Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.133
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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1.133 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.132 2010/04/14 22:27:42 djm Exp $
! 38: .Dd $Mdocdate: April 14 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.
1.38 jmc 322: .It Cm DynamicForward
1.74 jmc 323: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 324: over the secure channel, and the application
325: protocol is then used to determine where to connect to from the
326: remote machine.
1.62 djm 327: .Pp
328: The argument must be
329: .Sm off
330: .Oo Ar bind_address : Oc Ar port .
331: .Sm on
332: IPv6 addresses can be specified by enclosing addresses in square brackets or
333: by using an alternative syntax:
334: .Oo Ar bind_address Ns / Oc Ns Ar port .
335: By default, the local port is bound in accordance with the
336: .Cm GatewayPorts
337: setting.
338: However, an explicit
339: .Ar bind_address
340: may be used to bind the connection to a specific address.
341: The
342: .Ar bind_address
343: of
344: .Dq localhost
345: indicates that the listening port be bound for local use only, while an
346: empty address or
347: .Sq *
348: indicates that the port should be available from all interfaces.
349: .Pp
1.38 jmc 350: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 351: .Xr ssh 1
1.38 jmc 352: will act as a SOCKS server.
353: Multiple forwardings may be specified, and
354: additional forwardings can be given on the command line.
355: Only the superuser can forward privileged ports.
1.14 markus 356: .It Cm EnableSSHKeysign
357: Setting this option to
358: .Dq yes
359: in the global client configuration file
360: .Pa /etc/ssh/ssh_config
361: enables the use of the helper program
362: .Xr ssh-keysign 8
363: during
364: .Cm HostbasedAuthentication .
365: The argument must be
366: .Dq yes
367: or
368: .Dq no .
369: The default is
370: .Dq no .
1.23 jmc 371: This option should be placed in the non-hostspecific section.
1.14 markus 372: See
373: .Xr ssh-keysign 8
374: for more information.
1.1 stevesk 375: .It Cm EscapeChar
376: Sets the escape character (default:
377: .Ql ~ ) .
378: The escape character can also
379: be set on the command line.
380: The argument should be a single character,
381: .Ql ^
382: followed by a letter, or
383: .Dq none
384: to disable the escape
385: character entirely (making the connection transparent for binary
386: data).
1.96 markus 387: .It Cm ExitOnForwardFailure
388: Specifies whether
389: .Xr ssh 1
390: should terminate the connection if it cannot set up all requested
1.102 stevesk 391: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 392: The argument must be
393: .Dq yes
394: or
395: .Dq no .
396: The default is
397: .Dq no .
1.1 stevesk 398: .It Cm ForwardAgent
399: Specifies whether the connection to the authentication agent (if any)
400: will be forwarded to the remote machine.
401: The argument must be
402: .Dq yes
403: or
404: .Dq no .
405: The default is
406: .Dq no .
1.3 stevesk 407: .Pp
1.7 jmc 408: Agent forwarding should be enabled with caution.
409: Users with the ability to bypass file permissions on the remote host
410: (for the agent's Unix-domain socket)
411: can access the local agent through the forwarded connection.
412: An attacker cannot obtain key material from the agent,
1.3 stevesk 413: however they can perform operations on the keys that enable them to
414: authenticate using the identities loaded into the agent.
1.1 stevesk 415: .It Cm ForwardX11
416: Specifies whether X11 connections will be automatically redirected
417: over the secure channel and
418: .Ev DISPLAY
419: set.
420: The argument must be
421: .Dq yes
422: or
423: .Dq no .
424: The default is
425: .Dq no .
1.3 stevesk 426: .Pp
1.7 jmc 427: X11 forwarding should be enabled with caution.
428: Users with the ability to bypass file permissions on the remote host
1.22 markus 429: (for the user's X11 authorization database)
1.7 jmc 430: can access the local X11 display through the forwarded connection.
1.22 markus 431: An attacker may then be able to perform activities such as keystroke monitoring
432: if the
433: .Cm ForwardX11Trusted
434: option is also enabled.
