Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.109
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
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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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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1.109 ! dtucker 37: .\" $OpenBSD: ssh_config.5,v 1.108 2008/06/11 23:03:56 grunk Exp $
1.108 grunk 38: .Dd $Mdocdate: June 11 2008 $
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.
1.106 dtucker 106: If more than one pattern is provided, they should be separated by whitepsace.
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
164: .Dq fingerprint ,
1.108 grunk 165: not only the host IP address will be checked, but also a fingerprint
166: along with an ASCII art
1.107 grunk 167: representation of the key will be printed.
1.1 stevesk 168: If the option is set to
169: .Dq no ,
170: the check will not be executed.
171: The default is
172: .Dq yes .
173: .It Cm Cipher
174: Specifies the cipher to use for encrypting the session
175: in protocol version 1.
176: Currently,
177: .Dq blowfish ,
178: .Dq 3des ,
179: and
180: .Dq des
181: are supported.
182: .Ar des
183: is only supported in the
1.84 jmc 184: .Xr ssh 1
1.1 stevesk 185: client for interoperability with legacy protocol 1 implementations
186: that do not support the
187: .Ar 3des
1.7 jmc 188: cipher.
189: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 190: The default is
191: .Dq 3des .
192: .It Cm Ciphers
193: Specifies the ciphers allowed for protocol version 2
194: in order of preference.
195: Multiple ciphers must be comma-separated.
1.35 dtucker 196: The supported ciphers are
197: .Dq 3des-cbc ,
198: .Dq aes128-cbc ,
199: .Dq aes192-cbc ,
200: .Dq aes256-cbc ,
201: .Dq aes128-ctr ,
202: .Dq aes192-ctr ,
203: .Dq aes256-ctr ,
1.54 djm 204: .Dq arcfour128 ,
205: .Dq arcfour256 ,
1.35 dtucker 206: .Dq arcfour ,
207: .Dq blowfish-cbc ,
208: and
209: .Dq cast128-cbc .
1.84 jmc 210: The default is:
211: .Bd -literal -offset 3n
212: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
213: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
214: aes192-ctr,aes256-ctr
1.1 stevesk 215: .Ed
216: .It Cm ClearAllForwardings
1.84 jmc 217: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 218: specified in the configuration files or on the command line be
1.7 jmc 219: cleared.
220: This option is primarily useful when used from the
1.84 jmc 221: .Xr ssh 1
1.1 stevesk 222: command line to clear port forwardings set in
223: configuration files, and is automatically set by
224: .Xr scp 1
225: and
226: .Xr sftp 1 .
227: The argument must be
228: .Dq yes
229: or
230: .Dq no .
231: The default is
232: .Dq no .
233: .It Cm Compression
234: Specifies whether to use compression.
235: The argument must be
236: .Dq yes
237: or
238: .Dq no .
239: The default is
240: .Dq no .
241: .It Cm CompressionLevel
242: Specifies the compression level to use if compression is enabled.
243: The argument must be an integer from 1 (fast) to 9 (slow, best).
244: The default level is 6, which is good for most applications.
245: The meaning of the values is the same as in
246: .Xr gzip 1 .
247: Note that this option applies to protocol version 1 only.
248: .It Cm ConnectionAttempts
249: Specifies the number of tries (one per second) to make before exiting.
250: The argument must be an integer.
251: This may be useful in scripts if the connection sometimes fails.
252: The default is 1.
1.9 djm 253: .It Cm ConnectTimeout
1.84 jmc 254: Specifies the timeout (in seconds) used when connecting to the
255: SSH server, instead of using the default system TCP timeout.
1.11 jmc 256: This value is used only when the target is down or really unreachable,
257: not when it refuses the connection.
1.36 djm 258: .It Cm ControlMaster
259: Enables the sharing of multiple sessions over a single network connection.
260: When set to
1.84 jmc 261: .Dq yes ,
262: .Xr ssh 1
1.36 djm 263: will listen for connections on a control socket specified using the
264: .Cm ControlPath
265: argument.
266: Additional sessions can connect to this socket using the same
267: .Cm ControlPath
268: with
269: .Cm ControlMaster
270: set to
271: .Dq no
1.38 jmc 272: (the default).
1.64 jmc 273: These sessions will try to reuse the master instance's network connection
1.63 djm 274: rather than initiating new ones, but will fall back to connecting normally
275: if the control socket does not exist, or is not listening.
