Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.174
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
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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1.174 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.173 2013/10/16 22:49:39 djm Exp $
1.172 jmc 37: .Dd $Mdocdate: October 16 2013 $
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
1.1 stevesk 65: .Dq Host
66: specifications, and that section is only applied for hosts that
67: match one of the patterns given in the specification.
68: The matched host name is the one given on the command line.
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
1.1 stevesk 74: The configuration file has the following format:
75: .Pp
76: Empty lines and lines starting with
77: .Ql #
78: are comments.
79: Otherwise a line is of the format
80: .Dq keyword arguments .
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.
1.88 dtucker 92: Arguments may optionally be enclosed in double quotes
93: .Pq \&"
94: in order to represent arguments containing spaces.
1.1 stevesk 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.
112: The host is the
113: .Ar hostname
1.83 jmc 114: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 115: a canonicalized host name before matching).
1.148 djm 116: .Pp
117: A pattern entry may be negated by prefixing it with an exclamation mark
118: .Pq Sq !\& .
119: If a negated entry is matched, then the
120: .Cm Host
121: entry is ignored, regardless of whether any other patterns on the line
122: match.
123: Negated matches are therefore useful to provide exceptions for wildcard
124: matches.
1.81 jmc 125: .Pp
126: See
127: .Sx PATTERNS
128: for more information on patterns.
1.170 jmc 129: .It Cm Match
1.169 djm 130: Restricts the following declarations (up to the next
131: .Cm Host
132: or
133: .Cm Match
134: keyword) to be used only when the conditions following the
135: .Cm Match
136: keyword are satisfied.
137: Match conditions are specified using one or more keyword/criteria pairs.
138: The available keywords are:
139: .Cm command ,
140: .Cm host ,
141: .Cm originalhost ,
142: .Cm user ,
143: and
144: .Cm localuser .
145: .Pp
146: The criteria for the
147: .Cm command
148: keyword is a path to a command that is executed.
149: If the command returns a zero exit status then the condition is considered true.
150: Commands containing whitespace characters must be quoted.
151: .Pp
152: The other keywords' criteria must be single entries or comma-separated
153: lists and may use the wildcard and negation operators described in the
154: .Sx PATTERNS
155: section.
156: The criteria for the
157: .Cm host
158: keyword are matched against the target hostname, after any substitution
159: by the
160: .Cm Hostname
161: option.
162: The
163: .Cm originalhost
164: keyword matches against the hostname as it was specified on the command-line.
165: The
166: .Cm user
167: keyword matches against the target username on the remote host.
168: The
169: .Cm localuser
170: keyword matches against the name of the local user running
171: .Xr ssh 1
172: (this keyword may be useful in system-wide
173: .Nm
174: files).
1.10 djm 175: .It Cm AddressFamily
1.11 jmc 176: Specifies which address family to use when connecting.
177: Valid arguments are
1.10 djm 178: .Dq any ,
179: .Dq inet
1.84 jmc 180: (use IPv4 only), or
1.10 djm 181: .Dq inet6
1.40 jmc 182: (use IPv6 only).
1.1 stevesk 183: .It Cm BatchMode
184: If set to
185: .Dq yes ,
186: passphrase/password querying will be disabled.
187: This option is useful in scripts and other batch jobs where no user
188: is present to supply the password.
189: The argument must be
190: .Dq yes
191: or
192: .Dq no .
193: The default is
194: .Dq no .
195: .It Cm BindAddress
1.60 dtucker 196: Use the specified address on the local machine as the source address of
1.61 jmc 197: the connection.
198: Only useful on systems with more than one address.
1.1 stevesk 199: Note that this option does not work if
200: .Cm UsePrivilegedPort
201: is set to
202: .Dq yes .
1.171 djm 203: .It Cm CanonicalDomains
1.172 jmc 204: When
1.173 djm 205: .Cm CanonicalizeHostname
1.171 djm 206: is enabled, this option specifies the list of domain suffixes in which to
207: search for the specified destination host.
1.173 djm 208: .It Cm CanonicalizeFallbackLocal
1.174 ! djm 209: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 210: The default,
211: .Dq no ,
212: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 213: search rules.
214: A value of
215: .Dq yes
216: will cause
217: .Xr ssh 1
218: to fail instantly if
1.173 djm 219: .Cm CanonicalizeHostname
1.171 djm 220: is enabled and the target hostname cannot be found in any of the domains
221: specified by
222: .Cm CanonicalDomains .
1.173 djm 223: .It Cm CanonicalizeHostname
1.174 ! djm 224: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 225: The default,
226: .Dq no ,
1.171 djm 227: is not to perform any name rewriting and let the system resolver handle all
228: hostname lookups.
229: If set to
230: .Dq yes
231: then, for connections that do not use a
232: .Cm ProxyCommand ,
233: .Xr ssh 1
1.173 djm 234: will attempt to canonicalize the hostname specified on the command line
1.171 djm 235: using the
236: .Cm CanonicalDomains
237: suffixes and
1.173 djm 238: .Cm CanonicalizePermittedCNAMEs
1.171 djm 239: rules.
240: If
1.173 djm 241: .Cm CanonicalizeHostname
1.171 djm 242: is set to
243: .Dq always ,
1.174 ! djm 244: then canonicalization is applied to proxied connections too.
1.173 djm 245: .It Cm CanonicalizeMaxDots
1.172 jmc 246: Specifies the maximum number of dot characters in a hostname before
1.174 ! djm 247: canonicalization is disabled.
1.172 jmc 248: The default,
249: .Dq 1 ,
250: allows a single dot (i.e. hostname.subdomain).
1.173 djm 251: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 252: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 253: canonicalizing hostnames.
1.171 djm 254: The rules consist of one or more arguments of
1.172 jmc 255: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 256: where
257: .Ar source_domain_list
1.174 ! djm 258: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 259: and
260: .Ar target_domain_list
1.172 jmc 261: is a pattern-list of domains that they may resolve to.
1.171 djm 262: .Pp
263: For example,
264: .Dq *.a.example.com:*.b.example.com,*.c.example.com
265: will allow hostnames matching
266: .Dq *.a.example.com
1.173 djm 267: to be canonicalized to names in the
1.171 djm 268: .Dq *.b.example.com
269: or
270: .Dq *.c.example.com
271: domains.