435: .It Cm ForwardX11Trusted
1.34 jmc 436: If this option is set to
1.84 jmc 437: .Dq yes ,
438: remote X11 clients will have full access to the original X11 display.
1.42 djm 439: .Pp
1.22 markus 440: If this option is set to
1.84 jmc 441: .Dq no ,
442: remote X11 clients will be considered untrusted and prevented
1.22 markus 443: from stealing or tampering with data belonging to trusted X11
444: clients.
1.42 djm 445: Furthermore, the
446: .Xr xauth 1
447: token used for the session will be set to expire after 20 minutes.
448: Remote clients will be refused access after this time.
1.22 markus 449: .Pp
450: The default is
451: .Dq no .
452: .Pp
453: See the X11 SECURITY extension specification for full details on
454: the restrictions imposed on untrusted clients.
1.1 stevesk 455: .It Cm GatewayPorts
456: Specifies whether remote hosts are allowed to connect to local
457: forwarded ports.
458: By default,
1.84 jmc 459: .Xr ssh 1
1.7 jmc 460: binds local port forwardings to the loopback address.
461: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 462: .Cm GatewayPorts
1.84 jmc 463: can be used to specify that ssh
1.1 stevesk 464: should bind local port forwardings to the wildcard address,
465: thus allowing remote hosts to connect to forwarded ports.
466: The argument must be
467: .Dq yes
468: or
469: .Dq no .
470: The default is
471: .Dq no .
472: .It Cm GlobalKnownHostsFile
473: Specifies a file to use for the global
474: host key database instead of
475: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 476: .It Cm GSSAPIAuthentication
1.27 markus 477: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 478: The default is
1.21 markus 479: .Dq no .
1.18 markus 480: Note that this option applies to protocol version 2 only.
481: .It Cm GSSAPIDelegateCredentials
482: Forward (delegate) credentials to the server.
483: The default is
484: .Dq no .
485: Note that this option applies to protocol version 2 only.
1.44 djm 486: .It Cm HashKnownHosts
487: Indicates that
1.84 jmc 488: .Xr ssh 1
1.44 djm 489: should hash host names and addresses when they are added to
1.50 djm 490: .Pa ~/.ssh/known_hosts .
1.44 djm 491: These hashed names may be used normally by
1.84 jmc 492: .Xr ssh 1
1.44 djm 493: and
1.84 jmc 494: .Xr sshd 8 ,
1.44 djm 495: but they do not reveal identifying information should the file's contents
496: be disclosed.
497: The default is
498: .Dq no .
1.97 jmc 499: Note that existing names and addresses in known hosts files
500: will not be converted automatically,
501: but may be manually hashed using
1.45 djm 502: .Xr ssh-keygen 1 .
1.1 stevesk 503: .It Cm HostbasedAuthentication
504: Specifies whether to try rhosts based authentication with public key
505: authentication.
506: The argument must be
507: .Dq yes
508: or
509: .Dq no .
510: The default is
511: .Dq no .
512: This option applies to protocol version 2 only and
513: is similar to
514: .Cm RhostsRSAAuthentication .
515: .It Cm HostKeyAlgorithms
516: Specifies the protocol version 2 host key algorithms
517: that the client wants to use in order of preference.
518: The default for this option is:
519: .Dq ssh-rsa,ssh-dss .
520: .It Cm HostKeyAlias
521: Specifies an alias that should be used instead of the
522: real host name when looking up or saving the host key
523: in the host key database files.
1.84 jmc 524: This option is useful for tunneling SSH connections
1.1 stevesk 525: or for multiple servers running on a single host.
526: .It Cm HostName
527: Specifies the real host name to log into.
528: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 529: The default is the name given on the command line.
1.1 stevesk 530: Numeric IP addresses are also permitted (both on the command line and in
531: .Cm HostName
532: specifications).
