Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.248
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
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29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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1.248 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.247 2017/05/03 21:49:18 naddy Exp $
1.247 naddy 37: .Dd $Mdocdate: May 3 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 SYNOPSIS
1.98 jmc 44: .Nm ~/.ssh/config
45: .Nm /etc/ssh/ssh_config
1.1 stevesk 46: .Sh DESCRIPTION
1.84 jmc 47: .Xr ssh 1
1.1 stevesk 48: obtains configuration data from the following sources in
49: the following order:
1.79 jmc 50: .Pp
1.2 stevesk 51: .Bl -enum -offset indent -compact
52: .It
53: command-line options
54: .It
55: user's configuration file
1.50 djm 56: .Pq Pa ~/.ssh/config
1.2 stevesk 57: .It
58: system-wide configuration file
59: .Pq Pa /etc/ssh/ssh_config
60: .El
1.1 stevesk 61: .Pp
62: For each parameter, the first obtained value
63: will be used.
1.41 jmc 64: The configuration files contain sections separated by
1.240 jmc 65: .Cm Host
1.1 stevesk 66: specifications, and that section is only applied for hosts that
67: match one of the patterns given in the specification.
1.193 djm 68: The matched host name is usually the one given on the command line
69: (see the
70: .Cm CanonicalizeHostname
1.240 jmc 71: option for exceptions).
1.1 stevesk 72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 jmc 76: .Pp
1.240 jmc 77: The file contains keyword-argument pairs, one per line.
78: Lines starting with
1.1 stevesk 79: .Ql #
1.240 jmc 80: and empty lines are interpreted as comments.
81: Arguments may optionally be enclosed in double quotes
82: .Pq \&"
83: in order to represent arguments containing spaces.
1.1 stevesk 84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
1.87 jmc 90: .Nm scp ,
1.1 stevesk 91: and
92: .Nm sftp
93: .Fl o
94: option.
95: .Pp
96: The possible
97: keywords and their meanings are as follows (note that
98: keywords are case-insensitive and arguments are case-sensitive):
99: .Bl -tag -width Ds
100: .It Cm Host
101: Restricts the following declarations (up to the next
102: .Cm Host
1.169 djm 103: or
104: .Cm Match
1.1 stevesk 105: keyword) to be only for those hosts that match one of the patterns
106: given after the keyword.
1.112 krw 107: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 108: A single
1.83 jmc 109: .Ql *
1.1 stevesk 110: as a pattern can be used to provide global
111: defaults for all hosts.
1.193 djm 112: The host is usually the
1.1 stevesk 113: .Ar hostname
1.193 djm 114: argument given on the command line
115: (see the
116: .Cm CanonicalizeHostname
1.240 jmc 117: keyword for exceptions).
1.148 djm 118: .Pp
119: A pattern entry may be negated by prefixing it with an exclamation mark
120: .Pq Sq !\& .
121: If a negated entry is matched, then the
122: .Cm Host
123: entry is ignored, regardless of whether any other patterns on the line
124: match.
125: Negated matches are therefore useful to provide exceptions for wildcard
126: matches.
1.81 jmc 127: .Pp
128: See
129: .Sx PATTERNS
130: for more information on patterns.
1.170 jmc 131: .It Cm Match
1.169 djm 132: Restricts the following declarations (up to the next
133: .Cm Host
134: or
135: .Cm Match
136: keyword) to be used only when the conditions following the
137: .Cm Match
138: keyword are satisfied.
1.220 sobrado 139: Match conditions are specified using one or more criteria
1.178 dtucker 140: or the single token
141: .Cm all
1.193 djm 142: which always matches.
143: The available criteria keywords are:
144: .Cm canonical ,
1.176 djm 145: .Cm exec ,
1.169 djm 146: .Cm host ,
147: .Cm originalhost ,
148: .Cm user ,
149: and
150: .Cm localuser .
1.193 djm 151: The
152: .Cm all
153: criteria must appear alone or immediately after
1.194 jmc 154: .Cm canonical .
1.193 djm 155: Other criteria may be combined arbitrarily.
156: All criteria but
157: .Cm all
158: and
159: .Cm canonical
160: require an argument.
161: Criteria may be negated by prepending an exclamation mark
162: .Pq Sq !\& .
1.169 djm 163: .Pp
1.177 jmc 164: The
1.193 djm 165: .Cm canonical
1.210 dtucker 166: keyword matches only when the configuration file is being re-parsed
1.193 djm 167: after hostname canonicalization (see the
168: .Cm CanonicalizeHostname
169: option.)
170: This may be useful to specify conditions that work with canonical host
171: names only.
172: The
1.176 djm 173: .Cm exec
1.177 jmc 174: keyword executes the specified command under the user's shell.
1.169 djm 175: If the command returns a zero exit status then the condition is considered true.
176: Commands containing whitespace characters must be quoted.
1.239 jmc 177: Arguments to
178: .Cm exec
179: accept the tokens described in the
180: .Sx TOKENS
181: section.
1.169 djm 182: .Pp
183: The other keywords' criteria must be single entries or comma-separated
184: lists and may use the wildcard and negation operators described in the
185: .Sx PATTERNS
186: section.
187: The criteria for the
188: .Cm host
189: keyword are matched against the target hostname, after any substitution
190: by the
191: .Cm Hostname
1.193 djm 192: or
193: .Cm CanonicalizeHostname
194: options.
1.169 djm 195: The
196: .Cm originalhost
197: keyword matches against the hostname as it was specified on the command-line.
198: The
199: .Cm user
200: keyword matches against the target username on the remote host.
201: The
202: .Cm localuser
203: keyword matches against the name of the local user running
204: .Xr ssh 1
205: (this keyword may be useful in system-wide
206: .Nm
207: files).
1.222 jcs 208: .It Cm AddKeysToAgent
209: Specifies whether keys should be automatically added to a running
1.223 jmc 210: .Xr ssh-agent 1 .
1.222 jcs 211: If this option is set to
1.240 jmc 212: .Cm yes
1.222 jcs 213: and a key is loaded from a file, the key and its passphrase are added to
214: the agent with the default lifetime, as if by
215: .Xr ssh-add 1 .
216: If this option is set to
1.240 jmc 217: .Cm ask ,
218: .Xr ssh 1
1.222 jcs 219: will require confirmation using the
220: .Ev SSH_ASKPASS
221: program before adding a key (see
222: .Xr ssh-add 1
223: for details).
224: If this option is set to
1.240 jmc 225: .Cm confirm ,
1.222 jcs 226: each use of the key must be confirmed, as if the
227: .Fl c
228: option was specified to
229: .Xr ssh-add 1 .
230: If this option is set to
1.240 jmc 231: .Cm no ,
1.222 jcs 232: no keys are added to the agent.
233: The argument must be
1.240 jmc 234: .Cm yes ,
235: .Cm confirm ,
236: .Cm ask ,
1.222 jcs 237: or
1.240 jmc 238: .Cm no
239: (the default).
1.10 djm 240: .It Cm AddressFamily
1.11 jmc 241: Specifies which address family to use when connecting.
242: Valid arguments are
1.240 jmc 243: .Cm any
244: (the default),
245: .Cm inet
1.84 jmc 246: (use IPv4 only), or
1.240 jmc 247: .Cm inet6
1.40 jmc 248: (use IPv6 only).
1.1 stevesk 249: .It Cm BatchMode
250: If set to
1.240 jmc 251: .Cm yes ,
1.1 stevesk 252: passphrase/password querying will be disabled.
253: This option is useful in scripts and other batch jobs where no user
254: is present to supply the password.
255: The argument must be
1.240 jmc 256: .Cm yes
1.1 stevesk 257: or
1.240 jmc 258: .Cm no
259: (the default).
1.1 stevesk 260: .It Cm BindAddress
1.60 dtucker 261: Use the specified address on the local machine as the source address of
1.61 jmc 262: the connection.
263: Only useful on systems with more than one address.
1.1 stevesk 264: Note that this option does not work if
265: .Cm UsePrivilegedPort
266: is set to
1.240 jmc 267: .Cm yes .
1.171 djm 268: .It Cm CanonicalDomains
1.172 jmc 269: When
1.173 djm 270: .Cm CanonicalizeHostname
1.171 djm 271: is enabled, this option specifies the list of domain suffixes in which to
272: search for the specified destination host.
