Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.272
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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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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1.272 ! jmc 36: .\" $OpenBSD: ssh_config.5,v 1.271 2018/04/06 13:02:39 djm Exp $
! 37: .Dd $Mdocdate: April 6 2018 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
42: .Nd OpenSSH SSH client configuration files
43: .Sh DESCRIPTION
1.84 jmc 44: .Xr ssh 1
1.1 stevesk 45: obtains configuration data from the following sources in
46: the following order:
1.79 jmc 47: .Pp
1.2 stevesk 48: .Bl -enum -offset indent -compact
49: .It
50: command-line options
51: .It
52: user's configuration file
1.50 djm 53: .Pq Pa ~/.ssh/config
1.2 stevesk 54: .It
55: system-wide configuration file
56: .Pq Pa /etc/ssh/ssh_config
57: .El
1.1 stevesk 58: .Pp
59: For each parameter, the first obtained value
60: will be used.
1.41 jmc 61: The configuration files contain sections separated by
1.240 jmc 62: .Cm Host
1.1 stevesk 63: specifications, and that section is only applied for hosts that
64: match one of the patterns given in the specification.
1.193 djm 65: The matched host name is usually the one given on the command line
66: (see the
67: .Cm CanonicalizeHostname
1.240 jmc 68: option for exceptions).
1.1 stevesk 69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.240 jmc 74: The file contains keyword-argument pairs, one per line.
75: Lines starting with
1.1 stevesk 76: .Ql #
1.240 jmc 77: and empty lines are interpreted as comments.
78: Arguments may optionally be enclosed in double quotes
79: .Pq \&"
80: in order to represent arguments containing spaces.
1.1 stevesk 81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
92: .Pp
93: The possible
94: keywords and their meanings are as follows (note that
95: keywords are case-insensitive and arguments are case-sensitive):
96: .Bl -tag -width Ds
97: .It Cm Host
98: Restricts the following declarations (up to the next
99: .Cm Host
1.169 djm 100: or
101: .Cm Match
1.1 stevesk 102: keyword) to be only for those hosts that match one of the patterns
103: given after the keyword.
1.112 krw 104: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
1.193 djm 109: The host is usually the
1.1 stevesk 110: .Ar hostname
1.193 djm 111: argument given on the command line
112: (see the
113: .Cm CanonicalizeHostname
1.240 jmc 114: keyword for exceptions).
1.148 djm 115: .Pp
116: A pattern entry may be negated by prefixing it with an exclamation mark
117: .Pq Sq !\& .
118: If a negated entry is matched, then the
119: .Cm Host
120: entry is ignored, regardless of whether any other patterns on the line
121: match.
122: Negated matches are therefore useful to provide exceptions for wildcard
123: matches.
1.81 jmc 124: .Pp
125: See
126: .Sx PATTERNS
127: for more information on patterns.
1.170 jmc 128: .It Cm Match
1.169 djm 129: Restricts the following declarations (up to the next
130: .Cm Host
131: or
132: .Cm Match
133: keyword) to be used only when the conditions following the
134: .Cm Match
135: keyword are satisfied.
1.220 sobrado 136: Match conditions are specified using one or more criteria
1.178 dtucker 137: or the single token
138: .Cm all
1.193 djm 139: which always matches.
140: The available criteria keywords are:
141: .Cm canonical ,
1.176 djm 142: .Cm exec ,
1.169 djm 143: .Cm host ,
144: .Cm originalhost ,
145: .Cm user ,
146: and
147: .Cm localuser .
1.193 djm 148: The
149: .Cm all
150: criteria must appear alone or immediately after
1.194 jmc 151: .Cm canonical .
1.193 djm 152: Other criteria may be combined arbitrarily.
153: All criteria but
154: .Cm all
155: and
156: .Cm canonical
157: require an argument.
158: Criteria may be negated by prepending an exclamation mark
159: .Pq Sq !\& .
1.169 djm 160: .Pp
1.177 jmc 161: The
1.193 djm 162: .Cm canonical
1.210 dtucker 163: keyword matches only when the configuration file is being re-parsed
1.193 djm 164: after hostname canonicalization (see the
165: .Cm CanonicalizeHostname
166: option.)
167: This may be useful to specify conditions that work with canonical host
168: names only.
169: The
1.176 djm 170: .Cm exec
1.177 jmc 171: keyword executes the specified command under the user's shell.
1.169 djm 172: If the command returns a zero exit status then the condition is considered true.
173: Commands containing whitespace characters must be quoted.
1.239 jmc 174: Arguments to
175: .Cm exec
176: accept the tokens described in the
177: .Sx TOKENS
178: section.
1.169 djm 179: .Pp
180: The other keywords' criteria must be single entries or comma-separated
181: lists and may use the wildcard and negation operators described in the
182: .Sx PATTERNS
183: section.
184: The criteria for the
185: .Cm host
186: keyword are matched against the target hostname, after any substitution
187: by the
188: .Cm Hostname
1.193 djm 189: or
190: .Cm CanonicalizeHostname
191: options.
1.169 djm 192: The
193: .Cm originalhost
194: keyword matches against the hostname as it was specified on the command-line.
195: The
196: .Cm user
197: keyword matches against the target username on the remote host.
198: The
199: .Cm localuser
200: keyword matches against the name of the local user running
201: .Xr ssh 1
202: (this keyword may be useful in system-wide
203: .Nm
204: files).
1.222 jcs 205: .It Cm AddKeysToAgent
206: Specifies whether keys should be automatically added to a running
1.223 jmc 207: .Xr ssh-agent 1 .
1.222 jcs 208: If this option is set to
1.240 jmc 209: .Cm yes
1.222 jcs 210: and a key is loaded from a file, the key and its passphrase are added to
211: the agent with the default lifetime, as if by
212: .Xr ssh-add 1 .
213: If this option is set to
1.240 jmc 214: .Cm ask ,
215: .Xr ssh 1
1.222 jcs 216: will require confirmation using the
217: .Ev SSH_ASKPASS
218: program before adding a key (see
219: .Xr ssh-add 1
220: for details).
221: If this option is set to
1.240 jmc 222: .Cm confirm ,
1.222 jcs 223: each use of the key must be confirmed, as if the
224: .Fl c
225: option was specified to
226: .Xr ssh-add 1 .
227: If this option is set to
1.240 jmc 228: .Cm no ,
1.222 jcs 229: no keys are added to the agent.
230: The argument must be
1.240 jmc 231: .Cm yes ,
232: .Cm confirm ,
233: .Cm ask ,
1.222 jcs 234: or
1.240 jmc 235: .Cm no
236: (the default).
1.10 djm 237: .It Cm AddressFamily
1.11 jmc 238: Specifies which address family to use when connecting.
239: Valid arguments are
1.240 jmc 240: .Cm any
241: (the default),
242: .Cm inet
1.84 jmc 243: (use IPv4 only), or
1.240 jmc 244: .Cm inet6
1.40 jmc 245: (use IPv6 only).
1.1 stevesk 246: .It Cm BatchMode
247: If set to
1.240 jmc 248: .Cm yes ,
1.1 stevesk 249: passphrase/password querying will be disabled.
250: This option is useful in scripts and other batch jobs where no user
251: is present to supply the password.
252: The argument must be
1.240 jmc 253: .Cm yes
1.1 stevesk 254: or
1.240 jmc 255: .Cm no
256: (the default).
1.268 jmc 257: .It Cm BindAddress
258: Use the specified address on the local machine as the source address of
259: the connection.
260: Only useful on systems with more than one address.
1.267 djm 261: Note that this option does not work if
262: .Cm UsePrivilegedPort
263: is set to
264: .Cm yes .
1.268 jmc 265: .It Cm BindInterface
266: Use the address of the specified interface on the local machine as the
267: source address of the connection.
1.1 stevesk 268: Note that this option does not work if
269: .Cm UsePrivilegedPort
270: is set to
1.240 jmc 271: .Cm yes .
1.171 djm 272: .It Cm CanonicalDomains
1.172 jmc 273: When
1.173 djm 274: .Cm CanonicalizeHostname
1.171 djm 275: is enabled, this option specifies the list of domain suffixes in which to
276: search for the specified destination host.
1.173 djm 277: .It Cm CanonicalizeFallbackLocal
1.174 djm 278: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 279: The default,
1.240 jmc 280: .Cm yes ,
1.172 jmc 281: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 282: search rules.
283: A value of
1.240 jmc 284: .Cm no
1.171 djm 285: will cause
286: .Xr ssh 1
287: to fail instantly if
1.173 djm 288: .Cm CanonicalizeHostname
1.171 djm 289: is enabled and the target hostname cannot be found in any of the domains
290: specified by
291: .Cm CanonicalDomains .
