Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.247
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
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19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
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24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.247 ! naddy 36: .\" $OpenBSD: ssh_config.5,v 1.246 2017/05/03 21:08:09 naddy Exp $
! 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: arcfour
418: arcfour128
419: arcfour256
420: blowfish-cbc
421: cast128-cbc
422: chacha20-poly1305@openssh.com
1.240 jmc 423: .Ed
1.180 djm 424: .Pp
1.84 jmc 425: The default is:
1.186 naddy 426: .Bd -literal -offset indent
1.215 jmc 427: chacha20-poly1305@openssh.com,
1.186 naddy 428: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 429: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.237 djm 430: aes128-cbc,aes192-cbc,aes256-cbc
1.1 stevesk 431: .Ed
1.180 djm 432: .Pp
1.240 jmc 433: The list of available ciphers may also be obtained using
434: .Qq ssh -Q cipher .
1.1 stevesk 435: .It Cm ClearAllForwardings
1.84 jmc 436: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 437: specified in the configuration files or on the command line be
1.7 jmc 438: cleared.
439: This option is primarily useful when used from the
1.84 jmc 440: .Xr ssh 1
1.1 stevesk 441: command line to clear port forwardings set in
442: configuration files, and is automatically set by
443: .Xr scp 1
444: and
445: .Xr sftp 1 .
446: The argument must be
1.240 jmc 447: .Cm yes
1.1 stevesk 448: or
1.240 jmc 449: .Cm no
450: (the default).
1.1 stevesk 451: .It Cm Compression
452: Specifies whether to use compression.
453: The argument must be
1.240 jmc 454: .Cm yes
1.1 stevesk 455: or
1.240 jmc 456: .Cm no
457: (the default).
1.247 ! naddy 458: .It Cm ConnectionAttempts
! 459: Specifies the number of tries (one per second) to make before exiting.
! 460: The argument must be an integer.
! 461: This may be useful in scripts if the connection sometimes fails.
! 462: The default is 1.
1.9 djm 463: .It Cm ConnectTimeout
1.84 jmc 464: Specifies the timeout (in seconds) used when connecting to the
465: SSH server, instead of using the default system TCP timeout.
1.11 jmc 466: This value is used only when the target is down or really unreachable,
467: not when it refuses the connection.
1.36 djm 468: .It Cm ControlMaster
469: Enables the sharing of multiple sessions over a single network connection.
470: When set to
1.240 jmc 471: .Cm yes ,
1.84 jmc 472: .Xr ssh 1
1.36 djm 473: will listen for connections on a control socket specified using the
474: .Cm ControlPath
475: argument.
476: Additional sessions can connect to this socket using the same
477: .Cm ControlPath
478: with
479: .Cm ControlMaster
480: set to
1.240 jmc 481: .Cm no
1.38 jmc 482: (the default).
1.64 jmc 483: These sessions will try to reuse the master instance's network connection
1.63 djm 484: rather than initiating new ones, but will fall back to connecting normally
485: if the control socket does not exist, or is not listening.
486: .Pp
1.37 djm 487: Setting this to
1.240 jmc 488: .Cm ask
489: will cause
490: .Xr ssh 1
1.206 jmc 491: to listen for control connections, but require confirmation using
492: .Xr ssh-askpass 1 .
1.51 jakob 493: If the
494: .Cm ControlPath
1.84 jmc 495: cannot be opened,
1.240 jmc 496: .Xr ssh 1
497: will continue without connecting to a master instance.
1.58 djm 498: .Pp
499: X11 and
1.59 jmc 500: .Xr ssh-agent 1
1.58 djm 501: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 502: display and agent forwarded will be the one belonging to the master
1.59 jmc 503: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 504: .Pp
505: Two additional options allow for opportunistic multiplexing: try to use a
506: master connection but fall back to creating a new one if one does not already
507: exist.
508: These options are:
1.240 jmc 509: .Cm auto
1.56 djm 510: and
1.240 jmc 511: .Cm autoask .
1.56 djm 512: The latter requires confirmation like the
1.240 jmc 513: .Cm ask
1.56 djm 514: option.
1.36 djm 515: .It Cm ControlPath
1.55 djm 516: Specify the path to the control socket used for connection sharing as described
517: in the
1.36 djm 518: .Cm ControlMaster
1.57 djm 519: section above or the string
1.240 jmc 520: .Cm none
1.57 djm 521: to disable connection sharing.
1.239 jmc 522: Arguments to
523: .Cm ControlPath
524: may use the tilde syntax to refer to a user's home directory
525: or the tokens described in the
526: .Sx TOKENS
527: section.
1.56 djm 528: It is recommended that any
529: .Cm ControlPath
530: used for opportunistic connection sharing include
1.195 djm 531: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
532: that is not writable by other users.
1.56 djm 533: This ensures that shared connections are uniquely identified.
1.137 djm 534: .It Cm ControlPersist
535: When used in conjunction with
536: .Cm ControlMaster ,
537: specifies that the master connection should remain open
538: in the background (waiting for future client connections)
539: after the initial client connection has been closed.
540: If set to
1.240 jmc 541: .Cm no ,
1.137 djm 542: then the master connection will not be placed into the background,
543: and will close as soon as the initial client connection is closed.
544: If set to
1.240 jmc 545: .Cm yes
546: or 0,
1.137 djm 547: then the master connection will remain in the background indefinitely
548: (until killed or closed via a mechanism such as the
1.240 jmc 549: .Qq ssh -O exit ) .
1.137 djm 550: If set to a time in seconds, or a time in any of the formats documented in
551: .Xr sshd_config 5 ,
552: then the backgrounded master connection will automatically terminate
553: after it has remained idle (with no client connections) for the
554: specified time.
1.38 jmc 555: .It Cm DynamicForward
1.74 jmc 556: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 557: over the secure channel, and the application
558: protocol is then used to determine where to connect to from the
559: remote machine.
1.62 djm 560: .Pp
561: The argument must be
562: .Sm off
563: .Oo Ar bind_address : Oc Ar port .
564: .Sm on
1.138 djm 565: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 566: By default, the local port is bound in accordance with the
567: .Cm GatewayPorts
568: setting.
569: However, an explicit
570: .Ar bind_address
571: may be used to bind the connection to a specific address.
572: The
573: .Ar bind_address
574: of
1.240 jmc 575: .Cm localhost
1.62 djm 576: indicates that the listening port be bound for local use only, while an
577: empty address or
578: .Sq *
579: indicates that the port should be available from all interfaces.
580: .Pp
1.38 jmc 581: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 582: .Xr ssh 1
1.38 jmc 583: will act as a SOCKS server.
