Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.137
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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1.137 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.136 2010/07/12 22:41:13 djm Exp $
! 38: .Dd $Mdocdate: July 12 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
354: IPv6 addresses can be specified by enclosing addresses in square brackets or
355: by using an alternative syntax:
356: .Oo Ar bind_address Ns / Oc Ns Ar port .
357: By default, the local port is bound in accordance with the
358: .Cm GatewayPorts
359: setting.
360: However, an explicit
361: .Ar bind_address
362: may be used to bind the connection to a specific address.
363: The
364: .Ar bind_address
365: of
366: .Dq localhost
367: indicates that the listening port be bound for local use only, while an
368: empty address or
369: .Sq *
370: indicates that the port should be available from all interfaces.
371: .Pp
1.38 jmc 372: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 373: .Xr ssh 1
1.38 jmc 374: will act as a SOCKS server.
375: Multiple forwardings may be specified, and
376: additional forwardings can be given on the command line.
377: Only the superuser can forward privileged ports.
1.14 markus 378: .It Cm EnableSSHKeysign
379: Setting this option to
380: .Dq yes
381: in the global client configuration file
382: .Pa /etc/ssh/ssh_config
383: enables the use of the helper program
384: .Xr ssh-keysign 8
385: during
386: .Cm HostbasedAuthentication .
387: The argument must be
388: .Dq yes
389: or
390: .Dq no .
391: The default is
392: .Dq no .
1.23 jmc 393: This option should be placed in the non-hostspecific section.
1.14 markus 394: See
395: .Xr ssh-keysign 8
396: for more information.
1.1 stevesk 397: .It Cm EscapeChar
398: Sets the escape character (default:
399: .Ql ~ ) .
400: The escape character can also
401: be set on the command line.
402: The argument should be a single character,
403: .Ql ^
404: followed by a letter, or
405: .Dq none
406: to disable the escape
407: character entirely (making the connection transparent for binary
408: data).
1.96 markus 409: .It Cm ExitOnForwardFailure
410: Specifies whether
411: .Xr ssh 1
412: should terminate the connection if it cannot set up all requested
1.102 stevesk 413: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 414: The argument must be
415: .Dq yes
416: or
417: .Dq no .
418: The default is
419: .Dq no .
1.1 stevesk 420: .It Cm ForwardAgent
421: Specifies whether the connection to the authentication agent (if any)
422: will be forwarded to the remote machine.
423: The argument must be
424: .Dq yes
425: or
426: .Dq no .
427: The default is
428: .Dq no .
1.3 stevesk 429: .Pp
1.7 jmc 430: Agent forwarding should be enabled with caution.
431: Users with the ability to bypass file permissions on the remote host
432: (for the agent's Unix-domain socket)
433: can access the local agent through the forwarded connection.
434: An attacker cannot obtain key material from the agent,
1.3 stevesk 435: however they can perform operations on the keys that enable them to
436: authenticate using the identities loaded into the agent.
1.1 stevesk 437: .It Cm ForwardX11
438: Specifies whether X11 connections will be automatically redirected
439: over the secure channel and
440: .Ev DISPLAY
441: set.
442: The argument must be
443: .Dq yes
444: or
445: .Dq no .
446: The default is
447: .Dq no .
1.3 stevesk 448: .Pp
1.7 jmc 449: X11 forwarding should be enabled with caution.
450: Users with the ability to bypass file permissions on the remote host
1.22 markus 451: (for the user's X11 authorization database)
1.7 jmc 452: can access the local X11 display through the forwarded connection.
1.22 markus 453: An attacker may then be able to perform activities such as keystroke monitoring
454: if the
455: .Cm ForwardX11Trusted
456: option is also enabled.
1.134 djm 457: .It Cm ForwardX11Timeout
1.135 jmc 458: Specify a timeout for untrusted X11 forwarding
459: using the format described in the
1.134 djm 460: .Sx TIME FORMATS
461: section of
462: .Xr sshd_config 5 .