1.173 djm 292: .It Cm CanonicalizeHostname
1.174 djm 293: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 294: The default,
1.240 jmc 295: .Cm no ,
1.171 djm 296: is not to perform any name rewriting and let the system resolver handle all
297: hostname lookups.
298: If set to
1.240 jmc 299: .Cm yes
1.171 djm 300: then, for connections that do not use a
301: .Cm ProxyCommand ,
302: .Xr ssh 1
1.173 djm 303: will attempt to canonicalize the hostname specified on the command line
1.171 djm 304: using the
305: .Cm CanonicalDomains
306: suffixes and
1.173 djm 307: .Cm CanonicalizePermittedCNAMEs
1.171 djm 308: rules.
309: If
1.173 djm 310: .Cm CanonicalizeHostname
1.171 djm 311: is set to
1.240 jmc 312: .Cm always ,
1.174 djm 313: then canonicalization is applied to proxied connections too.
1.185 djm 314: .Pp
1.193 djm 315: If this option is enabled, then the configuration files are processed
316: again using the new target name to pick up any new configuration in matching
1.185 djm 317: .Cm Host
1.193 djm 318: and
319: .Cm Match
1.185 djm 320: stanzas.
1.173 djm 321: .It Cm CanonicalizeMaxDots
1.172 jmc 322: Specifies the maximum number of dot characters in a hostname before
1.174 djm 323: canonicalization is disabled.
1.240 jmc 324: The default, 1,
1.172 jmc 325: allows a single dot (i.e. hostname.subdomain).
1.173 djm 326: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 327: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 328: canonicalizing hostnames.
1.171 djm 329: The rules consist of one or more arguments of
1.172 jmc 330: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 331: where
332: .Ar source_domain_list
1.174 djm 333: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 334: and
335: .Ar target_domain_list
1.172 jmc 336: is a pattern-list of domains that they may resolve to.
1.171 djm 337: .Pp
338: For example,
1.240 jmc 339: .Qq *.a.example.com:*.b.example.com,*.c.example.com
1.171 djm 340: will allow hostnames matching
1.240 jmc 341: .Qq *.a.example.com
1.173 djm 342: to be canonicalized to names in the
1.240 jmc 343: .Qq *.b.example.com
1.171 djm 344: or
1.240 jmc 345: .Qq *.c.example.com
1.171 djm 346: domains.
1.221 djm 347: .It Cm CertificateFile
348: Specifies a file from which the user's certificate is read.
349: A corresponding private key must be provided separately in order
350: to use this certificate either
351: from an
352: .Cm IdentityFile
353: directive or
354: .Fl i
355: flag to
356: .Xr ssh 1 ,
357: via
358: .Xr ssh-agent 1 ,
359: or via a
360: .Cm PKCS11Provider .
361: .Pp
1.239 jmc 362: Arguments to
363: .Cm CertificateFile
364: may use the tilde syntax to refer to a user's home directory
365: or the tokens described in the
366: .Sx TOKENS
367: section.
1.221 djm 368: .Pp
369: It is possible to have multiple certificate files specified in
370: configuration files; these certificates will be tried in sequence.
371: Multiple
372: .Cm CertificateFile
373: directives will add to the list of certificates used for
374: authentication.
1.1 stevesk 375: .It Cm ChallengeResponseAuthentication
1.82 jmc 376: Specifies whether to use challenge-response authentication.
1.1 stevesk 377: The argument to this keyword must be
1.240 jmc 378: .Cm yes
379: (the default)
1.1 stevesk 380: or
1.240 jmc 381: .Cm no .
1.1 stevesk 382: .It Cm CheckHostIP
1.240 jmc 383: If set to
384: .Cm yes
385: (the default),
1.84 jmc 386: .Xr ssh 1
387: will additionally check the host IP address in the
1.1 stevesk 388: .Pa known_hosts
389: file.
1.240 jmc 390: This allows it to detect if a host key changed due to DNS spoofing
1.211 djm 391: and will add addresses of destination hosts to
392: .Pa ~/.ssh/known_hosts
393: in the process, regardless of the setting of
394: .Cm StrictHostKeyChecking .
1.107 grunk 395: If the option is set to
1.240 jmc 396: .Cm no ,
1.1 stevesk 397: the check will not be executed.
398: .It Cm Ciphers
1.245 djm 399: Specifies the ciphers allowed and their order of preference.
1.1 stevesk 400: Multiple ciphers must be comma-separated.
1.214 djm 401: If the specified value begins with a
402: .Sq +
403: character, then the specified ciphers will be appended to the default set
404: instead of replacing them.
1.241 djm 405: If the specified value begins with a
406: .Sq -
407: character, then the specified ciphers (including wildcards) will be removed
408: from the default set instead of replacing them.
1.214 djm 409: .Pp
1.180 djm 410: The supported ciphers are:
1.240 jmc 411: .Bd -literal -offset indent
1.186 naddy 412: 3des-cbc
413: aes128-cbc
414: aes192-cbc
415: aes256-cbc
416: aes128-ctr
417: aes192-ctr
418: aes256-ctr
419: aes128-gcm@openssh.com
420: aes256-gcm@openssh.com
421: chacha20-poly1305@openssh.com
1.240 jmc 422: .Ed
1.180 djm 423: .Pp
1.84 jmc 424: The default is:
1.186 naddy 425: .Bd -literal -offset indent
1.215 jmc 426: chacha20-poly1305@openssh.com,
1.186 naddy 427: aes128-ctr,aes192-ctr,aes256-ctr,
1.270 djm 428: aes128-gcm@openssh.com,aes256-gcm@openssh.com
1.1 stevesk 429: .Ed
1.180 djm 430: .Pp
1.240 jmc 431: The list of available ciphers may also be obtained using
432: .Qq ssh -Q cipher .
1.1 stevesk 433: .It Cm ClearAllForwardings
1.84 jmc 434: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 435: specified in the configuration files or on the command line be
1.7 jmc 436: cleared.
437: This option is primarily useful when used from the
1.84 jmc 438: .Xr ssh 1
1.1 stevesk 439: command line to clear port forwardings set in
440: configuration files, and is automatically set by
441: .Xr scp 1
442: and
443: .Xr sftp 1 .
444: The argument must be
1.240 jmc 445: .Cm yes
1.1 stevesk 446: or
1.240 jmc 447: .Cm no
448: (the default).
1.1 stevesk 449: .It Cm Compression
450: Specifies whether to use compression.
451: The argument must be
1.240 jmc 452: .Cm yes
1.1 stevesk 453: or
1.240 jmc 454: .Cm no
455: (the default).
1.247 naddy 456: .It Cm ConnectionAttempts
457: Specifies the number of tries (one per second) to make before exiting.
458: The argument must be an integer.
459: This may be useful in scripts if the connection sometimes fails.
460: The default is 1.
1.9 djm 461: .It Cm ConnectTimeout
1.84 jmc 462: Specifies the timeout (in seconds) used when connecting to the
463: SSH server, instead of using the default system TCP timeout.
1.11 jmc 464: This value is used only when the target is down or really unreachable,
465: not when it refuses the connection.
1.36 djm 466: .It Cm ControlMaster
467: Enables the sharing of multiple sessions over a single network connection.
468: When set to
1.240 jmc 469: .Cm yes ,
1.84 jmc 470: .Xr ssh 1
1.36 djm 471: will listen for connections on a control socket specified using the
472: .Cm ControlPath
473: argument.
474: Additional sessions can connect to this socket using the same
475: .Cm ControlPath
476: with
477: .Cm ControlMaster
478: set to
1.240 jmc 479: .Cm no
1.38 jmc 480: (the default).
1.64 jmc 481: These sessions will try to reuse the master instance's network connection
1.63 djm 482: rather than initiating new ones, but will fall back to connecting normally
483: if the control socket does not exist, or is not listening.
484: .Pp
1.37 djm 485: Setting this to
1.240 jmc 486: .Cm ask
487: will cause
488: .Xr ssh 1
1.206 jmc 489: to listen for control connections, but require confirmation using
490: .Xr ssh-askpass 1 .
1.51 jakob 491: If the
492: .Cm ControlPath
1.84 jmc 493: cannot be opened,
1.240 jmc 494: .Xr ssh 1
495: will continue without connecting to a master instance.
1.58 djm 496: .Pp
497: X11 and
1.59 jmc 498: .Xr ssh-agent 1
1.58 djm 499: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 500: display and agent forwarded will be the one belonging to the master
1.59 jmc 501: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 502: .Pp
503: Two additional options allow for opportunistic multiplexing: try to use a
504: master connection but fall back to creating a new one if one does not already
505: exist.
506: These options are:
1.240 jmc 507: .Cm auto
1.56 djm 508: and
1.240 jmc 509: .Cm autoask .
