Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.178
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
28: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
29: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
31: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
32: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
33: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
34: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
35: .\"
1.178 ! dtucker 36: .\" $OpenBSD: ssh_config.5,v 1.177 2013/10/20 18:00:13 jmc Exp $
1.176 djm 37: .Dd $Mdocdate: October 20 2013 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
42: .Nd OpenSSH SSH client configuration files
43: .Sh SYNOPSIS
1.98 jmc 44: .Nm ~/.ssh/config
45: .Nm /etc/ssh/ssh_config
1.1 stevesk 46: .Sh DESCRIPTION
1.84 jmc 47: .Xr ssh 1
1.1 stevesk 48: obtains configuration data from the following sources in
49: the following order:
1.79 jmc 50: .Pp
1.2 stevesk 51: .Bl -enum -offset indent -compact
52: .It
53: command-line options
54: .It
55: user's configuration file
1.50 djm 56: .Pq Pa ~/.ssh/config
1.2 stevesk 57: .It
58: system-wide configuration file
59: .Pq Pa /etc/ssh/ssh_config
60: .El
1.1 stevesk 61: .Pp
62: For each parameter, the first obtained value
63: will be used.
1.41 jmc 64: The configuration files contain sections separated by
1.1 stevesk 65: .Dq Host
66: specifications, and that section is only applied for hosts that
67: match one of the patterns given in the specification.
68: The matched host name is the one given on the command line.
69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.1 stevesk 74: The configuration file has the following format:
75: .Pp
76: Empty lines and lines starting with
77: .Ql #
78: are comments.
79: Otherwise a line is of the format
80: .Dq keyword arguments .
81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
1.88 dtucker 92: Arguments may optionally be enclosed in double quotes
93: .Pq \&"
94: in order to represent arguments containing spaces.
1.1 stevesk 95: .Pp
96: The possible
97: keywords and their meanings are as follows (note that
98: keywords are case-insensitive and arguments are case-sensitive):
99: .Bl -tag -width Ds
100: .It Cm Host
101: Restricts the following declarations (up to the next
102: .Cm Host
1.169 djm 103: or
104: .Cm Match
1.1 stevesk 105: keyword) to be only for those hosts that match one of the patterns
106: given after the keyword.
1.112 krw 107: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 108: A single
1.83 jmc 109: .Ql *
1.1 stevesk 110: as a pattern can be used to provide global
111: defaults for all hosts.
112: The host is the
113: .Ar hostname
1.83 jmc 114: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 115: a canonicalized host name before matching).
1.148 djm 116: .Pp
117: A pattern entry may be negated by prefixing it with an exclamation mark
118: .Pq Sq !\& .
119: If a negated entry is matched, then the
120: .Cm Host
121: entry is ignored, regardless of whether any other patterns on the line
122: match.
123: Negated matches are therefore useful to provide exceptions for wildcard
124: matches.
1.81 jmc 125: .Pp
126: See
127: .Sx PATTERNS
128: for more information on patterns.
1.170 jmc 129: .It Cm Match
1.169 djm 130: Restricts the following declarations (up to the next
131: .Cm Host
132: or
133: .Cm Match
134: keyword) to be used only when the conditions following the
135: .Cm Match
136: keyword are satisfied.
1.178 ! dtucker 137: Match conditions are specified using one or more keyword/criteria pairs
! 138: or the single token
! 139: .Cm all
! 140: which matches all criteria.
1.169 djm 141: The available keywords are:
1.176 djm 142: .Cm exec ,
1.169 djm 143: .Cm host ,
144: .Cm originalhost ,
145: .Cm user ,
146: and
147: .Cm localuser .
148: .Pp
1.177 jmc 149: The
1.176 djm 150: .Cm exec
1.177 jmc 151: keyword executes the specified command under the user's shell.
1.169 djm 152: If the command returns a zero exit status then the condition is considered true.
153: Commands containing whitespace characters must be quoted.
1.175 djm 154: The following character sequences in the command will be expanded prior to
155: execution:
156: .Ql %L
157: will be substituted by the first component of the local host name,
158: .Ql %l
159: will be substituted by the local host name (including any domain name),
160: .Ql %h
161: will be substituted by the target host name,
162: .Ql %n
163: will be substituted by the original target host name
1.176 djm 164: specified on the command-line,
1.175 djm 165: .Ql %p
166: the destination port,
167: .Ql %r
168: by the remote login username, and
169: .Ql %u
170: by the username of the user running
171: .Xr ssh 1 .
1.169 djm 172: .Pp
173: The other keywords' criteria must be single entries or comma-separated
174: lists and may use the wildcard and negation operators described in the
175: .Sx PATTERNS
176: section.
177: The criteria for the
178: .Cm host
179: keyword are matched against the target hostname, after any substitution
180: by the
181: .Cm Hostname
182: option.
183: The
184: .Cm originalhost
185: keyword matches against the hostname as it was specified on the command-line.
186: The
187: .Cm user
188: keyword matches against the target username on the remote host.
189: The
190: .Cm localuser
191: keyword matches against the name of the local user running
192: .Xr ssh 1
193: (this keyword may be useful in system-wide
194: .Nm
195: files).
1.10 djm 196: .It Cm AddressFamily
1.11 jmc 197: Specifies which address family to use when connecting.
198: Valid arguments are
1.10 djm 199: .Dq any ,
200: .Dq inet
1.84 jmc 201: (use IPv4 only), or
1.10 djm 202: .Dq inet6
1.40 jmc 203: (use IPv6 only).
1.1 stevesk 204: .It Cm BatchMode
205: If set to
206: .Dq yes ,
207: passphrase/password querying will be disabled.
208: This option is useful in scripts and other batch jobs where no user
209: is present to supply the password.
210: The argument must be
211: .Dq yes
212: or
213: .Dq no .
214: The default is
215: .Dq no .
216: .It Cm BindAddress
1.60 dtucker 217: Use the specified address on the local machine as the source address of
1.61 jmc 218: the connection.
219: Only useful on systems with more than one address.
1.1 stevesk 220: Note that this option does not work if
221: .Cm UsePrivilegedPort
222: is set to
223: .Dq yes .
1.171 djm 224: .It Cm CanonicalDomains
1.172 jmc 225: When
1.173 djm 226: .Cm CanonicalizeHostname
1.171 djm 227: is enabled, this option specifies the list of domain suffixes in which to
228: search for the specified destination host.
1.173 djm 229: .It Cm CanonicalizeFallbackLocal
1.174 djm 230: Specifies whether to fail with an error when hostname canonicalization fails.
1.172 jmc 231: The default,
232: .Dq no ,
233: will attempt to look up the unqualified hostname using the system resolver's
1.171 djm 234: search rules.
