Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.97
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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18: .\" modification, are permitted provided that the following conditions
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22: .\" 2. Redistributions in binary form must reproduce the above copyright
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1.97 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.96 2006/07/11 18:50:48 markus 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: .Pp
1.1 stevesk 77: The configuration file has the following format:
78: .Pp
79: Empty lines and lines starting with
80: .Ql #
81: are comments.
82: Otherwise a line is of the format
83: .Dq keyword arguments .
84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
1.87 jmc 90: .Nm scp ,
1.1 stevesk 91: and
92: .Nm sftp
93: .Fl o
94: option.
1.88 dtucker 95: Arguments may optionally be enclosed in double quotes
96: .Pq \&"
97: in order to represent arguments containing spaces.
1.1 stevesk 98: .Pp
99: The possible
100: keywords and their meanings are as follows (note that
101: keywords are case-insensitive and arguments are case-sensitive):
102: .Bl -tag -width Ds
103: .It Cm Host
104: Restricts the following declarations (up to the next
105: .Cm Host
106: keyword) to be only for those hosts that match one of the patterns
107: given after the keyword.
108: A single
1.83 jmc 109: .Ql *
1.1 stevesk 110: as a pattern can be used to provide global
111: defaults for all hosts.
112: The host is the
113: .Ar hostname
1.83 jmc 114: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 115: a canonicalized host name before matching).
1.81 jmc 116: .Pp
117: See
118: .Sx PATTERNS
119: for more information on patterns.
1.10 djm 120: .It Cm AddressFamily
1.11 jmc 121: Specifies which address family to use when connecting.
122: Valid arguments are
1.10 djm 123: .Dq any ,
124: .Dq inet
1.84 jmc 125: (use IPv4 only), or
1.10 djm 126: .Dq inet6
1.40 jmc 127: (use IPv6 only).
1.1 stevesk 128: .It Cm BatchMode
129: If set to
130: .Dq yes ,
131: passphrase/password querying will be disabled.
132: This option is useful in scripts and other batch jobs where no user
133: is present to supply the password.
134: The argument must be
135: .Dq yes
136: or
137: .Dq no .
138: The default is
139: .Dq no .
140: .It Cm BindAddress
1.60 dtucker 141: Use the specified address on the local machine as the source address of
1.61 jmc 142: the connection.
143: Only useful on systems with more than one address.
1.1 stevesk 144: Note that this option does not work if
145: .Cm UsePrivilegedPort
146: is set to
147: .Dq yes .
148: .It Cm ChallengeResponseAuthentication
1.82 jmc 149: Specifies whether to use challenge-response authentication.
1.1 stevesk 150: The argument to this keyword must be
151: .Dq yes
152: or
153: .Dq no .
154: The default is
155: .Dq yes .
156: .It Cm CheckHostIP
157: If this flag is set to
158: .Dq yes ,
1.84 jmc 159: .Xr ssh 1
160: will additionally check the host IP address in the
1.1 stevesk 161: .Pa known_hosts
162: file.
163: This allows ssh to detect if a host key changed due to DNS spoofing.
164: If the option is set to
165: .Dq no ,
166: the check will not be executed.
167: The default is
168: .Dq yes .
169: .It Cm Cipher
170: Specifies the cipher to use for encrypting the session
171: in protocol version 1.
172: Currently,
173: .Dq blowfish ,
174: .Dq 3des ,
175: and
176: .Dq des
177: are supported.
178: .Ar des
179: is only supported in the
1.84 jmc 180: .Xr ssh 1
1.1 stevesk 181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
1.7 jmc 184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 186: The default is
187: .Dq 3des .
188: .It Cm Ciphers
189: Specifies the ciphers allowed for protocol version 2
190: in order of preference.
191: Multiple ciphers must be comma-separated.
1.35 dtucker 192: The supported ciphers are
193: .Dq 3des-cbc ,
194: .Dq aes128-cbc ,
195: .Dq aes192-cbc ,
196: .Dq aes256-cbc ,
197: .Dq aes128-ctr ,
198: .Dq aes192-ctr ,
199: .Dq aes256-ctr ,
1.54 djm 200: .Dq arcfour128 ,
201: .Dq arcfour256 ,
1.35 dtucker 202: .Dq arcfour ,
203: .Dq blowfish-cbc ,
204: and
205: .Dq cast128-cbc .
1.84 jmc 206: The default is:
207: .Bd -literal -offset 3n
208: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
209: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
210: aes192-ctr,aes256-ctr
1.1 stevesk 211: .Ed
212: .It Cm ClearAllForwardings
1.84 jmc 213: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 214: specified in the configuration files or on the command line be
1.7 jmc 215: cleared.
