Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.216
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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1.216 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.215 2015/08/14 15:32:41 jmc Exp $
! 37: .Dd $Mdocdate: August 14 2015 $
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.
1.193 djm 68: The matched host name is usually the one given on the command line
69: (see the
70: .Cm CanonicalizeHostname
71: option for exceptions.)
1.1 stevesk 72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 jmc 76: .Pp
1.1 stevesk 77: The configuration file has the following format:
78: .Pp
79: Empty lines and lines starting with
80: .Ql #
81: are comments.
82: Otherwise a line is of the format
83: .Dq keyword arguments .
84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
1.87 jmc 90: .Nm scp ,
1.1 stevesk 91: and
92: .Nm sftp
93: .Fl o
94: option.
1.88 dtucker 95: Arguments may optionally be enclosed in double quotes
96: .Pq \&"
97: in order to represent arguments containing spaces.
1.1 stevesk 98: .Pp
99: The possible
100: keywords and their meanings are as follows (note that
101: keywords are case-insensitive and arguments are case-sensitive):
102: .Bl -tag -width Ds
103: .It Cm Host
104: Restricts the following declarations (up to the next
105: .Cm Host
1.169 djm 106: or
107: .Cm Match
1.1 stevesk 108: keyword) to be only for those hosts that match one of the patterns
109: given after the keyword.
1.112 krw 110: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 111: A single
1.83 jmc 112: .Ql *
1.1 stevesk 113: as a pattern can be used to provide global
114: defaults for all hosts.
1.193 djm 115: The host is usually the
1.1 stevesk 116: .Ar hostname
1.193 djm 117: argument given on the command line
118: (see the
119: .Cm CanonicalizeHostname
120: option for exceptions.)
1.148 djm 121: .Pp
122: A pattern entry may be negated by prefixing it with an exclamation mark
123: .Pq Sq !\& .
124: If a negated entry is matched, then the
125: .Cm Host
126: entry is ignored, regardless of whether any other patterns on the line
127: match.
128: Negated matches are therefore useful to provide exceptions for wildcard
129: matches.
1.81 jmc 130: .Pp
131: See
132: .Sx PATTERNS
133: for more information on patterns.
1.170 jmc 134: .It Cm Match
1.169 djm 135: Restricts the following declarations (up to the next
136: .Cm Host
137: or
138: .Cm Match
139: keyword) to be used only when the conditions following the
140: .Cm Match
141: keyword are satisfied.
1.193 djm 142: Match conditions are specified using one or more critera
1.178 dtucker 143: or the single token
144: .Cm all
1.193 djm 145: which always matches.
146: The available criteria keywords are:
147: .Cm canonical ,
1.176 djm 148: .Cm exec ,
1.169 djm 149: .Cm host ,
150: .Cm originalhost ,
151: .Cm user ,
152: and
153: .Cm localuser .
1.193 djm 154: The
155: .Cm all
156: criteria must appear alone or immediately after
1.194 jmc 157: .Cm canonical .
1.193 djm 158: Other criteria may be combined arbitrarily.
159: All criteria but
160: .Cm all
161: and
162: .Cm canonical
163: require an argument.
164: Criteria may be negated by prepending an exclamation mark
165: .Pq Sq !\& .
1.169 djm 166: .Pp
1.177 jmc 167: The
1.193 djm 168: .Cm canonical
1.210 dtucker 169: keyword matches only when the configuration file is being re-parsed
1.193 djm 170: after hostname canonicalization (see the
171: .Cm CanonicalizeHostname
172: option.)
173: This may be useful to specify conditions that work with canonical host
174: names only.
175: The
1.176 djm 176: .Cm exec
1.177 jmc 177: keyword executes the specified command under the user's shell.
1.169 djm 178: If the command returns a zero exit status then the condition is considered true.
179: Commands containing whitespace characters must be quoted.
1.175 djm 180: The following character sequences in the command will be expanded prior to
181: execution:
182: .Ql %L
183: will be substituted by the first component of the local host name,
184: .Ql %l
185: will be substituted by the local host name (including any domain name),
186: .Ql %h
187: will be substituted by the target host name,
188: .Ql %n
189: will be substituted by the original target host name
1.176 djm 190: specified on the command-line,
1.175 djm 191: .Ql %p
192: the destination port,
193: .Ql %r
194: by the remote login username, and
195: .Ql %u
196: by the username of the user running
197: .Xr ssh 1 .
1.169 djm 198: .Pp
199: The other keywords' criteria must be single entries or comma-separated
200: lists and may use the wildcard and negation operators described in the
201: .Sx PATTERNS
202: section.
203: The criteria for the
204: .Cm host
205: keyword are matched against the target hostname, after any substitution
206: by the
207: .Cm Hostname
1.193 djm 208: or
209: .Cm CanonicalizeHostname
210: options.
1.169 djm 211: The
212: .Cm originalhost
213: keyword matches against the hostname as it was specified on the command-line.
214: The
215: .Cm user
216: keyword matches against the target username on the remote host.
217: The
218: .Cm localuser
219: keyword matches against the name of the local user running
220: .Xr ssh 1
221: (this keyword may be useful in system-wide
222: .Nm
223: files).
1.10 djm 224: .It Cm AddressFamily
1.11 jmc 225: Specifies which address family to use when connecting.
226: Valid arguments are
1.10 djm 227: .Dq any ,
228: .Dq inet
1.84 jmc 229: (use IPv4 only), or
1.10 djm 230: .Dq inet6
1.40 jmc 231: (use IPv6 only).
1.1 stevesk 232: .It Cm BatchMode
233: If set to
234: .Dq yes ,
235: passphrase/password querying will be disabled.
236: This option is useful in scripts and other batch jobs where no user
237: is present to supply the password.
238: The argument must be
239: .Dq yes
240: or
241: .Dq no .
242: The default is
243: .Dq no .
244: .It Cm BindAddress
1.60 dtucker 245: Use the specified address on the local machine as the source address of
1.61 jmc 246: the connection.
247: Only useful on systems with more than one address.
1.1 stevesk 248: Note that this option does not work if
249: .Cm UsePrivilegedPort
250: is set to
251: .Dq yes .
1.171 djm 252: .It Cm CanonicalDomains
1.172 jmc 253: When
1.173 djm 254: .Cm CanonicalizeHostname
1.171 djm 255: is enabled, this option specifies the list of domain suffixes in which to
256: search for the specified destination host.
1.173 djm 257: .It Cm CanonicalizeFallbackLocal
1.174 djm 258: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 259: The default,
1.184 djm 260: .Dq yes ,
1.172 jmc 261: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 262: search rules.
263: A value of
1.184 djm 264: .Dq no
1.171 djm 265: will cause
266: .Xr ssh 1
267: to fail instantly if
1.173 djm 268: .Cm CanonicalizeHostname
1.171 djm 269: is enabled and the target hostname cannot be found in any of the domains
270: specified by
271: .Cm CanonicalDomains .
1.173 djm 272: .It Cm CanonicalizeHostname
1.174 djm 273: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 274: The default,
275: .Dq no ,
1.171 djm 276: is not to perform any name rewriting and let the system resolver handle all
277: hostname lookups.
278: If set to
279: .Dq yes
280: then, for connections that do not use a
281: .Cm ProxyCommand ,
282: .Xr ssh 1
1.173 djm 283: will attempt to canonicalize the hostname specified on the command line
1.171 djm 284: using the
285: .Cm CanonicalDomains
286: suffixes and
1.173 djm 287: .Cm CanonicalizePermittedCNAMEs
1.171 djm 288: rules.
289: If
1.173 djm 290: .Cm CanonicalizeHostname
1.171 djm 291: is set to
292: .Dq always ,
1.174 djm 293: then canonicalization is applied to proxied connections too.
