Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.148
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
18: .\" are met:
19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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30: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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1.148 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.147 2011/05/06 21:18:02 djm Exp $
! 37: .Dd $Mdocdate: May 6 2011 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
42: .Nd OpenSSH SSH client configuration files
43: .Sh SYNOPSIS
1.98 jmc 44: .Nm ~/.ssh/config
45: .Nm /etc/ssh/ssh_config
1.1 stevesk 46: .Sh DESCRIPTION
1.84 jmc 47: .Xr ssh 1
1.1 stevesk 48: obtains configuration data from the following sources in
49: the following order:
1.79 jmc 50: .Pp
1.2 stevesk 51: .Bl -enum -offset indent -compact
52: .It
53: command-line options
54: .It
55: user's configuration file
1.50 djm 56: .Pq Pa ~/.ssh/config
1.2 stevesk 57: .It
58: system-wide configuration file
59: .Pq Pa /etc/ssh/ssh_config
60: .El
1.1 stevesk 61: .Pp
62: For each parameter, the first obtained value
63: will be used.
1.41 jmc 64: The configuration files contain sections separated by
1.1 stevesk 65: .Dq Host
66: specifications, and that section is only applied for hosts that
67: match one of the patterns given in the specification.
68: The matched host name is the one given on the command line.
69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.1 stevesk 74: The configuration file has the following format:
75: .Pp
76: Empty lines and lines starting with
77: .Ql #
78: are comments.
79: Otherwise a line is of the format
80: .Dq keyword arguments .
81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
1.88 dtucker 92: Arguments may optionally be enclosed in double quotes
93: .Pq \&"
94: in order to represent arguments containing spaces.
1.1 stevesk 95: .Pp
96: The possible
97: keywords and their meanings are as follows (note that
98: keywords are case-insensitive and arguments are case-sensitive):
99: .Bl -tag -width Ds
100: .It Cm Host
101: Restricts the following declarations (up to the next
102: .Cm Host
103: keyword) to be only for those hosts that match one of the patterns
104: given after the keyword.
1.112 krw 105: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 106: A single
1.83 jmc 107: .Ql *
1.1 stevesk 108: as a pattern can be used to provide global
109: defaults for all hosts.
110: The host is the
111: .Ar hostname
1.83 jmc 112: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 113: a canonicalized host name before matching).
1.148 ! djm 114: .Pp
! 115: A pattern entry may be negated by prefixing it with an exclamation mark
! 116: .Pq Sq !\& .
! 117: If a negated entry is matched, then the
! 118: .Cm Host
! 119: entry is ignored, regardless of whether any other patterns on the line
! 120: match.
! 121: Negated matches are therefore useful to provide exceptions for wildcard
! 122: matches.
1.81 jmc 123: .Pp
124: See
125: .Sx PATTERNS
126: for more information on patterns.
1.10 djm 127: .It Cm AddressFamily
1.11 jmc 128: Specifies which address family to use when connecting.
129: Valid arguments are
1.10 djm 130: .Dq any ,
131: .Dq inet
1.84 jmc 132: (use IPv4 only), or
1.10 djm 133: .Dq inet6
1.40 jmc 134: (use IPv6 only).
1.1 stevesk 135: .It Cm BatchMode
136: If set to
137: .Dq yes ,
138: passphrase/password querying will be disabled.
139: This option is useful in scripts and other batch jobs where no user
140: is present to supply the password.
141: The argument must be
142: .Dq yes
143: or
144: .Dq no .
145: The default is
146: .Dq no .
147: .It Cm BindAddress
1.60 dtucker 148: Use the specified address on the local machine as the source address of
1.61 jmc 149: the connection.
150: Only useful on systems with more than one address.
1.1 stevesk 151: Note that this option does not work if
152: .Cm UsePrivilegedPort
153: is set to
154: .Dq yes .
155: .It Cm ChallengeResponseAuthentication
1.82 jmc 156: Specifies whether to use challenge-response authentication.
1.1 stevesk 157: The argument to this keyword must be
158: .Dq yes
159: or
160: .Dq no .
161: The default is
162: .Dq yes .
163: .It Cm CheckHostIP
164: If this flag is set to
165: .Dq yes ,
1.84 jmc 166: .Xr ssh 1
167: will additionally check the host IP address in the
1.1 stevesk 168: .Pa known_hosts
169: file.
170: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 171: If the option is set to
1.1 stevesk 172: .Dq no ,
173: the check will not be executed.
174: The default is
175: .Dq yes .
176: .It Cm Cipher
177: Specifies the cipher to use for encrypting the session
178: in protocol version 1.
179: Currently,
180: .Dq blowfish ,
181: .Dq 3des ,
182: and
183: .Dq des
184: are supported.
185: .Ar des
186: is only supported in the
1.84 jmc 187: .Xr ssh 1
1.1 stevesk 188: client for interoperability with legacy protocol 1 implementations
189: that do not support the
190: .Ar 3des
1.7 jmc 191: cipher.
192: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 193: The default is
194: .Dq 3des .
195: .It Cm Ciphers
196: Specifies the ciphers allowed for protocol version 2
197: in order of preference.
198: Multiple ciphers must be comma-separated.
1.35 dtucker 199: The supported ciphers are
200: .Dq 3des-cbc ,
201: .Dq aes128-cbc ,
202: .Dq aes192-cbc ,
203: .Dq aes256-cbc ,
204: .Dq aes128-ctr ,
205: .Dq aes192-ctr ,
206: .Dq aes256-ctr ,
1.54 djm 207: .Dq arcfour128 ,
208: .Dq arcfour256 ,
1.35 dtucker 209: .Dq arcfour ,
210: .Dq blowfish-cbc ,
211: and
212: .Dq cast128-cbc .