1.1 stevesk 272: .It Cm ChallengeResponseAuthentication
1.82 jmc 273: Specifies whether to use challenge-response authentication.
1.1 stevesk 274: The argument to this keyword must be
275: .Dq yes
276: or
277: .Dq no .
278: The default is
279: .Dq yes .
280: .It Cm CheckHostIP
281: If this flag is set to
282: .Dq yes ,
1.84 jmc 283: .Xr ssh 1
284: will additionally check the host IP address in the
1.1 stevesk 285: .Pa known_hosts
286: file.
287: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 288: If the option is set to
1.1 stevesk 289: .Dq no ,
290: the check will not be executed.
291: The default is
292: .Dq yes .
293: .It Cm Cipher
294: Specifies the cipher to use for encrypting the session
295: in protocol version 1.
296: Currently,
297: .Dq blowfish ,
298: .Dq 3des ,
299: and
300: .Dq des
301: are supported.
302: .Ar des
303: is only supported in the
1.84 jmc 304: .Xr ssh 1
1.1 stevesk 305: client for interoperability with legacy protocol 1 implementations
306: that do not support the
307: .Ar 3des
1.7 jmc 308: cipher.
309: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 310: The default is
311: .Dq 3des .
312: .It Cm Ciphers
313: Specifies the ciphers allowed for protocol version 2
314: in order of preference.
315: Multiple ciphers must be comma-separated.
1.35 dtucker 316: The supported ciphers are
317: .Dq 3des-cbc ,
318: .Dq aes128-cbc ,
319: .Dq aes192-cbc ,
320: .Dq aes256-cbc ,
321: .Dq aes128-ctr ,
322: .Dq aes192-ctr ,
323: .Dq aes256-ctr ,
1.161 markus 324: .Dq aes128-gcm@openssh.com ,
325: .Dq aes256-gcm@openssh.com ,
1.54 djm 326: .Dq arcfour128 ,
327: .Dq arcfour256 ,
1.35 dtucker 328: .Dq arcfour ,
329: .Dq blowfish-cbc ,
330: and
331: .Dq cast128-cbc .
1.84 jmc 332: The default is:
333: .Bd -literal -offset 3n
1.116 naddy 334: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
1.161 markus 335: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.116 naddy 336: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
337: aes256-cbc,arcfour
1.1 stevesk 338: .Ed
339: .It Cm ClearAllForwardings
1.84 jmc 340: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 341: specified in the configuration files or on the command line be
1.7 jmc 342: cleared.
343: This option is primarily useful when used from the
1.84 jmc 344: .Xr ssh 1
1.1 stevesk 345: command line to clear port forwardings set in
346: configuration files, and is automatically set by
347: .Xr scp 1
348: and
349: .Xr sftp 1 .
350: The argument must be
351: .Dq yes
352: or
353: .Dq no .
354: The default is
355: .Dq no .
356: .It Cm Compression
357: Specifies whether to use compression.
358: The argument must be
359: .Dq yes
360: or
361: .Dq no .
362: The default is
363: .Dq no .
364: .It Cm CompressionLevel
365: Specifies the compression level to use if compression is enabled.
366: The argument must be an integer from 1 (fast) to 9 (slow, best).
367: The default level is 6, which is good for most applications.
368: The meaning of the values is the same as in
369: .Xr gzip 1 .
370: Note that this option applies to protocol version 1 only.
371: .It Cm ConnectionAttempts
372: Specifies the number of tries (one per second) to make before exiting.
373: The argument must be an integer.
374: This may be useful in scripts if the connection sometimes fails.
375: The default is 1.
1.9 djm 376: .It Cm ConnectTimeout
1.84 jmc 377: Specifies the timeout (in seconds) used when connecting to the
378: SSH server, instead of using the default system TCP timeout.
1.11 jmc 379: This value is used only when the target is down or really unreachable,
380: not when it refuses the connection.
1.36 djm 381: .It Cm ControlMaster
382: Enables the sharing of multiple sessions over a single network connection.
383: When set to
1.84 jmc 384: .Dq yes ,
385: .Xr ssh 1
1.36 djm 386: will listen for connections on a control socket specified using the
387: .Cm ControlPath
388: argument.
389: Additional sessions can connect to this socket using the same
390: .Cm ControlPath
391: with
392: .Cm ControlMaster
393: set to
394: .Dq no
1.38 jmc 395: (the default).
1.64 jmc 396: These sessions will try to reuse the master instance's network connection
1.63 djm 397: rather than initiating new ones, but will fall back to connecting normally
398: if the control socket does not exist, or is not listening.
399: .Pp
1.37 djm 400: Setting this to
401: .Dq ask
1.84 jmc 402: will cause ssh
1.37 djm 403: to listen for control connections, but require confirmation using the
404: .Ev SSH_ASKPASS
405: program before they are accepted (see
406: .Xr ssh-add 1
1.38 jmc 407: for details).
1.51 jakob 408: If the
409: .Cm ControlPath
1.84 jmc 410: cannot be opened,
411: ssh will continue without connecting to a master instance.
1.58 djm 412: .Pp
413: X11 and
1.59 jmc 414: .Xr ssh-agent 1
1.58 djm 415: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 416: display and agent forwarded will be the one belonging to the master
1.59 jmc 417: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 418: .Pp
419: Two additional options allow for opportunistic multiplexing: try to use a
420: master connection but fall back to creating a new one if one does not already
421: exist.
422: These options are:
423: .Dq auto
424: and
425: .Dq autoask .
426: The latter requires confirmation like the
427: .Dq ask
428: option.
1.36 djm 429: .It Cm ControlPath
1.55 djm 430: Specify the path to the control socket used for connection sharing as described
431: in the
1.36 djm 432: .Cm ControlMaster
1.57 djm 433: section above or the string
434: .Dq none
435: to disable connection sharing.
1.55 djm 436: In the path,
1.147 djm 437: .Ql %L
438: will be substituted by the first component of the local host name,
1.77 djm 439: .Ql %l
1.147 djm 440: will be substituted by the local host name (including any domain name),
1.55 djm 441: .Ql %h
442: will be substituted by the target host name,
1.150 jmc 443: .Ql %n
444: will be substituted by the original target host name
445: specified on the command line,
1.55 djm 446: .Ql %p
1.147 djm 447: the port,
1.55 djm 448: .Ql %r
1.147 djm 449: by the remote login username, and
450: .Ql %u
451: by the username of the user running
452: .Xr ssh 1 .