216: This option is primarily useful when used from the
1.84 jmc 217: .Xr ssh 1
1.1 stevesk 218: command line to clear port forwardings set in
219: configuration files, and is automatically set by
220: .Xr scp 1
221: and
222: .Xr sftp 1 .
223: The argument must be
224: .Dq yes
225: or
226: .Dq no .
227: The default is
228: .Dq no .
229: .It Cm Compression
230: Specifies whether to use compression.
231: The argument must be
232: .Dq yes
233: or
234: .Dq no .
235: The default is
236: .Dq no .
237: .It Cm CompressionLevel
238: Specifies the compression level to use if compression is enabled.
239: The argument must be an integer from 1 (fast) to 9 (slow, best).
240: The default level is 6, which is good for most applications.
241: The meaning of the values is the same as in
242: .Xr gzip 1 .
243: Note that this option applies to protocol version 1 only.
244: .It Cm ConnectionAttempts
245: Specifies the number of tries (one per second) to make before exiting.
246: The argument must be an integer.
247: This may be useful in scripts if the connection sometimes fails.
248: The default is 1.
1.9 djm 249: .It Cm ConnectTimeout
1.84 jmc 250: Specifies the timeout (in seconds) used when connecting to the
251: SSH server, instead of using the default system TCP timeout.
1.11 jmc 252: This value is used only when the target is down or really unreachable,
253: not when it refuses the connection.
1.36 djm 254: .It Cm ControlMaster
255: Enables the sharing of multiple sessions over a single network connection.
256: When set to
1.84 jmc 257: .Dq yes ,
258: .Xr ssh 1
1.36 djm 259: will listen for connections on a control socket specified using the
260: .Cm ControlPath
261: argument.
262: Additional sessions can connect to this socket using the same
263: .Cm ControlPath
264: with
265: .Cm ControlMaster
266: set to
267: .Dq no
1.38 jmc 268: (the default).
1.64 jmc 269: These sessions will try to reuse the master instance's network connection
1.63 djm 270: rather than initiating new ones, but will fall back to connecting normally
271: if the control socket does not exist, or is not listening.
272: .Pp
1.37 djm 273: Setting this to
274: .Dq ask
1.84 jmc 275: will cause ssh
1.37 djm 276: to listen for control connections, but require confirmation using the
277: .Ev SSH_ASKPASS
278: program before they are accepted (see
279: .Xr ssh-add 1
1.38 jmc 280: for details).
1.51 jakob 281: If the
282: .Cm ControlPath
1.84 jmc 283: cannot be opened,
284: ssh will continue without connecting to a master instance.
1.58 djm 285: .Pp
286: X11 and
1.59 jmc 287: .Xr ssh-agent 1
1.58 djm 288: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 289: display and agent forwarded will be the one belonging to the master
1.59 jmc 290: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 291: .Pp
292: Two additional options allow for opportunistic multiplexing: try to use a
293: master connection but fall back to creating a new one if one does not already
294: exist.
295: These options are:
296: .Dq auto
297: and
298: .Dq autoask .
299: The latter requires confirmation like the
300: .Dq ask
301: option.
1.36 djm 302: .It Cm ControlPath
1.55 djm 303: Specify the path to the control socket used for connection sharing as described
304: in the
1.36 djm 305: .Cm ControlMaster
1.57 djm 306: section above or the string
307: .Dq none
308: to disable connection sharing.
1.55 djm 309: In the path,
1.77 djm 310: .Ql %l
311: will be substituted by the local host name,
1.55 djm 312: .Ql %h
313: will be substituted by the target host name,
314: .Ql %p
1.84 jmc 315: the port, and
1.55 djm 316: .Ql %r
317: by the remote login username.
1.56 djm 318: It is recommended that any
319: .Cm ControlPath
320: used for opportunistic connection sharing include
1.78 jmc 321: at least %h, %p, and %r.
1.56 djm 322: This ensures that shared connections are uniquely identified.
1.38 jmc 323: .It Cm DynamicForward
1.74 jmc 324: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 325: over the secure channel, and the application
326: protocol is then used to determine where to connect to from the
327: remote machine.
1.62 djm 328: .Pp
329: The argument must be
330: .Sm off
331: .Oo Ar bind_address : Oc Ar port .
332: .Sm on
333: IPv6 addresses can be specified by enclosing addresses in square brackets or
334: by using an alternative syntax:
335: .Oo Ar bind_address Ns / Oc Ns Ar port .
336: By default, the local port is bound in accordance with the
337: .Cm GatewayPorts
338: setting.
339: However, an explicit
340: .Ar bind_address
341: may be used to bind the connection to a specific address.
342: The
343: .Ar bind_address
344: of
345: .Dq localhost
346: indicates that the listening port be bound for local use only, while an
347: empty address or
348: .Sq *
349: indicates that the port should be available from all interfaces.