463: X11 connections received by
464: .Xr ssh 1
465: after this time will be refused.
466: The default is to disable untrusted X11 forwarding after twenty minutes has
467: elapsed.
1.22 markus 468: .It Cm ForwardX11Trusted
1.34 jmc 469: If this option is set to
1.84 jmc 470: .Dq yes ,
471: remote X11 clients will have full access to the original X11 display.
1.42 djm 472: .Pp
1.22 markus 473: If this option is set to
1.84 jmc 474: .Dq no ,
475: remote X11 clients will be considered untrusted and prevented
1.22 markus 476: from stealing or tampering with data belonging to trusted X11
477: clients.
1.42 djm 478: Furthermore, the
479: .Xr xauth 1
480: token used for the session will be set to expire after 20 minutes.
481: Remote clients will be refused access after this time.
1.22 markus 482: .Pp
483: The default is
484: .Dq no .
485: .Pp
486: See the X11 SECURITY extension specification for full details on
487: the restrictions imposed on untrusted clients.
1.1 stevesk 488: .It Cm GatewayPorts
489: Specifies whether remote hosts are allowed to connect to local
490: forwarded ports.
491: By default,
1.84 jmc 492: .Xr ssh 1
1.7 jmc 493: binds local port forwardings to the loopback address.
494: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 495: .Cm GatewayPorts
1.84 jmc 496: can be used to specify that ssh
1.1 stevesk 497: should bind local port forwardings to the wildcard address,
498: thus allowing remote hosts to connect to forwarded ports.
499: The argument must be
500: .Dq yes
501: or
502: .Dq no .
503: The default is
504: .Dq no .
505: .It Cm GlobalKnownHostsFile
506: Specifies a file to use for the global
507: host key database instead of
508: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 509: .It Cm GSSAPIAuthentication
1.27 markus 510: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 511: The default is
1.21 markus 512: .Dq no .
1.18 markus 513: Note that this option applies to protocol version 2 only.
514: .It Cm GSSAPIDelegateCredentials
515: Forward (delegate) credentials to the server.
516: The default is
517: .Dq no .
518: Note that this option applies to protocol version 2 only.
1.44 djm 519: .It Cm HashKnownHosts
520: Indicates that
1.84 jmc 521: .Xr ssh 1
1.44 djm 522: should hash host names and addresses when they are added to
1.50 djm 523: .Pa ~/.ssh/known_hosts .
1.44 djm 524: These hashed names may be used normally by
1.84 jmc 525: .Xr ssh 1
1.44 djm 526: and
1.84 jmc 527: .Xr sshd 8 ,
1.44 djm 528: but they do not reveal identifying information should the file's contents
529: be disclosed.
530: The default is
531: .Dq no .
1.97 jmc 532: Note that existing names and addresses in known hosts files
533: will not be converted automatically,
534: but may be manually hashed using
1.45 djm 535: .Xr ssh-keygen 1 .
1.1 stevesk 536: .It Cm HostbasedAuthentication
537: Specifies whether to try rhosts based authentication with public key
538: authentication.
539: The argument must be
540: .Dq yes
541: or
542: .Dq no .
543: The default is
544: .Dq no .
545: This option applies to protocol version 2 only and
546: is similar to
547: .Cm RhostsRSAAuthentication .
548: .It Cm HostKeyAlgorithms
549: Specifies the protocol version 2 host key algorithms
550: that the client wants to use in order of preference.
551: The default for this option is:
552: .Dq ssh-rsa,ssh-dss .
553: .It Cm HostKeyAlias
554: Specifies an alias that should be used instead of the
555: real host name when looking up or saving the host key
556: in the host key database files.
1.84 jmc 557: This option is useful for tunneling SSH connections
1.1 stevesk 558: or for multiple servers running on a single host.
559: .It Cm HostName
560: Specifies the real host name to log into.
561: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 562: If the hostname contains the character sequence
563: .Ql %h ,
564: then this will be replaced with the host name specified on the commandline
565: (this is useful for manipulating unqualified names).
