Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.136
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
19: .\" are met:
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
24: .\" documentation and/or other materials provided with the distribution.
25: .\"
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
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36: .\"
1.136 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.135 2010/06/26 00:57:07 jmc Exp $
! 38: .Dd $Mdocdate: June 26 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.
1.134 djm 435: .It Cm ForwardX11Timeout
1.135 jmc 436: Specify a timeout for untrusted X11 forwarding
437: using the format described in the
1.134 djm 438: .Sx TIME FORMATS
439: section of
440: .Xr sshd_config 5 .
441: X11 connections received by
442: .Xr ssh 1
443: after this time will be refused.
444: The default is to disable untrusted X11 forwarding after twenty minutes has
445: elapsed.
1.22 markus 446: .It Cm ForwardX11Trusted
1.34 jmc 447: If this option is set to
1.84 jmc 448: .Dq yes ,
449: remote X11 clients will have full access to the original X11 display.
1.42 djm 450: .Pp
1.22 markus 451: If this option is set to
1.84 jmc 452: .Dq no ,
453: remote X11 clients will be considered untrusted and prevented
1.22 markus 454: from stealing or tampering with data belonging to trusted X11
455: clients.
1.42 djm 456: Furthermore, the
457: .Xr xauth 1
458: token used for the session will be set to expire after 20 minutes.
459: Remote clients will be refused access after this time.
1.22 markus 460: .Pp
461: The default is
462: .Dq no .
463: .Pp
464: See the X11 SECURITY extension specification for full details on
465: the restrictions imposed on untrusted clients.
1.1 stevesk 466: .It Cm GatewayPorts
467: Specifies whether remote hosts are allowed to connect to local
468: forwarded ports.
469: By default,
1.84 jmc 470: .Xr ssh 1
1.7 jmc 471: binds local port forwardings to the loopback address.
472: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 473: .Cm GatewayPorts
1.84 jmc 474: can be used to specify that ssh
1.1 stevesk 475: should bind local port forwardings to the wildcard address,
476: thus allowing remote hosts to connect to forwarded ports.
477: The argument must be
478: .Dq yes
479: or
480: .Dq no .
481: The default is
482: .Dq no .
483: .It Cm GlobalKnownHostsFile
484: Specifies a file to use for the global
485: host key database instead of
486: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 487: .It Cm GSSAPIAuthentication
1.27 markus 488: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 489: The default is
1.21 markus 490: .Dq no .
1.18 markus 491: Note that this option applies to protocol version 2 only.
492: .It Cm GSSAPIDelegateCredentials
493: Forward (delegate) credentials to the server.
494: The default is
495: .Dq no .
496: Note that this option applies to protocol version 2 only.
1.44 djm 497: .It Cm HashKnownHosts
498: Indicates that
1.84 jmc 499: .Xr ssh 1
1.44 djm 500: should hash host names and addresses when they are added to
1.50 djm 501: .Pa ~/.ssh/known_hosts .
1.44 djm 502: These hashed names may be used normally by
1.84 jmc 503: .Xr ssh 1
1.44 djm 504: and
1.84 jmc 505: .Xr sshd 8 ,
1.44 djm 506: but they do not reveal identifying information should the file's contents
507: be disclosed.
508: The default is
509: .Dq no .
1.97 jmc 510: Note that existing names and addresses in known hosts files
511: will not be converted automatically,
512: but may be manually hashed using
1.45 djm 513: .Xr ssh-keygen 1 .
1.1 stevesk 514: .It Cm HostbasedAuthentication
515: Specifies whether to try rhosts based authentication with public key
516: authentication.
517: The argument must be
518: .Dq yes
519: or
520: .Dq no .
521: The default is
522: .Dq no .
523: This option applies to protocol version 2 only and
524: is similar to
525: .Cm RhostsRSAAuthentication .
526: .It Cm HostKeyAlgorithms
527: Specifies the protocol version 2 host key algorithms
528: that the client wants to use in order of preference.
529: The default for this option is:
530: .Dq ssh-rsa,ssh-dss .
