Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.140
1.1 stevesk 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
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20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
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26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.140 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.139 2010/08/31 11:54:45 djm Exp $
! 38: .Dd $Mdocdate: August 31 2010 $
1.1 stevesk 39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
1.98 jmc 45: .Nm ~/.ssh/config
46: .Nm /etc/ssh/ssh_config
1.1 stevesk 47: .Sh DESCRIPTION
1.84 jmc 48: .Xr ssh 1
1.1 stevesk 49: obtains configuration data from the following sources in
50: the following order:
1.79 jmc 51: .Pp
1.2 stevesk 52: .Bl -enum -offset indent -compact
53: .It
54: command-line options
55: .It
56: user's configuration file
1.50 djm 57: .Pq Pa ~/.ssh/config
1.2 stevesk 58: .It
59: system-wide configuration file
60: .Pq Pa /etc/ssh/ssh_config
61: .El
1.1 stevesk 62: .Pp
63: For each parameter, the first obtained value
64: will be used.
1.41 jmc 65: The configuration files contain sections separated by
1.1 stevesk 66: .Dq Host
67: specifications, and that section is only applied for hosts that
68: match one of the patterns given in the specification.
69: The matched host name is the one given on the command line.
70: .Pp
71: Since the first obtained value for each parameter is used, more
72: host-specific declarations should be given near the beginning of the
73: file, and general defaults at the end.
1.80 jmc 74: .Pp
1.1 stevesk 75: The configuration file has the following format:
76: .Pp
77: Empty lines and lines starting with
78: .Ql #
79: are comments.
80: Otherwise a line is of the format
81: .Dq keyword arguments .
82: Configuration options may be separated by whitespace or
83: optional whitespace and exactly one
84: .Ql = ;
85: the latter format is useful to avoid the need to quote whitespace
86: when specifying configuration options using the
87: .Nm ssh ,
1.87 jmc 88: .Nm scp ,
1.1 stevesk 89: and
90: .Nm sftp
91: .Fl o
92: option.
1.88 dtucker 93: Arguments may optionally be enclosed in double quotes
94: .Pq \&"
95: in order to represent arguments containing spaces.
1.1 stevesk 96: .Pp
97: The possible
98: keywords and their meanings are as follows (note that
99: keywords are case-insensitive and arguments are case-sensitive):
100: .Bl -tag -width Ds
101: .It Cm Host
102: Restricts the following declarations (up to the next
103: .Cm Host
104: keyword) to be only for those hosts that match one of the patterns
105: given after the keyword.
1.112 krw 106: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 107: A single
1.83 jmc 108: .Ql *
1.1 stevesk 109: as a pattern can be used to provide global
110: defaults for all hosts.
111: The host is the
112: .Ar hostname
1.83 jmc 113: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 114: a canonicalized host name before matching).
1.81 jmc 115: .Pp
116: See
117: .Sx PATTERNS
118: for more information on patterns.
1.10 djm 119: .It Cm AddressFamily
1.11 jmc 120: Specifies which address family to use when connecting.
121: Valid arguments are
1.10 djm 122: .Dq any ,
123: .Dq inet
1.84 jmc 124: (use IPv4 only), or
1.10 djm 125: .Dq inet6
1.40 jmc 126: (use IPv6 only).
1.1 stevesk 127: .It Cm BatchMode
128: If set to
129: .Dq yes ,
130: passphrase/password querying will be disabled.
131: This option is useful in scripts and other batch jobs where no user
132: is present to supply the password.
133: The argument must be
134: .Dq yes
135: or
136: .Dq no .
137: The default is
138: .Dq no .
139: .It Cm BindAddress
1.60 dtucker 140: Use the specified address on the local machine as the source address of
1.61 jmc 141: the connection.
142: Only useful on systems with more than one address.
1.1 stevesk 143: Note that this option does not work if
144: .Cm UsePrivilegedPort
145: is set to
146: .Dq yes .
147: .It Cm ChallengeResponseAuthentication
1.82 jmc 148: Specifies whether to use challenge-response authentication.
1.1 stevesk 149: The argument to this keyword must be
150: .Dq yes
151: or
152: .Dq no .
153: The default is
154: .Dq yes .
155: .It Cm CheckHostIP
156: If this flag is set to
157: .Dq yes ,
1.84 jmc 158: .Xr ssh 1
159: will additionally check the host IP address in the
1.1 stevesk 160: .Pa known_hosts
161: file.
162: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 163: If the option is set to
1.1 stevesk 164: .Dq no ,
165: the check will not be executed.
166: The default is
167: .Dq yes .
168: .It Cm Cipher
169: Specifies the cipher to use for encrypting the session
170: in protocol version 1.
171: Currently,
172: .Dq blowfish ,
173: .Dq 3des ,
174: and
175: .Dq des
176: are supported.
177: .Ar des
178: is only supported in the
1.84 jmc 179: .Xr ssh 1
1.1 stevesk 180: client for interoperability with legacy protocol 1 implementations
181: that do not support the
182: .Ar 3des
1.7 jmc 183: cipher.
184: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 185: The default is
186: .Dq 3des .
187: .It Cm Ciphers
188: Specifies the ciphers allowed for protocol version 2
189: in order of preference.
190: Multiple ciphers must be comma-separated.