1.29 markus 533: .It Cm IdentitiesOnly
534: Specifies that
1.84 jmc 535: .Xr ssh 1
1.29 markus 536: should only use the authentication identity files configured in the
1.31 jmc 537: .Nm
1.29 markus 538: files,
1.84 jmc 539: even if
540: .Xr ssh-agent 1
1.29 markus 541: offers more identities.
542: The argument to this keyword must be
543: .Dq yes
544: or
545: .Dq no .
1.84 jmc 546: This option is intended for situations where ssh-agent
1.29 markus 547: offers many different identities.
548: The default is
549: .Dq no .
1.67 jmc 550: .It Cm IdentityFile
551: Specifies a file from which the user's RSA or DSA authentication identity
552: is read.
553: The default is
554: .Pa ~/.ssh/identity
555: for protocol version 1, and
556: .Pa ~/.ssh/id_rsa
557: and
558: .Pa ~/.ssh/id_dsa
559: for protocol version 2.
560: Additionally, any identities represented by the authentication agent
561: will be used for authentication.
1.129 djm 562: .Xr ssh 1
563: will try to load certificate information from the filename obtained by
564: appending
565: .Pa -cert.pub
566: to the path of a specified
567: .Cm IdentityFile .
1.90 djm 568: .Pp
1.67 jmc 569: The file name may use the tilde
1.91 jmc 570: syntax to refer to a user's home directory or one of the following
1.90 djm 571: escape characters:
572: .Ql %d
573: (local user's home directory),
574: .Ql %u
575: (local user name),
576: .Ql %l
577: (local host name),
578: .Ql %h
579: (remote host name) or
1.92 djm 580: .Ql %r
1.90 djm 581: (remote user name).
582: .Pp
1.67 jmc 583: It is possible to have
584: multiple identity files specified in configuration files; all these
585: identities will be tried in sequence.
1.103 djm 586: .It Cm KbdInteractiveAuthentication
587: Specifies whether to use keyboard-interactive authentication.
588: The argument to this keyword must be
589: .Dq yes
590: or
591: .Dq no .
592: The default is
593: .Dq yes .
1.39 djm 594: .It Cm KbdInteractiveDevices
595: Specifies the list of methods to use in keyboard-interactive authentication.
596: Multiple method names must be comma-separated.
597: The default is to use the server specified list.
1.85 jmc 598: The methods available vary depending on what the server supports.
599: For an OpenSSH server,
600: it may be zero or more of:
601: .Dq bsdauth ,
602: .Dq pam ,
603: and
604: .Dq skey .
1.65 reyk 605: .It Cm LocalCommand
606: Specifies a command to execute on the local machine after successfully
607: connecting to the server.
608: The command string extends to the end of the line, and is executed with
1.105 jmc 609: the user's shell.
1.109 dtucker 610: The following escape character substitutions will be performed:
611: .Ql %d
612: (local user's home directory),
613: .Ql %h
614: (remote host name),
615: .Ql %l
616: (local host name),
617: .Ql %n
618: (host name as provided on the command line),
619: .Ql %p
620: (remote port),
621: .Ql %r
622: (remote user name) or
623: .Ql %u
624: (local user name).
1.123 djm 625: .Pp
626: The command is run synchronously and does not have access to the
627: session of the
628: .Xr ssh 1
629: that spawned it.
630: It should not be used for interactive commands.
631: .Pp
1.65 reyk 632: This directive is ignored unless
633: .Cm PermitLocalCommand
634: has been enabled.
1.1 stevesk 635: .It Cm LocalForward
1.74 jmc 636: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 637: the secure channel to the specified host and port from the remote machine.
1.49 jmc 638: The first argument must be
1.43 djm 639: .Sm off
1.49 jmc 640: .Oo Ar bind_address : Oc Ar port
1.43 djm 641: .Sm on
1.49 jmc 642: and the second argument must be
643: .Ar host : Ns Ar hostport .