276: .Pp
1.37 djm 277: Setting this to
278: .Dq ask
1.84 jmc 279: will cause ssh
1.37 djm 280: to listen for control connections, but require confirmation using the
281: .Ev SSH_ASKPASS
282: program before they are accepted (see
283: .Xr ssh-add 1
1.38 jmc 284: for details).
1.51 jakob 285: If the
286: .Cm ControlPath
1.84 jmc 287: cannot be opened,
288: ssh will continue without connecting to a master instance.
1.58 djm 289: .Pp
290: X11 and
1.59 jmc 291: .Xr ssh-agent 1
1.58 djm 292: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 293: display and agent forwarded will be the one belonging to the master
1.59 jmc 294: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 295: .Pp
296: Two additional options allow for opportunistic multiplexing: try to use a
297: master connection but fall back to creating a new one if one does not already
298: exist.
299: These options are:
300: .Dq auto
301: and
302: .Dq autoask .
303: The latter requires confirmation like the
304: .Dq ask
305: option.
1.36 djm 306: .It Cm ControlPath
1.55 djm 307: Specify the path to the control socket used for connection sharing as described
308: in the
1.36 djm 309: .Cm ControlMaster
1.57 djm 310: section above or the string
311: .Dq none
312: to disable connection sharing.
1.55 djm 313: In the path,
1.77 djm 314: .Ql %l
315: will be substituted by the local host name,
1.55 djm 316: .Ql %h
317: will be substituted by the target host name,
318: .Ql %p
1.84 jmc 319: the port, and
1.55 djm 320: .Ql %r
321: by the remote login username.
1.56 djm 322: It is recommended that any
323: .Cm ControlPath
324: used for opportunistic connection sharing include
1.78 jmc 325: at least %h, %p, and %r.
1.56 djm 326: This ensures that shared connections are uniquely identified.
1.38 jmc 327: .It Cm DynamicForward
1.74 jmc 328: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 329: over the secure channel, and the application
330: protocol is then used to determine where to connect to from the
331: remote machine.
1.62 djm 332: .Pp
333: The argument must be
334: .Sm off
335: .Oo Ar bind_address : Oc Ar port .
336: .Sm on
337: IPv6 addresses can be specified by enclosing addresses in square brackets or
338: by using an alternative syntax:
339: .Oo Ar bind_address Ns / Oc Ns Ar port .
340: By default, the local port is bound in accordance with the
341: .Cm GatewayPorts
342: setting.
343: However, an explicit
344: .Ar bind_address
345: may be used to bind the connection to a specific address.
346: The
347: .Ar bind_address
348: of
349: .Dq localhost
350: indicates that the listening port be bound for local use only, while an
351: empty address or
352: .Sq *
353: indicates that the port should be available from all interfaces.
354: .Pp
1.38 jmc 355: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 356: .Xr ssh 1
1.38 jmc 357: will act as a SOCKS server.
358: Multiple forwardings may be specified, and
359: additional forwardings can be given on the command line.
360: Only the superuser can forward privileged ports.
1.14 markus 361: .It Cm EnableSSHKeysign
362: Setting this option to
363: .Dq yes
364: in the global client configuration file
365: .Pa /etc/ssh/ssh_config
366: enables the use of the helper program
367: .Xr ssh-keysign 8
368: during
369: .Cm HostbasedAuthentication .
370: The argument must be
371: .Dq yes
372: or
373: .Dq no .
374: The default is
375: .Dq no .
1.23 jmc 376: This option should be placed in the non-hostspecific section.
1.14 markus 377: See
378: .Xr ssh-keysign 8
379: for more information.
1.1 stevesk 380: .It Cm EscapeChar
381: Sets the escape character (default:
382: .Ql ~ ) .
383: The escape character can also
384: be set on the command line.
385: The argument should be a single character,
386: .Ql ^
387: followed by a letter, or
388: .Dq none
389: to disable the escape
390: character entirely (making the connection transparent for binary
391: data).
1.96 markus 392: .It Cm ExitOnForwardFailure
393: Specifies whether
394: .Xr ssh 1
395: should terminate the connection if it cannot set up all requested
1.102 stevesk 396: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 397: The argument must be
398: .Dq yes
399: or
400: .Dq no .
401: The default is
402: .Dq no .
1.1 stevesk 403: .It Cm ForwardAgent
404: Specifies whether the connection to the authentication agent (if any)
405: will be forwarded to the remote machine.
406: The argument must be
407: .Dq yes
408: or
409: .Dq no .
410: The default is
411: .Dq no .
1.3 stevesk 412: .Pp
1.7 jmc 413: Agent forwarding should be enabled with caution.