1.84 jmc 566: The default is the name given on the command line.
1.1 stevesk 567: Numeric IP addresses are also permitted (both on the command line and in
568: .Cm HostName
569: specifications).
1.29 markus 570: .It Cm IdentitiesOnly
571: Specifies that
1.84 jmc 572: .Xr ssh 1
1.29 markus 573: should only use the authentication identity files configured in the
1.31 jmc 574: .Nm
1.29 markus 575: files,
1.84 jmc 576: even if
577: .Xr ssh-agent 1
1.29 markus 578: offers more identities.
579: The argument to this keyword must be
580: .Dq yes
581: or
582: .Dq no .
1.84 jmc 583: This option is intended for situations where ssh-agent
1.29 markus 584: offers many different identities.
585: The default is
586: .Dq no .
1.67 jmc 587: .It Cm IdentityFile
588: Specifies a file from which the user's RSA or DSA authentication identity
589: is read.
590: The default is
591: .Pa ~/.ssh/identity
592: for protocol version 1, and
593: .Pa ~/.ssh/id_rsa
594: and
595: .Pa ~/.ssh/id_dsa
596: for protocol version 2.
597: Additionally, any identities represented by the authentication agent
598: will be used for authentication.
1.129 djm 599: .Xr ssh 1
600: will try to load certificate information from the filename obtained by
601: appending
602: .Pa -cert.pub
603: to the path of a specified
604: .Cm IdentityFile .
1.90 djm 605: .Pp
1.67 jmc 606: The file name may use the tilde
1.91 jmc 607: syntax to refer to a user's home directory or one of the following
1.90 djm 608: escape characters:
609: .Ql %d
610: (local user's home directory),
611: .Ql %u
612: (local user name),
613: .Ql %l
614: (local host name),
615: .Ql %h
616: (remote host name) or
1.92 djm 617: .Ql %r
1.90 djm 618: (remote user name).
619: .Pp
1.67 jmc 620: It is possible to have
621: multiple identity files specified in configuration files; all these
622: identities will be tried in sequence.
1.103 djm 623: .It Cm KbdInteractiveAuthentication
624: Specifies whether to use keyboard-interactive authentication.
625: The argument to this keyword must be
626: .Dq yes
627: or
628: .Dq no .
629: The default is
630: .Dq yes .
1.39 djm 631: .It Cm KbdInteractiveDevices
632: Specifies the list of methods to use in keyboard-interactive authentication.
633: Multiple method names must be comma-separated.
634: The default is to use the server specified list.
1.85 jmc 635: The methods available vary depending on what the server supports.
636: For an OpenSSH server,
637: it may be zero or more of:
638: .Dq bsdauth ,
639: .Dq pam ,
640: and
641: .Dq skey .
1.65 reyk 642: .It Cm LocalCommand
643: Specifies a command to execute on the local machine after successfully
644: connecting to the server.
645: The command string extends to the end of the line, and is executed with
1.105 jmc 646: the user's shell.
1.109 dtucker 647: The following escape character substitutions will be performed:
648: .Ql %d
649: (local user's home directory),
650: .Ql %h
651: (remote host name),
652: .Ql %l
653: (local host name),
654: .Ql %n
655: (host name as provided on the command line),
656: .Ql %p
657: (remote port),
658: .Ql %r
659: (remote user name) or
660: .Ql %u
661: (local user name).
1.123 djm 662: .Pp
663: The command is run synchronously and does not have access to the
664: session of the
665: .Xr ssh 1
666: that spawned it.
667: It should not be used for interactive commands.
668: .Pp
1.65 reyk 669: This directive is ignored unless
670: .Cm PermitLocalCommand
671: has been enabled.
1.1 stevesk 672: .It Cm LocalForward
1.74 jmc 673: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 674: the secure channel to the specified host and port from the remote machine.
1.49 jmc 675: The first argument must be
1.43 djm 676: .Sm off
1.49 jmc 677: .Oo Ar bind_address : Oc Ar port
1.43 djm 678: .Sm on
1.49 jmc 679: and the second argument must be
680: .Ar host : Ns Ar hostport .