1.46 jmc 644: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 645: by using an alternative syntax:
1.49 jmc 646: .Oo Ar bind_address Ns / Oc Ns Ar port
647: and
648: .Ar host Ns / Ns Ar hostport .
1.46 jmc 649: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 650: given on the command line.
1.1 stevesk 651: Only the superuser can forward privileged ports.
1.43 djm 652: By default, the local port is bound in accordance with the
653: .Cm GatewayPorts
654: setting.
655: However, an explicit
656: .Ar bind_address
657: may be used to bind the connection to a specific address.
658: The
659: .Ar bind_address
660: of
661: .Dq localhost
1.46 jmc 662: indicates that the listening port be bound for local use only, while an
663: empty address or
664: .Sq *
1.43 djm 665: indicates that the port should be available from all interfaces.
1.1 stevesk 666: .It Cm LogLevel
667: Gives the verbosity level that is used when logging messages from
1.84 jmc 668: .Xr ssh 1 .
1.1 stevesk 669: The possible values are:
1.84 jmc 670: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 671: The default is INFO.
672: DEBUG and DEBUG1 are equivalent.
673: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 674: .It Cm MACs
675: Specifies the MAC (message authentication code) algorithms
676: in order of preference.
677: The MAC algorithm is used in protocol version 2
678: for data integrity protection.
679: Multiple algorithms must be comma-separated.
1.84 jmc 680: The default is:
1.101 jmc 681: .Bd -literal -offset indent
682: hmac-md5,hmac-sha1,umac-64@openssh.com,
683: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
684: .Ed
1.1 stevesk 685: .It Cm NoHostAuthenticationForLocalhost
686: This option can be used if the home directory is shared across machines.
687: In this case localhost will refer to a different machine on each of
688: the machines and the user will get many warnings about changed host keys.
689: However, this option disables host authentication for localhost.
690: The argument to this keyword must be
691: .Dq yes
692: or
693: .Dq no .
694: The default is to check the host key for localhost.
695: .It Cm NumberOfPasswordPrompts
696: Specifies the number of password prompts before giving up.
697: The argument to this keyword must be an integer.
1.84 jmc 698: The default is 3.
1.1 stevesk 699: .It Cm PasswordAuthentication
700: Specifies whether to use password authentication.
701: The argument to this keyword must be
702: .Dq yes
703: or
704: .Dq no .
705: The default is
706: .Dq yes .
1.65 reyk 707: .It Cm PermitLocalCommand
708: Allow local command execution via the
709: .Ic LocalCommand
710: option or using the
1.66 jmc 711: .Ic !\& Ns Ar command
1.65 reyk 712: escape sequence in
713: .Xr ssh 1 .
714: The argument must be
715: .Dq yes
716: or
717: .Dq no .
718: The default is
719: .Dq no .
1.127 markus 720: .It Cm PKCS11Provider
721: Specifies which PKCS#11 provider to use.
722: The argument to this keyword is the PKCS#11 shared libary
723: .Xr ssh 1
1.128 markus 724: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 725: private RSA key.
1.67 jmc 726: .It Cm Port
727: Specifies the port number to connect on the remote host.
1.84 jmc 728: The default is 22.
1.1 stevesk 729: .It Cm PreferredAuthentications
730: Specifies the order in which the client should try protocol 2
1.11 jmc 731: authentication methods.
1.48 jmc 732: This allows a client to prefer one method (e.g.\&
1.1 stevesk 733: .Cm keyboard-interactive )
1.48 jmc 734: over another method (e.g.\&
1.131 jmc 735: .Cm password ) .
736: The default is:
737: .Bd -literal -offset indent
738: gssapi-with-mic,hostbased,publickey,
739: keyboard-interactive,password
740: .Ed
1.1 stevesk 741: .It Cm Protocol
742: Specifies the protocol versions
1.84 jmc 743: .Xr ssh 1
1.1 stevesk 744: should support in order of preference.
745: The possible values are
1.84 jmc 746: .Sq 1
1.1 stevesk 747: and
1.84 jmc 748: .Sq 2 .