414: Users with the ability to bypass file permissions on the remote host
415: (for the agent's Unix-domain socket)
416: can access the local agent through the forwarded connection.
417: An attacker cannot obtain key material from the agent,
1.3 stevesk 418: however they can perform operations on the keys that enable them to
419: authenticate using the identities loaded into the agent.
1.1 stevesk 420: .It Cm ForwardX11
421: Specifies whether X11 connections will be automatically redirected
422: over the secure channel and
423: .Ev DISPLAY
424: set.
425: The argument must be
426: .Dq yes
427: or
428: .Dq no .
429: The default is
430: .Dq no .
1.3 stevesk 431: .Pp
1.7 jmc 432: X11 forwarding should be enabled with caution.
433: Users with the ability to bypass file permissions on the remote host
1.22 markus 434: (for the user's X11 authorization database)
1.7 jmc 435: can access the local X11 display through the forwarded connection.
1.22 markus 436: An attacker may then be able to perform activities such as keystroke monitoring
437: if the
438: .Cm ForwardX11Trusted
439: option is also enabled.
440: .It Cm ForwardX11Trusted
1.34 jmc 441: If this option is set to
1.84 jmc 442: .Dq yes ,
443: remote X11 clients will have full access to the original X11 display.
1.42 djm 444: .Pp
1.22 markus 445: If this option is set to
1.84 jmc 446: .Dq no ,
447: remote X11 clients will be considered untrusted and prevented
1.22 markus 448: from stealing or tampering with data belonging to trusted X11
449: clients.
1.42 djm 450: Furthermore, the
451: .Xr xauth 1
452: token used for the session will be set to expire after 20 minutes.
453: Remote clients will be refused access after this time.
1.22 markus 454: .Pp
455: The default is
456: .Dq no .
457: .Pp
458: See the X11 SECURITY extension specification for full details on
459: the restrictions imposed on untrusted clients.
1.1 stevesk 460: .It Cm GatewayPorts
461: Specifies whether remote hosts are allowed to connect to local
462: forwarded ports.
463: By default,
1.84 jmc 464: .Xr ssh 1
1.7 jmc 465: binds local port forwardings to the loopback address.
466: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 467: .Cm GatewayPorts
1.84 jmc 468: can be used to specify that ssh
1.1 stevesk 469: should bind local port forwardings to the wildcard address,
470: thus allowing remote hosts to connect to forwarded ports.
471: The argument must be
472: .Dq yes
473: or
474: .Dq no .
475: The default is
476: .Dq no .
477: .It Cm GlobalKnownHostsFile
478: Specifies a file to use for the global
479: host key database instead of
480: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 481: .It Cm GSSAPIAuthentication
1.27 markus 482: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 483: The default is
1.21 markus 484: .Dq no .
1.18 markus 485: Note that this option applies to protocol version 2 only.
486: .It Cm GSSAPIDelegateCredentials
487: Forward (delegate) credentials to the server.
488: The default is
489: .Dq no .
490: Note that this option applies to protocol version 2 only.
1.44 djm 491: .It Cm HashKnownHosts
492: Indicates that
1.84 jmc 493: .Xr ssh 1
1.44 djm 494: should hash host names and addresses when they are added to
1.50 djm 495: .Pa ~/.ssh/known_hosts .
1.44 djm 496: These hashed names may be used normally by
1.84 jmc 497: .Xr ssh 1
1.44 djm 498: and
1.84 jmc 499: .Xr sshd 8 ,
1.44 djm 500: but they do not reveal identifying information should the file's contents
501: be disclosed.
502: The default is
503: .Dq no .
1.97 jmc 504: Note that existing names and addresses in known hosts files
505: will not be converted automatically,
506: but may be manually hashed using
1.45 djm 507: .Xr ssh-keygen 1 .
1.1 stevesk 508: .It Cm HostbasedAuthentication
509: Specifies whether to try rhosts based authentication with public key
510: authentication.
511: The argument must be
512: .Dq yes
513: or
514: .Dq no .
515: The default is
516: .Dq no .
517: This option applies to protocol version 2 only and
518: is similar to
519: .Cm RhostsRSAAuthentication .
520: .It Cm HostKeyAlgorithms
521: Specifies the protocol version 2 host key algorithms
522: that the client wants to use in order of preference.
523: The default for this option is:
524: .Dq ssh-rsa,ssh-dss .
525: .It Cm HostKeyAlias
526: Specifies an alias that should be used instead of the
527: real host name when looking up or saving the host key
528: in the host key database files.
1.84 jmc 529: This option is useful for tunneling SSH connections
1.1 stevesk 530: or for multiple servers running on a single host.