1.84 jmc 213: The default is:
214: .Bd -literal -offset 3n
1.116 naddy 215: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
216: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
217: aes256-cbc,arcfour
1.1 stevesk 218: .Ed
219: .It Cm ClearAllForwardings
1.84 jmc 220: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 221: specified in the configuration files or on the command line be
1.7 jmc 222: cleared.
223: This option is primarily useful when used from the
1.84 jmc 224: .Xr ssh 1
1.1 stevesk 225: command line to clear port forwardings set in
226: configuration files, and is automatically set by
227: .Xr scp 1
228: and
229: .Xr sftp 1 .
230: The argument must be
231: .Dq yes
232: or
233: .Dq no .
234: The default is
235: .Dq no .
236: .It Cm Compression
237: Specifies whether to use compression.
238: The argument must be
239: .Dq yes
240: or
241: .Dq no .
242: The default is
243: .Dq no .
244: .It Cm CompressionLevel
245: Specifies the compression level to use if compression is enabled.
246: The argument must be an integer from 1 (fast) to 9 (slow, best).
247: The default level is 6, which is good for most applications.
248: The meaning of the values is the same as in
249: .Xr gzip 1 .
250: Note that this option applies to protocol version 1 only.
251: .It Cm ConnectionAttempts
252: Specifies the number of tries (one per second) to make before exiting.
253: The argument must be an integer.
254: This may be useful in scripts if the connection sometimes fails.
255: The default is 1.
1.9 djm 256: .It Cm ConnectTimeout
1.84 jmc 257: Specifies the timeout (in seconds) used when connecting to the
258: SSH server, instead of using the default system TCP timeout.
1.11 jmc 259: This value is used only when the target is down or really unreachable,
260: not when it refuses the connection.
1.36 djm 261: .It Cm ControlMaster
262: Enables the sharing of multiple sessions over a single network connection.
263: When set to
1.84 jmc 264: .Dq yes ,
265: .Xr ssh 1
1.36 djm 266: will listen for connections on a control socket specified using the
267: .Cm ControlPath
268: argument.
269: Additional sessions can connect to this socket using the same
270: .Cm ControlPath
271: with
272: .Cm ControlMaster
273: set to
274: .Dq no
1.38 jmc 275: (the default).
1.64 jmc 276: These sessions will try to reuse the master instance's network connection
1.63 djm 277: rather than initiating new ones, but will fall back to connecting normally
278: if the control socket does not exist, or is not listening.
279: .Pp
1.37 djm 280: Setting this to
281: .Dq ask
1.84 jmc 282: will cause ssh
1.37 djm 283: to listen for control connections, but require confirmation using the
284: .Ev SSH_ASKPASS
285: program before they are accepted (see
286: .Xr ssh-add 1
1.38 jmc 287: for details).
1.51 jakob 288: If the
289: .Cm ControlPath
1.84 jmc 290: cannot be opened,
291: ssh will continue without connecting to a master instance.
1.58 djm 292: .Pp
293: X11 and
1.59 jmc 294: .Xr ssh-agent 1
1.58 djm 295: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 296: display and agent forwarded will be the one belonging to the master
1.59 jmc 297: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 298: .Pp
299: Two additional options allow for opportunistic multiplexing: try to use a
300: master connection but fall back to creating a new one if one does not already
301: exist.
302: These options are:
303: .Dq auto
304: and
305: .Dq autoask .
306: The latter requires confirmation like the
307: .Dq ask
308: option.
1.36 djm 309: .It Cm ControlPath
1.55 djm 310: Specify the path to the control socket used for connection sharing as described
311: in the
1.36 djm 312: .Cm ControlMaster
1.57 djm 313: section above or the string
314: .Dq none
315: to disable connection sharing.
1.55 djm 316: In the path,
1.147 djm 317: .Ql %L
318: will be substituted by the first component of the local host name,
1.77 djm 319: .Ql %l
1.147 djm 320: will be substituted by the local host name (including any domain name),
1.55 djm 321: .Ql %h
322: will be substituted by the target host name,
1.147 djm 323: .Ql %h
324: will be substituted by original target host name specified on the commandline,
1.55 djm 325: .Ql %p
1.147 djm 326: the port,
1.55 djm 327: .Ql %r
1.147 djm 328: by the remote login username, and
329: .Ql %u
330: by the username of the user running
331: .Xr ssh 1 .
1.56 djm 332: It is recommended that any
333: .Cm ControlPath
334: used for opportunistic connection sharing include
1.78 jmc 335: at least %h, %p, and %r.
1.56 djm 336: This ensures that shared connections are uniquely identified.
1.137 djm 337: .It Cm ControlPersist
338: When used in conjunction with
339: .Cm ControlMaster ,
340: specifies that the master connection should remain open
341: in the background (waiting for future client connections)
342: after the initial client connection has been closed.
343: If set to
344: .Dq no ,
345: then the master connection will not be placed into the background,
346: and will close as soon as the initial client connection is closed.
347: If set to
348: .Dq yes ,
349: then the master connection will remain in the background indefinitely
350: (until killed or closed via a mechanism such as the
351: .Xr ssh 1
352: .Dq Fl O No exit
353: option).
354: If set to a time in seconds, or a time in any of the formats documented in
355: .Xr sshd_config 5 ,
356: then the backgrounded master connection will automatically terminate
357: after it has remained idle (with no client connections) for the
358: specified time.
1.38 jmc 359: .It Cm DynamicForward
1.74 jmc 360: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 361: over the secure channel, and the application
362: protocol is then used to determine where to connect to from the
363: remote machine.