1.1 stevesk 749: Multiple versions must be comma-separated.
1.120 markus 750: When this option is set to
1.121 jmc 751: .Dq 2,1
1.120 markus 752: .Nm ssh
753: will try version 2 and fall back to version 1
754: if version 2 is not available.
1.1 stevesk 755: The default is
1.121 jmc 756: .Sq 2 .
1.1 stevesk 757: .It Cm ProxyCommand
758: Specifies the command to use to connect to the server.
759: The command
760: string extends to the end of the line, and is executed with
1.105 jmc 761: the user's shell.
1.133 ! jmc 762: In the command string, any occurrence of
1.1 stevesk 763: .Ql %h
764: will be substituted by the host name to
1.132 djm 765: connect,
1.1 stevesk 766: .Ql %p
1.133 ! jmc 767: by the port, and
! 768: .Ql %r
1.132 djm 769: by the remote user name.
1.1 stevesk 770: The command can be basically anything,
771: and should read from its standard input and write to its standard output.
772: It should eventually connect an
773: .Xr sshd 8
774: server running on some machine, or execute
775: .Ic sshd -i
776: somewhere.
777: Host key management will be done using the
778: HostName of the host being connected (defaulting to the name typed by
779: the user).
1.7 jmc 780: Setting the command to
781: .Dq none
1.6 markus 782: disables this option entirely.
1.1 stevesk 783: Note that
784: .Cm CheckHostIP
785: is not available for connects with a proxy command.
1.52 djm 786: .Pp
787: This directive is useful in conjunction with
788: .Xr nc 1
789: and its proxy support.
1.53 jmc 790: For example, the following directive would connect via an HTTP proxy at
1.52 djm 791: 192.0.2.0:
792: .Bd -literal -offset 3n
793: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
794: .Ed
1.1 stevesk 795: .It Cm PubkeyAuthentication
796: Specifies whether to try public key authentication.
797: The argument to this keyword must be
798: .Dq yes
799: or
800: .Dq no .
801: The default is
802: .Dq yes .
803: This option applies to protocol version 2 only.
1.75 dtucker 804: .It Cm RekeyLimit
805: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 806: session key is renegotiated.
1.75 dtucker 807: The argument is the number of bytes, with an optional suffix of
1.76 jmc 808: .Sq K ,
809: .Sq M ,
1.75 dtucker 810: or
1.76 jmc 811: .Sq G
1.75 dtucker 812: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
813: The default is between
1.84 jmc 814: .Sq 1G
1.75 dtucker 815: and
1.84 jmc 816: .Sq 4G ,
1.75 dtucker 817: depending on the cipher.
1.76 jmc 818: This option applies to protocol version 2 only.
1.1 stevesk 819: .It Cm RemoteForward
1.74 jmc 820: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 821: the secure channel to the specified host and port from the local machine.
1.49 jmc 822: The first argument must be
1.43 djm 823: .Sm off
1.49 jmc 824: .Oo Ar bind_address : Oc Ar port
1.43 djm 825: .Sm on
1.49 jmc 826: and the second argument must be
827: .Ar host : Ns Ar hostport .
828: IPv6 addresses can be specified by enclosing addresses in square brackets
829: or by using an alternative syntax:
830: .Oo Ar bind_address Ns / Oc Ns Ar port
831: and
832: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 833: Multiple forwardings may be specified, and additional
834: forwardings can be given on the command line.
1.113 stevesk 835: Privileged ports can be forwarded only when
836: logging in as root on the remote machine.
1.118 jmc 837: .Pp
1.117 djm 838: If the
839: .Ar port
840: argument is
841: .Ql 0 ,
842: the listen port will be dynamically allocated on the server and reported
843: to the client at run time.
1.43 djm 844: .Pp
845: If the
846: .Ar bind_address
847: is not specified, the default is to only bind to loopback addresses.
848: If the
849: .Ar bind_address
850: is
851: .Ql *
852: or an empty string, then the forwarding is requested to listen on all
853: interfaces.