1.46 jmc 681: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 682: by using an alternative syntax:
1.49 jmc 683: .Oo Ar bind_address Ns / Oc Ns Ar port
684: and
685: .Ar host Ns / Ns Ar hostport .
1.46 jmc 686: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 687: given on the command line.
1.1 stevesk 688: Only the superuser can forward privileged ports.
1.43 djm 689: By default, the local port is bound in accordance with the
690: .Cm GatewayPorts
691: setting.
692: However, an explicit
693: .Ar bind_address
694: may be used to bind the connection to a specific address.
695: The
696: .Ar bind_address
697: of
698: .Dq localhost
1.46 jmc 699: indicates that the listening port be bound for local use only, while an
700: empty address or
701: .Sq *
1.43 djm 702: indicates that the port should be available from all interfaces.
1.1 stevesk 703: .It Cm LogLevel
704: Gives the verbosity level that is used when logging messages from
1.84 jmc 705: .Xr ssh 1 .
1.1 stevesk 706: The possible values are:
1.84 jmc 707: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 708: The default is INFO.
709: DEBUG and DEBUG1 are equivalent.
710: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 711: .It Cm MACs
712: Specifies the MAC (message authentication code) algorithms
713: in order of preference.
714: The MAC algorithm is used in protocol version 2
715: for data integrity protection.
716: Multiple algorithms must be comma-separated.
1.84 jmc 717: The default is:
1.101 jmc 718: .Bd -literal -offset indent
719: hmac-md5,hmac-sha1,umac-64@openssh.com,
720: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
721: .Ed
1.1 stevesk 722: .It Cm NoHostAuthenticationForLocalhost
723: This option can be used if the home directory is shared across machines.
724: In this case localhost will refer to a different machine on each of
725: the machines and the user will get many warnings about changed host keys.
726: However, this option disables host authentication for localhost.
727: The argument to this keyword must be
728: .Dq yes
729: or
730: .Dq no .
731: The default is to check the host key for localhost.
732: .It Cm NumberOfPasswordPrompts
733: Specifies the number of password prompts before giving up.
734: The argument to this keyword must be an integer.
1.84 jmc 735: The default is 3.
1.1 stevesk 736: .It Cm PasswordAuthentication
737: Specifies whether to use password authentication.
738: The argument to this keyword must be
739: .Dq yes
740: or
741: .Dq no .
742: The default is
743: .Dq yes .
1.65 reyk 744: .It Cm PermitLocalCommand
745: Allow local command execution via the
746: .Ic LocalCommand
747: option or using the
1.66 jmc 748: .Ic !\& Ns Ar command
1.65 reyk 749: escape sequence in
750: .Xr ssh 1 .
751: The argument must be
752: .Dq yes
753: or
754: .Dq no .
755: The default is
756: .Dq no .
1.127 markus 757: .It Cm PKCS11Provider
758: Specifies which PKCS#11 provider to use.
759: The argument to this keyword is the PKCS#11 shared libary
760: .Xr ssh 1
1.128 markus 761: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 762: private RSA key.
1.67 jmc 763: .It Cm Port
764: Specifies the port number to connect on the remote host.
1.84 jmc 765: The default is 22.
1.1 stevesk 766: .It Cm PreferredAuthentications
767: Specifies the order in which the client should try protocol 2
1.11 jmc 768: authentication methods.
1.48 jmc 769: This allows a client to prefer one method (e.g.\&
1.1 stevesk 770: .Cm keyboard-interactive )
1.48 jmc 771: over another method (e.g.\&
1.131 jmc 772: .Cm password ) .
773: The default is:
774: .Bd -literal -offset indent
775: gssapi-with-mic,hostbased,publickey,
776: keyboard-interactive,password
777: .Ed
1.1 stevesk 778: .It Cm Protocol
779: Specifies the protocol versions
1.84 jmc 780: .Xr ssh 1
1.1 stevesk 781: should support in order of preference.