235: A value of
236: .Dq yes
237: will cause
238: .Xr ssh 1
239: to fail instantly if
1.173 djm 240: .Cm CanonicalizeHostname
1.171 djm 241: is enabled and the target hostname cannot be found in any of the domains
242: specified by
243: .Cm CanonicalDomains .
1.173 djm 244: .It Cm CanonicalizeHostname
1.174 djm 245: Controls whether explicit hostname canonicalization is performed.
1.172 jmc 246: The default,
247: .Dq no ,
1.171 djm 248: is not to perform any name rewriting and let the system resolver handle all
249: hostname lookups.
250: If set to
251: .Dq yes
252: then, for connections that do not use a
253: .Cm ProxyCommand ,
254: .Xr ssh 1
1.173 djm 255: will attempt to canonicalize the hostname specified on the command line
1.171 djm 256: using the
257: .Cm CanonicalDomains
258: suffixes and
1.173 djm 259: .Cm CanonicalizePermittedCNAMEs
1.171 djm 260: rules.
261: If
1.173 djm 262: .Cm CanonicalizeHostname
1.171 djm 263: is set to
264: .Dq always ,
1.174 djm 265: then canonicalization is applied to proxied connections too.
1.173 djm 266: .It Cm CanonicalizeMaxDots
1.172 jmc 267: Specifies the maximum number of dot characters in a hostname before
1.174 djm 268: canonicalization is disabled.
1.172 jmc 269: The default,
270: .Dq 1 ,
271: allows a single dot (i.e. hostname.subdomain).
1.173 djm 272: .It Cm CanonicalizePermittedCNAMEs
1.172 jmc 273: Specifies rules to determine whether CNAMEs should be followed when
1.173 djm 274: canonicalizing hostnames.
1.171 djm 275: The rules consist of one or more arguments of
1.172 jmc 276: .Ar source_domain_list : Ns Ar target_domain_list ,
1.171 djm 277: where
278: .Ar source_domain_list
1.174 djm 279: is a pattern-list of domains that may follow CNAMEs in canonicalization,
1.171 djm 280: and
281: .Ar target_domain_list
1.172 jmc 282: is a pattern-list of domains that they may resolve to.
1.171 djm 283: .Pp
284: For example,
285: .Dq *.a.example.com:*.b.example.com,*.c.example.com
286: will allow hostnames matching
287: .Dq *.a.example.com
1.173 djm 288: to be canonicalized to names in the
1.171 djm 289: .Dq *.b.example.com
290: or
291: .Dq *.c.example.com
292: domains.
1.1 stevesk 293: .It Cm ChallengeResponseAuthentication
1.82 jmc 294: Specifies whether to use challenge-response authentication.
1.1 stevesk 295: The argument to this keyword must be
296: .Dq yes
297: or
298: .Dq no .
299: The default is
300: .Dq yes .
301: .It Cm CheckHostIP
302: If this flag is set to
303: .Dq yes ,
1.84 jmc 304: .Xr ssh 1
305: will additionally check the host IP address in the
1.1 stevesk 306: .Pa known_hosts
307: file.
308: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 309: If the option is set to
1.1 stevesk 310: .Dq no ,
311: the check will not be executed.
312: The default is
313: .Dq yes .
314: .It Cm Cipher
315: Specifies the cipher to use for encrypting the session
316: in protocol version 1.
317: Currently,
318: .Dq blowfish ,
319: .Dq 3des ,
320: and
321: .Dq des
322: are supported.
323: .Ar des
324: is only supported in the
1.84 jmc 325: .Xr ssh 1
1.1 stevesk 326: client for interoperability with legacy protocol 1 implementations
327: that do not support the
328: .Ar 3des
1.7 jmc 329: cipher.
330: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 331: The default is
332: .Dq 3des .
333: .It Cm Ciphers
334: Specifies the ciphers allowed for protocol version 2
335: in order of preference.
336: Multiple ciphers must be comma-separated.
1.35 dtucker 337: The supported ciphers are
338: .Dq 3des-cbc ,
339: .Dq aes128-cbc ,
340: .Dq aes192-cbc ,
341: .Dq aes256-cbc ,
342: .Dq aes128-ctr ,
343: .Dq aes192-ctr ,
344: .Dq aes256-ctr ,
1.161 markus 345: .Dq aes128-gcm@openssh.com ,
346: .Dq aes256-gcm@openssh.com ,
1.54 djm 347: .Dq arcfour128 ,
348: .Dq arcfour256 ,
1.35 dtucker 349: .Dq arcfour ,
350: .Dq blowfish-cbc ,
351: and
352: .Dq cast128-cbc .
1.84 jmc 353: The default is:
354: .Bd -literal -offset 3n
1.116 naddy 355: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
1.161 markus 356: aes128-gcm@openssh.com,aes256-gcm@openssh.com,
1.116 naddy 357: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
358: aes256-cbc,arcfour
1.1 stevesk 359: .Ed
360: .It Cm ClearAllForwardings
1.84 jmc 361: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 362: specified in the configuration files or on the command line be
1.7 jmc 363: cleared.
364: This option is primarily useful when used from the
1.84 jmc 365: .Xr ssh 1
1.1 stevesk 366: command line to clear port forwardings set in
367: configuration files, and is automatically set by
368: .Xr scp 1
369: and
370: .Xr sftp 1 .
371: The argument must be
372: .Dq yes
373: or
374: .Dq no .
375: The default is
376: .Dq no .
377: .It Cm Compression
378: Specifies whether to use compression.
379: The argument must be
380: .Dq yes
381: or
382: .Dq no .
383: The default is
384: .Dq no .
385: .It Cm CompressionLevel
386: Specifies the compression level to use if compression is enabled.
387: The argument must be an integer from 1 (fast) to 9 (slow, best).
388: The default level is 6, which is good for most applications.
389: The meaning of the values is the same as in
390: .Xr gzip 1 .
391: Note that this option applies to protocol version 1 only.
392: .It Cm ConnectionAttempts
393: Specifies the number of tries (one per second) to make before exiting.
394: The argument must be an integer.
395: This may be useful in scripts if the connection sometimes fails.
396: The default is 1.
1.9 djm 397: .It Cm ConnectTimeout
1.84 jmc 398: Specifies the timeout (in seconds) used when connecting to the
399: SSH server, instead of using the default system TCP timeout.
1.11 jmc 400: This value is used only when the target is down or really unreachable,
401: not when it refuses the connection.
1.36 djm 402: .It Cm ControlMaster
403: Enables the sharing of multiple sessions over a single network connection.
404: When set to
1.84 jmc 405: .Dq yes ,
406: .Xr ssh 1
1.36 djm 407: will listen for connections on a control socket specified using the
408: .Cm ControlPath
409: argument.