584: Multiple forwardings may be specified, and
585: additional forwardings can be given on the command line.
586: Only the superuser can forward privileged ports.
1.14 markus 587: .It Cm EnableSSHKeysign
588: Setting this option to
1.240 jmc 589: .Cm yes
1.14 markus 590: in the global client configuration file
591: .Pa /etc/ssh/ssh_config
592: enables the use of the helper program
593: .Xr ssh-keysign 8
594: during
595: .Cm HostbasedAuthentication .
596: The argument must be
1.240 jmc 597: .Cm yes
1.14 markus 598: or
1.240 jmc 599: .Cm no
600: (the default).
1.23 jmc 601: This option should be placed in the non-hostspecific section.
1.14 markus 602: See
603: .Xr ssh-keysign 8
604: for more information.
1.1 stevesk 605: .It Cm EscapeChar
606: Sets the escape character (default:
607: .Ql ~ ) .
608: The escape character can also
609: be set on the command line.
610: The argument should be a single character,
611: .Ql ^
612: followed by a letter, or
1.240 jmc 613: .Cm none
1.1 stevesk 614: to disable the escape
615: character entirely (making the connection transparent for binary
616: data).
1.96 markus 617: .It Cm ExitOnForwardFailure
618: Specifies whether
619: .Xr ssh 1
620: should terminate the connection if it cannot set up all requested
1.216 djm 621: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 622: if either end is unable to bind and listen on a specified port).
1.216 djm 623: Note that
624: .Cm ExitOnForwardFailure
625: does not apply to connections made over port forwardings and will not,
626: for example, cause
627: .Xr ssh 1
628: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 629: The argument must be
1.240 jmc 630: .Cm yes
1.96 markus 631: or
1.240 jmc 632: .Cm no
633: (the default).
1.197 djm 634: .It Cm FingerprintHash
635: Specifies the hash algorithm used when displaying key fingerprints.
636: Valid options are:
1.240 jmc 637: .Cm md5
1.197 djm 638: and
1.240 jmc 639: .Cm sha256
640: (the default).
1.1 stevesk 641: .It Cm ForwardAgent
642: Specifies whether the connection to the authentication agent (if any)
643: will be forwarded to the remote machine.
644: The argument must be
1.240 jmc 645: .Cm yes
1.1 stevesk 646: or
1.240 jmc 647: .Cm no
648: (the default).
1.3 stevesk 649: .Pp
1.7 jmc 650: Agent forwarding should be enabled with caution.
651: Users with the ability to bypass file permissions on the remote host
652: (for the agent's Unix-domain socket)
653: can access the local agent through the forwarded connection.
654: An attacker cannot obtain key material from the agent,
1.3 stevesk 655: however they can perform operations on the keys that enable them to
656: authenticate using the identities loaded into the agent.
1.1 stevesk 657: .It Cm ForwardX11
658: Specifies whether X11 connections will be automatically redirected
659: over the secure channel and
660: .Ev DISPLAY
661: set.
662: The argument must be
1.240 jmc 663: .Cm yes
1.1 stevesk 664: or
1.240 jmc 665: .Cm no
666: (the default).
1.3 stevesk 667: .Pp
1.7 jmc 668: X11 forwarding should be enabled with caution.
669: Users with the ability to bypass file permissions on the remote host
1.22 markus 670: (for the user's X11 authorization database)
1.7 jmc 671: can access the local X11 display through the forwarded connection.
1.22 markus 672: An attacker may then be able to perform activities such as keystroke monitoring
673: if the
674: .Cm ForwardX11Trusted
675: option is also enabled.
1.134 djm 676: .It Cm ForwardX11Timeout
1.135 jmc 677: Specify a timeout for untrusted X11 forwarding
678: using the format described in the
1.240 jmc 679: .Sx TIME FORMATS
680: section of
1.134 djm 681: .Xr sshd_config 5 .
682: X11 connections received by
683: .Xr ssh 1
684: after this time will be refused.
685: The default is to disable untrusted X11 forwarding after twenty minutes has
686: elapsed.
1.22 markus 687: .It Cm ForwardX11Trusted
1.34 jmc 688: If this option is set to
1.240 jmc 689: .Cm yes ,
1.84 jmc 690: remote X11 clients will have full access to the original X11 display.
1.42 djm 691: .Pp
1.22 markus 692: If this option is set to
1.240 jmc 693: .Cm no
694: (the default),
1.84 jmc 695: remote X11 clients will be considered untrusted and prevented
1.22 markus 696: from stealing or tampering with data belonging to trusted X11
697: clients.
1.42 djm 698: Furthermore, the
699: .Xr xauth 1
700: token used for the session will be set to expire after 20 minutes.
701: Remote clients will be refused access after this time.
1.22 markus 702: .Pp
703: See the X11 SECURITY extension specification for full details on
704: the restrictions imposed on untrusted clients.
1.1 stevesk 705: .It Cm GatewayPorts
706: Specifies whether remote hosts are allowed to connect to local
707: forwarded ports.
708: By default,
1.84 jmc 709: .Xr ssh 1
1.7 jmc 710: binds local port forwardings to the loopback address.
711: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 712: .Cm GatewayPorts
1.84 jmc 713: can be used to specify that ssh
1.1 stevesk 714: should bind local port forwardings to the wildcard address,
715: thus allowing remote hosts to connect to forwarded ports.
716: The argument must be
1.240 jmc 717: .Cm yes
1.1 stevesk 718: or
1.240 jmc 719: .Cm no
720: (the default).
1.1 stevesk 721: .It Cm GlobalKnownHostsFile
1.151 djm 722: Specifies one or more files to use for the global
723: host key database, separated by whitespace.
724: The default is
725: .Pa /etc/ssh/ssh_known_hosts ,
726: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 727: .It Cm GSSAPIAuthentication
1.27 markus 728: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 729: The default is
1.240 jmc 730: .Cm no .
1.18 markus 731: .It Cm GSSAPIDelegateCredentials
732: Forward (delegate) credentials to the server.
733: The default is
1.240 jmc 734: .Cm no .
1.44 djm 735: .It Cm HashKnownHosts
736: Indicates that
1.84 jmc 737: .Xr ssh 1
1.44 djm 738: should hash host names and addresses when they are added to
1.50 djm 739: .Pa ~/.ssh/known_hosts .
1.44 djm 740: These hashed names may be used normally by
1.84 jmc 741: .Xr ssh 1
1.44 djm 742: and
1.84 jmc 743: .Xr sshd 8 ,
1.44 djm 744: but they do not reveal identifying information should the file's contents
745: be disclosed.