1.56 djm 510: The latter requires confirmation like the
1.240 jmc 511: .Cm ask
1.56 djm 512: option.
1.36 djm 513: .It Cm ControlPath
1.55 djm 514: Specify the path to the control socket used for connection sharing as described
515: in the
1.36 djm 516: .Cm ControlMaster
1.57 djm 517: section above or the string
1.240 jmc 518: .Cm none
1.57 djm 519: to disable connection sharing.
1.239 jmc 520: Arguments to
521: .Cm ControlPath
522: may use the tilde syntax to refer to a user's home directory
523: or the tokens described in the
524: .Sx TOKENS
525: section.
1.56 djm 526: It is recommended that any
527: .Cm ControlPath
528: used for opportunistic connection sharing include
1.195 djm 529: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
530: that is not writable by other users.
1.56 djm 531: This ensures that shared connections are uniquely identified.
1.137 djm 532: .It Cm ControlPersist
533: When used in conjunction with
534: .Cm ControlMaster ,
535: specifies that the master connection should remain open
536: in the background (waiting for future client connections)
537: after the initial client connection has been closed.
538: If set to
1.240 jmc 539: .Cm no ,
1.137 djm 540: then the master connection will not be placed into the background,
541: and will close as soon as the initial client connection is closed.
542: If set to
1.240 jmc 543: .Cm yes
544: or 0,
1.137 djm 545: then the master connection will remain in the background indefinitely
546: (until killed or closed via a mechanism such as the
1.240 jmc 547: .Qq ssh -O exit ) .
1.137 djm 548: If set to a time in seconds, or a time in any of the formats documented in
549: .Xr sshd_config 5 ,
550: then the backgrounded master connection will automatically terminate
551: after it has remained idle (with no client connections) for the
552: specified time.
1.38 jmc 553: .It Cm DynamicForward
1.74 jmc 554: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 555: over the secure channel, and the application
556: protocol is then used to determine where to connect to from the
557: remote machine.
1.62 djm 558: .Pp
559: The argument must be
560: .Sm off
561: .Oo Ar bind_address : Oc Ar port .
562: .Sm on
1.138 djm 563: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 564: By default, the local port is bound in accordance with the
565: .Cm GatewayPorts
566: setting.
567: However, an explicit
568: .Ar bind_address
569: may be used to bind the connection to a specific address.
570: The
571: .Ar bind_address
572: of
1.240 jmc 573: .Cm localhost
1.62 djm 574: indicates that the listening port be bound for local use only, while an
575: empty address or
576: .Sq *
577: indicates that the port should be available from all interfaces.
578: .Pp
1.38 jmc 579: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 580: .Xr ssh 1
1.38 jmc 581: will act as a SOCKS server.
582: Multiple forwardings may be specified, and
583: additional forwardings can be given on the command line.
584: Only the superuser can forward privileged ports.
1.14 markus 585: .It Cm EnableSSHKeysign
586: Setting this option to
1.240 jmc 587: .Cm yes
1.14 markus 588: in the global client configuration file
589: .Pa /etc/ssh/ssh_config
590: enables the use of the helper program
591: .Xr ssh-keysign 8
592: during
593: .Cm HostbasedAuthentication .
594: The argument must be
1.240 jmc 595: .Cm yes
1.14 markus 596: or
1.240 jmc 597: .Cm no
598: (the default).
1.23 jmc 599: This option should be placed in the non-hostspecific section.
1.14 markus 600: See
601: .Xr ssh-keysign 8
602: for more information.
1.1 stevesk 603: .It Cm EscapeChar
604: Sets the escape character (default:
605: .Ql ~ ) .
606: The escape character can also
607: be set on the command line.
608: The argument should be a single character,
609: .Ql ^
610: followed by a letter, or
1.240 jmc 611: .Cm none
1.1 stevesk 612: to disable the escape
613: character entirely (making the connection transparent for binary
614: data).
1.96 markus 615: .It Cm ExitOnForwardFailure
616: Specifies whether
617: .Xr ssh 1
618: should terminate the connection if it cannot set up all requested
1.216 djm 619: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 620: if either end is unable to bind and listen on a specified port).
1.216 djm 621: Note that
622: .Cm ExitOnForwardFailure
623: does not apply to connections made over port forwardings and will not,
624: for example, cause
625: .Xr ssh 1
626: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 627: The argument must be
1.240 jmc 628: .Cm yes
1.96 markus 629: or
1.240 jmc 630: .Cm no
631: (the default).
1.197 djm 632: .It Cm FingerprintHash
633: Specifies the hash algorithm used when displaying key fingerprints.
634: Valid options are:
1.240 jmc 635: .Cm md5
1.197 djm 636: and
1.240 jmc 637: .Cm sha256
638: (the default).
1.1 stevesk 639: .It Cm ForwardAgent
640: Specifies whether the connection to the authentication agent (if any)
641: will be forwarded to the remote machine.
642: The argument must be
1.240 jmc 643: .Cm yes
1.1 stevesk 644: or
1.240 jmc 645: .Cm no
646: (the default).
1.3 stevesk 647: .Pp
1.7 jmc 648: Agent forwarding should be enabled with caution.
649: Users with the ability to bypass file permissions on the remote host
650: (for the agent's Unix-domain socket)
651: can access the local agent through the forwarded connection.
652: An attacker cannot obtain key material from the agent,
1.3 stevesk 653: however they can perform operations on the keys that enable them to
654: authenticate using the identities loaded into the agent.
1.1 stevesk 655: .It Cm ForwardX11
656: Specifies whether X11 connections will be automatically redirected
657: over the secure channel and
658: .Ev DISPLAY
659: set.
660: The argument must be
1.240 jmc 661: .Cm yes
1.1 stevesk 662: or
1.240 jmc 663: .Cm no
664: (the default).
1.3 stevesk 665: .Pp
1.7 jmc 666: X11 forwarding should be enabled with caution.
667: Users with the ability to bypass file permissions on the remote host
1.22 markus 668: (for the user's X11 authorization database)
1.7 jmc 669: can access the local X11 display through the forwarded connection.
1.22 markus 670: An attacker may then be able to perform activities such as keystroke monitoring
671: if the
672: .Cm ForwardX11Trusted
673: option is also enabled.
1.134 djm 674: .It Cm ForwardX11Timeout
1.135 jmc 675: Specify a timeout for untrusted X11 forwarding
676: using the format described in the
1.240 jmc 677: .Sx TIME FORMATS
678: section of
1.134 djm 679: .Xr sshd_config 5 .
680: X11 connections received by
681: .Xr ssh 1
682: after this time will be refused.
683: The default is to disable untrusted X11 forwarding after twenty minutes has
684: elapsed.
1.22 markus 685: .It Cm ForwardX11Trusted
1.34 jmc 686: If this option is set to
1.240 jmc 687: .Cm yes ,
1.84 jmc 688: remote X11 clients will have full access to the original X11 display.
1.42 djm 689: .Pp
1.22 markus 690: If this option is set to
1.240 jmc 691: .Cm no
692: (the default),
1.84 jmc 693: remote X11 clients will be considered untrusted and prevented
1.22 markus 694: from stealing or tampering with data belonging to trusted X11
695: clients.
1.42 djm 696: Furthermore, the
697: .Xr xauth 1
698: token used for the session will be set to expire after 20 minutes.
699: Remote clients will be refused access after this time.
1.22 markus 700: .Pp
701: See the X11 SECURITY extension specification for full details on
702: the restrictions imposed on untrusted clients.
1.1 stevesk 703: .It Cm GatewayPorts
704: Specifies whether remote hosts are allowed to connect to local
705: forwarded ports.
706: By default,
1.84 jmc 707: .Xr ssh 1
1.7 jmc 708: binds local port forwardings to the loopback address.
709: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 710: .Cm GatewayPorts
1.84 jmc 711: can be used to specify that ssh
1.1 stevesk 712: should bind local port forwardings to the wildcard address,
713: thus allowing remote hosts to connect to forwarded ports.
714: The argument must be
1.240 jmc 715: .Cm yes
1.1 stevesk 716: or
1.240 jmc 717: .Cm no
718: (the default).
1.1 stevesk 719: .It Cm GlobalKnownHostsFile
1.151 djm 720: Specifies one or more files to use for the global
721: host key database, separated by whitespace.
722: The default is
723: .Pa /etc/ssh/ssh_known_hosts ,
724: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 725: .It Cm GSSAPIAuthentication
1.27 markus 726: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 727: The default is
1.240 jmc 728: .Cm no .
1.18 markus 729: .It Cm GSSAPIDelegateCredentials
730: Forward (delegate) credentials to the server.
731: The default is
1.240 jmc 732: .Cm no .