531: .It Cm HostKeyAlias
532: Specifies an alias that should be used instead of the
533: real host name when looking up or saving the host key
534: in the host key database files.
1.84 jmc 535: This option is useful for tunneling SSH connections
1.1 stevesk 536: or for multiple servers running on a single host.
537: .It Cm HostName
538: Specifies the real host name to log into.
539: This can be used to specify nicknames or abbreviations for hosts.
1.136 ! djm 540: If the hostname contains the character sequence
! 541: .Ql %h ,
! 542: then this will be replaced with the host name specified on the commandline
! 543: (this is useful for manipulating unqualified names).
1.84 jmc 544: The default is the name given on the command line.
1.1 stevesk 545: Numeric IP addresses are also permitted (both on the command line and in
546: .Cm HostName
547: specifications).
1.29 markus 548: .It Cm IdentitiesOnly
549: Specifies that
1.84 jmc 550: .Xr ssh 1
1.29 markus 551: should only use the authentication identity files configured in the
1.31 jmc 552: .Nm
1.29 markus 553: files,
1.84 jmc 554: even if
555: .Xr ssh-agent 1
1.29 markus 556: offers more identities.
557: The argument to this keyword must be
558: .Dq yes
559: or
560: .Dq no .
1.84 jmc 561: This option is intended for situations where ssh-agent
1.29 markus 562: offers many different identities.
563: The default is
564: .Dq no .
1.67 jmc 565: .It Cm IdentityFile
566: Specifies a file from which the user's RSA or DSA authentication identity
567: is read.
568: The default is
569: .Pa ~/.ssh/identity
570: for protocol version 1, and
571: .Pa ~/.ssh/id_rsa
572: and
573: .Pa ~/.ssh/id_dsa
574: for protocol version 2.
575: Additionally, any identities represented by the authentication agent
576: will be used for authentication.
1.129 djm 577: .Xr ssh 1
578: will try to load certificate information from the filename obtained by
579: appending
580: .Pa -cert.pub
581: to the path of a specified
582: .Cm IdentityFile .
1.90 djm 583: .Pp
1.67 jmc 584: The file name may use the tilde
1.91 jmc 585: syntax to refer to a user's home directory or one of the following
1.90 djm 586: escape characters:
587: .Ql %d
588: (local user's home directory),
589: .Ql %u
590: (local user name),
591: .Ql %l
592: (local host name),
593: .Ql %h
594: (remote host name) or
1.92 djm 595: .Ql %r
1.90 djm 596: (remote user name).
597: .Pp
1.67 jmc 598: It is possible to have
599: multiple identity files specified in configuration files; all these
600: identities will be tried in sequence.
1.103 djm 601: .It Cm KbdInteractiveAuthentication
602: Specifies whether to use keyboard-interactive authentication.
603: The argument to this keyword must be
604: .Dq yes
605: or
606: .Dq no .
607: The default is
608: .Dq yes .
1.39 djm 609: .It Cm KbdInteractiveDevices
610: Specifies the list of methods to use in keyboard-interactive authentication.
611: Multiple method names must be comma-separated.
612: The default is to use the server specified list.
1.85 jmc 613: The methods available vary depending on what the server supports.
614: For an OpenSSH server,
615: it may be zero or more of:
616: .Dq bsdauth ,
617: .Dq pam ,
618: and
619: .Dq skey .
1.65 reyk 620: .It Cm LocalCommand
621: Specifies a command to execute on the local machine after successfully
622: connecting to the server.
623: The command string extends to the end of the line, and is executed with
1.105 jmc 624: the user's shell.
1.109 dtucker 625: The following escape character substitutions will be performed:
626: .Ql %d
627: (local user's home directory),
628: .Ql %h
629: (remote host name),
630: .Ql %l
631: (local host name),
632: .Ql %n
633: (host name as provided on the command line),
634: .Ql %p
635: (remote port),
636: .Ql %r
637: (remote user name) or
638: .Ql %u
639: (local user name).
1.123 djm 640: .Pp
641: The command is run synchronously and does not have access to the
642: session of the
643: .Xr ssh 1
644: that spawned it.
645: It should not be used for interactive commands.
