Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.222
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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1.222 ! jcs 36: .\" $OpenBSD: ssh_config.5,v 1.221 2015/09/24 06:15:11 djm Exp $
! 37: .Dd $Mdocdate: September 24 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.
1.220 sobrado 142: Match conditions are specified using one or more criteria
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).
1.222 ! jcs 224: .It Cm AddKeysToAgent
! 225: Specifies whether keys should be automatically added to a running
! 226: .Xr ssh-agent 5 .
! 227: If this option is set to
! 228: .Dq yes
! 229: and a key is loaded from a file, the key and its passphrase are added to
! 230: the agent with the default lifetime, as if by
! 231: .Xr ssh-add 1 .
! 232: If this option is set to
! 233: .Dq ask ,
! 234: .Nm ssh
! 235: will require confirmation using the
! 236: .Ev SSH_ASKPASS
! 237: program before adding a key (see
! 238: .Xr ssh-add 1
! 239: for details).
! 240: If this option is set to
! 241: .Dq confirm ,
! 242: each use of the key must be confirmed, as if the
! 243: .Fl c
! 244: option was specified to
! 245: .Xr ssh-add 1 .
! 246: If this option is set to
! 247: .Dq no ,
! 248: no keys are added to the agent.
! 249: The argument must be
! 250: .Dq yes ,
! 251: .Dq confirm ,
! 252: .Dq ask ,
! 253: or
! 254: .Dq no .
! 255: The default is
! 256: .Dq no .
1.10 djm 257: .It Cm AddressFamily
1.11 jmc 258: Specifies which address family to use when connecting.
259: Valid arguments are
1.10 djm 260: .Dq any ,
261: .Dq inet
1.84 jmc 262: (use IPv4 only), or
1.10 djm 263: .Dq inet6
1.40 jmc 264: (use IPv6 only).
1.1 stevesk 265: .It Cm BatchMode
266: If set to
267: .Dq yes ,
268: passphrase/password querying will be disabled.
269: This option is useful in scripts and other batch jobs where no user
270: is present to supply the password.
271: The argument must be
272: .Dq yes
273: or
274: .Dq no .
275: The default is
276: .Dq no .
277: .It Cm BindAddress
1.60 dtucker 278: Use the specified address on the local machine as the source address of
1.61 jmc 279: the connection.
280: Only useful on systems with more than one address.
1.1 stevesk 281: Note that this option does not work if
282: .Cm UsePrivilegedPort
283: is set to
284: .Dq yes .
1.171 djm 285: .It Cm CanonicalDomains
1.172 jmc 286: When
1.173 djm 287: .Cm CanonicalizeHostname
1.171 djm 288: is enabled, this option specifies the list of domain suffixes in which to
289: search for the specified destination host.
1.173 djm 290: .It Cm CanonicalizeFallbackLocal
1.174 djm 291: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 292: The default,
1.184 djm 293: .Dq yes ,
1.172 jmc 294: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 295: search rules.
296: A value of
1.184 djm 297: .Dq no
1.171 djm 298: will cause
299: .Xr ssh 1
300: to fail instantly if
1.173 djm 301: .Cm CanonicalizeHostname
1.171 djm 302: is enabled and the target hostname cannot be found in any of the domains
303: specified by
304: .Cm CanonicalDomains .
1.173 djm 305: .It Cm CanonicalizeHostname
1.174 djm 306: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 307: The default,
308: .Dq no ,
1.171 djm 309: is not to perform any name rewriting and let the system resolver handle all
310: hostname lookups.
311: If set to
312: .Dq yes
313: then, for connections that do not use a
314: .Cm ProxyCommand ,
315: .Xr ssh 1
1.173 djm 316: will attempt to canonicalize the hostname specified on the command line
1.171 djm 317: using the
318: .Cm CanonicalDomains
319: suffixes and
1.173 djm 320: .Cm CanonicalizePermittedCNAMEs
1.171 djm 321: rules.
322: If
1.173 djm 323: .Cm CanonicalizeHostname
1.171 djm 324: is set to
325: .Dq always ,
1.174 djm 326: then canonicalization is applied to proxied connections too.
1.185 djm 327: .Pp
1.193 djm 328: If this option is enabled, then the configuration files are processed
329: again using the new target name to pick up any new configuration in matching
1.185 djm 330: .Cm Host
1.193 djm 331: and
332: .Cm Match
1.185 djm 333: stanzas.
1.173 djm 334: .It Cm CanonicalizeMaxDots
1.172 jmc 335: Specifies the maximum number of dot characters in a hostname before
1.174 djm 336: canonicalization is disabled.
1.172 jmc 337: The default,
338: .Dq 1 ,
339: allows a single dot (i.e. hostname.subdomain).
1.173 djm 340: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 341: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 342: canonicalizing hostnames.
1.171 djm 343: The rules consist of one or more arguments of
1.172 jmc 344: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 345: where
346: .Ar source_domain_list
1.174 djm 347: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 348: and
349: .Ar target_domain_list
1.172 jmc 350: is a pattern-list of domains that they may resolve to.
1.171 djm 351: .Pp
352: For example,
353: .Dq *.a.example.com:*.b.example.com,*.c.example.com
354: will allow hostnames matching
355: .Dq *.a.example.com
1.173 djm 356: to be canonicalized to names in the
1.171 djm 357: .Dq *.b.example.com
358: or
359: .Dq *.c.example.com
360: domains.
1.221 djm 361: .It Cm CertificateFile
362: Specifies a file from which the user's certificate is read.
363: A corresponding private key must be provided separately in order
364: to use this certificate either
365: from an
366: .Cm IdentityFile
367: directive or
368: .Fl i
369: flag to
370: .Xr ssh 1 ,
371: via
372: .Xr ssh-agent 1 ,
373: or via a
374: .Cm PKCS11Provider .
375: .Pp
376: The file name may use the tilde
377: syntax to refer to a user's home directory or one of the following
378: escape characters:
379: .Ql %d
380: (local user's home directory),
381: .Ql %u
382: (local user name),
383: .Ql %l
384: (local host name),
385: .Ql %h
386: (remote host name) or
387: .Ql %r
388: (remote user name).
389: .Pp
390: It is possible to have multiple certificate files specified in
391: configuration files; these certificates will be tried in sequence.
392: Multiple
393: .Cm CertificateFile
394: directives will add to the list of certificates used for
395: authentication.
1.1 stevesk 396: .It Cm ChallengeResponseAuthentication
1.82 jmc 397: Specifies whether to use challenge-response authentication.
1.1 stevesk 398: The argument to this keyword must be
399: .Dq yes
400: or
401: .Dq no .
402: The default is
403: .Dq yes .
404: .It Cm CheckHostIP
405: If this flag is set to
406: .Dq yes ,
1.84 jmc 407: .Xr ssh 1
408: will additionally check the host IP address in the
1.1 stevesk 409: .Pa known_hosts
410: file.
1.211 djm 411: This allows ssh to detect if a host key changed due to DNS spoofing
412: and will add addresses of destination hosts to
413: .Pa ~/.ssh/known_hosts
414: in the process, regardless of the setting of
415: .Cm StrictHostKeyChecking .
1.107 grunk 416: If the option is set to
1.1 stevesk 417: .Dq no ,
418: the check will not be executed.
419: The default is
420: .Dq yes .
421: .It Cm Cipher
422: Specifies the cipher to use for encrypting the session
423: in protocol version 1.
424: Currently,
425: .Dq blowfish ,
426: .Dq 3des ,
427: and
428: .Dq des
429: are supported.