1.173 djm 273: .It Cm CanonicalizeFallbackLocal
1.174 djm 274: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 275: The default,
1.240 jmc 276: .Cm yes ,
1.172 jmc 277: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 278: search rules.
279: A value of
1.240 jmc 280: .Cm no
1.171 djm 281: will cause
282: .Xr ssh 1
283: to fail instantly if
1.173 djm 284: .Cm CanonicalizeHostname
1.171 djm 285: is enabled and the target hostname cannot be found in any of the domains
286: specified by
287: .Cm CanonicalDomains .
1.173 djm 288: .It Cm CanonicalizeHostname
1.174 djm 289: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 290: The default,
1.240 jmc 291: .Cm no ,
1.171 djm 292: is not to perform any name rewriting and let the system resolver handle all
293: hostname lookups.
294: If set to
1.240 jmc 295: .Cm yes
1.171 djm 296: then, for connections that do not use a
297: .Cm ProxyCommand ,
298: .Xr ssh 1
1.173 djm 299: will attempt to canonicalize the hostname specified on the command line
1.171 djm 300: using the
301: .Cm CanonicalDomains
302: suffixes and
1.173 djm 303: .Cm CanonicalizePermittedCNAMEs
1.171 djm 304: rules.
305: If
1.173 djm 306: .Cm CanonicalizeHostname
1.171 djm 307: is set to
1.240 jmc 308: .Cm always ,
1.174 djm 309: then canonicalization is applied to proxied connections too.
1.185 djm 310: .Pp
1.193 djm 311: If this option is enabled, then the configuration files are processed
312: again using the new target name to pick up any new configuration in matching
1.185 djm 313: .Cm Host
1.193 djm 314: and
315: .Cm Match
1.185 djm 316: stanzas.
1.173 djm 317: .It Cm CanonicalizeMaxDots
1.172 jmc 318: Specifies the maximum number of dot characters in a hostname before
1.174 djm 319: canonicalization is disabled.
1.240 jmc 320: The default, 1,
1.172 jmc 321: allows a single dot (i.e. hostname.subdomain).
1.173 djm 322: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 323: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 324: canonicalizing hostnames.
1.171 djm 325: The rules consist of one or more arguments of
1.172 jmc 326: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 327: where
328: .Ar source_domain_list
1.174 djm 329: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 330: and
331: .Ar target_domain_list
1.172 jmc 332: is a pattern-list of domains that they may resolve to.
1.171 djm 333: .Pp
334: For example,
1.240 jmc 335: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 336: will allow hostnames matching
1.240 jmc 337: .Qq *.a.example.com
1.173 djm 338: to be canonicalized to names in the
1.240 jmc 339: .Qq *.b.example.com
1.171 djm 340: or
1.240 jmc 341: .Qq *.c.example.com
1.171 djm 342: domains.
1.221 djm 343: .It Cm CertificateFile
344: Specifies a file from which the user's certificate is read.
345: A corresponding private key must be provided separately in order
346: to use this certificate either
347: from an
348: .Cm IdentityFile
349: directive or
350: .Fl i
351: flag to
352: .Xr ssh 1 ,
353: via
354: .Xr ssh-agent 1 ,
355: or via a
356: .Cm PKCS11Provider .
357: .Pp
1.239 jmc 358: Arguments to
359: .Cm CertificateFile
360: may use the tilde syntax to refer to a user's home directory
361: or the tokens described in the
362: .Sx TOKENS
363: section.
1.221 djm 364: .Pp
365: It is possible to have multiple certificate files specified in
366: configuration files; these certificates will be tried in sequence.
367: Multiple
368: .Cm CertificateFile
369: directives will add to the list of certificates used for
370: authentication.
1.1 stevesk 371: .It Cm ChallengeResponseAuthentication
1.82 jmc 372: Specifies whether to use challenge-response authentication.
1.1 stevesk 373: The argument to this keyword must be
1.240 jmc 374: .Cm yes
375: (the default)
1.1 stevesk 376: or
1.240 jmc 377: .Cm no .
1.1 stevesk 378: .It Cm CheckHostIP
1.240 jmc 379: If set to
380: .Cm yes
381: (the default),
1.84 jmc 382: .Xr ssh 1
383: will additionally check the host IP address in the
1.1 stevesk 384: .Pa known_hosts
385: file.
1.240 jmc 386: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 387: and will add addresses of destination hosts to
388: .Pa ~/.ssh/known_hosts
389: in the process, regardless of the setting of
390: .Cm StrictHostKeyChecking .
1.107 grunk 391: If the option is set to
1.240 jmc 392: .Cm no ,
1.1 stevesk 393: the check will not be executed.
394: .It Cm Ciphers
1.245 djm 395: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 396: Multiple ciphers must be comma-separated.
1.214 djm 397: If the specified value begins with a
398: .Sq +
399: character, then the specified ciphers will be appended to the default set
400: instead of replacing them.
1.241 djm 401: If the specified value begins with a
402: .Sq -
403: character, then the specified ciphers (including wildcards) will be removed
404: from the default set instead of replacing them.
1.214 djm 405: .Pp
1.180 djm 406: The supported ciphers are:
1.240 jmc 407: .Bd -literal -offset indent
1.186 naddy 408: 3des-cbc
409: aes128-cbc
410: aes192-cbc
411: aes256-cbc
412: aes128-ctr
413: aes192-ctr
414: aes256-ctr
415: aes128-gcm@openssh.com
416: aes256-gcm@openssh.com
417: chacha20-poly1305@openssh.com
1.240 jmc 418: .Ed
1.180 djm 419: .Pp
1.84 jmc 420: The default is:
1.186 naddy 421: .Bd -literal -offset indent
1.215 jmc 422: chacha20-poly1305@openssh.com,
1.186 naddy 423: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 424: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.237 djm 425: aes128-cbc,aes192-cbc,aes256-cbc
1.1 stevesk 426: .Ed
1.180 djm 427: .Pp
1.240 jmc 428: The list of available ciphers may also be obtained using
429: .Qq ssh -Q cipher .
1.1 stevesk 430: .It Cm ClearAllForwardings
1.84 jmc 431: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 432: specified in the configuration files or on the command line be
1.7 jmc 433: cleared.
434: This option is primarily useful when used from the
1.84 jmc 435: .Xr ssh 1
1.1 stevesk 436: command line to clear port forwardings set in
437: configuration files, and is automatically set by
438: .Xr scp 1
439: and
440: .Xr sftp 1 .
441: The argument must be
1.240 jmc 442: .Cm yes
1.1 stevesk 443: or
1.240 jmc 444: .Cm no
445: (the default).
1.1 stevesk 446: .It Cm Compression
447: Specifies whether to use compression.
448: The argument must be
1.240 jmc 449: .Cm yes
1.1 stevesk 450: or
1.240 jmc 451: .Cm no
452: (the default).
1.247 naddy 453: .It Cm ConnectionAttempts
454: Specifies the number of tries (one per second) to make before exiting.
455: The argument must be an integer.
456: This may be useful in scripts if the connection sometimes fails.
457: The default is 1.
1.9 djm 458: .It Cm ConnectTimeout
1.84 jmc 459: Specifies the timeout (in seconds) used when connecting to the
460: SSH server, instead of using the default system TCP timeout.
1.11 jmc 461: This value is used only when the target is down or really unreachable,
462: not when it refuses the connection.
1.36 djm 463: .It Cm ControlMaster
464: Enables the sharing of multiple sessions over a single network connection.
465: When set to
1.240 jmc 466: .Cm yes ,
1.84 jmc 467: .Xr ssh 1
1.36 djm 468: will listen for connections on a control socket specified using the
469: .Cm ControlPath
470: argument.
471: Additional sessions can connect to this socket using the same
472: .Cm ControlPath
473: with
474: .Cm ControlMaster
475: set to
1.240 jmc 476: .Cm no
1.38 jmc 477: (the default).
1.64 jmc 478: These sessions will try to reuse the master instance's network connection
1.63 djm 479: rather than initiating new ones, but will fall back to connecting normally
480: if the control socket does not exist, or is not listening.
