Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.189
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.
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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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1.189 ! jmc 36: .\" $OpenBSD: ssh_config.5,v 1.188 2014/07/03 06:39:19 djm Exp $
1.188 djm 37: .Dd $Mdocdate: July 3 2014 $
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.
1.178 dtucker 137: Match conditions are specified using one or more keyword/criteria pairs
138: or the single token
139: .Cm all
140: which matches all criteria.
1.169 djm 141: The available keywords are:
1.176 djm 142: .Cm exec ,
1.169 djm 143: .Cm host ,
144: .Cm originalhost ,
145: .Cm user ,
146: and
147: .Cm localuser .
148: .Pp
1.177 jmc 149: The
1.176 djm 150: .Cm exec
1.177 jmc 151: keyword executes the specified command under the user's shell.
1.169 djm 152: If the command returns a zero exit status then the condition is considered true.
153: Commands containing whitespace characters must be quoted.
1.175 djm 154: The following character sequences in the command will be expanded prior to
155: execution:
156: .Ql %L
157: will be substituted by the first component of the local host name,
158: .Ql %l
159: will be substituted by the local host name (including any domain name),
160: .Ql %h
161: will be substituted by the target host name,
162: .Ql %n
163: will be substituted by the original target host name
1.176 djm 164: specified on the command-line,
1.175 djm 165: .Ql %p
166: the destination port,
167: .Ql %r
168: by the remote login username, and
169: .Ql %u
170: by the username of the user running
171: .Xr ssh 1 .
1.169 djm 172: .Pp
173: The other keywords' criteria must be single entries or comma-separated
174: lists and may use the wildcard and negation operators described in the
175: .Sx PATTERNS
176: section.
177: The criteria for the
178: .Cm host
179: keyword are matched against the target hostname, after any substitution
180: by the
181: .Cm Hostname
182: option.
183: The
184: .Cm originalhost
185: keyword matches against the hostname as it was specified on the command-line.
186: The
187: .Cm user
188: keyword matches against the target username on the remote host.
189: The
190: .Cm localuser
191: keyword matches against the name of the local user running
192: .Xr ssh 1
193: (this keyword may be useful in system-wide
194: .Nm
195: files).
1.10 djm 196: .It Cm AddressFamily
1.11 jmc 197: Specifies which address family to use when connecting.
198: Valid arguments are
1.10 djm 199: .Dq any ,
200: .Dq inet
1.84 jmc 201: (use IPv4 only), or
1.10 djm 202: .Dq inet6
1.40 jmc 203: (use IPv6 only).
1.1 stevesk 204: .It Cm BatchMode
205: If set to
206: .Dq yes ,
207: passphrase/password querying will be disabled.
208: This option is useful in scripts and other batch jobs where no user
209: is present to supply the password.
210: The argument must be
211: .Dq yes
212: or
213: .Dq no .
214: The default is
215: .Dq no .
216: .It Cm BindAddress
1.60 dtucker 217: Use the specified address on the local machine as the source address of
1.61 jmc 218: the connection.
219: Only useful on systems with more than one address.
1.1 stevesk 220: Note that this option does not work if
221: .Cm UsePrivilegedPort
222: is set to
223: .Dq yes .
1.171 djm 224: .It Cm CanonicalDomains
1.172 jmc 225: When
1.173 djm 226: .Cm CanonicalizeHostname
1.171 djm 227: is enabled, this option specifies the list of domain suffixes in which to
228: search for the specified destination host.
1.173 djm 229: .It Cm CanonicalizeFallbackLocal
1.174 djm 230: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 231: The default,
1.184 djm 232: .Dq yes ,
1.172 jmc 233: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 234: search rules.
235: A value of
1.184 djm 236: .Dq no
1.171 djm 237: will cause
238: .Xr ssh 1
239: to fail instantly if
1.173 djm 240: .Cm CanonicalizeHostname
1.171 djm 241: is enabled and the target hostname cannot be found in any of the domains
242: specified by
243: .Cm CanonicalDomains .
1.173 djm 244: .It Cm CanonicalizeHostname
1.174 djm 245: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 246: The default,
247: .Dq no ,
1.171 djm 248: is not to perform any name rewriting and let the system resolver handle all
249: hostname lookups.
250: If set to
251: .Dq yes
252: then, for connections that do not use a
253: .Cm ProxyCommand ,
254: .Xr ssh 1
1.173 djm 255: will attempt to canonicalize the hostname specified on the command line
1.171 djm 256: using the
257: .Cm CanonicalDomains
258: suffixes and
1.173 djm 259: .Cm CanonicalizePermittedCNAMEs
1.171 djm 260: rules.
261: If
1.173 djm 262: .Cm CanonicalizeHostname
1.171 djm 263: is set to
264: .Dq always ,
1.174 djm 265: then canonicalization is applied to proxied connections too.
1.185 djm 266: .Pp
267: If this option is enabled and canonicalisation results in the target hostname
268: changing, then the configuration files are processed again using the new
269: target name to pick up any new configuration in matching
270: .Cm Host
271: stanzas.
1.173 djm 272: .It Cm CanonicalizeMaxDots
1.172 jmc 273: Specifies the maximum number of dot characters in a hostname before
1.174 djm 274: canonicalization is disabled.
1.172 jmc 275: The default,
276: .Dq 1 ,
277: allows a single dot (i.e. hostname.subdomain).
1.173 djm 278: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 279: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 280: canonicalizing hostnames.
1.171 djm 281: The rules consist of one or more arguments of
1.172 jmc 282: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 283: where
284: .Ar source_domain_list
1.174 djm 285: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 286: and
287: .Ar target_domain_list
1.172 jmc 288: is a pattern-list of domains that they may resolve to.
1.171 djm 289: .Pp
290: For example,
291: .Dq *.a.example.com:*.b.example.com,*.c.example.com
292: will allow hostnames matching
293: .Dq *.a.example.com
1.173 djm 294: to be canonicalized to names in the
1.171 djm 295: .Dq *.b.example.com
296: or
297: .Dq *.c.example.com
298: domains.
1.1 stevesk 299: .It Cm ChallengeResponseAuthentication
1.82 jmc 300: Specifies whether to use challenge-response authentication.
1.1 stevesk 301: The argument to this keyword must be
302: .Dq yes
303: or
304: .Dq no .
305: The default is
306: .Dq yes .