746: The default is
1.240 jmc 747: .Cm no .
1.97 jmc 748: Note that existing names and addresses in known hosts files
749: will not be converted automatically,
750: but may be manually hashed using
1.45 djm 751: .Xr ssh-keygen 1 .
1.1 stevesk 752: .It Cm HostbasedAuthentication
753: Specifies whether to try rhosts based authentication with public key
754: authentication.
755: The argument must be
1.240 jmc 756: .Cm yes
1.1 stevesk 757: or
1.240 jmc 758: .Cm no
759: (the default).
1.202 djm 760: .It Cm HostbasedKeyTypes
761: Specifies the key types that will be used for hostbased authentication
762: as a comma-separated pattern list.
1.214 djm 763: Alternately if the specified value begins with a
764: .Sq +
765: character, then the specified key types will be appended to the default set
766: instead of replacing them.
1.241 djm 767: If the specified value begins with a
768: .Sq -
769: character, then the specified key types (including wildcards) will be removed
770: from the default set instead of replacing them.
1.213 markus 771: The default for this option is:
772: .Bd -literal -offset 3n
773: ecdsa-sha2-nistp256-cert-v01@openssh.com,
774: ecdsa-sha2-nistp384-cert-v01@openssh.com,
775: ecdsa-sha2-nistp521-cert-v01@openssh.com,
776: ssh-ed25519-cert-v01@openssh.com,
777: ssh-rsa-cert-v01@openssh.com,
778: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 779: ssh-ed25519,ssh-rsa
1.213 markus 780: .Ed
781: .Pp
1.202 djm 782: The
783: .Fl Q
784: option of
785: .Xr ssh 1
786: may be used to list supported key types.
1.1 stevesk 787: .It Cm HostKeyAlgorithms
1.226 jmc 788: Specifies the host key algorithms
1.1 stevesk 789: that the client wants to use in order of preference.
1.214 djm 790: Alternately if the specified value begins with a
791: .Sq +
792: character, then the specified key types will be appended to the default set
793: instead of replacing them.
1.241 djm 794: If the specified value begins with a
795: .Sq -
796: character, then the specified key types (including wildcards) will be removed
797: from the default set instead of replacing them.
1.1 stevesk 798: The default for this option is:
1.139 djm 799: .Bd -literal -offset 3n
800: ecdsa-sha2-nistp256-cert-v01@openssh.com,
801: ecdsa-sha2-nistp384-cert-v01@openssh.com,
802: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 803: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 804: ssh-rsa-cert-v01@openssh.com,
1.139 djm 805: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 806: ssh-ed25519,ssh-rsa
1.139 djm 807: .Ed
1.145 djm 808: .Pp
809: If hostkeys are known for the destination host then this default is modified
810: to prefer their algorithms.
1.198 djm 811: .Pp
1.240 jmc 812: The list of available key types may also be obtained using
813: .Qq ssh -Q key .
1.1 stevesk 814: .It Cm HostKeyAlias
815: Specifies an alias that should be used instead of the
816: real host name when looking up or saving the host key
817: in the host key database files.
1.84 jmc 818: This option is useful for tunneling SSH connections
1.1 stevesk 819: or for multiple servers running on a single host.
820: .It Cm HostName
821: Specifies the real host name to log into.
822: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 823: Arguments to
824: .Cm HostName
825: accept the tokens described in the
826: .Sx TOKENS
827: section.
1.1 stevesk 828: Numeric IP addresses are also permitted (both on the command line and in
829: .Cm HostName
830: specifications).
1.239 jmc 831: The default is the name given on the command line.
1.29 markus 832: .It Cm IdentitiesOnly
833: Specifies that
1.84 jmc 834: .Xr ssh 1
1.221 djm 835: should only use the authentication identity and certificate files explicitly
836: configured in the
1.31 jmc 837: .Nm
1.221 djm 838: files
839: or passed on the
840: .Xr ssh 1
841: command-line,
1.84 jmc 842: even if
843: .Xr ssh-agent 1
1.159 djm 844: or a
845: .Cm PKCS11Provider
1.29 markus 846: offers more identities.
847: The argument to this keyword must be
1.240 jmc 848: .Cm yes
1.29 markus 849: or
1.240 jmc 850: .Cm no
851: (the default).
1.84 jmc 852: This option is intended for situations where ssh-agent
1.29 markus 853: offers many different identities.
1.231 markus 854: .It Cm IdentityAgent
855: Specifies the
856: .Ux Ns -domain
857: socket used to communicate with the authentication agent.
858: .Pp
859: This option overrides the
1.240 jmc 860: .Ev SSH_AUTH_SOCK
1.231 markus 861: environment variable and can be used to select a specific agent.
862: Setting the socket name to
1.240 jmc 863: .Cm none
1.231 markus 864: disables the use of an authentication agent.
1.232 markus 865: If the string
1.240 jmc 866: .Qq SSH_AUTH_SOCK
1.232 markus 867: is specified, the location of the socket will be read from the
868: .Ev SSH_AUTH_SOCK
869: environment variable.
1.231 markus 870: .Pp
1.239 jmc 871: Arguments to
872: .Cm IdentityAgent
873: may use the tilde syntax to refer to a user's home directory
874: or the tokens described in the
875: .Sx TOKENS
876: section.
1.67 jmc 877: .It Cm IdentityFile
1.192 sobrado 878: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 879: identity is read.
1.67 jmc 880: The default is
1.139 djm 881: .Pa ~/.ssh/id_dsa ,
1.183 naddy 882: .Pa ~/.ssh/id_ecdsa ,
883: .Pa ~/.ssh/id_ed25519
1.139 djm 884: and
1.245 djm 885: .Pa ~/.ssh/id_rsa .
1.67 jmc 886: Additionally, any identities represented by the authentication agent
1.165 djm 887: will be used for authentication unless
888: .Cm IdentitiesOnly
889: is set.
1.221 djm 890: If no certificates have been explicitly specified by
891: .Cm CertificateFile ,
1.129 djm 892: .Xr ssh 1
893: will try to load certificate information from the filename obtained by
894: appending
895: .Pa -cert.pub
896: to the path of a specified
897: .Cm IdentityFile .
1.90 djm 898: .Pp
1.239 jmc 899: Arguments to
900: .Cm IdentityFile
901: may use the tilde syntax to refer to a user's home directory
902: or the tokens described in the
903: .Sx TOKENS
904: section.
1.90 djm 905: .Pp
1.67 jmc 906: It is possible to have
907: multiple identity files specified in configuration files; all these
908: identities will be tried in sequence.