854: Specifying a remote
855: .Ar bind_address
1.46 jmc 856: will only succeed if the server's
857: .Cm GatewayPorts
1.43 djm 858: option is enabled (see
1.46 jmc 859: .Xr sshd_config 5 ) .
1.1 stevesk 860: .It Cm RhostsRSAAuthentication
861: Specifies whether to try rhosts based authentication with RSA host
862: authentication.
863: The argument must be
864: .Dq yes
865: or
866: .Dq no .
867: The default is
868: .Dq no .
869: This option applies to protocol version 1 only and requires
1.84 jmc 870: .Xr ssh 1
1.1 stevesk 871: to be setuid root.
872: .It Cm RSAAuthentication
873: Specifies whether to try RSA authentication.
874: The argument to this keyword must be
875: .Dq yes
876: or
877: .Dq no .
878: RSA authentication will only be
879: attempted if the identity file exists, or an authentication agent is
880: running.
881: The default is
882: .Dq yes .
883: Note that this option applies to protocol version 1 only.
1.32 djm 884: .It Cm SendEnv
885: Specifies what variables from the local
886: .Xr environ 7
887: should be sent to the server.
1.84 jmc 888: Note that environment passing is only supported for protocol 2.
889: The server must also support it, and the server must be configured to
1.33 djm 890: accept these environment variables.
1.32 djm 891: Refer to
892: .Cm AcceptEnv
893: in
894: .Xr sshd_config 5
895: for how to configure the server.
1.80 jmc 896: Variables are specified by name, which may contain wildcard characters.
1.33 djm 897: Multiple environment variables may be separated by whitespace or spread
1.32 djm 898: across multiple
899: .Cm SendEnv
900: directives.
901: The default is not to send any environment variables.
1.81 jmc 902: .Pp
903: See
904: .Sx PATTERNS
905: for more information on patterns.
1.28 markus 906: .It Cm ServerAliveCountMax
1.73 jmc 907: Sets the number of server alive messages (see below) which may be
1.28 markus 908: sent without
1.84 jmc 909: .Xr ssh 1
1.28 markus 910: receiving any messages back from the server.
911: If this threshold is reached while server alive messages are being sent,
1.84 jmc 912: ssh will disconnect from the server, terminating the session.
1.28 markus 913: It is important to note that the use of server alive messages is very
914: different from
915: .Cm TCPKeepAlive
916: (below).
917: The server alive messages are sent through the encrypted channel
918: and therefore will not be spoofable.
919: The TCP keepalive option enabled by
920: .Cm TCPKeepAlive
921: is spoofable.
922: The server alive mechanism is valuable when the client or
923: server depend on knowing when a connection has become inactive.
924: .Pp
925: The default value is 3.
926: If, for example,
927: .Cm ServerAliveInterval
1.84 jmc 928: (see below) is set to 15 and
1.28 markus 929: .Cm ServerAliveCountMax
1.84 jmc 930: is left at the default, if the server becomes unresponsive,
931: ssh will disconnect after approximately 45 seconds.
1.89 markus 932: This option applies to protocol version 2 only.
1.67 jmc 933: .It Cm ServerAliveInterval
934: Sets a timeout interval in seconds after which if no data has been received
935: from the server,
1.84 jmc 936: .Xr ssh 1
1.67 jmc 937: will send a message through the encrypted
938: channel to request a response from the server.
939: The default
940: is 0, indicating that these messages will not be sent to the server.
941: This option applies to protocol version 2 only.
1.1 stevesk 942: .It Cm StrictHostKeyChecking
943: If this flag is set to
944: .Dq yes ,
1.84 jmc 945: .Xr ssh 1
1.1 stevesk 946: will never automatically add host keys to the
1.50 djm 947: .Pa ~/.ssh/known_hosts
1.1 stevesk 948: file, and refuses to connect to hosts whose host key has changed.
