Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.85
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: .\"
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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1.85 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.84 2006/02/24 23:20:07 jmc Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
1.50 djm 46: .It Pa ~/.ssh/config
1.1 stevesk 47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
1.84 jmc 50: .Xr ssh 1
1.1 stevesk 51: obtains configuration data from the following sources in
52: the following order:
1.79 jmc 53: .Pp
1.2 stevesk 54: .Bl -enum -offset indent -compact
55: .It
56: command-line options
57: .It
58: user's configuration file
1.50 djm 59: .Pq Pa ~/.ssh/config
1.2 stevesk 60: .It
61: system-wide configuration file
62: .Pq Pa /etc/ssh/ssh_config
63: .El
1.1 stevesk 64: .Pp
65: For each parameter, the first obtained value
66: will be used.
1.41 jmc 67: The configuration files contain sections separated by
1.1 stevesk 68: .Dq Host
69: specifications, and that section is only applied for hosts that
70: match one of the patterns given in the specification.
71: The matched host name is the one given on the command line.
72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 jmc 76: .Sh PATTERNS
77: A
78: .Em pattern
79: consists of zero or more non-whitespace characters,
80: .Sq *
81: (a wildcard that matches zero or more characters),
82: or
83: .Sq ?\&
84: (a wildcard that matches exactly one character).
85: For example, to specify a set of declarations for any host in the
86: .Dq .co.uk
87: set of domains,
88: the following pattern could be used:
89: .Pp
90: .Dl Host *.co.uk
91: .Pp
92: The following pattern
93: would match any host in the 192.168.0.[0-9] network range:
94: .Pp
95: .Dl Host 192.168.0.?
96: .Pp
97: A
98: .Em pattern-list
99: is a comma-separated list of patterns.
100: Patterns within pattern-lists may be negated
101: by preceding them with an exclamation mark
102: .Pq Sq !\& .
103: For example,
104: to allow a key to be used from anywhere within an organisation
105: except from the
106: .Dq dialup
107: pool,
108: the following entry (in authorized_keys) could be used:
1.1 stevesk 109: .Pp
1.80 jmc 110: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
111: .Sh FILE FORMAT
1.1 stevesk 112: The configuration file has the following format:
113: .Pp
114: Empty lines and lines starting with
115: .Ql #
116: are comments.
117: Otherwise a line is of the format
118: .Dq keyword arguments .
119: Configuration options may be separated by whitespace or
120: optional whitespace and exactly one
121: .Ql = ;
122: the latter format is useful to avoid the need to quote whitespace
123: when specifying configuration options using the
124: .Nm ssh ,
125: .Nm scp
126: and
127: .Nm sftp
128: .Fl o
129: option.
130: .Pp
131: The possible
132: keywords and their meanings are as follows (note that
133: keywords are case-insensitive and arguments are case-sensitive):
134: .Bl -tag -width Ds
135: .It Cm Host
136: Restricts the following declarations (up to the next
137: .Cm Host
138: keyword) to be only for those hosts that match one of the patterns
139: given after the keyword.
140: A single
1.83 jmc 141: .Ql *
1.1 stevesk 142: as a pattern can be used to provide global
143: defaults for all hosts.
144: The host is the
145: .Ar hostname
1.83 jmc 146: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 147: a canonicalized host name before matching).
1.81 jmc 148: .Pp
149: See
150: .Sx PATTERNS
151: for more information on patterns.
1.10 djm 152: .It Cm AddressFamily
1.11 jmc 153: Specifies which address family to use when connecting.
154: Valid arguments are
1.10 djm 155: .Dq any ,
156: .Dq inet
1.84 jmc 157: (use IPv4 only), or
1.10 djm 158: .Dq inet6
1.40 jmc 159: (use IPv6 only).
1.1 stevesk 160: .It Cm BatchMode
161: If set to
162: .Dq yes ,
163: passphrase/password querying will be disabled.
164: This option is useful in scripts and other batch jobs where no user
165: is present to supply the password.
166: The argument must be
167: .Dq yes
168: or
169: .Dq no .
170: The default is
171: .Dq no .
172: .It Cm BindAddress
1.60 dtucker 173: Use the specified address on the local machine as the source address of
1.61 jmc 174: the connection.
175: Only useful on systems with more than one address.
1.1 stevesk 176: Note that this option does not work if
177: .Cm UsePrivilegedPort
178: is set to
179: .Dq yes .
180: .It Cm ChallengeResponseAuthentication
1.82 jmc 181: Specifies whether to use challenge-response authentication.
1.1 stevesk 182: The argument to this keyword must be
183: .Dq yes
184: or
185: .Dq no .