646: .Pp
1.65 reyk 647: This directive is ignored unless
648: .Cm PermitLocalCommand
649: has been enabled.
1.1 stevesk 650: .It Cm LocalForward
1.74 jmc 651: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 652: the secure channel to the specified host and port from the remote machine.
1.49 jmc 653: The first argument must be
1.43 djm 654: .Sm off
1.49 jmc 655: .Oo Ar bind_address : Oc Ar port
1.43 djm 656: .Sm on
1.49 jmc 657: and the second argument must be
658: .Ar host : Ns Ar hostport .
1.46 jmc 659: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 660: by using an alternative syntax:
1.49 jmc 661: .Oo Ar bind_address Ns / Oc Ns Ar port
662: and
663: .Ar host Ns / Ns Ar hostport .
1.46 jmc 664: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 665: given on the command line.
1.1 stevesk 666: Only the superuser can forward privileged ports.
1.43 djm 667: By default, the local port is bound in accordance with the
668: .Cm GatewayPorts
669: setting.
670: However, an explicit
671: .Ar bind_address
672: may be used to bind the connection to a specific address.
673: The
674: .Ar bind_address
675: of
676: .Dq localhost
1.46 jmc 677: indicates that the listening port be bound for local use only, while an
678: empty address or
679: .Sq *
1.43 djm 680: indicates that the port should be available from all interfaces.
1.1 stevesk 681: .It Cm LogLevel
682: Gives the verbosity level that is used when logging messages from
1.84 jmc 683: .Xr ssh 1 .
1.1 stevesk 684: The possible values are:
1.84 jmc 685: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 686: The default is INFO.
687: DEBUG and DEBUG1 are equivalent.
688: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 689: .It Cm MACs
690: Specifies the MAC (message authentication code) algorithms
691: in order of preference.
692: The MAC algorithm is used in protocol version 2
693: for data integrity protection.
694: Multiple algorithms must be comma-separated.
1.84 jmc 695: The default is:
1.101 jmc 696: .Bd -literal -offset indent
697: hmac-md5,hmac-sha1,umac-64@openssh.com,
698: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
699: .Ed
1.1 stevesk 700: .It Cm NoHostAuthenticationForLocalhost
701: This option can be used if the home directory is shared across machines.
702: In this case localhost will refer to a different machine on each of
703: the machines and the user will get many warnings about changed host keys.
704: However, this option disables host authentication for localhost.
705: The argument to this keyword must be
706: .Dq yes
707: or
708: .Dq no .
709: The default is to check the host key for localhost.
710: .It Cm NumberOfPasswordPrompts
711: Specifies the number of password prompts before giving up.
712: The argument to this keyword must be an integer.
1.84 jmc 713: The default is 3.
1.1 stevesk 714: .It Cm PasswordAuthentication
715: Specifies whether to use password authentication.
716: The argument to this keyword must be
717: .Dq yes
718: or
719: .Dq no .
720: The default is
721: .Dq yes .
1.65 reyk 722: .It Cm PermitLocalCommand
723: Allow local command execution via the
724: .Ic LocalCommand
725: option or using the
1.66 jmc 726: .Ic !\& Ns Ar command
1.65 reyk 727: escape sequence in
728: .Xr ssh 1 .
729: The argument must be
730: .Dq yes
731: or
732: .Dq no .
733: The default is
734: .Dq no .
1.127 markus 735: .It Cm PKCS11Provider
736: Specifies which PKCS#11 provider to use.
737: The argument to this keyword is the PKCS#11 shared libary
738: .Xr ssh 1
1.128 markus 739: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 740: private RSA key.
1.67 jmc 741: .It Cm Port
742: Specifies the port number to connect on the remote host.
1.84 jmc 743: The default is 22.
1.1 stevesk 744: .It Cm PreferredAuthentications
745: Specifies the order in which the client should try protocol 2
1.11 jmc 746: authentication methods.
1.48 jmc 747: This allows a client to prefer one method (e.g.\&
1.1 stevesk 748: .Cm keyboard-interactive )
1.48 jmc 749: over another method (e.g.\&
1.131 jmc 750: .Cm password ) .