1.56 djm 453: It is recommended that any
454: .Cm ControlPath
455: used for opportunistic connection sharing include
1.78 jmc 456: at least %h, %p, and %r.
1.56 djm 457: This ensures that shared connections are uniquely identified.
1.137 djm 458: .It Cm ControlPersist
459: When used in conjunction with
460: .Cm ControlMaster ,
461: specifies that the master connection should remain open
462: in the background (waiting for future client connections)
463: after the initial client connection has been closed.
464: If set to
465: .Dq no ,
466: then the master connection will not be placed into the background,
467: and will close as soon as the initial client connection is closed.
468: If set to
469: .Dq yes ,
470: then the master connection will remain in the background indefinitely
471: (until killed or closed via a mechanism such as the
472: .Xr ssh 1
473: .Dq Fl O No exit
474: option).
475: If set to a time in seconds, or a time in any of the formats documented in
476: .Xr sshd_config 5 ,
477: then the backgrounded master connection will automatically terminate
478: after it has remained idle (with no client connections) for the
479: specified time.
1.38 jmc 480: .It Cm DynamicForward
1.74 jmc 481: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 482: over the secure channel, and the application
483: protocol is then used to determine where to connect to from the
484: remote machine.
1.62 djm 485: .Pp
486: The argument must be
487: .Sm off
488: .Oo Ar bind_address : Oc Ar port .
489: .Sm on
1.138 djm 490: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 491: By default, the local port is bound in accordance with the
492: .Cm GatewayPorts
493: setting.
494: However, an explicit
495: .Ar bind_address
496: may be used to bind the connection to a specific address.
497: The
498: .Ar bind_address
499: of
500: .Dq localhost
501: indicates that the listening port be bound for local use only, while an
502: empty address or
503: .Sq *
504: indicates that the port should be available from all interfaces.
505: .Pp
1.38 jmc 506: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 507: .Xr ssh 1
1.38 jmc 508: will act as a SOCKS server.
509: Multiple forwardings may be specified, and
510: additional forwardings can be given on the command line.
511: Only the superuser can forward privileged ports.
1.14 markus 512: .It Cm EnableSSHKeysign
513: Setting this option to
514: .Dq yes
515: in the global client configuration file
516: .Pa /etc/ssh/ssh_config
517: enables the use of the helper program
518: .Xr ssh-keysign 8
519: during
520: .Cm HostbasedAuthentication .
521: The argument must be
522: .Dq yes
523: or
524: .Dq no .
525: The default is
526: .Dq no .
1.23 jmc 527: This option should be placed in the non-hostspecific section.
1.14 markus 528: See
529: .Xr ssh-keysign 8
530: for more information.
1.1 stevesk 531: .It Cm EscapeChar
532: Sets the escape character (default:
533: .Ql ~ ) .
534: The escape character can also
535: be set on the command line.
536: The argument should be a single character,
537: .Ql ^
538: followed by a letter, or
539: .Dq none
540: to disable the escape
541: character entirely (making the connection transparent for binary
542: data).
1.96 markus 543: .It Cm ExitOnForwardFailure
544: Specifies whether
545: .Xr ssh 1
546: should terminate the connection if it cannot set up all requested
1.102 stevesk 547: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 548: The argument must be
549: .Dq yes
550: or
551: .Dq no .
552: The default is
553: .Dq no .
1.1 stevesk 554: .It Cm ForwardAgent
555: Specifies whether the connection to the authentication agent (if any)
556: will be forwarded to the remote machine.
557: The argument must be
558: .Dq yes
559: or
560: .Dq no .
561: The default is
562: .Dq no .
1.3 stevesk 563: .Pp
1.7 jmc 564: Agent forwarding should be enabled with caution.
565: Users with the ability to bypass file permissions on the remote host
566: (for the agent's Unix-domain socket)
567: can access the local agent through the forwarded connection.
568: An attacker cannot obtain key material from the agent,
1.3 stevesk 569: however they can perform operations on the keys that enable them to
570: authenticate using the identities loaded into the agent.
1.1 stevesk 571: .It Cm ForwardX11
572: Specifies whether X11 connections will be automatically redirected
573: over the secure channel and
574: .Ev DISPLAY
575: set.
576: The argument must be
577: .Dq yes
578: or
579: .Dq no .
580: The default is
581: .Dq no .
1.3 stevesk 582: .Pp
1.7 jmc 583: X11 forwarding should be enabled with caution.
584: Users with the ability to bypass file permissions on the remote host
1.22 markus 585: (for the user's X11 authorization database)
1.7 jmc 586: can access the local X11 display through the forwarded connection.
1.22 markus 587: An attacker may then be able to perform activities such as keystroke monitoring
588: if the
589: .Cm ForwardX11Trusted
590: option is also enabled.
1.134 djm 591: .It Cm ForwardX11Timeout
1.135 jmc 592: Specify a timeout for untrusted X11 forwarding
593: using the format described in the
1.166 jmc 594: TIME FORMATS section of
1.134 djm 595: .Xr sshd_config 5 .
596: X11 connections received by
597: .Xr ssh 1
598: after this time will be refused.
599: The default is to disable untrusted X11 forwarding after twenty minutes has
600: elapsed.
1.22 markus 601: .It Cm ForwardX11Trusted
1.34 jmc 602: If this option is set to
1.84 jmc 603: .Dq yes ,
604: remote X11 clients will have full access to the original X11 display.
1.42 djm 605: .Pp
1.22 markus 606: If this option is set to
1.84 jmc 607: .Dq no ,
608: remote X11 clients will be considered untrusted and prevented
1.22 markus 609: from stealing or tampering with data belonging to trusted X11
610: clients.
1.42 djm 611: Furthermore, the
612: .Xr xauth 1
613: token used for the session will be set to expire after 20 minutes.
614: Remote clients will be refused access after this time.
1.22 markus 615: .Pp
616: The default is
617: .Dq no .
618: .Pp
619: See the X11 SECURITY extension specification for full details on
620: the restrictions imposed on untrusted clients.
1.1 stevesk 621: .It Cm GatewayPorts
622: Specifies whether remote hosts are allowed to connect to local
623: forwarded ports.