186: The default is
187: .Dq yes .
188: .It Cm CheckHostIP
189: If this flag is set to
190: .Dq yes ,
1.84 jmc 191: .Xr ssh 1
192: will additionally check the host IP address in the
1.1 stevesk 193: .Pa known_hosts
194: file.
195: This allows ssh to detect if a host key changed due to DNS spoofing.
196: If the option is set to
197: .Dq no ,
198: the check will not be executed.
199: The default is
200: .Dq yes .
201: .It Cm Cipher
202: Specifies the cipher to use for encrypting the session
203: in protocol version 1.
204: Currently,
205: .Dq blowfish ,
206: .Dq 3des ,
207: and
208: .Dq des
209: are supported.
210: .Ar des
211: is only supported in the
1.84 jmc 212: .Xr ssh 1
1.1 stevesk 213: client for interoperability with legacy protocol 1 implementations
214: that do not support the
215: .Ar 3des
1.7 jmc 216: cipher.
217: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 218: The default is
219: .Dq 3des .
220: .It Cm Ciphers
221: Specifies the ciphers allowed for protocol version 2
222: in order of preference.
223: Multiple ciphers must be comma-separated.
1.35 dtucker 224: The supported ciphers are
225: .Dq 3des-cbc ,
226: .Dq aes128-cbc ,
227: .Dq aes192-cbc ,
228: .Dq aes256-cbc ,
229: .Dq aes128-ctr ,
230: .Dq aes192-ctr ,
231: .Dq aes256-ctr ,
1.54 djm 232: .Dq arcfour128 ,
233: .Dq arcfour256 ,
1.35 dtucker 234: .Dq arcfour ,
235: .Dq blowfish-cbc ,
236: and
237: .Dq cast128-cbc .
1.84 jmc 238: The default is:
239: .Bd -literal -offset 3n
240: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
241: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
242: aes192-ctr,aes256-ctr
1.1 stevesk 243: .Ed
244: .It Cm ClearAllForwardings
1.84 jmc 245: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 246: specified in the configuration files or on the command line be
1.7 jmc 247: cleared.
248: This option is primarily useful when used from the
1.84 jmc 249: .Xr ssh 1
1.1 stevesk 250: command line to clear port forwardings set in
251: configuration files, and is automatically set by
252: .Xr scp 1
253: and
254: .Xr sftp 1 .
255: The argument must be
256: .Dq yes
257: or
258: .Dq no .
259: The default is
260: .Dq no .
261: .It Cm Compression
262: Specifies whether to use compression.
263: The argument must be
264: .Dq yes
265: or
266: .Dq no .
267: The default is
268: .Dq no .
269: .It Cm CompressionLevel
270: Specifies the compression level to use if compression is enabled.
271: The argument must be an integer from 1 (fast) to 9 (slow, best).
272: The default level is 6, which is good for most applications.
273: The meaning of the values is the same as in
274: .Xr gzip 1 .
275: Note that this option applies to protocol version 1 only.
276: .It Cm ConnectionAttempts
277: Specifies the number of tries (one per second) to make before exiting.
278: The argument must be an integer.
279: This may be useful in scripts if the connection sometimes fails.
280: The default is 1.
1.9 djm 281: .It Cm ConnectTimeout
1.84 jmc 282: Specifies the timeout (in seconds) used when connecting to the
283: SSH server, instead of using the default system TCP timeout.
1.11 jmc 284: This value is used only when the target is down or really unreachable,
285: not when it refuses the connection.
1.36 djm 286: .It Cm ControlMaster
287: Enables the sharing of multiple sessions over a single network connection.
288: When set to
1.84 jmc 289: .Dq yes ,
290: .Xr ssh 1
1.36 djm 291: will listen for connections on a control socket specified using the
292: .Cm ControlPath
293: argument.
294: Additional sessions can connect to this socket using the same
295: .Cm ControlPath
296: with
297: .Cm ControlMaster
298: set to
299: .Dq no
1.38 jmc 300: (the default).
1.64 jmc 301: These sessions will try to reuse the master instance's network connection
1.63 djm 302: rather than initiating new ones, but will fall back to connecting normally
303: if the control socket does not exist, or is not listening.
304: .Pp
1.37 djm 305: Setting this to
306: .Dq ask
1.84 jmc 307: will cause ssh
1.37 djm 308: to listen for control connections, but require confirmation using the
309: .Ev SSH_ASKPASS
310: program before they are accepted (see
311: .Xr ssh-add 1
1.38 jmc 312: for details).
1.51 jakob 313: If the
314: .Cm ControlPath
1.84 jmc 315: cannot be opened,
316: ssh will continue without connecting to a master instance.