531: .It Cm HostName
532: Specifies the real host name to log into.
533: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 534: The default is the name given on the command line.
1.1 stevesk 535: Numeric IP addresses are also permitted (both on the command line and in
536: .Cm HostName
537: specifications).
1.29 markus 538: .It Cm IdentitiesOnly
539: Specifies that
1.84 jmc 540: .Xr ssh 1
1.29 markus 541: should only use the authentication identity files configured in the
1.31 jmc 542: .Nm
1.29 markus 543: files,
1.84 jmc 544: even if
545: .Xr ssh-agent 1
1.29 markus 546: offers more identities.
547: The argument to this keyword must be
548: .Dq yes
549: or
550: .Dq no .
1.84 jmc 551: This option is intended for situations where ssh-agent
1.29 markus 552: offers many different identities.
553: The default is
554: .Dq no .
1.67 jmc 555: .It Cm IdentityFile
556: Specifies a file from which the user's RSA or DSA authentication identity
557: is read.
558: The default is
559: .Pa ~/.ssh/identity
560: for protocol version 1, and
561: .Pa ~/.ssh/id_rsa
562: and
563: .Pa ~/.ssh/id_dsa
564: for protocol version 2.
565: Additionally, any identities represented by the authentication agent
566: will be used for authentication.
1.90 djm 567: .Pp
1.67 jmc 568: The file name may use the tilde
1.91 jmc 569: syntax to refer to a user's home directory or one of the following
1.90 djm 570: escape characters:
571: .Ql %d
572: (local user's home directory),
573: .Ql %u
574: (local user name),
575: .Ql %l
576: (local host name),
577: .Ql %h
578: (remote host name) or
1.92 djm 579: .Ql %r
1.90 djm 580: (remote user name).
581: .Pp
1.67 jmc 582: It is possible to have
583: multiple identity files specified in configuration files; all these
584: identities will be tried in sequence.
1.103 djm 585: .It Cm KbdInteractiveAuthentication
586: Specifies whether to use keyboard-interactive authentication.
587: The argument to this keyword must be
588: .Dq yes
589: or
590: .Dq no .
591: The default is
592: .Dq yes .
1.39 djm 593: .It Cm KbdInteractiveDevices
594: Specifies the list of methods to use in keyboard-interactive authentication.
595: Multiple method names must be comma-separated.
596: The default is to use the server specified list.
1.85 jmc 597: The methods available vary depending on what the server supports.
598: For an OpenSSH server,
599: it may be zero or more of:
600: .Dq bsdauth ,
601: .Dq pam ,
602: and
603: .Dq skey .
1.65 reyk 604: .It Cm LocalCommand
605: Specifies a command to execute on the local machine after successfully
606: connecting to the server.
607: The command string extends to the end of the line, and is executed with
1.105 jmc 608: the user's shell.
1.109 ! dtucker 609: The following escape character substitutions will be performed:
! 610: .Ql %d
! 611: (local user's home directory),
! 612: .Ql %h
! 613: (remote host name),
! 614: .Ql %l
! 615: (local host name),
! 616: .Ql %n
! 617: (host name as provided on the command line),
! 618: .Ql %p
! 619: (remote port),
! 620: .Ql %r
! 621: (remote user name) or
! 622: .Ql %u
! 623: (local user name).
1.65 reyk 624: This directive is ignored unless
625: .Cm PermitLocalCommand
626: has been enabled.
1.1 stevesk 627: .It Cm LocalForward
1.74 jmc 628: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 629: the secure channel to the specified host and port from the remote machine.
1.49 jmc 630: The first argument must be
1.43 djm 631: .Sm off
1.49 jmc 632: .Oo Ar bind_address : Oc Ar port
1.43 djm 633: .Sm on
1.49 jmc 634: and the second argument must be
635: .Ar host : Ns Ar hostport .
1.46 jmc 636: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 637: by using an alternative syntax:
1.49 jmc 638: .Oo Ar bind_address Ns / Oc Ns Ar port
639: and
640: .Ar host Ns / Ns Ar hostport .
1.46 jmc 641: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 642: given on the command line.
1.1 stevesk 643: Only the superuser can forward privileged ports.
1.43 djm 644: By default, the local port is bound in accordance with the
645: .Cm GatewayPorts
646: setting.
647: However, an explicit
648: .Ar bind_address
649: may be used to bind the connection to a specific address.