1.44 djm 733: .It Cm HashKnownHosts
734: Indicates that
1.84 jmc 735: .Xr ssh 1
1.44 djm 736: should hash host names and addresses when they are added to
1.50 djm 737: .Pa ~/.ssh/known_hosts .
1.44 djm 738: These hashed names may be used normally by
1.84 jmc 739: .Xr ssh 1
1.44 djm 740: and
1.84 jmc 741: .Xr sshd 8 ,
1.44 djm 742: but they do not reveal identifying information should the file's contents
743: be disclosed.
744: The default is
1.240 jmc 745: .Cm no .
1.97 jmc 746: Note that existing names and addresses in known hosts files
747: will not be converted automatically,
748: but may be manually hashed using
1.45 djm 749: .Xr ssh-keygen 1 .
1.1 stevesk 750: .It Cm HostbasedAuthentication
751: Specifies whether to try rhosts based authentication with public key
752: authentication.
753: The argument must be
1.240 jmc 754: .Cm yes
1.1 stevesk 755: or
1.240 jmc 756: .Cm no
757: (the default).
1.202 djm 758: .It Cm HostbasedKeyTypes
759: Specifies the key types that will be used for hostbased authentication
760: as a comma-separated pattern list.
1.214 djm 761: Alternately if the specified value begins with a
762: .Sq +
763: character, then the specified key types will be appended to the default set
764: instead of replacing them.
1.241 djm 765: If the specified value begins with a
766: .Sq -
767: character, then the specified key types (including wildcards) will be removed
768: from the default set instead of replacing them.
1.213 markus 769: The default for this option is:
770: .Bd -literal -offset 3n
771: ecdsa-sha2-nistp256-cert-v01@openssh.com,
772: ecdsa-sha2-nistp384-cert-v01@openssh.com,
773: ecdsa-sha2-nistp521-cert-v01@openssh.com,
774: ssh-ed25519-cert-v01@openssh.com,
775: ssh-rsa-cert-v01@openssh.com,
776: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 777: ssh-ed25519,ssh-rsa
1.213 markus 778: .Ed
779: .Pp
1.202 djm 780: The
781: .Fl Q
782: option of
783: .Xr ssh 1
784: may be used to list supported key types.
1.1 stevesk 785: .It Cm HostKeyAlgorithms
1.226 jmc 786: Specifies the host key algorithms
1.1 stevesk 787: that the client wants to use in order of preference.
1.214 djm 788: Alternately if the specified value begins with a
789: .Sq +
790: character, then the specified key types will be appended to the default set
791: instead of replacing them.
1.241 djm 792: If the specified value begins with a
793: .Sq -
794: character, then the specified key types (including wildcards) will be removed
795: from the default set instead of replacing them.
1.1 stevesk 796: The default for this option is:
1.139 djm 797: .Bd -literal -offset 3n
798: ecdsa-sha2-nistp256-cert-v01@openssh.com,
799: ecdsa-sha2-nistp384-cert-v01@openssh.com,
800: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 801: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 802: ssh-rsa-cert-v01@openssh.com,
1.139 djm 803: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 804: ssh-ed25519,ssh-rsa
1.139 djm 805: .Ed
1.145 djm 806: .Pp
807: If hostkeys are known for the destination host then this default is modified
808: to prefer their algorithms.
1.198 djm 809: .Pp
1.240 jmc 810: The list of available key types may also be obtained using
811: .Qq ssh -Q key .
1.1 stevesk 812: .It Cm HostKeyAlias
813: Specifies an alias that should be used instead of the
814: real host name when looking up or saving the host key
1.251 djm 815: in the host key database files and when validating host certificates.
1.84 jmc 816: This option is useful for tunneling SSH connections
1.1 stevesk 817: or for multiple servers running on a single host.
818: .It Cm HostName
819: Specifies the real host name to log into.
820: This can be used to specify nicknames or abbreviations for hosts.
1.239 jmc 821: Arguments to
822: .Cm HostName
823: accept the tokens described in the
824: .Sx TOKENS
825: section.
1.1 stevesk 826: Numeric IP addresses are also permitted (both on the command line and in
827: .Cm HostName
828: specifications).
1.239 jmc 829: The default is the name given on the command line.
1.29 markus 830: .It Cm IdentitiesOnly
831: Specifies that
1.84 jmc 832: .Xr ssh 1
1.221 djm 833: should only use the authentication identity and certificate files explicitly
834: configured in the
1.31 jmc 835: .Nm
1.221 djm 836: files
837: or passed on the
838: .Xr ssh 1
839: command-line,
1.84 jmc 840: even if
841: .Xr ssh-agent 1
1.159 djm 842: or a
843: .Cm PKCS11Provider
1.29 markus 844: offers more identities.
845: The argument to this keyword must be
1.240 jmc 846: .Cm yes
1.29 markus 847: or
1.240 jmc 848: .Cm no
849: (the default).
1.84 jmc 850: This option is intended for situations where ssh-agent
1.29 markus 851: offers many different identities.
1.231 markus 852: .It Cm IdentityAgent
853: Specifies the
854: .Ux Ns -domain
855: socket used to communicate with the authentication agent.
856: .Pp
857: This option overrides the
1.240 jmc 858: .Ev SSH_AUTH_SOCK
1.231 markus 859: environment variable and can be used to select a specific agent.
860: Setting the socket name to
1.240 jmc 861: .Cm none
1.231 markus 862: disables the use of an authentication agent.
1.232 markus 863: If the string
1.240 jmc 864: .Qq SSH_AUTH_SOCK
1.232 markus 865: is specified, the location of the socket will be read from the
866: .Ev SSH_AUTH_SOCK
867: environment variable.
1.231 markus 868: .Pp
1.239 jmc 869: Arguments to
870: .Cm IdentityAgent
871: may use the tilde syntax to refer to a user's home directory
872: or the tokens described in the
873: .Sx TOKENS
874: section.
1.67 jmc 875: .It Cm IdentityFile
1.192 sobrado 876: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 877: identity is read.
1.67 jmc 878: The default is
1.139 djm 879: .Pa ~/.ssh/id_dsa ,
1.183 naddy 880: .Pa ~/.ssh/id_ecdsa ,
881: .Pa ~/.ssh/id_ed25519
1.139 djm 882: and
1.245 djm 883: .Pa ~/.ssh/id_rsa .
1.67 jmc 884: Additionally, any identities represented by the authentication agent
1.165 djm 885: will be used for authentication unless
886: .Cm IdentitiesOnly
887: is set.
1.221 djm 888: If no certificates have been explicitly specified by
889: .Cm CertificateFile ,
1.129 djm 890: .Xr ssh 1
891: will try to load certificate information from the filename obtained by
892: appending
893: .Pa -cert.pub
894: to the path of a specified
895: .Cm IdentityFile .
1.90 djm 896: .Pp
1.239 jmc 897: Arguments to
898: .Cm IdentityFile
899: may use the tilde syntax to refer to a user's home directory
900: or the tokens described in the
901: .Sx TOKENS
902: section.
1.90 djm 903: .Pp
1.67 jmc 904: It is possible to have
905: multiple identity files specified in configuration files; all these
906: identities will be tried in sequence.
1.152 djm 907: Multiple
908: .Cm IdentityFile
909: directives will add to the list of identities tried (this behaviour
910: differs from that of other configuration directives).
1.165 djm 911: .Pp
912: .Cm IdentityFile
913: may be used in conjunction with
914: .Cm IdentitiesOnly
915: to select which identities in an agent are offered during authentication.
1.221 djm 916: .Cm IdentityFile
917: may also be used in conjunction with
918: .Cm CertificateFile
919: in order to provide any certificate also needed for authentication with
920: the identity.
1.164 jmc 921: .It Cm IgnoreUnknown
922: Specifies a pattern-list of unknown options to be ignored if they are
923: encountered in configuration parsing.
924: This may be used to suppress errors if
925: .Nm
926: contains options that are unrecognised by
927: .Xr ssh 1 .
928: It is recommended that
929: .Cm IgnoreUnknown
930: be listed early in the configuration file as it will not be applied
931: to unknown options that appear before it.
1.229 djm 932: .It Cm Include
933: Include the specified configuration file(s).
1.230 jmc 934: Multiple pathnames may be specified and each pathname may contain
1.229 djm 935: .Xr glob 3
936: wildcards and, for user configurations, shell-like
1.240 jmc 937: .Sq ~
1.229 djm 938: references to user home directories.
939: Files without absolute paths are assumed to be in
940: .Pa ~/.ssh
1.230 jmc 941: if included in a user configuration file or
1.229 djm 942: .Pa /etc/ssh
943: if included from the system configuration file.