782: The possible values are
1.84 jmc 783: .Sq 1
1.1 stevesk 784: and
1.84 jmc 785: .Sq 2 .
1.1 stevesk 786: Multiple versions must be comma-separated.
1.120 markus 787: When this option is set to
1.121 jmc 788: .Dq 2,1
1.120 markus 789: .Nm ssh
790: will try version 2 and fall back to version 1
791: if version 2 is not available.
1.1 stevesk 792: The default is
1.121 jmc 793: .Sq 2 .
1.1 stevesk 794: .It Cm ProxyCommand
795: Specifies the command to use to connect to the server.
796: The command
797: string extends to the end of the line, and is executed with
1.105 jmc 798: the user's shell.
1.133 jmc 799: In the command string, any occurrence of
1.1 stevesk 800: .Ql %h
801: will be substituted by the host name to
1.132 djm 802: connect,
1.1 stevesk 803: .Ql %p
1.133 jmc 804: by the port, and
805: .Ql %r
1.132 djm 806: by the remote user name.
1.1 stevesk 807: The command can be basically anything,
808: and should read from its standard input and write to its standard output.
809: It should eventually connect an
810: .Xr sshd 8
811: server running on some machine, or execute
812: .Ic sshd -i
813: somewhere.
814: Host key management will be done using the
815: HostName of the host being connected (defaulting to the name typed by
816: the user).
1.7 jmc 817: Setting the command to
818: .Dq none
1.6 markus 819: disables this option entirely.
1.1 stevesk 820: Note that
821: .Cm CheckHostIP
822: is not available for connects with a proxy command.
1.52 djm 823: .Pp
824: This directive is useful in conjunction with
825: .Xr nc 1
826: and its proxy support.
1.53 jmc 827: For example, the following directive would connect via an HTTP proxy at
1.52 djm 828: 192.0.2.0:
829: .Bd -literal -offset 3n
830: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
831: .Ed
1.1 stevesk 832: .It Cm PubkeyAuthentication
833: Specifies whether to try public key authentication.
834: The argument to this keyword must be
835: .Dq yes
836: or
837: .Dq no .
838: The default is
839: .Dq yes .
840: This option applies to protocol version 2 only.
1.75 dtucker 841: .It Cm RekeyLimit
842: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 843: session key is renegotiated.
1.75 dtucker 844: The argument is the number of bytes, with an optional suffix of
1.76 jmc 845: .Sq K ,
846: .Sq M ,
1.75 dtucker 847: or
1.76 jmc 848: .Sq G
1.75 dtucker 849: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
850: The default is between
1.84 jmc 851: .Sq 1G
1.75 dtucker 852: and
1.84 jmc 853: .Sq 4G ,
1.75 dtucker 854: depending on the cipher.
1.76 jmc 855: This option applies to protocol version 2 only.
1.1 stevesk 856: .It Cm RemoteForward
1.74 jmc 857: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 858: the secure channel to the specified host and port from the local machine.
1.49 jmc 859: The first argument must be
1.43 djm 860: .Sm off
1.49 jmc 861: .Oo Ar bind_address : Oc Ar port
1.43 djm 862: .Sm on
1.49 jmc 863: and the second argument must be
864: .Ar host : Ns Ar hostport .
865: IPv6 addresses can be specified by enclosing addresses in square brackets
866: or by using an alternative syntax:
867: .Oo Ar bind_address Ns / Oc Ns Ar port
868: and
869: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 870: Multiple forwardings may be specified, and additional
871: forwardings can be given on the command line.
1.113 stevesk 872: Privileged ports can be forwarded only when
873: logging in as root on the remote machine.
1.118 jmc 874: .Pp
1.117 djm 875: If the
876: .Ar port
877: argument is
878: .Ql 0 ,
879: the listen port will be dynamically allocated on the server and reported
880: to the client at run time.
1.43 djm 881: .Pp
882: If the
883: .Ar bind_address
884: is not specified, the default is to only bind to loopback addresses.