410: Additional sessions can connect to this socket using the same
411: .Cm ControlPath
412: with
413: .Cm ControlMaster
414: set to
415: .Dq no
1.38 jmc 416: (the default).
1.64 jmc 417: These sessions will try to reuse the master instance's network connection
1.63 djm 418: rather than initiating new ones, but will fall back to connecting normally
419: if the control socket does not exist, or is not listening.
420: .Pp
1.37 djm 421: Setting this to
422: .Dq ask
1.84 jmc 423: will cause ssh
1.37 djm 424: to listen for control connections, but require confirmation using the
425: .Ev SSH_ASKPASS
426: program before they are accepted (see
427: .Xr ssh-add 1
1.38 jmc 428: for details).
1.51 jakob 429: If the
430: .Cm ControlPath
1.84 jmc 431: cannot be opened,
432: ssh will continue without connecting to a master instance.
1.58 djm 433: .Pp
434: X11 and
1.59 jmc 435: .Xr ssh-agent 1
1.58 djm 436: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 437: display and agent forwarded will be the one belonging to the master
1.59 jmc 438: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 439: .Pp
440: Two additional options allow for opportunistic multiplexing: try to use a
441: master connection but fall back to creating a new one if one does not already
442: exist.
443: These options are:
444: .Dq auto
445: and
446: .Dq autoask .
447: The latter requires confirmation like the
448: .Dq ask
449: option.
1.36 djm 450: .It Cm ControlPath
1.55 djm 451: Specify the path to the control socket used for connection sharing as described
452: in the
1.36 djm 453: .Cm ControlMaster
1.57 djm 454: section above or the string
455: .Dq none
456: to disable connection sharing.
1.55 djm 457: In the path,
1.147 djm 458: .Ql %L
459: will be substituted by the first component of the local host name,
1.77 djm 460: .Ql %l
1.147 djm 461: will be substituted by the local host name (including any domain name),
1.55 djm 462: .Ql %h
463: will be substituted by the target host name,
1.150 jmc 464: .Ql %n
465: will be substituted by the original target host name
466: specified on the command line,
1.55 djm 467: .Ql %p
1.175 djm 468: the destination port,
1.55 djm 469: .Ql %r
1.147 djm 470: by the remote login username, and
471: .Ql %u
472: by the username of the user running
473: .Xr ssh 1 .
1.56 djm 474: It is recommended that any
475: .Cm ControlPath
476: used for opportunistic connection sharing include
1.78 jmc 477: at least %h, %p, and %r.
1.56 djm 478: This ensures that shared connections are uniquely identified.
1.137 djm 479: .It Cm ControlPersist
480: When used in conjunction with
481: .Cm ControlMaster ,
482: specifies that the master connection should remain open
483: in the background (waiting for future client connections)
484: after the initial client connection has been closed.
485: If set to
486: .Dq no ,
487: then the master connection will not be placed into the background,
488: and will close as soon as the initial client connection is closed.
489: If set to
490: .Dq yes ,
491: then the master connection will remain in the background indefinitely
492: (until killed or closed via a mechanism such as the
493: .Xr ssh 1
494: .Dq Fl O No exit
495: option).
496: If set to a time in seconds, or a time in any of the formats documented in
497: .Xr sshd_config 5 ,
498: then the backgrounded master connection will automatically terminate
499: after it has remained idle (with no client connections) for the
500: specified time.
1.38 jmc 501: .It Cm DynamicForward
1.74 jmc 502: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 503: over the secure channel, and the application
504: protocol is then used to determine where to connect to from the
505: remote machine.
1.62 djm 506: .Pp
507: The argument must be
508: .Sm off
509: .Oo Ar bind_address : Oc Ar port .
510: .Sm on
1.138 djm 511: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 512: By default, the local port is bound in accordance with the
513: .Cm GatewayPorts
514: setting.
515: However, an explicit
516: .Ar bind_address
517: may be used to bind the connection to a specific address.
518: The
519: .Ar bind_address
520: of
521: .Dq localhost
522: indicates that the listening port be bound for local use only, while an
523: empty address or
524: .Sq *
525: indicates that the port should be available from all interfaces.
526: .Pp
1.38 jmc 527: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 528: .Xr ssh 1
1.38 jmc 529: will act as a SOCKS server.
530: Multiple forwardings may be specified, and
531: additional forwardings can be given on the command line.
532: Only the superuser can forward privileged ports.
1.14 markus 533: .It Cm EnableSSHKeysign
534: Setting this option to
535: .Dq yes
536: in the global client configuration file
537: .Pa /etc/ssh/ssh_config
538: enables the use of the helper program
539: .Xr ssh-keysign 8
540: during
541: .Cm HostbasedAuthentication .
542: The argument must be
543: .Dq yes
544: or
545: .Dq no .
546: The default is
547: .Dq no .
1.23 jmc 548: This option should be placed in the non-hostspecific section.
1.14 markus 549: See
550: .Xr ssh-keysign 8
551: for more information.
1.1 stevesk 552: .It Cm EscapeChar
553: Sets the escape character (default:
554: .Ql ~ ) .
555: The escape character can also
556: be set on the command line.
557: The argument should be a single character,
558: .Ql ^
559: followed by a letter, or
560: .Dq none
561: to disable the escape
562: character entirely (making the connection transparent for binary
563: data).
1.96 markus 564: .It Cm ExitOnForwardFailure
565: Specifies whether
566: .Xr ssh 1
567: should terminate the connection if it cannot set up all requested
1.102 stevesk 568: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 569: The argument must be
570: .Dq yes
571: or
572: .Dq no .
573: The default is
574: .Dq no .
1.1 stevesk 575: .It Cm ForwardAgent
576: Specifies whether the connection to the authentication agent (if any)
577: will be forwarded to the remote machine.
578: The argument must be
579: .Dq yes
580: or
581: .Dq no .
582: The default is
583: .Dq no .
1.3 stevesk 584: .Pp
1.7 jmc 585: Agent forwarding should be enabled with caution.
586: Users with the ability to bypass file permissions on the remote host
587: (for the agent's Unix-domain socket)
588: can access the local agent through the forwarded connection.
589: An attacker cannot obtain key material from the agent,
1.3 stevesk 590: however they can perform operations on the keys that enable them to
591: authenticate using the identities loaded into the agent.
1.1 stevesk 592: .It Cm ForwardX11
593: Specifies whether X11 connections will be automatically redirected
594: over the secure channel and
595: .Ev DISPLAY
596: set.
597: The argument must be
598: .Dq yes
599: or
600: .Dq no .
601: The default is
602: .Dq no .
1.3 stevesk 603: .Pp
1.7 jmc 604: X11 forwarding should be enabled with caution.
605: Users with the ability to bypass file permissions on the remote host
1.22 markus 606: (for the user's X11 authorization database)
1.7 jmc 607: can access the local X11 display through the forwarded connection.