350: .Pp
1.38 jmc 351: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 352: .Xr ssh 1
1.38 jmc 353: will act as a SOCKS server.
354: Multiple forwardings may be specified, and
355: additional forwardings can be given on the command line.
356: Only the superuser can forward privileged ports.
1.14 markus 357: .It Cm EnableSSHKeysign
358: Setting this option to
359: .Dq yes
360: in the global client configuration file
361: .Pa /etc/ssh/ssh_config
362: enables the use of the helper program
363: .Xr ssh-keysign 8
364: during
365: .Cm HostbasedAuthentication .
366: The argument must be
367: .Dq yes
368: or
369: .Dq no .
370: The default is
371: .Dq no .
1.23 jmc 372: This option should be placed in the non-hostspecific section.
1.14 markus 373: See
374: .Xr ssh-keysign 8
375: for more information.
1.1 stevesk 376: .It Cm EscapeChar
377: Sets the escape character (default:
378: .Ql ~ ) .
379: The escape character can also
380: be set on the command line.
381: The argument should be a single character,
382: .Ql ^
383: followed by a letter, or
384: .Dq none
385: to disable the escape
386: character entirely (making the connection transparent for binary
387: data).
1.96 markus 388: .It Cm ExitOnForwardFailure
389: Specifies whether
390: .Xr ssh 1
391: should terminate the connection if it cannot set up all requested
392: dynamic, local, and remote port forwardings.
393: The argument must be
394: .Dq yes
395: or
396: .Dq no .
397: The default is
398: .Dq no .
1.1 stevesk 399: .It Cm ForwardAgent
400: Specifies whether the connection to the authentication agent (if any)
401: will be forwarded to the remote machine.
402: The argument must be
403: .Dq yes
404: or
405: .Dq no .
406: The default is
407: .Dq no .
1.3 stevesk 408: .Pp
1.7 jmc 409: Agent forwarding should be enabled with caution.
410: Users with the ability to bypass file permissions on the remote host
411: (for the agent's Unix-domain socket)
412: can access the local agent through the forwarded connection.
413: An attacker cannot obtain key material from the agent,
1.3 stevesk 414: however they can perform operations on the keys that enable them to
415: authenticate using the identities loaded into the agent.
1.1 stevesk 416: .It Cm ForwardX11
417: Specifies whether X11 connections will be automatically redirected
418: over the secure channel and
419: .Ev DISPLAY
420: set.
421: The argument must be
422: .Dq yes
423: or
424: .Dq no .
425: The default is
426: .Dq no .
1.3 stevesk 427: .Pp
1.7 jmc 428: X11 forwarding should be enabled with caution.
429: Users with the ability to bypass file permissions on the remote host
1.22 markus 430: (for the user's X11 authorization database)
1.7 jmc 431: can access the local X11 display through the forwarded connection.
1.22 markus 432: An attacker may then be able to perform activities such as keystroke monitoring
433: if the
434: .Cm ForwardX11Trusted
435: option is also enabled.
436: .It Cm ForwardX11Trusted
1.34 jmc 437: If this option is set to
1.84 jmc 438: .Dq yes ,
439: remote X11 clients will have full access to the original X11 display.
1.42 djm 440: .Pp
1.22 markus 441: If this option is set to
1.84 jmc 442: .Dq no ,
443: remote X11 clients will be considered untrusted and prevented
1.22 markus 444: from stealing or tampering with data belonging to trusted X11
445: clients.
1.42 djm 446: Furthermore, the
447: .Xr xauth 1
448: token used for the session will be set to expire after 20 minutes.
449: Remote clients will be refused access after this time.
1.22 markus 450: .Pp
451: The default is
452: .Dq no .
453: .Pp
454: See the X11 SECURITY extension specification for full details on
455: the restrictions imposed on untrusted clients.
1.1 stevesk 456: .It Cm GatewayPorts
457: Specifies whether remote hosts are allowed to connect to local
458: forwarded ports.
459: By default,
1.84 jmc 460: .Xr ssh 1
1.7 jmc 461: binds local port forwardings to the loopback address.
462: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 463: .Cm GatewayPorts
1.84 jmc 464: can be used to specify that ssh
1.1 stevesk 465: should bind local port forwardings to the wildcard address,
466: thus allowing remote hosts to connect to forwarded ports.
467: The argument must be
468: .Dq yes
469: or
470: .Dq no .
471: The default is
472: .Dq no .
473: .It Cm GlobalKnownHostsFile
474: Specifies a file to use for the global
475: host key database instead of
476: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 477: .It Cm GSSAPIAuthentication
1.27 markus 478: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 479: The default is
1.21 markus 480: .Dq no .