751: The default is:
752: .Bd -literal -offset indent
753: gssapi-with-mic,hostbased,publickey,
754: keyboard-interactive,password
755: .Ed
1.1 stevesk 756: .It Cm Protocol
757: Specifies the protocol versions
1.84 jmc 758: .Xr ssh 1
1.1 stevesk 759: should support in order of preference.
760: The possible values are
1.84 jmc 761: .Sq 1
1.1 stevesk 762: and
1.84 jmc 763: .Sq 2 .
1.1 stevesk 764: Multiple versions must be comma-separated.
1.120 markus 765: When this option is set to
1.121 jmc 766: .Dq 2,1
1.120 markus 767: .Nm ssh
768: will try version 2 and fall back to version 1
769: if version 2 is not available.
1.1 stevesk 770: The default is
1.121 jmc 771: .Sq 2 .
1.1 stevesk 772: .It Cm ProxyCommand
773: Specifies the command to use to connect to the server.
774: The command
775: string extends to the end of the line, and is executed with
1.105 jmc 776: the user's shell.
1.133 jmc 777: In the command string, any occurrence of
1.1 stevesk 778: .Ql %h
779: will be substituted by the host name to
1.132 djm 780: connect,
1.1 stevesk 781: .Ql %p
1.133 jmc 782: by the port, and
783: .Ql %r
1.132 djm 784: by the remote user name.
1.1 stevesk 785: The command can be basically anything,
786: and should read from its standard input and write to its standard output.
787: It should eventually connect an
788: .Xr sshd 8
789: server running on some machine, or execute
790: .Ic sshd -i
791: somewhere.
792: Host key management will be done using the
793: HostName of the host being connected (defaulting to the name typed by
794: the user).
1.7 jmc 795: Setting the command to
796: .Dq none
1.6 markus 797: disables this option entirely.
1.1 stevesk 798: Note that
799: .Cm CheckHostIP
800: is not available for connects with a proxy command.
1.52 djm 801: .Pp
802: This directive is useful in conjunction with
803: .Xr nc 1
804: and its proxy support.
1.53 jmc 805: For example, the following directive would connect via an HTTP proxy at
1.52 djm 806: 192.0.2.0:
807: .Bd -literal -offset 3n
808: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
809: .Ed
1.1 stevesk 810: .It Cm PubkeyAuthentication
811: Specifies whether to try public key authentication.
812: The argument to this keyword must be
813: .Dq yes
814: or
815: .Dq no .
816: The default is
817: .Dq yes .
818: This option applies to protocol version 2 only.
1.75 dtucker 819: .It Cm RekeyLimit
820: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 821: session key is renegotiated.
1.75 dtucker 822: The argument is the number of bytes, with an optional suffix of
1.76 jmc 823: .Sq K ,
824: .Sq M ,
1.75 dtucker 825: or
1.76 jmc 826: .Sq G
1.75 dtucker 827: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
828: The default is between
1.84 jmc 829: .Sq 1G
1.75 dtucker 830: and
1.84 jmc 831: .Sq 4G ,
1.75 dtucker 832: depending on the cipher.
1.76 jmc 833: This option applies to protocol version 2 only.
1.1 stevesk 834: .It Cm RemoteForward
1.74 jmc 835: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 836: the secure channel to the specified host and port from the local machine.
1.49 jmc 837: The first argument must be
1.43 djm 838: .Sm off
1.49 jmc 839: .Oo Ar bind_address : Oc Ar port
1.43 djm 840: .Sm on
1.49 jmc 841: and the second argument must be
842: .Ar host : Ns Ar hostport .
843: IPv6 addresses can be specified by enclosing addresses in square brackets
844: or by using an alternative syntax:
845: .Oo Ar bind_address Ns / Oc Ns Ar port
846: and
847: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 848: Multiple forwardings may be specified, and additional
849: forwardings can be given on the command line.
1.113 stevesk 850: Privileged ports can be forwarded only when
851: logging in as root on the remote machine.
