Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.171
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.171 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.170 2013/10/15 14:10:25 jmc Exp $
! 37: .Dd $Mdocdate: October 15 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
! 204: when
! 205: .Cm CanonicaliseHostname
! 206: is enabled, this option specifies the list of domain suffixes in which to
! 207: search for the specified destination host.
! 208: .It Cm CanonicaliseFallbackLocal
! 209: specified whether to fail with an error when hostname canonicalisation fails.
! 210: The default of
! 211: .Dq no
! 212: will attempt to lookup the unqualified hostname using the system resolver's
! 213: search rules.
! 214: A value of
! 215: .Dq yes
! 216: will cause
! 217: .Xr ssh 1
! 218: to fail instantly if
! 219: .Cm CanonicaliseHostname
! 220: is enabled and the target hostname cannot be found in any of the domains
! 221: specified by
! 222: .Cm CanonicalDomains .
! 223: .It Cm CanonicaliseHostname
! 224: controls whether explicit hostname canonicalisation is performed.
! 225: The default
! 226: .Dq no
! 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
! 234: will attempt to canonicalise the hostname specified on the command line
! 235: using the
! 236: .Cm CanonicalDomains
! 237: suffixes and
! 238: .Cm CanonicalisePermittedCNAMEs
! 239: rules.
! 240: If
! 241: .Cm CanonicaliseHostname
! 242: is set to
! 243: .Dq always ,
! 244: then canonicalisation is applied to proxied connections to.
! 245: .It Cm CanonicaliseMaxDots
! 246: specifies the maximum number of dot characters in a hostname name before
! 247: canonicalisation is disabled.
! 248: The default of
! 249: .Dq 1
! 250: allows a single dot (i.e. hostname.subdomain)
! 251: .It Cm CanonicalisePermittedCNAMEs
! 252: specifies rules to determine whether CNAMEs should be followed when
! 253: canonicalising hostnames.
! 254: The rules consist of one or more arguments of
! 255: .Sm off
! 256: .Ar source_domain_list : Ar target_domain_list
! 257: .Sm on
! 258: where
! 259: .Ar source_domain_list
! 260: is a pattern-list of domains that are may follow CNAMEs in canonicalisation
! 261: and
! 262: .Ar target_domain_list
! 263: is a pattern-list of domains that they may resove to.
! 264: .Pp
! 265: For example,
! 266: .Dq *.a.example.com:*.b.example.com,*.c.example.com
! 267: will allow hostnames matching
! 268: .Dq *.a.example.com
! 269: to be canonicalised to names in the
! 270: .Dq *.b.example.com
! 271: or
! 272: .Dq *.c.example.com
! 273: domains.
1.1 stevesk 274: .It Cm ChallengeResponseAuthentication
1.82 jmc 275: Specifies whether to use challenge-response authentication.
1.1 stevesk 276: The argument to this keyword must be
277: .Dq yes
278: or
279: .Dq no .
280: The default is
281: .Dq yes .
282: .It Cm CheckHostIP
283: If this flag is set to
284: .Dq yes ,
1.84 jmc 285: .Xr ssh 1
286: will additionally check the host IP address in the
1.1 stevesk 287: .Pa known_hosts
288: file.
289: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 290: If the option is set to
1.1 stevesk 291: .Dq no ,
292: the check will not be executed.
293: The default is
294: .Dq yes .
295: .It Cm Cipher
296: Specifies the cipher to use for encrypting the session
297: in protocol version 1.
298: Currently,
299: .Dq blowfish ,
300: .Dq 3des ,
301: and
302: .Dq des
303: are supported.
304: .Ar des
305: is only supported in the
1.84 jmc 306: .Xr ssh 1
1.1 stevesk 307: client for interoperability with legacy protocol 1 implementations
308: that do not support the
309: .Ar 3des
1.7 jmc 310: cipher.
311: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 312: The default is
313: .Dq 3des .
314: .It Cm Ciphers
315: Specifies the ciphers allowed for protocol version 2
316: in order of preference.
317: Multiple ciphers must be comma-separated.
1.35 dtucker 318: The supported ciphers are
319: .Dq 3des-cbc ,
320: .Dq aes128-cbc ,
321: .Dq aes192-cbc ,
322: .Dq aes256-cbc ,
323: .Dq aes128-ctr ,
324: .Dq aes192-ctr ,
325: .Dq aes256-ctr ,
1.161 markus 326: .Dq aes128-gcm@openssh.com ,
327: .Dq aes256-gcm@openssh.com ,
1.54 djm 328: .Dq arcfour128 ,
329: .Dq arcfour256 ,
1.35 dtucker 330: .Dq arcfour ,
331: .Dq blowfish-cbc ,
332: and
333: .Dq cast128-cbc .
1.84 jmc 334: The default is:
335: .Bd -literal -offset 3n
1.116 naddy 336: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
1.161 markus 337: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.116 naddy 338: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
339: aes256-cbc,arcfour
1.1 stevesk 340: .Ed
341: .It Cm ClearAllForwardings
1.84 jmc 342: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 343: specified in the configuration files or on the command line be
1.7 jmc 344: cleared.
345: This option is primarily useful when used from the
1.84 jmc 346: .Xr ssh 1
1.1 stevesk 347: command line to clear port forwardings set in
348: configuration files, and is automatically set by
349: .Xr scp 1
350: and
351: .Xr sftp 1 .
352: The argument must be
353: .Dq yes
354: or
355: .Dq no .
356: The default is
357: .Dq no .
358: .It Cm Compression
359: Specifies whether to use compression.
360: The argument must be
361: .Dq yes
362: or
363: .Dq no .
364: The default is
365: .Dq no .
366: .It Cm CompressionLevel
367: Specifies the compression level to use if compression is enabled.
368: The argument must be an integer from 1 (fast) to 9 (slow, best).
369: The default level is 6, which is good for most applications.