944: .Cm Include
945: directive may appear inside a
946: .Cm Match
947: or
948: .Cm Host
949: block
950: to perform conditional inclusion.
1.143 djm 951: .It Cm IPQoS
952: Specifies the IPv4 type-of-service or DSCP class for connections.
953: Accepted values are
1.240 jmc 954: .Cm af11 ,
955: .Cm af12 ,
956: .Cm af13 ,
957: .Cm af21 ,
958: .Cm af22 ,
959: .Cm af23 ,
960: .Cm af31 ,
961: .Cm af32 ,
962: .Cm af33 ,
963: .Cm af41 ,
964: .Cm af42 ,
965: .Cm af43 ,
966: .Cm cs0 ,
967: .Cm cs1 ,
968: .Cm cs2 ,
969: .Cm cs3 ,
970: .Cm cs4 ,
971: .Cm cs5 ,
972: .Cm cs6 ,
973: .Cm cs7 ,
974: .Cm ef ,
975: .Cm lowdelay ,
976: .Cm throughput ,
977: .Cm reliability ,
1.253 djm 978: a numeric value, or
979: .Cm none
980: to use the operating system default.
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
1.269 job 986: .Cm af21
1.272 ! jmc 987: (Low-Latency Data)
1.143 djm 988: for interactive sessions and
1.269 job 989: .Cm cs1
1.272 ! jmc 990: (Lower Effort)
1.143 djm 991: for non-interactive sessions.
1.103 djm 992: .It Cm KbdInteractiveAuthentication
993: Specifies whether to use keyboard-interactive authentication.
994: The argument to this keyword must be
1.240 jmc 995: .Cm yes
996: (the default)
1.103 djm 997: or
1.240 jmc 998: .Cm no .
1.39 djm 999: .It Cm KbdInteractiveDevices
1000: Specifies the list of methods to use in keyboard-interactive authentication.
1001: Multiple method names must be comma-separated.
1002: The default is to use the server specified list.
1.85 jmc 1003: The methods available vary depending on what the server supports.
1004: For an OpenSSH server,
1005: it may be zero or more of:
1.240 jmc 1006: .Cm bsdauth ,
1007: .Cm pam ,
1.85 jmc 1008: and
1.240 jmc 1009: .Cm skey .
1.140 djm 1010: .It Cm KexAlgorithms
1011: Specifies the available KEX (Key Exchange) algorithms.
1012: Multiple algorithms must be comma-separated.
1.214 djm 1013: Alternately if the specified value begins with a
1014: .Sq +
1015: character, then the specified methods will be appended to the default set
1016: instead of replacing them.
1.241 djm 1017: If the specified value begins with a
1018: .Sq -
1019: character, then the specified methods (including wildcards) will be removed
1020: from the default set instead of replacing them.
1.141 jmc 1021: The default is:
1022: .Bd -literal -offset indent
1.238 djm 1023: curve25519-sha256,curve25519-sha256@libssh.org,
1.141 jmc 1024: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1025: diffie-hellman-group-exchange-sha256,
1.266 djm 1026: diffie-hellman-group16-sha512,
1027: diffie-hellman-group18-sha512,
1.209 dtucker 1028: diffie-hellman-group-exchange-sha1,
1.266 djm 1029: diffie-hellman-group14-sha256,
1.212 djm 1030: diffie-hellman-group14-sha1
1.141 jmc 1031: .Ed
1.198 djm 1032: .Pp
1.240 jmc 1033: The list of available key exchange algorithms may also be obtained using
1034: .Qq ssh -Q kex .
1.65 reyk 1035: .It Cm LocalCommand
1036: Specifies a command to execute on the local machine after successfully
1037: connecting to the server.
1038: The command string extends to the end of the line, and is executed with
1.105 jmc 1039: the user's shell.
1.239 jmc 1040: Arguments to
1041: .Cm LocalCommand
1042: accept the tokens described in the
1043: .Sx TOKENS
1044: section.
1.123 djm 1045: .Pp
1046: The command is run synchronously and does not have access to the
1047: session of the
1048: .Xr ssh 1
1049: that spawned it.
1050: It should not be used for interactive commands.
1051: .Pp
1.65 reyk 1052: This directive is ignored unless
1053: .Cm PermitLocalCommand
1054: has been enabled.
1.1 stevesk 1055: .It Cm LocalForward
1.74 jmc 1056: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1057: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1058: The first argument must be
1.43 djm 1059: .Sm off
1.49 jmc 1060: .Oo Ar bind_address : Oc Ar port
1.43 djm 1061: .Sm on
1.49 jmc 1062: and the second argument must be
1063: .Ar host : Ns Ar hostport .
1.138 djm 1064: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1065: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1066: given on the command line.
1.1 stevesk 1067: Only the superuser can forward privileged ports.
1.43 djm 1068: By default, the local port is bound in accordance with the
1069: .Cm GatewayPorts
1070: setting.
1071: However, an explicit
1072: .Ar bind_address
1073: may be used to bind the connection to a specific address.
1074: The
1075: .Ar bind_address
1076: of
1.240 jmc 1077: .Cm localhost
1.46 jmc 1078: indicates that the listening port be bound for local use only, while an
1079: empty address or
1080: .Sq *
1.43 djm 1081: indicates that the port should be available from all interfaces.
1.1 stevesk 1082: .It Cm LogLevel
1083: Gives the verbosity level that is used when logging messages from
1.84 jmc 1084: .Xr ssh 1 .
1.1 stevesk 1085: The possible values are:
1.84 jmc 1086: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1087: The default is INFO.
1088: DEBUG and DEBUG1 are equivalent.
1089: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1090: .It Cm MACs
1091: Specifies the MAC (message authentication code) algorithms
1092: in order of preference.
1.226 jmc 1093: The MAC algorithm is used for data integrity protection.
1.1 stevesk 1094: Multiple algorithms must be comma-separated.
1.214 djm 1095: If the specified value begins with a
1096: .Sq +
1097: character, then the specified algorithms will be appended to the default set
1098: instead of replacing them.
1.241 djm 1099: If the specified value begins with a
1100: .Sq -
1101: character, then the specified algorithms (including wildcards) will be removed
1102: from the default set instead of replacing them.
1.214 djm 1103: .Pp
1.160 markus 1104: The algorithms that contain
1.240 jmc 1105: .Qq -etm
1.160 markus 1106: calculate the MAC after encryption (encrypt-then-mac).
1107: These are considered safer and their use recommended.
1.214 djm 1108: .Pp
1.84 jmc 1109: The default is:
1.101 jmc 1110: .Bd -literal -offset indent
1.160 markus 1111: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1112: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.224 djm 1113: hmac-sha1-etm@openssh.com,
1.186 naddy 1114: umac-64@openssh.com,umac-128@openssh.com,
1.224 djm 1115: hmac-sha2-256,hmac-sha2-512,hmac-sha1
1.101 jmc 1116: .Ed
1.198 djm 1117: .Pp
1.240 jmc 1118: The list of available MAC algorithms may also be obtained using
1119: .Qq ssh -Q mac .
1.1 stevesk 1120: .It Cm NoHostAuthenticationForLocalhost
1.264 djm 1121: Disable host authentication for localhost (loopback addresses).
1.1 stevesk 1122: The argument to this keyword must be
1.240 jmc 1123: .Cm yes
1.1 stevesk 1124: or
1.242 jmc 1125: .Cm no
1.240 jmc 1126: (the default).
1.1 stevesk 1127: .It Cm NumberOfPasswordPrompts
1128: Specifies the number of password prompts before giving up.
1129: The argument to this keyword must be an integer.
1.84 jmc 1130: The default is 3.
1.1 stevesk 1131: .It Cm PasswordAuthentication
1132: Specifies whether to use password authentication.
1133: The argument to this keyword must be
1.240 jmc 1134: .Cm yes
1135: (the default)
1.1 stevesk 1136: or
1.240 jmc 1137: .Cm no .
1.65 reyk 1138: .It Cm PermitLocalCommand
1139: Allow local command execution via the
1140: .Ic LocalCommand
1141: option or using the
1.66 jmc 1142: .Ic !\& Ns Ar command
1.65 reyk 1143: escape sequence in
1144: .Xr ssh 1 .
1145: The argument must be
1.240 jmc 1146: .Cm yes
1.65 reyk 1147: or
1.240 jmc 1148: .Cm no
1149: (the default).
1.127 markus 1150: .It Cm PKCS11Provider
1151: Specifies which PKCS#11 provider to use.
1.144 jmc 1152: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1153: .Xr ssh 1
1.128 markus 1154: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1155: private RSA key.
1.67 jmc 1156: .It Cm Port
1157: Specifies the port number to connect on the remote host.
1.84 jmc 1158: The default is 22.