1.152 djm 909: Multiple
910: .Cm IdentityFile
911: directives will add to the list of identities tried (this behaviour
912: differs from that of other configuration directives).
1.165 djm 913: .Pp
914: .Cm IdentityFile
915: may be used in conjunction with
916: .Cm IdentitiesOnly
917: to select which identities in an agent are offered during authentication.
1.221 djm 918: .Cm IdentityFile
919: may also be used in conjunction with
920: .Cm CertificateFile
921: in order to provide any certificate also needed for authentication with
922: the identity.
1.164 jmc 923: .It Cm IgnoreUnknown
924: Specifies a pattern-list of unknown options to be ignored if they are
925: encountered in configuration parsing.
926: This may be used to suppress errors if
927: .Nm
928: contains options that are unrecognised by
929: .Xr ssh 1 .
930: It is recommended that
931: .Cm IgnoreUnknown
932: be listed early in the configuration file as it will not be applied
933: to unknown options that appear before it.
1.229 djm 934: .It Cm Include
935: Include the specified configuration file(s).
1.230 jmc 936: Multiple pathnames may be specified and each pathname may contain
1.229 djm 937: .Xr glob 3
938: wildcards and, for user configurations, shell-like
1.240 jmc 939: .Sq ~
1.229 djm 940: references to user home directories.
941: Files without absolute paths are assumed to be in
942: .Pa ~/.ssh
1.230 jmc 943: if included in a user configuration file or
1.229 djm 944: .Pa /etc/ssh
945: if included from the system configuration file.
946: .Cm Include
947: directive may appear inside a
948: .Cm Match
949: or
950: .Cm Host
951: block
952: to perform conditional inclusion.
1.143 djm 953: .It Cm IPQoS
954: Specifies the IPv4 type-of-service or DSCP class for connections.
955: Accepted values are
1.240 jmc 956: .Cm af11 ,
957: .Cm af12 ,
958: .Cm af13 ,
959: .Cm af21 ,
960: .Cm af22 ,
961: .Cm af23 ,
962: .Cm af31 ,
963: .Cm af32 ,
964: .Cm af33 ,
965: .Cm af41 ,
966: .Cm af42 ,
967: .Cm af43 ,
968: .Cm cs0 ,
969: .Cm cs1 ,
970: .Cm cs2 ,
971: .Cm cs3 ,
972: .Cm cs4 ,
973: .Cm cs5 ,
974: .Cm cs6 ,
975: .Cm cs7 ,
976: .Cm ef ,
977: .Cm lowdelay ,
978: .Cm throughput ,
979: .Cm reliability ,
1.143 djm 980: or a numeric value.
1.146 djm 981: This option may take one or two arguments, separated by whitespace.
1.143 djm 982: If one argument is specified, it is used as the packet class unconditionally.
983: If two values are specified, the first is automatically selected for
984: interactive sessions and the second for non-interactive sessions.
985: The default is
1.240 jmc 986: .Cm lowdelay
1.143 djm 987: for interactive sessions and
1.240 jmc 988: .Cm throughput
1.143 djm 989: for non-interactive sessions.
1.103 djm 990: .It Cm KbdInteractiveAuthentication
991: Specifies whether to use keyboard-interactive authentication.
992: The argument to this keyword must be
1.240 jmc 993: .Cm yes
994: (the default)
1.103 djm 995: or
1.240 jmc 996: .Cm no .
1.39 djm 997: .It Cm KbdInteractiveDevices
998: Specifies the list of methods to use in keyboard-interactive authentication.
999: Multiple method names must be comma-separated.
1000: The default is to use the server specified list.
1.85 jmc 1001: The methods available vary depending on what the server supports.
1002: For an OpenSSH server,
1003: it may be zero or more of:
1.240 jmc 1004: .Cm bsdauth ,
1005: .Cm pam ,
1.85 jmc 1006: and
1.240 jmc 1007: .Cm skey .
1.140 djm 1008: .It Cm KexAlgorithms
1009: Specifies the available KEX (Key Exchange) algorithms.
1010: Multiple algorithms must be comma-separated.
1.214 djm 1011: Alternately if the specified value begins with a
1012: .Sq +
1013: character, then the specified methods will be appended to the default set
1014: instead of replacing them.
1.241 djm 1015: If the specified value begins with a
1016: .Sq -
1017: character, then the specified methods (including wildcards) will be removed
1018: from the default set instead of replacing them.
1.141 jmc 1019: The default is:
1020: .Bd -literal -offset indent
1.238 djm 1021: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1022: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1023: diffie-hellman-group-exchange-sha256,
1.209 dtucker 1024: diffie-hellman-group-exchange-sha1,
1.212 djm 1025: diffie-hellman-group14-sha1
1.141 jmc 1026: .Ed
1.198 djm 1027: .Pp
1.240 jmc 1028: The list of available key exchange algorithms may also be obtained using
1029: .Qq ssh -Q kex .
1.65 reyk 1030: .It Cm LocalCommand
1031: Specifies a command to execute on the local machine after successfully
1032: connecting to the server.
1033: The command string extends to the end of the line, and is executed with
1.105 jmc 1034: the user's shell.
1.239 jmc 1035: Arguments to
1036: .Cm LocalCommand
1037: accept the tokens described in the
1038: .Sx TOKENS
1039: section.
1.123 djm 1040: .Pp
1041: The command is run synchronously and does not have access to the
1042: session of the
1043: .Xr ssh 1
1044: that spawned it.
1045: It should not be used for interactive commands.
1046: .Pp
1.65 reyk 1047: This directive is ignored unless
1048: .Cm PermitLocalCommand
1049: has been enabled.
1.1 stevesk 1050: .It Cm LocalForward
1.74 jmc 1051: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1052: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1053: The first argument must be
1.43 djm 1054: .Sm off
1.49 jmc 1055: .Oo Ar bind_address : Oc Ar port
1.43 djm 1056: .Sm on
1.49 jmc 1057: and the second argument must be
1058: .Ar host : Ns Ar hostport .
1.138 djm 1059: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1060: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1061: given on the command line.
1.1 stevesk 1062: Only the superuser can forward privileged ports.
1.43 djm 1063: By default, the local port is bound in accordance with the
1064: .Cm GatewayPorts
1065: setting.
1066: However, an explicit
1067: .Ar bind_address
1068: may be used to bind the connection to a specific address.
1069: The
1070: .Ar bind_address
1071: of
1.240 jmc 1072: .Cm localhost
1.46 jmc 1073: indicates that the listening port be bound for local use only, while an
1074: empty address or
1075: .Sq *
1.43 djm 1076: indicates that the port should be available from all interfaces.