481: .Pp
1.37 djm 482: Setting this to
1.240 jmc 483: .Cm ask
484: will cause
485: .Xr ssh 1
1.206 jmc 486: to listen for control connections, but require confirmation using
487: .Xr ssh-askpass 1 .
1.51 jakob 488: If the
489: .Cm ControlPath
1.84 jmc 490: cannot be opened,
1.240 jmc 491: .Xr ssh 1
492: will continue without connecting to a master instance.
1.58 djm 493: .Pp
494: X11 and
1.59 jmc 495: .Xr ssh-agent 1
1.58 djm 496: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 497: display and agent forwarded will be the one belonging to the master
1.59 jmc 498: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 499: .Pp
500: Two additional options allow for opportunistic multiplexing: try to use a
501: master connection but fall back to creating a new one if one does not already
502: exist.
503: These options are:
1.240 jmc 504: .Cm auto
1.56 djm 505: and
1.240 jmc 506: .Cm autoask .
1.56 djm 507: The latter requires confirmation like the
1.240 jmc 508: .Cm ask
1.56 djm 509: option.
1.36 djm 510: .It Cm ControlPath
1.55 djm 511: Specify the path to the control socket used for connection sharing as described
512: in the
1.36 djm 513: .Cm ControlMaster
1.57 djm 514: section above or the string
1.240 jmc 515: .Cm none
1.57 djm 516: to disable connection sharing.
1.239 jmc 517: Arguments to
518: .Cm ControlPath
519: may use the tilde syntax to refer to a user's home directory
520: or the tokens described in the
521: .Sx TOKENS
522: section.
1.56 djm 523: It is recommended that any
524: .Cm ControlPath
525: used for opportunistic connection sharing include
1.195 djm 526: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
527: that is not writable by other users.
1.56 djm 528: This ensures that shared connections are uniquely identified.
1.137 djm 529: .It Cm ControlPersist
530: When used in conjunction with
531: .Cm ControlMaster ,
532: specifies that the master connection should remain open
533: in the background (waiting for future client connections)
534: after the initial client connection has been closed.
535: If set to
1.240 jmc 536: .Cm no ,
1.137 djm 537: then the master connection will not be placed into the background,
538: and will close as soon as the initial client connection is closed.
539: If set to
1.240 jmc 540: .Cm yes
541: or 0,
1.137 djm 542: then the master connection will remain in the background indefinitely
543: (until killed or closed via a mechanism such as the
1.240 jmc 544: .Qq ssh -O exit ) .
1.137 djm 545: If set to a time in seconds, or a time in any of the formats documented in
546: .Xr sshd_config 5 ,
547: then the backgrounded master connection will automatically terminate
548: after it has remained idle (with no client connections) for the
549: specified time.
1.38 jmc 550: .It Cm DynamicForward
1.74 jmc 551: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 552: over the secure channel, and the application
553: protocol is then used to determine where to connect to from the
554: remote machine.
1.62 djm 555: .Pp
556: The argument must be
557: .Sm off
558: .Oo Ar bind_address : Oc Ar port .
559: .Sm on
1.138 djm 560: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 561: By default, the local port is bound in accordance with the
562: .Cm GatewayPorts
563: setting.
564: However, an explicit
565: .Ar bind_address
566: may be used to bind the connection to a specific address.
567: The
568: .Ar bind_address
569: of
1.240 jmc 570: .Cm localhost
1.62 djm 571: indicates that the listening port be bound for local use only, while an
572: empty address or
573: .Sq *
574: indicates that the port should be available from all interfaces.
575: .Pp
1.38 jmc 576: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 577: .Xr ssh 1
1.38 jmc 578: will act as a SOCKS server.
579: Multiple forwardings may be specified, and
580: additional forwardings can be given on the command line.
581: Only the superuser can forward privileged ports.
1.14 markus 582: .It Cm EnableSSHKeysign
583: Setting this option to
1.240 jmc 584: .Cm yes
1.14 markus 585: in the global client configuration file
586: .Pa /etc/ssh/ssh_config
587: enables the use of the helper program
588: .Xr ssh-keysign 8
589: during
590: .Cm HostbasedAuthentication .
591: The argument must be
1.240 jmc 592: .Cm yes
1.14 markus 593: or
1.240 jmc 594: .Cm no
595: (the default).
1.23 jmc 596: This option should be placed in the non-hostspecific section.
1.14 markus 597: See
598: .Xr ssh-keysign 8
599: for more information.
1.1 stevesk 600: .It Cm EscapeChar
601: Sets the escape character (default:
602: .Ql ~ ) .
603: The escape character can also
604: be set on the command line.
605: The argument should be a single character,
606: .Ql ^
607: followed by a letter, or
1.240 jmc 608: .Cm none
1.1 stevesk 609: to disable the escape
610: character entirely (making the connection transparent for binary
611: data).
1.96 markus 612: .It Cm ExitOnForwardFailure
613: Specifies whether
614: .Xr ssh 1
615: should terminate the connection if it cannot set up all requested
1.216 djm 616: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 617: if either end is unable to bind and listen on a specified port).
1.216 djm 618: Note that
619: .Cm ExitOnForwardFailure
620: does not apply to connections made over port forwardings and will not,
621: for example, cause
622: .Xr ssh 1
623: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 624: The argument must be
1.240 jmc 625: .Cm yes
1.96 markus 626: or
1.240 jmc 627: .Cm no
628: (the default).
1.197 djm 629: .It Cm FingerprintHash
630: Specifies the hash algorithm used when displaying key fingerprints.
631: Valid options are:
1.240 jmc 632: .Cm md5
1.197 djm 633: and
1.240 jmc 634: .Cm sha256
635: (the default).
1.1 stevesk 636: .It Cm ForwardAgent
637: Specifies whether the connection to the authentication agent (if any)
638: will be forwarded to the remote machine.
639: The argument must be
1.240 jmc 640: .Cm yes
1.1 stevesk 641: or
1.240 jmc 642: .Cm no
643: (the default).
1.3 stevesk 644: .Pp
1.7 jmc 645: Agent forwarding should be enabled with caution.
646: Users with the ability to bypass file permissions on the remote host
647: (for the agent's Unix-domain socket)
648: can access the local agent through the forwarded connection.
649: An attacker cannot obtain key material from the agent,
1.3 stevesk 650: however they can perform operations on the keys that enable them to
651: authenticate using the identities loaded into the agent.
1.1 stevesk 652: .It Cm ForwardX11
653: Specifies whether X11 connections will be automatically redirected
654: over the secure channel and
655: .Ev DISPLAY
656: set.
657: The argument must be
1.240 jmc 658: .Cm yes
1.1 stevesk 659: or
1.240 jmc 660: .Cm no
661: (the default).
1.3 stevesk 662: .Pp
1.7 jmc 663: X11 forwarding should be enabled with caution.
664: Users with the ability to bypass file permissions on the remote host
1.22 markus 665: (for the user's X11 authorization database)
1.7 jmc 666: can access the local X11 display through the forwarded connection.
1.22 markus 667: An attacker may then be able to perform activities such as keystroke monitoring
668: if the
669: .Cm ForwardX11Trusted
670: option is also enabled.
1.134 djm 671: .It Cm ForwardX11Timeout
1.135 jmc 672: Specify a timeout for untrusted X11 forwarding
673: using the format described in the
1.240 jmc 674: .Sx TIME FORMATS
675: section of
1.134 djm 676: .Xr sshd_config 5 .
677: X11 connections received by
678: .Xr ssh 1
679: after this time will be refused.
680: The default is to disable untrusted X11 forwarding after twenty minutes has
681: elapsed.
1.22 markus 682: .It Cm ForwardX11Trusted
1.34 jmc 683: If this option is set to
1.240 jmc 684: .Cm yes ,
1.84 jmc 685: remote X11 clients will have full access to the original X11 display.
1.42 djm 686: .Pp
1.22 markus 687: If this option is set to
1.240 jmc 688: .Cm no
689: (the default),
1.84 jmc 690: remote X11 clients will be considered untrusted and prevented
1.22 markus 691: from stealing or tampering with data belonging to trusted X11
692: clients.
1.42 djm 693: Furthermore, the
694: .Xr xauth 1
695: token used for the session will be set to expire after 20 minutes.
696: Remote clients will be refused access after this time.