430: .Ar des
431: is only supported in the
1.84 jmc 432: .Xr ssh 1
1.1 stevesk 433: client for interoperability with legacy protocol 1 implementations
434: that do not support the
435: .Ar 3des
1.7 jmc 436: cipher.
437: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 438: The default is
439: .Dq 3des .
440: .It Cm Ciphers
441: Specifies the ciphers allowed for protocol version 2
442: in order of preference.
443: Multiple ciphers must be comma-separated.
1.214 djm 444: If the specified value begins with a
445: .Sq +
446: character, then the specified ciphers will be appended to the default set
447: instead of replacing them.
448: .Pp
1.180 djm 449: The supported ciphers are:
450: .Pp
1.186 naddy 451: .Bl -item -compact -offset indent
452: .It
453: 3des-cbc
454: .It
455: aes128-cbc
456: .It
457: aes192-cbc
458: .It
459: aes256-cbc
460: .It
461: aes128-ctr
462: .It
463: aes192-ctr
464: .It
465: aes256-ctr
466: .It
467: aes128-gcm@openssh.com
468: .It
469: aes256-gcm@openssh.com
470: .It
471: arcfour
472: .It
473: arcfour128
474: .It
475: arcfour256
476: .It
477: blowfish-cbc
478: .It
479: cast128-cbc
480: .It
481: chacha20-poly1305@openssh.com
482: .El
1.180 djm 483: .Pp
1.84 jmc 484: The default is:
1.186 naddy 485: .Bd -literal -offset indent
1.215 jmc 486: chacha20-poly1305@openssh.com,
1.186 naddy 487: aes128-ctr,aes192-ctr,aes256-ctr,
1.161 markus 488: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.186 naddy 489: arcfour256,arcfour128,
490: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,
491: aes192-cbc,aes256-cbc,arcfour
1.1 stevesk 492: .Ed
1.180 djm 493: .Pp
494: The list of available ciphers may also be obtained using the
495: .Fl Q
496: option of
1.198 djm 497: .Xr ssh 1
498: with an argument of
499: .Dq cipher .
1.1 stevesk 500: .It Cm ClearAllForwardings
1.84 jmc 501: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 502: specified in the configuration files or on the command line be
1.7 jmc 503: cleared.
504: This option is primarily useful when used from the
1.84 jmc 505: .Xr ssh 1
1.1 stevesk 506: command line to clear port forwardings set in
507: configuration files, and is automatically set by
508: .Xr scp 1
509: and
510: .Xr sftp 1 .
511: The argument must be
512: .Dq yes
513: or
514: .Dq no .
515: The default is
516: .Dq no .
517: .It Cm Compression
518: Specifies whether to use compression.
519: The argument must be
520: .Dq yes
521: or
522: .Dq no .
523: The default is
524: .Dq no .
525: .It Cm CompressionLevel
526: Specifies the compression level to use if compression is enabled.
527: The argument must be an integer from 1 (fast) to 9 (slow, best).
528: The default level is 6, which is good for most applications.
529: The meaning of the values is the same as in
530: .Xr gzip 1 .
531: Note that this option applies to protocol version 1 only.
532: .It Cm ConnectionAttempts
533: Specifies the number of tries (one per second) to make before exiting.
534: The argument must be an integer.
535: This may be useful in scripts if the connection sometimes fails.
536: The default is 1.
1.9 djm 537: .It Cm ConnectTimeout
1.84 jmc 538: Specifies the timeout (in seconds) used when connecting to the
539: SSH server, instead of using the default system TCP timeout.
1.11 jmc 540: This value is used only when the target is down or really unreachable,
541: not when it refuses the connection.
1.36 djm 542: .It Cm ControlMaster
543: Enables the sharing of multiple sessions over a single network connection.
544: When set to
1.84 jmc 545: .Dq yes ,
546: .Xr ssh 1
1.36 djm 547: will listen for connections on a control socket specified using the
548: .Cm ControlPath
549: argument.
550: Additional sessions can connect to this socket using the same
551: .Cm ControlPath
552: with
553: .Cm ControlMaster
554: set to
555: .Dq no
1.38 jmc 556: (the default).
1.64 jmc 557: These sessions will try to reuse the master instance's network connection
1.63 djm 558: rather than initiating new ones, but will fall back to connecting normally
559: if the control socket does not exist, or is not listening.
560: .Pp
1.37 djm 561: Setting this to
562: .Dq ask
1.84 jmc 563: will cause ssh
1.206 jmc 564: to listen for control connections, but require confirmation using
565: .Xr ssh-askpass 1 .
1.51 jakob 566: If the
567: .Cm ControlPath
1.84 jmc 568: cannot be opened,
569: ssh will continue without connecting to a master instance.
1.58 djm 570: .Pp
571: X11 and
1.59 jmc 572: .Xr ssh-agent 1
1.58 djm 573: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 574: display and agent forwarded will be the one belonging to the master
1.59 jmc 575: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 576: .Pp
577: Two additional options allow for opportunistic multiplexing: try to use a
578: master connection but fall back to creating a new one if one does not already
579: exist.
580: These options are:
581: .Dq auto
582: and
583: .Dq autoask .
584: The latter requires confirmation like the
585: .Dq ask
586: option.
1.36 djm 587: .It Cm ControlPath
1.55 djm 588: Specify the path to the control socket used for connection sharing as described
589: in the
1.36 djm 590: .Cm ControlMaster
1.57 djm 591: section above or the string
592: .Dq none
593: to disable connection sharing.
1.55 djm 594: In the path,
1.147 djm 595: .Ql %L
596: will be substituted by the first component of the local host name,
1.77 djm 597: .Ql %l
1.147 djm 598: will be substituted by the local host name (including any domain name),
1.55 djm 599: .Ql %h
600: will be substituted by the target host name,
1.150 jmc 601: .Ql %n
602: will be substituted by the original target host name
603: specified on the command line,
1.55 djm 604: .Ql %p
1.175 djm 605: the destination port,
1.55 djm 606: .Ql %r
1.188 djm 607: by the remote login username,
1.147 djm 608: .Ql %u
1.218 djm 609: by the username and
610: .Ql %i
1.219 jmc 611: by the numeric user ID (uid) of the user running
612: .Xr ssh 1 ,
613: and
1.189 jmc 614: .Ql \&%C
1.188 djm 615: by a hash of the concatenation: %l%h%p%r.
1.56 djm 616: It is recommended that any
617: .Cm ControlPath
618: used for opportunistic connection sharing include
1.195 djm 619: at least %h, %p, and %r (or alternatively %C) and be placed in a directory
620: that is not writable by other users.
1.56 djm 621: This ensures that shared connections are uniquely identified.
1.137 djm 622: .It Cm ControlPersist
623: When used in conjunction with
624: .Cm ControlMaster ,
625: specifies that the master connection should remain open
626: in the background (waiting for future client connections)
627: after the initial client connection has been closed.
628: If set to
629: .Dq no ,
630: then the master connection will not be placed into the background,
631: and will close as soon as the initial client connection is closed.
632: If set to
1.195 djm 633: .Dq yes
634: or
635: .Dq 0 ,
1.137 djm 636: then the master connection will remain in the background indefinitely
637: (until killed or closed via a mechanism such as the
638: .Xr ssh 1
639: .Dq Fl O No exit
640: option).
641: If set to a time in seconds, or a time in any of the formats documented in
642: .Xr sshd_config 5 ,
643: then the backgrounded master connection will automatically terminate
644: after it has remained idle (with no client connections) for the
645: specified time.