1.1 stevesk 1077: .It Cm LogLevel
1078: Gives the verbosity level that is used when logging messages from
1.84 jmc 1079: .Xr ssh 1 .
1.1 stevesk 1080: The possible values are:
1.84 jmc 1081: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1082: The default is INFO.
1083: DEBUG and DEBUG1 are equivalent.
1084: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1085: .It Cm MACs
1086: Specifies the MAC (message authentication code) algorithms
1087: in order of preference.
1.226 jmc 1088: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1089: Multiple algorithms must be comma-separated.
1.214 djm 1090: If the specified value begins with a
1091: .Sq +
1092: character, then the specified algorithms will be appended to the default set
1093: instead of replacing them.
1.241 djm 1094: If the specified value begins with a
1095: .Sq -
1096: character, then the specified algorithms (including wildcards) will be removed
1097: from the default set instead of replacing them.
1.214 djm 1098: .Pp
1.160 markus 1099: The algorithms that contain
1.240 jmc 1100: .Qq -etm
1.160 markus 1101: calculate the MAC after encryption (encrypt-then-mac).
1102: These are considered safer and their use recommended.
1.214 djm 1103: .Pp
1.84 jmc 1104: The default is:
1.101 jmc 1105: .Bd -literal -offset indent
1.160 markus 1106: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1107: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1108: hmac-sha1-etm@openssh.com,
1.186 naddy 1109: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1110: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1111: .Ed
1.198 djm 1112: .Pp
1.240 jmc 1113: The list of available MAC algorithms may also be obtained using
1114: .Qq ssh -Q mac .
1.1 stevesk 1115: .It Cm NoHostAuthenticationForLocalhost
1116: This option can be used if the home directory is shared across machines.
1117: In this case localhost will refer to a different machine on each of
1118: the machines and the user will get many warnings about changed host keys.
1119: However, this option disables host authentication for localhost.
1120: The argument to this keyword must be
1.240 jmc 1121: .Cm yes
1.1 stevesk 1122: or
1.242 jmc 1123: .Cm no
1.240 jmc 1124: (the default).
1.1 stevesk 1125: .It Cm NumberOfPasswordPrompts
1126: Specifies the number of password prompts before giving up.
1127: The argument to this keyword must be an integer.
1.84 jmc 1128: The default is 3.
1.1 stevesk 1129: .It Cm PasswordAuthentication
1130: Specifies whether to use password authentication.
1131: The argument to this keyword must be
1.240 jmc 1132: .Cm yes
1133: (the default)
1.1 stevesk 1134: or
1.240 jmc 1135: .Cm no .
1.65 reyk 1136: .It Cm PermitLocalCommand
1137: Allow local command execution via the
1138: .Ic LocalCommand
1139: option or using the
1.66 jmc 1140: .Ic !\& Ns Ar command
1.65 reyk 1141: escape sequence in
1142: .Xr ssh 1 .
1143: The argument must be
1.240 jmc 1144: .Cm yes
1.65 reyk 1145: or
1.240 jmc 1146: .Cm no
1147: (the default).
1.127 markus 1148: .It Cm PKCS11Provider
1149: Specifies which PKCS#11 provider to use.
1.144 jmc 1150: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1151: .Xr ssh 1
1.128 markus 1152: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1153: private RSA key.
1.67 jmc 1154: .It Cm Port
1155: Specifies the port number to connect on the remote host.
1.84 jmc 1156: The default is 22.
1.1 stevesk 1157: .It Cm PreferredAuthentications
1.226 jmc 1158: Specifies the order in which the client should try authentication methods.
1.48 jmc 1159: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1160: .Cm keyboard-interactive )
1.48 jmc 1161: over another method (e.g.\&
1.131 jmc 1162: .Cm password ) .
1163: The default is:
1164: .Bd -literal -offset indent
1165: gssapi-with-mic,hostbased,publickey,
1166: keyboard-interactive,password
1167: .Ed
1.1 stevesk 1168: .It Cm ProxyCommand
1169: Specifies the command to use to connect to the server.
1170: The command
1.190 djm 1171: string extends to the end of the line, and is executed
1172: using the user's shell
1173: .Ql exec
1174: directive to avoid a lingering shell process.
1175: .Pp
1.239 jmc 1176: Arguments to
1177: .Cm ProxyCommand
1178: accept the tokens described in the
1179: .Sx TOKENS
1180: section.
1.1 stevesk 1181: The command can be basically anything,
1182: and should read from its standard input and write to its standard output.
1183: It should eventually connect an
1184: .Xr sshd 8
1185: server running on some machine, or execute
1186: .Ic sshd -i
1187: somewhere.
1188: Host key management will be done using the
1189: HostName of the host being connected (defaulting to the name typed by
1190: the user).
1.7 jmc 1191: Setting the command to
1.240 jmc 1192: .Cm none
1.6 markus 1193: disables this option entirely.
1.1 stevesk 1194: Note that
1195: .Cm CheckHostIP
1196: is not available for connects with a proxy command.
1.52 djm 1197: .Pp
1198: This directive is useful in conjunction with
1199: .Xr nc 1
1200: and its proxy support.
1.53 jmc 1201: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1202: 192.0.2.0:
1203: .Bd -literal -offset 3n
1204: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1205: .Ed
1.233 djm 1206: .It Cm ProxyJump
1207: Specifies one or more jump proxies as
1208: .Xo
1209: .Sm off
1.234 jmc 1210: .Op Ar user No @
1.233 djm 1211: .Ar host
1.234 jmc 1212: .Op : Ns Ar port
1.233 djm 1213: .Sm on
1214: .Xc .
1.235 djm 1215: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1216: sequentially.
1.233 djm 1217: Setting this option will cause
1218: .Xr ssh 1
1219: to connect to the target host by first making a
1220: .Xr ssh 1
1221: connection to the specified
1222: .Cm ProxyJump
1223: host and then establishing a
1.234 jmc 1224: TCP forwarding to the ultimate target from there.
1.233 djm 1225: .Pp
1226: Note that this option will compete with the
1227: .Cm ProxyCommand
1228: option - whichever is specified first will prevent later instances of the
1229: other from taking effect.
1.167 djm 1230: .It Cm ProxyUseFdpass
1.168 jmc 1231: Specifies that
1.167 djm 1232: .Cm ProxyCommand
1233: will pass a connected file descriptor back to
1.168 jmc 1234: .Xr ssh 1
1.167 djm 1235: instead of continuing to execute and pass data.
1236: The default is
1.240 jmc 1237: .Cm no .
1.213 markus 1238: .It Cm PubkeyAcceptedKeyTypes
1239: Specifies the key types that will be used for public key authentication
1240: as a comma-separated pattern list.
