Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.90
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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27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.90 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.89 2006/03/14 16:32:48 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).
388: .It Cm ForwardAgent
389: Specifies whether the connection to the authentication agent (if any)
390: will be forwarded to the remote machine.
391: The argument must be
392: .Dq yes
393: or
394: .Dq no .
395: The default is
396: .Dq no .
1.3 stevesk 397: .Pp
1.7 jmc 398: Agent forwarding should be enabled with caution.
399: Users with the ability to bypass file permissions on the remote host
400: (for the agent's Unix-domain socket)
401: can access the local agent through the forwarded connection.
402: An attacker cannot obtain key material from the agent,
1.3 stevesk 403: however they can perform operations on the keys that enable them to
404: authenticate using the identities loaded into the agent.
1.1 stevesk 405: .It Cm ForwardX11
406: Specifies whether X11 connections will be automatically redirected
407: over the secure channel and
408: .Ev DISPLAY
409: set.
410: The argument must be
411: .Dq yes
412: or
413: .Dq no .
414: The default is
415: .Dq no .
1.3 stevesk 416: .Pp
1.7 jmc 417: X11 forwarding should be enabled with caution.
418: Users with the ability to bypass file permissions on the remote host
1.22 markus 419: (for the user's X11 authorization database)
1.7 jmc 420: can access the local X11 display through the forwarded connection.
1.22 markus 421: An attacker may then be able to perform activities such as keystroke monitoring
422: if the
423: .Cm ForwardX11Trusted
424: option is also enabled.
425: .It Cm ForwardX11Trusted
1.34 jmc 426: If this option is set to
1.84 jmc 427: .Dq yes ,
428: remote X11 clients will have full access to the original X11 display.
1.42 djm 429: .Pp
1.22 markus 430: If this option is set to
1.84 jmc 431: .Dq no ,
432: remote X11 clients will be considered untrusted and prevented
1.22 markus 433: from stealing or tampering with data belonging to trusted X11
434: clients.
1.42 djm 435: Furthermore, the
436: .Xr xauth 1
437: token used for the session will be set to expire after 20 minutes.
438: Remote clients will be refused access after this time.
1.22 markus 439: .Pp
440: The default is
441: .Dq no .
442: .Pp
443: See the X11 SECURITY extension specification for full details on
444: the restrictions imposed on untrusted clients.
1.1 stevesk 445: .It Cm GatewayPorts
446: Specifies whether remote hosts are allowed to connect to local
447: forwarded ports.
448: By default,
1.84 jmc 449: .Xr ssh 1
1.7 jmc 450: binds local port forwardings to the loopback address.
451: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 452: .Cm GatewayPorts
1.84 jmc 453: can be used to specify that ssh
1.1 stevesk 454: should bind local port forwardings to the wildcard address,
455: thus allowing remote hosts to connect to forwarded ports.
456: The argument must be
457: .Dq yes
458: or
459: .Dq no .
460: The default is
461: .Dq no .
462: .It Cm GlobalKnownHostsFile
463: Specifies a file to use for the global
464: host key database instead of
465: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 466: .It Cm GSSAPIAuthentication
1.27 markus 467: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 468: The default is
1.21 markus 469: .Dq no .
1.18 markus 470: Note that this option applies to protocol version 2 only.
471: .It Cm GSSAPIDelegateCredentials
472: Forward (delegate) credentials to the server.
473: The default is
474: .Dq no .
475: Note that this option applies to protocol version 2 only.
1.44 djm 476: .It Cm HashKnownHosts
477: Indicates that
1.84 jmc 478: .Xr ssh 1
1.44 djm 479: should hash host names and addresses when they are added to
1.50 djm 480: .Pa ~/.ssh/known_hosts .
1.44 djm 481: These hashed names may be used normally by
1.84 jmc 482: .Xr ssh 1
1.44 djm 483: and
1.84 jmc 484: .Xr sshd 8 ,
1.44 djm 485: but they do not reveal identifying information should the file's contents
486: be disclosed.
487: The default is
488: .Dq no .