307: .It Cm CheckHostIP
308: If this flag is set to
309: .Dq yes ,
1.84 jmc 310: .Xr ssh 1
311: will additionally check the host IP address in the
1.1 stevesk 312: .Pa known_hosts
313: file.
314: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 315: If the option is set to
1.1 stevesk 316: .Dq no ,
317: the check will not be executed.
318: The default is
319: .Dq yes .
320: .It Cm Cipher
321: Specifies the cipher to use for encrypting the session
322: in protocol version 1.
323: Currently,
324: .Dq blowfish ,
325: .Dq 3des ,
326: and
327: .Dq des
328: are supported.
329: .Ar des
330: is only supported in the
1.84 jmc 331: .Xr ssh 1
1.1 stevesk 332: client for interoperability with legacy protocol 1 implementations
333: that do not support the
334: .Ar 3des
1.7 jmc 335: cipher.
336: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 337: The default is
338: .Dq 3des .
339: .It Cm Ciphers
340: Specifies the ciphers allowed for protocol version 2
341: in order of preference.
342: Multiple ciphers must be comma-separated.
1.180 djm 343: The supported ciphers are:
344: .Pp
1.186 naddy 345: .Bl -item -compact -offset indent
346: .It
347: 3des-cbc
348: .It
349: aes128-cbc
350: .It
351: aes192-cbc
352: .It
353: aes256-cbc
354: .It
355: aes128-ctr
356: .It
357: aes192-ctr
358: .It
359: aes256-ctr
360: .It
361: aes128-gcm@openssh.com
362: .It
363: aes256-gcm@openssh.com
364: .It
365: arcfour
366: .It
367: arcfour128
368: .It
369: arcfour256
370: .It
371: blowfish-cbc
372: .It
373: cast128-cbc
374: .It
375: chacha20-poly1305@openssh.com
376: .El
1.180 djm 377: .Pp
1.84 jmc 378: The default is:
1.186 naddy 379: .Bd -literal -offset indent
380: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 381: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.180 djm 382: chacha20-poly1305@openssh.com,
1.186 naddy 383: arcfour256,arcfour128,
384: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,
385: aes192-cbc,aes256-cbc,arcfour
1.1 stevesk 386: .Ed
1.180 djm 387: .Pp
388: The list of available ciphers may also be obtained using the
389: .Fl Q
390: option of
391: .Xr ssh 1 .
1.1 stevesk 392: .It Cm ClearAllForwardings
1.84 jmc 393: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 394: specified in the configuration files or on the command line be
1.7 jmc 395: cleared.
396: This option is primarily useful when used from the
1.84 jmc 397: .Xr ssh 1
1.1 stevesk 398: command line to clear port forwardings set in
399: configuration files, and is automatically set by
400: .Xr scp 1
401: and
402: .Xr sftp 1 .
403: The argument must be
404: .Dq yes
405: or
406: .Dq no .
407: The default is
408: .Dq no .
409: .It Cm Compression
410: Specifies whether to use compression.
411: The argument must be
412: .Dq yes
413: or
414: .Dq no .
415: The default is
416: .Dq no .
417: .It Cm CompressionLevel
418: Specifies the compression level to use if compression is enabled.
419: The argument must be an integer from 1 (fast) to 9 (slow, best).
420: The default level is 6, which is good for most applications.
421: The meaning of the values is the same as in
422: .Xr gzip 1 .
423: Note that this option applies to protocol version 1 only.
424: .It Cm ConnectionAttempts
425: Specifies the number of tries (one per second) to make before exiting.
426: The argument must be an integer.
427: This may be useful in scripts if the connection sometimes fails.
428: The default is 1.
1.9 djm 429: .It Cm ConnectTimeout
1.84 jmc 430: Specifies the timeout (in seconds) used when connecting to the
431: SSH server, instead of using the default system TCP timeout.
1.11 jmc 432: This value is used only when the target is down or really unreachable,
433: not when it refuses the connection.
1.36 djm 434: .It Cm ControlMaster
435: Enables the sharing of multiple sessions over a single network connection.
436: When set to
1.84 jmc 437: .Dq yes ,
438: .Xr ssh 1
1.36 djm 439: will listen for connections on a control socket specified using the
440: .Cm ControlPath
441: argument.
442: Additional sessions can connect to this socket using the same
443: .Cm ControlPath
444: with
445: .Cm ControlMaster
446: set to
447: .Dq no
1.38 jmc 448: (the default).
1.64 jmc 449: These sessions will try to reuse the master instance's network connection
1.63 djm 450: rather than initiating new ones, but will fall back to connecting normally
451: if the control socket does not exist, or is not listening.
452: .Pp
1.37 djm 453: Setting this to
454: .Dq ask
1.84 jmc 455: will cause ssh
1.37 djm 456: to listen for control connections, but require confirmation using the
457: .Ev SSH_ASKPASS
458: program before they are accepted (see
459: .Xr ssh-add 1
1.38 jmc 460: for details).
1.51 jakob 461: If the
462: .Cm ControlPath
1.84 jmc 463: cannot be opened,
464: ssh will continue without connecting to a master instance.
1.58 djm 465: .Pp
466: X11 and
1.59 jmc 467: .Xr ssh-agent 1
1.58 djm 468: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 469: display and agent forwarded will be the one belonging to the master
1.59 jmc 470: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 471: .Pp
472: Two additional options allow for opportunistic multiplexing: try to use a
473: master connection but fall back to creating a new one if one does not already
474: exist.
475: These options are:
476: .Dq auto
477: and
478: .Dq autoask .
479: The latter requires confirmation like the
480: .Dq ask
481: option.
1.36 djm 482: .It Cm ControlPath
1.55 djm 483: Specify the path to the control socket used for connection sharing as described
484: in the
1.36 djm 485: .Cm ControlMaster
1.57 djm 486: section above or the string
487: .Dq none
488: to disable connection sharing.
1.55 djm 489: In the path,
1.147 djm 490: .Ql %L
491: will be substituted by the first component of the local host name,
1.77 djm 492: .Ql %l
1.147 djm 493: will be substituted by the local host name (including any domain name),
1.55 djm 494: .Ql %h
495: will be substituted by the target host name,
1.150 jmc 496: .Ql %n
497: will be substituted by the original target host name
498: specified on the command line,
1.55 djm 499: .Ql %p
1.175 djm 500: the destination port,
1.55 djm 501: .Ql %r
1.188 djm 502: by the remote login username,
1.147 djm 503: .Ql %u
504: by the username of the user running
1.188 djm 505: .Xr ssh 1 , and
1.189 ! jmc 506: .Ql \&%C
1.188 djm 507: by a hash of the concatenation: %l%h%p%r.