650: The
651: .Ar bind_address
652: of
653: .Dq localhost
1.46 jmc 654: indicates that the listening port be bound for local use only, while an
655: empty address or
656: .Sq *
1.43 djm 657: indicates that the port should be available from all interfaces.
1.1 stevesk 658: .It Cm LogLevel
659: Gives the verbosity level that is used when logging messages from
1.84 jmc 660: .Xr ssh 1 .
1.1 stevesk 661: The possible values are:
1.84 jmc 662: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 663: The default is INFO.
664: DEBUG and DEBUG1 are equivalent.
665: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 666: .It Cm MACs
667: Specifies the MAC (message authentication code) algorithms
668: in order of preference.
669: The MAC algorithm is used in protocol version 2
670: for data integrity protection.
671: Multiple algorithms must be comma-separated.
1.84 jmc 672: The default is:
1.101 jmc 673: .Bd -literal -offset indent
674: hmac-md5,hmac-sha1,umac-64@openssh.com,
675: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
676: .Ed
1.1 stevesk 677: .It Cm NoHostAuthenticationForLocalhost
678: This option can be used if the home directory is shared across machines.
679: In this case localhost will refer to a different machine on each of
680: the machines and the user will get many warnings about changed host keys.
681: However, this option disables host authentication for localhost.
682: The argument to this keyword must be
683: .Dq yes
684: or
685: .Dq no .
686: The default is to check the host key for localhost.
687: .It Cm NumberOfPasswordPrompts
688: Specifies the number of password prompts before giving up.
689: The argument to this keyword must be an integer.
1.84 jmc 690: The default is 3.
1.1 stevesk 691: .It Cm PasswordAuthentication
692: Specifies whether to use password authentication.
693: The argument to this keyword must be
694: .Dq yes
695: or
696: .Dq no .
697: The default is
698: .Dq yes .
1.65 reyk 699: .It Cm PermitLocalCommand
700: Allow local command execution via the
701: .Ic LocalCommand
702: option or using the
1.66 jmc 703: .Ic !\& Ns Ar command
1.65 reyk 704: escape sequence in
705: .Xr ssh 1 .
706: The argument must be
707: .Dq yes
708: or
709: .Dq no .
710: The default is
711: .Dq no .
1.67 jmc 712: .It Cm Port
713: Specifies the port number to connect on the remote host.
1.84 jmc 714: The default is 22.
1.1 stevesk 715: .It Cm PreferredAuthentications
716: Specifies the order in which the client should try protocol 2
1.11 jmc 717: authentication methods.
1.48 jmc 718: This allows a client to prefer one method (e.g.\&
1.1 stevesk 719: .Cm keyboard-interactive )
1.48 jmc 720: over another method (e.g.\&
1.1 stevesk 721: .Cm password )
722: The default for this option is:
1.94 jmc 723: .Do gssapi-with-mic ,
724: hostbased,
725: publickey,
726: keyboard-interactive,
727: password
728: .Dc .
1.1 stevesk 729: .It Cm Protocol
730: Specifies the protocol versions
1.84 jmc 731: .Xr ssh 1
1.1 stevesk 732: should support in order of preference.
733: The possible values are
1.84 jmc 734: .Sq 1
1.1 stevesk 735: and
1.84 jmc 736: .Sq 2 .
1.1 stevesk 737: Multiple versions must be comma-separated.
738: The default is
739: .Dq 2,1 .
1.84 jmc 740: This means that ssh
1.1 stevesk 741: tries version 2 and falls back to version 1
742: if version 2 is not available.
743: .It Cm ProxyCommand
744: Specifies the command to use to connect to the server.
745: The command
746: string extends to the end of the line, and is executed with
1.105 jmc 747: the user's shell.
1.1 stevesk 748: In the command string,
749: .Ql %h
750: will be substituted by the host name to
751: connect and
752: .Ql %p
753: by the port.
754: The command can be basically anything,
755: and should read from its standard input and write to its standard output.
756: It should eventually connect an
757: .Xr sshd 8
758: server running on some machine, or execute
759: .Ic sshd -i
760: somewhere.
761: Host key management will be done using the
762: HostName of the host being connected (defaulting to the name typed by
763: the user).
1.7 jmc 764: Setting the command to
765: .Dq none
1.6 markus 766: disables this option entirely.
1.1 stevesk 767: Note that
768: .Cm CheckHostIP
769: is not available for connects with a proxy command.
1.52 djm 770: .Pp
771: This directive is useful in conjunction with
772: .Xr nc 1
773: and its proxy support.