1.214 djm 1241: Alternately if the specified value begins with a
1242: .Sq +
1243: character, then the key types after it will be appended to the default
1244: instead of replacing it.
1.241 djm 1245: If the specified value begins with a
1246: .Sq -
1247: character, then the specified key types (including wildcards) will be removed
1248: from the default set instead of replacing them.
1.213 markus 1249: The default for this option is:
1250: .Bd -literal -offset 3n
1251: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1252: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1253: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1254: ssh-ed25519-cert-v01@openssh.com,
1255: ssh-rsa-cert-v01@openssh.com,
1256: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 1257: ssh-ed25519,ssh-rsa
1.213 markus 1258: .Ed
1259: .Pp
1.240 jmc 1260: The list of available key types may also be obtained using
1261: .Qq ssh -Q key .
1.1 stevesk 1262: .It Cm PubkeyAuthentication
1263: Specifies whether to try public key authentication.
1264: The argument to this keyword must be
1.240 jmc 1265: .Cm yes
1266: (the default)
1.1 stevesk 1267: or
1.240 jmc 1268: .Cm no .
1.75 dtucker 1269: .It Cm RekeyLimit
1270: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1271: session key is renegotiated, optionally followed a maximum amount of
1272: time that may pass before the session key is renegotiated.
1273: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1274: .Sq K ,
1275: .Sq M ,
1.75 dtucker 1276: or
1.76 jmc 1277: .Sq G
1.75 dtucker 1278: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1279: The default is between
1.84 jmc 1280: .Sq 1G
1.75 dtucker 1281: and
1.84 jmc 1282: .Sq 4G ,
1.75 dtucker 1283: depending on the cipher.
1.162 dtucker 1284: The optional second value is specified in seconds and may use any of the
1285: units documented in the
1.240 jmc 1286: .Sx TIME FORMATS
1287: section of
1.162 dtucker 1288: .Xr sshd_config 5 .
1289: The default value for
1290: .Cm RekeyLimit
1291: is
1.240 jmc 1292: .Cm default none ,
1.162 dtucker 1293: which means that rekeying is performed after the cipher's default amount
1294: of data has been sent or received and no time based rekeying is done.
1.1 stevesk 1295: .It Cm RemoteForward
1.74 jmc 1296: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1297: the secure channel to the specified host and port from the local machine.
1.49 jmc 1298: The first argument must be
1.43 djm 1299: .Sm off
1.49 jmc 1300: .Oo Ar bind_address : Oc Ar port
1.43 djm 1301: .Sm on
1.49 jmc 1302: and the second argument must be
1303: .Ar host : Ns Ar hostport .
1.138 djm 1304: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1305: Multiple forwardings may be specified, and additional
1306: forwardings can be given on the command line.
1.113 stevesk 1307: Privileged ports can be forwarded only when
1308: logging in as root on the remote machine.
1.118 jmc 1309: .Pp
1.117 djm 1310: If the
1311: .Ar port
1.240 jmc 1312: argument is 0,
1.117 djm 1313: the listen port will be dynamically allocated on the server and reported
1314: to the client at run time.
1.43 djm 1315: .Pp
1316: If the
1317: .Ar bind_address
1318: is not specified, the default is to only bind to loopback addresses.
1319: If the
1320: .Ar bind_address
1321: is
1322: .Ql *
1323: or an empty string, then the forwarding is requested to listen on all
1324: interfaces.
1325: Specifying a remote
1326: .Ar bind_address
1.46 jmc 1327: will only succeed if the server's
1328: .Cm GatewayPorts
1.43 djm 1329: option is enabled (see
1.46 jmc 1330: .Xr sshd_config 5 ) .
1.149 djm 1331: .It Cm RequestTTY
1332: Specifies whether to request a pseudo-tty for the session.
1333: The argument may be one of:
1.240 jmc 1334: .Cm no
1.149 djm 1335: (never request a TTY),
1.240 jmc 1336: .Cm yes
1.149 djm 1337: (always request a TTY when standard input is a TTY),
1.240 jmc 1338: .Cm force
1.149 djm 1339: (always request a TTY) or
1.240 jmc 1340: .Cm auto
1.149 djm 1341: (request a TTY when opening a login session).
1342: This option mirrors the
1343: .Fl t
1344: and
1345: .Fl T
1346: flags for
1347: .Xr ssh 1 .
1.196 djm 1348: .It Cm RevokedHostKeys
1349: Specifies revoked host public keys.
1350: Keys listed in this file will be refused for host authentication.
1351: Note that if this file does not exist or is not readable,
1352: then host authentication will be refused for all hosts.
1353: Keys may be specified as a text file, listing one public key per line, or as
1354: an OpenSSH Key Revocation List (KRL) as generated by
1355: .Xr ssh-keygen 1 .
1356: For more information on KRLs, see the KEY REVOCATION LISTS section in
1357: .Xr ssh-keygen 1 .
1.32 djm 1358: .It Cm SendEnv
1359: Specifies what variables from the local
1360: .Xr environ 7
1361: should be sent to the server.
1.84 jmc 1362: The server must also support it, and the server must be configured to
1.33 djm 1363: accept these environment variables.
1.207 dtucker 1364: Note that the
1365: .Ev TERM
1.208 jmc 1366: environment variable is always sent whenever a
1.207 dtucker 1367: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1368: Refer to
1369: .Cm AcceptEnv
1370: in
1371: .Xr sshd_config 5
1372: for how to configure the server.
1.80 jmc 1373: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1374: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1375: across multiple
1376: .Cm SendEnv
1377: directives.
1378: The default is not to send any environment variables.
1.81 jmc 1379: .Pp
1380: See
1381: .Sx PATTERNS
1382: for more information on patterns.
1.28 markus 1383: .It Cm ServerAliveCountMax
1.73 jmc 1384: Sets the number of server alive messages (see below) which may be
1.28 markus 1385: sent without
1.84 jmc 1386: .Xr ssh 1
1.28 markus 1387: receiving any messages back from the server.
1388: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1389: ssh will disconnect from the server, terminating the session.
1.28 markus 1390: It is important to note that the use of server alive messages is very
1391: different from
1392: .Cm TCPKeepAlive
1393: (below).
1394: The server alive messages are sent through the encrypted channel
1395: and therefore will not be spoofable.
1396: The TCP keepalive option enabled by
1397: .Cm TCPKeepAlive
1398: is spoofable.
1399: The server alive mechanism is valuable when the client or
1400: server depend on knowing when a connection has become inactive.
1401: .Pp
1402: The default value is 3.