1.18 markus 481: Note that this option applies to protocol version 2 only.
482: .It Cm GSSAPIDelegateCredentials
483: Forward (delegate) credentials to the server.
484: The default is
485: .Dq no .
486: Note that this option applies to protocol version 2 only.
1.44 djm 487: .It Cm HashKnownHosts
488: Indicates that
1.84 jmc 489: .Xr ssh 1
1.44 djm 490: should hash host names and addresses when they are added to
1.50 djm 491: .Pa ~/.ssh/known_hosts .
1.44 djm 492: These hashed names may be used normally by
1.84 jmc 493: .Xr ssh 1
1.44 djm 494: and
1.84 jmc 495: .Xr sshd 8 ,
1.44 djm 496: but they do not reveal identifying information should the file's contents
497: be disclosed.
498: The default is
499: .Dq no .
1.97 ! jmc 500: Note that existing names and addresses in known hosts files
! 501: will not be converted automatically,
! 502: but may be manually hashed using
1.45 djm 503: .Xr ssh-keygen 1 .
1.1 stevesk 504: .It Cm HostbasedAuthentication
505: Specifies whether to try rhosts based authentication with public key
506: authentication.
507: The argument must be
508: .Dq yes
509: or
510: .Dq no .
511: The default is
512: .Dq no .
513: This option applies to protocol version 2 only and
514: is similar to
515: .Cm RhostsRSAAuthentication .
516: .It Cm HostKeyAlgorithms
517: Specifies the protocol version 2 host key algorithms
518: that the client wants to use in order of preference.
519: The default for this option is:
520: .Dq ssh-rsa,ssh-dss .
521: .It Cm HostKeyAlias
522: Specifies an alias that should be used instead of the
523: real host name when looking up or saving the host key
524: in the host key database files.
1.84 jmc 525: This option is useful for tunneling SSH connections
1.1 stevesk 526: or for multiple servers running on a single host.
527: .It Cm HostName
528: Specifies the real host name to log into.
529: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 530: The default is the name given on the command line.
1.1 stevesk 531: Numeric IP addresses are also permitted (both on the command line and in
532: .Cm HostName
533: specifications).
1.29 markus 534: .It Cm IdentitiesOnly
535: Specifies that
1.84 jmc 536: .Xr ssh 1
1.29 markus 537: should only use the authentication identity files configured in the
1.31 jmc 538: .Nm
1.29 markus 539: files,
1.84 jmc 540: even if
541: .Xr ssh-agent 1
1.29 markus 542: offers more identities.
543: The argument to this keyword must be
544: .Dq yes
545: or
546: .Dq no .
1.84 jmc 547: This option is intended for situations where ssh-agent
1.29 markus 548: offers many different identities.
549: The default is
550: .Dq no .
1.67 jmc 551: .It Cm IdentityFile
552: Specifies a file from which the user's RSA or DSA authentication identity
553: is read.
554: The default is
555: .Pa ~/.ssh/identity
556: for protocol version 1, and
557: .Pa ~/.ssh/id_rsa
558: and
559: .Pa ~/.ssh/id_dsa
560: for protocol version 2.
561: Additionally, any identities represented by the authentication agent
562: will be used for authentication.
1.90 djm 563: .Pp
1.67 jmc 564: The file name may use the tilde
1.91 jmc 565: syntax to refer to a user's home directory or one of the following
1.90 djm 566: escape characters:
567: .Ql %d
568: (local user's home directory),
569: .Ql %u
570: (local user name),
571: .Ql %l
572: (local host name),
573: .Ql %h
574: (remote host name) or
1.92 djm 575: .Ql %r
1.90 djm 576: (remote user name).
577: .Pp
1.67 jmc 578: It is possible to have
579: multiple identity files specified in configuration files; all these
580: identities will be tried in sequence.
1.39 djm 581: .It Cm KbdInteractiveDevices
582: Specifies the list of methods to use in keyboard-interactive authentication.
583: Multiple method names must be comma-separated.
584: The default is to use the server specified list.
1.85 jmc 585: The methods available vary depending on what the server supports.
586: For an OpenSSH server,
587: it may be zero or more of:
588: .Dq bsdauth ,
589: .Dq pam ,
590: and
591: .Dq skey .
1.65 reyk 592: .It Cm LocalCommand
593: Specifies a command to execute on the local machine after successfully
594: connecting to the server.
595: The command string extends to the end of the line, and is executed with
596: .Pa /bin/sh .
597: This directive is ignored unless
598: .Cm PermitLocalCommand
599: has been enabled.
1.1 stevesk 600: .It Cm LocalForward
1.74 jmc 601: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 602: the secure channel to the specified host and port from the remote machine.