1.22 markus 697: .Pp
698: See the X11 SECURITY extension specification for full details on
699: the restrictions imposed on untrusted clients.
1.1 stevesk 700: .It Cm GatewayPorts
701: Specifies whether remote hosts are allowed to connect to local
702: forwarded ports.
703: By default,
1.84 jmc 704: .Xr ssh 1
1.7 jmc 705: binds local port forwardings to the loopback address.
706: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 707: .Cm GatewayPorts
1.84 jmc 708: can be used to specify that ssh
1.1 stevesk 709: should bind local port forwardings to the wildcard address,
710: thus allowing remote hosts to connect to forwarded ports.
711: The argument must be
1.240 jmc 712: .Cm yes
1.1 stevesk 713: or
1.240 jmc 714: .Cm no
715: (the default).
1.1 stevesk 716: .It Cm GlobalKnownHostsFile
1.151 djm 717: Specifies one or more files to use for the global
718: host key database, separated by whitespace.
719: The default is
720: .Pa /etc/ssh/ssh_known_hosts ,
721: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 722: .It Cm GSSAPIAuthentication
1.27 markus 723: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 724: The default is
1.240 jmc 725: .Cm no .
1.18 markus 726: .It Cm GSSAPIDelegateCredentials
727: Forward (delegate) credentials to the server.
728: The default is
1.240 jmc 729: .Cm no .
1.44 djm 730: .It Cm HashKnownHosts
731: Indicates that
1.84 jmc 732: .Xr ssh 1
1.44 djm 733: should hash host names and addresses when they are added to
1.50 djm 734: .Pa ~/.ssh/known_hosts .
1.44 djm 735: These hashed names may be used normally by
1.84 jmc 736: .Xr ssh 1
1.44 djm 737: and
1.84 jmc 738: .Xr sshd 8 ,
1.44 djm 739: but they do not reveal identifying information should the file's contents
740: be disclosed.
741: The default is
1.240 jmc 742: .Cm no .
1.97 jmc 743: Note that existing names and addresses in known hosts files
744: will not be converted automatically,
745: but may be manually hashed using
1.45 djm 746: .Xr ssh-keygen 1 .
1.1 stevesk 747: .It Cm HostbasedAuthentication
748: Specifies whether to try rhosts based authentication with public key
749: authentication.
750: The argument must be
1.240 jmc 751: .Cm yes
1.1 stevesk 752: or
1.240 jmc 753: .Cm no
754: (the default).
1.202 djm 755: .It Cm HostbasedKeyTypes
756: Specifies the key types that will be used for hostbased authentication
757: as a comma-separated pattern list.
1.214 djm 758: Alternately if the specified value begins with a
759: .Sq +
760: character, then the specified key types will be appended to the default set
761: instead of replacing them.
1.241 djm 762: If the specified value begins with a
763: .Sq -
764: character, then the specified key types (including wildcards) will be removed
765: from the default set instead of replacing them.
1.213 markus 766: The default for this option is:
767: .Bd -literal -offset 3n
768: ecdsa-sha2-nistp256-cert-v01@openssh.com,
769: ecdsa-sha2-nistp384-cert-v01@openssh.com,
770: ecdsa-sha2-nistp521-cert-v01@openssh.com,
771: ssh-ed25519-cert-v01@openssh.com,
772: ssh-rsa-cert-v01@openssh.com,
773: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 774: ssh-ed25519,ssh-rsa
1.213 markus 775: .Ed
776: .Pp
1.202 djm 777: The
778: .Fl Q
779: option of
780: .Xr ssh 1
781: may be used to list supported key types.
1.1 stevesk 782: .It Cm HostKeyAlgorithms
1.226 jmc 783: Specifies the host key algorithms
1.1 stevesk 784: that the client wants to use in order of preference.
1.214 djm 785: Alternately if the specified value begins with a
786: .Sq +
787: character, then the specified key types will be appended to the default set
788: instead of replacing them.
1.241 djm 789: If the specified value begins with a
790: .Sq -
791: character, then the specified key types (including wildcards) will be removed
792: from the default set instead of replacing them.
1.1 stevesk 793: The default for this option is:
1.139 djm 794: .Bd -literal -offset 3n
795: ecdsa-sha2-nistp256-cert-v01@openssh.com,
796: ecdsa-sha2-nistp384-cert-v01@openssh.com,
797: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 798: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 799: ssh-rsa-cert-v01@openssh.com,
1.139 djm 800: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 801: ssh-ed25519,ssh-rsa
1.139 djm 802: .Ed
1.145 djm 803: .Pp
804: If hostkeys are known for the destination host then this default is modified
805: to prefer their algorithms.
1.198 djm 806: .Pp
1.240 jmc 807: The list of available key types may also be obtained using
808: .Qq ssh -Q key .
1.1 stevesk 809: .It Cm HostKeyAlias
810: Specifies an alias that should be used instead of the
811: real host name when looking up or saving the host key
812: in the host key database files.
1.84 jmc 813: This option is useful for tunneling SSH connections
1.1 stevesk 814: or for multiple servers running on a single host.
815: .It Cm HostName
816: Specifies the real host name to log into.
817: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 818: Arguments to
819: .Cm HostName
820: accept the tokens described in the
821: .Sx TOKENS
822: section.
1.1 stevesk 823: Numeric IP addresses are also permitted (both on the command line and in
824: .Cm HostName
825: specifications).
1.239 jmc 826: The default is the name given on the command line.
1.29 markus 827: .It Cm IdentitiesOnly
828: Specifies that
1.84 jmc 829: .Xr ssh 1
1.221 djm 830: should only use the authentication identity and certificate files explicitly
831: configured in the
1.31 jmc 832: .Nm
1.221 djm 833: files
834: or passed on the
835: .Xr ssh 1
836: command-line,
1.84 jmc 837: even if
838: .Xr ssh-agent 1
1.159 djm 839: or a
840: .Cm PKCS11Provider
1.29 markus 841: offers more identities.
842: The argument to this keyword must be
1.240 jmc 843: .Cm yes
1.29 markus 844: or
1.240 jmc 845: .Cm no
846: (the default).
1.84 jmc 847: This option is intended for situations where ssh-agent
1.29 markus 848: offers many different identities.
1.231 markus 849: .It Cm IdentityAgent
850: Specifies the
851: .Ux Ns -domain
852: socket used to communicate with the authentication agent.
853: .Pp
854: This option overrides the
1.240 jmc 855: .Ev SSH_AUTH_SOCK
1.231 markus 856: environment variable and can be used to select a specific agent.
857: Setting the socket name to
1.240 jmc 858: .Cm none
1.231 markus 859: disables the use of an authentication agent.
1.232 markus 860: If the string
1.240 jmc 861: .Qq SSH_AUTH_SOCK
1.232 markus 862: is specified, the location of the socket will be read from the
863: .Ev SSH_AUTH_SOCK
864: environment variable.
1.231 markus 865: .Pp
1.239 jmc 866: Arguments to
867: .Cm IdentityAgent
868: may use the tilde syntax to refer to a user's home directory
869: or the tokens described in the
870: .Sx TOKENS
871: section.
1.67 jmc 872: .It Cm IdentityFile
1.192 sobrado 873: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 874: identity is read.
1.67 jmc 875: The default is
1.139 djm 876: .Pa ~/.ssh/id_dsa ,
1.183 naddy 877: .Pa ~/.ssh/id_ecdsa ,
878: .Pa ~/.ssh/id_ed25519
1.139 djm 879: and
1.245 djm 880: .Pa ~/.ssh/id_rsa .
1.67 jmc 881: Additionally, any identities represented by the authentication agent
1.165 djm 882: will be used for authentication unless
883: .Cm IdentitiesOnly
884: is set.
1.221 djm 885: If no certificates have been explicitly specified by
886: .Cm CertificateFile ,
1.129 djm 887: .Xr ssh 1
888: will try to load certificate information from the filename obtained by
889: appending
890: .Pa -cert.pub
891: to the path of a specified
892: .Cm IdentityFile .
1.90 djm 893: .Pp
1.239 jmc 894: Arguments to
895: .Cm IdentityFile
896: may use the tilde syntax to refer to a user's home directory
897: or the tokens described in the
898: .Sx TOKENS
899: section.