1.38 jmc 646: .It Cm DynamicForward
1.74 jmc 647: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 648: over the secure channel, and the application
649: protocol is then used to determine where to connect to from the
650: remote machine.
1.62 djm 651: .Pp
652: The argument must be
653: .Sm off
654: .Oo Ar bind_address : Oc Ar port .
655: .Sm on
1.138 djm 656: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 657: By default, the local port is bound in accordance with the
658: .Cm GatewayPorts
659: setting.
660: However, an explicit
661: .Ar bind_address
662: may be used to bind the connection to a specific address.
663: The
664: .Ar bind_address
665: of
666: .Dq localhost
667: indicates that the listening port be bound for local use only, while an
668: empty address or
669: .Sq *
670: indicates that the port should be available from all interfaces.
671: .Pp
1.38 jmc 672: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 673: .Xr ssh 1
1.38 jmc 674: will act as a SOCKS server.
675: Multiple forwardings may be specified, and
676: additional forwardings can be given on the command line.
677: Only the superuser can forward privileged ports.
1.14 markus 678: .It Cm EnableSSHKeysign
679: Setting this option to
680: .Dq yes
681: in the global client configuration file
682: .Pa /etc/ssh/ssh_config
683: enables the use of the helper program
684: .Xr ssh-keysign 8
685: during
686: .Cm HostbasedAuthentication .
687: The argument must be
688: .Dq yes
689: or
690: .Dq no .
691: The default is
692: .Dq no .
1.23 jmc 693: This option should be placed in the non-hostspecific section.
1.14 markus 694: See
695: .Xr ssh-keysign 8
696: for more information.
1.1 stevesk 697: .It Cm EscapeChar
698: Sets the escape character (default:
699: .Ql ~ ) .
700: The escape character can also
701: be set on the command line.
702: The argument should be a single character,
703: .Ql ^
704: followed by a letter, or
705: .Dq none
706: to disable the escape
707: character entirely (making the connection transparent for binary
708: data).
1.96 markus 709: .It Cm ExitOnForwardFailure
710: Specifies whether
711: .Xr ssh 1
712: should terminate the connection if it cannot set up all requested
1.216 djm 713: dynamic, tunnel, local, and remote port forwardings, (e.g.\&
1.217 jmc 714: if either end is unable to bind and listen on a specified port).
1.216 djm 715: Note that
716: .Cm ExitOnForwardFailure
717: does not apply to connections made over port forwardings and will not,
718: for example, cause
719: .Xr ssh 1
720: to exit if TCP connections to the ultimate forwarding destination fail.
1.96 markus 721: The argument must be
722: .Dq yes
723: or
724: .Dq no .
725: The default is
726: .Dq no .
1.197 djm 727: .It Cm FingerprintHash
728: Specifies the hash algorithm used when displaying key fingerprints.
729: Valid options are:
730: .Dq md5
731: and
732: .Dq sha256 .
733: The default is
734: .Dq sha256 .
1.1 stevesk 735: .It Cm ForwardAgent
736: Specifies whether the connection to the authentication agent (if any)
737: will be forwarded to the remote machine.
738: The argument must be
739: .Dq yes
740: or
741: .Dq no .
742: The default is
743: .Dq no .
1.3 stevesk 744: .Pp
1.7 jmc 745: Agent forwarding should be enabled with caution.
746: Users with the ability to bypass file permissions on the remote host
747: (for the agent's Unix-domain socket)
748: can access the local agent through the forwarded connection.
749: An attacker cannot obtain key material from the agent,
1.3 stevesk 750: however they can perform operations on the keys that enable them to
751: authenticate using the identities loaded into the agent.
1.1 stevesk 752: .It Cm ForwardX11
753: Specifies whether X11 connections will be automatically redirected
754: over the secure channel and
755: .Ev DISPLAY
756: set.
757: The argument must be
758: .Dq yes
759: or
760: .Dq no .
761: The default is
762: .Dq no .
1.3 stevesk 763: .Pp
1.7 jmc 764: X11 forwarding should be enabled with caution.
765: Users with the ability to bypass file permissions on the remote host
1.22 markus 766: (for the user's X11 authorization database)
1.7 jmc 767: can access the local X11 display through the forwarded connection.
1.22 markus 768: An attacker may then be able to perform activities such as keystroke monitoring
769: if the
770: .Cm ForwardX11Trusted
771: option is also enabled.
1.134 djm 772: .It Cm ForwardX11Timeout
1.135 jmc 773: Specify a timeout for untrusted X11 forwarding
774: using the format described in the
1.166 jmc 775: TIME FORMATS section of
1.134 djm 776: .Xr sshd_config 5 .
777: X11 connections received by
778: .Xr ssh 1
779: after this time will be refused.
780: The default is to disable untrusted X11 forwarding after twenty minutes has
781: elapsed.
1.22 markus 782: .It Cm ForwardX11Trusted
1.34 jmc 783: If this option is set to
1.84 jmc 784: .Dq yes ,
785: remote X11 clients will have full access to the original X11 display.
1.42 djm 786: .Pp
1.22 markus 787: If this option is set to
1.84 jmc 788: .Dq no ,
789: remote X11 clients will be considered untrusted and prevented
1.22 markus 790: from stealing or tampering with data belonging to trusted X11
791: clients.
1.42 djm 792: Furthermore, the
793: .Xr xauth 1
794: token used for the session will be set to expire after 20 minutes.
795: Remote clients will be refused access after this time.
1.22 markus 796: .Pp
797: The default is
798: .Dq no .
799: .Pp
800: See the X11 SECURITY extension specification for full details on
801: the restrictions imposed on untrusted clients.
1.1 stevesk 802: .It Cm GatewayPorts
803: Specifies whether remote hosts are allowed to connect to local
804: forwarded ports.
805: By default,
1.84 jmc 806: .Xr ssh 1
1.7 jmc 807: binds local port forwardings to the loopback address.
808: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 809: .Cm GatewayPorts
1.84 jmc 810: can be used to specify that ssh
1.1 stevesk 811: should bind local port forwardings to the wildcard address,
812: thus allowing remote hosts to connect to forwarded ports.
813: The argument must be
814: .Dq yes
815: or
816: .Dq no .
817: The default is
818: .Dq no .
819: .It Cm GlobalKnownHostsFile
1.151 djm 820: Specifies one or more files to use for the global
821: host key database, separated by whitespace.
822: The default is
823: .Pa /etc/ssh/ssh_known_hosts ,
824: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 825: .It Cm GSSAPIAuthentication
1.27 markus 826: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 827: The default is
1.21 markus 828: .Dq no .
1.18 markus 829: Note that this option applies to protocol version 2 only.
830: .It Cm GSSAPIDelegateCredentials
831: Forward (delegate) credentials to the server.
832: The default is
833: .Dq no .
834: Note that this option applies to protocol version 2 only.
1.44 djm 835: .It Cm HashKnownHosts
836: Indicates that
1.84 jmc 837: .Xr ssh 1
1.44 djm 838: should hash host names and addresses when they are added to
1.50 djm 839: .Pa ~/.ssh/known_hosts .
1.44 djm 840: These hashed names may be used normally by
1.84 jmc 841: .Xr ssh 1
1.44 djm 842: and
1.84 jmc 843: .Xr sshd 8 ,
1.44 djm 844: but they do not reveal identifying information should the file's contents
845: be disclosed.
846: The default is
847: .Dq no .
1.97 jmc 848: Note that existing names and addresses in known hosts files
849: will not be converted automatically,
850: but may be manually hashed using
1.45 djm 851: .Xr ssh-keygen 1 .