1.56 djm 508: It is recommended that any
509: .Cm ControlPath
510: used for opportunistic connection sharing include
1.188 djm 511: at least %h, %p, and %r (or alternatively %C).
1.56 djm 512: This ensures that shared connections are uniquely identified.
1.137 djm 513: .It Cm ControlPersist
514: When used in conjunction with
515: .Cm ControlMaster ,
516: specifies that the master connection should remain open
517: in the background (waiting for future client connections)
518: after the initial client connection has been closed.
519: If set to
520: .Dq no ,
521: then the master connection will not be placed into the background,
522: and will close as soon as the initial client connection is closed.
523: If set to
524: .Dq yes ,
525: then the master connection will remain in the background indefinitely
526: (until killed or closed via a mechanism such as the
527: .Xr ssh 1
528: .Dq Fl O No exit
529: option).
530: If set to a time in seconds, or a time in any of the formats documented in
531: .Xr sshd_config 5 ,
532: then the backgrounded master connection will automatically terminate
533: after it has remained idle (with no client connections) for the
534: specified time.
1.38 jmc 535: .It Cm DynamicForward
1.74 jmc 536: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 537: over the secure channel, and the application
538: protocol is then used to determine where to connect to from the
539: remote machine.
1.62 djm 540: .Pp
541: The argument must be
542: .Sm off
543: .Oo Ar bind_address : Oc Ar port .
544: .Sm on
1.138 djm 545: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 546: By default, the local port is bound in accordance with the
547: .Cm GatewayPorts
548: setting.
549: However, an explicit
550: .Ar bind_address
551: may be used to bind the connection to a specific address.
552: The
553: .Ar bind_address
554: of
555: .Dq localhost
556: indicates that the listening port be bound for local use only, while an
557: empty address or
558: .Sq *
559: indicates that the port should be available from all interfaces.
560: .Pp
1.38 jmc 561: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 562: .Xr ssh 1
1.38 jmc 563: will act as a SOCKS server.
564: Multiple forwardings may be specified, and
565: additional forwardings can be given on the command line.
566: Only the superuser can forward privileged ports.
1.14 markus 567: .It Cm EnableSSHKeysign
568: Setting this option to
569: .Dq yes
570: in the global client configuration file
571: .Pa /etc/ssh/ssh_config
572: enables the use of the helper program
573: .Xr ssh-keysign 8
574: during
575: .Cm HostbasedAuthentication .
576: The argument must be
577: .Dq yes
578: or
579: .Dq no .
580: The default is
581: .Dq no .
1.23 jmc 582: This option should be placed in the non-hostspecific section.
1.14 markus 583: See
584: .Xr ssh-keysign 8
585: for more information.
1.1 stevesk 586: .It Cm EscapeChar
587: Sets the escape character (default:
588: .Ql ~ ) .
589: The escape character can also
590: be set on the command line.
591: The argument should be a single character,
592: .Ql ^
593: followed by a letter, or
594: .Dq none
595: to disable the escape
596: character entirely (making the connection transparent for binary
597: data).
1.96 markus 598: .It Cm ExitOnForwardFailure
599: Specifies whether
600: .Xr ssh 1
601: should terminate the connection if it cannot set up all requested
1.102 stevesk 602: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 603: The argument must be
604: .Dq yes
605: or
606: .Dq no .
607: The default is
608: .Dq no .
1.1 stevesk 609: .It Cm ForwardAgent
610: Specifies whether the connection to the authentication agent (if any)
611: will be forwarded to the remote machine.
612: The argument must be
613: .Dq yes
614: or
615: .Dq no .
616: The default is
617: .Dq no .
1.3 stevesk 618: .Pp
1.7 jmc 619: Agent forwarding should be enabled with caution.
620: Users with the ability to bypass file permissions on the remote host
621: (for the agent's Unix-domain socket)
622: can access the local agent through the forwarded connection.
623: An attacker cannot obtain key material from the agent,
1.3 stevesk 624: however they can perform operations on the keys that enable them to
625: authenticate using the identities loaded into the agent.
1.1 stevesk 626: .It Cm ForwardX11
627: Specifies whether X11 connections will be automatically redirected
628: over the secure channel and
629: .Ev DISPLAY
630: set.
631: The argument must be
632: .Dq yes
633: or
634: .Dq no .
635: The default is
636: .Dq no .
1.3 stevesk 637: .Pp
1.7 jmc 638: X11 forwarding should be enabled with caution.
639: Users with the ability to bypass file permissions on the remote host
1.22 markus 640: (for the user's X11 authorization database)
1.7 jmc 641: can access the local X11 display through the forwarded connection.
1.22 markus 642: An attacker may then be able to perform activities such as keystroke monitoring
643: if the
644: .Cm ForwardX11Trusted
645: option is also enabled.
1.134 djm 646: .It Cm ForwardX11Timeout
1.135 jmc 647: Specify a timeout for untrusted X11 forwarding
648: using the format described in the
1.166 jmc 649: TIME FORMATS section of
1.134 djm 650: .Xr sshd_config 5 .
651: X11 connections received by
652: .Xr ssh 1
653: after this time will be refused.
654: The default is to disable untrusted X11 forwarding after twenty minutes has
655: elapsed.
1.22 markus 656: .It Cm ForwardX11Trusted
1.34 jmc 657: If this option is set to
1.84 jmc 658: .Dq yes ,
659: remote X11 clients will have full access to the original X11 display.
1.42 djm 660: .Pp
1.22 markus 661: If this option is set to
1.84 jmc 662: .Dq no ,
663: remote X11 clients will be considered untrusted and prevented
1.22 markus 664: from stealing or tampering with data belonging to trusted X11
665: clients.
1.42 djm 666: Furthermore, the
667: .Xr xauth 1
668: token used for the session will be set to expire after 20 minutes.
669: Remote clients will be refused access after this time.
1.22 markus 670: .Pp
671: The default is
672: .Dq no .
673: .Pp
674: See the X11 SECURITY extension specification for full details on
675: the restrictions imposed on untrusted clients.
1.1 stevesk 676: .It Cm GatewayPorts
677: Specifies whether remote hosts are allowed to connect to local
678: forwarded ports.
679: By default,
1.84 jmc 680: .Xr ssh 1
1.7 jmc 681: binds local port forwardings to the loopback address.