370: The meaning of the values is the same as in
371: .Xr gzip 1 .
372: Note that this option applies to protocol version 1 only.
373: .It Cm ConnectionAttempts
374: Specifies the number of tries (one per second) to make before exiting.
375: The argument must be an integer.
376: This may be useful in scripts if the connection sometimes fails.
377: The default is 1.
1.9 djm 378: .It Cm ConnectTimeout
1.84 jmc 379: Specifies the timeout (in seconds) used when connecting to the
380: SSH server, instead of using the default system TCP timeout.
1.11 jmc 381: This value is used only when the target is down or really unreachable,
382: not when it refuses the connection.
1.36 djm 383: .It Cm ControlMaster
384: Enables the sharing of multiple sessions over a single network connection.
385: When set to
1.84 jmc 386: .Dq yes ,
387: .Xr ssh 1
1.36 djm 388: will listen for connections on a control socket specified using the
389: .Cm ControlPath
390: argument.
391: Additional sessions can connect to this socket using the same
392: .Cm ControlPath
393: with
394: .Cm ControlMaster
395: set to
396: .Dq no
1.38 jmc 397: (the default).
1.64 jmc 398: These sessions will try to reuse the master instance's network connection
1.63 djm 399: rather than initiating new ones, but will fall back to connecting normally
400: if the control socket does not exist, or is not listening.
401: .Pp
1.37 djm 402: Setting this to
403: .Dq ask
1.84 jmc 404: will cause ssh
1.37 djm 405: to listen for control connections, but require confirmation using the
406: .Ev SSH_ASKPASS
407: program before they are accepted (see
408: .Xr ssh-add 1
1.38 jmc 409: for details).
1.51 jakob 410: If the
411: .Cm ControlPath
1.84 jmc 412: cannot be opened,
413: ssh will continue without connecting to a master instance.
1.58 djm 414: .Pp
415: X11 and
1.59 jmc 416: .Xr ssh-agent 1
1.58 djm 417: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 418: display and agent forwarded will be the one belonging to the master
1.59 jmc 419: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 420: .Pp
421: Two additional options allow for opportunistic multiplexing: try to use a
422: master connection but fall back to creating a new one if one does not already
423: exist.
424: These options are:
425: .Dq auto
426: and
427: .Dq autoask .
428: The latter requires confirmation like the
429: .Dq ask
430: option.
1.36 djm 431: .It Cm ControlPath
1.55 djm 432: Specify the path to the control socket used for connection sharing as described
433: in the
1.36 djm 434: .Cm ControlMaster
1.57 djm 435: section above or the string
436: .Dq none
437: to disable connection sharing.
1.55 djm 438: In the path,
1.147 djm 439: .Ql %L
440: will be substituted by the first component of the local host name,
1.77 djm 441: .Ql %l
1.147 djm 442: will be substituted by the local host name (including any domain name),
1.55 djm 443: .Ql %h
444: will be substituted by the target host name,
1.150 jmc 445: .Ql %n
446: will be substituted by the original target host name
447: specified on the command line,
1.55 djm 448: .Ql %p
1.147 djm 449: the port,
1.55 djm 450: .Ql %r
1.147 djm 451: by the remote login username, and
452: .Ql %u
453: by the username of the user running
454: .Xr ssh 1 .
1.56 djm 455: It is recommended that any
456: .Cm ControlPath
457: used for opportunistic connection sharing include
1.78 jmc 458: at least %h, %p, and %r.
1.56 djm 459: This ensures that shared connections are uniquely identified.
1.137 djm 460: .It Cm ControlPersist
461: When used in conjunction with
462: .Cm ControlMaster ,
463: specifies that the master connection should remain open
464: in the background (waiting for future client connections)
465: after the initial client connection has been closed.
466: If set to
467: .Dq no ,
468: then the master connection will not be placed into the background,
469: and will close as soon as the initial client connection is closed.
470: If set to
471: .Dq yes ,
472: then the master connection will remain in the background indefinitely
473: (until killed or closed via a mechanism such as the
474: .Xr ssh 1
475: .Dq Fl O No exit
476: option).
477: If set to a time in seconds, or a time in any of the formats documented in
478: .Xr sshd_config 5 ,
479: then the backgrounded master connection will automatically terminate
480: after it has remained idle (with no client connections) for the
481: specified time.
1.38 jmc 482: .It Cm DynamicForward
1.74 jmc 483: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 484: over the secure channel, and the application
485: protocol is then used to determine where to connect to from the
486: remote machine.
1.62 djm 487: .Pp
488: The argument must be
489: .Sm off
490: .Oo Ar bind_address : Oc Ar port .
491: .Sm on
1.138 djm 492: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 493: By default, the local port is bound in accordance with the
494: .Cm GatewayPorts
495: setting.
496: However, an explicit
497: .Ar bind_address
498: may be used to bind the connection to a specific address.
499: The
500: .Ar bind_address
501: of
502: .Dq localhost
503: indicates that the listening port be bound for local use only, while an
504: empty address or
505: .Sq *
506: indicates that the port should be available from all interfaces.
507: .Pp
1.38 jmc 508: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 509: .Xr ssh 1
1.38 jmc 510: will act as a SOCKS server.
511: Multiple forwardings may be specified, and
512: additional forwardings can be given on the command line.
513: Only the superuser can forward privileged ports.
1.14 markus 514: .It Cm EnableSSHKeysign
515: Setting this option to
516: .Dq yes
517: in the global client configuration file
518: .Pa /etc/ssh/ssh_config
519: enables the use of the helper program
520: .Xr ssh-keysign 8
521: during
522: .Cm HostbasedAuthentication .
523: The argument must be
524: .Dq yes
525: or
526: .Dq no .
527: The default is
528: .Dq no .
1.23 jmc 529: This option should be placed in the non-hostspecific section.
1.14 markus 530: See
531: .Xr ssh-keysign 8
532: for more information.