1.22 markus 608: An attacker may then be able to perform activities such as keystroke monitoring
609: if the
610: .Cm ForwardX11Trusted
611: option is also enabled.
1.134 djm 612: .It Cm ForwardX11Timeout
1.135 jmc 613: Specify a timeout for untrusted X11 forwarding
614: using the format described in the
1.166 jmc 615: TIME FORMATS section of
1.134 djm 616: .Xr sshd_config 5 .
617: X11 connections received by
618: .Xr ssh 1
619: after this time will be refused.
620: The default is to disable untrusted X11 forwarding after twenty minutes has
621: elapsed.
1.22 markus 622: .It Cm ForwardX11Trusted
1.34 jmc 623: If this option is set to
1.84 jmc 624: .Dq yes ,
625: remote X11 clients will have full access to the original X11 display.
1.42 djm 626: .Pp
1.22 markus 627: If this option is set to
1.84 jmc 628: .Dq no ,
629: remote X11 clients will be considered untrusted and prevented
1.22 markus 630: from stealing or tampering with data belonging to trusted X11
631: clients.
1.42 djm 632: Furthermore, the
633: .Xr xauth 1
634: token used for the session will be set to expire after 20 minutes.
635: Remote clients will be refused access after this time.
1.22 markus 636: .Pp
637: The default is
638: .Dq no .
639: .Pp
640: See the X11 SECURITY extension specification for full details on
641: the restrictions imposed on untrusted clients.
1.1 stevesk 642: .It Cm GatewayPorts
643: Specifies whether remote hosts are allowed to connect to local
644: forwarded ports.
645: By default,
1.84 jmc 646: .Xr ssh 1
1.7 jmc 647: binds local port forwardings to the loopback address.
648: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 649: .Cm GatewayPorts
1.84 jmc 650: can be used to specify that ssh
1.1 stevesk 651: should bind local port forwardings to the wildcard address,
652: thus allowing remote hosts to connect to forwarded ports.
653: The argument must be
654: .Dq yes
655: or
656: .Dq no .
657: The default is
658: .Dq no .
659: .It Cm GlobalKnownHostsFile
1.151 djm 660: Specifies one or more files to use for the global
661: host key database, separated by whitespace.
662: The default is
663: .Pa /etc/ssh/ssh_known_hosts ,
664: .Pa /etc/ssh/ssh_known_hosts2 .
1.18 markus 665: .It Cm GSSAPIAuthentication
1.27 markus 666: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 667: The default is
1.21 markus 668: .Dq no .
1.18 markus 669: Note that this option applies to protocol version 2 only.
670: .It Cm GSSAPIDelegateCredentials
671: Forward (delegate) credentials to the server.
672: The default is
673: .Dq no .
674: Note that this option applies to protocol version 2 only.
1.44 djm 675: .It Cm HashKnownHosts
676: Indicates that
1.84 jmc 677: .Xr ssh 1
1.44 djm 678: should hash host names and addresses when they are added to
1.50 djm 679: .Pa ~/.ssh/known_hosts .
1.44 djm 680: These hashed names may be used normally by
1.84 jmc 681: .Xr ssh 1
1.44 djm 682: and
1.84 jmc 683: .Xr sshd 8 ,
1.44 djm 684: but they do not reveal identifying information should the file's contents
685: be disclosed.
686: The default is
687: .Dq no .
1.97 jmc 688: Note that existing names and addresses in known hosts files
689: will not be converted automatically,
690: but may be manually hashed using
1.45 djm 691: .Xr ssh-keygen 1 .
1.1 stevesk 692: .It Cm HostbasedAuthentication
693: Specifies whether to try rhosts based authentication with public key
694: authentication.
695: The argument must be
696: .Dq yes
697: or
698: .Dq no .
699: The default is
700: .Dq no .
701: This option applies to protocol version 2 only and
702: is similar to
703: .Cm RhostsRSAAuthentication .
704: .It Cm HostKeyAlgorithms
705: Specifies the protocol version 2 host key algorithms
706: that the client wants to use in order of preference.
707: The default for this option is:
1.139 djm 708: .Bd -literal -offset 3n
709: ecdsa-sha2-nistp256-cert-v01@openssh.com,
710: ecdsa-sha2-nistp384-cert-v01@openssh.com,
711: ecdsa-sha2-nistp521-cert-v01@openssh.com,
712: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
713: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
714: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
715: ssh-rsa,ssh-dss
716: .Ed
1.145 djm 717: .Pp
718: If hostkeys are known for the destination host then this default is modified
719: to prefer their algorithms.
1.1 stevesk 720: .It Cm HostKeyAlias
721: Specifies an alias that should be used instead of the
722: real host name when looking up or saving the host key
723: in the host key database files.
1.84 jmc 724: This option is useful for tunneling SSH connections
1.1 stevesk 725: or for multiple servers running on a single host.
726: .It Cm HostName
727: Specifies the real host name to log into.
728: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 729: If the hostname contains the character sequence
730: .Ql %h ,
1.150 jmc 731: then this will be replaced with the host name specified on the command line
1.136 djm 732: (this is useful for manipulating unqualified names).
1.84 jmc 733: The default is the name given on the command line.
1.1 stevesk 734: Numeric IP addresses are also permitted (both on the command line and in
735: .Cm HostName
736: specifications).
1.29 markus 737: .It Cm IdentitiesOnly
738: Specifies that
1.84 jmc 739: .Xr ssh 1
1.29 markus 740: should only use the authentication identity files configured in the
1.31 jmc 741: .Nm
1.29 markus 742: files,
1.84 jmc 743: even if
744: .Xr ssh-agent 1
1.159 djm 745: or a
746: .Cm PKCS11Provider
1.29 markus 747: offers more identities.
748: The argument to this keyword must be
749: .Dq yes
750: or
751: .Dq no .
1.84 jmc 752: This option is intended for situations where ssh-agent
1.29 markus 753: offers many different identities.
754: The default is
755: .Dq no .
1.67 jmc 756: .It Cm IdentityFile
1.155 dtucker 757: Specifies a file from which the user's DSA, ECDSA or RSA authentication
1.139 djm 758: identity is read.
1.67 jmc 759: The default is
760: .Pa ~/.ssh/identity
761: for protocol version 1, and
1.139 djm 762: .Pa ~/.ssh/id_dsa ,
763: .Pa ~/.ssh/id_ecdsa
764: and
1.67 jmc 765: .Pa ~/.ssh/id_rsa
766: for protocol version 2.
767: Additionally, any identities represented by the authentication agent
1.165 djm 768: will be used for authentication unless
769: .Cm IdentitiesOnly
770: is set.
1.129 djm 771: .Xr ssh 1
772: will try to load certificate information from the filename obtained by
773: appending
774: .Pa -cert.pub
775: to the path of a specified
776: .Cm IdentityFile .