1.62 djm 364: .Pp
365: The argument must be
366: .Sm off
367: .Oo Ar bind_address : Oc Ar port .
368: .Sm on
1.138 djm 369: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 370: By default, the local port is bound in accordance with the
371: .Cm GatewayPorts
372: setting.
373: However, an explicit
374: .Ar bind_address
375: may be used to bind the connection to a specific address.
376: The
377: .Ar bind_address
378: of
379: .Dq localhost
380: indicates that the listening port be bound for local use only, while an
381: empty address or
382: .Sq *
383: indicates that the port should be available from all interfaces.
384: .Pp
1.38 jmc 385: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 386: .Xr ssh 1
1.38 jmc 387: will act as a SOCKS server.
388: Multiple forwardings may be specified, and
389: additional forwardings can be given on the command line.
390: Only the superuser can forward privileged ports.
1.14 markus 391: .It Cm EnableSSHKeysign
392: Setting this option to
393: .Dq yes
394: in the global client configuration file
395: .Pa /etc/ssh/ssh_config
396: enables the use of the helper program
397: .Xr ssh-keysign 8
398: during
399: .Cm HostbasedAuthentication .
400: The argument must be
401: .Dq yes
402: or
403: .Dq no .
404: The default is
405: .Dq no .
1.23 jmc 406: This option should be placed in the non-hostspecific section.
1.14 markus 407: See
408: .Xr ssh-keysign 8
409: for more information.
1.1 stevesk 410: .It Cm EscapeChar
411: Sets the escape character (default:
412: .Ql ~ ) .
413: The escape character can also
414: be set on the command line.
415: The argument should be a single character,
416: .Ql ^
417: followed by a letter, or
418: .Dq none
419: to disable the escape
420: character entirely (making the connection transparent for binary
421: data).
1.96 markus 422: .It Cm ExitOnForwardFailure
423: Specifies whether
424: .Xr ssh 1
425: should terminate the connection if it cannot set up all requested
1.102 stevesk 426: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 427: The argument must be
428: .Dq yes
429: or
430: .Dq no .
431: The default is
432: .Dq no .
1.1 stevesk 433: .It Cm ForwardAgent
434: Specifies whether the connection to the authentication agent (if any)
435: will be forwarded to the remote machine.
436: The argument must be
437: .Dq yes
438: or
439: .Dq no .
440: The default is
441: .Dq no .
1.3 stevesk 442: .Pp
1.7 jmc 443: Agent forwarding should be enabled with caution.
444: Users with the ability to bypass file permissions on the remote host
445: (for the agent's Unix-domain socket)
446: can access the local agent through the forwarded connection.
447: An attacker cannot obtain key material from the agent,
1.3 stevesk 448: however they can perform operations on the keys that enable them to
449: authenticate using the identities loaded into the agent.
1.1 stevesk 450: .It Cm ForwardX11
451: Specifies whether X11 connections will be automatically redirected
452: over the secure channel and
453: .Ev DISPLAY
454: set.
455: The argument must be
456: .Dq yes
457: or
458: .Dq no .
459: The default is
460: .Dq no .
1.3 stevesk 461: .Pp
1.7 jmc 462: X11 forwarding should be enabled with caution.
463: Users with the ability to bypass file permissions on the remote host
1.22 markus 464: (for the user's X11 authorization database)
1.7 jmc 465: can access the local X11 display through the forwarded connection.
1.22 markus 466: An attacker may then be able to perform activities such as keystroke monitoring
467: if the
468: .Cm ForwardX11Trusted
469: option is also enabled.
1.134 djm 470: .It Cm ForwardX11Timeout
1.135 jmc 471: Specify a timeout for untrusted X11 forwarding
472: using the format described in the
1.134 djm 473: .Sx TIME FORMATS
474: section of
475: .Xr sshd_config 5 .
476: X11 connections received by
477: .Xr ssh 1
478: after this time will be refused.
479: The default is to disable untrusted X11 forwarding after twenty minutes has
480: elapsed.
1.22 markus 481: .It Cm ForwardX11Trusted
1.34 jmc 482: If this option is set to
1.84 jmc 483: .Dq yes ,
484: remote X11 clients will have full access to the original X11 display.
1.42 djm 485: .Pp
1.22 markus 486: If this option is set to
1.84 jmc 487: .Dq no ,
488: remote X11 clients will be considered untrusted and prevented
1.22 markus 489: from stealing or tampering with data belonging to trusted X11
490: clients.
1.42 djm 491: Furthermore, the
492: .Xr xauth 1
493: token used for the session will be set to expire after 20 minutes.
494: Remote clients will be refused access after this time.
1.22 markus 495: .Pp
496: The default is
497: .Dq no .
498: .Pp
499: See the X11 SECURITY extension specification for full details on
500: the restrictions imposed on untrusted clients.
1.1 stevesk 501: .It Cm GatewayPorts
502: Specifies whether remote hosts are allowed to connect to local
503: forwarded ports.
504: By default,
1.84 jmc 505: .Xr ssh 1
1.7 jmc 506: binds local port forwardings to the loopback address.
507: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 508: .Cm GatewayPorts
1.84 jmc 509: can be used to specify that ssh
1.1 stevesk 510: should bind local port forwardings to the wildcard address,
511: thus allowing remote hosts to connect to forwarded ports.
512: The argument must be
513: .Dq yes
514: or
515: .Dq no .
516: The default is
517: .Dq no .
518: .It Cm GlobalKnownHostsFile
519: Specifies a file to use for the global
520: host key database instead of
521: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 522: .It Cm GSSAPIAuthentication
1.27 markus 523: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 524: The default is
1.21 markus 525: .Dq no .