1.1 stevesk 852: .It Cm HostbasedAuthentication
853: Specifies whether to try rhosts based authentication with public key
854: authentication.
855: The argument must be
856: .Dq yes
857: or
858: .Dq no .
859: The default is
860: .Dq no .
861: This option applies to protocol version 2 only and
862: is similar to
863: .Cm RhostsRSAAuthentication .
1.202 djm 864: .It Cm HostbasedKeyTypes
865: Specifies the key types that will be used for hostbased authentication
866: as a comma-separated pattern list.
1.214 djm 867: Alternately if the specified value begins with a
868: .Sq +
869: character, then the specified key types will be appended to the default set
870: instead of replacing them.
1.213 markus 871: The default for this option is:
872: .Bd -literal -offset 3n
873: ecdsa-sha2-nistp256-cert-v01@openssh.com,
874: ecdsa-sha2-nistp384-cert-v01@openssh.com,
875: ecdsa-sha2-nistp521-cert-v01@openssh.com,
876: ssh-ed25519-cert-v01@openssh.com,
877: ssh-rsa-cert-v01@openssh.com,
878: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
879: ssh-ed25519,ssh-rsa
880: .Ed
881: .Pp
1.202 djm 882: The
883: .Fl Q
884: option of
885: .Xr ssh 1
886: may be used to list supported key types.
1.1 stevesk 887: .It Cm HostKeyAlgorithms
888: Specifies the protocol version 2 host key algorithms
889: that the client wants to use in order of preference.
1.214 djm 890: Alternately if the specified value begins with a
891: .Sq +
892: character, then the specified key types will be appended to the default set
893: instead of replacing them.
1.1 stevesk 894: The default for this option is:
1.139 djm 895: .Bd -literal -offset 3n
896: ecdsa-sha2-nistp256-cert-v01@openssh.com,
897: ecdsa-sha2-nistp384-cert-v01@openssh.com,
898: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1.183 naddy 899: ssh-ed25519-cert-v01@openssh.com,
1.213 markus 900: ssh-rsa-cert-v01@openssh.com,
1.139 djm 901: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1.213 markus 902: ssh-ed25519,ssh-rsa
1.139 djm 903: .Ed
1.145 djm 904: .Pp
905: If hostkeys are known for the destination host then this default is modified
906: to prefer their algorithms.
1.198 djm 907: .Pp
908: The list of available key types may also be obtained using the
909: .Fl Q
910: option of
911: .Xr ssh 1
912: with an argument of
913: .Dq key .
1.1 stevesk 914: .It Cm HostKeyAlias
915: Specifies an alias that should be used instead of the
916: real host name when looking up or saving the host key
917: in the host key database files.
1.84 jmc 918: This option is useful for tunneling SSH connections
1.1 stevesk 919: or for multiple servers running on a single host.
920: .It Cm HostName
921: Specifies the real host name to log into.
922: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 923: If the hostname contains the character sequence
924: .Ql %h ,
1.150 jmc 925: then this will be replaced with the host name specified on the command line
1.136 djm 926: (this is useful for manipulating unqualified names).
1.187 djm 927: The character sequence
928: .Ql %%
929: will be replaced by a single
930: .Ql %
931: character, which may be used when specifying IPv6 link-local addresses.
932: .Pp
1.84 jmc 933: The default is the name given on the command line.
1.1 stevesk 934: Numeric IP addresses are also permitted (both on the command line and in
935: .Cm HostName
936: specifications).
1.29 markus 937: .It Cm IdentitiesOnly
938: Specifies that
1.84 jmc 939: .Xr ssh 1
1.221 djm 940: should only use the authentication identity and certificate files explicitly
941: configured in the
1.31 jmc 942: .Nm
1.221 djm 943: files
944: or passed on the
945: .Xr ssh 1
946: command-line,
1.84 jmc 947: even if
948: .Xr ssh-agent 1
1.159 djm 949: or a
950: .Cm PKCS11Provider
1.29 markus 951: offers more identities.
952: The argument to this keyword must be
953: .Dq yes
954: or
955: .Dq no .
1.84 jmc 956: This option is intended for situations where ssh-agent
1.29 markus 957: offers many different identities.
958: The default is
959: .Dq no .
1.67 jmc 960: .It Cm IdentityFile
1.192 sobrado 961: Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA authentication
1.139 djm 962: identity is read.
1.67 jmc 963: The default is
964: .Pa ~/.ssh/identity
965: for protocol version 1, and
1.139 djm 966: .Pa ~/.ssh/id_dsa ,
1.183 naddy 967: .Pa ~/.ssh/id_ecdsa ,
968: .Pa ~/.ssh/id_ed25519
1.139 djm 969: and
1.67 jmc 970: .Pa ~/.ssh/id_rsa
971: for protocol version 2.
972: Additionally, any identities represented by the authentication agent
1.165 djm 973: will be used for authentication unless
974: .Cm IdentitiesOnly
975: is set.
1.221 djm 976: If no certificates have been explicitly specified by
977: .Cm CertificateFile ,
1.129 djm 978: .Xr ssh 1
979: will try to load certificate information from the filename obtained by
980: appending
981: .Pa -cert.pub
982: to the path of a specified
983: .Cm IdentityFile .
1.90 djm 984: .Pp
1.67 jmc 985: The file name may use the tilde
1.91 jmc 986: syntax to refer to a user's home directory or one of the following
1.90 djm 987: escape characters:
988: .Ql %d
989: (local user's home directory),
990: .Ql %u
991: (local user name),
992: .Ql %l
993: (local host name),
994: .Ql %h
995: (remote host name) or
1.92 djm 996: .Ql %r
1.90 djm 997: (remote user name).
998: .Pp
1.67 jmc 999: It is possible to have
1000: multiple identity files specified in configuration files; all these
1001: identities will be tried in sequence.
1.152 djm 1002: Multiple
1003: .Cm IdentityFile
1004: directives will add to the list of identities tried (this behaviour
1005: differs from that of other configuration directives).
1.165 djm 1006: .Pp
1007: .Cm IdentityFile
1008: may be used in conjunction with
1009: .Cm IdentitiesOnly
1010: to select which identities in an agent are offered during authentication.
1.221 djm 1011: .Cm IdentityFile
1012: may also be used in conjunction with
1013: .Cm CertificateFile
1014: in order to provide any certificate also needed for authentication with
1015: the identity.
1.164 jmc 1016: .It Cm IgnoreUnknown
1017: Specifies a pattern-list of unknown options to be ignored if they are
1018: encountered in configuration parsing.
1019: This may be used to suppress errors if
1020: .Nm
1021: contains options that are unrecognised by
1022: .Xr ssh 1 .
1023: It is recommended that
1024: .Cm IgnoreUnknown
1025: be listed early in the configuration file as it will not be applied
1026: to unknown options that appear before it.
1.143 djm 1027: .It Cm IPQoS
1028: Specifies the IPv4 type-of-service or DSCP class for connections.
1029: Accepted values are
1030: .Dq af11 ,
1031: .Dq af12 ,
1032: .Dq af13 ,
1.154 djm 1033: .Dq af21 ,
1.143 djm 1034: .Dq af22 ,
1035: .Dq af23 ,
1036: .Dq af31 ,
1037: .Dq af32 ,
1038: .Dq af33 ,
1039: .Dq af41 ,
1040: .Dq af42 ,
1041: .Dq af43 ,
1042: .Dq cs0 ,
1043: .Dq cs1 ,
1044: .Dq cs2 ,
1045: .Dq cs3 ,
1046: .Dq cs4 ,
1047: .Dq cs5 ,
1048: .Dq cs6 ,
1049: .Dq cs7 ,
1050: .Dq ef ,
1051: .Dq lowdelay ,
1052: .Dq throughput ,
1053: .Dq reliability ,
1054: or a numeric value.