1.185 djm 294: .Pp
1.193 djm 295: If this option is enabled, then the configuration files are processed
296: again using the new target name to pick up any new configuration in matching
1.185 djm 297: .Cm Host
1.193 djm 298: and
299: .Cm Match
1.185 djm 300: stanzas.
1.173 djm 301: .It Cm CanonicalizeMaxDots
1.172 jmc 302: Specifies the maximum number of dot characters in a hostname before
1.174 djm 303: canonicalization is disabled.
1.172 jmc 304: The default,
305: .Dq 1 ,
306: allows a single dot (i.e. hostname.subdomain).
1.173 djm 307: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 308: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 309: canonicalizing hostnames.
1.171 djm 310: The rules consist of one or more arguments of
1.172 jmc 311: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 312: where
313: .Ar source_domain_list
1.174 djm 314: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 315: and
316: .Ar target_domain_list
1.172 jmc 317: is a pattern-list of domains that they may resolve to.
1.171 djm 318: .Pp
319: For example,
320: .Dq *.a.example.com:*.b.example.com,*.c.example.com
321: will allow hostnames matching
322: .Dq *.a.example.com
1.173 djm 323: to be canonicalized to names in the
1.171 djm 324: .Dq *.b.example.com
325: or
326: .Dq *.c.example.com
327: domains.
1.1 stevesk 328: .It Cm ChallengeResponseAuthentication
1.82 jmc 329: Specifies whether to use challenge-response authentication.
1.1 stevesk 330: The argument to this keyword must be
331: .Dq yes
332: or
333: .Dq no .
334: The default is
335: .Dq yes .
336: .It Cm CheckHostIP
337: If this flag is set to
338: .Dq yes ,
1.84 jmc 339: .Xr ssh 1
340: will additionally check the host IP address in the
1.1 stevesk 341: .Pa known_hosts
342: file.
1.211 djm 343: This allows ssh to detect if a host key changed due to DNS spoofing
344: and will add addresses of destination hosts to
345: .Pa ~/.ssh/known_hosts
346: in the process, regardless of the setting of
347: .Cm StrictHostKeyChecking .
1.107 grunk 348: If the option is set to
1.1 stevesk 349: .Dq no ,
350: the check will not be executed.
351: The default is
352: .Dq yes .
353: .It Cm Cipher
354: Specifies the cipher to use for encrypting the session
355: in protocol version 1.
356: Currently,
357: .Dq blowfish ,
358: .Dq 3des ,
359: and
360: .Dq des
361: are supported.
362: .Ar des
363: is only supported in the
1.84 jmc 364: .Xr ssh 1
1.1 stevesk 365: client for interoperability with legacy protocol 1 implementations
366: that do not support the
367: .Ar 3des
1.7 jmc 368: cipher.
369: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 370: The default is
371: .Dq 3des .
372: .It Cm Ciphers
373: Specifies the ciphers allowed for protocol version 2
374: in order of preference.
375: Multiple ciphers must be comma-separated.
1.214 djm 376: If the specified value begins with a
377: .Sq +
378: character, then the specified ciphers will be appended to the default set
379: instead of replacing them.
380: .Pp
1.180 djm 381: The supported ciphers are:
382: .Pp
1.186 naddy 383: .Bl -item -compact -offset indent
384: .It
385: 3des-cbc
386: .It
387: aes128-cbc
388: .It
389: aes192-cbc
390: .It
391: aes256-cbc
392: .It
393: aes128-ctr
394: .It
395: aes192-ctr
396: .It
397: aes256-ctr
398: .It
399: aes128-gcm@openssh.com
400: .It
401: aes256-gcm@openssh.com
402: .It
403: arcfour
404: .It
405: arcfour128
406: .It
407: arcfour256
408: .It
409: blowfish-cbc
410: .It
411: cast128-cbc
412: .It
413: chacha20-poly1305@openssh.com
414: .El
1.180 djm 415: .Pp
1.84 jmc 416: The default is:
1.186 naddy 417: .Bd -literal -offset indent
1.215 jmc 418: chacha20-poly1305@openssh.com,
1.186 naddy 419: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 420: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.186 naddy 421: arcfour256,arcfour128,
422: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,
423: aes192-cbc,aes256-cbc,arcfour
1.1 stevesk 424: .Ed
1.180 djm 425: .Pp
426: The list of available ciphers may also be obtained using the
427: .Fl Q
428: option of
1.198 djm 429: .Xr ssh 1
430: with an argument of
431: .Dq cipher .
1.1 stevesk 432: .It Cm ClearAllForwardings
1.84 jmc 433: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 434: specified in the configuration files or on the command line be
1.7 jmc 435: cleared.
436: This option is primarily useful when used from the
1.84 jmc 437: .Xr ssh 1
1.1 stevesk 438: command line to clear port forwardings set in
439: configuration files, and is automatically set by
440: .Xr scp 1
441: and
442: .Xr sftp 1 .
443: The argument must be
444: .Dq yes
445: or
446: .Dq no .
447: The default is
448: .Dq no .
449: .It Cm Compression
450: Specifies whether to use compression.
451: The argument must be
452: .Dq yes
453: or
454: .Dq no .
455: The default is
456: .Dq no .
457: .It Cm CompressionLevel
458: Specifies the compression level to use if compression is enabled.
459: The argument must be an integer from 1 (fast) to 9 (slow, best).
460: The default level is 6, which is good for most applications.
461: The meaning of the values is the same as in
462: .Xr gzip 1 .
463: Note that this option applies to protocol version 1 only.
464: .It Cm ConnectionAttempts
465: Specifies the number of tries (one per second) to make before exiting.
466: The argument must be an integer.
467: This may be useful in scripts if the connection sometimes fails.
468: The default is 1.
1.9 djm 469: .It Cm ConnectTimeout
1.84 jmc 470: Specifies the timeout (in seconds) used when connecting to the
471: SSH server, instead of using the default system TCP timeout.
1.11 jmc 472: This value is used only when the target is down or really unreachable,
473: not when it refuses the connection.
1.36 djm 474: .It Cm ControlMaster
475: Enables the sharing of multiple sessions over a single network connection.
476: When set to
1.84 jmc 477: .Dq yes ,
478: .Xr ssh 1
1.36 djm 479: will listen for connections on a control socket specified using the
480: .Cm ControlPath
481: argument.
482: Additional sessions can connect to this socket using the same
483: .Cm ControlPath
484: with
485: .Cm ControlMaster
486: set to
487: .Dq no
1.38 jmc 488: (the default).
1.64 jmc 489: These sessions will try to reuse the master instance's network connection
1.63 djm 490: rather than initiating new ones, but will fall back to connecting normally
491: if the control socket does not exist, or is not listening.
492: .Pp
1.37 djm 493: Setting this to
494: .Dq ask
1.84 jmc 495: will cause ssh
1.206 jmc 496: to listen for control connections, but require confirmation using
497: .Xr ssh-askpass 1 .
1.51 jakob 498: If the
499: .Cm ControlPath
1.84 jmc 500: cannot be opened,
501: ssh will continue without connecting to a master instance.
1.58 djm 502: .Pp
503: X11 and
1.59 jmc 504: .Xr ssh-agent 1
1.58 djm 505: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 506: display and agent forwarded will be the one belonging to the master
1.59 jmc 507: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 508: .Pp
509: Two additional options allow for opportunistic multiplexing: try to use a
510: master connection but fall back to creating a new one if one does not already
511: exist.
512: These options are:
513: .Dq auto
514: and
515: .Dq autoask .
516: The latter requires confirmation like the
517: .Dq ask
518: option.