1.18 markus 526: Note that this option applies to protocol version 2 only.
527: .It Cm GSSAPIDelegateCredentials
528: Forward (delegate) credentials to the server.
529: The default is
530: .Dq no .
531: Note that this option applies to protocol version 2 only.
1.44 djm 532: .It Cm HashKnownHosts
533: Indicates that
1.84 jmc 534: .Xr ssh 1
1.44 djm 535: should hash host names and addresses when they are added to
1.50 djm 536: .Pa ~/.ssh/known_hosts .
1.44 djm 537: These hashed names may be used normally by
1.84 jmc 538: .Xr ssh 1
1.44 djm 539: and
1.84 jmc 540: .Xr sshd 8 ,
1.44 djm 541: but they do not reveal identifying information should the file's contents
542: be disclosed.
543: The default is
544: .Dq no .
1.97 jmc 545: Note that existing names and addresses in known hosts files
546: will not be converted automatically,
547: but may be manually hashed using
1.45 djm 548: .Xr ssh-keygen 1 .
1.1 stevesk 549: .It Cm HostbasedAuthentication
550: Specifies whether to try rhosts based authentication with public key
551: authentication.
552: The argument must be
553: .Dq yes
554: or
555: .Dq no .
556: The default is
557: .Dq no .
558: This option applies to protocol version 2 only and
559: is similar to
560: .Cm RhostsRSAAuthentication .
561: .It Cm HostKeyAlgorithms
562: Specifies the protocol version 2 host key algorithms
563: that the client wants to use in order of preference.
564: The default for this option is:
1.139 djm 565: .Bd -literal -offset 3n
566: ecdsa-sha2-nistp256-cert-v01@openssh.com,
567: ecdsa-sha2-nistp384-cert-v01@openssh.com,
568: ecdsa-sha2-nistp521-cert-v01@openssh.com,
569: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
570: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
571: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
572: ssh-rsa,ssh-dss
573: .Ed
1.145 djm 574: .Pp
575: If hostkeys are known for the destination host then this default is modified
576: to prefer their algorithms.
1.1 stevesk 577: .It Cm HostKeyAlias
578: Specifies an alias that should be used instead of the
579: real host name when looking up or saving the host key
580: in the host key database files.
1.84 jmc 581: This option is useful for tunneling SSH connections
1.1 stevesk 582: or for multiple servers running on a single host.
583: .It Cm HostName
584: Specifies the real host name to log into.
585: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 586: If the hostname contains the character sequence
587: .Ql %h ,
588: then this will be replaced with the host name specified on the commandline
589: (this is useful for manipulating unqualified names).
1.84 jmc 590: The default is the name given on the command line.
1.1 stevesk 591: Numeric IP addresses are also permitted (both on the command line and in
592: .Cm HostName
593: specifications).
1.29 markus 594: .It Cm IdentitiesOnly
595: Specifies that
1.84 jmc 596: .Xr ssh 1
1.29 markus 597: should only use the authentication identity files configured in the
1.31 jmc 598: .Nm
1.29 markus 599: files,
1.84 jmc 600: even if
601: .Xr ssh-agent 1
1.29 markus 602: offers more identities.
603: The argument to this keyword must be
604: .Dq yes
605: or
606: .Dq no .
1.84 jmc 607: This option is intended for situations where ssh-agent
1.29 markus 608: offers many different identities.
609: The default is
610: .Dq no .
1.67 jmc 611: .It Cm IdentityFile
1.139 djm 612: Specifies a file from which the user's DSA, ECDSA or DSA authentication
613: identity is read.
1.67 jmc 614: The default is
615: .Pa ~/.ssh/identity
616: for protocol version 1, and
1.139 djm 617: .Pa ~/.ssh/id_dsa ,
618: .Pa ~/.ssh/id_ecdsa
619: and
1.67 jmc 620: .Pa ~/.ssh/id_rsa
621: for protocol version 2.
622: Additionally, any identities represented by the authentication agent
623: will be used for authentication.
1.129 djm 624: .Xr ssh 1
625: will try to load certificate information from the filename obtained by
626: appending
627: .Pa -cert.pub
628: to the path of a specified
629: .Cm IdentityFile .
1.90 djm 630: .Pp
1.67 jmc 631: The file name may use the tilde
1.91 jmc 632: syntax to refer to a user's home directory or one of the following
1.90 djm 633: escape characters:
634: .Ql %d
635: (local user's home directory),
636: .Ql %u
637: (local user name),
638: .Ql %l
639: (local host name),
640: .Ql %h
641: (remote host name) or
1.92 djm 642: .Ql %r
1.90 djm 643: (remote user name).
644: .Pp
1.67 jmc 645: It is possible to have
646: multiple identity files specified in configuration files; all these
647: identities will be tried in sequence.
1.143 djm 648: .It Cm IPQoS
649: Specifies the IPv4 type-of-service or DSCP class for connections.
650: Accepted values are
651: .Dq af11 ,
652: .Dq af12 ,
653: .Dq af13 ,
654: .Dq af14 ,
655: .Dq af22 ,
656: .Dq af23 ,
657: .Dq af31 ,
658: .Dq af32 ,
659: .Dq af33 ,
660: .Dq af41 ,
661: .Dq af42 ,
662: .Dq af43 ,
663: .Dq cs0 ,
664: .Dq cs1 ,
665: .Dq cs2 ,
666: .Dq cs3 ,
667: .Dq cs4 ,
668: .Dq cs5 ,
669: .Dq cs6 ,
670: .Dq cs7 ,
671: .Dq ef ,
672: .Dq lowdelay ,
673: .Dq throughput ,
674: .Dq reliability ,
675: or a numeric value.