1.58 djm 317: .Pp
318: X11 and
1.59 jmc 319: .Xr ssh-agent 1
1.58 djm 320: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 321: display and agent forwarded will be the one belonging to the master
1.59 jmc 322: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 323: .Pp
324: Two additional options allow for opportunistic multiplexing: try to use a
325: master connection but fall back to creating a new one if one does not already
326: exist.
327: These options are:
328: .Dq auto
329: and
330: .Dq autoask .
331: The latter requires confirmation like the
332: .Dq ask
333: option.
1.36 djm 334: .It Cm ControlPath
1.55 djm 335: Specify the path to the control socket used for connection sharing as described
336: in the
1.36 djm 337: .Cm ControlMaster
1.57 djm 338: section above or the string
339: .Dq none
340: to disable connection sharing.
1.55 djm 341: In the path,
1.77 djm 342: .Ql %l
343: will be substituted by the local host name,
1.55 djm 344: .Ql %h
345: will be substituted by the target host name,
346: .Ql %p
1.84 jmc 347: the port, and
1.55 djm 348: .Ql %r
349: by the remote login username.
1.56 djm 350: It is recommended that any
351: .Cm ControlPath
352: used for opportunistic connection sharing include
1.78 jmc 353: at least %h, %p, and %r.
1.56 djm 354: This ensures that shared connections are uniquely identified.
1.38 jmc 355: .It Cm DynamicForward
1.74 jmc 356: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 357: over the secure channel, and the application
358: protocol is then used to determine where to connect to from the
359: remote machine.
1.62 djm 360: .Pp
361: The argument must be
362: .Sm off
363: .Oo Ar bind_address : Oc Ar port .
364: .Sm on
365: IPv6 addresses can be specified by enclosing addresses in square brackets or
366: by using an alternative syntax:
367: .Oo Ar bind_address Ns / Oc Ns Ar port .
368: By default, the local port is bound in accordance with the
369: .Cm GatewayPorts
370: setting.
371: However, an explicit
372: .Ar bind_address
373: may be used to bind the connection to a specific address.
374: The
375: .Ar bind_address
376: of
377: .Dq localhost
378: indicates that the listening port be bound for local use only, while an
379: empty address or
380: .Sq *
381: indicates that the port should be available from all interfaces.
382: .Pp
1.38 jmc 383: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 384: .Xr ssh 1
1.38 jmc 385: will act as a SOCKS server.
386: Multiple forwardings may be specified, and
387: additional forwardings can be given on the command line.
388: Only the superuser can forward privileged ports.
1.14 markus 389: .It Cm EnableSSHKeysign
390: Setting this option to
391: .Dq yes
392: in the global client configuration file
393: .Pa /etc/ssh/ssh_config
394: enables the use of the helper program
395: .Xr ssh-keysign 8
396: during
397: .Cm HostbasedAuthentication .
398: The argument must be
399: .Dq yes
400: or
401: .Dq no .
402: The default is
403: .Dq no .
1.23 jmc 404: This option should be placed in the non-hostspecific section.
1.14 markus 405: See
406: .Xr ssh-keysign 8
407: for more information.
1.1 stevesk 408: .It Cm EscapeChar
409: Sets the escape character (default:
410: .Ql ~ ) .
411: The escape character can also
412: be set on the command line.
413: The argument should be a single character,
414: .Ql ^
415: followed by a letter, or
416: .Dq none
417: to disable the escape
418: character entirely (making the connection transparent for binary
419: data).
420: .It Cm ForwardAgent
421: Specifies whether the connection to the authentication agent (if any)
422: will be forwarded to the remote machine.
423: The argument must be
424: .Dq yes
425: or
426: .Dq no .
427: The default is
428: .Dq no .
1.3 stevesk 429: .Pp
1.7 jmc 430: Agent forwarding should be enabled with caution.
431: Users with the ability to bypass file permissions on the remote host
432: (for the agent's Unix-domain socket)
433: can access the local agent through the forwarded connection.
434: An attacker cannot obtain key material from the agent,
1.3 stevesk 435: however they can perform operations on the keys that enable them to
436: authenticate using the identities loaded into the agent.
1.1 stevesk 437: .It Cm ForwardX11
438: Specifies whether X11 connections will be automatically redirected
439: over the secure channel and
440: .Ev DISPLAY
441: set.
442: The argument must be
443: .Dq yes
444: or
445: .Dq no .
446: The default is
447: .Dq no .
1.3 stevesk 448: .Pp
1.7 jmc 449: X11 forwarding should be enabled with caution.