1.90 djm 777: .Pp
1.67 jmc 778: The file name may use the tilde
1.91 jmc 779: syntax to refer to a user's home directory or one of the following
1.90 djm 780: escape characters:
781: .Ql %d
782: (local user's home directory),
783: .Ql %u
784: (local user name),
785: .Ql %l
786: (local host name),
787: .Ql %h
788: (remote host name) or
1.92 djm 789: .Ql %r
1.90 djm 790: (remote user name).
791: .Pp
1.67 jmc 792: It is possible to have
793: multiple identity files specified in configuration files; all these
794: identities will be tried in sequence.
1.152 djm 795: Multiple
796: .Cm IdentityFile
797: directives will add to the list of identities tried (this behaviour
798: differs from that of other configuration directives).
1.165 djm 799: .Pp
800: .Cm IdentityFile
801: may be used in conjunction with
802: .Cm IdentitiesOnly
803: to select which identities in an agent are offered during authentication.
1.164 jmc 804: .It Cm IgnoreUnknown
805: Specifies a pattern-list of unknown options to be ignored if they are
806: encountered in configuration parsing.
807: This may be used to suppress errors if
808: .Nm
809: contains options that are unrecognised by
810: .Xr ssh 1 .
811: It is recommended that
812: .Cm IgnoreUnknown
813: be listed early in the configuration file as it will not be applied
814: to unknown options that appear before it.
1.143 djm 815: .It Cm IPQoS
816: Specifies the IPv4 type-of-service or DSCP class for connections.
817: Accepted values are
818: .Dq af11 ,
819: .Dq af12 ,
820: .Dq af13 ,
1.154 djm 821: .Dq af21 ,
1.143 djm 822: .Dq af22 ,
823: .Dq af23 ,
824: .Dq af31 ,
825: .Dq af32 ,
826: .Dq af33 ,
827: .Dq af41 ,
828: .Dq af42 ,
829: .Dq af43 ,
830: .Dq cs0 ,
831: .Dq cs1 ,
832: .Dq cs2 ,
833: .Dq cs3 ,
834: .Dq cs4 ,
835: .Dq cs5 ,
836: .Dq cs6 ,
837: .Dq cs7 ,
838: .Dq ef ,
839: .Dq lowdelay ,
840: .Dq throughput ,
841: .Dq reliability ,
842: or a numeric value.
1.146 djm 843: This option may take one or two arguments, separated by whitespace.
1.143 djm 844: If one argument is specified, it is used as the packet class unconditionally.
845: If two values are specified, the first is automatically selected for
846: interactive sessions and the second for non-interactive sessions.
847: The default is
848: .Dq lowdelay
849: for interactive sessions and
850: .Dq throughput
851: for non-interactive sessions.
1.103 djm 852: .It Cm KbdInteractiveAuthentication
853: Specifies whether to use keyboard-interactive authentication.
854: The argument to this keyword must be
855: .Dq yes
856: or
857: .Dq no .
858: The default is
859: .Dq yes .
1.39 djm 860: .It Cm KbdInteractiveDevices
861: Specifies the list of methods to use in keyboard-interactive authentication.
862: Multiple method names must be comma-separated.
863: The default is to use the server specified list.
1.85 jmc 864: The methods available vary depending on what the server supports.
865: For an OpenSSH server,
866: it may be zero or more of:
867: .Dq bsdauth ,
868: .Dq pam ,
869: and
870: .Dq skey .
1.140 djm 871: .It Cm KexAlgorithms
872: Specifies the available KEX (Key Exchange) algorithms.
873: Multiple algorithms must be comma-separated.
1.141 jmc 874: The default is:
875: .Bd -literal -offset indent
876: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
877: diffie-hellman-group-exchange-sha256,
878: diffie-hellman-group-exchange-sha1,
879: diffie-hellman-group14-sha1,
880: diffie-hellman-group1-sha1
881: .Ed
1.65 reyk 882: .It Cm LocalCommand
883: Specifies a command to execute on the local machine after successfully
884: connecting to the server.
885: The command string extends to the end of the line, and is executed with
1.105 jmc 886: the user's shell.
1.109 dtucker 887: The following escape character substitutions will be performed:
888: .Ql %d
889: (local user's home directory),
890: .Ql %h
891: (remote host name),
892: .Ql %l
893: (local host name),
894: .Ql %n
895: (host name as provided on the command line),
896: .Ql %p
897: (remote port),
898: .Ql %r
899: (remote user name) or
900: .Ql %u
901: (local user name).
1.123 djm 902: .Pp
903: The command is run synchronously and does not have access to the
904: session of the
905: .Xr ssh 1
906: that spawned it.
907: It should not be used for interactive commands.
908: .Pp
1.65 reyk 909: This directive is ignored unless
910: .Cm PermitLocalCommand
911: has been enabled.
1.1 stevesk 912: .It Cm LocalForward
1.74 jmc 913: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 914: the secure channel to the specified host and port from the remote machine.
1.49 jmc 915: The first argument must be
1.43 djm 916: .Sm off
1.49 jmc 917: .Oo Ar bind_address : Oc Ar port
1.43 djm 918: .Sm on
1.49 jmc 919: and the second argument must be
920: .Ar host : Ns Ar hostport .
1.138 djm 921: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 922: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 923: given on the command line.
1.1 stevesk 924: Only the superuser can forward privileged ports.
1.43 djm 925: By default, the local port is bound in accordance with the
926: .Cm GatewayPorts
927: setting.
928: However, an explicit
929: .Ar bind_address
930: may be used to bind the connection to a specific address.
931: The
932: .Ar bind_address
933: of
934: .Dq localhost
1.46 jmc 935: indicates that the listening port be bound for local use only, while an
936: empty address or
937: .Sq *
1.43 djm 938: indicates that the port should be available from all interfaces.
1.1 stevesk 939: .It Cm LogLevel
940: Gives the verbosity level that is used when logging messages from
1.84 jmc 941: .Xr ssh 1 .
1.1 stevesk 942: The possible values are:
1.84 jmc 943: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 944: The default is INFO.
945: DEBUG and DEBUG1 are equivalent.
946: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 947: .It Cm MACs
948: Specifies the MAC (message authentication code) algorithms
949: in order of preference.
950: The MAC algorithm is used in protocol version 2
951: for data integrity protection.
952: Multiple algorithms must be comma-separated.
1.160 markus 953: The algorithms that contain
954: .Dq -etm
955: calculate the MAC after encryption (encrypt-then-mac).
956: These are considered safer and their use recommended.