682: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 683: .Cm GatewayPorts
1.84 jmc 684: can be used to specify that ssh
1.1 stevesk 685: should bind local port forwardings to the wildcard address,
686: thus allowing remote hosts to connect to forwarded ports.
687: The argument must be
688: .Dq yes
689: or
690: .Dq no .
691: The default is
692: .Dq no .
693: .It Cm GlobalKnownHostsFile
1.151 djm 694: Specifies one or more files to use for the global
695: host key database, separated by whitespace.
696: The default is
697: .Pa /etc/ssh/ssh_known_hosts ,
698: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 699: .It Cm GSSAPIAuthentication
1.27 markus 700: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 701: The default is
1.21 markus 702: .Dq no .
1.18 markus 703: Note that this option applies to protocol version 2 only.
704: .It Cm GSSAPIDelegateCredentials
705: Forward (delegate) credentials to the server.
706: The default is
707: .Dq no .
708: Note that this option applies to protocol version 2 only.
1.44 djm 709: .It Cm HashKnownHosts
710: Indicates that
1.84 jmc 711: .Xr ssh 1
1.44 djm 712: should hash host names and addresses when they are added to
1.50 djm 713: .Pa ~/.ssh/known_hosts .
1.44 djm 714: These hashed names may be used normally by
1.84 jmc 715: .Xr ssh 1
1.44 djm 716: and
1.84 jmc 717: .Xr sshd 8 ,
1.44 djm 718: but they do not reveal identifying information should the file's contents
719: be disclosed.
720: The default is
721: .Dq no .
1.97 jmc 722: Note that existing names and addresses in known hosts files
723: will not be converted automatically,
724: but may be manually hashed using
1.45 djm 725: .Xr ssh-keygen 1 .
1.1 stevesk 726: .It Cm HostbasedAuthentication
727: Specifies whether to try rhosts based authentication with public key
728: authentication.
729: The argument must be
730: .Dq yes
731: or
732: .Dq no .
733: The default is
734: .Dq no .
735: This option applies to protocol version 2 only and
736: is similar to
737: .Cm RhostsRSAAuthentication .
738: .It Cm HostKeyAlgorithms
739: Specifies the protocol version 2 host key algorithms
740: that the client wants to use in order of preference.
741: The default for this option is:
1.139 djm 742: .Bd -literal -offset 3n
743: ecdsa-sha2-nistp256-cert-v01@openssh.com,
744: ecdsa-sha2-nistp384-cert-v01@openssh.com,
745: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 746: ssh-ed25519-cert-v01@openssh.com,
1.139 djm 747: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
748: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
749: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.182 markus 750: ssh-ed25519,ssh-rsa,ssh-dss
1.139 djm 751: .Ed
1.145 djm 752: .Pp
753: If hostkeys are known for the destination host then this default is modified
754: to prefer their algorithms.
1.1 stevesk 755: .It Cm HostKeyAlias
756: Specifies an alias that should be used instead of the
757: real host name when looking up or saving the host key
758: in the host key database files.
1.84 jmc 759: This option is useful for tunneling SSH connections
1.1 stevesk 760: or for multiple servers running on a single host.
761: .It Cm HostName
762: Specifies the real host name to log into.
763: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 764: If the hostname contains the character sequence
765: .Ql %h ,
1.150 jmc 766: then this will be replaced with the host name specified on the command line
1.136 djm 767: (this is useful for manipulating unqualified names).
1.187 djm 768: The character sequence
769: .Ql %%
770: will be replaced by a single
771: .Ql %
772: character, which may be used when specifying IPv6 link-local addresses.
773: .Pp
1.84 jmc 774: The default is the name given on the command line.
1.1 stevesk 775: Numeric IP addresses are also permitted (both on the command line and in
776: .Cm HostName
777: specifications).
1.29 markus 778: .It Cm IdentitiesOnly
779: Specifies that
1.84 jmc 780: .Xr ssh 1
1.29 markus 781: should only use the authentication identity files configured in the
1.31 jmc 782: .Nm
1.29 markus 783: files,
1.84 jmc 784: even if
785: .Xr ssh-agent 1
1.159 djm 786: or a
787: .Cm PKCS11Provider
1.29 markus 788: offers more identities.
789: The argument to this keyword must be
790: .Dq yes
791: or
792: .Dq no .
1.84 jmc 793: This option is intended for situations where ssh-agent
1.29 markus 794: offers many different identities.
795: The default is
796: .Dq no .
1.67 jmc 797: .It Cm IdentityFile
1.183 naddy 798: Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA authentication
1.139 djm 799: identity is read.
1.67 jmc 800: The default is
801: .Pa ~/.ssh/identity
802: for protocol version 1, and
1.139 djm 803: .Pa ~/.ssh/id_dsa ,
1.183 naddy 804: .Pa ~/.ssh/id_ecdsa ,
805: .Pa ~/.ssh/id_ed25519
1.139 djm 806: and
1.67 jmc 807: .Pa ~/.ssh/id_rsa
808: for protocol version 2.
809: Additionally, any identities represented by the authentication agent
1.165 djm 810: will be used for authentication unless
811: .Cm IdentitiesOnly
812: is set.
1.129 djm 813: .Xr ssh 1
814: will try to load certificate information from the filename obtained by
815: appending
816: .Pa -cert.pub
817: to the path of a specified
818: .Cm IdentityFile .
1.90 djm 819: .Pp
1.67 jmc 820: The file name may use the tilde
1.91 jmc 821: syntax to refer to a user's home directory or one of the following
1.90 djm 822: escape characters:
823: .Ql %d
824: (local user's home directory),
825: .Ql %u
826: (local user name),
827: .Ql %l
828: (local host name),
829: .Ql %h
830: (remote host name) or
1.92 djm 831: .Ql %r
1.90 djm 832: (remote user name).
833: .Pp
1.67 jmc 834: It is possible to have
835: multiple identity files specified in configuration files; all these
836: identities will be tried in sequence.
1.152 djm 837: Multiple
838: .Cm IdentityFile
839: directives will add to the list of identities tried (this behaviour
840: differs from that of other configuration directives).
1.165 djm 841: .Pp
842: .Cm IdentityFile
843: may be used in conjunction with
844: .Cm IdentitiesOnly
845: to select which identities in an agent are offered during authentication.
1.164 jmc 846: .It Cm IgnoreUnknown
847: Specifies a pattern-list of unknown options to be ignored if they are
848: encountered in configuration parsing.