1.90 djm 900: .Pp
1.67 jmc 901: It is possible to have
902: multiple identity files specified in configuration files; all these
903: identities will be tried in sequence.
1.152 djm 904: Multiple
905: .Cm IdentityFile
906: directives will add to the list of identities tried (this behaviour
907: differs from that of other configuration directives).
1.165 djm 908: .Pp
909: .Cm IdentityFile
910: may be used in conjunction with
911: .Cm IdentitiesOnly
912: to select which identities in an agent are offered during authentication.
1.221 djm 913: .Cm IdentityFile
914: may also be used in conjunction with
915: .Cm CertificateFile
916: in order to provide any certificate also needed for authentication with
917: the identity.
1.164 jmc 918: .It Cm IgnoreUnknown
919: Specifies a pattern-list of unknown options to be ignored if they are
920: encountered in configuration parsing.
921: This may be used to suppress errors if
922: .Nm
923: contains options that are unrecognised by
924: .Xr ssh 1 .
925: It is recommended that
926: .Cm IgnoreUnknown
927: be listed early in the configuration file as it will not be applied
928: to unknown options that appear before it.
1.229 djm 929: .It Cm Include
930: Include the specified configuration file(s).
1.230 jmc 931: Multiple pathnames may be specified and each pathname may contain
1.229 djm 932: .Xr glob 3
933: wildcards and, for user configurations, shell-like
1.240 jmc 934: .Sq ~
1.229 djm 935: references to user home directories.
936: Files without absolute paths are assumed to be in
937: .Pa ~/.ssh
1.230 jmc 938: if included in a user configuration file or
1.229 djm 939: .Pa /etc/ssh
940: if included from the system configuration file.
941: .Cm Include
942: directive may appear inside a
943: .Cm Match
944: or
945: .Cm Host
946: block
947: to perform conditional inclusion.
1.143 djm 948: .It Cm IPQoS
949: Specifies the IPv4 type-of-service or DSCP class for connections.
950: Accepted values are
1.240 jmc 951: .Cm af11 ,
952: .Cm af12 ,
953: .Cm af13 ,
954: .Cm af21 ,
955: .Cm af22 ,
956: .Cm af23 ,
957: .Cm af31 ,
958: .Cm af32 ,
959: .Cm af33 ,
960: .Cm af41 ,
961: .Cm af42 ,
962: .Cm af43 ,
963: .Cm cs0 ,
964: .Cm cs1 ,
965: .Cm cs2 ,
966: .Cm cs3 ,
967: .Cm cs4 ,
968: .Cm cs5 ,
969: .Cm cs6 ,
970: .Cm cs7 ,
971: .Cm ef ,
972: .Cm lowdelay ,
973: .Cm throughput ,
974: .Cm reliability ,
1.143 djm 975: or a numeric value.
1.146 djm 976: This option may take one or two arguments, separated by whitespace.
1.143 djm 977: If one argument is specified, it is used as the packet class unconditionally.
978: If two values are specified, the first is automatically selected for
979: interactive sessions and the second for non-interactive sessions.
980: The default is
1.240 jmc 981: .Cm lowdelay
1.143 djm 982: for interactive sessions and
1.240 jmc 983: .Cm throughput
1.143 djm 984: for non-interactive sessions.
1.103 djm 985: .It Cm KbdInteractiveAuthentication
986: Specifies whether to use keyboard-interactive authentication.
987: The argument to this keyword must be
1.240 jmc 988: .Cm yes
989: (the default)
1.103 djm 990: or
1.240 jmc 991: .Cm no .
1.39 djm 992: .It Cm KbdInteractiveDevices
993: Specifies the list of methods to use in keyboard-interactive authentication.
994: Multiple method names must be comma-separated.
995: The default is to use the server specified list.
1.85 jmc 996: The methods available vary depending on what the server supports.
997: For an OpenSSH server,
998: it may be zero or more of:
1.240 jmc 999: .Cm bsdauth ,
1000: .Cm pam ,
1.85 jmc 1001: and
1.240 jmc 1002: .Cm skey .
1.140 djm 1003: .It Cm KexAlgorithms
1004: Specifies the available KEX (Key Exchange) algorithms.
1005: Multiple algorithms must be comma-separated.
1.214 djm 1006: Alternately if the specified value begins with a
1007: .Sq +
1008: character, then the specified methods will be appended to the default set
1009: instead of replacing them.
1.241 djm 1010: If the specified value begins with a
1011: .Sq -
1012: character, then the specified methods (including wildcards) will be removed
1013: from the default set instead of replacing them.
1.141 jmc 1014: The default is:
1015: .Bd -literal -offset indent
1.238 djm 1016: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1017: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1018: diffie-hellman-group-exchange-sha256,
1.209 dtucker 1019: diffie-hellman-group-exchange-sha1,
1.212 djm 1020: diffie-hellman-group14-sha1
1.141 jmc 1021: .Ed
1.198 djm 1022: .Pp
1.240 jmc 1023: The list of available key exchange algorithms may also be obtained using
1024: .Qq ssh -Q kex .
1.65 reyk 1025: .It Cm LocalCommand
1026: Specifies a command to execute on the local machine after successfully
1027: connecting to the server.
1028: The command string extends to the end of the line, and is executed with
1.105 jmc 1029: the user's shell.
1.239 jmc 1030: Arguments to
1031: .Cm LocalCommand
1032: accept the tokens described in the
1033: .Sx TOKENS
1034: section.
1.123 djm 1035: .Pp
1036: The command is run synchronously and does not have access to the
1037: session of the
1038: .Xr ssh 1
1039: that spawned it.
1040: It should not be used for interactive commands.
1041: .Pp
1.65 reyk 1042: This directive is ignored unless
1043: .Cm PermitLocalCommand
1044: has been enabled.
1.1 stevesk 1045: .It Cm LocalForward
1.74 jmc 1046: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1047: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1048: The first argument must be
1.43 djm 1049: .Sm off
1.49 jmc 1050: .Oo Ar bind_address : Oc Ar port
1.43 djm 1051: .Sm on
1.49 jmc 1052: and the second argument must be
1053: .Ar host : Ns Ar hostport .
1.138 djm 1054: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1055: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1056: given on the command line.
1.1 stevesk 1057: Only the superuser can forward privileged ports.
1.43 djm 1058: By default, the local port is bound in accordance with the
1059: .Cm GatewayPorts
1060: setting.
1061: However, an explicit
1062: .Ar bind_address
1063: may be used to bind the connection to a specific address.
1064: The
1065: .Ar bind_address
1066: of
1.240 jmc 1067: .Cm localhost
1.46 jmc 1068: indicates that the listening port be bound for local use only, while an
1069: empty address or
1070: .Sq *
1.43 djm 1071: indicates that the port should be available from all interfaces.
1.1 stevesk 1072: .It Cm LogLevel
1073: Gives the verbosity level that is used when logging messages from
1.84 jmc 1074: .Xr ssh 1 .
1.1 stevesk 1075: The possible values are:
1.84 jmc 1076: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1077: The default is INFO.
1078: DEBUG and DEBUG1 are equivalent.
1079: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1080: .It Cm MACs
1081: Specifies the MAC (message authentication code) algorithms
1082: in order of preference.
1.226 jmc 1083: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1084: Multiple algorithms must be comma-separated.
1.214 djm 1085: If the specified value begins with a
1086: .Sq +
1087: character, then the specified algorithms will be appended to the default set
1088: instead of replacing them.
1.241 djm 1089: If the specified value begins with a
1090: .Sq -
1091: character, then the specified algorithms (including wildcards) will be removed
1092: from the default set instead of replacing them.
1.214 djm 1093: .Pp
1.160 markus 1094: The algorithms that contain
1.240 jmc 1095: .Qq -etm
1.160 markus 1096: calculate the MAC after encryption (encrypt-then-mac).
1097: These are considered safer and their use recommended.
1.214 djm 1098: .Pp
1.84 jmc 1099: The default is:
1.101 jmc 1100: .Bd -literal -offset indent
1.160 markus 1101: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1102: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1103: hmac-sha1-etm@openssh.com,
1.186 naddy 1104: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1105: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1106: .Ed
1.198 djm 1107: .Pp
1.240 jmc 1108: The list of available MAC algorithms may also be obtained using
1109: .Qq ssh -Q mac .