885: If the
886: .Ar bind_address
887: is
888: .Ql *
889: or an empty string, then the forwarding is requested to listen on all
890: interfaces.
891: Specifying a remote
892: .Ar bind_address
1.46 jmc 893: will only succeed if the server's
894: .Cm GatewayPorts
1.43 djm 895: option is enabled (see
1.46 jmc 896: .Xr sshd_config 5 ) .
1.1 stevesk 897: .It Cm RhostsRSAAuthentication
898: Specifies whether to try rhosts based authentication with RSA host
899: authentication.
900: The argument must be
901: .Dq yes
902: or
903: .Dq no .
904: The default is
905: .Dq no .
906: This option applies to protocol version 1 only and requires
1.84 jmc 907: .Xr ssh 1
1.1 stevesk 908: to be setuid root.
909: .It Cm RSAAuthentication
910: Specifies whether to try RSA authentication.
911: The argument to this keyword must be
912: .Dq yes
913: or
914: .Dq no .
915: RSA authentication will only be
916: attempted if the identity file exists, or an authentication agent is
917: running.
918: The default is
919: .Dq yes .
920: Note that this option applies to protocol version 1 only.
1.32 djm 921: .It Cm SendEnv
922: Specifies what variables from the local
923: .Xr environ 7
924: should be sent to the server.
1.84 jmc 925: Note that environment passing is only supported for protocol 2.
926: The server must also support it, and the server must be configured to
1.33 djm 927: accept these environment variables.
1.32 djm 928: Refer to
929: .Cm AcceptEnv
930: in
931: .Xr sshd_config 5
932: for how to configure the server.
1.80 jmc 933: Variables are specified by name, which may contain wildcard characters.
1.33 djm 934: Multiple environment variables may be separated by whitespace or spread
1.32 djm 935: across multiple
936: .Cm SendEnv
937: directives.
938: The default is not to send any environment variables.
1.81 jmc 939: .Pp
940: See
941: .Sx PATTERNS
942: for more information on patterns.
1.28 markus 943: .It Cm ServerAliveCountMax
1.73 jmc 944: Sets the number of server alive messages (see below) which may be
1.28 markus 945: sent without
1.84 jmc 946: .Xr ssh 1
1.28 markus 947: receiving any messages back from the server.
948: If this threshold is reached while server alive messages are being sent,
1.84 jmc 949: ssh will disconnect from the server, terminating the session.
1.28 markus 950: It is important to note that the use of server alive messages is very
951: different from
952: .Cm TCPKeepAlive
953: (below).
954: The server alive messages are sent through the encrypted channel
955: and therefore will not be spoofable.
956: The TCP keepalive option enabled by
957: .Cm TCPKeepAlive
958: is spoofable.
959: The server alive mechanism is valuable when the client or
960: server depend on knowing when a connection has become inactive.
961: .Pp
962: The default value is 3.
963: If, for example,
964: .Cm ServerAliveInterval
1.84 jmc 965: (see below) is set to 15 and
1.28 markus 966: .Cm ServerAliveCountMax
1.84 jmc 967: is left at the default, if the server becomes unresponsive,
968: ssh will disconnect after approximately 45 seconds.
1.89 markus 969: This option applies to protocol version 2 only.
1.67 jmc 970: .It Cm ServerAliveInterval
971: Sets a timeout interval in seconds after which if no data has been received
972: from the server,
1.84 jmc 973: .Xr ssh 1
1.67 jmc 974: will send a message through the encrypted
975: channel to request a response from the server.
976: The default
977: is 0, indicating that these messages will not be sent to the server.
978: This option applies to protocol version 2 only.
1.1 stevesk 979: .It Cm StrictHostKeyChecking
980: If this flag is set to
981: .Dq yes ,
1.84 jmc 982: .Xr ssh 1
1.1 stevesk 983: will never automatically add host keys to the
1.50 djm 984: .Pa ~/.ssh/known_hosts
1.1 stevesk 985: file, and refuses to connect to hosts whose host key has changed.