1.1 stevesk 533: .It Cm EscapeChar
534: Sets the escape character (default:
535: .Ql ~ ) .
536: The escape character can also
537: be set on the command line.
538: The argument should be a single character,
539: .Ql ^
540: followed by a letter, or
541: .Dq none
542: to disable the escape
543: character entirely (making the connection transparent for binary
544: data).
1.96 markus 545: .It Cm ExitOnForwardFailure
546: Specifies whether
547: .Xr ssh 1
548: should terminate the connection if it cannot set up all requested
1.102 stevesk 549: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 550: The argument must be
551: .Dq yes
552: or
553: .Dq no .
554: The default is
555: .Dq no .
1.1 stevesk 556: .It Cm ForwardAgent
557: Specifies whether the connection to the authentication agent (if any)
558: will be forwarded to the remote machine.
559: The argument must be
560: .Dq yes
561: or
562: .Dq no .
563: The default is
564: .Dq no .
1.3 stevesk 565: .Pp
1.7 jmc 566: Agent forwarding should be enabled with caution.
567: Users with the ability to bypass file permissions on the remote host
568: (for the agent's Unix-domain socket)
569: can access the local agent through the forwarded connection.
570: An attacker cannot obtain key material from the agent,
1.3 stevesk 571: however they can perform operations on the keys that enable them to
572: authenticate using the identities loaded into the agent.
1.1 stevesk 573: .It Cm ForwardX11
574: Specifies whether X11 connections will be automatically redirected
575: over the secure channel and
576: .Ev DISPLAY
577: set.
578: The argument must be
579: .Dq yes
580: or
581: .Dq no .
582: The default is
583: .Dq no .
1.3 stevesk 584: .Pp
1.7 jmc 585: X11 forwarding should be enabled with caution.
586: Users with the ability to bypass file permissions on the remote host
1.22 markus 587: (for the user's X11 authorization database)
1.7 jmc 588: can access the local X11 display through the forwarded connection.
1.22 markus 589: An attacker may then be able to perform activities such as keystroke monitoring
590: if the
591: .Cm ForwardX11Trusted
592: option is also enabled.
1.134 djm 593: .It Cm ForwardX11Timeout
1.135 jmc 594: Specify a timeout for untrusted X11 forwarding
595: using the format described in the
1.166 jmc 596: TIME FORMATS section of
1.134 djm 597: .Xr sshd_config 5 .
598: X11 connections received by
599: .Xr ssh 1
600: after this time will be refused.
601: The default is to disable untrusted X11 forwarding after twenty minutes has
602: elapsed.
1.22 markus 603: .It Cm ForwardX11Trusted
1.34 jmc 604: If this option is set to
1.84 jmc 605: .Dq yes ,
606: remote X11 clients will have full access to the original X11 display.
1.42 djm 607: .Pp
1.22 markus 608: If this option is set to
1.84 jmc 609: .Dq no ,
610: remote X11 clients will be considered untrusted and prevented
1.22 markus 611: from stealing or tampering with data belonging to trusted X11
612: clients.
1.42 djm 613: Furthermore, the
614: .Xr xauth 1
615: token used for the session will be set to expire after 20 minutes.
616: Remote clients will be refused access after this time.
1.22 markus 617: .Pp
618: The default is
619: .Dq no .
620: .Pp
621: See the X11 SECURITY extension specification for full details on
622: the restrictions imposed on untrusted clients.
1.1 stevesk 623: .It Cm GatewayPorts
624: Specifies whether remote hosts are allowed to connect to local
625: forwarded ports.
626: By default,
1.84 jmc 627: .Xr ssh 1
1.7 jmc 628: binds local port forwardings to the loopback address.
629: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 630: .Cm GatewayPorts
1.84 jmc 631: can be used to specify that ssh
1.1 stevesk 632: should bind local port forwardings to the wildcard address,
633: thus allowing remote hosts to connect to forwarded ports.
634: The argument must be
635: .Dq yes
636: or
637: .Dq no .
638: The default is
639: .Dq no .
640: .It Cm GlobalKnownHostsFile
1.151 djm 641: Specifies one or more files to use for the global
642: host key database, separated by whitespace.
643: The default is
644: .Pa /etc/ssh/ssh_known_hosts ,
645: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 646: .It Cm GSSAPIAuthentication
1.27 markus 647: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 648: The default is
1.21 markus 649: .Dq no .
1.18 markus 650: Note that this option applies to protocol version 2 only.
651: .It Cm GSSAPIDelegateCredentials
652: Forward (delegate) credentials to the server.
653: The default is
654: .Dq no .
655: Note that this option applies to protocol version 2 only.
1.44 djm 656: .It Cm HashKnownHosts
657: Indicates that
1.84 jmc 658: .Xr ssh 1
1.44 djm 659: should hash host names and addresses when they are added to
1.50 djm 660: .Pa ~/.ssh/known_hosts .
1.44 djm 661: These hashed names may be used normally by
1.84 jmc 662: .Xr ssh 1
1.44 djm 663: and
1.84 jmc 664: .Xr sshd 8 ,
1.44 djm 665: but they do not reveal identifying information should the file's contents
666: be disclosed.
667: The default is
668: .Dq no .
1.97 jmc 669: Note that existing names and addresses in known hosts files
670: will not be converted automatically,
671: but may be manually hashed using
1.45 djm 672: .Xr ssh-keygen 1 .
1.1 stevesk 673: .It Cm HostbasedAuthentication
674: Specifies whether to try rhosts based authentication with public key
675: authentication.
676: The argument must be
677: .Dq yes
678: or
679: .Dq no .
680: The default is
681: .Dq no .
682: This option applies to protocol version 2 only and
683: is similar to
684: .Cm RhostsRSAAuthentication .
685: .It Cm HostKeyAlgorithms
686: Specifies the protocol version 2 host key algorithms
687: that the client wants to use in order of preference.