1.146 djm 1055: This option may take one or two arguments, separated by whitespace.
1.143 djm 1056: If one argument is specified, it is used as the packet class unconditionally.
1057: If two values are specified, the first is automatically selected for
1058: interactive sessions and the second for non-interactive sessions.
1059: The default is
1060: .Dq lowdelay
1061: for interactive sessions and
1062: .Dq throughput
1063: for non-interactive sessions.
1.103 djm 1064: .It Cm KbdInteractiveAuthentication
1065: Specifies whether to use keyboard-interactive authentication.
1066: The argument to this keyword must be
1067: .Dq yes
1068: or
1069: .Dq no .
1070: The default is
1071: .Dq yes .
1.39 djm 1072: .It Cm KbdInteractiveDevices
1073: Specifies the list of methods to use in keyboard-interactive authentication.
1074: Multiple method names must be comma-separated.
1075: The default is to use the server specified list.
1.85 jmc 1076: The methods available vary depending on what the server supports.
1077: For an OpenSSH server,
1078: it may be zero or more of:
1079: .Dq bsdauth ,
1080: .Dq pam ,
1081: and
1082: .Dq skey .
1.140 djm 1083: .It Cm KexAlgorithms
1084: Specifies the available KEX (Key Exchange) algorithms.
1085: Multiple algorithms must be comma-separated.
1.214 djm 1086: Alternately if the specified value begins with a
1087: .Sq +
1088: character, then the specified methods will be appended to the default set
1089: instead of replacing them.
1.141 jmc 1090: The default is:
1091: .Bd -literal -offset indent
1.179 markus 1092: curve25519-sha256@libssh.org,
1.141 jmc 1093: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
1094: diffie-hellman-group-exchange-sha256,
1.209 dtucker 1095: diffie-hellman-group-exchange-sha1,
1.212 djm 1096: diffie-hellman-group14-sha1
1.141 jmc 1097: .Ed
1.198 djm 1098: .Pp
1099: The list of available key exchange algorithms may also be obtained using the
1100: .Fl Q
1101: option of
1102: .Xr ssh 1
1103: with an argument of
1104: .Dq kex .
1.65 reyk 1105: .It Cm LocalCommand
1106: Specifies a command to execute on the local machine after successfully
1107: connecting to the server.
1108: The command string extends to the end of the line, and is executed with
1.105 jmc 1109: the user's shell.
1.109 dtucker 1110: The following escape character substitutions will be performed:
1111: .Ql %d
1112: (local user's home directory),
1113: .Ql %h
1114: (remote host name),
1115: .Ql %l
1116: (local host name),
1117: .Ql %n
1118: (host name as provided on the command line),
1119: .Ql %p
1120: (remote port),
1121: .Ql %r
1122: (remote user name) or
1123: .Ql %u
1.188 djm 1124: (local user name) or
1.189 jmc 1125: .Ql \&%C
1.188 djm 1126: by a hash of the concatenation: %l%h%p%r.
1.123 djm 1127: .Pp
1128: The command is run synchronously and does not have access to the
1129: session of the
1130: .Xr ssh 1
1131: that spawned it.
1132: It should not be used for interactive commands.
1133: .Pp
1.65 reyk 1134: This directive is ignored unless
1135: .Cm PermitLocalCommand
1136: has been enabled.
1.1 stevesk 1137: .It Cm LocalForward
1.74 jmc 1138: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 1139: the secure channel to the specified host and port from the remote machine.
1.49 jmc 1140: The first argument must be
1.43 djm 1141: .Sm off
1.49 jmc 1142: .Oo Ar bind_address : Oc Ar port
1.43 djm 1143: .Sm on
1.49 jmc 1144: and the second argument must be
1145: .Ar host : Ns Ar hostport .
1.138 djm 1146: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 1147: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 1148: given on the command line.
1.1 stevesk 1149: Only the superuser can forward privileged ports.
1.43 djm 1150: By default, the local port is bound in accordance with the
1151: .Cm GatewayPorts
1152: setting.
1153: However, an explicit
1154: .Ar bind_address
1155: may be used to bind the connection to a specific address.
1156: The
1157: .Ar bind_address
1158: of
1159: .Dq localhost
1.46 jmc 1160: indicates that the listening port be bound for local use only, while an
1161: empty address or
1162: .Sq *
1.43 djm 1163: indicates that the port should be available from all interfaces.
1.1 stevesk 1164: .It Cm LogLevel
1165: Gives the verbosity level that is used when logging messages from
1.84 jmc 1166: .Xr ssh 1 .
1.1 stevesk 1167: The possible values are:
1.84 jmc 1168: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 1169: The default is INFO.
1170: DEBUG and DEBUG1 are equivalent.
1171: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 1172: .It Cm MACs
1173: Specifies the MAC (message authentication code) algorithms
1174: in order of preference.
1175: The MAC algorithm is used in protocol version 2
1176: for data integrity protection.
1177: Multiple algorithms must be comma-separated.
1.214 djm 1178: If the specified value begins with a
1179: .Sq +
1180: character, then the specified algorithms will be appended to the default set
1181: instead of replacing them.
1182: .Pp
1.160 markus 1183: The algorithms that contain
1184: .Dq -etm
1185: calculate the MAC after encryption (encrypt-then-mac).
1186: These are considered safer and their use recommended.
1.214 djm 1187: .Pp
1.84 jmc 1188: The default is:
1.101 jmc 1189: .Bd -literal -offset indent
1.160 markus 1190: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
1191: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
1.186 naddy 1192: umac-64@openssh.com,umac-128@openssh.com,
1193: hmac-sha2-256,hmac-sha2-512,
1194: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
1195: hmac-ripemd160-etm@openssh.com,
1196: hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,
1197: hmac-md5,hmac-sha1,hmac-ripemd160,
1.157 naddy 1198: hmac-sha1-96,hmac-md5-96
1.101 jmc 1199: .Ed
1.198 djm 1200: .Pp
1201: The list of available MAC algorithms may also be obtained using the
1202: .Fl Q
1203: option of
1204: .Xr ssh 1
1205: with an argument of
1206: .Dq mac .
1.1 stevesk 1207: .It Cm NoHostAuthenticationForLocalhost
1208: This option can be used if the home directory is shared across machines.
1209: In this case localhost will refer to a different machine on each of
1210: the machines and the user will get many warnings about changed host keys.
1211: However, this option disables host authentication for localhost.
1212: The argument to this keyword must be
1213: .Dq yes
1214: or
1215: .Dq no .
1216: The default is to check the host key for localhost.
1217: .It Cm NumberOfPasswordPrompts
1218: Specifies the number of password prompts before giving up.
1219: The argument to this keyword must be an integer.
1.84 jmc 1220: The default is 3.
1.1 stevesk 1221: .It Cm PasswordAuthentication
1222: Specifies whether to use password authentication.
1223: The argument to this keyword must be
1224: .Dq yes
1225: or
1226: .Dq no .
1227: The default is
1228: .Dq yes .
1.65 reyk 1229: .It Cm PermitLocalCommand
1230: Allow local command execution via the
1231: .Ic LocalCommand
1232: option or using the
1.66 jmc 1233: .Ic !\& Ns Ar command
1.65 reyk 1234: escape sequence in
1235: .Xr ssh 1 .
1236: The argument must be
1237: .Dq yes
1238: or
1239: .Dq no .
1240: The default is
1241: .Dq no .