624: By default,
1.84 jmc 625: .Xr ssh 1
1.7 jmc 626: binds local port forwardings to the loopback address.
627: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 628: .Cm GatewayPorts
1.84 jmc 629: can be used to specify that ssh
1.1 stevesk 630: should bind local port forwardings to the wildcard address,
631: thus allowing remote hosts to connect to forwarded ports.
632: The argument must be
633: .Dq yes
634: or
635: .Dq no .
636: The default is
637: .Dq no .
638: .It Cm GlobalKnownHostsFile
1.151 djm 639: Specifies one or more files to use for the global
640: host key database, separated by whitespace.
641: The default is
642: .Pa /etc/ssh/ssh_known_hosts ,
643: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 644: .It Cm GSSAPIAuthentication
1.27 markus 645: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 646: The default is
1.21 markus 647: .Dq no .
1.18 markus 648: Note that this option applies to protocol version 2 only.
649: .It Cm GSSAPIDelegateCredentials
650: Forward (delegate) credentials to the server.
651: The default is
652: .Dq no .
653: Note that this option applies to protocol version 2 only.
1.44 djm 654: .It Cm HashKnownHosts
655: Indicates that
1.84 jmc 656: .Xr ssh 1
1.44 djm 657: should hash host names and addresses when they are added to
1.50 djm 658: .Pa ~/.ssh/known_hosts .
1.44 djm 659: These hashed names may be used normally by
1.84 jmc 660: .Xr ssh 1
1.44 djm 661: and
1.84 jmc 662: .Xr sshd 8 ,
1.44 djm 663: but they do not reveal identifying information should the file's contents
664: be disclosed.
665: The default is
666: .Dq no .
1.97 jmc 667: Note that existing names and addresses in known hosts files
668: will not be converted automatically,
669: but may be manually hashed using
1.45 djm 670: .Xr ssh-keygen 1 .
1.1 stevesk 671: .It Cm HostbasedAuthentication
672: Specifies whether to try rhosts based authentication with public key
673: authentication.
674: The argument must be
675: .Dq yes
676: or
677: .Dq no .
678: The default is
679: .Dq no .
680: This option applies to protocol version 2 only and
681: is similar to
682: .Cm RhostsRSAAuthentication .
683: .It Cm HostKeyAlgorithms
684: Specifies the protocol version 2 host key algorithms
685: that the client wants to use in order of preference.
686: The default for this option is:
1.139 djm 687: .Bd -literal -offset 3n
688: ecdsa-sha2-nistp256-cert-v01@openssh.com,
689: ecdsa-sha2-nistp384-cert-v01@openssh.com,
690: ecdsa-sha2-nistp521-cert-v01@openssh.com,
691: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
692: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
693: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
694: ssh-rsa,ssh-dss
695: .Ed
1.145 djm 696: .Pp
697: If hostkeys are known for the destination host then this default is modified
698: to prefer their algorithms.
1.1 stevesk 699: .It Cm HostKeyAlias
700: Specifies an alias that should be used instead of the
701: real host name when looking up or saving the host key
702: in the host key database files.
1.84 jmc 703: This option is useful for tunneling SSH connections
1.1 stevesk 704: or for multiple servers running on a single host.
705: .It Cm HostName
706: Specifies the real host name to log into.
707: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 708: If the hostname contains the character sequence
709: .Ql %h ,
1.150 jmc 710: then this will be replaced with the host name specified on the command line
1.136 djm 711: (this is useful for manipulating unqualified names).
1.84 jmc 712: The default is the name given on the command line.
1.1 stevesk 713: Numeric IP addresses are also permitted (both on the command line and in
714: .Cm HostName
715: specifications).
1.29 markus 716: .It Cm IdentitiesOnly
717: Specifies that
1.84 jmc 718: .Xr ssh 1
1.29 markus 719: should only use the authentication identity files configured in the
1.31 jmc 720: .Nm
1.29 markus 721: files,
1.84 jmc 722: even if
723: .Xr ssh-agent 1
1.159 djm 724: or a
725: .Cm PKCS11Provider
1.29 markus 726: offers more identities.
727: The argument to this keyword must be
728: .Dq yes
729: or
730: .Dq no .
1.84 jmc 731: This option is intended for situations where ssh-agent
1.29 markus 732: offers many different identities.
733: The default is
734: .Dq no .
1.67 jmc 735: .It Cm IdentityFile
1.155 dtucker 736: Specifies a file from which the user's DSA, ECDSA or RSA authentication
1.139 djm 737: identity is read.
1.67 jmc 738: The default is
739: .Pa ~/.ssh/identity
740: for protocol version 1, and
1.139 djm 741: .Pa ~/.ssh/id_dsa ,
742: .Pa ~/.ssh/id_ecdsa
743: and
1.67 jmc 744: .Pa ~/.ssh/id_rsa
745: for protocol version 2.
746: Additionally, any identities represented by the authentication agent
1.165 djm 747: will be used for authentication unless
748: .Cm IdentitiesOnly
749: is set.
1.129 djm 750: .Xr ssh 1
751: will try to load certificate information from the filename obtained by
752: appending
753: .Pa -cert.pub
754: to the path of a specified
755: .Cm IdentityFile .
1.90 djm 756: .Pp
1.67 jmc 757: The file name may use the tilde
1.91 jmc 758: syntax to refer to a user's home directory or one of the following
1.90 djm 759: escape characters:
760: .Ql %d
761: (local user's home directory),
762: .Ql %u
763: (local user name),
764: .Ql %l
765: (local host name),
766: .Ql %h
767: (remote host name) or
1.92 djm 768: .Ql %r
1.90 djm 769: (remote user name).
770: .Pp
1.67 jmc 771: It is possible to have
772: multiple identity files specified in configuration files; all these
773: identities will be tried in sequence.
1.152 djm 774: Multiple
775: .Cm IdentityFile
776: directives will add to the list of identities tried (this behaviour
777: differs from that of other configuration directives).
1.165 djm 778: .Pp
779: .Cm IdentityFile
780: may be used in conjunction with
781: .Cm IdentitiesOnly
782: to select which identities in an agent are offered during authentication.
1.164 jmc 783: .It Cm IgnoreUnknown
784: Specifies a pattern-list of unknown options to be ignored if they are
785: encountered in configuration parsing.
786: This may be used to suppress errors if
787: .Nm
788: contains options that are unrecognised by
789: .Xr ssh 1 .