1.49 jmc 603: The first argument must be
1.43 djm 604: .Sm off
1.49 jmc 605: .Oo Ar bind_address : Oc Ar port
1.43 djm 606: .Sm on
1.49 jmc 607: and the second argument must be
608: .Ar host : Ns Ar hostport .
1.46 jmc 609: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 610: by using an alternative syntax:
1.49 jmc 611: .Oo Ar bind_address Ns / Oc Ns Ar port
612: and
613: .Ar host Ns / Ns Ar hostport .
1.46 jmc 614: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 615: given on the command line.
1.1 stevesk 616: Only the superuser can forward privileged ports.
1.43 djm 617: By default, the local port is bound in accordance with the
618: .Cm GatewayPorts
619: setting.
620: However, an explicit
621: .Ar bind_address
622: may be used to bind the connection to a specific address.
623: The
624: .Ar bind_address
625: of
626: .Dq localhost
1.46 jmc 627: indicates that the listening port be bound for local use only, while an
628: empty address or
629: .Sq *
1.43 djm 630: indicates that the port should be available from all interfaces.
1.1 stevesk 631: .It Cm LogLevel
632: Gives the verbosity level that is used when logging messages from
1.84 jmc 633: .Xr ssh 1 .
1.1 stevesk 634: The possible values are:
1.84 jmc 635: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 636: The default is INFO.
637: DEBUG and DEBUG1 are equivalent.
638: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 639: .It Cm MACs
640: Specifies the MAC (message authentication code) algorithms
641: in order of preference.
642: The MAC algorithm is used in protocol version 2
643: for data integrity protection.
644: Multiple algorithms must be comma-separated.
1.84 jmc 645: The default is:
1.1 stevesk 646: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
647: .It Cm NoHostAuthenticationForLocalhost
648: This option can be used if the home directory is shared across machines.
649: In this case localhost will refer to a different machine on each of
650: the machines and the user will get many warnings about changed host keys.
651: However, this option disables host authentication for localhost.
652: The argument to this keyword must be
653: .Dq yes
654: or
655: .Dq no .
656: The default is to check the host key for localhost.
657: .It Cm NumberOfPasswordPrompts
658: Specifies the number of password prompts before giving up.
659: The argument to this keyword must be an integer.
1.84 jmc 660: The default is 3.
1.1 stevesk 661: .It Cm PasswordAuthentication
662: Specifies whether to use password authentication.
663: The argument to this keyword must be
664: .Dq yes
665: or
666: .Dq no .
667: The default is
668: .Dq yes .
1.65 reyk 669: .It Cm PermitLocalCommand
670: Allow local command execution via the
671: .Ic LocalCommand
672: option or using the
1.66 jmc 673: .Ic !\& Ns Ar command
1.65 reyk 674: escape sequence in
675: .Xr ssh 1 .
676: The argument must be
677: .Dq yes
678: or
679: .Dq no .
680: The default is
681: .Dq no .
1.67 jmc 682: .It Cm Port
683: Specifies the port number to connect on the remote host.
1.84 jmc 684: The default is 22.
1.1 stevesk 685: .It Cm PreferredAuthentications
686: Specifies the order in which the client should try protocol 2
1.11 jmc 687: authentication methods.
1.48 jmc 688: This allows a client to prefer one method (e.g.\&
1.1 stevesk 689: .Cm keyboard-interactive )
1.48 jmc 690: over another method (e.g.\&
1.1 stevesk 691: .Cm password )
692: The default for this option is:
1.94 jmc 693: .Do gssapi-with-mic ,
694: hostbased,
695: publickey,
696: keyboard-interactive,
697: password
698: .Dc .
1.1 stevesk 699: .It Cm Protocol
700: Specifies the protocol versions
1.84 jmc 701: .Xr ssh 1
1.1 stevesk 702: should support in order of preference.
703: The possible values are
1.84 jmc 704: .Sq 1
1.1 stevesk 705: and
1.84 jmc 706: .Sq 2 .
1.1 stevesk 707: Multiple versions must be comma-separated.
708: The default is
709: .Dq 2,1 .
1.84 jmc 710: This means that ssh
1.1 stevesk 711: tries version 2 and falls back to version 1
712: if version 2 is not available.
713: .It Cm ProxyCommand
714: Specifies the command to use to connect to the server.
715: The command
716: string extends to the end of the line, and is executed with
717: .Pa /bin/sh .
718: In the command string,
719: .Ql %h
720: will be substituted by the host name to
721: connect and
722: .Ql %p
723: by the port.
724: The command can be basically anything,
725: and should read from its standard input and write to its standard output.
726: It should eventually connect an
727: .Xr sshd 8
728: server running on some machine, or execute
729: .Ic sshd -i
730: somewhere.