688: The default for this option is:
1.139 djm 689: .Bd -literal -offset 3n
690: ecdsa-sha2-nistp256-cert-v01@openssh.com,
691: ecdsa-sha2-nistp384-cert-v01@openssh.com,
692: ecdsa-sha2-nistp521-cert-v01@openssh.com,
693: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
694: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
695: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
696: ssh-rsa,ssh-dss
697: .Ed
1.145 djm 698: .Pp
699: If hostkeys are known for the destination host then this default is modified
700: to prefer their algorithms.
1.1 stevesk 701: .It Cm HostKeyAlias
702: Specifies an alias that should be used instead of the
703: real host name when looking up or saving the host key
704: in the host key database files.
1.84 jmc 705: This option is useful for tunneling SSH connections
1.1 stevesk 706: or for multiple servers running on a single host.
707: .It Cm HostName
708: Specifies the real host name to log into.
709: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 710: If the hostname contains the character sequence
711: .Ql %h ,
1.150 jmc 712: then this will be replaced with the host name specified on the command line
1.136 djm 713: (this is useful for manipulating unqualified names).
1.84 jmc 714: The default is the name given on the command line.
1.1 stevesk 715: Numeric IP addresses are also permitted (both on the command line and in
716: .Cm HostName
717: specifications).
1.29 markus 718: .It Cm IdentitiesOnly
719: Specifies that
1.84 jmc 720: .Xr ssh 1
1.29 markus 721: should only use the authentication identity files configured in the
1.31 jmc 722: .Nm
1.29 markus 723: files,
1.84 jmc 724: even if
725: .Xr ssh-agent 1
1.159 djm 726: or a
727: .Cm PKCS11Provider
1.29 markus 728: offers more identities.
729: The argument to this keyword must be
730: .Dq yes
731: or
732: .Dq no .
1.84 jmc 733: This option is intended for situations where ssh-agent
1.29 markus 734: offers many different identities.
735: The default is
736: .Dq no .
1.67 jmc 737: .It Cm IdentityFile
1.155 dtucker 738: Specifies a file from which the user's DSA, ECDSA or RSA authentication
1.139 djm 739: identity is read.
1.67 jmc 740: The default is
741: .Pa ~/.ssh/identity
742: for protocol version 1, and
1.139 djm 743: .Pa ~/.ssh/id_dsa ,
744: .Pa ~/.ssh/id_ecdsa
745: and
1.67 jmc 746: .Pa ~/.ssh/id_rsa
747: for protocol version 2.
748: Additionally, any identities represented by the authentication agent
1.165 djm 749: will be used for authentication unless
750: .Cm IdentitiesOnly
751: is set.
1.129 djm 752: .Xr ssh 1
753: will try to load certificate information from the filename obtained by
754: appending
755: .Pa -cert.pub
756: to the path of a specified
757: .Cm IdentityFile .
1.90 djm 758: .Pp
1.67 jmc 759: The file name may use the tilde
1.91 jmc 760: syntax to refer to a user's home directory or one of the following
1.90 djm 761: escape characters:
762: .Ql %d
763: (local user's home directory),
764: .Ql %u
765: (local user name),
766: .Ql %l
767: (local host name),
768: .Ql %h
769: (remote host name) or
1.92 djm 770: .Ql %r
1.90 djm 771: (remote user name).
772: .Pp
1.67 jmc 773: It is possible to have
774: multiple identity files specified in configuration files; all these
775: identities will be tried in sequence.
1.152 djm 776: Multiple
777: .Cm IdentityFile
778: directives will add to the list of identities tried (this behaviour
779: differs from that of other configuration directives).
1.165 djm 780: .Pp
781: .Cm IdentityFile
782: may be used in conjunction with
783: .Cm IdentitiesOnly
784: to select which identities in an agent are offered during authentication.
1.164 jmc 785: .It Cm IgnoreUnknown
786: Specifies a pattern-list of unknown options to be ignored if they are
787: encountered in configuration parsing.
788: This may be used to suppress errors if
789: .Nm
790: contains options that are unrecognised by
791: .Xr ssh 1 .
792: It is recommended that
793: .Cm IgnoreUnknown
794: be listed early in the configuration file as it will not be applied
795: to unknown options that appear before it.
1.143 djm 796: .It Cm IPQoS
797: Specifies the IPv4 type-of-service or DSCP class for connections.
798: Accepted values are
799: .Dq af11 ,
800: .Dq af12 ,
801: .Dq af13 ,
1.154 djm 802: .Dq af21 ,
1.143 djm 803: .Dq af22 ,
804: .Dq af23 ,
805: .Dq af31 ,
806: .Dq af32 ,
807: .Dq af33 ,
808: .Dq af41 ,
809: .Dq af42 ,
810: .Dq af43 ,
811: .Dq cs0 ,
812: .Dq cs1 ,
813: .Dq cs2 ,
814: .Dq cs3 ,
815: .Dq cs4 ,
816: .Dq cs5 ,
817: .Dq cs6 ,
818: .Dq cs7 ,
819: .Dq ef ,
820: .Dq lowdelay ,
821: .Dq throughput ,
822: .Dq reliability ,
823: or a numeric value.
1.146 djm 824: This option may take one or two arguments, separated by whitespace.
1.143 djm 825: If one argument is specified, it is used as the packet class unconditionally.
826: If two values are specified, the first is automatically selected for
827: interactive sessions and the second for non-interactive sessions.
828: The default is
829: .Dq lowdelay
830: for interactive sessions and
831: .Dq throughput
832: for non-interactive sessions.
1.103 djm 833: .It Cm KbdInteractiveAuthentication
834: Specifies whether to use keyboard-interactive authentication.
835: The argument to this keyword must be
836: .Dq yes
837: or
838: .Dq no .
839: The default is
840: .Dq yes .