1.35 dtucker 191: The supported ciphers are
192: .Dq 3des-cbc ,
193: .Dq aes128-cbc ,
194: .Dq aes192-cbc ,
195: .Dq aes256-cbc ,
196: .Dq aes128-ctr ,
197: .Dq aes192-ctr ,
198: .Dq aes256-ctr ,
1.54 djm 199: .Dq arcfour128 ,
200: .Dq arcfour256 ,
1.35 dtucker 201: .Dq arcfour ,
202: .Dq blowfish-cbc ,
203: and
204: .Dq cast128-cbc .
1.84 jmc 205: The default is:
206: .Bd -literal -offset 3n
1.116 naddy 207: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
208: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
209: aes256-cbc,arcfour
1.1 stevesk 210: .Ed
211: .It Cm ClearAllForwardings
1.84 jmc 212: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 213: specified in the configuration files or on the command line be
1.7 jmc 214: cleared.
215: This option is primarily useful when used from the
1.84 jmc 216: .Xr ssh 1
1.1 stevesk 217: command line to clear port forwardings set in
218: configuration files, and is automatically set by
219: .Xr scp 1
220: and
221: .Xr sftp 1 .
222: The argument must be
223: .Dq yes
224: or
225: .Dq no .
226: The default is
227: .Dq no .
228: .It Cm Compression
229: Specifies whether to use compression.
230: The argument must be
231: .Dq yes
232: or
233: .Dq no .
234: The default is
235: .Dq no .
236: .It Cm CompressionLevel
237: Specifies the compression level to use if compression is enabled.
238: The argument must be an integer from 1 (fast) to 9 (slow, best).
239: The default level is 6, which is good for most applications.
240: The meaning of the values is the same as in
241: .Xr gzip 1 .
242: Note that this option applies to protocol version 1 only.
243: .It Cm ConnectionAttempts
244: Specifies the number of tries (one per second) to make before exiting.
245: The argument must be an integer.
246: This may be useful in scripts if the connection sometimes fails.
247: The default is 1.
1.9 djm 248: .It Cm ConnectTimeout
1.84 jmc 249: Specifies the timeout (in seconds) used when connecting to the
250: SSH server, instead of using the default system TCP timeout.
1.11 jmc 251: This value is used only when the target is down or really unreachable,
252: not when it refuses the connection.
1.36 djm 253: .It Cm ControlMaster
254: Enables the sharing of multiple sessions over a single network connection.
255: When set to
1.84 jmc 256: .Dq yes ,
257: .Xr ssh 1
1.36 djm 258: will listen for connections on a control socket specified using the
259: .Cm ControlPath
260: argument.
261: Additional sessions can connect to this socket using the same
262: .Cm ControlPath
263: with
264: .Cm ControlMaster
265: set to
266: .Dq no
1.38 jmc 267: (the default).
1.64 jmc 268: These sessions will try to reuse the master instance's network connection
1.63 djm 269: rather than initiating new ones, but will fall back to connecting normally
270: if the control socket does not exist, or is not listening.
271: .Pp
1.37 djm 272: Setting this to
273: .Dq ask
1.84 jmc 274: will cause ssh
1.37 djm 275: to listen for control connections, but require confirmation using the
276: .Ev SSH_ASKPASS
277: program before they are accepted (see
278: .Xr ssh-add 1
1.38 jmc 279: for details).
1.51 jakob 280: If the
281: .Cm ControlPath
1.84 jmc 282: cannot be opened,
283: ssh will continue without connecting to a master instance.
1.58 djm 284: .Pp
285: X11 and
1.59 jmc 286: .Xr ssh-agent 1
1.58 djm 287: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 288: display and agent forwarded will be the one belonging to the master
1.59 jmc 289: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 290: .Pp
291: Two additional options allow for opportunistic multiplexing: try to use a
292: master connection but fall back to creating a new one if one does not already
293: exist.
294: These options are:
295: .Dq auto
296: and
297: .Dq autoask .
298: The latter requires confirmation like the
299: .Dq ask
300: option.
1.36 djm 301: .It Cm ControlPath
1.55 djm 302: Specify the path to the control socket used for connection sharing as described
303: in the
1.36 djm 304: .Cm ControlMaster
1.57 djm 305: section above or the string
306: .Dq none
307: to disable connection sharing.
1.55 djm 308: In the path,
1.77 djm 309: .Ql %l
310: will be substituted by the local host name,
1.55 djm 311: .Ql %h
312: will be substituted by the target host name,
313: .Ql %p
1.84 jmc 314: the port, and
1.55 djm 315: .Ql %r
316: by the remote login username.
1.56 djm 317: It is recommended that any
318: .Cm ControlPath
319: used for opportunistic connection sharing include
1.78 jmc 320: at least %h, %p, and %r.
1.56 djm 321: This ensures that shared connections are uniquely identified.
1.137 djm 322: .It Cm ControlPersist
323: When used in conjunction with
324: .Cm ControlMaster ,
325: specifies that the master connection should remain open
326: in the background (waiting for future client connections)
327: after the initial client connection has been closed.
328: If set to
329: .Dq no ,
330: then the master connection will not be placed into the background,
331: and will close as soon as the initial client connection is closed.
332: If set to
333: .Dq yes ,
334: then the master connection will remain in the background indefinitely
335: (until killed or closed via a mechanism such as the
336: .Xr ssh 1
337: .Dq Fl O No exit
338: option).
339: If set to a time in seconds, or a time in any of the formats documented in
340: .Xr sshd_config 5 ,
341: then the backgrounded master connection will automatically terminate
342: after it has remained idle (with no client connections) for the
343: specified time.