450: Users with the ability to bypass file permissions on the remote host
1.22 markus 451: (for the user's X11 authorization database)
1.7 jmc 452: can access the local X11 display through the forwarded connection.
1.22 markus 453: An attacker may then be able to perform activities such as keystroke monitoring
454: if the
455: .Cm ForwardX11Trusted
456: option is also enabled.
457: .It Cm ForwardX11Trusted
1.34 jmc 458: If this option is set to
1.84 jmc 459: .Dq yes ,
460: remote X11 clients will have full access to the original X11 display.
1.42 djm 461: .Pp
1.22 markus 462: If this option is set to
1.84 jmc 463: .Dq no ,
464: remote X11 clients will be considered untrusted and prevented
1.22 markus 465: from stealing or tampering with data belonging to trusted X11
466: clients.
1.42 djm 467: Furthermore, the
468: .Xr xauth 1
469: token used for the session will be set to expire after 20 minutes.
470: Remote clients will be refused access after this time.
1.22 markus 471: .Pp
472: The default is
473: .Dq no .
474: .Pp
475: See the X11 SECURITY extension specification for full details on
476: the restrictions imposed on untrusted clients.
1.1 stevesk 477: .It Cm GatewayPorts
478: Specifies whether remote hosts are allowed to connect to local
479: forwarded ports.
480: By default,
1.84 jmc 481: .Xr ssh 1
1.7 jmc 482: binds local port forwardings to the loopback address.
483: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 484: .Cm GatewayPorts
1.84 jmc 485: can be used to specify that ssh
1.1 stevesk 486: should bind local port forwardings to the wildcard address,
487: thus allowing remote hosts to connect to forwarded ports.
488: The argument must be
489: .Dq yes
490: or
491: .Dq no .
492: The default is
493: .Dq no .
494: .It Cm GlobalKnownHostsFile
495: Specifies a file to use for the global
496: host key database instead of
497: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 498: .It Cm GSSAPIAuthentication
1.27 markus 499: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 500: The default is
1.21 markus 501: .Dq no .
1.18 markus 502: Note that this option applies to protocol version 2 only.
503: .It Cm GSSAPIDelegateCredentials
504: Forward (delegate) credentials to the server.
505: The default is
506: .Dq no .
507: Note that this option applies to protocol version 2 only.
1.44 djm 508: .It Cm HashKnownHosts
509: Indicates that
1.84 jmc 510: .Xr ssh 1
1.44 djm 511: should hash host names and addresses when they are added to
1.50 djm 512: .Pa ~/.ssh/known_hosts .
1.44 djm 513: These hashed names may be used normally by
1.84 jmc 514: .Xr ssh 1
1.44 djm 515: and
1.84 jmc 516: .Xr sshd 8 ,
1.44 djm 517: but they do not reveal identifying information should the file's contents
518: be disclosed.
519: The default is
520: .Dq no .
1.46 jmc 521: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 522: to existing known hosts files, but these may be manually hashed using
523: .Xr ssh-keygen 1 .
1.1 stevesk 524: .It Cm HostbasedAuthentication
525: Specifies whether to try rhosts based authentication with public key
526: authentication.
527: The argument must be
528: .Dq yes
529: or
530: .Dq no .
531: The default is
532: .Dq no .
533: This option applies to protocol version 2 only and
534: is similar to
535: .Cm RhostsRSAAuthentication .
536: .It Cm HostKeyAlgorithms
537: Specifies the protocol version 2 host key algorithms
538: that the client wants to use in order of preference.
539: The default for this option is:
540: .Dq ssh-rsa,ssh-dss .
541: .It Cm HostKeyAlias
542: Specifies an alias that should be used instead of the
543: real host name when looking up or saving the host key
544: in the host key database files.
1.84 jmc 545: This option is useful for tunneling SSH connections
1.1 stevesk 546: or for multiple servers running on a single host.
547: .It Cm HostName
548: Specifies the real host name to log into.
549: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 550: The default is the name given on the command line.
1.1 stevesk 551: Numeric IP addresses are also permitted (both on the command line and in
552: .Cm HostName
553: specifications).
1.29 markus 554: .It Cm IdentitiesOnly
555: Specifies that
1.84 jmc 556: .Xr ssh 1
1.29 markus 557: should only use the authentication identity files configured in the
1.31 jmc 558: .Nm
1.29 markus 559: files,
1.84 jmc 560: even if
561: .Xr ssh-agent 1
1.29 markus 562: offers more identities.
563: The argument to this keyword must be
564: .Dq yes
565: or
566: .Dq no .
1.84 jmc 567: This option is intended for situations where ssh-agent
1.29 markus 568: offers many different identities.