1.118 jmc 852: .Pp
1.117 djm 853: If the
854: .Ar port
855: argument is
856: .Ql 0 ,
857: the listen port will be dynamically allocated on the server and reported
858: to the client at run time.
1.43 djm 859: .Pp
860: If the
861: .Ar bind_address
862: is not specified, the default is to only bind to loopback addresses.
863: If the
864: .Ar bind_address
865: is
866: .Ql *
867: or an empty string, then the forwarding is requested to listen on all
868: interfaces.
869: Specifying a remote
870: .Ar bind_address
1.46 jmc 871: will only succeed if the server's
872: .Cm GatewayPorts
1.43 djm 873: option is enabled (see
1.46 jmc 874: .Xr sshd_config 5 ) .
1.1 stevesk 875: .It Cm RhostsRSAAuthentication
876: Specifies whether to try rhosts based authentication with RSA host
877: authentication.
878: The argument must be
879: .Dq yes
880: or
881: .Dq no .
882: The default is
883: .Dq no .
884: This option applies to protocol version 1 only and requires
1.84 jmc 885: .Xr ssh 1
1.1 stevesk 886: to be setuid root.
887: .It Cm RSAAuthentication
888: Specifies whether to try RSA authentication.
889: The argument to this keyword must be
890: .Dq yes
891: or
892: .Dq no .
893: RSA authentication will only be
894: attempted if the identity file exists, or an authentication agent is
895: running.
896: The default is
897: .Dq yes .
898: Note that this option applies to protocol version 1 only.
1.32 djm 899: .It Cm SendEnv
900: Specifies what variables from the local
901: .Xr environ 7
902: should be sent to the server.
1.84 jmc 903: Note that environment passing is only supported for protocol 2.
904: The server must also support it, and the server must be configured to
1.33 djm 905: accept these environment variables.
1.32 djm 906: Refer to
907: .Cm AcceptEnv
908: in
909: .Xr sshd_config 5
910: for how to configure the server.
1.80 jmc 911: Variables are specified by name, which may contain wildcard characters.
1.33 djm 912: Multiple environment variables may be separated by whitespace or spread
1.32 djm 913: across multiple
914: .Cm SendEnv
915: directives.
916: The default is not to send any environment variables.
1.81 jmc 917: .Pp
918: See
919: .Sx PATTERNS
920: for more information on patterns.
1.28 markus 921: .It Cm ServerAliveCountMax
1.73 jmc 922: Sets the number of server alive messages (see below) which may be
1.28 markus 923: sent without
1.84 jmc 924: .Xr ssh 1
1.28 markus 925: receiving any messages back from the server.
926: If this threshold is reached while server alive messages are being sent,
1.84 jmc 927: ssh will disconnect from the server, terminating the session.
1.28 markus 928: It is important to note that the use of server alive messages is very
929: different from
930: .Cm TCPKeepAlive
931: (below).
932: The server alive messages are sent through the encrypted channel
933: and therefore will not be spoofable.
934: The TCP keepalive option enabled by
935: .Cm TCPKeepAlive
936: is spoofable.
937: The server alive mechanism is valuable when the client or
938: server depend on knowing when a connection has become inactive.
939: .Pp
940: The default value is 3.
941: If, for example,
942: .Cm ServerAliveInterval
1.84 jmc 943: (see below) is set to 15 and
1.28 markus 944: .Cm ServerAliveCountMax
1.84 jmc 945: is left at the default, if the server becomes unresponsive,
946: ssh will disconnect after approximately 45 seconds.
1.89 markus 947: This option applies to protocol version 2 only.
1.67 jmc 948: .It Cm ServerAliveInterval
949: Sets a timeout interval in seconds after which if no data has been received
950: from the server,
1.84 jmc 951: .Xr ssh 1
1.67 jmc 952: will send a message through the encrypted
953: channel to request a response from the server.
954: The default
955: is 0, indicating that these messages will not be sent to the server.
956: This option applies to protocol version 2 only.