790: It is recommended that
791: .Cm IgnoreUnknown
792: be listed early in the configuration file as it will not be applied
793: to unknown options that appear before it.
1.143 djm 794: .It Cm IPQoS
795: Specifies the IPv4 type-of-service or DSCP class for connections.
796: Accepted values are
797: .Dq af11 ,
798: .Dq af12 ,
799: .Dq af13 ,
1.154 djm 800: .Dq af21 ,
1.143 djm 801: .Dq af22 ,
802: .Dq af23 ,
803: .Dq af31 ,
804: .Dq af32 ,
805: .Dq af33 ,
806: .Dq af41 ,
807: .Dq af42 ,
808: .Dq af43 ,
809: .Dq cs0 ,
810: .Dq cs1 ,
811: .Dq cs2 ,
812: .Dq cs3 ,
813: .Dq cs4 ,
814: .Dq cs5 ,
815: .Dq cs6 ,
816: .Dq cs7 ,
817: .Dq ef ,
818: .Dq lowdelay ,
819: .Dq throughput ,
820: .Dq reliability ,
821: or a numeric value.
1.146 djm 822: This option may take one or two arguments, separated by whitespace.
1.143 djm 823: If one argument is specified, it is used as the packet class unconditionally.
824: If two values are specified, the first is automatically selected for
825: interactive sessions and the second for non-interactive sessions.
826: The default is
827: .Dq lowdelay
828: for interactive sessions and
829: .Dq throughput
830: for non-interactive sessions.
1.103 djm 831: .It Cm KbdInteractiveAuthentication
832: Specifies whether to use keyboard-interactive authentication.
833: The argument to this keyword must be
834: .Dq yes
835: or
836: .Dq no .
837: The default is
838: .Dq yes .
1.39 djm 839: .It Cm KbdInteractiveDevices
840: Specifies the list of methods to use in keyboard-interactive authentication.
841: Multiple method names must be comma-separated.
842: The default is to use the server specified list.
1.85 jmc 843: The methods available vary depending on what the server supports.
844: For an OpenSSH server,
845: it may be zero or more of:
846: .Dq bsdauth ,
847: .Dq pam ,
848: and
849: .Dq skey .
1.140 djm 850: .It Cm KexAlgorithms
851: Specifies the available KEX (Key Exchange) algorithms.
852: Multiple algorithms must be comma-separated.
1.141 jmc 853: The default is:
854: .Bd -literal -offset indent
855: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
856: diffie-hellman-group-exchange-sha256,
857: diffie-hellman-group-exchange-sha1,
858: diffie-hellman-group14-sha1,
859: diffie-hellman-group1-sha1
860: .Ed
1.65 reyk 861: .It Cm LocalCommand
862: Specifies a command to execute on the local machine after successfully
863: connecting to the server.
864: The command string extends to the end of the line, and is executed with
1.105 jmc 865: the user's shell.
1.109 dtucker 866: The following escape character substitutions will be performed:
867: .Ql %d
868: (local user's home directory),
869: .Ql %h
870: (remote host name),
871: .Ql %l
872: (local host name),
873: .Ql %n
874: (host name as provided on the command line),
875: .Ql %p
876: (remote port),
877: .Ql %r
878: (remote user name) or
879: .Ql %u
880: (local user name).
1.123 djm 881: .Pp
882: The command is run synchronously and does not have access to the
883: session of the
884: .Xr ssh 1
885: that spawned it.
886: It should not be used for interactive commands.
887: .Pp
1.65 reyk 888: This directive is ignored unless
889: .Cm PermitLocalCommand
890: has been enabled.
1.1 stevesk 891: .It Cm LocalForward
1.74 jmc 892: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 893: the secure channel to the specified host and port from the remote machine.
1.49 jmc 894: The first argument must be
1.43 djm 895: .Sm off
1.49 jmc 896: .Oo Ar bind_address : Oc Ar port
1.43 djm 897: .Sm on
1.49 jmc 898: and the second argument must be
899: .Ar host : Ns Ar hostport .
1.138 djm 900: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 901: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 902: given on the command line.
1.1 stevesk 903: Only the superuser can forward privileged ports.
1.43 djm 904: By default, the local port is bound in accordance with the
905: .Cm GatewayPorts
906: setting.
907: However, an explicit
908: .Ar bind_address
909: may be used to bind the connection to a specific address.
910: The
911: .Ar bind_address
912: of
913: .Dq localhost
1.46 jmc 914: indicates that the listening port be bound for local use only, while an
915: empty address or
916: .Sq *
1.43 djm 917: indicates that the port should be available from all interfaces.
1.1 stevesk 918: .It Cm LogLevel
919: Gives the verbosity level that is used when logging messages from
1.84 jmc 920: .Xr ssh 1 .
1.1 stevesk 921: The possible values are:
1.84 jmc 922: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 923: The default is INFO.
924: DEBUG and DEBUG1 are equivalent.
925: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 926: .It Cm MACs
927: Specifies the MAC (message authentication code) algorithms
928: in order of preference.
929: The MAC algorithm is used in protocol version 2
930: for data integrity protection.
931: Multiple algorithms must be comma-separated.
1.160 markus 932: The algorithms that contain
933: .Dq -etm
934: calculate the MAC after encryption (encrypt-then-mac).
935: These are considered safer and their use recommended.
1.84 jmc 936: The default is:
1.101 jmc 937: .Bd -literal -offset indent
1.160 markus 938: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
939: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
940: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
941: hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
942: hmac-md5-96-etm@openssh.com,
1.158 markus 943: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.157 naddy 944: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
945: hmac-sha1-96,hmac-md5-96
1.101 jmc 946: .Ed
1.1 stevesk 947: .It Cm NoHostAuthenticationForLocalhost
948: This option can be used if the home directory is shared across machines.
949: In this case localhost will refer to a different machine on each of
950: the machines and the user will get many warnings about changed host keys.
951: However, this option disables host authentication for localhost.
952: The argument to this keyword must be
953: .Dq yes
954: or
955: .Dq no .
956: The default is to check the host key for localhost.
957: .It Cm NumberOfPasswordPrompts
958: Specifies the number of password prompts before giving up.
959: The argument to this keyword must be an integer.
1.84 jmc 960: The default is 3.