569: The default is
570: .Dq no .
1.67 jmc 571: .It Cm IdentityFile
572: Specifies a file from which the user's RSA or DSA authentication identity
573: is read.
574: The default is
575: .Pa ~/.ssh/identity
576: for protocol version 1, and
577: .Pa ~/.ssh/id_rsa
578: and
579: .Pa ~/.ssh/id_dsa
580: for protocol version 2.
581: Additionally, any identities represented by the authentication agent
582: will be used for authentication.
583: The file name may use the tilde
584: syntax to refer to a user's home directory.
585: It is possible to have
586: multiple identity files specified in configuration files; all these
587: identities will be tried in sequence.
1.39 djm 588: .It Cm KbdInteractiveDevices
589: Specifies the list of methods to use in keyboard-interactive authentication.
590: Multiple method names must be comma-separated.
591: The default is to use the server specified list.
1.85 ! jmc 592: The methods available vary depending on what the server supports.
! 593: For an OpenSSH server,
! 594: it may be zero or more of:
! 595: .Dq bsdauth ,
! 596: .Dq pam ,
! 597: and
! 598: .Dq skey .
1.65 reyk 599: .It Cm LocalCommand
600: Specifies a command to execute on the local machine after successfully
601: connecting to the server.
602: The command string extends to the end of the line, and is executed with
603: .Pa /bin/sh .
604: This directive is ignored unless
605: .Cm PermitLocalCommand
606: has been enabled.
1.1 stevesk 607: .It Cm LocalForward
1.74 jmc 608: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 609: the secure channel to the specified host and port from the remote machine.
1.49 jmc 610: The first argument must be
1.43 djm 611: .Sm off
1.49 jmc 612: .Oo Ar bind_address : Oc Ar port
1.43 djm 613: .Sm on
1.49 jmc 614: and the second argument must be
615: .Ar host : Ns Ar hostport .
1.46 jmc 616: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 617: by using an alternative syntax:
1.49 jmc 618: .Oo Ar bind_address Ns / Oc Ns Ar port
619: and
620: .Ar host Ns / Ns Ar hostport .
1.46 jmc 621: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 622: given on the command line.
1.1 stevesk 623: Only the superuser can forward privileged ports.
1.43 djm 624: By default, the local port is bound in accordance with the
625: .Cm GatewayPorts
626: setting.
627: However, an explicit
628: .Ar bind_address
629: may be used to bind the connection to a specific address.
630: The
631: .Ar bind_address
632: of
633: .Dq localhost
1.46 jmc 634: indicates that the listening port be bound for local use only, while an
635: empty address or
636: .Sq *
1.43 djm 637: indicates that the port should be available from all interfaces.
1.1 stevesk 638: .It Cm LogLevel
639: Gives the verbosity level that is used when logging messages from
1.84 jmc 640: .Xr ssh 1 .
1.1 stevesk 641: The possible values are:
1.84 jmc 642: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 643: The default is INFO.
644: DEBUG and DEBUG1 are equivalent.
645: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 646: .It Cm MACs
647: Specifies the MAC (message authentication code) algorithms
648: in order of preference.
649: The MAC algorithm is used in protocol version 2
650: for data integrity protection.
651: Multiple algorithms must be comma-separated.
1.84 jmc 652: The default is:
1.1 stevesk 653: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
654: .It Cm NoHostAuthenticationForLocalhost
655: This option can be used if the home directory is shared across machines.
656: In this case localhost will refer to a different machine on each of
657: the machines and the user will get many warnings about changed host keys.
658: However, this option disables host authentication for localhost.
659: The argument to this keyword must be
660: .Dq yes
661: or
662: .Dq no .
663: The default is to check the host key for localhost.
664: .It Cm NumberOfPasswordPrompts
665: Specifies the number of password prompts before giving up.
666: The argument to this keyword must be an integer.
1.84 jmc 667: The default is 3.
1.1 stevesk 668: .It Cm PasswordAuthentication
669: Specifies whether to use password authentication.
670: The argument to this keyword must be
671: .Dq yes
672: or
673: .Dq no .
674: The default is
675: .Dq yes .
1.65 reyk 676: .It Cm PermitLocalCommand
677: Allow local command execution via the
678: .Ic LocalCommand
679: option or using the
1.66 jmc 680: .Ic !\& Ns Ar command
1.65 reyk 681: escape sequence in
682: .Xr ssh 1 .
683: The argument must be
684: .Dq yes
685: or
686: .Dq no .
687: The default is
688: .Dq no .
1.67 jmc 689: .It Cm Port
690: Specifies the port number to connect on the remote host.