731: Host key management will be done using the
732: HostName of the host being connected (defaulting to the name typed by
733: the user).
1.7 jmc 734: Setting the command to
735: .Dq none
1.6 markus 736: disables this option entirely.
1.1 stevesk 737: Note that
738: .Cm CheckHostIP
739: is not available for connects with a proxy command.
1.52 djm 740: .Pp
741: This directive is useful in conjunction with
742: .Xr nc 1
743: and its proxy support.
1.53 jmc 744: For example, the following directive would connect via an HTTP proxy at
1.52 djm 745: 192.0.2.0:
746: .Bd -literal -offset 3n
747: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
748: .Ed
1.1 stevesk 749: .It Cm PubkeyAuthentication
750: Specifies whether to try public key authentication.
751: The argument to this keyword must be
752: .Dq yes
753: or
754: .Dq no .
755: The default is
756: .Dq yes .
757: This option applies to protocol version 2 only.
1.75 dtucker 758: .It Cm RekeyLimit
759: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 760: session key is renegotiated.
1.75 dtucker 761: The argument is the number of bytes, with an optional suffix of
1.76 jmc 762: .Sq K ,
763: .Sq M ,
1.75 dtucker 764: or
1.76 jmc 765: .Sq G
1.75 dtucker 766: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
767: The default is between
1.84 jmc 768: .Sq 1G
1.75 dtucker 769: and
1.84 jmc 770: .Sq 4G ,
1.75 dtucker 771: depending on the cipher.
1.76 jmc 772: This option applies to protocol version 2 only.
1.1 stevesk 773: .It Cm RemoteForward
1.74 jmc 774: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 775: the secure channel to the specified host and port from the local machine.
1.49 jmc 776: The first argument must be
1.43 djm 777: .Sm off
1.49 jmc 778: .Oo Ar bind_address : Oc Ar port
1.43 djm 779: .Sm on
1.49 jmc 780: and the second argument must be
781: .Ar host : Ns Ar hostport .
782: IPv6 addresses can be specified by enclosing addresses in square brackets
783: or by using an alternative syntax:
784: .Oo Ar bind_address Ns / Oc Ns Ar port
785: and
786: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 787: Multiple forwardings may be specified, and additional
788: forwardings can be given on the command line.
789: Only the superuser can forward privileged ports.
1.43 djm 790: .Pp
791: If the
792: .Ar bind_address
793: is not specified, the default is to only bind to loopback addresses.
794: If the
795: .Ar bind_address
796: is
797: .Ql *
798: or an empty string, then the forwarding is requested to listen on all
799: interfaces.
800: Specifying a remote
801: .Ar bind_address
1.46 jmc 802: will only succeed if the server's
803: .Cm GatewayPorts
1.43 djm 804: option is enabled (see
1.46 jmc 805: .Xr sshd_config 5 ) .
1.1 stevesk 806: .It Cm RhostsRSAAuthentication
807: Specifies whether to try rhosts based authentication with RSA host
808: authentication.
809: The argument must be
810: .Dq yes
811: or
812: .Dq no .
813: The default is
814: .Dq no .
815: This option applies to protocol version 1 only and requires
1.84 jmc 816: .Xr ssh 1
1.1 stevesk 817: to be setuid root.
818: .It Cm RSAAuthentication
819: Specifies whether to try RSA authentication.
820: The argument to this keyword must be
821: .Dq yes
822: or
823: .Dq no .
824: RSA authentication will only be
825: attempted if the identity file exists, or an authentication agent is
826: running.
827: The default is
828: .Dq yes .
829: Note that this option applies to protocol version 1 only.
1.32 djm 830: .It Cm SendEnv
831: Specifies what variables from the local
832: .Xr environ 7
833: should be sent to the server.
1.84 jmc 834: Note that environment passing is only supported for protocol 2.
835: The server must also support it, and the server must be configured to
1.33 djm 836: accept these environment variables.
1.32 djm 837: Refer to
838: .Cm AcceptEnv
839: in
840: .Xr sshd_config 5
841: for how to configure the server.
1.80 jmc 842: Variables are specified by name, which may contain wildcard characters.
1.33 djm 843: Multiple environment variables may be separated by whitespace or spread
1.32 djm 844: across multiple
845: .Cm SendEnv
846: directives.
847: The default is not to send any environment variables.
1.81 jmc 848: .Pp
849: See
850: .Sx PATTERNS
851: for more information on patterns.
1.28 markus 852: .It Cm ServerAliveCountMax
1.73 jmc 853: Sets the number of server alive messages (see below) which may be
1.28 markus 854: sent without
1.84 jmc 855: .Xr ssh 1
1.28 markus 856: receiving any messages back from the server.
857: If this threshold is reached while server alive messages are being sent,
1.84 jmc 858: ssh will disconnect from the server, terminating the session.
1.28 markus 859: It is important to note that the use of server alive messages is very
860: different from
861: .Cm TCPKeepAlive
862: (below).
863: The server alive messages are sent through the encrypted channel
864: and therefore will not be spoofable.
865: The TCP keepalive option enabled by
866: .Cm TCPKeepAlive
867: is spoofable.
868: The server alive mechanism is valuable when the client or
869: server depend on knowing when a connection has become inactive.
870: .Pp
871: The default value is 3.
872: If, for example,
873: .Cm ServerAliveInterval
1.84 jmc 874: (see below) is set to 15 and
1.28 markus 875: .Cm ServerAliveCountMax
1.84 jmc 876: is left at the default, if the server becomes unresponsive,
877: ssh will disconnect after approximately 45 seconds.
1.89 markus 878: This option applies to protocol version 2 only.
1.67 jmc 879: .It Cm ServerAliveInterval
880: Sets a timeout interval in seconds after which if no data has been received
881: from the server,
1.84 jmc 882: .Xr ssh 1
1.67 jmc 883: will send a message through the encrypted
884: channel to request a response from the server.
885: The default
886: is 0, indicating that these messages will not be sent to the server.
887: This option applies to protocol version 2 only.
1.1 stevesk 888: .It Cm SmartcardDevice
1.11 jmc 889: Specifies which smartcard device to use.
890: The argument to this keyword is the device
1.84 jmc 891: .Xr ssh 1
1.1 stevesk 892: should use to communicate with a smartcard used for storing the user's
1.11 jmc 893: private RSA key.
894: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 895: .It Cm StrictHostKeyChecking
896: If this flag is set to
897: .Dq yes ,
1.84 jmc 898: .Xr ssh 1
1.1 stevesk 899: will never automatically add host keys to the
1.50 djm 900: .Pa ~/.ssh/known_hosts
1.1 stevesk 901: file, and refuses to connect to hosts whose host key has changed.
902: This provides maximum protection against trojan horse attacks,
1.84 jmc 903: though it can be annoying when the
1.1 stevesk 904: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 905: file is poorly maintained or when connections to new hosts are
1.1 stevesk 906: frequently made.
907: This option forces the user to manually
908: add all new hosts.
909: If this flag is set to
910: .Dq no ,
1.84 jmc 911: ssh will automatically add new host keys to the
1.1 stevesk 912: user known hosts files.
913: If this flag is set to
914: .Dq ask ,
915: new host keys
916: will be added to the user known host files only after the user
917: has confirmed that is what they really want to do, and
1.84 jmc 918: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 919: The host keys of
920: known hosts will be verified automatically in all cases.
921: The argument must be
922: .Dq yes ,
1.84 jmc 923: .Dq no ,
1.1 stevesk 924: or
925: .Dq ask .
926: The default is
927: .Dq ask .
1.26 markus 928: .It Cm TCPKeepAlive
929: Specifies whether the system should send TCP keepalive messages to the
930: other side.
931: If they are sent, death of the connection or crash of one
932: of the machines will be properly noticed.
933: However, this means that
934: connections will die if the route is down temporarily, and some people
935: find it annoying.
936: .Pp
937: The default is
938: .Dq yes
939: (to send TCP keepalive messages), and the client will notice
940: if the network goes down or the remote host dies.
941: This is important in scripts, and many users want it too.
942: .Pp
943: To disable TCP keepalive messages, the value should be set to
944: .Dq no .
1.65 reyk 945: .It Cm Tunnel
1.95 stevesk 946: Request
1.65 reyk 947: .Xr tun 4
1.69 jmc 948: device forwarding between the client and the server.
1.65 reyk 949: The argument must be
1.68 reyk 950: .Dq yes ,
1.95 stevesk 951: .Dq point-to-point
952: (layer 3),
953: .Dq ethernet
954: (layer 2),
1.65 reyk 955: or
956: .Dq no .
1.95 stevesk 957: Specifying
958: .Dq yes
959: requests the default tunnel mode, which is
960: .Dq point-to-point .
1.65 reyk 961: The default is
962: .Dq no .
963: .It Cm TunnelDevice
1.95 stevesk 964: Specifies the
1.65 reyk 965: .Xr tun 4
1.95 stevesk 966: devices to open on the client
967: .Pq Ar local_tun
968: and the server
969: .Pq Ar remote_tun .
970: .Pp
971: The argument must be
972: .Sm off
973: .Ar local_tun Op : Ar remote_tun .
974: .Sm on
975: The devices may be specified by numerical ID or the keyword
976: .Dq any ,
977: which uses the next available tunnel device.
978: If
979: .Ar remote_tun
980: is not specified, it defaults to
981: .Dq any .
982: The default is
983: .Dq any:any .
1.72 jmc 984: .It Cm UsePrivilegedPort
985: Specifies whether to use a privileged port for outgoing connections.
986: The argument must be
987: .Dq yes
988: or
989: .Dq no .
990: The default is
991: .Dq no .
992: If set to
1.84 jmc 993: .Dq yes ,
994: .Xr ssh 1
1.72 jmc 995: must be setuid root.
996: Note that this option must be set to
997: .Dq yes
998: for
999: .Cm RhostsRSAAuthentication
1000: with older servers.
1.1 stevesk 1001: .It Cm User
1002: Specifies the user to log in as.
1003: This can be useful when a different user name is used on different machines.
1004: This saves the trouble of
1005: having to remember to give the user name on the command line.
1006: .It Cm UserKnownHostsFile
1007: Specifies a file to use for the user
1008: host key database instead of
1.50 djm 1009: .Pa ~/.ssh/known_hosts .
1.8 jakob 1010: .It Cm VerifyHostKeyDNS
1011: Specifies whether to verify the remote key using DNS and SSHFP resource
1012: records.
1.24 jakob 1013: If this option is set to
1014: .Dq yes ,
1.25 jmc 1015: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1016: from DNS.
1017: Insecure fingerprints will be handled as if this option was set to
1018: .Dq ask .
1019: If this option is set to
1020: .Dq ask ,
1021: information on fingerprint match will be displayed, but the user will still
1022: need to confirm new host keys according to the
1023: .Cm StrictHostKeyChecking
1024: option.
1025: The argument must be
1026: .Dq yes ,
1.84 jmc 1027: .Dq no ,
1.25 jmc 1028: or
1029: .Dq ask .
1.8 jakob 1030: The default is
1031: .Dq no .
1.12 jakob 1032: Note that this option applies to protocol version 2 only.
1.84 jmc 1033: .Pp
1034: See also
1035: .Sx VERIFYING HOST KEYS
1036: in
1037: .Xr ssh 1 .
1.1 stevesk 1038: .It Cm XAuthLocation
1.5 stevesk 1039: Specifies the full pathname of the
1.1 stevesk 1040: .Xr xauth 1
1041: program.
1042: The default is
1043: .Pa /usr/X11R6/bin/xauth .
1044: .El
1.86 jmc 1045: .Sh PATTERNS
1046: A
1047: .Em pattern
1048: consists of zero or more non-whitespace characters,
1049: .Sq *
1050: (a wildcard that matches zero or more characters),
1051: or
1052: .Sq ?\&
1053: (a wildcard that matches exactly one character).
1054: For example, to specify a set of declarations for any host in the
1055: .Dq .co.uk
1056: set of domains,
1057: the following pattern could be used:
1058: .Pp
1059: .Dl Host *.co.uk
1060: .Pp
1061: The following pattern
1062: would match any host in the 192.168.0.[0-9] network range:
1063: .Pp
1064: .Dl Host 192.168.0.?
1065: .Pp
1066: A
1067: .Em pattern-list
1068: is a comma-separated list of patterns.
1069: Patterns within pattern-lists may be negated
1070: by preceding them with an exclamation mark
1071: .Pq Sq !\& .
1072: For example,
1073: to allow a key to be used from anywhere within an organisation
1074: except from the
1075: .Dq dialup
1076: pool,
1077: the following entry (in authorized_keys) could be used:
1078: .Pp
1079: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1080: .Sh FILES
1081: .Bl -tag -width Ds
1.50 djm 1082: .It Pa ~/.ssh/config
1.1 stevesk 1083: This is the per-user configuration file.
1084: The format of this file is described above.
1.84 jmc 1085: This file is used by the SSH client.
1.30 djm 1086: Because of the potential for abuse, this file must have strict permissions:
1087: read/write for the user, and not accessible by others.
1.1 stevesk 1088: .It Pa /etc/ssh/ssh_config
1089: Systemwide configuration file.
1090: This file provides defaults for those
1091: values that are not specified in the user's configuration file, and
1092: for those users who do not have a configuration file.
1093: This file must be world-readable.
1094: .El
1.13 jmc 1095: .Sh SEE ALSO
1096: .Xr ssh 1
1.1 stevesk 1097: .Sh AUTHORS
1098: OpenSSH is a derivative of the original and free
1099: ssh 1.2.12 release by Tatu Ylonen.
1100: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1101: Theo de Raadt and Dug Song
1102: removed many bugs, re-added newer features and
1103: created OpenSSH.
1104: Markus Friedl contributed the support for SSH
1105: protocol versions 1.5 and 2.0.
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