1403: If, for example,
1404: .Cm ServerAliveInterval
1.84 jmc 1405: (see below) is set to 15 and
1.28 markus 1406: .Cm ServerAliveCountMax
1.84 jmc 1407: is left at the default, if the server becomes unresponsive,
1408: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1409: .It Cm ServerAliveInterval
1410: Sets a timeout interval in seconds after which if no data has been received
1411: from the server,
1.84 jmc 1412: .Xr ssh 1
1.67 jmc 1413: will send a message through the encrypted
1414: channel to request a response from the server.
1415: The default
1416: is 0, indicating that these messages will not be sent to the server.
1.191 millert 1417: .It Cm StreamLocalBindMask
1418: Sets the octal file creation mode mask
1419: .Pq umask
1420: used when creating a Unix-domain socket file for local or remote
1421: port forwarding.
1422: This option is only used for port forwarding to a Unix-domain socket file.
1423: .Pp
1424: The default value is 0177, which creates a Unix-domain socket file that is
1425: readable and writable only by the owner.
1426: Note that not all operating systems honor the file mode on Unix-domain
1427: socket files.
1428: .It Cm StreamLocalBindUnlink
1429: Specifies whether to remove an existing Unix-domain socket file for local
1430: or remote port forwarding before creating a new one.
1431: If the socket file already exists and
1432: .Cm StreamLocalBindUnlink
1433: is not enabled,
1434: .Nm ssh
1435: will be unable to forward the port to the Unix-domain socket file.
1436: This option is only used for port forwarding to a Unix-domain socket file.
1437: .Pp
1438: The argument must be
1.240 jmc 1439: .Cm yes
1.191 millert 1440: or
1.240 jmc 1441: .Cm no
1442: (the default).
1.1 stevesk 1443: .It Cm StrictHostKeyChecking
1444: If this flag is set to
1.240 jmc 1445: .Cm yes ,
1.84 jmc 1446: .Xr ssh 1
1.1 stevesk 1447: will never automatically add host keys to the
1.50 djm 1448: .Pa ~/.ssh/known_hosts
1.1 stevesk 1449: file, and refuses to connect to hosts whose host key has changed.
1450: This provides maximum protection against trojan horse attacks,
1.84 jmc 1451: though it can be annoying when the
1.1 stevesk 1452: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1453: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1454: frequently made.
1455: This option forces the user to manually
1456: add all new hosts.
1457: If this flag is set to
1.240 jmc 1458: .Cm no ,
1.84 jmc 1459: ssh will automatically add new host keys to the
1.1 stevesk 1460: user known hosts files.
1461: If this flag is set to
1.240 jmc 1462: .Cm ask
1463: (the default),
1.1 stevesk 1464: new host keys
1465: will be added to the user known host files only after the user
1466: has confirmed that is what they really want to do, and
1.84 jmc 1467: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1468: The host keys of
1469: known hosts will be verified automatically in all cases.
1.244 jmc 1470: .It Cm SyslogFacility
1471: Gives the facility code that is used when logging messages from
1472: .Xr ssh 1 .
1473: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1474: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1475: The default is USER.
1.26 markus 1476: .It Cm TCPKeepAlive
1477: Specifies whether the system should send TCP keepalive messages to the
1478: other side.
1479: If they are sent, death of the connection or crash of one
1480: of the machines will be properly noticed.
1481: However, this means that
1482: connections will die if the route is down temporarily, and some people
1483: find it annoying.
1484: .Pp
1485: The default is
1.240 jmc 1486: .Cm yes
1.26 markus 1487: (to send TCP keepalive messages), and the client will notice
1488: if the network goes down or the remote host dies.
1489: This is important in scripts, and many users want it too.
1490: .Pp
1491: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1492: .Cm no .
1.65 reyk 1493: .It Cm Tunnel
1.95 stevesk 1494: Request
1.65 reyk 1495: .Xr tun 4
1.69 jmc 1496: device forwarding between the client and the server.
1.65 reyk 1497: The argument must be
1.240 jmc 1498: .Cm yes ,
1499: .Cm point-to-point
1.95 stevesk 1500: (layer 3),
1.240 jmc 1501: .Cm ethernet
1.95 stevesk 1502: (layer 2),
1.65 reyk 1503: or
1.240 jmc 1504: .Cm no
1505: (the default).
1.95 stevesk 1506: Specifying
1.240 jmc 1507: .Cm yes
1.95 stevesk 1508: requests the default tunnel mode, which is
1.240 jmc 1509: .Cm point-to-point .
1.65 reyk 1510: .It Cm TunnelDevice
1.95 stevesk 1511: Specifies the
1.65 reyk 1512: .Xr tun 4
1.95 stevesk 1513: devices to open on the client
1514: .Pq Ar local_tun
1515: and the server
1516: .Pq Ar remote_tun .
1517: .Pp
1518: The argument must be
1519: .Sm off
1520: .Ar local_tun Op : Ar remote_tun .
1521: .Sm on
1522: The devices may be specified by numerical ID or the keyword
1.240 jmc 1523: .Cm any ,
1.95 stevesk 1524: which uses the next available tunnel device.
1525: If
1526: .Ar remote_tun
1527: is not specified, it defaults to
1.240 jmc 1528: .Cm any .
1.95 stevesk 1529: The default is
1.240 jmc 1530: .Cm any:any .
1.201 djm 1531: .It Cm UpdateHostKeys
1.200 djm 1532: Specifies whether
1533: .Xr ssh 1
1534: should accept notifications of additional hostkeys from the server sent
1535: after authentication has completed and add them to
1536: .Cm UserKnownHostsFile .
1537: The argument must be
1.240 jmc 1538: .Cm yes ,
1539: .Cm no
1.204 djm 1540: (the default) or
1.240 jmc 1541: .Cm ask .
1.200 djm 1542: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1543: and supports graceful key rotation by allowing a server to send replacement
1544: public keys before old ones are removed.
1.200 djm 1545: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1546: host was already trusted or explicitly accepted by the user.
1.204 djm 1547: If
1548: .Cm UpdateHostKeys
1549: is set to
1.240 jmc 1550: .Cm ask ,
1.204 djm 1551: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1552: Confirmation is currently incompatible with
1553: .Cm ControlPersist ,
1554: and will be disabled if it is enabled.
1.200 djm 1555: .Pp
1556: Presently, only
1557: .Xr sshd 8
1558: from OpenSSH 6.8 and greater support the
1.240 jmc 1559: .Qq hostkeys@openssh.com
1.200 djm 1560: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1561: .It Cm UsePrivilegedPort
1562: Specifies whether to use a privileged port for outgoing connections.