1.36 djm 519: .It Cm ControlPath
1.55 djm 520: Specify the path to the control socket used for connection sharing as described
521: in the
1.36 djm 522: .Cm ControlMaster
1.57 djm 523: section above or the string
524: .Dq none
525: to disable connection sharing.
1.55 djm 526: In the path,
1.147 djm 527: .Ql %L
528: will be substituted by the first component of the local host name,
1.77 djm 529: .Ql %l
1.147 djm 530: will be substituted by the local host name (including any domain name),
1.55 djm 531: .Ql %h
532: will be substituted by the target host name,
1.150 jmc 533: .Ql %n
534: will be substituted by the original target host name
535: specified on the command line,
1.55 djm 536: .Ql %p
1.175 djm 537: the destination port,
1.55 djm 538: .Ql %r
1.188 djm 539: by the remote login username,
1.147 djm 540: .Ql %u
541: by the username of the user running
1.188 djm 542: .Xr ssh 1 , and
1.189 jmc 543: .Ql \&%C
1.188 djm 544: by a hash of the concatenation: %l%h%p%r.
1.56 djm 545: It is recommended that any
546: .Cm ControlPath
547: used for opportunistic connection sharing include
1.195 djm 548: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
549: that is not writable by other users.
1.56 djm 550: This ensures that shared connections are uniquely identified.
1.137 djm 551: .It Cm ControlPersist
552: When used in conjunction with
553: .Cm ControlMaster ,
554: specifies that the master connection should remain open
555: in the background (waiting for future client connections)
556: after the initial client connection has been closed.
557: If set to
558: .Dq no ,
559: then the master connection will not be placed into the background,
560: and will close as soon as the initial client connection is closed.
561: If set to
1.195 djm 562: .Dq yes
563: or
564: .Dq 0 ,
1.137 djm 565: then the master connection will remain in the background indefinitely
566: (until killed or closed via a mechanism such as the
567: .Xr ssh 1
568: .Dq Fl O No exit
569: option).
570: If set to a time in seconds, or a time in any of the formats documented in
571: .Xr sshd_config 5 ,
572: then the backgrounded master connection will automatically terminate
573: after it has remained idle (with no client connections) for the
574: specified time.
1.38 jmc 575: .It Cm DynamicForward
1.74 jmc 576: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 577: over the secure channel, and the application
578: protocol is then used to determine where to connect to from the
579: remote machine.
1.62 djm 580: .Pp
581: The argument must be
582: .Sm off
583: .Oo Ar bind_address : Oc Ar port .
584: .Sm on
1.138 djm 585: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 586: By default, the local port is bound in accordance with the
587: .Cm GatewayPorts
588: setting.
589: However, an explicit
590: .Ar bind_address
591: may be used to bind the connection to a specific address.
592: The
593: .Ar bind_address
594: of
595: .Dq localhost
596: indicates that the listening port be bound for local use only, while an
597: empty address or
598: .Sq *
599: indicates that the port should be available from all interfaces.
600: .Pp
1.38 jmc 601: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 602: .Xr ssh 1
1.38 jmc 603: will act as a SOCKS server.
604: Multiple forwardings may be specified, and
605: additional forwardings can be given on the command line.
606: Only the superuser can forward privileged ports.
1.14 markus 607: .It Cm EnableSSHKeysign
608: Setting this option to
609: .Dq yes
610: in the global client configuration file
611: .Pa /etc/ssh/ssh_config
612: enables the use of the helper program
613: .Xr ssh-keysign 8
614: during
615: .Cm HostbasedAuthentication .
616: The argument must be
617: .Dq yes
618: or
619: .Dq no .
620: The default is
621: .Dq no .
1.23 jmc 622: This option should be placed in the non-hostspecific section.
1.14 markus 623: See
624: .Xr ssh-keysign 8
625: for more information.
1.1 stevesk 626: .It Cm EscapeChar
627: Sets the escape character (default:
628: .Ql ~ ) .
629: The escape character can also
630: be set on the command line.
631: The argument should be a single character,
632: .Ql ^
633: followed by a letter, or
634: .Dq none
635: to disable the escape
636: character entirely (making the connection transparent for binary
637: data).
1.96 markus 638: .It Cm ExitOnForwardFailure
639: Specifies whether
640: .Xr ssh 1
641: should terminate the connection if it cannot set up all requested
1.216 ! djm 642: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
! 643: if either end is unable to bind and listen on a specified port.)
! 644: Note that
! 645: .Cm ExitOnForwardFailure
! 646: does not apply to connections made over port forwardings and will not,
! 647: for example, cause
! 648: .Xr ssh 1
! 649: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 650: The argument must be
651: .Dq yes
652: or
653: .Dq no .
654: The default is
655: .Dq no .
1.197 djm 656: .It Cm FingerprintHash
657: Specifies the hash algorithm used when displaying key fingerprints.
658: Valid options are:
659: .Dq md5
660: and
661: .Dq sha256 .
662: The default is
663: .Dq sha256 .
1.1 stevesk 664: .It Cm ForwardAgent
665: Specifies whether the connection to the authentication agent (if any)
666: will be forwarded to the remote machine.
667: The argument must be
668: .Dq yes
669: or
670: .Dq no .
671: The default is
672: .Dq no .
1.3 stevesk 673: .Pp
1.7 jmc 674: Agent forwarding should be enabled with caution.
675: Users with the ability to bypass file permissions on the remote host
676: (for the agent's Unix-domain socket)
677: can access the local agent through the forwarded connection.
678: An attacker cannot obtain key material from the agent,
1.3 stevesk 679: however they can perform operations on the keys that enable them to
680: authenticate using the identities loaded into the agent.
1.1 stevesk 681: .It Cm ForwardX11
682: Specifies whether X11 connections will be automatically redirected
683: over the secure channel and
684: .Ev DISPLAY
685: set.
686: The argument must be
687: .Dq yes
688: or
689: .Dq no .
690: The default is
691: .Dq no .
1.3 stevesk 692: .Pp
1.7 jmc 693: X11 forwarding should be enabled with caution.
694: Users with the ability to bypass file permissions on the remote host
1.22 markus 695: (for the user's X11 authorization database)
1.7 jmc 696: can access the local X11 display through the forwarded connection.
1.22 markus 697: An attacker may then be able to perform activities such as keystroke monitoring
698: if the
699: .Cm ForwardX11Trusted
700: option is also enabled.
1.134 djm 701: .It Cm ForwardX11Timeout
1.135 jmc 702: Specify a timeout for untrusted X11 forwarding
703: using the format described in the
1.166 jmc 704: TIME FORMATS section of
1.134 djm 705: .Xr sshd_config 5 .
706: X11 connections received by
707: .Xr ssh 1
708: after this time will be refused.
709: The default is to disable untrusted X11 forwarding after twenty minutes has
710: elapsed.
1.22 markus 711: .It Cm ForwardX11Trusted
1.34 jmc 712: If this option is set to
1.84 jmc 713: .Dq yes ,
714: remote X11 clients will have full access to the original X11 display.
1.42 djm 715: .Pp
1.22 markus 716: If this option is set to
1.84 jmc 717: .Dq no ,
718: remote X11 clients will be considered untrusted and prevented
1.22 markus 719: from stealing or tampering with data belonging to trusted X11
720: clients.
1.42 djm 721: Furthermore, the
722: .Xr xauth 1
723: token used for the session will be set to expire after 20 minutes.
724: Remote clients will be refused access after this time.
1.22 markus 725: .Pp
726: The default is
727: .Dq no .
728: .Pp
729: See the X11 SECURITY extension specification for full details on
730: the restrictions imposed on untrusted clients.
1.1 stevesk 731: .It Cm GatewayPorts
732: Specifies whether remote hosts are allowed to connect to local
733: forwarded ports.