1.84 jmc 691: The default is 22.
1.1 stevesk 692: .It Cm PreferredAuthentications
693: Specifies the order in which the client should try protocol 2
1.11 jmc 694: authentication methods.
1.48 jmc 695: This allows a client to prefer one method (e.g.\&
1.1 stevesk 696: .Cm keyboard-interactive )
1.48 jmc 697: over another method (e.g.\&
1.1 stevesk 698: .Cm password )
699: The default for this option is:
700: .Dq hostbased,publickey,keyboard-interactive,password .
701: .It Cm Protocol
702: Specifies the protocol versions
1.84 jmc 703: .Xr ssh 1
1.1 stevesk 704: should support in order of preference.
705: The possible values are
1.84 jmc 706: .Sq 1
1.1 stevesk 707: and
1.84 jmc 708: .Sq 2 .
1.1 stevesk 709: Multiple versions must be comma-separated.
710: The default is
711: .Dq 2,1 .
1.84 jmc 712: This means that ssh
1.1 stevesk 713: tries version 2 and falls back to version 1
714: if version 2 is not available.
715: .It Cm ProxyCommand
716: Specifies the command to use to connect to the server.
717: The command
718: string extends to the end of the line, and is executed with
719: .Pa /bin/sh .
720: In the command string,
721: .Ql %h
722: will be substituted by the host name to
723: connect and
724: .Ql %p
725: by the port.
726: The command can be basically anything,
727: and should read from its standard input and write to its standard output.
728: It should eventually connect an
729: .Xr sshd 8
730: server running on some machine, or execute
731: .Ic sshd -i
732: somewhere.
733: Host key management will be done using the
734: HostName of the host being connected (defaulting to the name typed by
735: the user).
1.7 jmc 736: Setting the command to
737: .Dq none
1.6 markus 738: disables this option entirely.
1.1 stevesk 739: Note that
740: .Cm CheckHostIP
741: is not available for connects with a proxy command.
1.52 djm 742: .Pp
743: This directive is useful in conjunction with
744: .Xr nc 1
745: and its proxy support.
1.53 jmc 746: For example, the following directive would connect via an HTTP proxy at
1.52 djm 747: 192.0.2.0:
748: .Bd -literal -offset 3n
749: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
750: .Ed
1.1 stevesk 751: .It Cm PubkeyAuthentication
752: Specifies whether to try public key authentication.
753: The argument to this keyword must be
754: .Dq yes
755: or
756: .Dq no .
757: The default is
758: .Dq yes .
759: This option applies to protocol version 2 only.
1.75 dtucker 760: .It Cm RekeyLimit
761: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 762: session key is renegotiated.
1.75 dtucker 763: The argument is the number of bytes, with an optional suffix of
1.76 jmc 764: .Sq K ,
765: .Sq M ,
1.75 dtucker 766: or
1.76 jmc 767: .Sq G
1.75 dtucker 768: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
769: The default is between
1.84 jmc 770: .Sq 1G
1.75 dtucker 771: and
1.84 jmc 772: .Sq 4G ,
1.75 dtucker 773: depending on the cipher.
1.76 jmc 774: This option applies to protocol version 2 only.
1.1 stevesk 775: .It Cm RemoteForward
1.74 jmc 776: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 777: the secure channel to the specified host and port from the local machine.
1.49 jmc 778: The first argument must be
1.43 djm 779: .Sm off
1.49 jmc 780: .Oo Ar bind_address : Oc Ar port
1.43 djm 781: .Sm on
1.49 jmc 782: and the second argument must be
783: .Ar host : Ns Ar hostport .
784: IPv6 addresses can be specified by enclosing addresses in square brackets
785: or by using an alternative syntax:
786: .Oo Ar bind_address Ns / Oc Ns Ar port
787: and
788: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 789: Multiple forwardings may be specified, and additional
790: forwardings can be given on the command line.
791: Only the superuser can forward privileged ports.
1.43 djm 792: .Pp
793: If the
794: .Ar bind_address
795: is not specified, the default is to only bind to loopback addresses.
796: If the
797: .Ar bind_address
798: is
799: .Ql *
800: or an empty string, then the forwarding is requested to listen on all
801: interfaces.
802: Specifying a remote
803: .Ar bind_address
1.46 jmc 804: will only succeed if the server's
805: .Cm GatewayPorts
1.43 djm 806: option is enabled (see
1.46 jmc 807: .Xr sshd_config 5 ) .
1.1 stevesk 808: .It Cm RhostsRSAAuthentication
809: Specifies whether to try rhosts based authentication with RSA host
810: authentication.
811: The argument must be
812: .Dq yes
813: or
814: .Dq no .