1.1 stevesk 1110: .It Cm NoHostAuthenticationForLocalhost
1111: This option can be used if the home directory is shared across machines.
1112: In this case localhost will refer to a different machine on each of
1113: the machines and the user will get many warnings about changed host keys.
1114: However, this option disables host authentication for localhost.
1115: The argument to this keyword must be
1.240 jmc 1116: .Cm yes
1.1 stevesk 1117: or
1.242 jmc 1118: .Cm no
1.240 jmc 1119: (the default).
1.1 stevesk 1120: .It Cm NumberOfPasswordPrompts
1121: Specifies the number of password prompts before giving up.
1122: The argument to this keyword must be an integer.
1.84 jmc 1123: The default is 3.
1.1 stevesk 1124: .It Cm PasswordAuthentication
1125: Specifies whether to use password authentication.
1126: The argument to this keyword must be
1.240 jmc 1127: .Cm yes
1128: (the default)
1.1 stevesk 1129: or
1.240 jmc 1130: .Cm no .
1.65 reyk 1131: .It Cm PermitLocalCommand
1132: Allow local command execution via the
1133: .Ic LocalCommand
1134: option or using the
1.66 jmc 1135: .Ic !\& Ns Ar command
1.65 reyk 1136: escape sequence in
1137: .Xr ssh 1 .
1138: The argument must be
1.240 jmc 1139: .Cm yes
1.65 reyk 1140: or
1.240 jmc 1141: .Cm no
1142: (the default).
1.127 markus 1143: .It Cm PKCS11Provider
1144: Specifies which PKCS#11 provider to use.
1.144 jmc 1145: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1146: .Xr ssh 1
1.128 markus 1147: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1148: private RSA key.
1.67 jmc 1149: .It Cm Port
1150: Specifies the port number to connect on the remote host.
1.84 jmc 1151: The default is 22.
1.1 stevesk 1152: .It Cm PreferredAuthentications
1.226 jmc 1153: Specifies the order in which the client should try authentication methods.
1.48 jmc 1154: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1155: .Cm keyboard-interactive )
1.48 jmc 1156: over another method (e.g.\&
1.131 jmc 1157: .Cm password ) .
1158: The default is:
1159: .Bd -literal -offset indent
1160: gssapi-with-mic,hostbased,publickey,
1161: keyboard-interactive,password
1162: .Ed
1.1 stevesk 1163: .It Cm ProxyCommand
1164: Specifies the command to use to connect to the server.
1165: The command
1.190 djm 1166: string extends to the end of the line, and is executed
1167: using the user's shell
1168: .Ql exec
1169: directive to avoid a lingering shell process.
1170: .Pp
1.239 jmc 1171: Arguments to
1172: .Cm ProxyCommand
1173: accept the tokens described in the
1174: .Sx TOKENS
1175: section.
1.1 stevesk 1176: The command can be basically anything,
1177: and should read from its standard input and write to its standard output.
1178: It should eventually connect an
1179: .Xr sshd 8
1180: server running on some machine, or execute
1181: .Ic sshd -i
1182: somewhere.
1183: Host key management will be done using the
1184: HostName of the host being connected (defaulting to the name typed by
1185: the user).
1.7 jmc 1186: Setting the command to
1.240 jmc 1187: .Cm none
1.6 markus 1188: disables this option entirely.
1.1 stevesk 1189: Note that
1190: .Cm CheckHostIP
1191: is not available for connects with a proxy command.
1.52 djm 1192: .Pp
1193: This directive is useful in conjunction with
1194: .Xr nc 1
1195: and its proxy support.
1.53 jmc 1196: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1197: 192.0.2.0:
1198: .Bd -literal -offset 3n
1199: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1200: .Ed
1.233 djm 1201: .It Cm ProxyJump
1202: Specifies one or more jump proxies as
1203: .Xo
1204: .Sm off
1.234 jmc 1205: .Op Ar user No @
1.233 djm 1206: .Ar host
1.234 jmc 1207: .Op : Ns Ar port
1.233 djm 1208: .Sm on
1209: .Xc .
1.235 djm 1210: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1211: sequentially.
1.233 djm 1212: Setting this option will cause
1213: .Xr ssh 1
1214: to connect to the target host by first making a
1215: .Xr ssh 1
1216: connection to the specified
1217: .Cm ProxyJump
1218: host and then establishing a
1.234 jmc 1219: TCP forwarding to the ultimate target from there.
1.233 djm 1220: .Pp
1221: Note that this option will compete with the
1222: .Cm ProxyCommand
1223: option - whichever is specified first will prevent later instances of the
1224: other from taking effect.
1.167 djm 1225: .It Cm ProxyUseFdpass
1.168 jmc 1226: Specifies that
1.167 djm 1227: .Cm ProxyCommand
1228: will pass a connected file descriptor back to
1.168 jmc 1229: .Xr ssh 1
1.167 djm 1230: instead of continuing to execute and pass data.
1231: The default is
1.240 jmc 1232: .Cm no .
1.213 markus 1233: .It Cm PubkeyAcceptedKeyTypes
1234: Specifies the key types that will be used for public key authentication
1235: as a comma-separated pattern list.
1.214 djm 1236: Alternately if the specified value begins with a
1237: .Sq +
1238: character, then the key types after it will be appended to the default
1239: instead of replacing it.
1.241 djm 1240: If the specified value begins with a
1241: .Sq -
1242: character, then the specified key types (including wildcards) will be removed
1243: from the default set instead of replacing them.
1.213 markus 1244: The default for this option is:
1245: .Bd -literal -offset 3n
1246: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1247: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1248: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1249: ssh-ed25519-cert-v01@openssh.com,
1250: ssh-rsa-cert-v01@openssh.com,
1251: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 1252: ssh-ed25519,ssh-rsa
1.213 markus 1253: .Ed
1254: .Pp
1.240 jmc 1255: The list of available key types may also be obtained using
1256: .Qq ssh -Q key .
1.1 stevesk 1257: .It Cm PubkeyAuthentication
1258: Specifies whether to try public key authentication.
1259: The argument to this keyword must be
1.240 jmc 1260: .Cm yes
1261: (the default)
1.1 stevesk 1262: or
1.240 jmc 1263: .Cm no .
1.75 dtucker 1264: .It Cm RekeyLimit
1265: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1266: session key is renegotiated, optionally followed a maximum amount of
1267: time that may pass before the session key is renegotiated.
1268: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1269: .Sq K ,
1270: .Sq M ,
1.75 dtucker 1271: or
1.76 jmc 1272: .Sq G
1.75 dtucker 1273: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1274: The default is between
1.84 jmc 1275: .Sq 1G
1.75 dtucker 1276: and
1.84 jmc 1277: .Sq 4G ,
1.75 dtucker 1278: depending on the cipher.
1.162 dtucker 1279: The optional second value is specified in seconds and may use any of the
1280: units documented in the
1.240 jmc 1281: .Sx TIME FORMATS
1282: section of
1.162 dtucker 1283: .Xr sshd_config 5 .
1284: The default value for
1285: .Cm RekeyLimit
1286: is
1.240 jmc 1287: .Cm default none ,
1.162 dtucker 1288: which means that rekeying is performed after the cipher's default amount
1289: of data has been sent or received and no time based rekeying is done.
1.1 stevesk 1290: .It Cm RemoteForward
1.74 jmc 1291: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1292: the secure channel to the specified host and port from the local machine.
1.49 jmc 1293: The first argument must be
1.43 djm 1294: .Sm off
1.49 jmc 1295: .Oo Ar bind_address : Oc Ar port
1.43 djm 1296: .Sm on
1.49 jmc 1297: and the second argument must be
1298: .Ar host : Ns Ar hostport .
1.138 djm 1299: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1300: Multiple forwardings may be specified, and additional
1301: forwardings can be given on the command line.
1.113 stevesk 1302: Privileged ports can be forwarded only when
1303: logging in as root on the remote machine.
1.118 jmc 1304: .Pp
1.117 djm 1305: If the
1306: .Ar port
1.240 jmc 1307: argument is 0,
1.117 djm 1308: the listen port will be dynamically allocated on the server and reported
1309: to the client at run time.
1.43 djm 1310: .Pp
1311: If the
1312: .Ar bind_address
1313: is not specified, the default is to only bind to loopback addresses.