1.146 djm 676: This option may take one or two arguments, separated by whitespace.
1.143 djm 677: If one argument is specified, it is used as the packet class unconditionally.
678: If two values are specified, the first is automatically selected for
679: interactive sessions and the second for non-interactive sessions.
680: The default is
681: .Dq lowdelay
682: for interactive sessions and
683: .Dq throughput
684: for non-interactive sessions.
1.103 djm 685: .It Cm KbdInteractiveAuthentication
686: Specifies whether to use keyboard-interactive authentication.
687: The argument to this keyword must be
688: .Dq yes
689: or
690: .Dq no .
691: The default is
692: .Dq yes .
1.39 djm 693: .It Cm KbdInteractiveDevices
694: Specifies the list of methods to use in keyboard-interactive authentication.
695: Multiple method names must be comma-separated.
696: The default is to use the server specified list.
1.85 jmc 697: The methods available vary depending on what the server supports.
698: For an OpenSSH server,
699: it may be zero or more of:
700: .Dq bsdauth ,
701: .Dq pam ,
702: and
703: .Dq skey .
1.140 djm 704: .It Cm KexAlgorithms
705: Specifies the available KEX (Key Exchange) algorithms.
706: Multiple algorithms must be comma-separated.
1.141 jmc 707: The default is:
708: .Bd -literal -offset indent
709: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
710: diffie-hellman-group-exchange-sha256,
711: diffie-hellman-group-exchange-sha1,
712: diffie-hellman-group14-sha1,
713: diffie-hellman-group1-sha1
714: .Ed
1.65 reyk 715: .It Cm LocalCommand
716: Specifies a command to execute on the local machine after successfully
717: connecting to the server.
718: The command string extends to the end of the line, and is executed with
1.105 jmc 719: the user's shell.
1.109 dtucker 720: The following escape character substitutions will be performed:
721: .Ql %d
722: (local user's home directory),
723: .Ql %h
724: (remote host name),
725: .Ql %l
726: (local host name),
727: .Ql %n
728: (host name as provided on the command line),
729: .Ql %p
730: (remote port),
731: .Ql %r
732: (remote user name) or
733: .Ql %u
734: (local user name).
1.123 djm 735: .Pp
736: The command is run synchronously and does not have access to the
737: session of the
738: .Xr ssh 1
739: that spawned it.
740: It should not be used for interactive commands.
741: .Pp
1.65 reyk 742: This directive is ignored unless
743: .Cm PermitLocalCommand
744: has been enabled.
1.1 stevesk 745: .It Cm LocalForward
1.74 jmc 746: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 747: the secure channel to the specified host and port from the remote machine.
1.49 jmc 748: The first argument must be
1.43 djm 749: .Sm off
1.49 jmc 750: .Oo Ar bind_address : Oc Ar port
1.43 djm 751: .Sm on
1.49 jmc 752: and the second argument must be
753: .Ar host : Ns Ar hostport .
1.138 djm 754: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 755: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 756: given on the command line.
1.1 stevesk 757: Only the superuser can forward privileged ports.
1.43 djm 758: By default, the local port is bound in accordance with the
759: .Cm GatewayPorts
760: setting.
761: However, an explicit
762: .Ar bind_address
763: may be used to bind the connection to a specific address.
764: The
765: .Ar bind_address
766: of
767: .Dq localhost
1.46 jmc 768: indicates that the listening port be bound for local use only, while an
769: empty address or
770: .Sq *
1.43 djm 771: indicates that the port should be available from all interfaces.
1.1 stevesk 772: .It Cm LogLevel
773: Gives the verbosity level that is used when logging messages from
1.84 jmc 774: .Xr ssh 1 .
1.1 stevesk 775: The possible values are:
1.84 jmc 776: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 777: The default is INFO.
778: DEBUG and DEBUG1 are equivalent.
779: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 780: .It Cm MACs
781: Specifies the MAC (message authentication code) algorithms
782: in order of preference.
783: The MAC algorithm is used in protocol version 2
784: for data integrity protection.
785: Multiple algorithms must be comma-separated.
1.84 jmc 786: The default is:
1.101 jmc 787: .Bd -literal -offset indent
788: hmac-md5,hmac-sha1,umac-64@openssh.com,
789: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
790: .Ed
1.1 stevesk 791: .It Cm NoHostAuthenticationForLocalhost
792: This option can be used if the home directory is shared across machines.
793: In this case localhost will refer to a different machine on each of
794: the machines and the user will get many warnings about changed host keys.
795: However, this option disables host authentication for localhost.
796: The argument to this keyword must be
797: .Dq yes
798: or
799: .Dq no .
800: The default is to check the host key for localhost.
801: .It Cm NumberOfPasswordPrompts
802: Specifies the number of password prompts before giving up.
803: The argument to this keyword must be an integer.
1.84 jmc 804: The default is 3.
1.1 stevesk 805: .It Cm PasswordAuthentication
806: Specifies whether to use password authentication.
807: The argument to this keyword must be
808: .Dq yes
809: or
810: .Dq no .
811: The default is
812: .Dq yes .
1.65 reyk 813: .It Cm PermitLocalCommand
814: Allow local command execution via the
815: .Ic LocalCommand
816: option or using the
1.66 jmc 817: .Ic !\& Ns Ar command
1.65 reyk 818: escape sequence in
819: .Xr ssh 1 .
820: The argument must be
821: .Dq yes
822: or
823: .Dq no .
824: The default is
825: .Dq no .