1.38 jmc 344: .It Cm DynamicForward
1.74 jmc 345: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 346: over the secure channel, and the application
347: protocol is then used to determine where to connect to from the
348: remote machine.
1.62 djm 349: .Pp
350: The argument must be
351: .Sm off
352: .Oo Ar bind_address : Oc Ar port .
353: .Sm on
1.138 djm 354: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 355: By default, the local port is bound in accordance with the
356: .Cm GatewayPorts
357: setting.
358: However, an explicit
359: .Ar bind_address
360: may be used to bind the connection to a specific address.
361: The
362: .Ar bind_address
363: of
364: .Dq localhost
365: indicates that the listening port be bound for local use only, while an
366: empty address or
367: .Sq *
368: indicates that the port should be available from all interfaces.
369: .Pp
1.38 jmc 370: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 371: .Xr ssh 1
1.38 jmc 372: will act as a SOCKS server.
373: Multiple forwardings may be specified, and
374: additional forwardings can be given on the command line.
375: Only the superuser can forward privileged ports.
1.14 markus 376: .It Cm EnableSSHKeysign
377: Setting this option to
378: .Dq yes
379: in the global client configuration file
380: .Pa /etc/ssh/ssh_config
381: enables the use of the helper program
382: .Xr ssh-keysign 8
383: during
384: .Cm HostbasedAuthentication .
385: The argument must be
386: .Dq yes
387: or
388: .Dq no .
389: The default is
390: .Dq no .
1.23 jmc 391: This option should be placed in the non-hostspecific section.
1.14 markus 392: See
393: .Xr ssh-keysign 8
394: for more information.
1.1 stevesk 395: .It Cm EscapeChar
396: Sets the escape character (default:
397: .Ql ~ ) .
398: The escape character can also
399: be set on the command line.
400: The argument should be a single character,
401: .Ql ^
402: followed by a letter, or
403: .Dq none
404: to disable the escape
405: character entirely (making the connection transparent for binary
406: data).
1.96 markus 407: .It Cm ExitOnForwardFailure
408: Specifies whether
409: .Xr ssh 1
410: should terminate the connection if it cannot set up all requested
1.102 stevesk 411: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 412: The argument must be
413: .Dq yes
414: or
415: .Dq no .
416: The default is
417: .Dq no .
1.1 stevesk 418: .It Cm ForwardAgent
419: Specifies whether the connection to the authentication agent (if any)
420: will be forwarded to the remote machine.
421: The argument must be
422: .Dq yes
423: or
424: .Dq no .
425: The default is
426: .Dq no .
1.3 stevesk 427: .Pp
1.7 jmc 428: Agent forwarding should be enabled with caution.
429: Users with the ability to bypass file permissions on the remote host
430: (for the agent's Unix-domain socket)
431: can access the local agent through the forwarded connection.
432: An attacker cannot obtain key material from the agent,
1.3 stevesk 433: however they can perform operations on the keys that enable them to
434: authenticate using the identities loaded into the agent.
1.1 stevesk 435: .It Cm ForwardX11
436: Specifies whether X11 connections will be automatically redirected
437: over the secure channel and
438: .Ev DISPLAY
439: set.
440: The argument must be
441: .Dq yes
442: or
443: .Dq no .
444: The default is
445: .Dq no .
1.3 stevesk 446: .Pp
1.7 jmc 447: X11 forwarding should be enabled with caution.
448: Users with the ability to bypass file permissions on the remote host
1.22 markus 449: (for the user's X11 authorization database)
1.7 jmc 450: can access the local X11 display through the forwarded connection.
1.22 markus 451: An attacker may then be able to perform activities such as keystroke monitoring
452: if the
453: .Cm ForwardX11Trusted
454: option is also enabled.
1.134 djm 455: .It Cm ForwardX11Timeout
1.135 jmc 456: Specify a timeout for untrusted X11 forwarding
457: using the format described in the
1.134 djm 458: .Sx TIME FORMATS
459: section of
460: .Xr sshd_config 5 .
461: X11 connections received by
462: .Xr ssh 1
463: after this time will be refused.
464: The default is to disable untrusted X11 forwarding after twenty minutes has
465: elapsed.
1.22 markus 466: .It Cm ForwardX11Trusted
1.34 jmc 467: If this option is set to
1.84 jmc 468: .Dq yes ,
469: remote X11 clients will have full access to the original X11 display.
1.42 djm 470: .Pp
1.22 markus 471: If this option is set to
1.84 jmc 472: .Dq no ,
473: remote X11 clients will be considered untrusted and prevented
1.22 markus 474: from stealing or tampering with data belonging to trusted X11
475: clients.
1.42 djm 476: Furthermore, the
477: .Xr xauth 1
478: token used for the session will be set to expire after 20 minutes.
479: Remote clients will be refused access after this time.
1.22 markus 480: .Pp
481: The default is
482: .Dq no .
483: .Pp
484: See the X11 SECURITY extension specification for full details on
485: the restrictions imposed on untrusted clients.
1.1 stevesk 486: .It Cm GatewayPorts
487: Specifies whether remote hosts are allowed to connect to local
488: forwarded ports.
489: By default,
1.84 jmc 490: .Xr ssh 1
1.7 jmc 491: binds local port forwardings to the loopback address.
492: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 493: .Cm GatewayPorts
1.84 jmc 494: can be used to specify that ssh
1.1 stevesk 495: should bind local port forwardings to the wildcard address,
496: thus allowing remote hosts to connect to forwarded ports.