734: By default,
1.84 jmc 735: .Xr ssh 1
1.7 jmc 736: binds local port forwardings to the loopback address.
737: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 738: .Cm GatewayPorts
1.84 jmc 739: can be used to specify that ssh
1.1 stevesk 740: should bind local port forwardings to the wildcard address,
741: thus allowing remote hosts to connect to forwarded ports.
742: The argument must be
743: .Dq yes
744: or
745: .Dq no .
746: The default is
747: .Dq no .
748: .It Cm GlobalKnownHostsFile
1.151 djm 749: Specifies one or more files to use for the global
750: host key database, separated by whitespace.
751: The default is
752: .Pa /etc/ssh/ssh_known_hosts ,
753: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 754: .It Cm GSSAPIAuthentication
1.27 markus 755: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 756: The default is
1.21 markus 757: .Dq no .
1.18 markus 758: Note that this option applies to protocol version 2 only.
759: .It Cm GSSAPIDelegateCredentials
760: Forward (delegate) credentials to the server.
761: The default is
762: .Dq no .
763: Note that this option applies to protocol version 2 only.
1.44 djm 764: .It Cm HashKnownHosts
765: Indicates that
1.84 jmc 766: .Xr ssh 1
1.44 djm 767: should hash host names and addresses when they are added to
1.50 djm 768: .Pa ~/.ssh/known_hosts .
1.44 djm 769: These hashed names may be used normally by
1.84 jmc 770: .Xr ssh 1
1.44 djm 771: and
1.84 jmc 772: .Xr sshd 8 ,
1.44 djm 773: but they do not reveal identifying information should the file's contents
774: be disclosed.
775: The default is
776: .Dq no .
1.97 jmc 777: Note that existing names and addresses in known hosts files
778: will not be converted automatically,
779: but may be manually hashed using
1.45 djm 780: .Xr ssh-keygen 1 .
1.1 stevesk 781: .It Cm HostbasedAuthentication
782: Specifies whether to try rhosts based authentication with public key
783: authentication.
784: The argument must be
785: .Dq yes
786: or
787: .Dq no .
788: The default is
789: .Dq no .
790: This option applies to protocol version 2 only and
791: is similar to
792: .Cm RhostsRSAAuthentication .
1.202 djm 793: .It Cm HostbasedKeyTypes
794: Specifies the key types that will be used for hostbased authentication
795: as a comma-separated pattern list.
1.214 djm 796: Alternately if the specified value begins with a
797: .Sq +
798: character, then the specified key types will be appended to the default set
799: instead of replacing them.
1.213 markus 800: The default for this option is:
801: .Bd -literal -offset 3n
802: ecdsa-sha2-nistp256-cert-v01@openssh.com,
803: ecdsa-sha2-nistp384-cert-v01@openssh.com,
804: ecdsa-sha2-nistp521-cert-v01@openssh.com,
805: ssh-ed25519-cert-v01@openssh.com,
806: ssh-rsa-cert-v01@openssh.com,
807: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
808: ssh-ed25519,ssh-rsa
809: .Ed
810: .Pp
1.202 djm 811: The
812: .Fl Q
813: option of
814: .Xr ssh 1
815: may be used to list supported key types.
1.1 stevesk 816: .It Cm HostKeyAlgorithms
817: Specifies the protocol version 2 host key algorithms
818: that the client wants to use in order of preference.
1.214 djm 819: Alternately if the specified value begins with a
820: .Sq +
821: character, then the specified key types will be appended to the default set
822: instead of replacing them.
1.1 stevesk 823: The default for this option is:
1.139 djm 824: .Bd -literal -offset 3n
825: ecdsa-sha2-nistp256-cert-v01@openssh.com,
826: ecdsa-sha2-nistp384-cert-v01@openssh.com,
827: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 828: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 829: ssh-rsa-cert-v01@openssh.com,
1.139 djm 830: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.213 markus 831: ssh-ed25519,ssh-rsa
1.139 djm 832: .Ed
1.145 djm 833: .Pp
834: If hostkeys are known for the destination host then this default is modified
835: to prefer their algorithms.
1.198 djm 836: .Pp
837: The list of available key types may also be obtained using the
838: .Fl Q
839: option of
840: .Xr ssh 1
841: with an argument of
842: .Dq key .
1.1 stevesk 843: .It Cm HostKeyAlias
844: Specifies an alias that should be used instead of the
845: real host name when looking up or saving the host key
846: in the host key database files.
1.84 jmc 847: This option is useful for tunneling SSH connections
1.1 stevesk 848: or for multiple servers running on a single host.
849: .It Cm HostName
850: Specifies the real host name to log into.
851: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 852: If the hostname contains the character sequence
853: .Ql %h ,
1.150 jmc 854: then this will be replaced with the host name specified on the command line
1.136 djm 855: (this is useful for manipulating unqualified names).
1.187 djm 856: The character sequence
857: .Ql %%
858: will be replaced by a single
859: .Ql %
860: character, which may be used when specifying IPv6 link-local addresses.
861: .Pp
1.84 jmc 862: The default is the name given on the command line.
1.1 stevesk 863: Numeric IP addresses are also permitted (both on the command line and in
864: .Cm HostName
865: specifications).
1.29 markus 866: .It Cm IdentitiesOnly
867: Specifies that
1.84 jmc 868: .Xr ssh 1
1.29 markus 869: should only use the authentication identity files configured in the
1.31 jmc 870: .Nm
1.29 markus 871: files,
1.84 jmc 872: even if
873: .Xr ssh-agent 1
1.159 djm 874: or a
875: .Cm PKCS11Provider
1.29 markus 876: offers more identities.
877: The argument to this keyword must be
878: .Dq yes
879: or
880: .Dq no .
1.84 jmc 881: This option is intended for situations where ssh-agent
1.29 markus 882: offers many different identities.
883: The default is
884: .Dq no .
1.67 jmc 885: .It Cm IdentityFile
1.192 sobrado 886: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 887: identity is read.
1.67 jmc 888: The default is
889: .Pa ~/.ssh/identity
890: for protocol version 1, and
1.139 djm 891: .Pa ~/.ssh/id_dsa ,
1.183 naddy 892: .Pa ~/.ssh/id_ecdsa ,
893: .Pa ~/.ssh/id_ed25519
1.139 djm 894: and
1.67 jmc 895: .Pa ~/.ssh/id_rsa
896: for protocol version 2.
897: Additionally, any identities represented by the authentication agent
1.165 djm 898: will be used for authentication unless
899: .Cm IdentitiesOnly
900: is set.
1.129 djm 901: .Xr ssh 1
902: will try to load certificate information from the filename obtained by
903: appending
904: .Pa -cert.pub
905: to the path of a specified
906: .Cm IdentityFile .
1.90 djm 907: .Pp
1.67 jmc 908: The file name may use the tilde
1.91 jmc 909: syntax to refer to a user's home directory or one of the following
1.90 djm 910: escape characters:
911: .Ql %d
912: (local user's home directory),
913: .Ql %u
914: (local user name),
915: .Ql %l
916: (local host name),
917: .Ql %h
918: (remote host name) or
1.92 djm 919: .Ql %r
1.90 djm 920: (remote user name).
921: .Pp
1.67 jmc 922: It is possible to have
923: multiple identity files specified in configuration files; all these
924: identities will be tried in sequence.
1.152 djm 925: Multiple
926: .Cm IdentityFile
927: directives will add to the list of identities tried (this behaviour
928: differs from that of other configuration directives).
1.165 djm 929: .Pp
930: .Cm IdentityFile
931: may be used in conjunction with
932: .Cm IdentitiesOnly
933: to select which identities in an agent are offered during authentication.