1.1 stevesk 961: .It Cm PasswordAuthentication
962: Specifies whether to use password authentication.
963: The argument to this keyword must be
964: .Dq yes
965: or
966: .Dq no .
967: The default is
968: .Dq yes .
1.65 reyk 969: .It Cm PermitLocalCommand
970: Allow local command execution via the
971: .Ic LocalCommand
972: option or using the
1.66 jmc 973: .Ic !\& Ns Ar command
1.65 reyk 974: escape sequence in
975: .Xr ssh 1 .
976: The argument must be
977: .Dq yes
978: or
979: .Dq no .
980: The default is
981: .Dq no .
1.127 markus 982: .It Cm PKCS11Provider
983: Specifies which PKCS#11 provider to use.
1.144 jmc 984: The argument to this keyword is the PKCS#11 shared library
1.127 markus 985: .Xr ssh 1
1.128 markus 986: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 987: private RSA key.
1.67 jmc 988: .It Cm Port
989: Specifies the port number to connect on the remote host.
1.84 jmc 990: The default is 22.
1.1 stevesk 991: .It Cm PreferredAuthentications
992: Specifies the order in which the client should try protocol 2
1.11 jmc 993: authentication methods.
1.48 jmc 994: This allows a client to prefer one method (e.g.\&
1.1 stevesk 995: .Cm keyboard-interactive )
1.48 jmc 996: over another method (e.g.\&
1.131 jmc 997: .Cm password ) .
998: The default is:
999: .Bd -literal -offset indent
1000: gssapi-with-mic,hostbased,publickey,
1001: keyboard-interactive,password
1002: .Ed
1.1 stevesk 1003: .It Cm Protocol
1004: Specifies the protocol versions
1.84 jmc 1005: .Xr ssh 1
1.1 stevesk 1006: should support in order of preference.
1007: The possible values are
1.84 jmc 1008: .Sq 1
1.1 stevesk 1009: and
1.84 jmc 1010: .Sq 2 .
1.1 stevesk 1011: Multiple versions must be comma-separated.
1.120 markus 1012: When this option is set to
1.121 jmc 1013: .Dq 2,1
1.120 markus 1014: .Nm ssh
1015: will try version 2 and fall back to version 1
1016: if version 2 is not available.
1.1 stevesk 1017: The default is
1.121 jmc 1018: .Sq 2 .
1.1 stevesk 1019: .It Cm ProxyCommand
1020: Specifies the command to use to connect to the server.
1021: The command
1022: string extends to the end of the line, and is executed with
1.105 jmc 1023: the user's shell.
1.133 jmc 1024: In the command string, any occurrence of
1.1 stevesk 1025: .Ql %h
1026: will be substituted by the host name to
1.132 djm 1027: connect,
1.1 stevesk 1028: .Ql %p
1.133 jmc 1029: by the port, and
1030: .Ql %r
1.132 djm 1031: by the remote user name.
1.1 stevesk 1032: The command can be basically anything,
1033: and should read from its standard input and write to its standard output.
1034: It should eventually connect an
1035: .Xr sshd 8
1036: server running on some machine, or execute
1037: .Ic sshd -i
1038: somewhere.
1039: Host key management will be done using the
1040: HostName of the host being connected (defaulting to the name typed by
1041: the user).
1.7 jmc 1042: Setting the command to
1043: .Dq none
1.6 markus 1044: disables this option entirely.
1.1 stevesk 1045: Note that
1046: .Cm CheckHostIP
1047: is not available for connects with a proxy command.
1.52 djm 1048: .Pp
1049: This directive is useful in conjunction with
1050: .Xr nc 1
1051: and its proxy support.
1.53 jmc 1052: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1053: 192.0.2.0:
1054: .Bd -literal -offset 3n
1055: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1056: .Ed
1.167 djm 1057: .It Cm ProxyUseFdpass
1.168 jmc 1058: Specifies that
1.167 djm 1059: .Cm ProxyCommand
1060: will pass a connected file descriptor back to
1.168 jmc 1061: .Xr ssh 1
1.167 djm 1062: instead of continuing to execute and pass data.
1063: The default is
1064: .Dq no .
1.1 stevesk 1065: .It Cm PubkeyAuthentication
1066: Specifies whether to try public key authentication.
1067: The argument to this keyword must be
1068: .Dq yes
1069: or
1070: .Dq no .
1071: The default is
1072: .Dq yes .
1073: This option applies to protocol version 2 only.
1.75 dtucker 1074: .It Cm RekeyLimit
1075: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1076: session key is renegotiated, optionally followed a maximum amount of
1077: time that may pass before the session key is renegotiated.
1078: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1079: .Sq K ,
1080: .Sq M ,
1.75 dtucker 1081: or
1.76 jmc 1082: .Sq G
1.75 dtucker 1083: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1084: The default is between
1.84 jmc 1085: .Sq 1G
1.75 dtucker 1086: and
1.84 jmc 1087: .Sq 4G ,
1.75 dtucker 1088: depending on the cipher.
1.162 dtucker 1089: The optional second value is specified in seconds and may use any of the
1090: units documented in the
1.166 jmc 1091: TIME FORMATS section of
1.162 dtucker 1092: .Xr sshd_config 5 .
1093: The default value for
1094: .Cm RekeyLimit
1095: is
1096: .Dq default none ,
1097: which means that rekeying is performed after the cipher's default amount
1098: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1099: This option applies to protocol version 2 only.
1.1 stevesk 1100: .It Cm RemoteForward
1.74 jmc 1101: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1102: the secure channel to the specified host and port from the local machine.
1.49 jmc 1103: The first argument must be
1.43 djm 1104: .Sm off
1.49 jmc 1105: .Oo Ar bind_address : Oc Ar port
1.43 djm 1106: .Sm on
1.49 jmc 1107: and the second argument must be
1108: .Ar host : Ns Ar hostport .
1.138 djm 1109: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1110: Multiple forwardings may be specified, and additional
1111: forwardings can be given on the command line.
1.113 stevesk 1112: Privileged ports can be forwarded only when
1113: logging in as root on the remote machine.
1.118 jmc 1114: .Pp
1.117 djm 1115: If the
1116: .Ar port
1117: argument is
1118: .Ql 0 ,
1119: the listen port will be dynamically allocated on the server and reported
1120: to the client at run time.