497: The argument must be
498: .Dq yes
499: or
500: .Dq no .
501: The default is
502: .Dq no .
503: .It Cm GlobalKnownHostsFile
504: Specifies a file to use for the global
505: host key database instead of
506: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 507: .It Cm GSSAPIAuthentication
1.27 markus 508: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 509: The default is
1.21 markus 510: .Dq no .
1.18 markus 511: Note that this option applies to protocol version 2 only.
512: .It Cm GSSAPIDelegateCredentials
513: Forward (delegate) credentials to the server.
514: The default is
515: .Dq no .
516: Note that this option applies to protocol version 2 only.
1.44 djm 517: .It Cm HashKnownHosts
518: Indicates that
1.84 jmc 519: .Xr ssh 1
1.44 djm 520: should hash host names and addresses when they are added to
1.50 djm 521: .Pa ~/.ssh/known_hosts .
1.44 djm 522: These hashed names may be used normally by
1.84 jmc 523: .Xr ssh 1
1.44 djm 524: and
1.84 jmc 525: .Xr sshd 8 ,
1.44 djm 526: but they do not reveal identifying information should the file's contents
527: be disclosed.
528: The default is
529: .Dq no .
1.97 jmc 530: Note that existing names and addresses in known hosts files
531: will not be converted automatically,
532: but may be manually hashed using
1.45 djm 533: .Xr ssh-keygen 1 .
1.1 stevesk 534: .It Cm HostbasedAuthentication
535: Specifies whether to try rhosts based authentication with public key
536: authentication.
537: The argument must be
538: .Dq yes
539: or
540: .Dq no .
541: The default is
542: .Dq no .
543: This option applies to protocol version 2 only and
544: is similar to
545: .Cm RhostsRSAAuthentication .
546: .It Cm HostKeyAlgorithms
547: Specifies the protocol version 2 host key algorithms
548: that the client wants to use in order of preference.
549: The default for this option is:
1.139 djm 550: .Bd -literal -offset 3n
551: ecdsa-sha2-nistp256-cert-v01@openssh.com,
552: ecdsa-sha2-nistp384-cert-v01@openssh.com,
553: ecdsa-sha2-nistp521-cert-v01@openssh.com,
554: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
555: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
556: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
557: ssh-rsa,ssh-dss
558: .Ed
1.1 stevesk 559: .It Cm HostKeyAlias
560: Specifies an alias that should be used instead of the
561: real host name when looking up or saving the host key
562: in the host key database files.
1.84 jmc 563: This option is useful for tunneling SSH connections
1.1 stevesk 564: or for multiple servers running on a single host.
565: .It Cm HostName
566: Specifies the real host name to log into.
567: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 568: If the hostname contains the character sequence
569: .Ql %h ,
570: then this will be replaced with the host name specified on the commandline
571: (this is useful for manipulating unqualified names).
1.84 jmc 572: The default is the name given on the command line.
1.1 stevesk 573: Numeric IP addresses are also permitted (both on the command line and in
574: .Cm HostName
575: specifications).
1.29 markus 576: .It Cm IdentitiesOnly
577: Specifies that
1.84 jmc 578: .Xr ssh 1
1.29 markus 579: should only use the authentication identity files configured in the
1.31 jmc 580: .Nm
1.29 markus 581: files,
1.84 jmc 582: even if
583: .Xr ssh-agent 1
1.29 markus 584: offers more identities.
585: The argument to this keyword must be
586: .Dq yes
587: or
588: .Dq no .
1.84 jmc 589: This option is intended for situations where ssh-agent
1.29 markus 590: offers many different identities.
591: The default is
592: .Dq no .
1.67 jmc 593: .It Cm IdentityFile
1.139 djm 594: Specifies a file from which the user's DSA, ECDSA or DSA authentication
595: identity is read.
1.67 jmc 596: The default is
597: .Pa ~/.ssh/identity
598: for protocol version 1, and
1.139 djm 599: .Pa ~/.ssh/id_dsa ,
600: .Pa ~/.ssh/id_ecdsa
601: and
1.67 jmc 602: .Pa ~/.ssh/id_rsa
603: for protocol version 2.
604: Additionally, any identities represented by the authentication agent
605: will be used for authentication.
1.129 djm 606: .Xr ssh 1
607: will try to load certificate information from the filename obtained by
608: appending
609: .Pa -cert.pub
610: to the path of a specified
611: .Cm IdentityFile .
1.90 djm 612: .Pp
1.67 jmc 613: The file name may use the tilde
1.91 jmc 614: syntax to refer to a user's home directory or one of the following
1.90 djm 615: escape characters:
616: .Ql %d
617: (local user's home directory),
618: .Ql %u
619: (local user name),
620: .Ql %l
621: (local host name),
622: .Ql %h
623: (remote host name) or
1.92 djm 624: .Ql %r
1.90 djm 625: (remote user name).
626: .Pp
1.67 jmc 627: It is possible to have
628: multiple identity files specified in configuration files; all these
629: identities will be tried in sequence.
1.103 djm 630: .It Cm KbdInteractiveAuthentication
631: Specifies whether to use keyboard-interactive authentication.
632: The argument to this keyword must be
633: .Dq yes
634: or
635: .Dq no .
636: The default is
637: .Dq yes .
1.39 djm 638: .It Cm KbdInteractiveDevices
639: Specifies the list of methods to use in keyboard-interactive authentication.