1.39 djm 841: .It Cm KbdInteractiveDevices
842: Specifies the list of methods to use in keyboard-interactive authentication.
843: Multiple method names must be comma-separated.
844: The default is to use the server specified list.
1.85 jmc 845: The methods available vary depending on what the server supports.
846: For an OpenSSH server,
847: it may be zero or more of:
848: .Dq bsdauth ,
849: .Dq pam ,
850: and
851: .Dq skey .
1.140 djm 852: .It Cm KexAlgorithms
853: Specifies the available KEX (Key Exchange) algorithms.
854: Multiple algorithms must be comma-separated.
1.141 jmc 855: The default is:
856: .Bd -literal -offset indent
857: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
858: diffie-hellman-group-exchange-sha256,
859: diffie-hellman-group-exchange-sha1,
860: diffie-hellman-group14-sha1,
861: diffie-hellman-group1-sha1
862: .Ed
1.65 reyk 863: .It Cm LocalCommand
864: Specifies a command to execute on the local machine after successfully
865: connecting to the server.
866: The command string extends to the end of the line, and is executed with
1.105 jmc 867: the user's shell.
1.109 dtucker 868: The following escape character substitutions will be performed:
869: .Ql %d
870: (local user's home directory),
871: .Ql %h
872: (remote host name),
873: .Ql %l
874: (local host name),
875: .Ql %n
876: (host name as provided on the command line),
877: .Ql %p
878: (remote port),
879: .Ql %r
880: (remote user name) or
881: .Ql %u
882: (local user name).
1.123 djm 883: .Pp
884: The command is run synchronously and does not have access to the
885: session of the
886: .Xr ssh 1
887: that spawned it.
888: It should not be used for interactive commands.
889: .Pp
1.65 reyk 890: This directive is ignored unless
891: .Cm PermitLocalCommand
892: has been enabled.
1.1 stevesk 893: .It Cm LocalForward
1.74 jmc 894: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 895: the secure channel to the specified host and port from the remote machine.
1.49 jmc 896: The first argument must be
1.43 djm 897: .Sm off
1.49 jmc 898: .Oo Ar bind_address : Oc Ar port
1.43 djm 899: .Sm on
1.49 jmc 900: and the second argument must be
901: .Ar host : Ns Ar hostport .
1.138 djm 902: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 903: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 904: given on the command line.
1.1 stevesk 905: Only the superuser can forward privileged ports.
1.43 djm 906: By default, the local port is bound in accordance with the
907: .Cm GatewayPorts
908: setting.
909: However, an explicit
910: .Ar bind_address
911: may be used to bind the connection to a specific address.
912: The
913: .Ar bind_address
914: of
915: .Dq localhost
1.46 jmc 916: indicates that the listening port be bound for local use only, while an
917: empty address or
918: .Sq *
1.43 djm 919: indicates that the port should be available from all interfaces.
1.1 stevesk 920: .It Cm LogLevel
921: Gives the verbosity level that is used when logging messages from
1.84 jmc 922: .Xr ssh 1 .
1.1 stevesk 923: The possible values are:
1.84 jmc 924: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 925: The default is INFO.
926: DEBUG and DEBUG1 are equivalent.
927: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 928: .It Cm MACs
929: Specifies the MAC (message authentication code) algorithms
930: in order of preference.
931: The MAC algorithm is used in protocol version 2
932: for data integrity protection.
933: Multiple algorithms must be comma-separated.
1.160 markus 934: The algorithms that contain
935: .Dq -etm
936: calculate the MAC after encryption (encrypt-then-mac).
937: These are considered safer and their use recommended.
1.84 jmc 938: The default is:
1.101 jmc 939: .Bd -literal -offset indent
1.160 markus 940: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
941: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
942: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
943: hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
944: hmac-md5-96-etm@openssh.com,
1.158 markus 945: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.157 naddy 946: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
947: hmac-sha1-96,hmac-md5-96
1.101 jmc 948: .Ed
1.1 stevesk 949: .It Cm NoHostAuthenticationForLocalhost
950: This option can be used if the home directory is shared across machines.
951: In this case localhost will refer to a different machine on each of
952: the machines and the user will get many warnings about changed host keys.
953: However, this option disables host authentication for localhost.
954: The argument to this keyword must be
955: .Dq yes
956: or
957: .Dq no .
958: The default is to check the host key for localhost.
959: .It Cm NumberOfPasswordPrompts
960: Specifies the number of password prompts before giving up.
961: The argument to this keyword must be an integer.
1.84 jmc 962: The default is 3.
1.1 stevesk 963: .It Cm PasswordAuthentication
964: Specifies whether to use password authentication.
965: The argument to this keyword must be
966: .Dq yes
967: or
968: .Dq no .
969: The default is
970: .Dq yes .
1.65 reyk 971: .It Cm PermitLocalCommand
972: Allow local command execution via the
973: .Ic LocalCommand
974: option or using the
1.66 jmc 975: .Ic !\& Ns Ar command
1.65 reyk 976: escape sequence in
977: .Xr ssh 1 .
978: The argument must be
979: .Dq yes
980: or
981: .Dq no .
982: The default is
983: .Dq no .
1.127 markus 984: .It Cm PKCS11Provider
985: Specifies which PKCS#11 provider to use.
1.144 jmc 986: The argument to this keyword is the PKCS#11 shared library
1.127 markus 987: .Xr ssh 1
1.128 markus 988: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 989: private RSA key.
1.67 jmc 990: .It Cm Port
991: Specifies the port number to connect on the remote host.
1.84 jmc 992: The default is 22.
1.1 stevesk 993: .It Cm PreferredAuthentications
994: Specifies the order in which the client should try protocol 2
1.11 jmc 995: authentication methods.
1.48 jmc 996: This allows a client to prefer one method (e.g.\&
1.1 stevesk 997: .Cm keyboard-interactive )
1.48 jmc 998: over another method (e.g.\&
1.131 jmc 999: .Cm password ) .