1.84 jmc 957: The default is:
1.101 jmc 958: .Bd -literal -offset indent
1.160 markus 959: hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
960: umac-64-etm@openssh.com,umac-128-etm@openssh.com,
961: hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
962: hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
963: hmac-md5-96-etm@openssh.com,
1.158 markus 964: hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
1.157 naddy 965: hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
966: hmac-sha1-96,hmac-md5-96
1.101 jmc 967: .Ed
1.1 stevesk 968: .It Cm NoHostAuthenticationForLocalhost
969: This option can be used if the home directory is shared across machines.
970: In this case localhost will refer to a different machine on each of
971: the machines and the user will get many warnings about changed host keys.
972: However, this option disables host authentication for localhost.
973: The argument to this keyword must be
974: .Dq yes
975: or
976: .Dq no .
977: The default is to check the host key for localhost.
978: .It Cm NumberOfPasswordPrompts
979: Specifies the number of password prompts before giving up.
980: The argument to this keyword must be an integer.
1.84 jmc 981: The default is 3.
1.1 stevesk 982: .It Cm PasswordAuthentication
983: Specifies whether to use password authentication.
984: The argument to this keyword must be
985: .Dq yes
986: or
987: .Dq no .
988: The default is
989: .Dq yes .
1.65 reyk 990: .It Cm PermitLocalCommand
991: Allow local command execution via the
992: .Ic LocalCommand
993: option or using the
1.66 jmc 994: .Ic !\& Ns Ar command
1.65 reyk 995: escape sequence in
996: .Xr ssh 1 .
997: The argument must be
998: .Dq yes
999: or
1000: .Dq no .
1001: The default is
1002: .Dq no .
1.127 markus 1003: .It Cm PKCS11Provider
1004: Specifies which PKCS#11 provider to use.
1.144 jmc 1005: The argument to this keyword is the PKCS#11 shared library
1.127 markus 1006: .Xr ssh 1
1.128 markus 1007: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 1008: private RSA key.
1.67 jmc 1009: .It Cm Port
1010: Specifies the port number to connect on the remote host.
1.84 jmc 1011: The default is 22.
1.1 stevesk 1012: .It Cm PreferredAuthentications
1013: Specifies the order in which the client should try protocol 2
1.11 jmc 1014: authentication methods.
1.48 jmc 1015: This allows a client to prefer one method (e.g.\&
1.1 stevesk 1016: .Cm keyboard-interactive )
1.48 jmc 1017: over another method (e.g.\&
1.131 jmc 1018: .Cm password ) .
1019: The default is:
1020: .Bd -literal -offset indent
1021: gssapi-with-mic,hostbased,publickey,
1022: keyboard-interactive,password
1023: .Ed
1.1 stevesk 1024: .It Cm Protocol
1025: Specifies the protocol versions
1.84 jmc 1026: .Xr ssh 1
1.1 stevesk 1027: should support in order of preference.
1028: The possible values are
1.84 jmc 1029: .Sq 1
1.1 stevesk 1030: and
1.84 jmc 1031: .Sq 2 .
1.1 stevesk 1032: Multiple versions must be comma-separated.
1.120 markus 1033: When this option is set to
1.121 jmc 1034: .Dq 2,1
1.120 markus 1035: .Nm ssh
1036: will try version 2 and fall back to version 1
1037: if version 2 is not available.
1.1 stevesk 1038: The default is
1.121 jmc 1039: .Sq 2 .
1.1 stevesk 1040: .It Cm ProxyCommand
1041: Specifies the command to use to connect to the server.
1042: The command
1043: string extends to the end of the line, and is executed with
1.105 jmc 1044: the user's shell.
1.133 jmc 1045: In the command string, any occurrence of
1.1 stevesk 1046: .Ql %h
1047: will be substituted by the host name to
1.132 djm 1048: connect,
1.1 stevesk 1049: .Ql %p
1.133 jmc 1050: by the port, and
1051: .Ql %r
1.132 djm 1052: by the remote user name.
1.1 stevesk 1053: The command can be basically anything,
1054: and should read from its standard input and write to its standard output.
1055: It should eventually connect an
1056: .Xr sshd 8
1057: server running on some machine, or execute
1058: .Ic sshd -i
1059: somewhere.
1060: Host key management will be done using the
1061: HostName of the host being connected (defaulting to the name typed by
1062: the user).
1.7 jmc 1063: Setting the command to
1064: .Dq none
1.6 markus 1065: disables this option entirely.
1.1 stevesk 1066: Note that
1067: .Cm CheckHostIP
1068: is not available for connects with a proxy command.
1.52 djm 1069: .Pp
1070: This directive is useful in conjunction with
1071: .Xr nc 1
1072: and its proxy support.
1.53 jmc 1073: For example, the following directive would connect via an HTTP proxy at
1.52 djm 1074: 192.0.2.0:
1075: .Bd -literal -offset 3n
1076: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
1077: .Ed
1.167 djm 1078: .It Cm ProxyUseFdpass
1.168 jmc 1079: Specifies that
1.167 djm 1080: .Cm ProxyCommand
1081: will pass a connected file descriptor back to
1.168 jmc 1082: .Xr ssh 1
1.167 djm 1083: instead of continuing to execute and pass data.
1084: The default is
1085: .Dq no .
1.1 stevesk 1086: .It Cm PubkeyAuthentication
1087: Specifies whether to try public key authentication.
1088: The argument to this keyword must be
1089: .Dq yes
1090: or
1091: .Dq no .
1092: The default is
1093: .Dq yes .
1094: This option applies to protocol version 2 only.
1.75 dtucker 1095: .It Cm RekeyLimit
1096: Specifies the maximum amount of data that may be transmitted before the
1.162 dtucker 1097: session key is renegotiated, optionally followed a maximum amount of
1098: time that may pass before the session key is renegotiated.
1099: The first argument is specified in bytes and may have a suffix of
1.76 jmc 1100: .Sq K ,
1101: .Sq M ,
1.75 dtucker 1102: or
1.76 jmc 1103: .Sq G
1.75 dtucker 1104: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
1105: The default is between
1.84 jmc 1106: .Sq 1G
1.75 dtucker 1107: and
1.84 jmc 1108: .Sq 4G ,
1.75 dtucker 1109: depending on the cipher.
1.162 dtucker 1110: The optional second value is specified in seconds and may use any of the
1111: units documented in the
1.166 jmc 1112: TIME FORMATS section of
1.162 dtucker 1113: .Xr sshd_config 5 .
1114: The default value for
1115: .Cm RekeyLimit
1116: is
1117: .Dq default none ,
1118: which means that rekeying is performed after the cipher's default amount
1119: of data has been sent or received and no time based rekeying is done.
1.76 jmc 1120: This option applies to protocol version 2 only.
1.1 stevesk 1121: .It Cm RemoteForward
1.74 jmc 1122: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 1123: the secure channel to the specified host and port from the local machine.