640: Multiple method names must be comma-separated.
641: The default is to use the server specified list.
1.85 jmc 642: The methods available vary depending on what the server supports.
643: For an OpenSSH server,
644: it may be zero or more of:
645: .Dq bsdauth ,
646: .Dq pam ,
647: and
648: .Dq skey .
1.140 ! djm 649: .It Cm KexAlgorithms
! 650: Specifies the available KEX (Key Exchange) algorithms.
! 651: Multiple algorithms must be comma-separated.
! 652: The default is
! 653: .Dq ecdh-sha2-nistp256 ,
! 654: .Dq ecdh-sha2-nistp384 ,
! 655: .Dq ecdh-sha2-nistp521 ,
! 656: .Dq diffie-hellman-group-exchange-sha256 ,
! 657: .Dq diffie-hellman-group-exchange-sha1 ,
! 658: .Dq diffie-hellman-group14-sha1 ,
! 659: .Dq diffie-hellman-group1-sha1 .
1.65 reyk 660: .It Cm LocalCommand
661: Specifies a command to execute on the local machine after successfully
662: connecting to the server.
663: The command string extends to the end of the line, and is executed with
1.105 jmc 664: the user's shell.
1.109 dtucker 665: The following escape character substitutions will be performed:
666: .Ql %d
667: (local user's home directory),
668: .Ql %h
669: (remote host name),
670: .Ql %l
671: (local host name),
672: .Ql %n
673: (host name as provided on the command line),
674: .Ql %p
675: (remote port),
676: .Ql %r
677: (remote user name) or
678: .Ql %u
679: (local user name).
1.123 djm 680: .Pp
681: The command is run synchronously and does not have access to the
682: session of the
683: .Xr ssh 1
684: that spawned it.
685: It should not be used for interactive commands.
686: .Pp
1.65 reyk 687: This directive is ignored unless
688: .Cm PermitLocalCommand
689: has been enabled.
1.1 stevesk 690: .It Cm LocalForward
1.74 jmc 691: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 692: the secure channel to the specified host and port from the remote machine.
1.49 jmc 693: The first argument must be
1.43 djm 694: .Sm off
1.49 jmc 695: .Oo Ar bind_address : Oc Ar port
1.43 djm 696: .Sm on
1.49 jmc 697: and the second argument must be
698: .Ar host : Ns Ar hostport .
1.138 djm 699: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 700: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 701: given on the command line.
1.1 stevesk 702: Only the superuser can forward privileged ports.
1.43 djm 703: By default, the local port is bound in accordance with the
704: .Cm GatewayPorts
705: setting.
706: However, an explicit
707: .Ar bind_address
708: may be used to bind the connection to a specific address.
709: The
710: .Ar bind_address
711: of
712: .Dq localhost
1.46 jmc 713: indicates that the listening port be bound for local use only, while an
714: empty address or
715: .Sq *
1.43 djm 716: indicates that the port should be available from all interfaces.
1.1 stevesk 717: .It Cm LogLevel
718: Gives the verbosity level that is used when logging messages from
1.84 jmc 719: .Xr ssh 1 .
1.1 stevesk 720: The possible values are:
1.84 jmc 721: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 722: The default is INFO.
723: DEBUG and DEBUG1 are equivalent.
724: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 725: .It Cm MACs
726: Specifies the MAC (message authentication code) algorithms
727: in order of preference.
728: The MAC algorithm is used in protocol version 2
729: for data integrity protection.
730: Multiple algorithms must be comma-separated.
1.84 jmc 731: The default is:
1.101 jmc 732: .Bd -literal -offset indent
733: hmac-md5,hmac-sha1,umac-64@openssh.com,
734: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
735: .Ed
1.1 stevesk 736: .It Cm NoHostAuthenticationForLocalhost
737: This option can be used if the home directory is shared across machines.
738: In this case localhost will refer to a different machine on each of
739: the machines and the user will get many warnings about changed host keys.
740: However, this option disables host authentication for localhost.
741: The argument to this keyword must be
742: .Dq yes
743: or
744: .Dq no .
745: The default is to check the host key for localhost.
746: .It Cm NumberOfPasswordPrompts
747: Specifies the number of password prompts before giving up.
748: The argument to this keyword must be an integer.
1.84 jmc 749: The default is 3.
1.1 stevesk 750: .It Cm PasswordAuthentication
751: Specifies whether to use password authentication.
752: The argument to this keyword must be
753: .Dq yes
754: or
755: .Dq no .
756: The default is
757: .Dq yes .
1.65 reyk 758: .It Cm PermitLocalCommand
759: Allow local command execution via the
760: .Ic LocalCommand
761: option or using the
1.66 jmc 762: .Ic !\& Ns Ar command
1.65 reyk 763: escape sequence in
764: .Xr ssh 1 .
765: The argument must be
766: .Dq yes
767: or
768: .Dq no .
769: The default is
770: .Dq no .
1.127 markus 771: .It Cm PKCS11Provider
772: Specifies which PKCS#11 provider to use.
773: The argument to this keyword is the PKCS#11 shared libary
774: .Xr ssh 1
1.128 markus 775: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 776: private RSA key.
1.67 jmc 777: .It Cm Port
778: Specifies the port number to connect on the remote host.
1.84 jmc 779: The default is 22.
1.1 stevesk 780: .It Cm PreferredAuthentications
781: Specifies the order in which the client should try protocol 2
1.11 jmc 782: authentication methods.