1.127 markus 1242: .It Cm PKCS11Provider
1243: Specifies which PKCS#11 provider to use.
1.144 jmc 1244: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1245: .Xr ssh 1
1.128 markus 1246: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1247: private RSA key.
1.67 jmc 1248: .It Cm Port
1249: Specifies the port number to connect on the remote host.
1.84 jmc 1250: The default is 22.
1.1 stevesk 1251: .It Cm PreferredAuthentications
1252: Specifies the order in which the client should try protocol 2
1.11 jmc 1253: authentication methods.
1.48 jmc 1254: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1255: .Cm keyboard-interactive )
1.48 jmc 1256: over another method (e.g.\&
1.131 jmc 1257: .Cm password ) .
1258: The default is:
1259: .Bd -literal -offset indent
1260: gssapi-with-mic,hostbased,publickey,
1261: keyboard-interactive,password
1262: .Ed
1.1 stevesk 1263: .It Cm Protocol
1264: Specifies the protocol versions
1.84 jmc 1265: .Xr ssh 1
1.1 stevesk 1266: should support in order of preference.
1267: The possible values are
1.84 jmc 1268: .Sq 1
1.1 stevesk 1269: and
1.84 jmc 1270: .Sq 2 .
1.1 stevesk 1271: Multiple versions must be comma-separated.
1.120 markus 1272: When this option is set to
1.121 jmc 1273: .Dq 2,1
1.120 markus 1274: .Nm ssh
1275: will try version 2 and fall back to version 1
1276: if version 2 is not available.
1.1 stevesk 1277: The default is
1.121 jmc 1278: .Sq 2 .
1.1 stevesk 1279: .It Cm ProxyCommand
1280: Specifies the command to use to connect to the server.
1281: The command
1.190 djm 1282: string extends to the end of the line, and is executed
1283: using the user's shell
1284: .Ql exec
1285: directive to avoid a lingering shell process.
1286: .Pp
1.133 jmc 1287: In the command string, any occurrence of
1.1 stevesk 1288: .Ql %h
1289: will be substituted by the host name to
1.132 djm 1290: connect,
1.1 stevesk 1291: .Ql %p
1.133 jmc 1292: by the port, and
1293: .Ql %r
1.132 djm 1294: by the remote user name.
1.1 stevesk 1295: The command can be basically anything,
1296: and should read from its standard input and write to its standard output.
1297: It should eventually connect an
1298: .Xr sshd 8
1299: server running on some machine, or execute
1300: .Ic sshd -i
1301: somewhere.
1302: Host key management will be done using the
1303: HostName of the host being connected (defaulting to the name typed by
1304: the user).
1.7 jmc 1305: Setting the command to
1306: .Dq none
1.6 markus 1307: disables this option entirely.
1.1 stevesk 1308: Note that
1309: .Cm CheckHostIP
1310: is not available for connects with a proxy command.
1.52 djm 1311: .Pp
1312: This directive is useful in conjunction with
1313: .Xr nc 1
1314: and its proxy support.
1.53 jmc 1315: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1316: 192.0.2.0:
1317: .Bd -literal -offset 3n
1318: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1319: .Ed
1.167 djm 1320: .It Cm ProxyUseFdpass
1.168 jmc 1321: Specifies that
1.167 djm 1322: .Cm ProxyCommand
1323: will pass a connected file descriptor back to
1.168 jmc 1324: .Xr ssh 1
1.167 djm 1325: instead of continuing to execute and pass data.
1326: The default is
1327: .Dq no .
1.213 markus 1328: .It Cm PubkeyAcceptedKeyTypes
1329: Specifies the key types that will be used for public key authentication
1330: as a comma-separated pattern list.
1.214 djm 1331: Alternately if the specified value begins with a
1332: .Sq +
1333: character, then the key types after it will be appended to the default
1334: instead of replacing it.
1.213 markus 1335: The default for this option is:
1336: .Bd -literal -offset 3n
1337: ecdsa-sha2-nistp256-cert-v01@openssh.com,
1338: ecdsa-sha2-nistp384-cert-v01@openssh.com,
1339: ecdsa-sha2-nistp521-cert-v01@openssh.com,
1340: ssh-ed25519-cert-v01@openssh.com,
1341: ssh-rsa-cert-v01@openssh.com,
1342: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
1343: ssh-ed25519,ssh-rsa
1344: .Ed
1345: .Pp
1346: The
1347: .Fl Q
1348: option of
1349: .Xr ssh 1
1350: may be used to list supported key types.
1.1 stevesk 1351: .It Cm PubkeyAuthentication
1352: Specifies whether to try public key authentication.
1353: The argument to this keyword must be
1354: .Dq yes
1355: or
1356: .Dq no .
1357: The default is
1358: .Dq yes .
1359: This option applies to protocol version 2 only.
1.75 dtucker 1360: .It Cm RekeyLimit
1361: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1362: session key is renegotiated, optionally followed a maximum amount of
1363: time that may pass before the session key is renegotiated.
1364: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1365: .Sq K ,
1366: .Sq M ,
1.75 dtucker 1367: or
1.76 jmc 1368: .Sq G
1.75 dtucker 1369: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1370: The default is between
1.84 jmc 1371: .Sq 1G
1.75 dtucker 1372: and
1.84 jmc 1373: .Sq 4G ,
1.75 dtucker 1374: depending on the cipher.
1.162 dtucker 1375: The optional second value is specified in seconds and may use any of the
1376: units documented in the
1.166 jmc 1377: TIME FORMATS section of
1.162 dtucker 1378: .Xr sshd_config 5 .
1379: The default value for
1380: .Cm RekeyLimit
1381: is
1382: .Dq default none ,
1383: which means that rekeying is performed after the cipher's default amount
1384: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1385: This option applies to protocol version 2 only.
1.1 stevesk 1386: .It Cm RemoteForward
1.74 jmc 1387: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1388: the secure channel to the specified host and port from the local machine.
1.49 jmc 1389: The first argument must be
1.43 djm 1390: .Sm off
1.49 jmc 1391: .Oo Ar bind_address : Oc Ar port
1.43 djm 1392: .Sm on
1.49 jmc 1393: and the second argument must be
1394: .Ar host : Ns Ar hostport .
1.138 djm 1395: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1396: Multiple forwardings may be specified, and additional
1397: forwardings can be given on the command line.
1.113 stevesk 1398: Privileged ports can be forwarded only when
1399: logging in as root on the remote machine.
1.118 jmc 1400: .Pp
1.117 djm 1401: If the
1402: .Ar port
1403: argument is
1404: .Ql 0 ,
1405: the listen port will be dynamically allocated on the server and reported
1406: to the client at run time.
1.43 djm 1407: .Pp
1408: If the
1409: .Ar bind_address
1410: is not specified, the default is to only bind to loopback addresses.
1411: If the
1412: .Ar bind_address
1413: is
1414: .Ql *
1415: or an empty string, then the forwarding is requested to listen on all
1416: interfaces.
1417: Specifying a remote
1418: .Ar bind_address
1.46 jmc 1419: will only succeed if the server's
1420: .Cm GatewayPorts
1.43 djm 1421: option is enabled (see
1.46 jmc 1422: .Xr sshd_config 5 ) .
1.149 djm 1423: .It Cm RequestTTY
1424: Specifies whether to request a pseudo-tty for the session.
1425: The argument may be one of:
1426: .Dq no
1427: (never request a TTY),
1428: .Dq yes
1429: (always request a TTY when standard input is a TTY),
1430: .Dq force
1431: (always request a TTY) or
1432: .Dq auto
1433: (request a TTY when opening a login session).