1.127 markus 826: .It Cm PKCS11Provider
827: Specifies which PKCS#11 provider to use.
1.144 jmc 828: The argument to this keyword is the PKCS#11 shared library
1.127 markus 829: .Xr ssh 1
1.128 markus 830: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 831: private RSA key.
1.67 jmc 832: .It Cm Port
833: Specifies the port number to connect on the remote host.
1.84 jmc 834: The default is 22.
1.1 stevesk 835: .It Cm PreferredAuthentications
836: Specifies the order in which the client should try protocol 2
1.11 jmc 837: authentication methods.
1.48 jmc 838: This allows a client to prefer one method (e.g.\&
1.1 stevesk 839: .Cm keyboard-interactive )
1.48 jmc 840: over another method (e.g.\&
1.131 jmc 841: .Cm password ) .
842: The default is:
843: .Bd -literal -offset indent
844: gssapi-with-mic,hostbased,publickey,
845: keyboard-interactive,password
846: .Ed
1.1 stevesk 847: .It Cm Protocol
848: Specifies the protocol versions
1.84 jmc 849: .Xr ssh 1
1.1 stevesk 850: should support in order of preference.
851: The possible values are
1.84 jmc 852: .Sq 1
1.1 stevesk 853: and
1.84 jmc 854: .Sq 2 .
1.1 stevesk 855: Multiple versions must be comma-separated.
1.120 markus 856: When this option is set to
1.121 jmc 857: .Dq 2,1
1.120 markus 858: .Nm ssh
859: will try version 2 and fall back to version 1
860: if version 2 is not available.
1.1 stevesk 861: The default is
1.121 jmc 862: .Sq 2 .
1.1 stevesk 863: .It Cm ProxyCommand
864: Specifies the command to use to connect to the server.
865: The command
866: string extends to the end of the line, and is executed with
1.105 jmc 867: the user's shell.
1.133 jmc 868: In the command string, any occurrence of
1.1 stevesk 869: .Ql %h
870: will be substituted by the host name to
1.132 djm 871: connect,
1.1 stevesk 872: .Ql %p
1.133 jmc 873: by the port, and
874: .Ql %r
1.132 djm 875: by the remote user name.
1.1 stevesk 876: The command can be basically anything,
877: and should read from its standard input and write to its standard output.
878: It should eventually connect an
879: .Xr sshd 8
880: server running on some machine, or execute
881: .Ic sshd -i
882: somewhere.
883: Host key management will be done using the
884: HostName of the host being connected (defaulting to the name typed by
885: the user).
1.7 jmc 886: Setting the command to
887: .Dq none
1.6 markus 888: disables this option entirely.
1.1 stevesk 889: Note that
890: .Cm CheckHostIP
891: is not available for connects with a proxy command.
1.52 djm 892: .Pp
893: This directive is useful in conjunction with
894: .Xr nc 1
895: and its proxy support.
1.53 jmc 896: For example, the following directive would connect via an HTTP proxy at
1.52 djm 897: 192.0.2.0:
898: .Bd -literal -offset 3n
899: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
900: .Ed
1.1 stevesk 901: .It Cm PubkeyAuthentication
902: Specifies whether to try public key authentication.
903: The argument to this keyword must be
904: .Dq yes
905: or
906: .Dq no .
907: The default is
908: .Dq yes .
909: This option applies to protocol version 2 only.
1.75 dtucker 910: .It Cm RekeyLimit
911: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 912: session key is renegotiated.
1.75 dtucker 913: The argument is the number of bytes, with an optional suffix of
1.76 jmc 914: .Sq K ,
915: .Sq M ,
1.75 dtucker 916: or
1.76 jmc 917: .Sq G
1.75 dtucker 918: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
919: The default is between
1.84 jmc 920: .Sq 1G
1.75 dtucker 921: and
1.84 jmc 922: .Sq 4G ,
1.75 dtucker 923: depending on the cipher.
1.76 jmc 924: This option applies to protocol version 2 only.
1.1 stevesk 925: .It Cm RemoteForward
1.74 jmc 926: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 927: the secure channel to the specified host and port from the local machine.
1.49 jmc 928: The first argument must be
1.43 djm 929: .Sm off
1.49 jmc 930: .Oo Ar bind_address : Oc Ar port
1.43 djm 931: .Sm on
1.49 jmc 932: and the second argument must be
933: .Ar host : Ns Ar hostport .
1.138 djm 934: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 935: Multiple forwardings may be specified, and additional
936: forwardings can be given on the command line.
1.113 stevesk 937: Privileged ports can be forwarded only when
938: logging in as root on the remote machine.
1.118 jmc 939: .Pp
1.117 djm 940: If the
941: .Ar port
942: argument is
943: .Ql 0 ,
944: the listen port will be dynamically allocated on the server and reported
945: to the client at run time.
1.43 djm 946: .Pp
947: If the
948: .Ar bind_address
949: is not specified, the default is to only bind to loopback addresses.
950: If the
951: .Ar bind_address
952: is
953: .Ql *
954: or an empty string, then the forwarding is requested to listen on all
955: interfaces.
956: Specifying a remote
957: .Ar bind_address
1.46 jmc 958: will only succeed if the server's
959: .Cm GatewayPorts
1.43 djm 960: option is enabled (see
1.46 jmc 961: .Xr sshd_config 5 ) .
1.1 stevesk 962: .It Cm RhostsRSAAuthentication
963: Specifies whether to try rhosts based authentication with RSA host
964: authentication.
965: The argument must be
966: .Dq yes
967: or
968: .Dq no .
969: The default is
970: .Dq no .