1.1 stevesk 1159: .It Cm PreferredAuthentications
1.226 jmc 1160: Specifies the order in which the client should try authentication methods.
1.48 jmc 1161: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1162: .Cm keyboard-interactive )
1.48 jmc 1163: over another method (e.g.\&
1.131 jmc 1164: .Cm password ) .
1165: The default is:
1166: .Bd -literal -offset indent
1167: gssapi-with-mic,hostbased,publickey,
1168: keyboard-interactive,password
1169: .Ed
1.1 stevesk 1170: .It Cm ProxyCommand
1171: Specifies the command to use to connect to the server.
1172: The command
1.190 djm 1173: string extends to the end of the line, and is executed
1174: using the user's shell
1175: .Ql exec
1176: directive to avoid a lingering shell process.
1177: .Pp
1.239 jmc 1178: Arguments to
1179: .Cm ProxyCommand
1180: accept the tokens described in the
1181: .Sx TOKENS
1182: section.
1.1 stevesk 1183: The command can be basically anything,
1184: and should read from its standard input and write to its standard output.
1185: It should eventually connect an
1186: .Xr sshd 8
1187: server running on some machine, or execute
1188: .Ic sshd -i
1189: somewhere.
1190: Host key management will be done using the
1191: HostName of the host being connected (defaulting to the name typed by
1192: the user).
1.7 jmc 1193: Setting the command to
1.240 jmc 1194: .Cm none
1.6 markus 1195: disables this option entirely.
1.1 stevesk 1196: Note that
1197: .Cm CheckHostIP
1198: is not available for connects with a proxy command.
1.52 djm 1199: .Pp
1200: This directive is useful in conjunction with
1201: .Xr nc 1
1202: and its proxy support.
1.53 jmc 1203: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1204: 192.0.2.0:
1205: .Bd -literal -offset 3n
1206: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1207: .Ed
1.233 djm 1208: .It Cm ProxyJump
1.260 millert 1209: Specifies one or more jump proxies as either
1.233 djm 1210: .Xo
1211: .Sm off
1.234 jmc 1212: .Op Ar user No @
1.233 djm 1213: .Ar host
1.234 jmc 1214: .Op : Ns Ar port
1.233 djm 1215: .Sm on
1.260 millert 1216: or an ssh URI
1.233 djm 1217: .Xc .
1.235 djm 1218: Multiple proxies may be separated by comma characters and will be visited
1.236 djm 1219: sequentially.
1.233 djm 1220: Setting this option will cause
1221: .Xr ssh 1
1222: to connect to the target host by first making a
1223: .Xr ssh 1
1224: connection to the specified
1225: .Cm ProxyJump
1226: host and then establishing a
1.234 jmc 1227: TCP forwarding to the ultimate target from there.
1.233 djm 1228: .Pp
1229: Note that this option will compete with the
1230: .Cm ProxyCommand
1231: option - whichever is specified first will prevent later instances of the
1232: other from taking effect.
1.167 djm 1233: .It Cm ProxyUseFdpass
1.168 jmc 1234: Specifies that
1.167 djm 1235: .Cm ProxyCommand
1236: will pass a connected file descriptor back to
1.168 jmc 1237: .Xr ssh 1
1.167 djm 1238: instead of continuing to execute and pass data.
1239: The default is
1.240 jmc 1240: .Cm no .
1.213 markus 1241: .It Cm PubkeyAcceptedKeyTypes
1242: Specifies the key types that will be used for public key authentication
1243: as a comma-separated pattern list.
1.214 djm 1244: Alternately if the specified value begins with a
1245: .Sq +
1246: character, then the key types after it will be appended to the default
1247: instead of replacing it.
1.241 djm 1248: If the specified value begins with a
1249: .Sq -
1250: character, then the specified key types (including wildcards) will be removed
1251: from the default set instead of replacing them.
1.213 markus 1252: The default for this option is:
1253: .Bd -literal -offset 3n
1254: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1255: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1256: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1257: ssh-ed25519-cert-v01@openssh.com,
1258: ssh-rsa-cert-v01@openssh.com,
1259: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.227 djm 1260: ssh-ed25519,ssh-rsa
1.213 markus 1261: .Ed
1262: .Pp
1.240 jmc 1263: The list of available key types may also be obtained using
1264: .Qq ssh -Q key .
1.1 stevesk 1265: .It Cm PubkeyAuthentication
1266: Specifies whether to try public key authentication.
1267: The argument to this keyword must be
1.240 jmc 1268: .Cm yes
1269: (the default)
1.1 stevesk 1270: or
1.240 jmc 1271: .Cm no .
1.75 dtucker 1272: .It Cm RekeyLimit
1273: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1274: session key is renegotiated, optionally followed a maximum amount of
1275: time that may pass before the session key is renegotiated.
1276: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1277: .Sq K ,
1278: .Sq M ,
1.75 dtucker 1279: or
1.76 jmc 1280: .Sq G
1.75 dtucker 1281: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1282: The default is between
1.84 jmc 1283: .Sq 1G
1.75 dtucker 1284: and
1.84 jmc 1285: .Sq 4G ,
1.75 dtucker 1286: depending on the cipher.
1.162 dtucker 1287: The optional second value is specified in seconds and may use any of the
1288: units documented in the
1.240 jmc 1289: .Sx TIME FORMATS
1290: section of
1.162 dtucker 1291: .Xr sshd_config 5 .
1292: The default value for
1293: .Cm RekeyLimit
1294: is
1.240 jmc 1295: .Cm default none ,
1.162 dtucker 1296: which means that rekeying is performed after the cipher's default amount
1297: of data has been sent or received and no time based rekeying is done.
1.249 bluhm 1298: .It Cm RemoteCommand
1299: Specifies a command to execute on the remote machine after successfully
1300: connecting to the server.
1301: The command string extends to the end of the line, and is executed with
1302: the user's shell.
1.250 jmc 1303: Arguments to
1304: .Cm RemoteCommand
1305: accept the tokens described in the
1306: .Sx TOKENS
1307: section.
1.1 stevesk 1308: .It Cm RemoteForward
1.74 jmc 1309: Specifies that a TCP port on the remote machine be forwarded over
1.256 markus 1310: the secure channel.
1311: The remote port may either be fowarded to a specified host and port
1312: from the local machine, or may act as a SOCKS 4/5 proxy that allows a remote
1313: client to connect to arbitrary destinations from the local machine.
1.49 jmc 1314: The first argument must be
1.43 djm 1315: .Sm off
1.49 jmc 1316: .Oo Ar bind_address : Oc Ar port
1.43 djm 1317: .Sm on
1.256 markus 1318: If forwarding to a specific destination then the second argument must be
1319: .Ar host : Ns Ar hostport ,
1320: otherwise if no destination argument is specified then the remote forwarding
1321: will be established as a SOCKS proxy.
1322: .Pp
1.138 djm 1323: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1324: Multiple forwardings may be specified, and additional
1325: forwardings can be given on the command line.
1.113 stevesk 1326: Privileged ports can be forwarded only when
1327: logging in as root on the remote machine.
1.118 jmc 1328: .Pp
1.117 djm 1329: If the
1330: .Ar port
1.240 jmc 1331: argument is 0,
1.117 djm 1332: the listen port will be dynamically allocated on the server and reported
1333: to the client at run time.
1.43 djm 1334: .Pp
1335: If the
1336: .Ar bind_address
1337: is not specified, the default is to only bind to loopback addresses.
1338: If the
1339: .Ar bind_address
1340: is
1341: .Ql *
1342: or an empty string, then the forwarding is requested to listen on all
1343: interfaces.
1344: Specifying a remote
1345: .Ar bind_address
1.46 jmc 1346: will only succeed if the server's
1347: .Cm GatewayPorts
1.43 djm 1348: option is enabled (see
1.46 jmc 1349: .Xr sshd_config 5 ) .
1.149 djm 1350: .It Cm RequestTTY
1351: Specifies whether to request a pseudo-tty for the session.
1352: The argument may be one of:
1.240 jmc 1353: .Cm no
1.149 djm 1354: (never request a TTY),
1.240 jmc 1355: .Cm yes
1.149 djm 1356: (always request a TTY when standard input is a TTY),
1.240 jmc 1357: .Cm force
1.149 djm 1358: (always request a TTY) or
1.240 jmc 1359: .Cm auto
1.149 djm 1360: (request a TTY when opening a login session).
1361: This option mirrors the
1362: .Fl t
1363: and
1364: .Fl T
1365: flags for
1366: .Xr ssh 1 .
1.196 djm 1367: .It Cm RevokedHostKeys
1368: Specifies revoked host public keys.
1369: Keys listed in this file will be refused for host authentication.
1370: Note that if this file does not exist or is not readable,
1371: then host authentication will be refused for all hosts.