849: This may be used to suppress errors if
850: .Nm
851: contains options that are unrecognised by
852: .Xr ssh 1 .
853: It is recommended that
854: .Cm IgnoreUnknown
855: be listed early in the configuration file as it will not be applied
856: to unknown options that appear before it.
1.143 djm 857: .It Cm IPQoS
858: Specifies the IPv4 type-of-service or DSCP class for connections.
859: Accepted values are
860: .Dq af11 ,
861: .Dq af12 ,
862: .Dq af13 ,
1.154 djm 863: .Dq af21 ,
1.143 djm 864: .Dq af22 ,
865: .Dq af23 ,
866: .Dq af31 ,
867: .Dq af32 ,
868: .Dq af33 ,
869: .Dq af41 ,
870: .Dq af42 ,
871: .Dq af43 ,
872: .Dq cs0 ,
873: .Dq cs1 ,
874: .Dq cs2 ,
875: .Dq cs3 ,
876: .Dq cs4 ,
877: .Dq cs5 ,
878: .Dq cs6 ,
879: .Dq cs7 ,
880: .Dq ef ,
881: .Dq lowdelay ,
882: .Dq throughput ,
883: .Dq reliability ,
884: or a numeric value.
1.146 djm 885: This option may take one or two arguments, separated by whitespace.
1.143 djm 886: If one argument is specified, it is used as the packet class unconditionally.
887: If two values are specified, the first is automatically selected for
888: interactive sessions and the second for non-interactive sessions.
889: The default is
890: .Dq lowdelay
891: for interactive sessions and
892: .Dq throughput
893: for non-interactive sessions.
1.103 djm 894: .It Cm KbdInteractiveAuthentication
895: Specifies whether to use keyboard-interactive authentication.
896: The argument to this keyword must be
897: .Dq yes
898: or
899: .Dq no .
900: The default is
901: .Dq yes .
1.39 djm 902: .It Cm KbdInteractiveDevices
903: Specifies the list of methods to use in keyboard-interactive authentication.
904: Multiple method names must be comma-separated.
905: The default is to use the server specified list.
1.85 jmc 906: The methods available vary depending on what the server supports.
907: For an OpenSSH server,
908: it may be zero or more of:
909: .Dq bsdauth ,
910: .Dq pam ,
911: and
912: .Dq skey .
1.140 djm 913: .It Cm KexAlgorithms
914: Specifies the available KEX (Key Exchange) algorithms.
915: Multiple algorithms must be comma-separated.
1.141 jmc 916: The default is:
917: .Bd -literal -offset indent
1.179 markus 918: curve25519-sha256@libssh.org,
1.141 jmc 919: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
920: diffie-hellman-group-exchange-sha256,
1.186 naddy 921: diffie-hellman-group14-sha1,
1.141 jmc 922: diffie-hellman-group-exchange-sha1,
923: diffie-hellman-group1-sha1
924: .Ed
1.65 reyk 925: .It Cm LocalCommand
926: Specifies a command to execute on the local machine after successfully
927: connecting to the server.
928: The command string extends to the end of the line, and is executed with
1.105 jmc 929: the user's shell.
1.109 dtucker 930: The following escape character substitutions will be performed:
931: .Ql %d
932: (local user's home directory),
933: .Ql %h
934: (remote host name),
935: .Ql %l
936: (local host name),
937: .Ql %n
938: (host name as provided on the command line),
939: .Ql %p
940: (remote port),
941: .Ql %r
942: (remote user name) or
943: .Ql %u
1.188 djm 944: (local user name) or
1.189 ! jmc 945: .Ql \&%C
1.188 djm 946: by a hash of the concatenation: %l%h%p%r.
1.123 djm 947: .Pp
948: The command is run synchronously and does not have access to the
949: session of the
950: .Xr ssh 1
951: that spawned it.
952: It should not be used for interactive commands.
953: .Pp
1.65 reyk 954: This directive is ignored unless
955: .Cm PermitLocalCommand
956: has been enabled.
1.1 stevesk 957: .It Cm LocalForward
1.74 jmc 958: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 959: the secure channel to the specified host and port from the remote machine.
1.49 jmc 960: The first argument must be
1.43 djm 961: .Sm off
1.49 jmc 962: .Oo Ar bind_address : Oc Ar port
1.43 djm 963: .Sm on
1.49 jmc 964: and the second argument must be
965: .Ar host : Ns Ar hostport .
1.138 djm 966: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 967: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 968: given on the command line.
1.1 stevesk 969: Only the superuser can forward privileged ports.
1.43 djm 970: By default, the local port is bound in accordance with the
971: .Cm GatewayPorts
972: setting.
973: However, an explicit
974: .Ar bind_address
975: may be used to bind the connection to a specific address.
976: The
977: .Ar bind_address
978: of
979: .Dq localhost
1.46 jmc 980: indicates that the listening port be bound for local use only, while an
981: empty address or
982: .Sq *
1.43 djm 983: indicates that the port should be available from all interfaces.
1.1 stevesk 984: .It Cm LogLevel
985: Gives the verbosity level that is used when logging messages from
1.84 jmc 986: .Xr ssh 1 .
1.1 stevesk 987: The possible values are:
1.84 jmc 988: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 989: The default is INFO.
990: DEBUG and DEBUG1 are equivalent.
991: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 992: .It Cm MACs
993: Specifies the MAC (message authentication code) algorithms
994: in order of preference.
995: The MAC algorithm is used in protocol version 2
996: for data integrity protection.
997: Multiple algorithms must be comma-separated.
1.160 markus 998: The algorithms that contain
999: .Dq -etm
1000: calculate the MAC after encryption (encrypt-then-mac).
1001: These are considered safer and their use recommended.
1.84 jmc 1002: The default is:
1.101 jmc 1003: .Bd -literal -offset indent
1.160 markus 1004: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1005: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.186 naddy 1006: umac-64@openssh.com,umac-128@openssh.com,
1007: hmac-sha2-256,hmac-sha2-512,
1008: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
1009: hmac-ripemd160-etm@openssh.com,
1010: hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,
1011: hmac-md5,hmac-sha1,hmac-ripemd160,
1.157 naddy 1012: hmac-sha1-96,hmac-md5-96
1.101 jmc 1013: .Ed
1.1 stevesk 1014: .It Cm NoHostAuthenticationForLocalhost
1015: This option can be used if the home directory is shared across machines.
1016: In this case localhost will refer to a different machine on each of
1017: the machines and the user will get many warnings about changed host keys.