1.48 jmc 783: This allows a client to prefer one method (e.g.\&
1.1 stevesk 784: .Cm keyboard-interactive )
1.48 jmc 785: over another method (e.g.\&
1.131 jmc 786: .Cm password ) .
787: The default is:
788: .Bd -literal -offset indent
789: gssapi-with-mic,hostbased,publickey,
790: keyboard-interactive,password
791: .Ed
1.1 stevesk 792: .It Cm Protocol
793: Specifies the protocol versions
1.84 jmc 794: .Xr ssh 1
1.1 stevesk 795: should support in order of preference.
796: The possible values are
1.84 jmc 797: .Sq 1
1.1 stevesk 798: and
1.84 jmc 799: .Sq 2 .
1.1 stevesk 800: Multiple versions must be comma-separated.
1.120 markus 801: When this option is set to
1.121 jmc 802: .Dq 2,1
1.120 markus 803: .Nm ssh
804: will try version 2 and fall back to version 1
805: if version 2 is not available.
1.1 stevesk 806: The default is
1.121 jmc 807: .Sq 2 .
1.1 stevesk 808: .It Cm ProxyCommand
809: Specifies the command to use to connect to the server.
810: The command
811: string extends to the end of the line, and is executed with
1.105 jmc 812: the user's shell.
1.133 jmc 813: In the command string, any occurrence of
1.1 stevesk 814: .Ql %h
815: will be substituted by the host name to
1.132 djm 816: connect,
1.1 stevesk 817: .Ql %p
1.133 jmc 818: by the port, and
819: .Ql %r
1.132 djm 820: by the remote user name.
1.1 stevesk 821: The command can be basically anything,
822: and should read from its standard input and write to its standard output.
823: It should eventually connect an
824: .Xr sshd 8
825: server running on some machine, or execute
826: .Ic sshd -i
827: somewhere.
828: Host key management will be done using the
829: HostName of the host being connected (defaulting to the name typed by
830: the user).
1.7 jmc 831: Setting the command to
832: .Dq none
1.6 markus 833: disables this option entirely.
1.1 stevesk 834: Note that
835: .Cm CheckHostIP
836: is not available for connects with a proxy command.
1.52 djm 837: .Pp
838: This directive is useful in conjunction with
839: .Xr nc 1
840: and its proxy support.
1.53 jmc 841: For example, the following directive would connect via an HTTP proxy at
1.52 djm 842: 192.0.2.0:
843: .Bd -literal -offset 3n
844: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
845: .Ed
1.1 stevesk 846: .It Cm PubkeyAuthentication
847: Specifies whether to try public key authentication.
848: The argument to this keyword must be
849: .Dq yes
850: or
851: .Dq no .
852: The default is
853: .Dq yes .
854: This option applies to protocol version 2 only.
1.75 dtucker 855: .It Cm RekeyLimit
856: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 857: session key is renegotiated.
1.75 dtucker 858: The argument is the number of bytes, with an optional suffix of
1.76 jmc 859: .Sq K ,
860: .Sq M ,
1.75 dtucker 861: or
1.76 jmc 862: .Sq G
1.75 dtucker 863: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
864: The default is between
1.84 jmc 865: .Sq 1G
1.75 dtucker 866: and
1.84 jmc 867: .Sq 4G ,
1.75 dtucker 868: depending on the cipher.
1.76 jmc 869: This option applies to protocol version 2 only.
1.1 stevesk 870: .It Cm RemoteForward
1.74 jmc 871: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 872: the secure channel to the specified host and port from the local machine.
1.49 jmc 873: The first argument must be
1.43 djm 874: .Sm off
1.49 jmc 875: .Oo Ar bind_address : Oc Ar port
1.43 djm 876: .Sm on
1.49 jmc 877: and the second argument must be
878: .Ar host : Ns Ar hostport .
1.138 djm 879: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 880: Multiple forwardings may be specified, and additional
881: forwardings can be given on the command line.
1.113 stevesk 882: Privileged ports can be forwarded only when
883: logging in as root on the remote machine.
1.118 jmc 884: .Pp
1.117 djm 885: If the
886: .Ar port
887: argument is
888: .Ql 0 ,
889: the listen port will be dynamically allocated on the server and reported
890: to the client at run time.
1.43 djm 891: .Pp
892: If the
893: .Ar bind_address
894: is not specified, the default is to only bind to loopback addresses.
895: If the
896: .Ar bind_address
897: is
898: .Ql *
899: or an empty string, then the forwarding is requested to listen on all
900: interfaces.
901: Specifying a remote
902: .Ar bind_address
1.46 jmc 903: will only succeed if the server's
904: .Cm GatewayPorts
1.43 djm 905: option is enabled (see
1.46 jmc 906: .Xr sshd_config 5 ) .
1.1 stevesk 907: .It Cm RhostsRSAAuthentication
908: Specifies whether to try rhosts based authentication with RSA host
909: authentication.
910: The argument must be
911: .Dq yes
912: or
913: .Dq no .
914: The default is
915: .Dq no .
916: This option applies to protocol version 1 only and requires
1.84 jmc 917: .Xr ssh 1
1.1 stevesk 918: to be setuid root.
919: .It Cm RSAAuthentication
920: Specifies whether to try RSA authentication.
921: The argument to this keyword must be
922: .Dq yes
923: or
924: .Dq no .
925: RSA authentication will only be
926: attempted if the identity file exists, or an authentication agent is
927: running.