1.43 djm 1121: .Pp
1122: If the
1123: .Ar bind_address
1124: is not specified, the default is to only bind to loopback addresses.
1125: If the
1126: .Ar bind_address
1127: is
1128: .Ql *
1129: or an empty string, then the forwarding is requested to listen on all
1130: interfaces.
1131: Specifying a remote
1132: .Ar bind_address
1.46 jmc 1133: will only succeed if the server's
1134: .Cm GatewayPorts
1.43 djm 1135: option is enabled (see
1.46 jmc 1136: .Xr sshd_config 5 ) .
1.149 djm 1137: .It Cm RequestTTY
1138: Specifies whether to request a pseudo-tty for the session.
1139: The argument may be one of:
1140: .Dq no
1141: (never request a TTY),
1142: .Dq yes
1143: (always request a TTY when standard input is a TTY),
1144: .Dq force
1145: (always request a TTY) or
1146: .Dq auto
1147: (request a TTY when opening a login session).
1148: This option mirrors the
1149: .Fl t
1150: and
1151: .Fl T
1152: flags for
1153: .Xr ssh 1 .
1.1 stevesk 1154: .It Cm RhostsRSAAuthentication
1155: Specifies whether to try rhosts based authentication with RSA host
1156: authentication.
1157: The argument must be
1158: .Dq yes
1159: or
1160: .Dq no .
1161: The default is
1162: .Dq no .
1163: This option applies to protocol version 1 only and requires
1.84 jmc 1164: .Xr ssh 1
1.1 stevesk 1165: to be setuid root.
1166: .It Cm RSAAuthentication
1167: Specifies whether to try RSA authentication.
1168: The argument to this keyword must be
1169: .Dq yes
1170: or
1171: .Dq no .
1172: RSA authentication will only be
1173: attempted if the identity file exists, or an authentication agent is
1174: running.
1175: The default is
1176: .Dq yes .
1177: Note that this option applies to protocol version 1 only.
1.32 djm 1178: .It Cm SendEnv
1179: Specifies what variables from the local
1180: .Xr environ 7
1181: should be sent to the server.
1.84 jmc 1182: Note that environment passing is only supported for protocol 2.
1183: The server must also support it, and the server must be configured to
1.33 djm 1184: accept these environment variables.
1.32 djm 1185: Refer to
1186: .Cm AcceptEnv
1187: in
1188: .Xr sshd_config 5
1189: for how to configure the server.
1.80 jmc 1190: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1191: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1192: across multiple
1193: .Cm SendEnv
1194: directives.
1195: The default is not to send any environment variables.
1.81 jmc 1196: .Pp
1197: See
1198: .Sx PATTERNS
1199: for more information on patterns.
1.28 markus 1200: .It Cm ServerAliveCountMax
1.73 jmc 1201: Sets the number of server alive messages (see below) which may be
1.28 markus 1202: sent without
1.84 jmc 1203: .Xr ssh 1
1.28 markus 1204: receiving any messages back from the server.
1205: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1206: ssh will disconnect from the server, terminating the session.
1.28 markus 1207: It is important to note that the use of server alive messages is very
1208: different from
1209: .Cm TCPKeepAlive
1210: (below).
1211: The server alive messages are sent through the encrypted channel
1212: and therefore will not be spoofable.
1213: The TCP keepalive option enabled by
1214: .Cm TCPKeepAlive
1215: is spoofable.
1216: The server alive mechanism is valuable when the client or
1217: server depend on knowing when a connection has become inactive.
1218: .Pp
1219: The default value is 3.
1220: If, for example,
1221: .Cm ServerAliveInterval
1.84 jmc 1222: (see below) is set to 15 and
1.28 markus 1223: .Cm ServerAliveCountMax
1.84 jmc 1224: is left at the default, if the server becomes unresponsive,
1225: ssh will disconnect after approximately 45 seconds.
1.89 markus 1226: This option applies to protocol version 2 only.
1.67 jmc 1227: .It Cm ServerAliveInterval
1228: Sets a timeout interval in seconds after which if no data has been received
1229: from the server,
1.84 jmc 1230: .Xr ssh 1
1.67 jmc 1231: will send a message through the encrypted
1232: channel to request a response from the server.
1233: The default
1234: is 0, indicating that these messages will not be sent to the server.
1235: This option applies to protocol version 2 only.
1.1 stevesk 1236: .It Cm StrictHostKeyChecking
1237: If this flag is set to
1238: .Dq yes ,
1.84 jmc 1239: .Xr ssh 1
1.1 stevesk 1240: will never automatically add host keys to the
1.50 djm 1241: .Pa ~/.ssh/known_hosts
1.1 stevesk 1242: file, and refuses to connect to hosts whose host key has changed.
1243: This provides maximum protection against trojan horse attacks,
1.84 jmc 1244: though it can be annoying when the
1.1 stevesk 1245: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1246: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1247: frequently made.
1248: This option forces the user to manually
1249: add all new hosts.
1250: If this flag is set to
1251: .Dq no ,
1.84 jmc 1252: ssh will automatically add new host keys to the
1.1 stevesk 1253: user known hosts files.
1254: If this flag is set to
1255: .Dq ask ,
1256: new host keys
1257: will be added to the user known host files only after the user
1258: has confirmed that is what they really want to do, and
1.84 jmc 1259: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1260: The host keys of
1261: known hosts will be verified automatically in all cases.
1262: The argument must be
1263: .Dq yes ,
1.84 jmc 1264: .Dq no ,
1.1 stevesk 1265: or
1266: .Dq ask .
1267: The default is
1268: .Dq ask .
1.26 markus 1269: .It Cm TCPKeepAlive
1270: Specifies whether the system should send TCP keepalive messages to the
1271: other side.
1272: If they are sent, death of the connection or crash of one
1273: of the machines will be properly noticed.
1274: However, this means that
1275: connections will die if the route is down temporarily, and some people
1276: find it annoying.
1277: .Pp
1278: The default is
1279: .Dq yes
1280: (to send TCP keepalive messages), and the client will notice
1281: if the network goes down or the remote host dies.
1282: This is important in scripts, and many users want it too.
1283: .Pp
1284: To disable TCP keepalive messages, the value should be set to
1285: .Dq no .
1.65 reyk 1286: .It Cm Tunnel
1.95 stevesk 1287: Request
1.65 reyk 1288: .Xr tun 4
1.69 jmc 1289: device forwarding between the client and the server.