1434: This option mirrors the
1435: .Fl t
1436: and
1437: .Fl T
1438: flags for
1439: .Xr ssh 1 .
1.196 djm 1440: .It Cm RevokedHostKeys
1441: Specifies revoked host public keys.
1442: Keys listed in this file will be refused for host authentication.
1443: Note that if this file does not exist or is not readable,
1444: then host authentication will be refused for all hosts.
1445: Keys may be specified as a text file, listing one public key per line, or as
1446: an OpenSSH Key Revocation List (KRL) as generated by
1447: .Xr ssh-keygen 1 .
1448: For more information on KRLs, see the KEY REVOCATION LISTS section in
1449: .Xr ssh-keygen 1 .
1.1 stevesk 1450: .It Cm RhostsRSAAuthentication
1451: Specifies whether to try rhosts based authentication with RSA host
1452: authentication.
1453: The argument must be
1454: .Dq yes
1455: or
1456: .Dq no .
1457: The default is
1458: .Dq no .
1459: This option applies to protocol version 1 only and requires
1.84 jmc 1460: .Xr ssh 1
1.1 stevesk 1461: to be setuid root.
1462: .It Cm RSAAuthentication
1463: Specifies whether to try RSA authentication.
1464: The argument to this keyword must be
1465: .Dq yes
1466: or
1467: .Dq no .
1468: RSA authentication will only be
1469: attempted if the identity file exists, or an authentication agent is
1470: running.
1471: The default is
1472: .Dq yes .
1473: Note that this option applies to protocol version 1 only.
1.32 djm 1474: .It Cm SendEnv
1475: Specifies what variables from the local
1476: .Xr environ 7
1477: should be sent to the server.
1.84 jmc 1478: Note that environment passing is only supported for protocol 2.
1479: The server must also support it, and the server must be configured to
1.33 djm 1480: accept these environment variables.
1.207 dtucker 1481: Note that the
1482: .Ev TERM
1.208 jmc 1483: environment variable is always sent whenever a
1.207 dtucker 1484: pseudo-terminal is requested as it is required by the protocol.
1.32 djm 1485: Refer to
1486: .Cm AcceptEnv
1487: in
1488: .Xr sshd_config 5
1489: for how to configure the server.
1.80 jmc 1490: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1491: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1492: across multiple
1493: .Cm SendEnv
1494: directives.
1495: The default is not to send any environment variables.
1.81 jmc 1496: .Pp
1497: See
1498: .Sx PATTERNS
1499: for more information on patterns.
1.28 markus 1500: .It Cm ServerAliveCountMax
1.73 jmc 1501: Sets the number of server alive messages (see below) which may be
1.28 markus 1502: sent without
1.84 jmc 1503: .Xr ssh 1
1.28 markus 1504: receiving any messages back from the server.
1505: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1506: ssh will disconnect from the server, terminating the session.
1.28 markus 1507: It is important to note that the use of server alive messages is very
1508: different from
1509: .Cm TCPKeepAlive
1510: (below).
1511: The server alive messages are sent through the encrypted channel
1512: and therefore will not be spoofable.
1513: The TCP keepalive option enabled by
1514: .Cm TCPKeepAlive
1515: is spoofable.
1516: The server alive mechanism is valuable when the client or
1517: server depend on knowing when a connection has become inactive.
1518: .Pp
1519: The default value is 3.
1520: If, for example,
1521: .Cm ServerAliveInterval
1.84 jmc 1522: (see below) is set to 15 and
1.28 markus 1523: .Cm ServerAliveCountMax
1.84 jmc 1524: is left at the default, if the server becomes unresponsive,
1525: ssh will disconnect after approximately 45 seconds.
1.89 markus 1526: This option applies to protocol version 2 only.
1.67 jmc 1527: .It Cm ServerAliveInterval
1528: Sets a timeout interval in seconds after which if no data has been received
1529: from the server,
1.84 jmc 1530: .Xr ssh 1
1.67 jmc 1531: will send a message through the encrypted
1532: channel to request a response from the server.
1533: The default
1534: is 0, indicating that these messages will not be sent to the server.
1535: This option applies to protocol version 2 only.
1.191 millert 1536: .It Cm StreamLocalBindMask
1537: Sets the octal file creation mode mask
1538: .Pq umask
1539: used when creating a Unix-domain socket file for local or remote
1540: port forwarding.
1541: This option is only used for port forwarding to a Unix-domain socket file.
1542: .Pp
1543: The default value is 0177, which creates a Unix-domain socket file that is
1544: readable and writable only by the owner.
1545: Note that not all operating systems honor the file mode on Unix-domain
1546: socket files.
1547: .It Cm StreamLocalBindUnlink
1548: Specifies whether to remove an existing Unix-domain socket file for local
1549: or remote port forwarding before creating a new one.
1550: If the socket file already exists and
1551: .Cm StreamLocalBindUnlink
1552: is not enabled,
1553: .Nm ssh
1554: will be unable to forward the port to the Unix-domain socket file.
1555: This option is only used for port forwarding to a Unix-domain socket file.
1556: .Pp
1557: The argument must be
1558: .Dq yes
1559: or
1560: .Dq no .
1561: The default is
1562: .Dq no .
1.1 stevesk 1563: .It Cm StrictHostKeyChecking
1564: If this flag is set to
1565: .Dq yes ,
1.84 jmc 1566: .Xr ssh 1
1.1 stevesk 1567: will never automatically add host keys to the
1.50 djm 1568: .Pa ~/.ssh/known_hosts
1.1 stevesk 1569: file, and refuses to connect to hosts whose host key has changed.
1570: This provides maximum protection against trojan horse attacks,
1.84 jmc 1571: though it can be annoying when the
1.1 stevesk 1572: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1573: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1574: frequently made.
1575: This option forces the user to manually
1576: add all new hosts.
1577: If this flag is set to
1578: .Dq no ,
1.84 jmc 1579: ssh will automatically add new host keys to the
1.1 stevesk 1580: user known hosts files.
1581: If this flag is set to
1582: .Dq ask ,
1583: new host keys
1584: will be added to the user known host files only after the user
1585: has confirmed that is what they really want to do, and
1.84 jmc 1586: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1587: The host keys of
1588: known hosts will be verified automatically in all cases.
1589: The argument must be
1590: .Dq yes ,
1.84 jmc 1591: .Dq no ,
1.1 stevesk 1592: or
1593: .Dq ask .
1594: The default is
1595: .Dq ask .
1.26 markus 1596: .It Cm TCPKeepAlive
1597: Specifies whether the system should send TCP keepalive messages to the
1598: other side.
1599: If they are sent, death of the connection or crash of one
1600: of the machines will be properly noticed.
1601: However, this means that
1602: connections will die if the route is down temporarily, and some people
1603: find it annoying.
1604: .Pp
1605: The default is
1606: .Dq yes
1607: (to send TCP keepalive messages), and the client will notice
1608: if the network goes down or the remote host dies.
1609: This is important in scripts, and many users want it too.
1610: .Pp
1611: To disable TCP keepalive messages, the value should be set to
1612: .Dq no .
1.65 reyk 1613: .It Cm Tunnel
1.95 stevesk 1614: Request
1.65 reyk 1615: .Xr tun 4
1.69 jmc 1616: device forwarding between the client and the server.
1.65 reyk 1617: The argument must be
1.68 reyk 1618: .Dq yes ,
1.95 stevesk 1619: .Dq point-to-point
1620: (layer 3),
1621: .Dq ethernet
1622: (layer 2),
1.65 reyk 1623: or
1624: .Dq no .