1000: The default is:
1001: .Bd -literal -offset indent
1002: gssapi-with-mic,hostbased,publickey,
1003: keyboard-interactive,password
1004: .Ed
1.1 stevesk 1005: .It Cm Protocol
1006: Specifies the protocol versions
1.84 jmc 1007: .Xr ssh 1
1.1 stevesk 1008: should support in order of preference.
1009: The possible values are
1.84 jmc 1010: .Sq 1
1.1 stevesk 1011: and
1.84 jmc 1012: .Sq 2 .
1.1 stevesk 1013: Multiple versions must be comma-separated.
1.120 markus 1014: When this option is set to
1.121 jmc 1015: .Dq 2,1
1.120 markus 1016: .Nm ssh
1017: will try version 2 and fall back to version 1
1018: if version 2 is not available.
1.1 stevesk 1019: The default is
1.121 jmc 1020: .Sq 2 .
1.1 stevesk 1021: .It Cm ProxyCommand
1022: Specifies the command to use to connect to the server.
1023: The command
1024: string extends to the end of the line, and is executed with
1.105 jmc 1025: the user's shell.
1.133 jmc 1026: In the command string, any occurrence of
1.1 stevesk 1027: .Ql %h
1028: will be substituted by the host name to
1.132 djm 1029: connect,
1.1 stevesk 1030: .Ql %p
1.133 jmc 1031: by the port, and
1032: .Ql %r
1.132 djm 1033: by the remote user name.
1.1 stevesk 1034: The command can be basically anything,
1035: and should read from its standard input and write to its standard output.
1036: It should eventually connect an
1037: .Xr sshd 8
1038: server running on some machine, or execute
1039: .Ic sshd -i
1040: somewhere.
1041: Host key management will be done using the
1042: HostName of the host being connected (defaulting to the name typed by
1043: the user).
1.7 jmc 1044: Setting the command to
1045: .Dq none
1.6 markus 1046: disables this option entirely.
1.1 stevesk 1047: Note that
1048: .Cm CheckHostIP
1049: is not available for connects with a proxy command.
1.52 djm 1050: .Pp
1051: This directive is useful in conjunction with
1052: .Xr nc 1
1053: and its proxy support.
1.53 jmc 1054: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1055: 192.0.2.0:
1056: .Bd -literal -offset 3n
1057: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1058: .Ed
1.167 djm 1059: .It Cm ProxyUseFdpass
1.168 jmc 1060: Specifies that
1.167 djm 1061: .Cm ProxyCommand
1062: will pass a connected file descriptor back to
1.168 jmc 1063: .Xr ssh 1
1.167 djm 1064: instead of continuing to execute and pass data.
1065: The default is
1066: .Dq no .
1.1 stevesk 1067: .It Cm PubkeyAuthentication
1068: Specifies whether to try public key authentication.
1069: The argument to this keyword must be
1070: .Dq yes
1071: or
1072: .Dq no .
1073: The default is
1074: .Dq yes .
1075: This option applies to protocol version 2 only.
1.75 dtucker 1076: .It Cm RekeyLimit
1077: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1078: session key is renegotiated, optionally followed a maximum amount of
1079: time that may pass before the session key is renegotiated.
1080: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1081: .Sq K ,
1082: .Sq M ,
1.75 dtucker 1083: or
1.76 jmc 1084: .Sq G
1.75 dtucker 1085: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1086: The default is between
1.84 jmc 1087: .Sq 1G
1.75 dtucker 1088: and
1.84 jmc 1089: .Sq 4G ,
1.75 dtucker 1090: depending on the cipher.
1.162 dtucker 1091: The optional second value is specified in seconds and may use any of the
1092: units documented in the
1.166 jmc 1093: TIME FORMATS section of
1.162 dtucker 1094: .Xr sshd_config 5 .
1095: The default value for
1096: .Cm RekeyLimit
1097: is
1098: .Dq default none ,
1099: which means that rekeying is performed after the cipher's default amount
1100: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1101: This option applies to protocol version 2 only.
1.1 stevesk 1102: .It Cm RemoteForward
1.74 jmc 1103: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1104: the secure channel to the specified host and port from the local machine.
1.49 jmc 1105: The first argument must be
1.43 djm 1106: .Sm off
1.49 jmc 1107: .Oo Ar bind_address : Oc Ar port
1.43 djm 1108: .Sm on
1.49 jmc 1109: and the second argument must be
1110: .Ar host : Ns Ar hostport .
1.138 djm 1111: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1112: Multiple forwardings may be specified, and additional
1113: forwardings can be given on the command line.
1.113 stevesk 1114: Privileged ports can be forwarded only when
1115: logging in as root on the remote machine.
1.118 jmc 1116: .Pp
1.117 djm 1117: If the
1118: .Ar port
1119: argument is
1120: .Ql 0 ,
1121: the listen port will be dynamically allocated on the server and reported
1122: to the client at run time.
1.43 djm 1123: .Pp
1124: If the
1125: .Ar bind_address
1126: is not specified, the default is to only bind to loopback addresses.
1127: If the
1128: .Ar bind_address
1129: is
1130: .Ql *
1131: or an empty string, then the forwarding is requested to listen on all
1132: interfaces.
1133: Specifying a remote
1134: .Ar bind_address
1.46 jmc 1135: will only succeed if the server's
1136: .Cm GatewayPorts
1.43 djm 1137: option is enabled (see
1.46 jmc 1138: .Xr sshd_config 5 ) .
1.149 djm 1139: .It Cm RequestTTY
1140: Specifies whether to request a pseudo-tty for the session.
1141: The argument may be one of:
1142: .Dq no
1143: (never request a TTY),
1144: .Dq yes
1145: (always request a TTY when standard input is a TTY),
1146: .Dq force
1147: (always request a TTY) or
1148: .Dq auto
1149: (request a TTY when opening a login session).