971: This option applies to protocol version 1 only and requires
1.84 jmc 972: .Xr ssh 1
1.1 stevesk 973: to be setuid root.
974: .It Cm RSAAuthentication
975: Specifies whether to try RSA authentication.
976: The argument to this keyword must be
977: .Dq yes
978: or
979: .Dq no .
980: RSA authentication will only be
981: attempted if the identity file exists, or an authentication agent is
982: running.
983: The default is
984: .Dq yes .
985: Note that this option applies to protocol version 1 only.
1.32 djm 986: .It Cm SendEnv
987: Specifies what variables from the local
988: .Xr environ 7
989: should be sent to the server.
1.84 jmc 990: Note that environment passing is only supported for protocol 2.
991: The server must also support it, and the server must be configured to
1.33 djm 992: accept these environment variables.
1.32 djm 993: Refer to
994: .Cm AcceptEnv
995: in
996: .Xr sshd_config 5
997: for how to configure the server.
1.80 jmc 998: Variables are specified by name, which may contain wildcard characters.
1.33 djm 999: Multiple environment variables may be separated by whitespace or spread
1.32 djm 1000: across multiple
1001: .Cm SendEnv
1002: directives.
1003: The default is not to send any environment variables.
1.81 jmc 1004: .Pp
1005: See
1006: .Sx PATTERNS
1007: for more information on patterns.
1.28 markus 1008: .It Cm ServerAliveCountMax
1.73 jmc 1009: Sets the number of server alive messages (see below) which may be
1.28 markus 1010: sent without
1.84 jmc 1011: .Xr ssh 1
1.28 markus 1012: receiving any messages back from the server.
1013: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1014: ssh will disconnect from the server, terminating the session.
1.28 markus 1015: It is important to note that the use of server alive messages is very
1016: different from
1017: .Cm TCPKeepAlive
1018: (below).
1019: The server alive messages are sent through the encrypted channel
1020: and therefore will not be spoofable.
1021: The TCP keepalive option enabled by
1022: .Cm TCPKeepAlive
1023: is spoofable.
1024: The server alive mechanism is valuable when the client or
1025: server depend on knowing when a connection has become inactive.
1026: .Pp
1027: The default value is 3.
1028: If, for example,
1029: .Cm ServerAliveInterval
1.84 jmc 1030: (see below) is set to 15 and
1.28 markus 1031: .Cm ServerAliveCountMax
1.84 jmc 1032: is left at the default, if the server becomes unresponsive,
1033: ssh will disconnect after approximately 45 seconds.
1.89 markus 1034: This option applies to protocol version 2 only.
1.67 jmc 1035: .It Cm ServerAliveInterval
1036: Sets a timeout interval in seconds after which if no data has been received
1037: from the server,
1.84 jmc 1038: .Xr ssh 1
1.67 jmc 1039: will send a message through the encrypted
1040: channel to request a response from the server.
1041: The default
1042: is 0, indicating that these messages will not be sent to the server.
1043: This option applies to protocol version 2 only.
1.1 stevesk 1044: .It Cm StrictHostKeyChecking
1045: If this flag is set to
1046: .Dq yes ,
1.84 jmc 1047: .Xr ssh 1
1.1 stevesk 1048: will never automatically add host keys to the
1.50 djm 1049: .Pa ~/.ssh/known_hosts
1.1 stevesk 1050: file, and refuses to connect to hosts whose host key has changed.
1051: This provides maximum protection against trojan horse attacks,
1.84 jmc 1052: though it can be annoying when the
1.1 stevesk 1053: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1054: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1055: frequently made.
1056: This option forces the user to manually
1057: add all new hosts.
1058: If this flag is set to
1059: .Dq no ,
1.84 jmc 1060: ssh will automatically add new host keys to the
1.1 stevesk 1061: user known hosts files.
1062: If this flag is set to
1063: .Dq ask ,
1064: new host keys
1065: will be added to the user known host files only after the user
1066: has confirmed that is what they really want to do, and
1.84 jmc 1067: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1068: The host keys of
1069: known hosts will be verified automatically in all cases.
1070: The argument must be
1071: .Dq yes ,
1.84 jmc 1072: .Dq no ,
1.1 stevesk 1073: or
1074: .Dq ask .
1075: The default is
1076: .Dq ask .
1.26 markus 1077: .It Cm TCPKeepAlive
1078: Specifies whether the system should send TCP keepalive messages to the
1079: other side.
1080: If they are sent, death of the connection or crash of one
1081: of the machines will be properly noticed.
1082: However, this means that
1083: connections will die if the route is down temporarily, and some people
1084: find it annoying.
1085: .Pp
1086: The default is
1087: .Dq yes
1088: (to send TCP keepalive messages), and the client will notice
1089: if the network goes down or the remote host dies.
1090: This is important in scripts, and many users want it too.
1091: .Pp
1092: To disable TCP keepalive messages, the value should be set to
1093: .Dq no .
1.65 reyk 1094: .It Cm Tunnel
1.95 stevesk 1095: Request
1.65 reyk 1096: .Xr tun 4
1.69 jmc 1097: device forwarding between the client and the server.
1.65 reyk 1098: The argument must be
1.68 reyk 1099: .Dq yes ,
1.95 stevesk 1100: .Dq point-to-point
1101: (layer 3),
1102: .Dq ethernet
1103: (layer 2),
1.65 reyk 1104: or
1105: .Dq no .
1.95 stevesk 1106: Specifying
1107: .Dq yes
1108: requests the default tunnel mode, which is
1109: .Dq point-to-point .
1.65 reyk 1110: The default is
1111: .Dq no .