949: This provides maximum protection against trojan horse attacks,
1.84 jmc 950: though it can be annoying when the
1.1 stevesk 951: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 952: file is poorly maintained or when connections to new hosts are
1.1 stevesk 953: frequently made.
954: This option forces the user to manually
955: add all new hosts.
956: If this flag is set to
957: .Dq no ,
1.84 jmc 958: ssh will automatically add new host keys to the
1.1 stevesk 959: user known hosts files.
960: If this flag is set to
961: .Dq ask ,
962: new host keys
963: will be added to the user known host files only after the user
964: has confirmed that is what they really want to do, and
1.84 jmc 965: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 966: The host keys of
967: known hosts will be verified automatically in all cases.
968: The argument must be
969: .Dq yes ,
1.84 jmc 970: .Dq no ,
1.1 stevesk 971: or
972: .Dq ask .
973: The default is
974: .Dq ask .
1.26 markus 975: .It Cm TCPKeepAlive
976: Specifies whether the system should send TCP keepalive messages to the
977: other side.
978: If they are sent, death of the connection or crash of one
979: of the machines will be properly noticed.
980: However, this means that
981: connections will die if the route is down temporarily, and some people
982: find it annoying.
983: .Pp
984: The default is
985: .Dq yes
986: (to send TCP keepalive messages), and the client will notice
987: if the network goes down or the remote host dies.
988: This is important in scripts, and many users want it too.
989: .Pp
990: To disable TCP keepalive messages, the value should be set to
991: .Dq no .
1.65 reyk 992: .It Cm Tunnel
1.95 stevesk 993: Request
1.65 reyk 994: .Xr tun 4
1.69 jmc 995: device forwarding between the client and the server.
1.65 reyk 996: The argument must be
1.68 reyk 997: .Dq yes ,
1.95 stevesk 998: .Dq point-to-point
999: (layer 3),
1000: .Dq ethernet
1001: (layer 2),
1.65 reyk 1002: or
1003: .Dq no .
1.95 stevesk 1004: Specifying
1005: .Dq yes
1006: requests the default tunnel mode, which is
1007: .Dq point-to-point .
1.65 reyk 1008: The default is
1009: .Dq no .
1010: .It Cm TunnelDevice
1.95 stevesk 1011: Specifies the
1.65 reyk 1012: .Xr tun 4
1.95 stevesk 1013: devices to open on the client
1014: .Pq Ar local_tun
1015: and the server
1016: .Pq Ar remote_tun .
1017: .Pp
1018: The argument must be
1019: .Sm off
1020: .Ar local_tun Op : Ar remote_tun .
1021: .Sm on
1022: The devices may be specified by numerical ID or the keyword
1023: .Dq any ,
1024: which uses the next available tunnel device.
1025: If
1026: .Ar remote_tun
1027: is not specified, it defaults to
1028: .Dq any .
1029: The default is
1030: .Dq any:any .
1.72 jmc 1031: .It Cm UsePrivilegedPort
1032: Specifies whether to use a privileged port for outgoing connections.
1033: The argument must be
1034: .Dq yes
1035: or
1036: .Dq no .
1037: The default is
1038: .Dq no .
1039: If set to
1.84 jmc 1040: .Dq yes ,
1041: .Xr ssh 1
1.72 jmc 1042: must be setuid root.
1043: Note that this option must be set to
1044: .Dq yes
1045: for
1046: .Cm RhostsRSAAuthentication
1047: with older servers.
1.1 stevesk 1048: .It Cm User
1049: Specifies the user to log in as.
1050: This can be useful when a different user name is used on different machines.
1051: This saves the trouble of
1052: having to remember to give the user name on the command line.
1053: .It Cm UserKnownHostsFile
1054: Specifies a file to use for the user
1055: host key database instead of
1.50 djm 1056: .Pa ~/.ssh/known_hosts .
1.8 jakob 1057: .It Cm VerifyHostKeyDNS
1058: Specifies whether to verify the remote key using DNS and SSHFP resource
1059: records.