1.53 jmc 774: For example, the following directive would connect via an HTTP proxy at
1.52 djm 775: 192.0.2.0:
776: .Bd -literal -offset 3n
777: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
778: .Ed
1.1 stevesk 779: .It Cm PubkeyAuthentication
780: Specifies whether to try public key authentication.
781: The argument to this keyword must be
782: .Dq yes
783: or
784: .Dq no .
785: The default is
786: .Dq yes .
787: This option applies to protocol version 2 only.
1.75 dtucker 788: .It Cm RekeyLimit
789: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 790: session key is renegotiated.
1.75 dtucker 791: The argument is the number of bytes, with an optional suffix of
1.76 jmc 792: .Sq K ,
793: .Sq M ,
1.75 dtucker 794: or
1.76 jmc 795: .Sq G
1.75 dtucker 796: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
797: The default is between
1.84 jmc 798: .Sq 1G
1.75 dtucker 799: and
1.84 jmc 800: .Sq 4G ,
1.75 dtucker 801: depending on the cipher.
1.76 jmc 802: This option applies to protocol version 2 only.
1.1 stevesk 803: .It Cm RemoteForward
1.74 jmc 804: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 805: the secure channel to the specified host and port from the local machine.
1.49 jmc 806: The first argument must be
1.43 djm 807: .Sm off
1.49 jmc 808: .Oo Ar bind_address : Oc Ar port
1.43 djm 809: .Sm on
1.49 jmc 810: and the second argument must be
811: .Ar host : Ns Ar hostport .
812: IPv6 addresses can be specified by enclosing addresses in square brackets
813: or by using an alternative syntax:
814: .Oo Ar bind_address Ns / Oc Ns Ar port
815: and
816: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 817: Multiple forwardings may be specified, and additional
818: forwardings can be given on the command line.
819: Only the superuser can forward privileged ports.
1.43 djm 820: .Pp
821: If the
822: .Ar bind_address
823: is not specified, the default is to only bind to loopback addresses.
824: If the
825: .Ar bind_address
826: is
827: .Ql *
828: or an empty string, then the forwarding is requested to listen on all
829: interfaces.
830: Specifying a remote
831: .Ar bind_address
1.46 jmc 832: will only succeed if the server's
833: .Cm GatewayPorts
1.43 djm 834: option is enabled (see
1.46 jmc 835: .Xr sshd_config 5 ) .
1.1 stevesk 836: .It Cm RhostsRSAAuthentication
837: Specifies whether to try rhosts based authentication with RSA host
838: authentication.
839: The argument must be
840: .Dq yes
841: or
842: .Dq no .
843: The default is
844: .Dq no .
845: This option applies to protocol version 1 only and requires
1.84 jmc 846: .Xr ssh 1
1.1 stevesk 847: to be setuid root.
848: .It Cm RSAAuthentication
849: Specifies whether to try RSA authentication.
850: The argument to this keyword must be
851: .Dq yes
852: or
853: .Dq no .
854: RSA authentication will only be
855: attempted if the identity file exists, or an authentication agent is
856: running.
857: The default is
858: .Dq yes .
859: Note that this option applies to protocol version 1 only.
1.32 djm 860: .It Cm SendEnv
861: Specifies what variables from the local
862: .Xr environ 7
863: should be sent to the server.
1.84 jmc 864: Note that environment passing is only supported for protocol 2.
865: The server must also support it, and the server must be configured to
1.33 djm 866: accept these environment variables.
1.32 djm 867: Refer to
868: .Cm AcceptEnv
869: in
870: .Xr sshd_config 5
871: for how to configure the server.
1.80 jmc 872: Variables are specified by name, which may contain wildcard characters.
1.33 djm 873: Multiple environment variables may be separated by whitespace or spread
1.32 djm 874: across multiple
875: .Cm SendEnv
876: directives.
877: The default is not to send any environment variables.
1.81 jmc 878: .Pp
879: See
880: .Sx PATTERNS
881: for more information on patterns.
1.28 markus 882: .It Cm ServerAliveCountMax
1.73 jmc 883: Sets the number of server alive messages (see below) which may be
1.28 markus 884: sent without
1.84 jmc 885: .Xr ssh 1
1.28 markus 886: receiving any messages back from the server.
887: If this threshold is reached while server alive messages are being sent,
1.84 jmc 888: ssh will disconnect from the server, terminating the session.
1.28 markus 889: It is important to note that the use of server alive messages is very
890: different from
891: .Cm TCPKeepAlive
892: (below).
893: The server alive messages are sent through the encrypted channel
894: and therefore will not be spoofable.
895: The TCP keepalive option enabled by
896: .Cm TCPKeepAlive
897: is spoofable.