1.46 jmc 489: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 490: to existing known hosts files, but these may be manually hashed using
491: .Xr ssh-keygen 1 .
1.1 stevesk 492: .It Cm HostbasedAuthentication
493: Specifies whether to try rhosts based authentication with public key
494: authentication.
495: The argument must be
496: .Dq yes
497: or
498: .Dq no .
499: The default is
500: .Dq no .
501: This option applies to protocol version 2 only and
502: is similar to
503: .Cm RhostsRSAAuthentication .
504: .It Cm HostKeyAlgorithms
505: Specifies the protocol version 2 host key algorithms
506: that the client wants to use in order of preference.
507: The default for this option is:
508: .Dq ssh-rsa,ssh-dss .
509: .It Cm HostKeyAlias
510: Specifies an alias that should be used instead of the
511: real host name when looking up or saving the host key
512: in the host key database files.
1.84 jmc 513: This option is useful for tunneling SSH connections
1.1 stevesk 514: or for multiple servers running on a single host.
515: .It Cm HostName
516: Specifies the real host name to log into.
517: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 518: The default is the name given on the command line.
1.1 stevesk 519: Numeric IP addresses are also permitted (both on the command line and in
520: .Cm HostName
521: specifications).
1.29 markus 522: .It Cm IdentitiesOnly
523: Specifies that
1.84 jmc 524: .Xr ssh 1
1.29 markus 525: should only use the authentication identity files configured in the
1.31 jmc 526: .Nm
1.29 markus 527: files,
1.84 jmc 528: even if
529: .Xr ssh-agent 1
1.29 markus 530: offers more identities.
531: The argument to this keyword must be
532: .Dq yes
533: or
534: .Dq no .
1.84 jmc 535: This option is intended for situations where ssh-agent
1.29 markus 536: offers many different identities.
537: The default is
538: .Dq no .
1.67 jmc 539: .It Cm IdentityFile
540: Specifies a file from which the user's RSA or DSA authentication identity
541: is read.
542: The default is
543: .Pa ~/.ssh/identity
544: for protocol version 1, and
545: .Pa ~/.ssh/id_rsa
546: and
547: .Pa ~/.ssh/id_dsa
548: for protocol version 2.
549: Additionally, any identities represented by the authentication agent
550: will be used for authentication.
1.90 ! djm 551: .Pp
1.67 jmc 552: The file name may use the tilde
1.90 ! djm 553: syntax to refer to a user's home directory or one of the following
! 554: escape characters:
! 555: .Ql %d
! 556: (local user's home directory),
! 557: .Ql %u
! 558: (local user name),
! 559: .Ql %l
! 560: (local host name),
! 561: .Ql %h
! 562: (remote host name) or
! 563: .Ql %h
! 564: (remote user name).
! 565: .Pp
1.67 jmc 566: It is possible to have
567: multiple identity files specified in configuration files; all these
568: identities will be tried in sequence.
1.39 djm 569: .It Cm KbdInteractiveDevices
570: Specifies the list of methods to use in keyboard-interactive authentication.
571: Multiple method names must be comma-separated.
572: The default is to use the server specified list.
1.85 jmc 573: The methods available vary depending on what the server supports.
574: For an OpenSSH server,
575: it may be zero or more of:
576: .Dq bsdauth ,
577: .Dq pam ,
578: and
579: .Dq skey .
1.65 reyk 580: .It Cm LocalCommand
581: Specifies a command to execute on the local machine after successfully
582: connecting to the server.
583: The command string extends to the end of the line, and is executed with
584: .Pa /bin/sh .
585: This directive is ignored unless
586: .Cm PermitLocalCommand
587: has been enabled.
1.1 stevesk 588: .It Cm LocalForward
1.74 jmc 589: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 590: the secure channel to the specified host and port from the remote machine.
1.49 jmc 591: The first argument must be
1.43 djm 592: .Sm off
1.49 jmc 593: .Oo Ar bind_address : Oc Ar port
1.43 djm 594: .Sm on
1.49 jmc 595: and the second argument must be
596: .Ar host : Ns Ar hostport .