1150: This option mirrors the
1151: .Fl t
1152: and
1153: .Fl T
1154: flags for
1155: .Xr ssh 1 .
1.1 stevesk 1156: .It Cm RhostsRSAAuthentication
1157: Specifies whether to try rhosts based authentication with RSA host
1158: authentication.
1159: The argument must be
1160: .Dq yes
1161: or
1162: .Dq no .
1163: The default is
1164: .Dq no .
1165: This option applies to protocol version 1 only and requires
1.84 jmc 1166: .Xr ssh 1
1.1 stevesk 1167: to be setuid root.
1168: .It Cm RSAAuthentication
1169: Specifies whether to try RSA authentication.
1170: The argument to this keyword must be
1171: .Dq yes
1172: or
1173: .Dq no .
1174: RSA authentication will only be
1175: attempted if the identity file exists, or an authentication agent is
1176: running.
1177: The default is
1178: .Dq yes .
1179: Note that this option applies to protocol version 1 only.
1.32 djm 1180: .It Cm SendEnv
1181: Specifies what variables from the local
1182: .Xr environ 7
1183: should be sent to the server.
1.84 jmc 1184: Note that environment passing is only supported for protocol 2.
1185: The server must also support it, and the server must be configured to
1.33 djm 1186: accept these environment variables.
1.32 djm 1187: Refer to
1188: .Cm AcceptEnv
1189: in
1190: .Xr sshd_config 5
1191: for how to configure the server.
1.80 jmc 1192: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1193: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1194: across multiple
1195: .Cm SendEnv
1196: directives.
1197: The default is not to send any environment variables.
1.81 jmc 1198: .Pp
1199: See
1200: .Sx PATTERNS
1201: for more information on patterns.
1.28 markus 1202: .It Cm ServerAliveCountMax
1.73 jmc 1203: Sets the number of server alive messages (see below) which may be
1.28 markus 1204: sent without
1.84 jmc 1205: .Xr ssh 1
1.28 markus 1206: receiving any messages back from the server.
1207: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1208: ssh will disconnect from the server, terminating the session.
1.28 markus 1209: It is important to note that the use of server alive messages is very
1210: different from
1211: .Cm TCPKeepAlive
1212: (below).
1213: The server alive messages are sent through the encrypted channel
1214: and therefore will not be spoofable.
1215: The TCP keepalive option enabled by
1216: .Cm TCPKeepAlive
1217: is spoofable.
1218: The server alive mechanism is valuable when the client or
1219: server depend on knowing when a connection has become inactive.
1220: .Pp
1221: The default value is 3.
1222: If, for example,
1223: .Cm ServerAliveInterval
1.84 jmc 1224: (see below) is set to 15 and
1.28 markus 1225: .Cm ServerAliveCountMax
1.84 jmc 1226: is left at the default, if the server becomes unresponsive,
1227: ssh will disconnect after approximately 45 seconds.
1.89 markus 1228: This option applies to protocol version 2 only.
1.67 jmc 1229: .It Cm ServerAliveInterval
1230: Sets a timeout interval in seconds after which if no data has been received
1231: from the server,
1.84 jmc 1232: .Xr ssh 1
1.67 jmc 1233: will send a message through the encrypted
1234: channel to request a response from the server.
1235: The default
1236: is 0, indicating that these messages will not be sent to the server.
1237: This option applies to protocol version 2 only.
1.1 stevesk 1238: .It Cm StrictHostKeyChecking
1239: If this flag is set to
1240: .Dq yes ,
1.84 jmc 1241: .Xr ssh 1
1.1 stevesk 1242: will never automatically add host keys to the
1.50 djm 1243: .Pa ~/.ssh/known_hosts
1.1 stevesk 1244: file, and refuses to connect to hosts whose host key has changed.
1245: This provides maximum protection against trojan horse attacks,
1.84 jmc 1246: though it can be annoying when the
1.1 stevesk 1247: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1248: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1249: frequently made.
1250: This option forces the user to manually
1251: add all new hosts.
1252: If this flag is set to
1253: .Dq no ,
1.84 jmc 1254: ssh will automatically add new host keys to the
1.1 stevesk 1255: user known hosts files.
1256: If this flag is set to
1257: .Dq ask ,
1258: new host keys
1259: will be added to the user known host files only after the user
1260: has confirmed that is what they really want to do, and
1.84 jmc 1261: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1262: The host keys of
1263: known hosts will be verified automatically in all cases.
1264: The argument must be
1265: .Dq yes ,
1.84 jmc 1266: .Dq no ,
1.1 stevesk 1267: or
1268: .Dq ask .
1269: The default is
1270: .Dq ask .
1.26 markus 1271: .It Cm TCPKeepAlive
1272: Specifies whether the system should send TCP keepalive messages to the
1273: other side.
1274: If they are sent, death of the connection or crash of one
1275: of the machines will be properly noticed.
1276: However, this means that
1277: connections will die if the route is down temporarily, and some people
1278: find it annoying.
1279: .Pp
1280: The default is
1281: .Dq yes
1282: (to send TCP keepalive messages), and the client will notice
1283: if the network goes down or the remote host dies.
1284: This is important in scripts, and many users want it too.
1285: .Pp
1286: To disable TCP keepalive messages, the value should be set to
1287: .Dq no .
1.65 reyk 1288: .It Cm Tunnel
1.95 stevesk 1289: Request
1.65 reyk 1290: .Xr tun 4
1.69 jmc 1291: device forwarding between the client and the server.
1.65 reyk 1292: The argument must be
1.68 reyk 1293: .Dq yes ,
1.95 stevesk 1294: .Dq point-to-point
1295: (layer 3),
1296: .Dq ethernet
1297: (layer 2),
1.65 reyk 1298: or
1299: .Dq no .
1.95 stevesk 1300: Specifying
1301: .Dq yes
1302: requests the default tunnel mode, which is
1303: .Dq point-to-point .