1.65 reyk 1290: The argument must be
1.68 reyk 1291: .Dq yes ,
1.95 stevesk 1292: .Dq point-to-point
1293: (layer 3),
1294: .Dq ethernet
1295: (layer 2),
1.65 reyk 1296: or
1297: .Dq no .
1.95 stevesk 1298: Specifying
1299: .Dq yes
1300: requests the default tunnel mode, which is
1301: .Dq point-to-point .
1.65 reyk 1302: The default is
1303: .Dq no .
1304: .It Cm TunnelDevice
1.95 stevesk 1305: Specifies the
1.65 reyk 1306: .Xr tun 4
1.95 stevesk 1307: devices to open on the client
1308: .Pq Ar local_tun
1309: and the server
1310: .Pq Ar remote_tun .
1311: .Pp
1312: The argument must be
1313: .Sm off
1314: .Ar local_tun Op : Ar remote_tun .
1315: .Sm on
1316: The devices may be specified by numerical ID or the keyword
1317: .Dq any ,
1318: which uses the next available tunnel device.
1319: If
1320: .Ar remote_tun
1321: is not specified, it defaults to
1322: .Dq any .
1323: The default is
1324: .Dq any:any .
1.72 jmc 1325: .It Cm UsePrivilegedPort
1326: Specifies whether to use a privileged port for outgoing connections.
1327: The argument must be
1328: .Dq yes
1329: or
1330: .Dq no .
1331: The default is
1332: .Dq no .
1333: If set to
1.84 jmc 1334: .Dq yes ,
1335: .Xr ssh 1
1.72 jmc 1336: must be setuid root.
1337: Note that this option must be set to
1338: .Dq yes
1339: for
1340: .Cm RhostsRSAAuthentication
1341: with older servers.
1.1 stevesk 1342: .It Cm User
1343: Specifies the user to log in as.
1344: This can be useful when a different user name is used on different machines.
1345: This saves the trouble of
1346: having to remember to give the user name on the command line.
1347: .It Cm UserKnownHostsFile
1.151 djm 1348: Specifies one or more files to use for the user
1349: host key database, separated by whitespace.
1350: The default is
1351: .Pa ~/.ssh/known_hosts ,
1352: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1353: .It Cm VerifyHostKeyDNS
1354: Specifies whether to verify the remote key using DNS and SSHFP resource
1355: records.
1.24 jakob 1356: If this option is set to
1357: .Dq yes ,
1.25 jmc 1358: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1359: from DNS.
1360: Insecure fingerprints will be handled as if this option was set to
1361: .Dq ask .
1362: If this option is set to
1363: .Dq ask ,
1364: information on fingerprint match will be displayed, but the user will still
1365: need to confirm new host keys according to the
1366: .Cm StrictHostKeyChecking
1367: option.
1368: The argument must be
1369: .Dq yes ,
1.84 jmc 1370: .Dq no ,
1.25 jmc 1371: or
1372: .Dq ask .
1.8 jakob 1373: The default is
1374: .Dq no .
1.12 jakob 1375: Note that this option applies to protocol version 2 only.
1.84 jmc 1376: .Pp
1.166 jmc 1377: See also VERIFYING HOST KEYS in
1.84 jmc 1378: .Xr ssh 1 .
1.111 grunk 1379: .It Cm VisualHostKey
1380: If this flag is set to
1381: .Dq yes ,
1382: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1383: printed in addition to the hex fingerprint string at login and
1384: for unknown host keys.
1.111 grunk 1385: If this flag is set to
1386: .Dq no ,
1.114 stevesk 1387: no fingerprint strings are printed at login and
1388: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1389: The default is
1390: .Dq no .
1.1 stevesk 1391: .It Cm XAuthLocation
1.5 stevesk 1392: Specifies the full pathname of the
1.1 stevesk 1393: .Xr xauth 1
1394: program.
1395: The default is
1396: .Pa /usr/X11R6/bin/xauth .
1397: .El
1.86 jmc 1398: .Sh PATTERNS
1399: A
1400: .Em pattern
1401: consists of zero or more non-whitespace characters,
1402: .Sq *
1403: (a wildcard that matches zero or more characters),
1404: or
1405: .Sq ?\&
1406: (a wildcard that matches exactly one character).
1407: For example, to specify a set of declarations for any host in the
1408: .Dq .co.uk
1409: set of domains,
1410: the following pattern could be used:
1411: .Pp
1412: .Dl Host *.co.uk
1413: .Pp
1414: The following pattern
1415: would match any host in the 192.168.0.[0-9] network range:
1416: .Pp
1417: .Dl Host 192.168.0.?
1418: .Pp
1419: A
1420: .Em pattern-list
1421: is a comma-separated list of patterns.
1422: Patterns within pattern-lists may be negated
1423: by preceding them with an exclamation mark
1424: .Pq Sq !\& .
1425: For example,
1.174 ! djm 1426: to allow a key to be used from anywhere within an organization
1.86 jmc 1427: except from the
1428: .Dq dialup
1429: pool,
1430: the following entry (in authorized_keys) could be used:
1431: .Pp
1432: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1433: .Sh FILES
1434: .Bl -tag -width Ds
1.50 djm 1435: .It Pa ~/.ssh/config
1.1 stevesk 1436: This is the per-user configuration file.
1437: The format of this file is described above.
1.84 jmc 1438: This file is used by the SSH client.
1.30 djm 1439: Because of the potential for abuse, this file must have strict permissions:
1440: read/write for the user, and not accessible by others.
1.1 stevesk 1441: .It Pa /etc/ssh/ssh_config
1442: Systemwide configuration file.
1443: This file provides defaults for those
1444: values that are not specified in the user's configuration file, and
1445: for those users who do not have a configuration file.
1446: This file must be world-readable.
1447: .El
1.13 jmc 1448: .Sh SEE ALSO
1449: .Xr ssh 1
1.1 stevesk 1450: .Sh AUTHORS
1451: OpenSSH is a derivative of the original and free
1452: ssh 1.2.12 release by Tatu Ylonen.
1453: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1454: Theo de Raadt and Dug Song
1455: removed many bugs, re-added newer features and
1456: created OpenSSH.
1457: Markus Friedl contributed the support for SSH
1458: protocol versions 1.5 and 2.0.
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