1018: However, this option disables host authentication for localhost.
1019: The argument to this keyword must be
1020: .Dq yes
1021: or
1022: .Dq no .
1023: The default is to check the host key for localhost.
1024: .It Cm NumberOfPasswordPrompts
1025: Specifies the number of password prompts before giving up.
1026: The argument to this keyword must be an integer.
1.84 jmc 1027: The default is 3.
1.1 stevesk 1028: .It Cm PasswordAuthentication
1029: Specifies whether to use password authentication.
1030: The argument to this keyword must be
1031: .Dq yes
1032: or
1033: .Dq no .
1034: The default is
1035: .Dq yes .
1.65 reyk 1036: .It Cm PermitLocalCommand
1037: Allow local command execution via the
1038: .Ic LocalCommand
1039: option or using the
1.66 jmc 1040: .Ic !\& Ns Ar command
1.65 reyk 1041: escape sequence in
1042: .Xr ssh 1 .
1043: The argument must be
1044: .Dq yes
1045: or
1046: .Dq no .
1047: The default is
1048: .Dq no .
1.127 markus 1049: .It Cm PKCS11Provider
1050: Specifies which PKCS#11 provider to use.
1.144 jmc 1051: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1052: .Xr ssh 1
1.128 markus 1053: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1054: private RSA key.
1.67 jmc 1055: .It Cm Port
1056: Specifies the port number to connect on the remote host.
1.84 jmc 1057: The default is 22.
1.1 stevesk 1058: .It Cm PreferredAuthentications
1059: Specifies the order in which the client should try protocol 2
1.11 jmc 1060: authentication methods.
1.48 jmc 1061: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1062: .Cm keyboard-interactive )
1.48 jmc 1063: over another method (e.g.\&
1.131 jmc 1064: .Cm password ) .
1065: The default is:
1066: .Bd -literal -offset indent
1067: gssapi-with-mic,hostbased,publickey,
1068: keyboard-interactive,password
1069: .Ed
1.1 stevesk 1070: .It Cm Protocol
1071: Specifies the protocol versions
1.84 jmc 1072: .Xr ssh 1
1.1 stevesk 1073: should support in order of preference.
1074: The possible values are
1.84 jmc 1075: .Sq 1
1.1 stevesk 1076: and
1.84 jmc 1077: .Sq 2 .
1.1 stevesk 1078: Multiple versions must be comma-separated.
1.120 markus 1079: When this option is set to
1.121 jmc 1080: .Dq 2,1
1.120 markus 1081: .Nm ssh
1082: will try version 2 and fall back to version 1
1083: if version 2 is not available.
1.1 stevesk 1084: The default is
1.121 jmc 1085: .Sq 2 .
1.1 stevesk 1086: .It Cm ProxyCommand
1087: Specifies the command to use to connect to the server.
1088: The command
1089: string extends to the end of the line, and is executed with
1.105 jmc 1090: the user's shell.
1.133 jmc 1091: In the command string, any occurrence of
1.1 stevesk 1092: .Ql %h
1093: will be substituted by the host name to
1.132 djm 1094: connect,
1.1 stevesk 1095: .Ql %p
1.133 jmc 1096: by the port, and
1097: .Ql %r
1.132 djm 1098: by the remote user name.
1.1 stevesk 1099: The command can be basically anything,
1100: and should read from its standard input and write to its standard output.
1101: It should eventually connect an
1102: .Xr sshd 8
1103: server running on some machine, or execute
1104: .Ic sshd -i
1105: somewhere.
1106: Host key management will be done using the
1107: HostName of the host being connected (defaulting to the name typed by
1108: the user).
1.7 jmc 1109: Setting the command to
1110: .Dq none
1.6 markus 1111: disables this option entirely.
1.1 stevesk 1112: Note that
1113: .Cm CheckHostIP
1114: is not available for connects with a proxy command.
1.52 djm 1115: .Pp
1116: This directive is useful in conjunction with
1117: .Xr nc 1
1118: and its proxy support.
1.53 jmc 1119: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1120: 192.0.2.0:
1121: .Bd -literal -offset 3n
1122: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1123: .Ed
1.167 djm 1124: .It Cm ProxyUseFdpass
1.168 jmc 1125: Specifies that
1.167 djm 1126: .Cm ProxyCommand
1127: will pass a connected file descriptor back to
1.168 jmc 1128: .Xr ssh 1
1.167 djm 1129: instead of continuing to execute and pass data.
1130: The default is
1131: .Dq no .
1.1 stevesk 1132: .It Cm PubkeyAuthentication
1133: Specifies whether to try public key authentication.
1134: The argument to this keyword must be
1135: .Dq yes
1136: or
1137: .Dq no .
1138: The default is
1139: .Dq yes .
1140: This option applies to protocol version 2 only.
1.75 dtucker 1141: .It Cm RekeyLimit
1142: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1143: session key is renegotiated, optionally followed a maximum amount of
1144: time that may pass before the session key is renegotiated.
1145: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1146: .Sq K ,
1147: .Sq M ,
1.75 dtucker 1148: or
1.76 jmc 1149: .Sq G
1.75 dtucker 1150: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1151: The default is between
1.84 jmc 1152: .Sq 1G
1.75 dtucker 1153: and
1.84 jmc 1154: .Sq 4G ,
1.75 dtucker 1155: depending on the cipher.
1.162 dtucker 1156: The optional second value is specified in seconds and may use any of the
1157: units documented in the
1.166 jmc 1158: TIME FORMATS section of
1.162 dtucker 1159: .Xr sshd_config 5 .
1160: The default value for
1161: .Cm RekeyLimit
1162: is
1163: .Dq default none ,
1164: which means that rekeying is performed after the cipher's default amount
1165: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1166: This option applies to protocol version 2 only.
1.1 stevesk 1167: .It Cm RemoteForward
1.74 jmc 1168: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1169: the secure channel to the specified host and port from the local machine.
1.49 jmc 1170: The first argument must be
1.43 djm 1171: .Sm off
1.49 jmc 1172: .Oo Ar bind_address : Oc Ar port
1.43 djm 1173: .Sm on
1.49 jmc 1174: and the second argument must be
1175: .Ar host : Ns Ar hostport .
1.138 djm 1176: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1177: Multiple forwardings may be specified, and additional
1178: forwardings can be given on the command line.
1.113 stevesk 1179: Privileged ports can be forwarded only when
1180: logging in as root on the remote machine.