1.95 stevesk 1625: Specifying
1626: .Dq yes
1627: requests the default tunnel mode, which is
1628: .Dq point-to-point .
1.65 reyk 1629: The default is
1630: .Dq no .
1631: .It Cm TunnelDevice
1.95 stevesk 1632: Specifies the
1.65 reyk 1633: .Xr tun 4
1.95 stevesk 1634: devices to open on the client
1635: .Pq Ar local_tun
1636: and the server
1637: .Pq Ar remote_tun .
1638: .Pp
1639: The argument must be
1640: .Sm off
1641: .Ar local_tun Op : Ar remote_tun .
1642: .Sm on
1643: The devices may be specified by numerical ID or the keyword
1644: .Dq any ,
1645: which uses the next available tunnel device.
1646: If
1647: .Ar remote_tun
1648: is not specified, it defaults to
1649: .Dq any .
1650: The default is
1651: .Dq any:any .
1.201 djm 1652: .It Cm UpdateHostKeys
1.200 djm 1653: Specifies whether
1654: .Xr ssh 1
1655: should accept notifications of additional hostkeys from the server sent
1656: after authentication has completed and add them to
1657: .Cm UserKnownHostsFile .
1658: The argument must be
1.204 djm 1659: .Dq yes ,
1.203 djm 1660: .Dq no
1.204 djm 1661: (the default) or
1662: .Dq ask .
1.200 djm 1663: Enabling this option allows learning alternate hostkeys for a server
1.201 djm 1664: and supports graceful key rotation by allowing a server to send replacement
1665: public keys before old ones are removed.
1.200 djm 1666: Additional hostkeys are only accepted if the key used to authenticate the
1.220 sobrado 1667: host was already trusted or explicitly accepted by the user.
1.204 djm 1668: If
1669: .Cm UpdateHostKeys
1670: is set to
1671: .Dq ask ,
1672: then the user is asked to confirm the modifications to the known_hosts file.
1.205 djm 1673: Confirmation is currently incompatible with
1674: .Cm ControlPersist ,
1675: and will be disabled if it is enabled.
1.200 djm 1676: .Pp
1677: Presently, only
1678: .Xr sshd 8
1679: from OpenSSH 6.8 and greater support the
1680: .Dq hostkeys@openssh.com
1681: protocol extension used to inform the client of all the server's hostkeys.
1.72 jmc 1682: .It Cm UsePrivilegedPort
1683: Specifies whether to use a privileged port for outgoing connections.
1684: The argument must be
1685: .Dq yes
1686: or
1687: .Dq no .
1688: The default is
1689: .Dq no .
1690: If set to
1.84 jmc 1691: .Dq yes ,
1692: .Xr ssh 1
1.72 jmc 1693: must be setuid root.
1694: Note that this option must be set to
1695: .Dq yes
1696: for
1697: .Cm RhostsRSAAuthentication
1698: with older servers.
1.1 stevesk 1699: .It Cm User
1700: Specifies the user to log in as.
1701: This can be useful when a different user name is used on different machines.
1702: This saves the trouble of
1703: having to remember to give the user name on the command line.
1704: .It Cm UserKnownHostsFile
1.151 djm 1705: Specifies one or more files to use for the user
1706: host key database, separated by whitespace.
1707: The default is
1708: .Pa ~/.ssh/known_hosts ,
1709: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1710: .It Cm VerifyHostKeyDNS
1711: Specifies whether to verify the remote key using DNS and SSHFP resource
1712: records.
1.24 jakob 1713: If this option is set to
1714: .Dq yes ,
1.25 jmc 1715: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1716: from DNS.
1717: Insecure fingerprints will be handled as if this option was set to
1718: .Dq ask .
1719: If this option is set to
1720: .Dq ask ,
1721: information on fingerprint match will be displayed, but the user will still
1722: need to confirm new host keys according to the
1723: .Cm StrictHostKeyChecking
1724: option.
1725: The argument must be
1726: .Dq yes ,
1.84 jmc 1727: .Dq no ,
1.25 jmc 1728: or
1729: .Dq ask .
1.8 jakob 1730: The default is
1731: .Dq no .
1.12 jakob 1732: Note that this option applies to protocol version 2 only.
1.84 jmc 1733: .Pp
1.166 jmc 1734: See also VERIFYING HOST KEYS in
1.84 jmc 1735: .Xr ssh 1 .
1.111 grunk 1736: .It Cm VisualHostKey
1737: If this flag is set to
1738: .Dq yes ,
1739: an ASCII art representation of the remote host key fingerprint is
1.197 djm 1740: printed in addition to the fingerprint string at login and
1.114 stevesk 1741: for unknown host keys.
1.111 grunk 1742: If this flag is set to
1743: .Dq no ,
1.114 stevesk 1744: no fingerprint strings are printed at login and
1.197 djm 1745: only the fingerprint string will be printed for unknown host keys.
1.111 grunk 1746: The default is
1747: .Dq no .
1.1 stevesk 1748: .It Cm XAuthLocation
1.5 stevesk 1749: Specifies the full pathname of the
1.1 stevesk 1750: .Xr xauth 1
1751: program.
1752: The default is
1753: .Pa /usr/X11R6/bin/xauth .
1754: .El
1.86 jmc 1755: .Sh PATTERNS
1756: A
1757: .Em pattern
1758: consists of zero or more non-whitespace characters,
1759: .Sq *
1760: (a wildcard that matches zero or more characters),
1761: or
1762: .Sq ?\&
1763: (a wildcard that matches exactly one character).
1764: For example, to specify a set of declarations for any host in the
1765: .Dq .co.uk
1766: set of domains,
1767: the following pattern could be used:
1768: .Pp
1769: .Dl Host *.co.uk
1770: .Pp
1771: The following pattern
1772: would match any host in the 192.168.0.[0-9] network range:
1773: .Pp
1774: .Dl Host 192.168.0.?
1775: .Pp
1776: A
1777: .Em pattern-list
1778: is a comma-separated list of patterns.
1779: Patterns within pattern-lists may be negated
1780: by preceding them with an exclamation mark
1781: .Pq Sq !\& .
1782: For example,
1.174 djm 1783: to allow a key to be used from anywhere within an organization
1.86 jmc 1784: except from the
1785: .Dq dialup
1786: pool,
1787: the following entry (in authorized_keys) could be used:
1788: .Pp
1789: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1790: .Sh FILES
1791: .Bl -tag -width Ds
1.50 djm 1792: .It Pa ~/.ssh/config
1.1 stevesk 1793: This is the per-user configuration file.
1794: The format of this file is described above.
1.84 jmc 1795: This file is used by the SSH client.
1.30 djm 1796: Because of the potential for abuse, this file must have strict permissions:
1797: read/write for the user, and not accessible by others.
1.1 stevesk 1798: .It Pa /etc/ssh/ssh_config
1799: Systemwide configuration file.
1800: This file provides defaults for those
1801: values that are not specified in the user's configuration file, and
1802: for those users who do not have a configuration file.
1803: This file must be world-readable.
1804: .El
1.13 jmc 1805: .Sh SEE ALSO
1806: .Xr ssh 1
1.1 stevesk 1807: .Sh AUTHORS
1808: OpenSSH is a derivative of the original and free
1809: ssh 1.2.12 release by Tatu Ylonen.
1810: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1811: Theo de Raadt and Dug Song
1812: removed many bugs, re-added newer features and
1813: created OpenSSH.
1814: Markus Friedl contributed the support for SSH
1815: protocol versions 1.5 and 2.0.
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