898: The server alive mechanism is valuable when the client or
899: server depend on knowing when a connection has become inactive.
900: .Pp
901: The default value is 3.
902: If, for example,
903: .Cm ServerAliveInterval
1.84 jmc 904: (see below) is set to 15 and
1.28 markus 905: .Cm ServerAliveCountMax
1.84 jmc 906: is left at the default, if the server becomes unresponsive,
907: ssh will disconnect after approximately 45 seconds.
1.89 markus 908: This option applies to protocol version 2 only.
1.67 jmc 909: .It Cm ServerAliveInterval
910: Sets a timeout interval in seconds after which if no data has been received
911: from the server,
1.84 jmc 912: .Xr ssh 1
1.67 jmc 913: will send a message through the encrypted
914: channel to request a response from the server.
915: The default
916: is 0, indicating that these messages will not be sent to the server.
917: This option applies to protocol version 2 only.
1.1 stevesk 918: .It Cm SmartcardDevice
1.11 jmc 919: Specifies which smartcard device to use.
920: The argument to this keyword is the device
1.84 jmc 921: .Xr ssh 1
1.1 stevesk 922: should use to communicate with a smartcard used for storing the user's
1.11 jmc 923: private RSA key.
924: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 925: .It Cm StrictHostKeyChecking
926: If this flag is set to
927: .Dq yes ,
1.84 jmc 928: .Xr ssh 1
1.1 stevesk 929: will never automatically add host keys to the
1.50 djm 930: .Pa ~/.ssh/known_hosts
1.1 stevesk 931: file, and refuses to connect to hosts whose host key has changed.
932: This provides maximum protection against trojan horse attacks,
1.84 jmc 933: though it can be annoying when the
1.1 stevesk 934: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 935: file is poorly maintained or when connections to new hosts are
1.1 stevesk 936: frequently made.
937: This option forces the user to manually
938: add all new hosts.
939: If this flag is set to
940: .Dq no ,
1.84 jmc 941: ssh will automatically add new host keys to the
1.1 stevesk 942: user known hosts files.
943: If this flag is set to
944: .Dq ask ,
945: new host keys
946: will be added to the user known host files only after the user
947: has confirmed that is what they really want to do, and
1.84 jmc 948: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 949: The host keys of
950: known hosts will be verified automatically in all cases.
951: The argument must be
952: .Dq yes ,
1.84 jmc 953: .Dq no ,
1.1 stevesk 954: or
955: .Dq ask .
956: The default is
957: .Dq ask .
1.26 markus 958: .It Cm TCPKeepAlive
959: Specifies whether the system should send TCP keepalive messages to the
960: other side.
961: If they are sent, death of the connection or crash of one
962: of the machines will be properly noticed.
963: However, this means that
964: connections will die if the route is down temporarily, and some people
965: find it annoying.
966: .Pp
967: The default is
968: .Dq yes
969: (to send TCP keepalive messages), and the client will notice
970: if the network goes down or the remote host dies.
971: This is important in scripts, and many users want it too.
972: .Pp
973: To disable TCP keepalive messages, the value should be set to
974: .Dq no .
1.65 reyk 975: .It Cm Tunnel
1.95 stevesk 976: Request
1.65 reyk 977: .Xr tun 4
1.69 jmc 978: device forwarding between the client and the server.
1.65 reyk 979: The argument must be
1.68 reyk 980: .Dq yes ,
1.95 stevesk 981: .Dq point-to-point
982: (layer 3),
983: .Dq ethernet
984: (layer 2),
1.65 reyk 985: or
986: .Dq no .
1.95 stevesk 987: Specifying
988: .Dq yes
989: requests the default tunnel mode, which is
990: .Dq point-to-point .
1.65 reyk 991: The default is
992: .Dq no .
993: .It Cm TunnelDevice
1.95 stevesk 994: Specifies the
1.65 reyk 995: .Xr tun 4
1.95 stevesk 996: devices to open on the client
997: .Pq Ar local_tun
998: and the server
999: .Pq Ar remote_tun .
1000: .Pp
1001: The argument must be
1002: .Sm off
1003: .Ar local_tun Op : Ar remote_tun .
1004: .Sm on
1005: The devices may be specified by numerical ID or the keyword
1006: .Dq any ,
1007: which uses the next available tunnel device.
1008: If
1009: .Ar remote_tun
1010: is not specified, it defaults to
1011: .Dq any .
1012: The default is
1013: .Dq any:any .
1.72 jmc 1014: .It Cm UsePrivilegedPort
1015: Specifies whether to use a privileged port for outgoing connections.