1.118 jmc 1181: .Pp
1.117 djm 1182: If the
1183: .Ar port
1184: argument is
1185: .Ql 0 ,
1186: the listen port will be dynamically allocated on the server and reported
1187: to the client at run time.
1.43 djm 1188: .Pp
1189: If the
1190: .Ar bind_address
1191: is not specified, the default is to only bind to loopback addresses.
1192: If the
1193: .Ar bind_address
1194: is
1195: .Ql *
1196: or an empty string, then the forwarding is requested to listen on all
1197: interfaces.
1198: Specifying a remote
1199: .Ar bind_address
1.46 jmc 1200: will only succeed if the server's
1201: .Cm GatewayPorts
1.43 djm 1202: option is enabled (see
1.46 jmc 1203: .Xr sshd_config 5 ) .
1.149 djm 1204: .It Cm RequestTTY
1205: Specifies whether to request a pseudo-tty for the session.
1206: The argument may be one of:
1207: .Dq no
1208: (never request a TTY),
1209: .Dq yes
1210: (always request a TTY when standard input is a TTY),
1211: .Dq force
1212: (always request a TTY) or
1213: .Dq auto
1214: (request a TTY when opening a login session).
1215: This option mirrors the
1216: .Fl t
1217: and
1218: .Fl T
1219: flags for
1220: .Xr ssh 1 .
1.1 stevesk 1221: .It Cm RhostsRSAAuthentication
1222: Specifies whether to try rhosts based authentication with RSA host
1223: authentication.
1224: The argument must be
1225: .Dq yes
1226: or
1227: .Dq no .
1228: The default is
1229: .Dq no .
1230: This option applies to protocol version 1 only and requires
1.84 jmc 1231: .Xr ssh 1
1.1 stevesk 1232: to be setuid root.
1233: .It Cm RSAAuthentication
1234: Specifies whether to try RSA authentication.
1235: The argument to this keyword must be
1236: .Dq yes
1237: or
1238: .Dq no .
1239: RSA authentication will only be
1240: attempted if the identity file exists, or an authentication agent is
1241: running.
1242: The default is
1243: .Dq yes .
1244: Note that this option applies to protocol version 1 only.
1.32 djm 1245: .It Cm SendEnv
1246: Specifies what variables from the local
1247: .Xr environ 7
1248: should be sent to the server.
1.84 jmc 1249: Note that environment passing is only supported for protocol 2.
1250: The server must also support it, and the server must be configured to
1.33 djm 1251: accept these environment variables.
1.32 djm 1252: Refer to
1253: .Cm AcceptEnv
1254: in
1255: .Xr sshd_config 5
1256: for how to configure the server.
1.80 jmc 1257: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1258: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1259: across multiple
1260: .Cm SendEnv
1261: directives.
1262: The default is not to send any environment variables.
1.81 jmc 1263: .Pp
1264: See
1265: .Sx PATTERNS
1266: for more information on patterns.
1.28 markus 1267: .It Cm ServerAliveCountMax
1.73 jmc 1268: Sets the number of server alive messages (see below) which may be
1.28 markus 1269: sent without
1.84 jmc 1270: .Xr ssh 1
1.28 markus 1271: receiving any messages back from the server.
1272: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1273: ssh will disconnect from the server, terminating the session.
1.28 markus 1274: It is important to note that the use of server alive messages is very
1275: different from
1276: .Cm TCPKeepAlive
1277: (below).
1278: The server alive messages are sent through the encrypted channel
1279: and therefore will not be spoofable.
1280: The TCP keepalive option enabled by
1281: .Cm TCPKeepAlive
1282: is spoofable.
1283: The server alive mechanism is valuable when the client or
1284: server depend on knowing when a connection has become inactive.
1285: .Pp
1286: The default value is 3.
1287: If, for example,
1288: .Cm ServerAliveInterval
1.84 jmc 1289: (see below) is set to 15 and
1.28 markus 1290: .Cm ServerAliveCountMax
1.84 jmc 1291: is left at the default, if the server becomes unresponsive,
1292: ssh will disconnect after approximately 45 seconds.
1.89 markus 1293: This option applies to protocol version 2 only.
1.67 jmc 1294: .It Cm ServerAliveInterval
1295: Sets a timeout interval in seconds after which if no data has been received
1296: from the server,
1.84 jmc 1297: .Xr ssh 1
1.67 jmc 1298: will send a message through the encrypted
1299: channel to request a response from the server.
1300: The default
1301: is 0, indicating that these messages will not be sent to the server.
1302: This option applies to protocol version 2 only.
1.1 stevesk 1303: .It Cm StrictHostKeyChecking
1304: If this flag is set to
1305: .Dq yes ,
1.84 jmc 1306: .Xr ssh 1
1.1 stevesk 1307: will never automatically add host keys to the
1.50 djm 1308: .Pa ~/.ssh/known_hosts
1.1 stevesk 1309: file, and refuses to connect to hosts whose host key has changed.
1310: This provides maximum protection against trojan horse attacks,
1.84 jmc 1311: though it can be annoying when the
1.1 stevesk 1312: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1313: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1314: frequently made.
1315: This option forces the user to manually
1316: add all new hosts.
1317: If this flag is set to
1318: .Dq no ,
1.84 jmc 1319: ssh will automatically add new host keys to the
1.1 stevesk 1320: user known hosts files.
1321: If this flag is set to
1322: .Dq ask ,
1323: new host keys
1324: will be added to the user known host files only after the user
1325: has confirmed that is what they really want to do, and
1.84 jmc 1326: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1327: The host keys of
1328: known hosts will be verified automatically in all cases.
1329: The argument must be
1330: .Dq yes ,
1.84 jmc 1331: .Dq no ,
1.1 stevesk 1332: or
1333: .Dq ask .
1334: The default is
1335: .Dq ask .
1.26 markus 1336: .It Cm TCPKeepAlive
1337: Specifies whether the system should send TCP keepalive messages to the
1338: other side.
1339: If they are sent, death of the connection or crash of one
1340: of the machines will be properly noticed.
1341: However, this means that
1342: connections will die if the route is down temporarily, and some people
1343: find it annoying.
1344: .Pp
1345: The default is
1346: .Dq yes
1347: (to send TCP keepalive messages), and the client will notice
1348: if the network goes down or the remote host dies.
1349: This is important in scripts, and many users want it too.
1350: .Pp
1351: To disable TCP keepalive messages, the value should be set to
1352: .Dq no .