928: The default is
929: .Dq yes .
930: Note that this option applies to protocol version 1 only.
1.32 djm 931: .It Cm SendEnv
932: Specifies what variables from the local
933: .Xr environ 7
934: should be sent to the server.
1.84 jmc 935: Note that environment passing is only supported for protocol 2.
936: The server must also support it, and the server must be configured to
1.33 djm 937: accept these environment variables.
1.32 djm 938: Refer to
939: .Cm AcceptEnv
940: in
941: .Xr sshd_config 5
942: for how to configure the server.
1.80 jmc 943: Variables are specified by name, which may contain wildcard characters.
1.33 djm 944: Multiple environment variables may be separated by whitespace or spread
1.32 djm 945: across multiple
946: .Cm SendEnv
947: directives.
948: The default is not to send any environment variables.
1.81 jmc 949: .Pp
950: See
951: .Sx PATTERNS
952: for more information on patterns.
1.28 markus 953: .It Cm ServerAliveCountMax
1.73 jmc 954: Sets the number of server alive messages (see below) which may be
1.28 markus 955: sent without
1.84 jmc 956: .Xr ssh 1
1.28 markus 957: receiving any messages back from the server.
958: If this threshold is reached while server alive messages are being sent,
1.84 jmc 959: ssh will disconnect from the server, terminating the session.
1.28 markus 960: It is important to note that the use of server alive messages is very
961: different from
962: .Cm TCPKeepAlive
963: (below).
964: The server alive messages are sent through the encrypted channel
965: and therefore will not be spoofable.
966: The TCP keepalive option enabled by
967: .Cm TCPKeepAlive
968: is spoofable.
969: The server alive mechanism is valuable when the client or
970: server depend on knowing when a connection has become inactive.
971: .Pp
972: The default value is 3.
973: If, for example,
974: .Cm ServerAliveInterval
1.84 jmc 975: (see below) is set to 15 and
1.28 markus 976: .Cm ServerAliveCountMax
1.84 jmc 977: is left at the default, if the server becomes unresponsive,
978: ssh will disconnect after approximately 45 seconds.
1.89 markus 979: This option applies to protocol version 2 only.
1.67 jmc 980: .It Cm ServerAliveInterval
981: Sets a timeout interval in seconds after which if no data has been received
982: from the server,
1.84 jmc 983: .Xr ssh 1
1.67 jmc 984: will send a message through the encrypted
985: channel to request a response from the server.
986: The default
987: is 0, indicating that these messages will not be sent to the server.
988: This option applies to protocol version 2 only.
1.1 stevesk 989: .It Cm StrictHostKeyChecking
990: If this flag is set to
991: .Dq yes ,
1.84 jmc 992: .Xr ssh 1
1.1 stevesk 993: will never automatically add host keys to the
1.50 djm 994: .Pa ~/.ssh/known_hosts
1.1 stevesk 995: file, and refuses to connect to hosts whose host key has changed.
996: This provides maximum protection against trojan horse attacks,
1.84 jmc 997: though it can be annoying when the
1.1 stevesk 998: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 999: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1000: frequently made.
1001: This option forces the user to manually
1002: add all new hosts.
1003: If this flag is set to
1004: .Dq no ,
1.84 jmc 1005: ssh will automatically add new host keys to the
1.1 stevesk 1006: user known hosts files.
1007: If this flag is set to
1008: .Dq ask ,
1009: new host keys
1010: will be added to the user known host files only after the user
1011: has confirmed that is what they really want to do, and
1.84 jmc 1012: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1013: The host keys of
1014: known hosts will be verified automatically in all cases.
1015: The argument must be
1016: .Dq yes ,
1.84 jmc 1017: .Dq no ,
1.1 stevesk 1018: or
1019: .Dq ask .
1020: The default is
1021: .Dq ask .
1.26 markus 1022: .It Cm TCPKeepAlive
1023: Specifies whether the system should send TCP keepalive messages to the
1024: other side.
1025: If they are sent, death of the connection or crash of one
1026: of the machines will be properly noticed.
1027: However, this means that
1028: connections will die if the route is down temporarily, and some people
1029: find it annoying.
1030: .Pp
1031: The default is
1032: .Dq yes
1033: (to send TCP keepalive messages), and the client will notice
1034: if the network goes down or the remote host dies.
1035: This is important in scripts, and many users want it too.
1036: .Pp
1037: To disable TCP keepalive messages, the value should be set to
1038: .Dq no .
1.65 reyk 1039: .It Cm Tunnel
1.95 stevesk 1040: Request
1.65 reyk 1041: .Xr tun 4
1.69 jmc 1042: device forwarding between the client and the server.
1.65 reyk 1043: The argument must be
1.68 reyk 1044: .Dq yes ,
1.95 stevesk 1045: .Dq point-to-point
1046: (layer 3),
1047: .Dq ethernet
1048: (layer 2),
1.65 reyk 1049: or
1050: .Dq no .
1.95 stevesk 1051: Specifying
1052: .Dq yes
1053: requests the default tunnel mode, which is
1054: .Dq point-to-point .
1.65 reyk 1055: The default is
1056: .Dq no .
1057: .It Cm TunnelDevice
1.95 stevesk 1058: Specifies the
1.65 reyk 1059: .Xr tun 4
1.95 stevesk 1060: devices to open on the client
1061: .Pq Ar local_tun
1062: and the server
1063: .Pq Ar remote_tun .