815: The default is
816: .Dq no .
817: This option applies to protocol version 1 only and requires
1.84 jmc 818: .Xr ssh 1
1.1 stevesk 819: to be setuid root.
820: .It Cm RSAAuthentication
821: Specifies whether to try RSA authentication.
822: The argument to this keyword must be
823: .Dq yes
824: or
825: .Dq no .
826: RSA authentication will only be
827: attempted if the identity file exists, or an authentication agent is
828: running.
829: The default is
830: .Dq yes .
831: Note that this option applies to protocol version 1 only.
1.32 djm 832: .It Cm SendEnv
833: Specifies what variables from the local
834: .Xr environ 7
835: should be sent to the server.
1.84 jmc 836: Note that environment passing is only supported for protocol 2.
837: The server must also support it, and the server must be configured to
1.33 djm 838: accept these environment variables.
1.32 djm 839: Refer to
840: .Cm AcceptEnv
841: in
842: .Xr sshd_config 5
843: for how to configure the server.
1.80 jmc 844: Variables are specified by name, which may contain wildcard characters.
1.33 djm 845: Multiple environment variables may be separated by whitespace or spread
1.32 djm 846: across multiple
847: .Cm SendEnv
848: directives.
849: The default is not to send any environment variables.
1.81 jmc 850: .Pp
851: See
852: .Sx PATTERNS
853: for more information on patterns.
1.28 markus 854: .It Cm ServerAliveCountMax
1.73 jmc 855: Sets the number of server alive messages (see below) which may be
1.28 markus 856: sent without
1.84 jmc 857: .Xr ssh 1
1.28 markus 858: receiving any messages back from the server.
859: If this threshold is reached while server alive messages are being sent,
1.84 jmc 860: ssh will disconnect from the server, terminating the session.
1.28 markus 861: It is important to note that the use of server alive messages is very
862: different from
863: .Cm TCPKeepAlive
864: (below).
865: The server alive messages are sent through the encrypted channel
866: and therefore will not be spoofable.
867: The TCP keepalive option enabled by
868: .Cm TCPKeepAlive
869: is spoofable.
870: The server alive mechanism is valuable when the client or
871: server depend on knowing when a connection has become inactive.
872: .Pp
873: The default value is 3.
874: If, for example,
875: .Cm ServerAliveInterval
1.84 jmc 876: (see below) is set to 15 and
1.28 markus 877: .Cm ServerAliveCountMax
1.84 jmc 878: is left at the default, if the server becomes unresponsive,
879: ssh will disconnect after approximately 45 seconds.
1.67 jmc 880: .It Cm ServerAliveInterval
881: Sets a timeout interval in seconds after which if no data has been received
882: from the server,
1.84 jmc 883: .Xr ssh 1
1.67 jmc 884: will send a message through the encrypted
885: channel to request a response from the server.
886: The default
887: is 0, indicating that these messages will not be sent to the server.
888: This option applies to protocol version 2 only.
1.1 stevesk 889: .It Cm SmartcardDevice
1.11 jmc 890: Specifies which smartcard device to use.
891: The argument to this keyword is the device
1.84 jmc 892: .Xr ssh 1
1.1 stevesk 893: should use to communicate with a smartcard used for storing the user's
1.11 jmc 894: private RSA key.
895: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 896: .It Cm StrictHostKeyChecking
897: If this flag is set to
898: .Dq yes ,
1.84 jmc 899: .Xr ssh 1
1.1 stevesk 900: will never automatically add host keys to the
1.50 djm 901: .Pa ~/.ssh/known_hosts
1.1 stevesk 902: file, and refuses to connect to hosts whose host key has changed.
903: This provides maximum protection against trojan horse attacks,
1.84 jmc 904: though it can be annoying when the
1.1 stevesk 905: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 906: file is poorly maintained or when connections to new hosts are
1.1 stevesk 907: frequently made.
908: This option forces the user to manually
909: add all new hosts.
910: If this flag is set to
911: .Dq no ,
1.84 jmc 912: ssh will automatically add new host keys to the
1.1 stevesk 913: user known hosts files.
914: If this flag is set to
915: .Dq ask ,
916: new host keys
917: will be added to the user known host files only after the user
918: has confirmed that is what they really want to do, and
1.84 jmc 919: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 920: The host keys of
921: known hosts will be verified automatically in all cases.
922: The argument must be
923: .Dq yes ,
1.84 jmc 924: .Dq no ,
1.1 stevesk 925: or
926: .Dq ask .
927: The default is
928: .Dq ask .