1.65 reyk 1353: .It Cm Tunnel
1.95 stevesk 1354: Request
1.65 reyk 1355: .Xr tun 4
1.69 jmc 1356: device forwarding between the client and the server.
1.65 reyk 1357: The argument must be
1.68 reyk 1358: .Dq yes ,
1.95 stevesk 1359: .Dq point-to-point
1360: (layer 3),
1361: .Dq ethernet
1362: (layer 2),
1.65 reyk 1363: or
1364: .Dq no .
1.95 stevesk 1365: Specifying
1366: .Dq yes
1367: requests the default tunnel mode, which is
1368: .Dq point-to-point .
1.65 reyk 1369: The default is
1370: .Dq no .
1371: .It Cm TunnelDevice
1.95 stevesk 1372: Specifies the
1.65 reyk 1373: .Xr tun 4
1.95 stevesk 1374: devices to open on the client
1375: .Pq Ar local_tun
1376: and the server
1377: .Pq Ar remote_tun .
1378: .Pp
1379: The argument must be
1380: .Sm off
1381: .Ar local_tun Op : Ar remote_tun .
1382: .Sm on
1383: The devices may be specified by numerical ID or the keyword
1384: .Dq any ,
1385: which uses the next available tunnel device.
1386: If
1387: .Ar remote_tun
1388: is not specified, it defaults to
1389: .Dq any .
1390: The default is
1391: .Dq any:any .
1.72 jmc 1392: .It Cm UsePrivilegedPort
1393: Specifies whether to use a privileged port for outgoing connections.
1394: The argument must be
1395: .Dq yes
1396: or
1397: .Dq no .
1398: The default is
1399: .Dq no .
1400: If set to
1.84 jmc 1401: .Dq yes ,
1402: .Xr ssh 1
1.72 jmc 1403: must be setuid root.
1404: Note that this option must be set to
1405: .Dq yes
1406: for
1407: .Cm RhostsRSAAuthentication
1408: with older servers.
1.1 stevesk 1409: .It Cm User
1410: Specifies the user to log in as.
1411: This can be useful when a different user name is used on different machines.
1412: This saves the trouble of
1413: having to remember to give the user name on the command line.
1414: .It Cm UserKnownHostsFile
1.151 djm 1415: Specifies one or more files to use for the user
1416: host key database, separated by whitespace.
1417: The default is
1418: .Pa ~/.ssh/known_hosts ,
1419: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1420: .It Cm VerifyHostKeyDNS
1421: Specifies whether to verify the remote key using DNS and SSHFP resource
1422: records.
1.24 jakob 1423: If this option is set to
1424: .Dq yes ,
1.25 jmc 1425: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1426: from DNS.
1427: Insecure fingerprints will be handled as if this option was set to
1428: .Dq ask .
1429: If this option is set to
1430: .Dq ask ,
1431: information on fingerprint match will be displayed, but the user will still
1432: need to confirm new host keys according to the
1433: .Cm StrictHostKeyChecking
1434: option.
1435: The argument must be
1436: .Dq yes ,
1.84 jmc 1437: .Dq no ,
1.25 jmc 1438: or
1439: .Dq ask .
1.8 jakob 1440: The default is
1441: .Dq no .
1.12 jakob 1442: Note that this option applies to protocol version 2 only.
1.84 jmc 1443: .Pp
1.166 jmc 1444: See also VERIFYING HOST KEYS in
1.84 jmc 1445: .Xr ssh 1 .
1.111 grunk 1446: .It Cm VisualHostKey
1447: If this flag is set to
1448: .Dq yes ,
1449: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1450: printed in addition to the hex fingerprint string at login and
1451: for unknown host keys.
1.111 grunk 1452: If this flag is set to
1453: .Dq no ,
1.114 stevesk 1454: no fingerprint strings are printed at login and
1455: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1456: The default is
1457: .Dq no .
1.1 stevesk 1458: .It Cm XAuthLocation
1.5 stevesk 1459: Specifies the full pathname of the
1.1 stevesk 1460: .Xr xauth 1
1461: program.
1462: The default is
1463: .Pa /usr/X11R6/bin/xauth .
1464: .El
1.86 jmc 1465: .Sh PATTERNS
1466: A
1467: .Em pattern
1468: consists of zero or more non-whitespace characters,
1469: .Sq *
1470: (a wildcard that matches zero or more characters),
1471: or
1472: .Sq ?\&
1473: (a wildcard that matches exactly one character).
1474: For example, to specify a set of declarations for any host in the
1475: .Dq .co.uk
1476: set of domains,
1477: the following pattern could be used:
1478: .Pp
1479: .Dl Host *.co.uk
1480: .Pp
1481: The following pattern
1482: would match any host in the 192.168.0.[0-9] network range:
1483: .Pp
1484: .Dl Host 192.168.0.?
1485: .Pp
1486: A
1487: .Em pattern-list
1488: is a comma-separated list of patterns.
1489: Patterns within pattern-lists may be negated
1490: by preceding them with an exclamation mark
1491: .Pq Sq !\& .
1492: For example,
1.174 djm 1493: to allow a key to be used from anywhere within an organization
1.86 jmc 1494: except from the
1495: .Dq dialup
1496: pool,
1497: the following entry (in authorized_keys) could be used:
1498: .Pp
1499: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1500: .Sh FILES
1501: .Bl -tag -width Ds
1.50 djm 1502: .It Pa ~/.ssh/config
1.1 stevesk 1503: This is the per-user configuration file.
1504: The format of this file is described above.
1.84 jmc 1505: This file is used by the SSH client.
1.30 djm 1506: Because of the potential for abuse, this file must have strict permissions:
1507: read/write for the user, and not accessible by others.
1.1 stevesk 1508: .It Pa /etc/ssh/ssh_config
1509: Systemwide configuration file.
1510: This file provides defaults for those
1511: values that are not specified in the user's configuration file, and
1512: for those users who do not have a configuration file.
1513: This file must be world-readable.
1514: .El
1.13 jmc 1515: .Sh SEE ALSO
1516: .Xr ssh 1
1.1 stevesk 1517: .Sh AUTHORS
1518: OpenSSH is a derivative of the original and free
1519: ssh 1.2.12 release by Tatu Ylonen.
1520: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1521: Theo de Raadt and Dug Song
1522: removed many bugs, re-added newer features and
1523: created OpenSSH.
1524: Markus Friedl contributed the support for SSH
1525: protocol versions 1.5 and 2.0.
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