1.164 jmc 934: .It Cm IgnoreUnknown
935: Specifies a pattern-list of unknown options to be ignored if they are
936: encountered in configuration parsing.
937: This may be used to suppress errors if
938: .Nm
939: contains options that are unrecognised by
940: .Xr ssh 1 .
941: It is recommended that
942: .Cm IgnoreUnknown
943: be listed early in the configuration file as it will not be applied
944: to unknown options that appear before it.
1.143 djm 945: .It Cm IPQoS
946: Specifies the IPv4 type-of-service or DSCP class for connections.
947: Accepted values are
948: .Dq af11 ,
949: .Dq af12 ,
950: .Dq af13 ,
1.154 djm 951: .Dq af21 ,
1.143 djm 952: .Dq af22 ,
953: .Dq af23 ,
954: .Dq af31 ,
955: .Dq af32 ,
956: .Dq af33 ,
957: .Dq af41 ,
958: .Dq af42 ,
959: .Dq af43 ,
960: .Dq cs0 ,
961: .Dq cs1 ,
962: .Dq cs2 ,
963: .Dq cs3 ,
964: .Dq cs4 ,
965: .Dq cs5 ,
966: .Dq cs6 ,
967: .Dq cs7 ,
968: .Dq ef ,
969: .Dq lowdelay ,
970: .Dq throughput ,
971: .Dq reliability ,
972: or a numeric value.
1.146 djm 973: This option may take one or two arguments, separated by whitespace.
1.143 djm 974: If one argument is specified, it is used as the packet class unconditionally.
975: If two values are specified, the first is automatically selected for
976: interactive sessions and the second for non-interactive sessions.
977: The default is
978: .Dq lowdelay
979: for interactive sessions and
980: .Dq throughput
981: for non-interactive sessions.
1.103 djm 982: .It Cm KbdInteractiveAuthentication
983: Specifies whether to use keyboard-interactive authentication.
984: The argument to this keyword must be
985: .Dq yes
986: or
987: .Dq no .
988: The default is
989: .Dq yes .
1.39 djm 990: .It Cm KbdInteractiveDevices
991: Specifies the list of methods to use in keyboard-interactive authentication.
992: Multiple method names must be comma-separated.
993: The default is to use the server specified list.
1.85 jmc 994: The methods available vary depending on what the server supports.
995: For an OpenSSH server,
996: it may be zero or more of:
997: .Dq bsdauth ,
998: .Dq pam ,
999: and
1000: .Dq skey .
1.140 djm 1001: .It Cm KexAlgorithms
1002: Specifies the available KEX (Key Exchange) algorithms.
1003: Multiple algorithms must be comma-separated.
1.214 djm 1004: Alternately if the specified value begins with a
1005: .Sq +
1006: character, then the specified methods will be appended to the default set
1007: instead of replacing them.
1.141 jmc 1008: The default is:
1009: .Bd -literal -offset indent
1.179 markus 1010: curve25519-sha256@libssh.org,
1.141 jmc 1011: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1012: diffie-hellman-group-exchange-sha256,
1.209 dtucker 1013: diffie-hellman-group-exchange-sha1,
1.212 djm 1014: diffie-hellman-group14-sha1
1.141 jmc 1015: .Ed
1.198 djm 1016: .Pp
1017: The list of available key exchange algorithms may also be obtained using the
1018: .Fl Q
1019: option of
1020: .Xr ssh 1
1021: with an argument of
1022: .Dq kex .
1.65 reyk 1023: .It Cm LocalCommand
1024: Specifies a command to execute on the local machine after successfully
1025: connecting to the server.
1026: The command string extends to the end of the line, and is executed with
1.105 jmc 1027: the user's shell.
1.109 dtucker 1028: The following escape character substitutions will be performed:
1029: .Ql %d
1030: (local user's home directory),
1031: .Ql %h
1032: (remote host name),
1033: .Ql %l
1034: (local host name),
1035: .Ql %n
1036: (host name as provided on the command line),
1037: .Ql %p
1038: (remote port),
1039: .Ql %r
1040: (remote user name) or
1041: .Ql %u
1.188 djm 1042: (local user name) or
1.189 jmc 1043: .Ql \&%C
1.188 djm 1044: by a hash of the concatenation: %l%h%p%r.
1.123 djm 1045: .Pp
1046: The command is run synchronously and does not have access to the
1047: session of the
1048: .Xr ssh 1
1049: that spawned it.
1050: It should not be used for interactive commands.
1051: .Pp
1.65 reyk 1052: This directive is ignored unless
1053: .Cm PermitLocalCommand
1054: has been enabled.
1.1 stevesk 1055: .It Cm LocalForward
1.74 jmc 1056: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1057: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1058: The first argument must be
1.43 djm 1059: .Sm off
1.49 jmc 1060: .Oo Ar bind_address : Oc Ar port
1.43 djm 1061: .Sm on
1.49 jmc 1062: and the second argument must be
1063: .Ar host : Ns Ar hostport .
1.138 djm 1064: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1065: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1066: given on the command line.
1.1 stevesk 1067: Only the superuser can forward privileged ports.
1.43 djm 1068: By default, the local port is bound in accordance with the
1069: .Cm GatewayPorts
1070: setting.
1071: However, an explicit
1072: .Ar bind_address
1073: may be used to bind the connection to a specific address.
1074: The
1075: .Ar bind_address
1076: of
1077: .Dq localhost
1.46 jmc 1078: indicates that the listening port be bound for local use only, while an
1079: empty address or
1080: .Sq *
1.43 djm 1081: indicates that the port should be available from all interfaces.
1.1 stevesk 1082: .It Cm LogLevel
1083: Gives the verbosity level that is used when logging messages from
1.84 jmc 1084: .Xr ssh 1 .
1.1 stevesk 1085: The possible values are:
1.84 jmc 1086: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1087: The default is INFO.
1088: DEBUG and DEBUG1 are equivalent.
1089: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1090: .It Cm MACs
1091: Specifies the MAC (message authentication code) algorithms
1092: in order of preference.
1093: The MAC algorithm is used in protocol version 2
1094: for data integrity protection.
1095: Multiple algorithms must be comma-separated.
1.214 djm 1096: If the specified value begins with a
1097: .Sq +
1098: character, then the specified algorithms will be appended to the default set
1099: instead of replacing them.
1100: .Pp
1.160 markus 1101: The algorithms that contain
1102: .Dq -etm
1103: calculate the MAC after encryption (encrypt-then-mac).
1104: These are considered safer and their use recommended.
1.214 djm 1105: .Pp
1.84 jmc 1106: The default is:
1.101 jmc 1107: .Bd -literal -offset indent
1.160 markus 1108: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1109: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.186 naddy 1110: umac-64@openssh.com,umac-128@openssh.com,
1111: hmac-sha2-256,hmac-sha2-512,
1112: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
1113: hmac-ripemd160-etm@openssh.com,
1114: hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,
1115: hmac-md5,hmac-sha1,hmac-ripemd160,
1.157 naddy 1116: hmac-sha1-96,hmac-md5-96
1.101 jmc 1117: .Ed
1.198 djm 1118: .Pp
1119: The list of available MAC algorithms may also be obtained using the
1120: .Fl Q
1121: option of
1122: .Xr ssh 1
1123: with an argument of
1124: .Dq mac .
1.1 stevesk 1125: .It Cm NoHostAuthenticationForLocalhost
1126: This option can be used if the home directory is shared across machines.
1127: In this case localhost will refer to a different machine on each of
1128: the machines and the user will get many warnings about changed host keys.
1129: However, this option disables host authentication for localhost.