1314: If the
1315: .Ar bind_address
1316: is
1317: .Ql *
1318: or an empty string, then the forwarding is requested to listen on all
1319: interfaces.
1320: Specifying a remote
1321: .Ar bind_address
1.46 jmc 1322: will only succeed if the server's
1323: .Cm GatewayPorts
1.43 djm 1324: option is enabled (see
1.46 jmc 1325: .Xr sshd_config 5 ) .
1.149 djm 1326: .It Cm RequestTTY
1327: Specifies whether to request a pseudo-tty for the session.
1328: The argument may be one of:
1.240 jmc 1329: .Cm no
1.149 djm 1330: (never request a TTY),
1.240 jmc 1331: .Cm yes
1.149 djm 1332: (always request a TTY when standard input is a TTY),
1.240 jmc 1333: .Cm force
1.149 djm 1334: (always request a TTY) or
1.240 jmc 1335: .Cm auto
1.149 djm 1336: (request a TTY when opening a login session).
1337: This option mirrors the
1338: .Fl t
1339: and
1340: .Fl T
1341: flags for
1342: .Xr ssh 1 .
1.196 djm 1343: .It Cm RevokedHostKeys
1344: Specifies revoked host public keys.
1345: Keys listed in this file will be refused for host authentication.
1346: Note that if this file does not exist or is not readable,
1347: then host authentication will be refused for all hosts.
1348: Keys may be specified as a text file, listing one public key per line, or as
1349: an OpenSSH Key Revocation List (KRL) as generated by
1350: .Xr ssh-keygen 1 .
1351: For more information on KRLs, see the KEY REVOCATION LISTS section in
1352: .Xr ssh-keygen 1 .
1.32 djm 1353: .It Cm SendEnv
1354: Specifies what variables from the local
1355: .Xr environ 7
1356: should be sent to the server.
1.84 jmc 1357: The server must also support it, and the server must be configured to
1.33 djm 1358: accept these environment variables.
1.207 dtucker 1359: Note that the
1360: .Ev TERM
1.208 jmc 1361: environment variable is always sent whenever a
1.207 dtucker 1362: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1363: Refer to
1364: .Cm AcceptEnv
1365: in
1366: .Xr sshd_config 5
1367: for how to configure the server.
1.80 jmc 1368: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1369: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1370: across multiple
1371: .Cm SendEnv
1372: directives.
1373: The default is not to send any environment variables.
1.81 jmc 1374: .Pp
1375: See
1376: .Sx PATTERNS
1377: for more information on patterns.
1.28 markus 1378: .It Cm ServerAliveCountMax
1.73 jmc 1379: Sets the number of server alive messages (see below) which may be
1.28 markus 1380: sent without
1.84 jmc 1381: .Xr ssh 1
1.28 markus 1382: receiving any messages back from the server.
1383: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1384: ssh will disconnect from the server, terminating the session.
1.28 markus 1385: It is important to note that the use of server alive messages is very
1386: different from
1387: .Cm TCPKeepAlive
1388: (below).
1389: The server alive messages are sent through the encrypted channel
1390: and therefore will not be spoofable.
1391: The TCP keepalive option enabled by
1392: .Cm TCPKeepAlive
1393: is spoofable.
1394: The server alive mechanism is valuable when the client or
1395: server depend on knowing when a connection has become inactive.
1396: .Pp
1397: The default value is 3.
1398: If, for example,
1399: .Cm ServerAliveInterval
1.84 jmc 1400: (see below) is set to 15 and
1.28 markus 1401: .Cm ServerAliveCountMax
1.84 jmc 1402: is left at the default, if the server becomes unresponsive,
1403: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1404: .It Cm ServerAliveInterval
1405: Sets a timeout interval in seconds after which if no data has been received
1406: from the server,
1.84 jmc 1407: .Xr ssh 1
1.67 jmc 1408: will send a message through the encrypted
1409: channel to request a response from the server.
1410: The default
1411: is 0, indicating that these messages will not be sent to the server.
1.191 millert 1412: .It Cm StreamLocalBindMask
1413: Sets the octal file creation mode mask
1414: .Pq umask
1415: used when creating a Unix-domain socket file for local or remote
1416: port forwarding.
1417: This option is only used for port forwarding to a Unix-domain socket file.
1418: .Pp
1419: The default value is 0177, which creates a Unix-domain socket file that is
1420: readable and writable only by the owner.
1421: Note that not all operating systems honor the file mode on Unix-domain
1422: socket files.
1423: .It Cm StreamLocalBindUnlink
1424: Specifies whether to remove an existing Unix-domain socket file for local
1425: or remote port forwarding before creating a new one.
1426: If the socket file already exists and
1427: .Cm StreamLocalBindUnlink
1428: is not enabled,
1429: .Nm ssh
1430: will be unable to forward the port to the Unix-domain socket file.
1431: This option is only used for port forwarding to a Unix-domain socket file.
1432: .Pp
1433: The argument must be
1.240 jmc 1434: .Cm yes
1.191 millert 1435: or
1.240 jmc 1436: .Cm no
1437: (the default).
1.1 stevesk 1438: .It Cm StrictHostKeyChecking
1439: If this flag is set to
1.240 jmc 1440: .Cm yes ,
1.84 jmc 1441: .Xr ssh 1
1.1 stevesk 1442: will never automatically add host keys to the
1.50 djm 1443: .Pa ~/.ssh/known_hosts
1.1 stevesk 1444: file, and refuses to connect to hosts whose host key has changed.
1445: This provides maximum protection against trojan horse attacks,
1.84 jmc 1446: though it can be annoying when the
1.1 stevesk 1447: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1448: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1449: frequently made.
1450: This option forces the user to manually
1451: add all new hosts.
1452: If this flag is set to
1.240 jmc 1453: .Cm no ,
1.84 jmc 1454: ssh will automatically add new host keys to the
1.1 stevesk 1455: user known hosts files.
1456: If this flag is set to
1.240 jmc 1457: .Cm ask
1458: (the default),
1.1 stevesk 1459: new host keys
1460: will be added to the user known host files only after the user
1461: has confirmed that is what they really want to do, and
1.84 jmc 1462: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1463: The host keys of
1464: known hosts will be verified automatically in all cases.
1.244 jmc 1465: .It Cm SyslogFacility
1466: Gives the facility code that is used when logging messages from
1467: .Xr ssh 1 .
1468: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1469: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1470: The default is USER.
1.26 markus 1471: .It Cm TCPKeepAlive
1472: Specifies whether the system should send TCP keepalive messages to the
1473: other side.
1474: If they are sent, death of the connection or crash of one
1475: of the machines will be properly noticed.
1476: However, this means that
1477: connections will die if the route is down temporarily, and some people
1478: find it annoying.
1479: .Pp
1480: The default is
1.240 jmc 1481: .Cm yes
1.26 markus 1482: (to send TCP keepalive messages), and the client will notice
1483: if the network goes down or the remote host dies.
1484: This is important in scripts, and many users want it too.
1485: .Pp
1486: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1487: .Cm no .
1.65 reyk 1488: .It Cm Tunnel
1.95 stevesk 1489: Request
1.65 reyk 1490: .Xr tun 4
1.69 jmc 1491: device forwarding between the client and the server.
1.65 reyk 1492: The argument must be
1.240 jmc 1493: .Cm yes ,
1494: .Cm point-to-point
1.95 stevesk 1495: (layer 3),
1.240 jmc 1496: .Cm ethernet
1.95 stevesk 1497: (layer 2),
1.65 reyk 1498: or
1.240 jmc 1499: .Cm no
1500: (the default).
1.95 stevesk 1501: Specifying
1.240 jmc 1502: .Cm yes
1.95 stevesk 1503: requests the default tunnel mode, which is
1.240 jmc 1504: .Cm point-to-point .
1.65 reyk 1505: .It Cm TunnelDevice
1.95 stevesk 1506: Specifies the
1.65 reyk 1507: .Xr tun 4
1.95 stevesk 1508: devices to open on the client
1509: .Pq Ar local_tun
1510: and the server
1511: .Pq Ar remote_tun .
1512: .Pp
1513: The argument must be
1514: .Sm off
1515: .Ar local_tun Op : Ar remote_tun .