1.26 markus 929: .It Cm TCPKeepAlive
930: Specifies whether the system should send TCP keepalive messages to the
931: other side.
932: If they are sent, death of the connection or crash of one
933: of the machines will be properly noticed.
934: However, this means that
935: connections will die if the route is down temporarily, and some people
936: find it annoying.
937: .Pp
938: The default is
939: .Dq yes
940: (to send TCP keepalive messages), and the client will notice
941: if the network goes down or the remote host dies.
942: This is important in scripts, and many users want it too.
943: .Pp
944: To disable TCP keepalive messages, the value should be set to
945: .Dq no .
1.65 reyk 946: .It Cm Tunnel
947: Request starting
948: .Xr tun 4
1.69 jmc 949: device forwarding between the client and the server.
950: This option also allows requesting layer 2 (ethernet)
951: instead of layer 3 (point-to-point) tunneling from the server.
1.65 reyk 952: The argument must be
1.68 reyk 953: .Dq yes ,
954: .Dq point-to-point ,
1.84 jmc 955: .Dq ethernet ,
1.65 reyk 956: or
957: .Dq no .
958: The default is
959: .Dq no .
960: .It Cm TunnelDevice
961: Force a specified
962: .Xr tun 4
963: device on the client.
964: Without this option, the next available device will be used.
1.72 jmc 965: .It Cm UsePrivilegedPort
966: Specifies whether to use a privileged port for outgoing connections.
967: The argument must be
968: .Dq yes
969: or
970: .Dq no .
971: The default is
972: .Dq no .
973: If set to
1.84 jmc 974: .Dq yes ,
975: .Xr ssh 1
1.72 jmc 976: must be setuid root.
977: Note that this option must be set to
978: .Dq yes
979: for
980: .Cm RhostsRSAAuthentication
981: with older servers.
1.1 stevesk 982: .It Cm User
983: Specifies the user to log in as.
984: This can be useful when a different user name is used on different machines.
985: This saves the trouble of
986: having to remember to give the user name on the command line.
987: .It Cm UserKnownHostsFile
988: Specifies a file to use for the user
989: host key database instead of
1.50 djm 990: .Pa ~/.ssh/known_hosts .
1.8 jakob 991: .It Cm VerifyHostKeyDNS
992: Specifies whether to verify the remote key using DNS and SSHFP resource
993: records.
1.24 jakob 994: If this option is set to
995: .Dq yes ,
1.25 jmc 996: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 997: from DNS.
998: Insecure fingerprints will be handled as if this option was set to
999: .Dq ask .
1000: If this option is set to
1001: .Dq ask ,
1002: information on fingerprint match will be displayed, but the user will still
1003: need to confirm new host keys according to the
1004: .Cm StrictHostKeyChecking
1005: option.
1006: The argument must be
1007: .Dq yes ,
1.84 jmc 1008: .Dq no ,
1.25 jmc 1009: or
1010: .Dq ask .
1.8 jakob 1011: The default is
1012: .Dq no .
1.12 jakob 1013: Note that this option applies to protocol version 2 only.
1.84 jmc 1014: .Pp
1015: See also
1016: .Sx VERIFYING HOST KEYS
1017: in
1018: .Xr ssh 1 .
1.1 stevesk 1019: .It Cm XAuthLocation
1.5 stevesk 1020: Specifies the full pathname of the
1.1 stevesk 1021: .Xr xauth 1
1022: program.
1023: The default is
1024: .Pa /usr/X11R6/bin/xauth .
1025: .El
1026: .Sh FILES
1027: .Bl -tag -width Ds
1.50 djm 1028: .It Pa ~/.ssh/config
1.1 stevesk 1029: This is the per-user configuration file.
1030: The format of this file is described above.
1.84 jmc 1031: This file is used by the SSH client.
1.30 djm 1032: Because of the potential for abuse, this file must have strict permissions:
1033: read/write for the user, and not accessible by others.
1.1 stevesk 1034: .It Pa /etc/ssh/ssh_config
1035: Systemwide configuration file.
1036: This file provides defaults for those
1037: values that are not specified in the user's configuration file, and
1038: for those users who do not have a configuration file.
1039: This file must be world-readable.
1040: .El
1.13 jmc 1041: .Sh SEE ALSO
1042: .Xr ssh 1
1.1 stevesk 1043: .Sh AUTHORS
1044: OpenSSH is a derivative of the original and free
1045: ssh 1.2.12 release by Tatu Ylonen.
1046: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1047: Theo de Raadt and Dug Song
1048: removed many bugs, re-added newer features and
1049: created OpenSSH.
1050: Markus Friedl contributed the support for SSH
1051: protocol versions 1.5 and 2.0.
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