1.1 stevesk 957: .It Cm StrictHostKeyChecking
958: If this flag is set to
959: .Dq yes ,
1.84 jmc 960: .Xr ssh 1
1.1 stevesk 961: will never automatically add host keys to the
1.50 djm 962: .Pa ~/.ssh/known_hosts
1.1 stevesk 963: file, and refuses to connect to hosts whose host key has changed.
964: This provides maximum protection against trojan horse attacks,
1.84 jmc 965: though it can be annoying when the
1.1 stevesk 966: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 967: file is poorly maintained or when connections to new hosts are
1.1 stevesk 968: frequently made.
969: This option forces the user to manually
970: add all new hosts.
971: If this flag is set to
972: .Dq no ,
1.84 jmc 973: ssh will automatically add new host keys to the
1.1 stevesk 974: user known hosts files.
975: If this flag is set to
976: .Dq ask ,
977: new host keys
978: will be added to the user known host files only after the user
979: has confirmed that is what they really want to do, and
1.84 jmc 980: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 981: The host keys of
982: known hosts will be verified automatically in all cases.
983: The argument must be
984: .Dq yes ,
1.84 jmc 985: .Dq no ,
1.1 stevesk 986: or
987: .Dq ask .
988: The default is
989: .Dq ask .
1.26 markus 990: .It Cm TCPKeepAlive
991: Specifies whether the system should send TCP keepalive messages to the
992: other side.
993: If they are sent, death of the connection or crash of one
994: of the machines will be properly noticed.
995: However, this means that
996: connections will die if the route is down temporarily, and some people
997: find it annoying.
998: .Pp
999: The default is
1000: .Dq yes
1001: (to send TCP keepalive messages), and the client will notice
1002: if the network goes down or the remote host dies.
1003: This is important in scripts, and many users want it too.
1004: .Pp
1005: To disable TCP keepalive messages, the value should be set to
1006: .Dq no .
1.65 reyk 1007: .It Cm Tunnel
1.95 stevesk 1008: Request
1.65 reyk 1009: .Xr tun 4
1.69 jmc 1010: device forwarding between the client and the server.
1.65 reyk 1011: The argument must be
1.68 reyk 1012: .Dq yes ,
1.95 stevesk 1013: .Dq point-to-point
1014: (layer 3),
1015: .Dq ethernet
1016: (layer 2),
1.65 reyk 1017: or
1018: .Dq no .
1.95 stevesk 1019: Specifying
1020: .Dq yes
1021: requests the default tunnel mode, which is
1022: .Dq point-to-point .
1.65 reyk 1023: The default is
1024: .Dq no .
1025: .It Cm TunnelDevice
1.95 stevesk 1026: Specifies the
1.65 reyk 1027: .Xr tun 4
1.95 stevesk 1028: devices to open on the client
1029: .Pq Ar local_tun
1030: and the server
1031: .Pq Ar remote_tun .
1032: .Pp
1033: The argument must be
1034: .Sm off
1035: .Ar local_tun Op : Ar remote_tun .
1036: .Sm on
1037: The devices may be specified by numerical ID or the keyword
1038: .Dq any ,
1039: which uses the next available tunnel device.
1040: If
1041: .Ar remote_tun
1042: is not specified, it defaults to
1043: .Dq any .
1044: The default is
1045: .Dq any:any .
1.72 jmc 1046: .It Cm UsePrivilegedPort
1047: Specifies whether to use a privileged port for outgoing connections.
1048: The argument must be
1049: .Dq yes
1050: or
1051: .Dq no .
1052: The default is
1053: .Dq no .
1054: If set to
1.84 jmc 1055: .Dq yes ,
1056: .Xr ssh 1
1.72 jmc 1057: must be setuid root.
1058: Note that this option must be set to
1059: .Dq yes
1060: for
1061: .Cm RhostsRSAAuthentication
1062: with older servers.
1.1 stevesk 1063: .It Cm User
1064: Specifies the user to log in as.
1065: This can be useful when a different user name is used on different machines.
1066: This saves the trouble of
1067: having to remember to give the user name on the command line.
1068: .It Cm UserKnownHostsFile
1069: Specifies a file to use for the user
1070: host key database instead of
1.50 djm 1071: .Pa ~/.ssh/known_hosts .