986: This provides maximum protection against trojan horse attacks,
1.84 jmc 987: though it can be annoying when the
1.1 stevesk 988: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 989: file is poorly maintained or when connections to new hosts are
1.1 stevesk 990: frequently made.
991: This option forces the user to manually
992: add all new hosts.
993: If this flag is set to
994: .Dq no ,
1.84 jmc 995: ssh will automatically add new host keys to the
1.1 stevesk 996: user known hosts files.
997: If this flag is set to
998: .Dq ask ,
999: new host keys
1000: will be added to the user known host files only after the user
1001: has confirmed that is what they really want to do, and
1.84 jmc 1002: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1003: The host keys of
1004: known hosts will be verified automatically in all cases.
1005: The argument must be
1006: .Dq yes ,
1.84 jmc 1007: .Dq no ,
1.1 stevesk 1008: or
1009: .Dq ask .
1010: The default is
1011: .Dq ask .
1.26 markus 1012: .It Cm TCPKeepAlive
1013: Specifies whether the system should send TCP keepalive messages to the
1014: other side.
1015: If they are sent, death of the connection or crash of one
1016: of the machines will be properly noticed.
1017: However, this means that
1018: connections will die if the route is down temporarily, and some people
1019: find it annoying.
1020: .Pp
1021: The default is
1022: .Dq yes
1023: (to send TCP keepalive messages), and the client will notice
1024: if the network goes down or the remote host dies.
1025: This is important in scripts, and many users want it too.
1026: .Pp
1027: To disable TCP keepalive messages, the value should be set to
1028: .Dq no .
1.65 reyk 1029: .It Cm Tunnel
1.95 stevesk 1030: Request
1.65 reyk 1031: .Xr tun 4
1.69 jmc 1032: device forwarding between the client and the server.
1.65 reyk 1033: The argument must be
1.68 reyk 1034: .Dq yes ,
1.95 stevesk 1035: .Dq point-to-point
1036: (layer 3),
1037: .Dq ethernet
1038: (layer 2),
1.65 reyk 1039: or
1040: .Dq no .
1.95 stevesk 1041: Specifying
1042: .Dq yes
1043: requests the default tunnel mode, which is
1044: .Dq point-to-point .
1.65 reyk 1045: The default is
1046: .Dq no .
1047: .It Cm TunnelDevice
1.95 stevesk 1048: Specifies the
1.65 reyk 1049: .Xr tun 4
1.95 stevesk 1050: devices to open on the client
1051: .Pq Ar local_tun
1052: and the server
1053: .Pq Ar remote_tun .
1054: .Pp
1055: The argument must be
1056: .Sm off
1057: .Ar local_tun Op : Ar remote_tun .
1058: .Sm on
1059: The devices may be specified by numerical ID or the keyword
1060: .Dq any ,
1061: which uses the next available tunnel device.
1062: If
1063: .Ar remote_tun
1064: is not specified, it defaults to
1065: .Dq any .
1066: The default is
1067: .Dq any:any .
1.72 jmc 1068: .It Cm UsePrivilegedPort
1069: Specifies whether to use a privileged port for outgoing connections.
1070: The argument must be
1071: .Dq yes
1072: or
1073: .Dq no .
1074: The default is
1075: .Dq no .
1076: If set to
1.84 jmc 1077: .Dq yes ,
1078: .Xr ssh 1
1.72 jmc 1079: must be setuid root.
1080: Note that this option must be set to
1081: .Dq yes
1082: for
1083: .Cm RhostsRSAAuthentication
1084: with older servers.
1.1 stevesk 1085: .It Cm User
1086: Specifies the user to log in as.
1087: This can be useful when a different user name is used on different machines.
1088: This saves the trouble of
1089: having to remember to give the user name on the command line.
1090: .It Cm UserKnownHostsFile
1091: Specifies a file to use for the user
1092: host key database instead of
1.50 djm 1093: .Pa ~/.ssh/known_hosts .