1130: The argument to this keyword must be
1131: .Dq yes
1132: or
1133: .Dq no .
1134: The default is to check the host key for localhost.
1135: .It Cm NumberOfPasswordPrompts
1136: Specifies the number of password prompts before giving up.
1137: The argument to this keyword must be an integer.
1.84 jmc 1138: The default is 3.
1.1 stevesk 1139: .It Cm PasswordAuthentication
1140: Specifies whether to use password authentication.
1141: The argument to this keyword must be
1142: .Dq yes
1143: or
1144: .Dq no .
1145: The default is
1146: .Dq yes .
1.65 reyk 1147: .It Cm PermitLocalCommand
1148: Allow local command execution via the
1149: .Ic LocalCommand
1150: option or using the
1.66 jmc 1151: .Ic !\& Ns Ar command
1.65 reyk 1152: escape sequence in
1153: .Xr ssh 1 .
1154: The argument must be
1155: .Dq yes
1156: or
1157: .Dq no .
1158: The default is
1159: .Dq no .
1.127 markus 1160: .It Cm PKCS11Provider
1161: Specifies which PKCS#11 provider to use.
1.144 jmc 1162: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1163: .Xr ssh 1
1.128 markus 1164: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1165: private RSA key.
1.67 jmc 1166: .It Cm Port
1167: Specifies the port number to connect on the remote host.
1.84 jmc 1168: The default is 22.
1.1 stevesk 1169: .It Cm PreferredAuthentications
1170: Specifies the order in which the client should try protocol 2
1.11 jmc 1171: authentication methods.
1.48 jmc 1172: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1173: .Cm keyboard-interactive )
1.48 jmc 1174: over another method (e.g.\&
1.131 jmc 1175: .Cm password ) .
1176: The default is:
1177: .Bd -literal -offset indent
1178: gssapi-with-mic,hostbased,publickey,
1179: keyboard-interactive,password
1180: .Ed
1.1 stevesk 1181: .It Cm Protocol
1182: Specifies the protocol versions
1.84 jmc 1183: .Xr ssh 1
1.1 stevesk 1184: should support in order of preference.
1185: The possible values are
1.84 jmc 1186: .Sq 1
1.1 stevesk 1187: and
1.84 jmc 1188: .Sq 2 .
1.1 stevesk 1189: Multiple versions must be comma-separated.
1.120 markus 1190: When this option is set to
1.121 jmc 1191: .Dq 2,1
1.120 markus 1192: .Nm ssh
1193: will try version 2 and fall back to version 1
1194: if version 2 is not available.
1.1 stevesk 1195: The default is
1.121 jmc 1196: .Sq 2 .
1.1 stevesk 1197: .It Cm ProxyCommand
1198: Specifies the command to use to connect to the server.
1199: The command
1.190 djm 1200: string extends to the end of the line, and is executed
1201: using the user's shell
1202: .Ql exec
1203: directive to avoid a lingering shell process.
1204: .Pp
1.133 jmc 1205: In the command string, any occurrence of
1.1 stevesk 1206: .Ql %h
1207: will be substituted by the host name to
1.132 djm 1208: connect,
1.1 stevesk 1209: .Ql %p
1.133 jmc 1210: by the port, and
1211: .Ql %r
1.132 djm 1212: by the remote user name.
1.1 stevesk 1213: The command can be basically anything,
1214: and should read from its standard input and write to its standard output.
1215: It should eventually connect an
1216: .Xr sshd 8
1217: server running on some machine, or execute
1218: .Ic sshd -i
1219: somewhere.
1220: Host key management will be done using the
1221: HostName of the host being connected (defaulting to the name typed by
1222: the user).
1.7 jmc 1223: Setting the command to
1224: .Dq none
1.6 markus 1225: disables this option entirely.
1.1 stevesk 1226: Note that
1227: .Cm CheckHostIP
1228: is not available for connects with a proxy command.
1.52 djm 1229: .Pp
1230: This directive is useful in conjunction with
1231: .Xr nc 1
1232: and its proxy support.
1.53 jmc 1233: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1234: 192.0.2.0:
1235: .Bd -literal -offset 3n
1236: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1237: .Ed
1.167 djm 1238: .It Cm ProxyUseFdpass
1.168 jmc 1239: Specifies that
1.167 djm 1240: .Cm ProxyCommand
1241: will pass a connected file descriptor back to
1.168 jmc 1242: .Xr ssh 1
1.167 djm 1243: instead of continuing to execute and pass data.
1244: The default is
1245: .Dq no .
1.213 markus 1246: .It Cm PubkeyAcceptedKeyTypes
1247: Specifies the key types that will be used for public key authentication
1248: as a comma-separated pattern list.
1.214 djm 1249: Alternately if the specified value begins with a
1250: .Sq +
1251: character, then the key types after it will be appended to the default
1252: instead of replacing it.
1.213 markus 1253: The default for this option is:
1254: .Bd -literal -offset 3n
1255: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1256: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1257: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1258: ssh-ed25519-cert-v01@openssh.com,
1259: ssh-rsa-cert-v01@openssh.com,
1260: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1261: ssh-ed25519,ssh-rsa
1262: .Ed
1263: .Pp
1264: The
1265: .Fl Q
1266: option of
1267: .Xr ssh 1
1268: may be used to list supported key types.
1.1 stevesk 1269: .It Cm PubkeyAuthentication
1270: Specifies whether to try public key authentication.
1271: The argument to this keyword must be
1272: .Dq yes
1273: or
1274: .Dq no .
1275: The default is
1276: .Dq yes .
1277: This option applies to protocol version 2 only.
1.75 dtucker 1278: .It Cm RekeyLimit
1279: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1280: session key is renegotiated, optionally followed a maximum amount of
1281: time that may pass before the session key is renegotiated.
1282: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1283: .Sq K ,
1284: .Sq M ,
1.75 dtucker 1285: or
1.76 jmc 1286: .Sq G
1.75 dtucker 1287: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1288: The default is between
1.84 jmc 1289: .Sq 1G
1.75 dtucker 1290: and
1.84 jmc 1291: .Sq 4G ,
1.75 dtucker 1292: depending on the cipher.
1.162 dtucker 1293: The optional second value is specified in seconds and may use any of the
1294: units documented in the
1.166 jmc 1295: TIME FORMATS section of
1.162 dtucker 1296: .Xr sshd_config 5 .
1297: The default value for
1298: .Cm RekeyLimit
1299: is
1300: .Dq default none ,
1301: which means that rekeying is performed after the cipher's default amount
1302: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1303: This option applies to protocol version 2 only.
1.1 stevesk 1304: .It Cm RemoteForward
1.74 jmc 1305: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1306: the secure channel to the specified host and port from the local machine.
1.49 jmc 1307: The first argument must be
1.43 djm 1308: .Sm off
1.49 jmc 1309: .Oo Ar bind_address : Oc Ar port
1.43 djm 1310: .Sm on
1.49 jmc 1311: and the second argument must be
1312: .Ar host : Ns Ar hostport .
1.138 djm 1313: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1314: Multiple forwardings may be specified, and additional
1315: forwardings can be given on the command line.
1.113 stevesk 1316: Privileged ports can be forwarded only when
1317: logging in as root on the remote machine.
1.118 jmc 1318: .Pp
1.117 djm 1319: If the
1320: .Ar port
1321: argument is
1322: .Ql 0 ,
1323: the listen port will be dynamically allocated on the server and reported
1324: to the client at run time.
1.43 djm 1325: .Pp
1326: If the
1327: .Ar bind_address
1328: is not specified, the default is to only bind to loopback addresses.
1329: If the
1330: .Ar bind_address
1331: is
1332: .Ql *
1333: or an empty string, then the forwarding is requested to listen on all
1334: interfaces.