1112: .It Cm TunnelDevice
1.95 stevesk 1113: Specifies the
1.65 reyk 1114: .Xr tun 4
1.95 stevesk 1115: devices to open on the client
1116: .Pq Ar local_tun
1117: and the server
1118: .Pq Ar remote_tun .
1119: .Pp
1120: The argument must be
1121: .Sm off
1122: .Ar local_tun Op : Ar remote_tun .
1123: .Sm on
1124: The devices may be specified by numerical ID or the keyword
1125: .Dq any ,
1126: which uses the next available tunnel device.
1127: If
1128: .Ar remote_tun
1129: is not specified, it defaults to
1130: .Dq any .
1131: The default is
1132: .Dq any:any .
1.72 jmc 1133: .It Cm UsePrivilegedPort
1134: Specifies whether to use a privileged port for outgoing connections.
1135: The argument must be
1136: .Dq yes
1137: or
1138: .Dq no .
1139: The default is
1140: .Dq no .
1141: If set to
1.84 jmc 1142: .Dq yes ,
1143: .Xr ssh 1
1.72 jmc 1144: must be setuid root.
1145: Note that this option must be set to
1146: .Dq yes
1147: for
1148: .Cm RhostsRSAAuthentication
1149: with older servers.
1.1 stevesk 1150: .It Cm User
1151: Specifies the user to log in as.
1152: This can be useful when a different user name is used on different machines.
1153: This saves the trouble of
1154: having to remember to give the user name on the command line.
1155: .It Cm UserKnownHostsFile
1156: Specifies a file to use for the user
1157: host key database instead of
1.50 djm 1158: .Pa ~/.ssh/known_hosts .
1.8 jakob 1159: .It Cm VerifyHostKeyDNS
1160: Specifies whether to verify the remote key using DNS and SSHFP resource
1161: records.
1.24 jakob 1162: If this option is set to
1163: .Dq yes ,
1.25 jmc 1164: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1165: from DNS.
1166: Insecure fingerprints will be handled as if this option was set to
1167: .Dq ask .
1168: If this option is set to
1169: .Dq ask ,
1170: information on fingerprint match will be displayed, but the user will still
1171: need to confirm new host keys according to the
1172: .Cm StrictHostKeyChecking
1173: option.
1174: The argument must be
1175: .Dq yes ,
1.84 jmc 1176: .Dq no ,
1.25 jmc 1177: or
1178: .Dq ask .
1.8 jakob 1179: The default is
1180: .Dq no .
1.12 jakob 1181: Note that this option applies to protocol version 2 only.
1.84 jmc 1182: .Pp
1183: See also
1184: .Sx VERIFYING HOST KEYS
1185: in
1186: .Xr ssh 1 .
1.111 grunk 1187: .It Cm VisualHostKey
1188: If this flag is set to
1189: .Dq yes ,
1190: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1191: printed in addition to the hex fingerprint string at login and
1192: for unknown host keys.
1.111 grunk 1193: If this flag is set to
1194: .Dq no ,
1.114 stevesk 1195: no fingerprint strings are printed at login and
1196: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1197: The default is
1198: .Dq no .
1.1 stevesk 1199: .It Cm XAuthLocation
1.5 stevesk 1200: Specifies the full pathname of the
1.1 stevesk 1201: .Xr xauth 1
1202: program.
1203: The default is
1204: .Pa /usr/X11R6/bin/xauth .
1205: .El
1.86 jmc 1206: .Sh PATTERNS
1207: A
1208: .Em pattern
1209: consists of zero or more non-whitespace characters,
1210: .Sq *
1211: (a wildcard that matches zero or more characters),
1212: or
1213: .Sq ?\&
1214: (a wildcard that matches exactly one character).
1215: For example, to specify a set of declarations for any host in the
1216: .Dq .co.uk
1217: set of domains,
1218: the following pattern could be used:
1219: .Pp
1220: .Dl Host *.co.uk
1221: .Pp
1222: The following pattern
1223: would match any host in the 192.168.0.[0-9] network range:
1224: .Pp
1225: .Dl Host 192.168.0.?
1226: .Pp
1227: A
1228: .Em pattern-list
1229: is a comma-separated list of patterns.
1230: Patterns within pattern-lists may be negated
1231: by preceding them with an exclamation mark
1232: .Pq Sq !\& .
1233: For example,
1234: to allow a key to be used from anywhere within an organisation
1235: except from the
1236: .Dq dialup
1237: pool,
1238: the following entry (in authorized_keys) could be used:
1239: .Pp
1240: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1241: .Sh FILES
1242: .Bl -tag -width Ds
1.50 djm 1243: .It Pa ~/.ssh/config
1.1 stevesk 1244: This is the per-user configuration file.
1245: The format of this file is described above.
1.84 jmc 1246: This file is used by the SSH client.
1.30 djm 1247: Because of the potential for abuse, this file must have strict permissions:
1248: read/write for the user, and not accessible by others.
1.1 stevesk 1249: .It Pa /etc/ssh/ssh_config
1250: Systemwide configuration file.
1251: This file provides defaults for those
1252: values that are not specified in the user's configuration file, and
1253: for those users who do not have a configuration file.
1254: This file must be world-readable.
1255: .El
1.13 jmc 1256: .Sh SEE ALSO
1257: .Xr ssh 1
1.1 stevesk 1258: .Sh AUTHORS
1259: OpenSSH is a derivative of the original and free
1260: ssh 1.2.12 release by Tatu Ylonen.
1261: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1262: Theo de Raadt and Dug Song
1263: removed many bugs, re-added newer features and
1264: created OpenSSH.
1265: Markus Friedl contributed the support for SSH
1266: protocol versions 1.5 and 2.0.