1.8 jakob 1072: .It Cm VerifyHostKeyDNS
1073: Specifies whether to verify the remote key using DNS and SSHFP resource
1074: records.
1.24 jakob 1075: If this option is set to
1076: .Dq yes ,
1.25 jmc 1077: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1078: from DNS.
1079: Insecure fingerprints will be handled as if this option was set to
1080: .Dq ask .
1081: If this option is set to
1082: .Dq ask ,
1083: information on fingerprint match will be displayed, but the user will still
1084: need to confirm new host keys according to the
1085: .Cm StrictHostKeyChecking
1086: option.
1087: The argument must be
1088: .Dq yes ,
1.84 jmc 1089: .Dq no ,
1.25 jmc 1090: or
1091: .Dq ask .
1.8 jakob 1092: The default is
1093: .Dq no .
1.12 jakob 1094: Note that this option applies to protocol version 2 only.
1.84 jmc 1095: .Pp
1096: See also
1097: .Sx VERIFYING HOST KEYS
1098: in
1099: .Xr ssh 1 .
1.111 grunk 1100: .It Cm VisualHostKey
1101: If this flag is set to
1102: .Dq yes ,
1103: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1104: printed in addition to the hex fingerprint string at login and
1105: for unknown host keys.
1.111 grunk 1106: If this flag is set to
1107: .Dq no ,
1.114 stevesk 1108: no fingerprint strings are printed at login and
1109: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1110: The default is
1111: .Dq no .
1.1 stevesk 1112: .It Cm XAuthLocation
1.5 stevesk 1113: Specifies the full pathname of the
1.1 stevesk 1114: .Xr xauth 1
1115: program.
1116: The default is
1117: .Pa /usr/X11R6/bin/xauth .
1118: .El
1.86 jmc 1119: .Sh PATTERNS
1120: A
1121: .Em pattern
1122: consists of zero or more non-whitespace characters,
1123: .Sq *
1124: (a wildcard that matches zero or more characters),
1125: or
1126: .Sq ?\&
1127: (a wildcard that matches exactly one character).
1128: For example, to specify a set of declarations for any host in the
1129: .Dq .co.uk
1130: set of domains,
1131: the following pattern could be used:
1132: .Pp
1133: .Dl Host *.co.uk
1134: .Pp
1135: The following pattern
1136: would match any host in the 192.168.0.[0-9] network range:
1137: .Pp
1138: .Dl Host 192.168.0.?
1139: .Pp
1140: A
1141: .Em pattern-list
1142: is a comma-separated list of patterns.
1143: Patterns within pattern-lists may be negated
1144: by preceding them with an exclamation mark
1145: .Pq Sq !\& .
1146: For example,
1147: to allow a key to be used from anywhere within an organisation
1148: except from the
1149: .Dq dialup
1150: pool,
1151: the following entry (in authorized_keys) could be used:
1152: .Pp
1153: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1154: .Sh FILES
1155: .Bl -tag -width Ds
1.50 djm 1156: .It Pa ~/.ssh/config
1.1 stevesk 1157: This is the per-user configuration file.
1158: The format of this file is described above.
1.84 jmc 1159: This file is used by the SSH client.
1.30 djm 1160: Because of the potential for abuse, this file must have strict permissions:
1161: read/write for the user, and not accessible by others.
1.1 stevesk 1162: .It Pa /etc/ssh/ssh_config
1163: Systemwide configuration file.
1164: This file provides defaults for those
1165: values that are not specified in the user's configuration file, and
1166: for those users who do not have a configuration file.
1167: This file must be world-readable.
1168: .El
1.13 jmc 1169: .Sh SEE ALSO
1170: .Xr ssh 1
1.1 stevesk 1171: .Sh AUTHORS
1172: OpenSSH is a derivative of the original and free
1173: ssh 1.2.12 release by Tatu Ylonen.
1174: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1175: Theo de Raadt and Dug Song
1176: removed many bugs, re-added newer features and
1177: created OpenSSH.
1178: Markus Friedl contributed the support for SSH
1179: protocol versions 1.5 and 2.0.