1563: The argument must be
1.240 jmc 1564: .Cm yes
1.72 jmc 1565: or
1.240 jmc 1566: .Cm no
1567: (the default).
1.72 jmc 1568: If set to
1.240 jmc 1569: .Cm yes ,
1.84 jmc 1570: .Xr ssh 1
1.72 jmc 1571: must be setuid root.
1.1 stevesk 1572: .It Cm User
1573: Specifies the user to log in as.
1574: This can be useful when a different user name is used on different machines.
1575: This saves the trouble of
1576: having to remember to give the user name on the command line.
1577: .It Cm UserKnownHostsFile
1.151 djm 1578: Specifies one or more files to use for the user
1579: host key database, separated by whitespace.
1580: The default is
1581: .Pa ~/.ssh/known_hosts ,
1582: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1583: .It Cm VerifyHostKeyDNS
1584: Specifies whether to verify the remote key using DNS and SSHFP resource
1585: records.
1.24 jakob 1586: If this option is set to
1.240 jmc 1587: .Cm yes ,
1.25 jmc 1588: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1589: from DNS.
1590: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1591: .Cm ask .
1.24 jakob 1592: If this option is set to
1.240 jmc 1593: .Cm ask ,
1.24 jakob 1594: information on fingerprint match will be displayed, but the user will still
1595: need to confirm new host keys according to the
1596: .Cm StrictHostKeyChecking
1597: option.
1.8 jakob 1598: The default is
1.240 jmc 1599: .Cm no .
1.84 jmc 1600: .Pp
1.240 jmc 1601: See also
1602: .Sx VERIFYING HOST KEYS
1603: in
1.84 jmc 1604: .Xr ssh 1 .
1.111 grunk 1605: .It Cm VisualHostKey
1606: If this flag is set to
1.240 jmc 1607: .Cm yes ,
1.111 grunk 1608: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1609: printed in addition to the fingerprint string at login and
1.114 stevesk 1610: for unknown host keys.
1.111 grunk 1611: If this flag is set to
1.240 jmc 1612: .Cm no
1613: (the default),
1.114 stevesk 1614: no fingerprint strings are printed at login and
1.197 djm 1615: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1616: .It Cm XAuthLocation
1.5 stevesk 1617: Specifies the full pathname of the
1.1 stevesk 1618: .Xr xauth 1
1619: program.
1620: The default is
1621: .Pa /usr/X11R6/bin/xauth .
1622: .El
1.86 jmc 1623: .Sh PATTERNS
1624: A
1625: .Em pattern
1626: consists of zero or more non-whitespace characters,
1627: .Sq *
1628: (a wildcard that matches zero or more characters),
1629: or
1630: .Sq ?\&
1631: (a wildcard that matches exactly one character).
1632: For example, to specify a set of declarations for any host in the
1.240 jmc 1633: .Qq .co.uk
1.86 jmc 1634: set of domains,
1635: the following pattern could be used:
1636: .Pp
1637: .Dl Host *.co.uk
1638: .Pp
1639: The following pattern
1640: would match any host in the 192.168.0.[0-9] network range:
1641: .Pp
1642: .Dl Host 192.168.0.?
1643: .Pp
1644: A
1645: .Em pattern-list
1646: is a comma-separated list of patterns.
1647: Patterns within pattern-lists may be negated
1648: by preceding them with an exclamation mark
1649: .Pq Sq !\& .
1650: For example,
1.174 djm 1651: to allow a key to be used from anywhere within an organization
1.86 jmc 1652: except from the
1.240 jmc 1653: .Qq dialup
1.86 jmc 1654: pool,
1655: the following entry (in authorized_keys) could be used:
1656: .Pp
1657: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.239 jmc 1658: .Sh TOKENS
1659: Arguments to some keywords can make use of tokens,
1660: which are expanded at runtime:
1661: .Pp
1662: .Bl -tag -width XXXX -offset indent -compact
1663: .It %%
1664: A literal
1665: .Sq % .
1666: .It \&%C
1667: Shorthand for %l%h%p%r.
1668: .It %d
1669: Local user's home directory.
1670: .It %h
1671: The remote hostname.
1672: .It %i
1673: The local user ID.
1674: .It %L
1675: The local hostname.
1676: .It %l
1677: The local hostname, including the domain name.
1678: .It %n
1679: The original remote hostname, as given on the command line.
1680: .It %p
1681: The remote port.
1682: .It %r
1683: The remote username.
1684: .It %u
1685: The local username.
1686: .El
1687: .Pp
1688: .Cm Match exec
1689: accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1690: .Pp
1691: .Cm CertificateFile
1692: accepts the tokens %%, %d, %h, %l, %r, and %u.
1693: .Pp
1694: .Cm ControlPath
1695: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1696: .Pp
1697: .Cm HostName
1698: accepts the tokens %% and %h.
1699: .Pp
1700: .Cm IdentityAgent
1701: and
1702: .Cm IdentityFile
1703: accept the tokens %%, %d, %h, %l, %r, and %u.
1704: .Pp
1705: .Cm LocalCommand
1706: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1707: .Pp
1708: .Cm ProxyCommand
1709: accepts the tokens %%, %h, %p, and %r.
1.1 stevesk 1710: .Sh FILES
1711: .Bl -tag -width Ds
1.50 djm 1712: .It Pa ~/.ssh/config
1.1 stevesk 1713: This is the per-user configuration file.
1714: The format of this file is described above.
1.84 jmc 1715: This file is used by the SSH client.
1.30 djm 1716: Because of the potential for abuse, this file must have strict permissions:
1717: read/write for the user, and not accessible by others.
1.1 stevesk 1718: .It Pa /etc/ssh/ssh_config
1719: Systemwide configuration file.
1720: This file provides defaults for those
1721: values that are not specified in the user's configuration file, and
1722: for those users who do not have a configuration file.
1723: This file must be world-readable.
1724: .El
1.13 jmc 1725: .Sh SEE ALSO
1726: .Xr ssh 1
1.1 stevesk 1727: .Sh AUTHORS
1.240 jmc 1728: .An -nosplit
1.1 stevesk 1729: OpenSSH is a derivative of the original and free
1.240 jmc 1730: ssh 1.2.12 release by
1731: .An Tatu Ylonen .
1732: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1733: .An Niels Provos , Theo de Raadt
1734: and
1735: .An Dug Song
1.1 stevesk 1736: removed many bugs, re-added newer features and
1737: created OpenSSH.
1.240 jmc 1738: .An Markus Friedl
1739: contributed the support for SSH protocol versions 1.5 and 2.0.
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