1372: Keys may be specified as a text file, listing one public key per line, or as
1373: an OpenSSH Key Revocation List (KRL) as generated by
1374: .Xr ssh-keygen 1 .
1375: For more information on KRLs, see the KEY REVOCATION LISTS section in
1376: .Xr ssh-keygen 1 .
1.32 djm 1377: .It Cm SendEnv
1378: Specifies what variables from the local
1379: .Xr environ 7
1380: should be sent to the server.
1.84 jmc 1381: The server must also support it, and the server must be configured to
1.33 djm 1382: accept these environment variables.
1.207 dtucker 1383: Note that the
1384: .Ev TERM
1.208 jmc 1385: environment variable is always sent whenever a
1.207 dtucker 1386: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1387: Refer to
1388: .Cm AcceptEnv
1389: in
1390: .Xr sshd_config 5
1391: for how to configure the server.
1.80 jmc 1392: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1393: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1394: across multiple
1395: .Cm SendEnv
1396: directives.
1.81 jmc 1397: .Pp
1398: See
1399: .Sx PATTERNS
1400: for more information on patterns.
1.271 djm 1401: .Pp
1.272 ! jmc 1402: It is possible to clear previously set
1.271 djm 1403: .Cm SendEnv
1404: variable names by prefixing patterns with
1405: .Pa - .
1406: The default is not to send any environment variables.
1.28 markus 1407: .It Cm ServerAliveCountMax
1.73 jmc 1408: Sets the number of server alive messages (see below) which may be
1.28 markus 1409: sent without
1.84 jmc 1410: .Xr ssh 1
1.28 markus 1411: receiving any messages back from the server.
1412: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1413: ssh will disconnect from the server, terminating the session.
1.28 markus 1414: It is important to note that the use of server alive messages is very
1415: different from
1416: .Cm TCPKeepAlive
1417: (below).
1418: The server alive messages are sent through the encrypted channel
1419: and therefore will not be spoofable.
1420: The TCP keepalive option enabled by
1421: .Cm TCPKeepAlive
1422: is spoofable.
1423: The server alive mechanism is valuable when the client or
1424: server depend on knowing when a connection has become inactive.
1425: .Pp
1426: The default value is 3.
1427: If, for example,
1428: .Cm ServerAliveInterval
1.84 jmc 1429: (see below) is set to 15 and
1.28 markus 1430: .Cm ServerAliveCountMax
1.84 jmc 1431: is left at the default, if the server becomes unresponsive,
1432: ssh will disconnect after approximately 45 seconds.
1.67 jmc 1433: .It Cm ServerAliveInterval
1434: Sets a timeout interval in seconds after which if no data has been received
1435: from the server,
1.84 jmc 1436: .Xr ssh 1
1.67 jmc 1437: will send a message through the encrypted
1438: channel to request a response from the server.
1439: The default
1440: is 0, indicating that these messages will not be sent to the server.
1.191 millert 1441: .It Cm StreamLocalBindMask
1442: Sets the octal file creation mode mask
1443: .Pq umask
1444: used when creating a Unix-domain socket file for local or remote
1445: port forwarding.
1446: This option is only used for port forwarding to a Unix-domain socket file.
1447: .Pp
1448: The default value is 0177, which creates a Unix-domain socket file that is
1449: readable and writable only by the owner.
1450: Note that not all operating systems honor the file mode on Unix-domain
1451: socket files.
1452: .It Cm StreamLocalBindUnlink
1453: Specifies whether to remove an existing Unix-domain socket file for local
1454: or remote port forwarding before creating a new one.
1455: If the socket file already exists and
1456: .Cm StreamLocalBindUnlink
1457: is not enabled,
1458: .Nm ssh
1459: will be unable to forward the port to the Unix-domain socket file.
1460: This option is only used for port forwarding to a Unix-domain socket file.
1461: .Pp
1462: The argument must be
1.240 jmc 1463: .Cm yes
1.191 millert 1464: or
1.240 jmc 1465: .Cm no
1466: (the default).
1.1 stevesk 1467: .It Cm StrictHostKeyChecking
1468: If this flag is set to
1.240 jmc 1469: .Cm yes ,
1.84 jmc 1470: .Xr ssh 1
1.1 stevesk 1471: will never automatically add host keys to the
1.50 djm 1472: .Pa ~/.ssh/known_hosts
1.1 stevesk 1473: file, and refuses to connect to hosts whose host key has changed.
1.263 dtucker 1474: This provides maximum protection against man-in-the-middle (MITM) attacks,
1.84 jmc 1475: though it can be annoying when the
1.1 stevesk 1476: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1477: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1478: frequently made.
1479: This option forces the user to manually
1480: add all new hosts.
1.255 jmc 1481: .Pp
1.1 stevesk 1482: If this flag is set to
1.254 djm 1483: .Dq accept-new
1.255 jmc 1484: then ssh will automatically add new host keys to the user
1.254 djm 1485: known hosts files, but will not permit connections to hosts with
1486: changed host keys.
1487: If this flag is set to
1488: .Dq no
1489: or
1490: .Dq off ,
1.255 jmc 1491: ssh will automatically add new host keys to the user known hosts files
1492: and allow connections to hosts with changed hostkeys to proceed,
1493: subject to some restrictions.
1.1 stevesk 1494: If this flag is set to
1.240 jmc 1495: .Cm ask
1496: (the default),
1.1 stevesk 1497: new host keys
1498: will be added to the user known host files only after the user
1499: has confirmed that is what they really want to do, and
1.84 jmc 1500: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1501: The host keys of
1502: known hosts will be verified automatically in all cases.
1.244 jmc 1503: .It Cm SyslogFacility
1504: Gives the facility code that is used when logging messages from
1505: .Xr ssh 1 .
1506: The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2,
1507: LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7.
1508: The default is USER.
1.26 markus 1509: .It Cm TCPKeepAlive
1510: Specifies whether the system should send TCP keepalive messages to the
1511: other side.
1512: If they are sent, death of the connection or crash of one
1513: of the machines will be properly noticed.
1514: However, this means that
1515: connections will die if the route is down temporarily, and some people
1516: find it annoying.
1517: .Pp
1518: The default is
1.240 jmc 1519: .Cm yes
1.26 markus 1520: (to send TCP keepalive messages), and the client will notice
1521: if the network goes down or the remote host dies.
1522: This is important in scripts, and many users want it too.
1523: .Pp
1524: To disable TCP keepalive messages, the value should be set to
1.240 jmc 1525: .Cm no .
1.265 djm 1526: See also
1527: .Cm ServerAliveInterval
1528: for protocol-level keepalives.
1.65 reyk 1529: .It Cm Tunnel
1.95 stevesk 1530: Request
1.65 reyk 1531: .Xr tun 4
1.69 jmc 1532: device forwarding between the client and the server.
1.65 reyk 1533: The argument must be
1.240 jmc 1534: .Cm yes ,
1535: .Cm point-to-point
1.95 stevesk 1536: (layer 3),
1.240 jmc 1537: .Cm ethernet
1.95 stevesk 1538: (layer 2),
1.65 reyk 1539: or
1.240 jmc 1540: .Cm no
1541: (the default).
1.95 stevesk 1542: Specifying
1.240 jmc 1543: .Cm yes
1.95 stevesk 1544: requests the default tunnel mode, which is
1.240 jmc 1545: .Cm point-to-point .
1.65 reyk 1546: .It Cm TunnelDevice
1.95 stevesk 1547: Specifies the
1.65 reyk 1548: .Xr tun 4
1.95 stevesk 1549: devices to open on the client
1550: .Pq Ar local_tun
1551: and the server
1552: .Pq Ar remote_tun .
1553: .Pp
1554: The argument must be
1555: .Sm off
1556: .Ar local_tun Op : Ar remote_tun .
1557: .Sm on
1558: The devices may be specified by numerical ID or the keyword
1.240 jmc 1559: .Cm any ,
1.95 stevesk 1560: which uses the next available tunnel device.
1561: If
1562: .Ar remote_tun
1563: is not specified, it defaults to
1.240 jmc 1564: .Cm any .
1.95 stevesk 1565: The default is
1.240 jmc 1566: .Cm any:any .
1.201 djm 1567: .It Cm UpdateHostKeys
1.200 djm 1568: Specifies whether
1569: .Xr ssh 1
1570: should accept notifications of additional hostkeys from the server sent
1571: after authentication has completed and add them to
1572: .Cm UserKnownHostsFile .
1573: The argument must be
1.240 jmc 1574: .Cm yes ,
1575: .Cm no
1.204 djm 1576: (the default) or
1.240 jmc 1577: .Cm ask .