1335: Specifying a remote
1336: .Ar bind_address
1.46 jmc 1337: will only succeed if the server's
1338: .Cm GatewayPorts
1.43 djm 1339: option is enabled (see
1.46 jmc 1340: .Xr sshd_config 5 ) .
1.149 djm 1341: .It Cm RequestTTY
1342: Specifies whether to request a pseudo-tty for the session.
1343: The argument may be one of:
1344: .Dq no
1345: (never request a TTY),
1346: .Dq yes
1347: (always request a TTY when standard input is a TTY),
1348: .Dq force
1349: (always request a TTY) or
1350: .Dq auto
1351: (request a TTY when opening a login session).
1352: This option mirrors the
1353: .Fl t
1354: and
1355: .Fl T
1356: flags for
1357: .Xr ssh 1 .
1.196 djm 1358: .It Cm RevokedHostKeys
1359: Specifies revoked host public keys.
1360: Keys listed in this file will be refused for host authentication.
1361: Note that if this file does not exist or is not readable,
1362: then host authentication will be refused for all hosts.
1363: Keys may be specified as a text file, listing one public key per line, or as
1364: an OpenSSH Key Revocation List (KRL) as generated by
1365: .Xr ssh-keygen 1 .
1366: For more information on KRLs, see the KEY REVOCATION LISTS section in
1367: .Xr ssh-keygen 1 .
1.1 stevesk 1368: .It Cm RhostsRSAAuthentication
1369: Specifies whether to try rhosts based authentication with RSA host
1370: authentication.
1371: The argument must be
1372: .Dq yes
1373: or
1374: .Dq no .
1375: The default is
1376: .Dq no .
1377: This option applies to protocol version 1 only and requires
1.84 jmc 1378: .Xr ssh 1
1.1 stevesk 1379: to be setuid root.
1380: .It Cm RSAAuthentication
1381: Specifies whether to try RSA authentication.
1382: The argument to this keyword must be
1383: .Dq yes
1384: or
1385: .Dq no .
1386: RSA authentication will only be
1387: attempted if the identity file exists, or an authentication agent is
1388: running.
1389: The default is
1390: .Dq yes .
1391: Note that this option applies to protocol version 1 only.
1.32 djm 1392: .It Cm SendEnv
1393: Specifies what variables from the local
1394: .Xr environ 7
1395: should be sent to the server.
1.84 jmc 1396: Note that environment passing is only supported for protocol 2.
1397: The server must also support it, and the server must be configured to
1.33 djm 1398: accept these environment variables.
1.207 dtucker 1399: Note that the
1400: .Ev TERM
1.208 jmc 1401: environment variable is always sent whenever a
1.207 dtucker 1402: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1403: Refer to
1404: .Cm AcceptEnv
1405: in
1406: .Xr sshd_config 5
1407: for how to configure the server.
1.80 jmc 1408: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1409: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1410: across multiple
1411: .Cm SendEnv
1412: directives.
1413: The default is not to send any environment variables.
1.81 jmc 1414: .Pp
1415: See
1416: .Sx PATTERNS
1417: for more information on patterns.
1.28 markus 1418: .It Cm ServerAliveCountMax
1.73 jmc 1419: Sets the number of server alive messages (see below) which may be
1.28 markus 1420: sent without
1.84 jmc 1421: .Xr ssh 1
1.28 markus 1422: receiving any messages back from the server.
1423: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1424: ssh will disconnect from the server, terminating the session.
1.28 markus 1425: It is important to note that the use of server alive messages is very
1426: different from
1427: .Cm TCPKeepAlive
1428: (below).
1429: The server alive messages are sent through the encrypted channel
1430: and therefore will not be spoofable.
1431: The TCP keepalive option enabled by
1432: .Cm TCPKeepAlive
1433: is spoofable.
1434: The server alive mechanism is valuable when the client or
1435: server depend on knowing when a connection has become inactive.
1436: .Pp
1437: The default value is 3.
1438: If, for example,
1439: .Cm ServerAliveInterval
1.84 jmc 1440: (see below) is set to 15 and
1.28 markus 1441: .Cm ServerAliveCountMax
1.84 jmc 1442: is left at the default, if the server becomes unresponsive,
1443: ssh will disconnect after approximately 45 seconds.
1.89 markus 1444: This option applies to protocol version 2 only.
1.67 jmc 1445: .It Cm ServerAliveInterval
1446: Sets a timeout interval in seconds after which if no data has been received
1447: from the server,
1.84 jmc 1448: .Xr ssh 1
1.67 jmc 1449: will send a message through the encrypted
1450: channel to request a response from the server.
1451: The default
1452: is 0, indicating that these messages will not be sent to the server.
1453: This option applies to protocol version 2 only.
1.191 millert 1454: .It Cm StreamLocalBindMask
1455: Sets the octal file creation mode mask
1456: .Pq umask
1457: used when creating a Unix-domain socket file for local or remote
1458: port forwarding.
1459: This option is only used for port forwarding to a Unix-domain socket file.
1460: .Pp
1461: The default value is 0177, which creates a Unix-domain socket file that is
1462: readable and writable only by the owner.
1463: Note that not all operating systems honor the file mode on Unix-domain
1464: socket files.
1465: .It Cm StreamLocalBindUnlink
1466: Specifies whether to remove an existing Unix-domain socket file for local
1467: or remote port forwarding before creating a new one.
1468: If the socket file already exists and
1469: .Cm StreamLocalBindUnlink
1470: is not enabled,
1471: .Nm ssh
1472: will be unable to forward the port to the Unix-domain socket file.
1473: This option is only used for port forwarding to a Unix-domain socket file.
1474: .Pp
1475: The argument must be
1476: .Dq yes
1477: or
1478: .Dq no .
1479: The default is
1480: .Dq no .
1.1 stevesk 1481: .It Cm StrictHostKeyChecking
1482: If this flag is set to
1483: .Dq yes ,
1.84 jmc 1484: .Xr ssh 1
1.1 stevesk 1485: will never automatically add host keys to the
1.50 djm 1486: .Pa ~/.ssh/known_hosts
1.1 stevesk 1487: file, and refuses to connect to hosts whose host key has changed.
1488: This provides maximum protection against trojan horse attacks,
1.84 jmc 1489: though it can be annoying when the
1.1 stevesk 1490: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1491: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1492: frequently made.
1493: This option forces the user to manually
1494: add all new hosts.
1495: If this flag is set to
1496: .Dq no ,
1.84 jmc 1497: ssh will automatically add new host keys to the
1.1 stevesk 1498: user known hosts files.
1499: If this flag is set to
1500: .Dq ask ,
1501: new host keys
1502: will be added to the user known host files only after the user
1503: has confirmed that is what they really want to do, and
1.84 jmc 1504: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1505: The host keys of
1506: known hosts will be verified automatically in all cases.
1507: The argument must be
1508: .Dq yes ,
1.84 jmc 1509: .Dq no ,
1.1 stevesk 1510: or
1511: .Dq ask .
1512: The default is
1513: .Dq ask .
1.26 markus 1514: .It Cm TCPKeepAlive
1515: Specifies whether the system should send TCP keepalive messages to the
1516: other side.
1517: If they are sent, death of the connection or crash of one
1518: of the machines will be properly noticed.
1519: However, this means that
1520: connections will die if the route is down temporarily, and some people
1521: find it annoying.
1522: .Pp
1523: The default is
1524: .Dq yes
1525: (to send TCP keepalive messages), and the client will notice
1526: if the network goes down or the remote host dies.
1527: This is important in scripts, and many users want it too.
1528: .Pp
1529: To disable TCP keepalive messages, the value should be set to
1530: .Dq no .