1064: .Pp
1065: The argument must be
1066: .Sm off
1067: .Ar local_tun Op : Ar remote_tun .
1068: .Sm on
1069: The devices may be specified by numerical ID or the keyword
1070: .Dq any ,
1071: which uses the next available tunnel device.
1072: If
1073: .Ar remote_tun
1074: is not specified, it defaults to
1075: .Dq any .
1076: The default is
1077: .Dq any:any .
1.72 jmc 1078: .It Cm UsePrivilegedPort
1079: Specifies whether to use a privileged port for outgoing connections.
1080: The argument must be
1081: .Dq yes
1082: or
1083: .Dq no .
1084: The default is
1085: .Dq no .
1086: If set to
1.84 jmc 1087: .Dq yes ,
1088: .Xr ssh 1
1.72 jmc 1089: must be setuid root.
1090: Note that this option must be set to
1091: .Dq yes
1092: for
1093: .Cm RhostsRSAAuthentication
1094: with older servers.
1.1 stevesk 1095: .It Cm User
1096: Specifies the user to log in as.
1097: This can be useful when a different user name is used on different machines.
1098: This saves the trouble of
1099: having to remember to give the user name on the command line.
1100: .It Cm UserKnownHostsFile
1101: Specifies a file to use for the user
1102: host key database instead of
1.50 djm 1103: .Pa ~/.ssh/known_hosts .
1.8 jakob 1104: .It Cm VerifyHostKeyDNS
1105: Specifies whether to verify the remote key using DNS and SSHFP resource
1106: records.
1.24 jakob 1107: If this option is set to
1108: .Dq yes ,
1.25 jmc 1109: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1110: from DNS.
1111: Insecure fingerprints will be handled as if this option was set to
1112: .Dq ask .
1113: If this option is set to
1114: .Dq ask ,
1115: information on fingerprint match will be displayed, but the user will still
1116: need to confirm new host keys according to the
1117: .Cm StrictHostKeyChecking
1118: option.
1119: The argument must be
1120: .Dq yes ,
1.84 jmc 1121: .Dq no ,
1.25 jmc 1122: or
1123: .Dq ask .
1.8 jakob 1124: The default is
1125: .Dq no .
1.12 jakob 1126: Note that this option applies to protocol version 2 only.
1.84 jmc 1127: .Pp
1128: See also
1129: .Sx VERIFYING HOST KEYS
1130: in
1131: .Xr ssh 1 .
1.111 grunk 1132: .It Cm VisualHostKey
1133: If this flag is set to
1134: .Dq yes ,
1135: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1136: printed in addition to the hex fingerprint string at login and
1137: for unknown host keys.
1.111 grunk 1138: If this flag is set to
1139: .Dq no ,
1.114 stevesk 1140: no fingerprint strings are printed at login and
1141: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1142: The default is
1143: .Dq no .
1.1 stevesk 1144: .It Cm XAuthLocation
1.5 stevesk 1145: Specifies the full pathname of the
1.1 stevesk 1146: .Xr xauth 1
1147: program.
1148: The default is
1149: .Pa /usr/X11R6/bin/xauth .
1150: .El
1.86 jmc 1151: .Sh PATTERNS
1152: A
1153: .Em pattern
1154: consists of zero or more non-whitespace characters,
1155: .Sq *
1156: (a wildcard that matches zero or more characters),
1157: or
1158: .Sq ?\&
1159: (a wildcard that matches exactly one character).
1160: For example, to specify a set of declarations for any host in the
1161: .Dq .co.uk
1162: set of domains,
1163: the following pattern could be used:
1164: .Pp
1165: .Dl Host *.co.uk
1166: .Pp
1167: The following pattern
1168: would match any host in the 192.168.0.[0-9] network range:
1169: .Pp
1170: .Dl Host 192.168.0.?
1171: .Pp
1172: A
1173: .Em pattern-list
1174: is a comma-separated list of patterns.
1175: Patterns within pattern-lists may be negated
1176: by preceding them with an exclamation mark
1177: .Pq Sq !\& .
1178: For example,
1179: to allow a key to be used from anywhere within an organisation
1180: except from the
1181: .Dq dialup
1182: pool,
1183: the following entry (in authorized_keys) could be used:
1184: .Pp
1185: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1186: .Sh FILES
1187: .Bl -tag -width Ds
1.50 djm 1188: .It Pa ~/.ssh/config
1.1 stevesk 1189: This is the per-user configuration file.
1190: The format of this file is described above.
1.84 jmc 1191: This file is used by the SSH client.
1.30 djm 1192: Because of the potential for abuse, this file must have strict permissions:
1193: read/write for the user, and not accessible by others.
1.1 stevesk 1194: .It Pa /etc/ssh/ssh_config
1195: Systemwide configuration file.
1196: This file provides defaults for those
1197: values that are not specified in the user's configuration file, and
1198: for those users who do not have a configuration file.
1199: This file must be world-readable.
1200: .El
1.13 jmc 1201: .Sh SEE ALSO
1202: .Xr ssh 1
1.1 stevesk 1203: .Sh AUTHORS
1204: OpenSSH is a derivative of the original and free
1205: ssh 1.2.12 release by Tatu Ylonen.
1206: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1207: Theo de Raadt and Dug Song
1208: removed many bugs, re-added newer features and
1209: created OpenSSH.
1210: Markus Friedl contributed the support for SSH
1211: protocol versions 1.5 and 2.0.
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