1016: The argument must be
1017: .Dq yes
1018: or
1019: .Dq no .
1020: The default is
1021: .Dq no .
1022: If set to
1.84 jmc 1023: .Dq yes ,
1024: .Xr ssh 1
1.72 jmc 1025: must be setuid root.
1026: Note that this option must be set to
1027: .Dq yes
1028: for
1029: .Cm RhostsRSAAuthentication
1030: with older servers.
1.1 stevesk 1031: .It Cm User
1032: Specifies the user to log in as.
1033: This can be useful when a different user name is used on different machines.
1034: This saves the trouble of
1035: having to remember to give the user name on the command line.
1036: .It Cm UserKnownHostsFile
1037: Specifies a file to use for the user
1038: host key database instead of
1.50 djm 1039: .Pa ~/.ssh/known_hosts .
1.8 jakob 1040: .It Cm VerifyHostKeyDNS
1041: Specifies whether to verify the remote key using DNS and SSHFP resource
1042: records.
1.24 jakob 1043: If this option is set to
1044: .Dq yes ,
1.25 jmc 1045: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1046: from DNS.
1047: Insecure fingerprints will be handled as if this option was set to
1048: .Dq ask .
1049: If this option is set to
1050: .Dq ask ,
1051: information on fingerprint match will be displayed, but the user will still
1052: need to confirm new host keys according to the
1053: .Cm StrictHostKeyChecking
1054: option.
1055: The argument must be
1056: .Dq yes ,
1.84 jmc 1057: .Dq no ,
1.25 jmc 1058: or
1059: .Dq ask .
1.8 jakob 1060: The default is
1061: .Dq no .
1.12 jakob 1062: Note that this option applies to protocol version 2 only.
1.84 jmc 1063: .Pp
1064: See also
1065: .Sx VERIFYING HOST KEYS
1066: in
1067: .Xr ssh 1 .
1.1 stevesk 1068: .It Cm XAuthLocation
1.5 stevesk 1069: Specifies the full pathname of the
1.1 stevesk 1070: .Xr xauth 1
1071: program.
1072: The default is
1073: .Pa /usr/X11R6/bin/xauth .
1074: .El
1.86 jmc 1075: .Sh PATTERNS
1076: A
1077: .Em pattern
1078: consists of zero or more non-whitespace characters,
1079: .Sq *
1080: (a wildcard that matches zero or more characters),
1081: or
1082: .Sq ?\&
1083: (a wildcard that matches exactly one character).
1084: For example, to specify a set of declarations for any host in the
1085: .Dq .co.uk
1086: set of domains,
1087: the following pattern could be used:
1088: .Pp
1089: .Dl Host *.co.uk
1090: .Pp
1091: The following pattern
1092: would match any host in the 192.168.0.[0-9] network range:
1093: .Pp
1094: .Dl Host 192.168.0.?
1095: .Pp
1096: A
1097: .Em pattern-list
1098: is a comma-separated list of patterns.
1099: Patterns within pattern-lists may be negated
1100: by preceding them with an exclamation mark
1101: .Pq Sq !\& .
1102: For example,
1103: to allow a key to be used from anywhere within an organisation
1104: except from the
1105: .Dq dialup
1106: pool,
1107: the following entry (in authorized_keys) could be used:
1108: .Pp
1109: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1110: .Sh FILES
1111: .Bl -tag -width Ds
1.50 djm 1112: .It Pa ~/.ssh/config
1.1 stevesk 1113: This is the per-user configuration file.
1114: The format of this file is described above.
1.84 jmc 1115: This file is used by the SSH client.
1.30 djm 1116: Because of the potential for abuse, this file must have strict permissions:
1117: read/write for the user, and not accessible by others.
1.1 stevesk 1118: .It Pa /etc/ssh/ssh_config
1119: Systemwide configuration file.
1120: This file provides defaults for those
1121: values that are not specified in the user's configuration file, and
1122: for those users who do not have a configuration file.
1123: This file must be world-readable.
1124: .El
1.13 jmc 1125: .Sh SEE ALSO
1126: .Xr ssh 1
1.1 stevesk 1127: .Sh AUTHORS
1128: OpenSSH is a derivative of the original and free
1129: ssh 1.2.12 release by Tatu Ylonen.
1130: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1131: Theo de Raadt and Dug Song
1132: removed many bugs, re-added newer features and
1133: created OpenSSH.
1134: Markus Friedl contributed the support for SSH
1135: protocol versions 1.5 and 2.0.
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