed at login and
1.197 djm 1619: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1620: .It Cm XAuthLocation
1.5 stevesk 1621: Specifies the full pathname of the
1.1 stevesk 1622: .Xr xauth 1
1623: program.
1624: The default is
1625: .Pa /usr/X11R6/bin/xauth .
1626: .El
1.86 jmc 1627: .Sh PATTERNS
1628: A
1629: .Em pattern
1630: consists of zero or more non-whitespace characters,
1631: .Sq *
1632: (a wildcard that matches zero or more characters),
1633: or
1634: .Sq ?\&
1635: (a wildcard that matches exactly one character).
1636: For example, to specify a set of declarations for any host in the
1.240 jmc 1637: .Qq .co.uk
1.86 jmc 1638: set of domains,
1639: the following pattern could be used:
1640: .Pp
1641: .Dl Host *.co.uk
1642: .Pp
1643: The following pattern
1644: would match any host in the 192.168.0.[0-9] network range:
1645: .Pp
1646: .Dl Host 192.168.0.?
1647: .Pp
1648: A
1649: .Em pattern-list
1650: is a comma-separated list of patterns.
1651: Patterns within pattern-lists may be negated
1652: by preceding them with an exclamation mark
1653: .Pq Sq !\& .
1654: For example,
1.174 djm 1655: to allow a key to be used from anywhere within an organization
1.86 jmc 1656: except from the
1.240 jmc 1657: .Qq dialup
1.86 jmc 1658: pool,
1659: the following entry (in authorized_keys) could be used:
1660: .Pp
1661: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.239 jmc 1662: .Sh TOKENS
1663: Arguments to some keywords can make use of tokens,
1664: which are expanded at runtime:
1665: .Pp
1666: .Bl -tag -width XXXX -offset indent -compact
1667: .It %%
1668: A literal
1669: .Sq % .
1670: .It \&%C
1671: Shorthand for %l%h%p%r.
1672: .It %d
1673: Local user's home directory.
1674: .It %h
1675: The remote hostname.
1676: .It %i
1677: The local user ID.
1678: .It %L
1679: The local hostname.
1680: .It %l
1681: The local hostname, including the domain name.
1682: .It %n
1683: The original remote hostname, as given on the command line.
1684: .It %p
1685: The remote port.
1686: .It %r
1687: The remote username.
1688: .It %u
1689: The local username.
1690: .El
1691: .Pp
1692: .Cm Match exec
1693: accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1694: .Pp
1695: .Cm CertificateFile
1696: accepts the tokens %%, %d, %h, %l, %r, and %u.
1697: .Pp
1698: .Cm ControlPath
1699: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1700: .Pp
1701: .Cm HostName
1702: accepts the tokens %% and %h.
1703: .Pp
1704: .Cm IdentityAgent
1705: and
1706: .Cm IdentityFile
1707: accept the tokens %%, %d, %h, %l, %r, and %u.
1708: .Pp
1709: .Cm LocalCommand
1710: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1711: .Pp
1712: .Cm ProxyCommand
1713: accepts the tokens %%, %h, %p, and %r.
1.250 jmc 1714: .Pp
1715: .Cm RemoteCommand
1716: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1.1 stevesk 1717: .Sh FILES
1718: .Bl -tag -width Ds
1.50 djm 1719: .It Pa ~/.ssh/config
1.1 stevesk 1720: This is the per-user configuration file.
1721: The format of this file is described above.
1.84 jmc 1722: This file is used by the SSH client.
1.30 djm 1723: Because of the potential for abuse, this file must have strict permissions:
1724: read/write for the user, and not accessible by others.
1.1 stevesk 1725: .It Pa /etc/ssh/ssh_config
1726: Systemwide configuration file.
1727: This file provides defaults for those
1728: values that are not specified in the user's configuration file, and
1729: for those users who do not have a configuration file.
1730: This file must be world-readable.
1731: .El
1.13 jmc 1732: .Sh SEE ALSO
1733: .Xr ssh 1
1.1 stevesk 1734: .Sh AUTHORS
1.240 jmc 1735: .An -nosplit
1.1 stevesk 1736: OpenSSH is a derivative of the original and free
1.240 jmc 1737: ssh 1.2.12 release by
1738: .An Tatu Ylonen .
1739: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1740: .An Niels Provos , Theo de Raadt
1741: and
1742: .An Dug Song
1.1 stevesk 1743: removed many bugs, re-added newer features and
1744: created OpenSSH.
1.240 jmc 1745: .An Markus Friedl
1746: contributed the support for SSH protocol versions 1.5 and 2.0.
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