1.65 reyk 1531: .It Cm Tunnel
1.95 stevesk 1532: Request
1.65 reyk 1533: .Xr tun 4
1.69 jmc 1534: device forwarding between the client and the server.
1.65 reyk 1535: The argument must be
1.68 reyk 1536: .Dq yes ,
1.95 stevesk 1537: .Dq point-to-point
1538: (layer 3),
1539: .Dq ethernet
1540: (layer 2),
1.65 reyk 1541: or
1542: .Dq no .
1.95 stevesk 1543: Specifying
1544: .Dq yes
1545: requests the default tunnel mode, which is
1546: .Dq point-to-point .
1.65 reyk 1547: The default is
1548: .Dq no .
1549: .It Cm TunnelDevice
1.95 stevesk 1550: Specifies the
1.65 reyk 1551: .Xr tun 4
1.95 stevesk 1552: devices to open on the client
1553: .Pq Ar local_tun
1554: and the server
1555: .Pq Ar remote_tun .
1556: .Pp
1557: The argument must be
1558: .Sm off
1559: .Ar local_tun Op : Ar remote_tun .
1560: .Sm on
1561: The devices may be specified by numerical ID or the keyword
1562: .Dq any ,
1563: which uses the next available tunnel device.
1564: If
1565: .Ar remote_tun
1566: is not specified, it defaults to
1567: .Dq any .
1568: The default is
1569: .Dq any:any .
1.201 djm 1570: .It Cm UpdateHostKeys
1.200 djm 1571: Specifies whether
1572: .Xr ssh 1
1573: should accept notifications of additional hostkeys from the server sent
1574: after authentication has completed and add them to
1575: .Cm UserKnownHostsFile .
1576: The argument must be
1.204 djm 1577: .Dq yes ,
1.203 djm 1578: .Dq no
1.204 djm 1579: (the default) or
1580: .Dq ask .
1.200 djm 1581: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1582: and supports graceful key rotation by allowing a server to send replacement
1583: public keys before old ones are removed.
1.200 djm 1584: Additional hostkeys are only accepted if the key used to authenticate the
1585: host was already trusted or explicity accepted by the user.
1.204 djm 1586: If
1587: .Cm UpdateHostKeys
1588: is set to
1589: .Dq ask ,
1590: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1591: Confirmation is currently incompatible with
1592: .Cm ControlPersist ,
1593: and will be disabled if it is enabled.
1.200 djm 1594: .Pp
1595: Presently, only
1596: .Xr sshd 8
1597: from OpenSSH 6.8 and greater support the
1598: .Dq hostkeys@openssh.com
1599: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1600: .It Cm UsePrivilegedPort
1601: Specifies whether to use a privileged port for outgoing connections.
1602: The argument must be
1603: .Dq yes
1604: or
1605: .Dq no .
1606: The default is
1607: .Dq no .
1608: If set to
1.84 jmc 1609: .Dq yes ,
1610: .Xr ssh 1
1.72 jmc 1611: must be setuid root.
1612: Note that this option must be set to
1613: .Dq yes
1614: for
1615: .Cm RhostsRSAAuthentication
1616: with older servers.
1.1 stevesk 1617: .It Cm User
1618: Specifies the user to log in as.
1619: This can be useful when a different user name is used on different machines.
1620: This saves the trouble of
1621: having to remember to give the user name on the command line.
1622: .It Cm UserKnownHostsFile
1.151 djm 1623: Specifies one or more files to use for the user
1624: host key database, separated by whitespace.
1625: The default is
1626: .Pa ~/.ssh/known_hosts ,
1627: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1628: .It Cm VerifyHostKeyDNS
1629: Specifies whether to verify the remote key using DNS and SSHFP resource
1630: records.
1.24 jakob 1631: If this option is set to
1632: .Dq yes ,
1.25 jmc 1633: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1634: from DNS.
1635: Insecure fingerprints will be handled as if this option was set to
1636: .Dq ask .
1637: If this option is set to
1638: .Dq ask ,
1639: information on fingerprint match will be displayed, but the user will still
1640: need to confirm new host keys according to the
1641: .Cm StrictHostKeyChecking
1642: option.
1643: The argument must be
1644: .Dq yes ,
1.84 jmc 1645: .Dq no ,
1.25 jmc 1646: or
1647: .Dq ask .
1.8 jakob 1648: The default is
1649: .Dq no .
1.12 jakob 1650: Note that this option applies to protocol version 2 only.
1.84 jmc 1651: .Pp
1.166 jmc 1652: See also VERIFYING HOST KEYS in
1.84 jmc 1653: .Xr ssh 1 .
1.111 grunk 1654: .It Cm VisualHostKey
1655: If this flag is set to
1656: .Dq yes ,
1657: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1658: printed in addition to the fingerprint string at login and
1.114 stevesk 1659: for unknown host keys.
1.111 grunk 1660: If this flag is set to
1661: .Dq no ,
1.114 stevesk 1662: no fingerprint strings are printed at login and
1.197 djm 1663: only the fingerprint string will be printed for unknown host keys.
1.111 grunk 1664: The default is
1665: .Dq no .
1.1 stevesk 1666: .It Cm XAuthLocation
1.5 stevesk 1667: Specifies the full pathname of the
1.1 stevesk 1668: .Xr xauth 1
1669: program.
1670: The default is
1671: .Pa /usr/X11R6/bin/xauth .
1672: .El
1.86 jmc 1673: .Sh PATTERNS
1674: A
1675: .Em pattern
1676: consists of zero or more non-whitespace characters,
1677: .Sq *
1678: (a wildcard that matches zero or more characters),
1679: or
1680: .Sq ?\&
1681: (a wildcard that matches exactly one character).
1682: For example, to specify a set of declarations for any host in the
1683: .Dq .co.uk
1684: set of domains,
1685: the following pattern could be used:
1686: .Pp
1687: .Dl Host *.co.uk
1688: .Pp
1689: The following pattern
1690: would match any host in the 192.168.0.[0-9] network range:
1691: .Pp
1692: .Dl Host 192.168.0.?
1693: .Pp
1694: A
1695: .Em pattern-list
1696: is a comma-separated list of patterns.
1697: Patterns within pattern-lists may be negated
1698: by preceding them with an exclamation mark
1699: .Pq Sq !\& .
1700: For example,
1.174 djm 1701: to allow a key to be used from anywhere within an organization
1.86 jmc 1702: except from the
1703: .Dq dialup
1704: pool,
1705: the following entry (in authorized_keys) could be used:
1706: .Pp
1707: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1708: .Sh FILES
1709: .Bl -tag -width Ds
1.50 djm 1710: .It Pa ~/.ssh/config
1.1 stevesk 1711: This is the per-user configuration file.
1712: The format of this file is described above.
1.84 jmc 1713: This file is used by the SSH client.
1.30 djm 1714: Because of the potential for abuse, this file must have strict permissions:
1715: read/write for the user, and not accessible by others.
1.1 stevesk 1716: .It Pa /etc/ssh/ssh_config
1717: Systemwide configuration file.
1718: This file provides defaults for those
1719: values that are not specified in the user's configuration file, and
1720: for those users who do not have a configuration file.
1721: This file must be world-readable.
1722: .El
1.13 jmc 1723: .Sh SEE ALSO
1724: .Xr ssh 1
1.1 stevesk 1725: .Sh AUTHORS
1726: OpenSSH is a derivative of the original and free
1727: ssh 1.2.12 release by Tatu Ylonen.
1728: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1729: Theo de Raadt and Dug Song
1730: removed many bugs, re-added newer features and
1731: created OpenSSH.
1732: Markus Friedl contributed the support for SSH
1733: protocol versions 1.5 and 2.0.
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