1.49 jmc 1124: The first argument must be
1.43 djm 1125: .Sm off
1.49 jmc 1126: .Oo Ar bind_address : Oc Ar port
1.43 djm 1127: .Sm on
1.49 jmc 1128: and the second argument must be
1129: .Ar host : Ns Ar hostport .
1.138 djm 1130: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 1131: Multiple forwardings may be specified, and additional
1132: forwardings can be given on the command line.
1.113 stevesk 1133: Privileged ports can be forwarded only when
1134: logging in as root on the remote machine.
1.118 jmc 1135: .Pp
1.117 djm 1136: If the
1137: .Ar port
1138: argument is
1139: .Ql 0 ,
1140: the listen port will be dynamically allocated on the server and reported
1141: to the client at run time.
1.43 djm 1142: .Pp
1143: If the
1144: .Ar bind_address
1145: is not specified, the default is to only bind to loopback addresses.
1146: If the
1147: .Ar bind_address
1148: is
1149: .Ql *
1150: or an empty string, then the forwarding is requested to listen on all
1151: interfaces.
1152: Specifying a remote
1153: .Ar bind_address
1.46 jmc 1154: will only succeed if the server's
1155: .Cm GatewayPorts
1.43 djm 1156: option is enabled (see
1.46 jmc 1157: .Xr sshd_config 5 ) .
1.149 djm 1158: .It Cm RequestTTY
1159: Specifies whether to request a pseudo-tty for the session.
1160: The argument may be one of:
1161: .Dq no
1162: (never request a TTY),
1163: .Dq yes
1164: (always request a TTY when standard input is a TTY),
1165: .Dq force
1166: (always request a TTY) or
1167: .Dq auto
1168: (request a TTY when opening a login session).
1169: This option mirrors the
1170: .Fl t
1171: and
1172: .Fl T
1173: flags for
1174: .Xr ssh 1 .
1.1 stevesk 1175: .It Cm RhostsRSAAuthentication
1176: Specifies whether to try rhosts based authentication with RSA host
1177: authentication.
1178: The argument must be
1179: .Dq yes
1180: or
1181: .Dq no .
1182: The default is
1183: .Dq no .
1184: This option applies to protocol version 1 only and requires
1.84 jmc 1185: .Xr ssh 1
1.1 stevesk 1186: to be setuid root.
1187: .It Cm RSAAuthentication
1188: Specifies whether to try RSA authentication.
1189: The argument to this keyword must be
1190: .Dq yes
1191: or
1192: .Dq no .
1193: RSA authentication will only be
1194: attempted if the identity file exists, or an authentication agent is
1195: running.
1196: The default is
1197: .Dq yes .
1198: Note that this option applies to protocol version 1 only.
1.32 djm 1199: .It Cm SendEnv
1200: Specifies what variables from the local
1201: .Xr environ 7
1202: should be sent to the server.
1.84 jmc 1203: Note that environment passing is only supported for protocol 2.
1204: The server must also support it, and the server must be configured to
1.33 djm 1205: accept these environment variables.
1.32 djm 1206: Refer to
1207: .Cm AcceptEnv
1208: in
1209: .Xr sshd_config 5
1210: for how to configure the server.
1.80 jmc 1211: Variables are specified by name, which may contain wildcard characters.
1.33 djm 1212: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1213: across multiple
1214: .Cm SendEnv
1215: directives.
1216: The default is not to send any environment variables.
1.81 jmc 1217: .Pp
1218: See
1219: .Sx PATTERNS
1220: for more information on patterns.
1.28 markus 1221: .It Cm ServerAliveCountMax
1.73 jmc 1222: Sets the number of server alive messages (see below) which may be
1.28 markus 1223: sent without
1.84 jmc 1224: .Xr ssh 1
1.28 markus 1225: receiving any messages back from the server.
1226: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1227: ssh will disconnect from the server, terminating the session.
1.28 markus 1228: It is important to note that the use of server alive messages is very
1229: different from
1230: .Cm TCPKeepAlive
1231: (below).
1232: The server alive messages are sent through the encrypted channel
1233: and therefore will not be spoofable.
1234: The TCP keepalive option enabled by
1235: .Cm TCPKeepAlive
1236: is spoofable.
1237: The server alive mechanism is valuable when the client or
1238: server depend on knowing when a connection has become inactive.
1239: .Pp
1240: The default value is 3.
1241: If, for example,
1242: .Cm ServerAliveInterval
1.84 jmc 1243: (see below) is set to 15 and
1.28 markus 1244: .Cm ServerAliveCountMax
1.84 jmc 1245: is left at the default, if the server becomes unresponsive,
1246: ssh will disconnect after approximately 45 seconds.
1.89 markus 1247: This option applies to protocol version 2 only.
1.67 jmc 1248: .It Cm ServerAliveInterval
1249: Sets a timeout interval in seconds after which if no data has been received
1250: from the server,
1.84 jmc 1251: .Xr ssh 1
1.67 jmc 1252: will send a message through the encrypted
1253: channel to request a response from the server.
1254: The default
1255: is 0, indicating that these messages will not be sent to the server.
1256: This option applies to protocol version 2 only.
1.1 stevesk 1257: .It Cm StrictHostKeyChecking
1258: If this flag is set to
1259: .Dq yes ,
1.84 jmc 1260: .Xr ssh 1
1.1 stevesk 1261: will never automatically add host keys to the
1.50 djm 1262: .Pa ~/.ssh/known_hosts
1.1 stevesk 1263: file, and refuses to connect to hosts whose host key has changed.
1264: This provides maximum protection against trojan horse attacks,
1.84 jmc 1265: though it can be annoying when the
1.1 stevesk 1266: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1267: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1268: frequently made.
1269: This option forces the user to manually
1270: add all new hosts.
1271: If this flag is set to
1272: .Dq no ,
1.84 jmc 1273: ssh will automatically add new host keys to the
1.1 stevesk 1274: user known hosts files.
1275: If this flag is set to
1276: .Dq ask ,
1277: new host keys
1278: will be added to the user known host files only after the user
1279: has confirmed that is what they really want to do, and
1.84 jmc 1280: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1281: The host keys of
1282: known hosts will be verified automatically in all cases.
1283: The argument must be
1284: .Dq yes ,
1.84 jmc 1285: .Dq no ,
1.1 stevesk 1286: or
1287: .Dq ask .
1288: The default is
1289: .Dq ask .
1.26 markus 1290: .It Cm TCPKeepAlive
1291: Specifies whether the system should send TCP keepalive messages to the
1292: other side.
1293: If they are sent, death of the connection or crash of one
1294: of the machines will be properly noticed.
1295: However, this means that
1296: connections will die if the route is down temporarily, and some people
1297: find it annoying.