1516: .Sm on
1517: The devices may be specified by numerical ID or the keyword
1.240 jmc 1518: .Cm any ,
1.95 stevesk 1519: which uses the next available tunnel device.
1520: If
1521: .Ar remote_tun
1522: is not specified, it defaults to
1.240 jmc 1523: .Cm any .
1.95 stevesk 1524: The default is
1.240 jmc 1525: .Cm any:any .
1.201 djm 1526: .It Cm UpdateHostKeys
1.200 djm 1527: Specifies whether
1528: .Xr ssh 1
1529: should accept notifications of additional hostkeys from the server sent
1530: after authentication has completed and add them to
1531: .Cm UserKnownHostsFile .
1532: The argument must be
1.240 jmc 1533: .Cm yes ,
1534: .Cm no
1.204 djm 1535: (the default) or
1.240 jmc 1536: .Cm ask .
1.200 djm 1537: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1538: and supports graceful key rotation by allowing a server to send replacement
1539: public keys before old ones are removed.
1.200 djm 1540: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1541: host was already trusted or explicitly accepted by the user.
1.204 djm 1542: If
1543: .Cm UpdateHostKeys
1544: is set to
1.240 jmc 1545: .Cm ask ,
1.204 djm 1546: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1547: Confirmation is currently incompatible with
1548: .Cm ControlPersist ,
1549: and will be disabled if it is enabled.
1.200 djm 1550: .Pp
1551: Presently, only
1552: .Xr sshd 8
1553: from OpenSSH 6.8 and greater support the
1.240 jmc 1554: .Qq hostkeys@openssh.com
1.200 djm 1555: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1556: .It Cm UsePrivilegedPort
1557: Specifies whether to use a privileged port for outgoing connections.
1558: The argument must be
1.240 jmc 1559: .Cm yes
1.72 jmc 1560: or
1.240 jmc 1561: .Cm no
1562: (the default).
1.72 jmc 1563: If set to
1.240 jmc 1564: .Cm yes ,
1.84 jmc 1565: .Xr ssh 1
1.72 jmc 1566: must be setuid root.
1.1 stevesk 1567: .It Cm User
1568: Specifies the user to log in as.
1569: This can be useful when a different user name is used on different machines.
1570: This saves the trouble of
1571: having to remember to give the user name on the command line.
1572: .It Cm UserKnownHostsFile
1.151 djm 1573: Specifies one or more files to use for the user
1574: host key database, separated by whitespace.
1575: The default is
1576: .Pa ~/.ssh/known_hosts ,
1577: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1578: .It Cm VerifyHostKeyDNS
1579: Specifies whether to verify the remote key using DNS and SSHFP resource
1580: records.
1.24 jakob 1581: If this option is set to
1.240 jmc 1582: .Cm yes ,
1.25 jmc 1583: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1584: from DNS.
1585: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1586: .Cm ask .
1.24 jakob 1587: If this option is set to
1.240 jmc 1588: .Cm ask ,
1.24 jakob 1589: information on fingerprint match will be displayed, but the user will still
1590: need to confirm new host keys according to the
1591: .Cm StrictHostKeyChecking
1592: option.
1.8 jakob 1593: The default is
1.240 jmc 1594: .Cm no .
1.84 jmc 1595: .Pp
1.240 jmc 1596: See also
1597: .Sx VERIFYING HOST KEYS
1598: in
1.84 jmc 1599: .Xr ssh 1 .
1.111 grunk 1600: .It Cm VisualHostKey
1601: If this flag is set to
1.240 jmc 1602: .Cm yes ,
1.111 grunk 1603: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1604: printed in addition to the fingerprint string at login and
1.114 stevesk 1605: for unknown host keys.
1.111 grunk 1606: If this flag is set to
1.240 jmc 1607: .Cm no
1608: (the default),
1.114 stevesk 1609: no fingerprint strings are printed at login and
1.197 djm 1610: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1611: .It Cm XAuthLocation
1.5 stevesk 1612: Specifies the full pathname of the
1.1 stevesk 1613: .Xr xauth 1
1614: program.
1615: The default is
1616: .Pa /usr/X11R6/bin/xauth .
1617: .El
1.86 jmc 1618: .Sh PATTERNS
1619: A
1620: .Em pattern
1621: consists of zero or more non-whitespace characters,
1622: .Sq *
1623: (a wildcard that matches zero or more characters),
1624: or
1625: .Sq ?\&
1626: (a wildcard that matches exactly one character).
1627: For example, to specify a set of declarations for any host in the
1.240 jmc 1628: .Qq .co.uk
1.86 jmc 1629: set of domains,
1630: the following pattern could be used:
1631: .Pp
1632: .Dl Host *.co.uk
1633: .Pp
1634: The following pattern
1635: would match any host in the 192.168.0.[0-9] network range:
1636: .Pp
1637: .Dl Host 192.168.0.?
1638: .Pp
1639: A
1640: .Em pattern-list
1641: is a comma-separated list of patterns.
1642: Patterns within pattern-lists may be negated
1643: by preceding them with an exclamation mark
1644: .Pq Sq !\& .
1645: For example,
1.174 djm 1646: to allow a key to be used from anywhere within an organization
1.86 jmc 1647: except from the
1.240 jmc 1648: .Qq dialup
1.86 jmc 1649: pool,
1650: the following entry (in authorized_keys) could be used:
1651: .Pp
1652: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.239 jmc 1653: .Sh TOKENS
1654: Arguments to some keywords can make use of tokens,
1655: which are expanded at runtime:
1656: .Pp
1657: .Bl -tag -width XXXX -offset indent -compact
1658: .It %%
1659: A literal
1660: .Sq % .
1661: .It \&%C
1662: Shorthand for %l%h%p%r.
1663: .It %d
1664: Local user's home directory.
1665: .It %h
1666: The remote hostname.
1667: .It %i
1668: The local user ID.
1669: .It %L
1670: The local hostname.
1671: .It %l
1672: The local hostname, including the domain name.
1673: .It %n
1674: The original remote hostname, as given on the command line.
1675: .It %p
1676: The remote port.
1677: .It %r
1678: The remote username.
1679: .It %u
1680: The local username.
1681: .El
1682: .Pp
1683: .Cm Match exec
1684: accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1685: .Pp
1686: .Cm CertificateFile
1687: accepts the tokens %%, %d, %h, %l, %r, and %u.
1688: .Pp
1689: .Cm ControlPath
1690: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1691: .Pp
1692: .Cm HostName
1693: accepts the tokens %% and %h.
1694: .Pp
1695: .Cm IdentityAgent
1696: and
1697: .Cm IdentityFile
1698: accept the tokens %%, %d, %h, %l, %r, and %u.
1699: .Pp
1700: .Cm LocalCommand
1701: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1702: .Pp
1703: .Cm ProxyCommand
1704: accepts the tokens %%, %h, %p, and %r.
1.1 stevesk 1705: .Sh FILES
1706: .Bl -tag -width Ds
1.50 djm 1707: .It Pa ~/.ssh/config
1.1 stevesk 1708: This is the per-user configuration file.
1709: The format of this file is described above.
1.84 jmc 1710: This file is used by the SSH client.
1.30 djm 1711: Because of the potential for abuse, this file must have strict permissions:
1712: read/write for the user, and not accessible by others.
1.1 stevesk 1713: .It Pa /etc/ssh/ssh_config
1714: Systemwide configuration file.
1715: This file provides defaults for those
1716: values that are not specified in the user's configuration file, and
1717: for those users who do not have a configuration file.
1718: This file must be world-readable.
1719: .El
1.13 jmc 1720: .Sh SEE ALSO
1721: .Xr ssh 1
1.1 stevesk 1722: .Sh AUTHORS
1.240 jmc 1723: .An -nosplit
1.1 stevesk 1724: OpenSSH is a derivative of the original and free
1.240 jmc 1725: ssh 1.2.12 release by
1726: .An Tatu Ylonen .
1727: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1728: .An Niels Provos , Theo de Raadt
1729: and
1730: .An Dug Song
1.1 stevesk 1731: removed many bugs, re-added newer features and
1732: created OpenSSH.
1.240 jmc 1733: .An Markus Friedl
1734: contributed the support for SSH protocol versions 1.5 and 2.0.
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