1.46 jmc 597: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 598: by using an alternative syntax:
1.49 jmc 599: .Oo Ar bind_address Ns / Oc Ns Ar port
600: and
601: .Ar host Ns / Ns Ar hostport .
1.46 jmc 602: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 603: given on the command line.
1.1 stevesk 604: Only the superuser can forward privileged ports.
1.43 djm 605: By default, the local port is bound in accordance with the
606: .Cm GatewayPorts
607: setting.
608: However, an explicit
609: .Ar bind_address
610: may be used to bind the connection to a specific address.
611: The
612: .Ar bind_address
613: of
614: .Dq localhost
1.46 jmc 615: indicates that the listening port be bound for local use only, while an
616: empty address or
617: .Sq *
1.43 djm 618: indicates that the port should be available from all interfaces.
1.1 stevesk 619: .It Cm LogLevel
620: Gives the verbosity level that is used when logging messages from
1.84 jmc 621: .Xr ssh 1 .
1.1 stevesk 622: The possible values are:
1.84 jmc 623: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 624: The default is INFO.
625: DEBUG and DEBUG1 are equivalent.
626: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 627: .It Cm MACs
628: Specifies the MAC (message authentication code) algorithms
629: in order of preference.
630: The MAC algorithm is used in protocol version 2
631: for data integrity protection.
632: Multiple algorithms must be comma-separated.
1.84 jmc 633: The default is:
1.1 stevesk 634: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
635: .It Cm NoHostAuthenticationForLocalhost
636: This option can be used if the home directory is shared across machines.
637: In this case localhost will refer to a different machine on each of
638: the machines and the user will get many warnings about changed host keys.
639: However, this option disables host authentication for localhost.
640: The argument to this keyword must be
641: .Dq yes
642: or
643: .Dq no .
644: The default is to check the host key for localhost.
645: .It Cm NumberOfPasswordPrompts
646: Specifies the number of password prompts before giving up.
647: The argument to this keyword must be an integer.
1.84 jmc 648: The default is 3.
1.1 stevesk 649: .It Cm PasswordAuthentication
650: Specifies whether to use password authentication.
651: The argument to this keyword must be
652: .Dq yes
653: or
654: .Dq no .
655: The default is
656: .Dq yes .
1.65 reyk 657: .It Cm PermitLocalCommand
658: Allow local command execution via the
659: .Ic LocalCommand
660: option or using the
1.66 jmc 661: .Ic !\& Ns Ar command
1.65 reyk 662: escape sequence in
663: .Xr ssh 1 .
664: The argument must be
665: .Dq yes
666: or
667: .Dq no .
668: The default is
669: .Dq no .
1.67 jmc 670: .It Cm Port
671: Specifies the port number to connect on the remote host.
1.84 jmc 672: The default is 22.
1.1 stevesk 673: .It Cm PreferredAuthentications
674: Specifies the order in which the client should try protocol 2
1.11 jmc 675: authentication methods.
1.48 jmc 676: This allows a client to prefer one method (e.g.\&
1.1 stevesk 677: .Cm keyboard-interactive )
1.48 jmc 678: over another method (e.g.\&
1.1 stevesk 679: .Cm password )
680: The default for this option is:
681: .Dq hostbased,publickey,keyboard-interactive,password .
682: .It Cm Protocol
683: Specifies the protocol versions
1.84 jmc 684: .Xr ssh 1
1.1 stevesk 685: should support in order of preference.
686: The possible values are
1.84 jmc 687: .Sq 1
1.1 stevesk 688: and
1.84 jmc 689: .Sq 2 .
1.1 stevesk 690: Multiple versions must be comma-separated.
691: The default is
692: .Dq 2,1 .
1.84 jmc 693: This means that ssh
1.1 stevesk 694: tries version 2 and falls back to version 1
695: if version 2 is not available.
696: .It Cm ProxyCommand
697: Specifies the command to use to connect to the server.
698: The command
699: string extends to the end of the line, and is executed with
700: .Pa /bin/sh .