1298: .Pp
1299: The default is
1300: .Dq yes
1301: (to send TCP keepalive messages), and the client will notice
1302: if the network goes down or the remote host dies.
1303: This is important in scripts, and many users want it too.
1304: .Pp
1305: To disable TCP keepalive messages, the value should be set to
1306: .Dq no .
1.65 reyk 1307: .It Cm Tunnel
1.95 stevesk 1308: Request
1.65 reyk 1309: .Xr tun 4
1.69 jmc 1310: device forwarding between the client and the server.
1.65 reyk 1311: The argument must be
1.68 reyk 1312: .Dq yes ,
1.95 stevesk 1313: .Dq point-to-point
1314: (layer 3),
1315: .Dq ethernet
1316: (layer 2),
1.65 reyk 1317: or
1318: .Dq no .
1.95 stevesk 1319: Specifying
1320: .Dq yes
1321: requests the default tunnel mode, which is
1322: .Dq point-to-point .
1.65 reyk 1323: The default is
1324: .Dq no .
1325: .It Cm TunnelDevice
1.95 stevesk 1326: Specifies the
1.65 reyk 1327: .Xr tun 4
1.95 stevesk 1328: devices to open on the client
1329: .Pq Ar local_tun
1330: and the server
1331: .Pq Ar remote_tun .
1332: .Pp
1333: The argument must be
1334: .Sm off
1335: .Ar local_tun Op : Ar remote_tun .
1336: .Sm on
1337: The devices may be specified by numerical ID or the keyword
1338: .Dq any ,
1339: which uses the next available tunnel device.
1340: If
1341: .Ar remote_tun
1342: is not specified, it defaults to
1343: .Dq any .
1344: The default is
1345: .Dq any:any .
1.72 jmc 1346: .It Cm UsePrivilegedPort
1347: Specifies whether to use a privileged port for outgoing connections.
1348: The argument must be
1349: .Dq yes
1350: or
1351: .Dq no .
1352: The default is
1353: .Dq no .
1354: If set to
1.84 jmc 1355: .Dq yes ,
1356: .Xr ssh 1
1.72 jmc 1357: must be setuid root.
1358: Note that this option must be set to
1359: .Dq yes
1360: for
1361: .Cm RhostsRSAAuthentication
1362: with older servers.
1.1 stevesk 1363: .It Cm User
1364: Specifies the user to log in as.
1365: This can be useful when a different user name is used on different machines.
1366: This saves the trouble of
1367: having to remember to give the user name on the command line.
1368: .It Cm UserKnownHostsFile
1.151 djm 1369: Specifies one or more files to use for the user
1370: host key database, separated by whitespace.
1371: The default is
1372: .Pa ~/.ssh/known_hosts ,
1373: .Pa ~/.ssh/known_hosts2 .
1.8 jakob 1374: .It Cm VerifyHostKeyDNS
1375: Specifies whether to verify the remote key using DNS and SSHFP resource
1376: records.
1.24 jakob 1377: If this option is set to
1378: .Dq yes ,
1.25 jmc 1379: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1380: from DNS.
1381: Insecure fingerprints will be handled as if this option was set to
1382: .Dq ask .
1383: If this option is set to
1384: .Dq ask ,
1385: information on fingerprint match will be displayed, but the user will still
1386: need to confirm new host keys according to the
1387: .Cm StrictHostKeyChecking
1388: option.
1389: The argument must be
1390: .Dq yes ,
1.84 jmc 1391: .Dq no ,
1.25 jmc 1392: or
1393: .Dq ask .
1.8 jakob 1394: The default is
1395: .Dq no .
1.12 jakob 1396: Note that this option applies to protocol version 2 only.
1.84 jmc 1397: .Pp
1.166 jmc 1398: See also VERIFYING HOST KEYS in
1.84 jmc 1399: .Xr ssh 1 .
1.111 grunk 1400: .It Cm VisualHostKey
1401: If this flag is set to
1402: .Dq yes ,
1403: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1404: printed in addition to the hex fingerprint string at login and
1405: for unknown host keys.
1.111 grunk 1406: If this flag is set to
1407: .Dq no ,
1.114 stevesk 1408: no fingerprint strings are printed at login and
1409: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1410: The default is
1411: .Dq no .
1.1 stevesk 1412: .It Cm XAuthLocation
1.5 stevesk 1413: Specifies the full pathname of the
1.1 stevesk 1414: .Xr xauth 1
1415: program.
1416: The default is
1417: .Pa /usr/X11R6/bin/xauth .
1418: .El
1.86 jmc 1419: .Sh PATTERNS
1420: A
1421: .Em pattern
1422: consists of zero or more non-whitespace characters,
1423: .Sq *
1424: (a wildcard that matches zero or more characters),
1425: or
1426: .Sq ?\&
1427: (a wildcard that matches exactly one character).
1428: For example, to specify a set of declarations for any host in the
1429: .Dq .co.uk
1430: set of domains,
1431: the following pattern could be used:
1432: .Pp
1433: .Dl Host *.co.uk
1434: .Pp
1435: The following pattern
1436: would match any host in the 192.168.0.[0-9] network range:
1437: .Pp
1438: .Dl Host 192.168.0.?
1439: .Pp
1440: A
1441: .Em pattern-list
1442: is a comma-separated list of patterns.
1443: Patterns within pattern-lists may be negated
1444: by preceding them with an exclamation mark
1445: .Pq Sq !\& .
1446: For example,
1.174 djm 1447: to allow a key to be used from anywhere within an organization
1.86 jmc 1448: except from the
1449: .Dq dialup
1450: pool,
1451: the following entry (in authorized_keys) could be used:
1452: .Pp
1453: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1454: .Sh FILES
1455: .Bl -tag -width Ds
1.50 djm 1456: .It Pa ~/.ssh/config
1.1 stevesk 1457: This is the per-user configuration file.
1458: The format of this file is described above.
1.84 jmc 1459: This file is used by the SSH client.
1.30 djm 1460: Because of the potential for abuse, this file must have strict permissions:
1461: read/write for the user, and not accessible by others.
1.1 stevesk 1462: .It Pa /etc/ssh/ssh_config
1463: Systemwide configuration file.
1464: This file provides defaults for those
1465: values that are not specified in the user's configuration file, and
1466: for those users who do not have a configuration file.
1467: This file must be world-readable.
1468: .El
1.13 jmc 1469: .Sh SEE ALSO
1470: .Xr ssh 1
1.1 stevesk 1471: .Sh AUTHORS
1472: OpenSSH is a derivative of the original and free
1473: ssh 1.2.12 release by Tatu Ylonen.
1474: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1475: Theo de Raadt and Dug Song
1476: removed many bugs, re-added newer features and
1477: created OpenSSH.
1478: Markus Friedl contributed the support for SSH
1479: protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh