Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.86
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
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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.
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1.86 ! jmc 37: .\" $OpenBSD: ssh_config.5,v 1.85 2006/02/25 12:26:17 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: .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 ,
90: .Nm scp
91: and
92: .Nm sftp
93: .Fl o
94: option.
95: .Pp
96: The possible
97: keywords and their meanings are as follows (note that
98: keywords are case-insensitive and arguments are case-sensitive):
99: .Bl -tag -width Ds
100: .It Cm Host
101: Restricts the following declarations (up to the next
102: .Cm Host
103: keyword) to be only for those hosts that match one of the patterns
104: given after the keyword.
105: A single
1.83 jmc 106: .Ql *
1.1 stevesk 107: as a pattern can be used to provide global
108: defaults for all hosts.
109: The host is the
110: .Ar hostname
1.83 jmc 111: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 112: a canonicalized host name before matching).
1.81 jmc 113: .Pp
114: See
115: .Sx PATTERNS
116: for more information on patterns.
1.10 djm 117: .It Cm AddressFamily
1.11 jmc 118: Specifies which address family to use when connecting.
119: Valid arguments are
1.10 djm 120: .Dq any ,
121: .Dq inet
1.84 jmc 122: (use IPv4 only), or
1.10 djm 123: .Dq inet6
1.40 jmc 124: (use IPv6 only).
1.1 stevesk 125: .It Cm BatchMode
126: If set to
127: .Dq yes ,
128: passphrase/password querying will be disabled.
129: This option is useful in scripts and other batch jobs where no user
130: is present to supply the password.
131: The argument must be
132: .Dq yes
133: or
134: .Dq no .
135: The default is
136: .Dq no .
137: .It Cm BindAddress
1.60 dtucker 138: Use the specified address on the local machine as the source address of
1.61 jmc 139: the connection.
140: Only useful on systems with more than one address.
1.1 stevesk 141: Note that this option does not work if
142: .Cm UsePrivilegedPort
143: is set to
144: .Dq yes .
145: .It Cm ChallengeResponseAuthentication
1.82 jmc 146: Specifies whether to use challenge-response authentication.
1.1 stevesk 147: The argument to this keyword must be
148: .Dq yes
149: or
150: .Dq no .
151: The default is
152: .Dq yes .
153: .It Cm CheckHostIP
154: If this flag is set to
155: .Dq yes ,
1.84 jmc 156: .Xr ssh 1
157: will additionally check the host IP address in the
1.1 stevesk 158: .Pa known_hosts
159: file.
160: This allows ssh to detect if a host key changed due to DNS spoofing.
161: If the option is set to
162: .Dq no ,
163: the check will not be executed.
164: The default is
165: .Dq yes .
166: .It Cm Cipher
167: Specifies the cipher to use for encrypting the session
168: in protocol version 1.
169: Currently,
170: .Dq blowfish ,
171: .Dq 3des ,
172: and
173: .Dq des
174: are supported.
175: .Ar des
176: is only supported in the
1.84 jmc 177: .Xr ssh 1
1.1 stevesk 178: client for interoperability with legacy protocol 1 implementations
179: that do not support the
180: .Ar 3des
1.7 jmc 181: cipher.
182: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 183: The default is
184: .Dq 3des .
185: .It Cm Ciphers
186: Specifies the ciphers allowed for protocol version 2
187: in order of preference.
188: Multiple ciphers must be comma-separated.
1.35 dtucker 189: The supported ciphers are
190: .Dq 3des-cbc ,
191: .Dq aes128-cbc ,
192: .Dq aes192-cbc ,
193: .Dq aes256-cbc ,
194: .Dq aes128-ctr ,
195: .Dq aes192-ctr ,
196: .Dq aes256-ctr ,
1.54 djm 197: .Dq arcfour128 ,
198: .Dq arcfour256 ,
1.35 dtucker 199: .Dq arcfour ,
200: .Dq blowfish-cbc ,
201: and
202: .Dq cast128-cbc .
1.84 jmc 203: The default is:
204: .Bd -literal -offset 3n
205: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
206: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
207: aes192-ctr,aes256-ctr
1.1 stevesk 208: .Ed
209: .It Cm ClearAllForwardings
1.84 jmc 210: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 211: specified in the configuration files or on the command line be
1.7 jmc 212: cleared.
213: This option is primarily useful when used from the
1.84 jmc 214: .Xr ssh 1
1.1 stevesk 215: command line to clear port forwardings set in
216: configuration files, and is automatically set by
217: .Xr scp 1
218: and
219: .Xr sftp 1 .
220: The argument must be
221: .Dq yes
222: or
223: .Dq no .
224: The default is
225: .Dq no .
226: .It Cm Compression
227: Specifies whether to use compression.
228: The argument must be
229: .Dq yes
230: or
231: .Dq no .
232: The default is
233: .Dq no .
234: .It Cm CompressionLevel
235: Specifies the compression level to use if compression is enabled.
236: The argument must be an integer from 1 (fast) to 9 (slow, best).
237: The default level is 6, which is good for most applications.
238: The meaning of the values is the same as in
239: .Xr gzip 1 .
240: Note that this option applies to protocol version 1 only.
241: .It Cm ConnectionAttempts
242: Specifies the number of tries (one per second) to make before exiting.
243: The argument must be an integer.
244: This may be useful in scripts if the connection sometimes fails.
245: The default is 1.
1.9 djm 246: .It Cm ConnectTimeout
1.84 jmc 247: Specifies the timeout (in seconds) used when connecting to the
248: SSH server, instead of using the default system TCP timeout.
1.11 jmc 249: This value is used only when the target is down or really unreachable,
250: not when it refuses the connection.
1.36 djm 251: .It Cm ControlMaster
252: Enables the sharing of multiple sessions over a single network connection.
253: When set to
1.84 jmc 254: .Dq yes ,
255: .Xr ssh 1
1.36 djm 256: will listen for connections on a control socket specified using the
257: .Cm ControlPath
258: argument.
259: Additional sessions can connect to this socket using the same
260: .Cm ControlPath
261: with
262: .Cm ControlMaster
263: set to
264: .Dq no
1.38 jmc 265: (the default).
1.64 jmc 266: These sessions will try to reuse the master instance's network connection
1.63 djm 267: rather than initiating new ones, but will fall back to connecting normally
268: if the control socket does not exist, or is not listening.
269: .Pp
1.37 djm 270: Setting this to
271: .Dq ask
1.84 jmc 272: will cause ssh
1.37 djm 273: to listen for control connections, but require confirmation using the
274: .Ev SSH_ASKPASS
275: program before they are accepted (see
276: .Xr ssh-add 1
1.38 jmc 277: for details).
1.51 jakob 278: If the
279: .Cm ControlPath
1.84 jmc 280: cannot be opened,
281: ssh will continue without connecting to a master instance.
1.58 djm 282: .Pp
283: X11 and
1.59 jmc 284: .Xr ssh-agent 1
1.58 djm 285: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 286: display and agent forwarded will be the one belonging to the master
1.59 jmc 287: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 288: .Pp
289: Two additional options allow for opportunistic multiplexing: try to use a
290: master connection but fall back to creating a new one if one does not already
291: exist.
292: These options are:
293: .Dq auto
294: and
295: .Dq autoask .
296: The latter requires confirmation like the
297: .Dq ask
298: option.
1.36 djm 299: .It Cm ControlPath
1.55 djm 300: Specify the path to the control socket used for connection sharing as described
301: in the
1.36 djm 302: .Cm ControlMaster
1.57 djm 303: section above or the string
304: .Dq none
305: to disable connection sharing.
1.55 djm 306: In the path,
1.77 djm 307: .Ql %l
308: will be substituted by the local host name,
1.55 djm 309: .Ql %h
310: will be substituted by the target host name,
311: .Ql %p
1.84 jmc 312: the port, and
1.55 djm 313: .Ql %r
314: by the remote login username.
1.56 djm 315: It is recommended that any
316: .Cm ControlPath
317: used for opportunistic connection sharing include
1.78 jmc 318: at least %h, %p, and %r.
1.56 djm 319: This ensures that shared connections are uniquely identified.
1.38 jmc 320: .It Cm DynamicForward
1.74 jmc 321: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 322: over the secure channel, and the application
323: protocol is then used to determine where to connect to from the
324: remote machine.
1.62 djm 325: .Pp
326: The argument must be
327: .Sm off
328: .Oo Ar bind_address : Oc Ar port .
329: .Sm on
330: IPv6 addresses can be specified by enclosing addresses in square brackets or
331: by using an alternative syntax:
332: .Oo Ar bind_address Ns / Oc Ns Ar port .
333: By default, the local port is bound in accordance with the
334: .Cm GatewayPorts
335: setting.
336: However, an explicit
337: .Ar bind_address
338: may be used to bind the connection to a specific address.
339: The
340: .Ar bind_address
341: of
342: .Dq localhost
343: indicates that the listening port be bound for local use only, while an
344: empty address or
345: .Sq *
346: indicates that the port should be available from all interfaces.
347: .Pp
1.38 jmc 348: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 349: .Xr ssh 1
1.38 jmc 350: will act as a SOCKS server.
351: Multiple forwardings may be specified, and
352: additional forwardings can be given on the command line.
353: Only the superuser can forward privileged ports.
1.14 markus 354: .It Cm EnableSSHKeysign
355: Setting this option to
356: .Dq yes
357: in the global client configuration file
358: .Pa /etc/ssh/ssh_config
359: enables the use of the helper program
360: .Xr ssh-keysign 8
361: during
362: .Cm HostbasedAuthentication .
363: The argument must be
364: .Dq yes
365: or
366: .Dq no .
367: The default is
368: .Dq no .
1.23 jmc 369: This option should be placed in the non-hostspecific section.
1.14 markus 370: See
371: .Xr ssh-keysign 8
372: for more information.
1.1 stevesk 373: .It Cm EscapeChar
374: Sets the escape character (default:
375: .Ql ~ ) .
376: The escape character can also
377: be set on the command line.
378: The argument should be a single character,
379: .Ql ^
380: followed by a letter, or
381: .Dq none
382: to disable the escape
383: character entirely (making the connection transparent for binary
384: data).
385: .It Cm ForwardAgent
386: Specifies whether the connection to the authentication agent (if any)
387: will be forwarded to the remote machine.
388: The argument must be
389: .Dq yes
390: or
391: .Dq no .
392: The default is
393: .Dq no .
1.3 stevesk 394: .Pp
1.7 jmc 395: Agent forwarding should be enabled with caution.
396: Users with the ability to bypass file permissions on the remote host
397: (for the agent's Unix-domain socket)
398: can access the local agent through the forwarded connection.
399: An attacker cannot obtain key material from the agent,
1.3 stevesk 400: however they can perform operations on the keys that enable them to
401: authenticate using the identities loaded into the agent.
1.1 stevesk 402: .It Cm ForwardX11
403: Specifies whether X11 connections will be automatically redirected
404: over the secure channel and
405: .Ev DISPLAY
406: set.
407: The argument must be
408: .Dq yes
409: or
410: .Dq no .
411: The default is
412: .Dq no .
1.3 stevesk 413: .Pp
1.7 jmc 414: X11 forwarding should be enabled with caution.
415: Users with the ability to bypass file permissions on the remote host
1.22 markus 416: (for the user's X11 authorization database)
1.7 jmc 417: can access the local X11 display through the forwarded connection.
1.22 markus 418: An attacker may then be able to perform activities such as keystroke monitoring
419: if the
420: .Cm ForwardX11Trusted
421: option is also enabled.
422: .It Cm ForwardX11Trusted
1.34 jmc 423: If this option is set to
1.84 jmc 424: .Dq yes ,
425: remote X11 clients will have full access to the original X11 display.
1.42 djm 426: .Pp
1.22 markus 427: If this option is set to
1.84 jmc 428: .Dq no ,
429: remote X11 clients will be considered untrusted and prevented
1.22 markus 430: from stealing or tampering with data belonging to trusted X11
431: clients.
1.42 djm 432: Furthermore, the
433: .Xr xauth 1
434: token used for the session will be set to expire after 20 minutes.
435: Remote clients will be refused access after this time.
1.22 markus 436: .Pp
437: The default is
438: .Dq no .
439: .Pp
440: See the X11 SECURITY extension specification for full details on
441: the restrictions imposed on untrusted clients.
1.1 stevesk 442: .It Cm GatewayPorts
443: Specifies whether remote hosts are allowed to connect to local
444: forwarded ports.
445: By default,
1.84 jmc 446: .Xr ssh 1
1.7 jmc 447: binds local port forwardings to the loopback address.
448: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 449: .Cm GatewayPorts
1.84 jmc 450: can be used to specify that ssh
1.1 stevesk 451: should bind local port forwardings to the wildcard address,
452: thus allowing remote hosts to connect to forwarded ports.
453: The argument must be
454: .Dq yes
455: or
456: .Dq no .
457: The default is
458: .Dq no .
459: .It Cm GlobalKnownHostsFile
460: Specifies a file to use for the global
461: host key database instead of
462: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 463: .It Cm GSSAPIAuthentication
1.27 markus 464: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 465: The default is
1.21 markus 466: .Dq no .
1.18 markus 467: Note that this option applies to protocol version 2 only.
468: .It Cm GSSAPIDelegateCredentials
469: Forward (delegate) credentials to the server.
470: The default is
471: .Dq no .
472: Note that this option applies to protocol version 2 only.
1.44 djm 473: .It Cm HashKnownHosts
474: Indicates that
1.84 jmc 475: .Xr ssh 1
1.44 djm 476: should hash host names and addresses when they are added to
1.50 djm 477: .Pa ~/.ssh/known_hosts .
1.44 djm 478: These hashed names may be used normally by
1.84 jmc 479: .Xr ssh 1
1.44 djm 480: and
1.84 jmc 481: .Xr sshd 8 ,
1.44 djm 482: but they do not reveal identifying information should the file's contents
483: be disclosed.
484: The default is
485: .Dq no .
1.46 jmc 486: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 487: to existing known hosts files, but these may be manually hashed using
488: .Xr ssh-keygen 1 .
1.1 stevesk 489: .It Cm HostbasedAuthentication
490: Specifies whether to try rhosts based authentication with public key
491: authentication.
492: The argument must be
493: .Dq yes
494: or
495: .Dq no .
496: The default is
497: .Dq no .
498: This option applies to protocol version 2 only and
499: is similar to
500: .Cm RhostsRSAAuthentication .
501: .It Cm HostKeyAlgorithms
502: Specifies the protocol version 2 host key algorithms
503: that the client wants to use in order of preference.
504: The default for this option is:
505: .Dq ssh-rsa,ssh-dss .
506: .It Cm HostKeyAlias
507: Specifies an alias that should be used instead of the
508: real host name when looking up or saving the host key
509: in the host key database files.
1.84 jmc 510: This option is useful for tunneling SSH connections
1.1 stevesk 511: or for multiple servers running on a single host.
512: .It Cm HostName
513: Specifies the real host name to log into.
514: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 515: The default is the name given on the command line.
1.1 stevesk 516: Numeric IP addresses are also permitted (both on the command line and in
517: .Cm HostName
518: specifications).
1.29 markus 519: .It Cm IdentitiesOnly
520: Specifies that
1.84 jmc 521: .Xr ssh 1
1.29 markus 522: should only use the authentication identity files configured in the
1.31 jmc 523: .Nm
1.29 markus 524: files,
1.84 jmc 525: even if
526: .Xr ssh-agent 1
1.29 markus 527: offers more identities.
528: The argument to this keyword must be
529: .Dq yes
530: or
531: .Dq no .
1.84 jmc 532: This option is intended for situations where ssh-agent
1.29 markus 533: offers many different identities.
534: The default is
535: .Dq no .
1.67 jmc 536: .It Cm IdentityFile
537: Specifies a file from which the user's RSA or DSA authentication identity
538: is read.
539: The default is
540: .Pa ~/.ssh/identity
541: for protocol version 1, and
542: .Pa ~/.ssh/id_rsa
543: and
544: .Pa ~/.ssh/id_dsa
545: for protocol version 2.
546: Additionally, any identities represented by the authentication agent
547: will be used for authentication.
548: The file name may use the tilde
549: syntax to refer to a user's home directory.
550: It is possible to have
551: multiple identity files specified in configuration files; all these
552: identities will be tried in sequence.
1.39 djm 553: .It Cm KbdInteractiveDevices
554: Specifies the list of methods to use in keyboard-interactive authentication.
555: Multiple method names must be comma-separated.
556: The default is to use the server specified list.
1.85 jmc 557: The methods available vary depending on what the server supports.
558: For an OpenSSH server,
559: it may be zero or more of:
560: .Dq bsdauth ,
561: .Dq pam ,
562: and
563: .Dq skey .
1.65 reyk 564: .It Cm LocalCommand
565: Specifies a command to execute on the local machine after successfully
566: connecting to the server.
567: The command string extends to the end of the line, and is executed with
568: .Pa /bin/sh .
569: This directive is ignored unless
570: .Cm PermitLocalCommand
571: has been enabled.
1.1 stevesk 572: .It Cm LocalForward
1.74 jmc 573: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 574: the secure channel to the specified host and port from the remote machine.
1.49 jmc 575: The first argument must be
1.43 djm 576: .Sm off
1.49 jmc 577: .Oo Ar bind_address : Oc Ar port
1.43 djm 578: .Sm on
1.49 jmc 579: and the second argument must be
580: .Ar host : Ns Ar hostport .
1.46 jmc 581: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 582: by using an alternative syntax:
1.49 jmc 583: .Oo Ar bind_address Ns / Oc Ns Ar port
584: and
585: .Ar host Ns / Ns Ar hostport .
1.46 jmc 586: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 587: given on the command line.
1.1 stevesk 588: Only the superuser can forward privileged ports.
1.43 djm 589: By default, the local port is bound in accordance with the
590: .Cm GatewayPorts
591: setting.
592: However, an explicit
593: .Ar bind_address
594: may be used to bind the connection to a specific address.
595: The
596: .Ar bind_address
597: of
598: .Dq localhost
1.46 jmc 599: indicates that the listening port be bound for local use only, while an
600: empty address or
601: .Sq *
1.43 djm 602: indicates that the port should be available from all interfaces.
1.1 stevesk 603: .It Cm LogLevel
604: Gives the verbosity level that is used when logging messages from
1.84 jmc 605: .Xr ssh 1 .
1.1 stevesk 606: The possible values are:
1.84 jmc 607: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 608: The default is INFO.
609: DEBUG and DEBUG1 are equivalent.
610: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 611: .It Cm MACs
612: Specifies the MAC (message authentication code) algorithms
613: in order of preference.
614: The MAC algorithm is used in protocol version 2
615: for data integrity protection.
616: Multiple algorithms must be comma-separated.
1.84 jmc 617: The default is:
1.1 stevesk 618: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
619: .It Cm NoHostAuthenticationForLocalhost
620: This option can be used if the home directory is shared across machines.
621: In this case localhost will refer to a different machine on each of
622: the machines and the user will get many warnings about changed host keys.
623: However, this option disables host authentication for localhost.
624: The argument to this keyword must be
625: .Dq yes
626: or
627: .Dq no .
628: The default is to check the host key for localhost.
629: .It Cm NumberOfPasswordPrompts
630: Specifies the number of password prompts before giving up.
631: The argument to this keyword must be an integer.
1.84 jmc 632: The default is 3.
1.1 stevesk 633: .It Cm PasswordAuthentication
634: Specifies whether to use password authentication.
635: The argument to this keyword must be
636: .Dq yes
637: or
638: .Dq no .
639: The default is
640: .Dq yes .
1.65 reyk 641: .It Cm PermitLocalCommand
642: Allow local command execution via the
643: .Ic LocalCommand
644: option or using the
1.66 jmc 645: .Ic !\& Ns Ar command
1.65 reyk 646: escape sequence in
647: .Xr ssh 1 .
648: The argument must be
649: .Dq yes
650: or
651: .Dq no .
652: The default is
653: .Dq no .
1.67 jmc 654: .It Cm Port
655: Specifies the port number to connect on the remote host.
1.84 jmc 656: The default is 22.
1.1 stevesk 657: .It Cm PreferredAuthentications
658: Specifies the order in which the client should try protocol 2
1.11 jmc 659: authentication methods.
1.48 jmc 660: This allows a client to prefer one method (e.g.\&
1.1 stevesk 661: .Cm keyboard-interactive )
1.48 jmc 662: over another method (e.g.\&
1.1 stevesk 663: .Cm password )
664: The default for this option is:
665: .Dq hostbased,publickey,keyboard-interactive,password .
666: .It Cm Protocol
667: Specifies the protocol versions
1.84 jmc 668: .Xr ssh 1
1.1 stevesk 669: should support in order of preference.
670: The possible values are
1.84 jmc 671: .Sq 1
1.1 stevesk 672: and
1.84 jmc 673: .Sq 2 .
1.1 stevesk 674: Multiple versions must be comma-separated.
675: The default is
676: .Dq 2,1 .
1.84 jmc 677: This means that ssh
1.1 stevesk 678: tries version 2 and falls back to version 1
679: if version 2 is not available.
680: .It Cm ProxyCommand
681: Specifies the command to use to connect to the server.
682: The command
683: string extends to the end of the line, and is executed with
684: .Pa /bin/sh .
685: In the command string,
686: .Ql %h
687: will be substituted by the host name to
688: connect and
689: .Ql %p
690: by the port.
691: The command can be basically anything,
692: and should read from its standard input and write to its standard output.
693: It should eventually connect an
694: .Xr sshd 8
695: server running on some machine, or execute
696: .Ic sshd -i
697: somewhere.
698: Host key management will be done using the
699: HostName of the host being connected (defaulting to the name typed by
700: the user).
1.7 jmc 701: Setting the command to
702: .Dq none
1.6 markus 703: disables this option entirely.
1.1 stevesk 704: Note that
705: .Cm CheckHostIP
706: is not available for connects with a proxy command.
1.52 djm 707: .Pp
708: This directive is useful in conjunction with
709: .Xr nc 1
710: and its proxy support.
1.53 jmc 711: For example, the following directive would connect via an HTTP proxy at
1.52 djm 712: 192.0.2.0:
713: .Bd -literal -offset 3n
714: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
715: .Ed
1.1 stevesk 716: .It Cm PubkeyAuthentication
717: Specifies whether to try public key authentication.
718: The argument to this keyword must be
719: .Dq yes
720: or
721: .Dq no .
722: The default is
723: .Dq yes .
724: This option applies to protocol version 2 only.
1.75 dtucker 725: .It Cm RekeyLimit
726: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 727: session key is renegotiated.
1.75 dtucker 728: The argument is the number of bytes, with an optional suffix of
1.76 jmc 729: .Sq K ,
730: .Sq M ,
1.75 dtucker 731: or
1.76 jmc 732: .Sq G
1.75 dtucker 733: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
734: The default is between
1.84 jmc 735: .Sq 1G
1.75 dtucker 736: and
1.84 jmc 737: .Sq 4G ,
1.75 dtucker 738: depending on the cipher.
1.76 jmc 739: This option applies to protocol version 2 only.
1.1 stevesk 740: .It Cm RemoteForward
1.74 jmc 741: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 742: the secure channel to the specified host and port from the local machine.
1.49 jmc 743: The first argument must be
1.43 djm 744: .Sm off
1.49 jmc 745: .Oo Ar bind_address : Oc Ar port
1.43 djm 746: .Sm on
1.49 jmc 747: and the second argument must be
748: .Ar host : Ns Ar hostport .
749: IPv6 addresses can be specified by enclosing addresses in square brackets
750: or by using an alternative syntax:
751: .Oo Ar bind_address Ns / Oc Ns Ar port
752: and
753: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 754: Multiple forwardings may be specified, and additional
755: forwardings can be given on the command line.
756: Only the superuser can forward privileged ports.
1.43 djm 757: .Pp
758: If the
759: .Ar bind_address
760: is not specified, the default is to only bind to loopback addresses.
761: If the
762: .Ar bind_address
763: is
764: .Ql *
765: or an empty string, then the forwarding is requested to listen on all
766: interfaces.
767: Specifying a remote
768: .Ar bind_address
1.46 jmc 769: will only succeed if the server's
770: .Cm GatewayPorts
1.43 djm 771: option is enabled (see
1.46 jmc 772: .Xr sshd_config 5 ) .
1.1 stevesk 773: .It Cm RhostsRSAAuthentication
774: Specifies whether to try rhosts based authentication with RSA host
775: authentication.
776: The argument must be
777: .Dq yes
778: or
779: .Dq no .
780: The default is
781: .Dq no .
782: This option applies to protocol version 1 only and requires
1.84 jmc 783: .Xr ssh 1
1.1 stevesk 784: to be setuid root.
785: .It Cm RSAAuthentication
786: Specifies whether to try RSA authentication.
787: The argument to this keyword must be
788: .Dq yes
789: or
790: .Dq no .
791: RSA authentication will only be
792: attempted if the identity file exists, or an authentication agent is
793: running.
794: The default is
795: .Dq yes .
796: Note that this option applies to protocol version 1 only.
1.32 djm 797: .It Cm SendEnv
798: Specifies what variables from the local
799: .Xr environ 7
800: should be sent to the server.
1.84 jmc 801: Note that environment passing is only supported for protocol 2.
802: The server must also support it, and the server must be configured to
1.33 djm 803: accept these environment variables.
1.32 djm 804: Refer to
805: .Cm AcceptEnv
806: in
807: .Xr sshd_config 5
808: for how to configure the server.
1.80 jmc 809: Variables are specified by name, which may contain wildcard characters.
1.33 djm 810: Multiple environment variables may be separated by whitespace or spread
1.32 djm 811: across multiple
812: .Cm SendEnv
813: directives.
814: The default is not to send any environment variables.
1.81 jmc 815: .Pp
816: See
817: .Sx PATTERNS
818: for more information on patterns.
1.28 markus 819: .It Cm ServerAliveCountMax
1.73 jmc 820: Sets the number of server alive messages (see below) which may be
1.28 markus 821: sent without
1.84 jmc 822: .Xr ssh 1
1.28 markus 823: receiving any messages back from the server.
824: If this threshold is reached while server alive messages are being sent,
1.84 jmc 825: ssh will disconnect from the server, terminating the session.
1.28 markus 826: It is important to note that the use of server alive messages is very
827: different from
828: .Cm TCPKeepAlive
829: (below).
830: The server alive messages are sent through the encrypted channel
831: and therefore will not be spoofable.
832: The TCP keepalive option enabled by
833: .Cm TCPKeepAlive
834: is spoofable.
835: The server alive mechanism is valuable when the client or
836: server depend on knowing when a connection has become inactive.
837: .Pp
838: The default value is 3.
839: If, for example,
840: .Cm ServerAliveInterval
1.84 jmc 841: (see below) is set to 15 and
1.28 markus 842: .Cm ServerAliveCountMax
1.84 jmc 843: is left at the default, if the server becomes unresponsive,
844: ssh will disconnect after approximately 45 seconds.
1.67 jmc 845: .It Cm ServerAliveInterval
846: Sets a timeout interval in seconds after which if no data has been received
847: from the server,
1.84 jmc 848: .Xr ssh 1
1.67 jmc 849: will send a message through the encrypted
850: channel to request a response from the server.
851: The default
852: is 0, indicating that these messages will not be sent to the server.
853: This option applies to protocol version 2 only.
1.1 stevesk 854: .It Cm SmartcardDevice
1.11 jmc 855: Specifies which smartcard device to use.
856: The argument to this keyword is the device
1.84 jmc 857: .Xr ssh 1
1.1 stevesk 858: should use to communicate with a smartcard used for storing the user's
1.11 jmc 859: private RSA key.
860: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 861: .It Cm StrictHostKeyChecking
862: If this flag is set to
863: .Dq yes ,
1.84 jmc 864: .Xr ssh 1
1.1 stevesk 865: will never automatically add host keys to the
1.50 djm 866: .Pa ~/.ssh/known_hosts
1.1 stevesk 867: file, and refuses to connect to hosts whose host key has changed.
868: This provides maximum protection against trojan horse attacks,
1.84 jmc 869: though it can be annoying when the
1.1 stevesk 870: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 871: file is poorly maintained or when connections to new hosts are
1.1 stevesk 872: frequently made.
873: This option forces the user to manually
874: add all new hosts.
875: If this flag is set to
876: .Dq no ,
1.84 jmc 877: ssh will automatically add new host keys to the
1.1 stevesk 878: user known hosts files.
879: If this flag is set to
880: .Dq ask ,
881: new host keys
882: will be added to the user known host files only after the user
883: has confirmed that is what they really want to do, and
1.84 jmc 884: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 885: The host keys of
886: known hosts will be verified automatically in all cases.
887: The argument must be
888: .Dq yes ,
1.84 jmc 889: .Dq no ,
1.1 stevesk 890: or
891: .Dq ask .
892: The default is
893: .Dq ask .
1.26 markus 894: .It Cm TCPKeepAlive
895: Specifies whether the system should send TCP keepalive messages to the
896: other side.
897: If they are sent, death of the connection or crash of one
898: of the machines will be properly noticed.
899: However, this means that
900: connections will die if the route is down temporarily, and some people
901: find it annoying.
902: .Pp
903: The default is
904: .Dq yes
905: (to send TCP keepalive messages), and the client will notice
906: if the network goes down or the remote host dies.
907: This is important in scripts, and many users want it too.
908: .Pp
909: To disable TCP keepalive messages, the value should be set to
910: .Dq no .
1.65 reyk 911: .It Cm Tunnel
912: Request starting
913: .Xr tun 4
1.69 jmc 914: device forwarding between the client and the server.
915: This option also allows requesting layer 2 (ethernet)
916: instead of layer 3 (point-to-point) tunneling from the server.
1.65 reyk 917: The argument must be
1.68 reyk 918: .Dq yes ,
919: .Dq point-to-point ,
1.84 jmc 920: .Dq ethernet ,
1.65 reyk 921: or
922: .Dq no .
923: The default is
924: .Dq no .
925: .It Cm TunnelDevice
926: Force a specified
927: .Xr tun 4
928: device on the client.
929: Without this option, the next available device will be used.
1.72 jmc 930: .It Cm UsePrivilegedPort
931: Specifies whether to use a privileged port for outgoing connections.
932: The argument must be
933: .Dq yes
934: or
935: .Dq no .
936: The default is
937: .Dq no .
938: If set to
1.84 jmc 939: .Dq yes ,
940: .Xr ssh 1
1.72 jmc 941: must be setuid root.
942: Note that this option must be set to
943: .Dq yes
944: for
945: .Cm RhostsRSAAuthentication
946: with older servers.
1.1 stevesk 947: .It Cm User
948: Specifies the user to log in as.
949: This can be useful when a different user name is used on different machines.
950: This saves the trouble of
951: having to remember to give the user name on the command line.
952: .It Cm UserKnownHostsFile
953: Specifies a file to use for the user
954: host key database instead of
1.50 djm 955: .Pa ~/.ssh/known_hosts .
1.8 jakob 956: .It Cm VerifyHostKeyDNS
957: Specifies whether to verify the remote key using DNS and SSHFP resource
958: records.
1.24 jakob 959: If this option is set to
960: .Dq yes ,
1.25 jmc 961: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 962: from DNS.
963: Insecure fingerprints will be handled as if this option was set to
964: .Dq ask .
965: If this option is set to
966: .Dq ask ,
967: information on fingerprint match will be displayed, but the user will still
968: need to confirm new host keys according to the
969: .Cm StrictHostKeyChecking
970: option.
971: The argument must be
972: .Dq yes ,
1.84 jmc 973: .Dq no ,
1.25 jmc 974: or
975: .Dq ask .
1.8 jakob 976: The default is
977: .Dq no .
1.12 jakob 978: Note that this option applies to protocol version 2 only.
1.84 jmc 979: .Pp
980: See also
981: .Sx VERIFYING HOST KEYS
982: in
983: .Xr ssh 1 .
1.1 stevesk 984: .It Cm XAuthLocation
1.5 stevesk 985: Specifies the full pathname of the
1.1 stevesk 986: .Xr xauth 1
987: program.
988: The default is
989: .Pa /usr/X11R6/bin/xauth .
990: .El
1.86 ! jmc 991: .Sh PATTERNS
! 992: A
! 993: .Em pattern
! 994: consists of zero or more non-whitespace characters,
! 995: .Sq *
! 996: (a wildcard that matches zero or more characters),
! 997: or
! 998: .Sq ?\&
! 999: (a wildcard that matches exactly one character).
! 1000: For example, to specify a set of declarations for any host in the
! 1001: .Dq .co.uk
! 1002: set of domains,
! 1003: the following pattern could be used:
! 1004: .Pp
! 1005: .Dl Host *.co.uk
! 1006: .Pp
! 1007: The following pattern
! 1008: would match any host in the 192.168.0.[0-9] network range:
! 1009: .Pp
! 1010: .Dl Host 192.168.0.?
! 1011: .Pp
! 1012: A
! 1013: .Em pattern-list
! 1014: is a comma-separated list of patterns.
! 1015: Patterns within pattern-lists may be negated
! 1016: by preceding them with an exclamation mark
! 1017: .Pq Sq !\& .
! 1018: For example,
! 1019: to allow a key to be used from anywhere within an organisation
! 1020: except from the
! 1021: .Dq dialup
! 1022: pool,
! 1023: the following entry (in authorized_keys) could be used:
! 1024: .Pp
! 1025: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 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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