1.200 djm 1578: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1579: and supports graceful key rotation by allowing a server to send replacement
1580: public keys before old ones are removed.
1.200 djm 1581: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1582: host was already trusted or explicitly accepted by the user.
1.204 djm 1583: If
1584: .Cm UpdateHostKeys
1585: is set to
1.240 jmc 1586: .Cm ask ,
1.204 djm 1587: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1588: Confirmation is currently incompatible with
1589: .Cm ControlPersist ,
1590: and will be disabled if it is enabled.
1.200 djm 1591: .Pp
1592: Presently, only
1593: .Xr sshd 8
1594: from OpenSSH 6.8 and greater support the
1.240 jmc 1595: .Qq hostkeys@openssh.com
1.200 djm 1596: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1597: .It Cm UsePrivilegedPort
1598: Specifies whether to use a privileged port for outgoing connections.
1599: The argument must be
1.240 jmc 1600: .Cm yes
1.72 jmc 1601: or
1.240 jmc 1602: .Cm no
1603: (the default).
1.72 jmc 1604: If set to
1.240 jmc 1605: .Cm yes ,
1.84 jmc 1606: .Xr ssh 1
1.72 jmc 1607: must be setuid root.
1.1 stevesk 1608: .It Cm User
1609: Specifies the user to log in as.
1610: This can be useful when a different user name is used on different machines.
1611: This saves the trouble of
1612: having to remember to give the user name on the command line.
1613: .It Cm UserKnownHostsFile
1.151 djm 1614: Specifies one or more files to use for the user
1615: host key database, separated by whitespace.
1616: The default is
1617: .Pa ~/.ssh/known_hosts ,
1618: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1619: .It Cm VerifyHostKeyDNS
1620: Specifies whether to verify the remote key using DNS and SSHFP resource
1621: records.
1.24 jakob 1622: If this option is set to
1.240 jmc 1623: .Cm yes ,
1.25 jmc 1624: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1625: from DNS.
1626: Insecure fingerprints will be handled as if this option was set to
1.240 jmc 1627: .Cm ask .
1.24 jakob 1628: If this option is set to
1.240 jmc 1629: .Cm ask ,
1.24 jakob 1630: information on fingerprint match will be displayed, but the user will still
1631: need to confirm new host keys according to the
1632: .Cm StrictHostKeyChecking
1633: option.
1.8 jakob 1634: The default is
1.240 jmc 1635: .Cm no .
1.84 jmc 1636: .Pp
1.240 jmc 1637: See also
1638: .Sx VERIFYING HOST KEYS
1639: in
1.84 jmc 1640: .Xr ssh 1 .
1.111 grunk 1641: .It Cm VisualHostKey
1642: If this flag is set to
1.240 jmc 1643: .Cm yes ,
1.111 grunk 1644: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1645: printed in addition to the fingerprint string at login and
1.114 stevesk 1646: for unknown host keys.
1.111 grunk 1647: If this flag is set to
1.240 jmc 1648: .Cm no
1649: (the default),
1.114 stevesk 1650: no fingerprint strings are printed at login and
1.197 djm 1651: only the fingerprint string will be printed for unknown host keys.
1.1 stevesk 1652: .It Cm XAuthLocation
1.5 stevesk 1653: Specifies the full pathname of the
1.1 stevesk 1654: .Xr xauth 1
1655: program.
1656: The default is
1657: .Pa /usr/X11R6/bin/xauth .
1658: .El
1.86 jmc 1659: .Sh PATTERNS
1660: A
1661: .Em pattern
1662: consists of zero or more non-whitespace characters,
1663: .Sq *
1664: (a wildcard that matches zero or more characters),
1665: or
1666: .Sq ?\&
1667: (a wildcard that matches exactly one character).
1668: For example, to specify a set of declarations for any host in the
1.240 jmc 1669: .Qq .co.uk
1.86 jmc 1670: set of domains,
1671: the following pattern could be used:
1672: .Pp
1673: .Dl Host *.co.uk
1674: .Pp
1675: The following pattern
1676: would match any host in the 192.168.0.[0-9] network range:
1677: .Pp
1678: .Dl Host 192.168.0.?
1679: .Pp
1680: A
1681: .Em pattern-list
1682: is a comma-separated list of patterns.
1683: Patterns within pattern-lists may be negated
1684: by preceding them with an exclamation mark
1685: .Pq Sq !\& .
1686: For example,
1.174 djm 1687: to allow a key to be used from anywhere within an organization
1.86 jmc 1688: except from the
1.240 jmc 1689: .Qq dialup
1.86 jmc 1690: pool,
1691: the following entry (in authorized_keys) could be used:
1692: .Pp
1693: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.258 djm 1694: .Pp
1695: Note that a negated match will never produce a positive result by itself.
1696: For example, attempting to match
1697: .Qq host3
1698: against the following pattern-list will fail:
1699: .Pp
1700: .Dl from=\&"!host1,!host2\&"
1701: .Pp
1702: The solution here is to include a term that will yield a positive match,
1703: such as a wildcard:
1704: .Pp
1705: .Dl from=\&"!host1,!host2,*\&"
1.239 jmc 1706: .Sh TOKENS
1707: Arguments to some keywords can make use of tokens,
1708: which are expanded at runtime:
1709: .Pp
1710: .Bl -tag -width XXXX -offset indent -compact
1711: .It %%
1712: A literal
1713: .Sq % .
1714: .It \&%C
1.257 jmc 1715: Hash of %l%h%p%r.
1.239 jmc 1716: .It %d
1717: Local user's home directory.
1718: .It %h
1719: The remote hostname.
1720: .It %i
1721: The local user ID.
1722: .It %L
1723: The local hostname.
1724: .It %l
1725: The local hostname, including the domain name.
1726: .It %n
1727: The original remote hostname, as given on the command line.
1728: .It %p
1729: The remote port.
1730: .It %r
1731: The remote username.
1.261 djm 1732: .It \&%T
1733: The local
1734: .Xr tun 4
1735: or
1736: .Xr tap 4
1737: network interface assigned if
1.262 jmc 1738: tunnel forwarding was requested, or
1739: .Qq NONE
1.261 djm 1740: otherwise.
1.239 jmc 1741: .It %u
1742: The local username.
1743: .El
1744: .Pp
1745: .Cm Match exec
1746: accepts the tokens %%, %h, %L, %l, %n, %p, %r, and %u.
1747: .Pp
1748: .Cm CertificateFile
1749: accepts the tokens %%, %d, %h, %l, %r, and %u.
1750: .Pp
1751: .Cm ControlPath
1752: accepts the tokens %%, %C, %h, %i, %L, %l, %n, %p, %r, and %u.
1753: .Pp
1754: .Cm HostName
1755: accepts the tokens %% and %h.
1756: .Pp
1757: .Cm IdentityAgent
1758: and
1759: .Cm IdentityFile
1760: accept the tokens %%, %d, %h, %l, %r, and %u.
1761: .Pp
1762: .Cm LocalCommand
1.261 djm 1763: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, %T, and %u.
1.239 jmc 1764: .Pp
1765: .Cm ProxyCommand
1766: accepts the tokens %%, %h, %p, and %r.
1.250 jmc 1767: .Pp
1768: .Cm RemoteCommand
1769: accepts the tokens %%, %C, %d, %h, %l, %n, %p, %r, and %u.
1.1 stevesk 1770: .Sh FILES
1771: .Bl -tag -width Ds
1.50 djm 1772: .It Pa ~/.ssh/config
1.1 stevesk 1773: This is the per-user configuration file.
1774: The format of this file is described above.
1.84 jmc 1775: This file is used by the SSH client.
1.30 djm 1776: Because of the potential for abuse, this file must have strict permissions:
1777: read/write for the user, and not accessible by others.
1.1 stevesk 1778: .It Pa /etc/ssh/ssh_config
1779: Systemwide configuration file.
1780: This file provides defaults for those
1781: values that are not specified in the user's configuration file, and
1782: for those users who do not have a configuration file.
1783: This file must be world-readable.
1784: .El
1.13 jmc 1785: .Sh SEE ALSO
1786: .Xr ssh 1
1.1 stevesk 1787: .Sh AUTHORS
1.240 jmc 1788: .An -nosplit
1.1 stevesk 1789: OpenSSH is a derivative of the original and free
1.240 jmc 1790: ssh 1.2.12 release by
1791: .An Tatu Ylonen .
1792: .An Aaron Campbell , Bob Beck , Markus Friedl ,
1793: .An Niels Provos , Theo de Raadt
1794: and
1795: .An Dug Song
1.1 stevesk 1796: removed many bugs, re-added newer features and
1797: created OpenSSH.
1.240 jmc 1798: .An Markus Friedl
1799: contributed the support for SSH protocol versions 1.5 and 2.0.
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