1.65 reyk 1304: The default is
1305: .Dq no .
1306: .It Cm TunnelDevice
1.95 stevesk 1307: Specifies the
1.65 reyk 1308: .Xr tun 4
1.95 stevesk 1309: devices to open on the client
1310: .Pq Ar local_tun
1311: and the server
1312: .Pq Ar remote_tun .
1313: .Pp
1314: The argument must be
1315: .Sm off
1316: .Ar local_tun Op : Ar remote_tun .
1317: .Sm on
1318: The devices may be specified by numerical ID or the keyword
1319: .Dq any ,
1320: which uses the next available tunnel device.
1321: If
1322: .Ar remote_tun
1323: is not specified, it defaults to
1324: .Dq any .
1325: The default is
1326: .Dq any:any .
1.72 jmc 1327: .It Cm UsePrivilegedPort
1328: Specifies whether to use a privileged port for outgoing connections.
1329: The argument must be
1330: .Dq yes
1331: or
1332: .Dq no .
1333: The default is
1334: .Dq no .
1335: If set to
1.84 jmc 1336: .Dq yes ,
1337: .Xr ssh 1
1.72 jmc 1338: must be setuid root.
1339: Note that this option must be set to
1340: .Dq yes
1341: for
1342: .Cm RhostsRSAAuthentication
1343: with older servers.
1.1 stevesk 1344: .It Cm User
1345: Specifies the user to log in as.
1346: This can be useful when a different user name is used on different machines.
1347: This saves the trouble of
1348: having to remember to give the user name on the command line.
1349: .It Cm UserKnownHostsFile
1.151 djm 1350: Specifies one or more files to use for the user
1351: host key database, separated by whitespace.
1352: The default is
1353: .Pa ~/.ssh/known_hosts ,
1354: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1355: .It Cm VerifyHostKeyDNS
1356: Specifies whether to verify the remote key using DNS and SSHFP resource
1357: records.
1.24 jakob 1358: If this option is set to
1359: .Dq yes ,
1.25 jmc 1360: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1361: from DNS.
1362: Insecure fingerprints will be handled as if this option was set to
1363: .Dq ask .
1364: If this option is set to
1365: .Dq ask ,
1366: information on fingerprint match will be displayed, but the user will still
1367: need to confirm new host keys according to the
1368: .Cm StrictHostKeyChecking
1369: option.
1370: The argument must be
1371: .Dq yes ,
1.84 jmc 1372: .Dq no ,
1.25 jmc 1373: or
1374: .Dq ask .
1.8 jakob 1375: The default is
1376: .Dq no .
1.12 jakob 1377: Note that this option applies to protocol version 2 only.
1.84 jmc 1378: .Pp
1.166 jmc 1379: See also VERIFYING HOST KEYS in
1.84 jmc 1380: .Xr ssh 1 .
1.111 grunk 1381: .It Cm VisualHostKey
1382: If this flag is set to
1383: .Dq yes ,
1384: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1385: printed in addition to the hex fingerprint string at login and
1386: for unknown host keys.
1.111 grunk 1387: If this flag is set to
1388: .Dq no ,
1.114 stevesk 1389: no fingerprint strings are printed at login and
1390: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1391: The default is
1392: .Dq no .
1.1 stevesk 1393: .It Cm XAuthLocation
1.5 stevesk 1394: Specifies the full pathname of the
1.1 stevesk 1395: .Xr xauth 1
1396: program.
1397: The default is
1398: .Pa /usr/X11R6/bin/xauth .
1399: .El
1.86 jmc 1400: .Sh PATTERNS
1401: A
1402: .Em pattern
1403: consists of zero or more non-whitespace characters,
1404: .Sq *
1405: (a wildcard that matches zero or more characters),
1406: or
1407: .Sq ?\&
1408: (a wildcard that matches exactly one character).
1409: For example, to specify a set of declarations for any host in the
1410: .Dq .co.uk
1411: set of domains,
1412: the following pattern could be used:
1413: .Pp
1414: .Dl Host *.co.uk
1415: .Pp
1416: The following pattern
1417: would match any host in the 192.168.0.[0-9] network range:
1418: .Pp
1419: .Dl Host 192.168.0.?
1420: .Pp
1421: A
1422: .Em pattern-list
1423: is a comma-separated list of patterns.
1424: Patterns within pattern-lists may be negated
1425: by preceding them with an exclamation mark
1426: .Pq Sq !\& .
1427: For example,
1428: to allow a key to be used from anywhere within an organisation
1429: except from the
1430: .Dq dialup
1431: pool,
1432: the following entry (in authorized_keys) could be used:
1433: .Pp
1434: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1435: .Sh FILES
1436: .Bl -tag -width Ds
1.50 djm 1437: .It Pa ~/.ssh/config
1.1 stevesk 1438: This is the per-user configuration file.
1439: The format of this file is described above.
1.84 jmc 1440: This file is used by the SSH client.
1.30 djm 1441: Because of the potential for abuse, this file must have strict permissions:
1442: read/write for the user, and not accessible by others.
1.1 stevesk 1443: .It Pa /etc/ssh/ssh_config
1444: Systemwide configuration file.
1445: This file provides defaults for those
1446: values that are not specified in the user's configuration file, and
1447: for those users who do not have a configuration file.
1448: This file must be world-readable.
1449: .El
1.13 jmc 1450: .Sh SEE ALSO
1451: .Xr ssh 1
1.1 stevesk 1452: .Sh AUTHORS
1453: OpenSSH is a derivative of the original and free
1454: ssh 1.2.12 release by Tatu Ylonen.
1455: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1456: Theo de Raadt and Dug Song
1457: removed many bugs, re-added newer features and
1458: created OpenSSH.
1459: Markus Friedl contributed the support for SSH
1460: protocol versions 1.5 and 2.0.
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