1.24 jakob 1060: If this option is set to
1061: .Dq yes ,
1.25 jmc 1062: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1063: from DNS.
1064: Insecure fingerprints will be handled as if this option was set to
1065: .Dq ask .
1066: If this option is set to
1067: .Dq ask ,
1068: information on fingerprint match will be displayed, but the user will still
1069: need to confirm new host keys according to the
1070: .Cm StrictHostKeyChecking
1071: option.
1072: The argument must be
1073: .Dq yes ,
1.84 jmc 1074: .Dq no ,
1.25 jmc 1075: or
1076: .Dq ask .
1.8 jakob 1077: The default is
1078: .Dq no .
1.12 jakob 1079: Note that this option applies to protocol version 2 only.
1.84 jmc 1080: .Pp
1081: See also
1082: .Sx VERIFYING HOST KEYS
1083: in
1084: .Xr ssh 1 .
1.111 grunk 1085: .It Cm VisualHostKey
1086: If this flag is set to
1087: .Dq yes ,
1088: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1089: printed in addition to the hex fingerprint string at login and
1090: for unknown host keys.
1.111 grunk 1091: If this flag is set to
1092: .Dq no ,
1.114 stevesk 1093: no fingerprint strings are printed at login and
1094: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1095: The default is
1096: .Dq no .
1.1 stevesk 1097: .It Cm XAuthLocation
1.5 stevesk 1098: Specifies the full pathname of the
1.1 stevesk 1099: .Xr xauth 1
1100: program.
1101: The default is
1102: .Pa /usr/X11R6/bin/xauth .
1103: .El
1.86 jmc 1104: .Sh PATTERNS
1105: A
1106: .Em pattern
1107: consists of zero or more non-whitespace characters,
1108: .Sq *
1109: (a wildcard that matches zero or more characters),
1110: or
1111: .Sq ?\&
1112: (a wildcard that matches exactly one character).
1113: For example, to specify a set of declarations for any host in the
1114: .Dq .co.uk
1115: set of domains,
1116: the following pattern could be used:
1117: .Pp
1118: .Dl Host *.co.uk
1119: .Pp
1120: The following pattern
1121: would match any host in the 192.168.0.[0-9] network range:
1122: .Pp
1123: .Dl Host 192.168.0.?
1124: .Pp
1125: A
1126: .Em pattern-list
1127: is a comma-separated list of patterns.
1128: Patterns within pattern-lists may be negated
1129: by preceding them with an exclamation mark
1130: .Pq Sq !\& .
1131: For example,
1132: to allow a key to be used from anywhere within an organisation
1133: except from the
1134: .Dq dialup
1135: pool,
1136: the following entry (in authorized_keys) could be used:
1137: .Pp
1138: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1139: .Sh FILES
1140: .Bl -tag -width Ds
1.50 djm 1141: .It Pa ~/.ssh/config
1.1 stevesk 1142: This is the per-user configuration file.
1143: The format of this file is described above.
1.84 jmc 1144: This file is used by the SSH client.
1.30 djm 1145: Because of the potential for abuse, this file must have strict permissions:
1146: read/write for the user, and not accessible by others.
1.1 stevesk 1147: .It Pa /etc/ssh/ssh_config
1148: Systemwide configuration file.
1149: This file provides defaults for those
1150: values that are not specified in the user's configuration file, and
1151: for those users who do not have a configuration file.
1152: This file must be world-readable.
1153: .El
1.13 jmc 1154: .Sh SEE ALSO
1155: .Xr ssh 1
1.1 stevesk 1156: .Sh AUTHORS
1157: OpenSSH is a derivative of the original and free
1158: ssh 1.2.12 release by Tatu Ylonen.
1159: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1160: Theo de Raadt and Dug Song
1161: removed many bugs, re-added newer features and
1162: created OpenSSH.
1163: Markus Friedl contributed the support for SSH
1164: protocol versions 1.5 and 2.0.
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