1.8 jakob 1094: .It Cm VerifyHostKeyDNS
1095: Specifies whether to verify the remote key using DNS and SSHFP resource
1096: records.
1.24 jakob 1097: If this option is set to
1098: .Dq yes ,
1.25 jmc 1099: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1100: from DNS.
1101: Insecure fingerprints will be handled as if this option was set to
1102: .Dq ask .
1103: If this option is set to
1104: .Dq ask ,
1105: information on fingerprint match will be displayed, but the user will still
1106: need to confirm new host keys according to the
1107: .Cm StrictHostKeyChecking
1108: option.
1109: The argument must be
1110: .Dq yes ,
1.84 jmc 1111: .Dq no ,
1.25 jmc 1112: or
1113: .Dq ask .
1.8 jakob 1114: The default is
1115: .Dq no .
1.12 jakob 1116: Note that this option applies to protocol version 2 only.
1.84 jmc 1117: .Pp
1118: See also
1119: .Sx VERIFYING HOST KEYS
1120: in
1121: .Xr ssh 1 .
1.111 grunk 1122: .It Cm VisualHostKey
1123: If this flag is set to
1124: .Dq yes ,
1125: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1126: printed in addition to the hex fingerprint string at login and
1127: for unknown host keys.
1.111 grunk 1128: If this flag is set to
1129: .Dq no ,
1.114 stevesk 1130: no fingerprint strings are printed at login and
1131: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1132: The default is
1133: .Dq no .
1.1 stevesk 1134: .It Cm XAuthLocation
1.5 stevesk 1135: Specifies the full pathname of the
1.1 stevesk 1136: .Xr xauth 1
1137: program.
1138: The default is
1139: .Pa /usr/X11R6/bin/xauth .
1140: .El
1.86 jmc 1141: .Sh PATTERNS
1142: A
1143: .Em pattern
1144: consists of zero or more non-whitespace characters,
1145: .Sq *
1146: (a wildcard that matches zero or more characters),
1147: or
1148: .Sq ?\&
1149: (a wildcard that matches exactly one character).
1150: For example, to specify a set of declarations for any host in the
1151: .Dq .co.uk
1152: set of domains,
1153: the following pattern could be used:
1154: .Pp
1155: .Dl Host *.co.uk
1156: .Pp
1157: The following pattern
1158: would match any host in the 192.168.0.[0-9] network range:
1159: .Pp
1160: .Dl Host 192.168.0.?
1161: .Pp
1162: A
1163: .Em pattern-list
1164: is a comma-separated list of patterns.
1165: Patterns within pattern-lists may be negated
1166: by preceding them with an exclamation mark
1167: .Pq Sq !\& .
1168: For example,
1169: to allow a key to be used from anywhere within an organisation
1170: except from the
1171: .Dq dialup
1172: pool,
1173: the following entry (in authorized_keys) could be used:
1174: .Pp
1175: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1176: .Sh FILES
1177: .Bl -tag -width Ds
1.50 djm 1178: .It Pa ~/.ssh/config
1.1 stevesk 1179: This is the per-user configuration file.
1180: The format of this file is described above.
1.84 jmc 1181: This file is used by the SSH client.
1.30 djm 1182: Because of the potential for abuse, this file must have strict permissions:
1183: read/write for the user, and not accessible by others.
1.1 stevesk 1184: .It Pa /etc/ssh/ssh_config
1185: Systemwide configuration file.
1186: This file provides defaults for those
1187: values that are not specified in the user's configuration file, and
1188: for those users who do not have a configuration file.
1189: This file must be world-readable.
1190: .El
1.13 jmc 1191: .Sh SEE ALSO
1192: .Xr ssh 1
1.1 stevesk 1193: .Sh AUTHORS
1194: OpenSSH is a derivative of the original and free
1195: ssh 1.2.12 release by Tatu Ylonen.
1196: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1197: Theo de Raadt and Dug Song
1198: removed many bugs, re-added newer features and
1199: created OpenSSH.
1200: Markus Friedl contributed the support for SSH
1201: protocol versions 1.5 and 2.0.
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