701: In the command string,
702: .Ql %h
703: will be substituted by the host name to
704: connect and
705: .Ql %p
706: by the port.
707: The command can be basically anything,
708: and should read from its standard input and write to its standard output.
709: It should eventually connect an
710: .Xr sshd 8
711: server running on some machine, or execute
712: .Ic sshd -i
713: somewhere.
714: Host key management will be done using the
715: HostName of the host being connected (defaulting to the name typed by
716: the user).
1.7 jmc 717: Setting the command to
718: .Dq none
1.6 markus 719: disables this option entirely.
1.1 stevesk 720: Note that
721: .Cm CheckHostIP
722: is not available for connects with a proxy command.
1.52 djm 723: .Pp
724: This directive is useful in conjunction with
725: .Xr nc 1
726: and its proxy support.
1.53 jmc 727: For example, the following directive would connect via an HTTP proxy at
1.52 djm 728: 192.0.2.0:
729: .Bd -literal -offset 3n
730: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
731: .Ed
1.1 stevesk 732: .It Cm PubkeyAuthentication
733: Specifies whether to try public key authentication.
734: The argument to this keyword must be
735: .Dq yes
736: or
737: .Dq no .
738: The default is
739: .Dq yes .
740: This option applies to protocol version 2 only.
1.75 dtucker 741: .It Cm RekeyLimit
742: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 743: session key is renegotiated.
1.75 dtucker 744: The argument is the number of bytes, with an optional suffix of
1.76 jmc 745: .Sq K ,
746: .Sq M ,
1.75 dtucker 747: or
1.76 jmc 748: .Sq G
1.75 dtucker 749: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
750: The default is between
1.84 jmc 751: .Sq 1G
1.75 dtucker 752: and
1.84 jmc 753: .Sq 4G ,
1.75 dtucker 754: depending on the cipher.
1.76 jmc 755: This option applies to protocol version 2 only.
1.1 stevesk 756: .It Cm RemoteForward
1.74 jmc 757: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 758: the secure channel to the specified host and port from the local machine.
1.49 jmc 759: The first argument must be
1.43 djm 760: .Sm off
1.49 jmc 761: .Oo Ar bind_address : Oc Ar port
1.43 djm 762: .Sm on
1.49 jmc 763: and the second argument must be
764: .Ar host : Ns Ar hostport .
765: IPv6 addresses can be specified by enclosing addresses in square brackets
766: or by using an alternative syntax:
767: .Oo Ar bind_address Ns / Oc Ns Ar port
768: and
769: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 770: Multiple forwardings may be specified, and additional
771: forwardings can be given on the command line.
772: Only the superuser can forward privileged ports.
1.43 djm 773: .Pp
774: If the
775: .Ar bind_address
776: is not specified, the default is to only bind to loopback addresses.
777: If the
778: .Ar bind_address
779: is
780: .Ql *
781: or an empty string, then the forwarding is requested to listen on all
782: interfaces.
783: Specifying a remote
784: .Ar bind_address
1.46 jmc 785: will only succeed if the server's
786: .Cm GatewayPorts
1.43 djm 787: option is enabled (see
1.46 jmc 788: .Xr sshd_config 5 ) .
1.1 stevesk 789: .It Cm RhostsRSAAuthentication
790: Specifies whether to try rhosts based authentication with RSA host
791: authentication.
792: The argument must be
793: .Dq yes
794: or
795: .Dq no .
796: The default is
797: .Dq no .
798: This option applies to protocol version 1 only and requires
1.84 jmc 799: .Xr ssh 1
1.1 stevesk 800: to be setuid root.
801: .It Cm RSAAuthentication
802: Specifies whether to try RSA authentication.
803: The argument to this keyword must be
804: .Dq yes
805: or
806: .Dq no .
807: RSA authentication will only be
808: attempted if the identity file exists, or an authentication agent is
809: running.
810: The default is
811: .Dq yes .
812: Note that this option applies to protocol version 1 only.
1.32 djm 813: .It Cm SendEnv
814: Specifies what variables from the local
815: .Xr environ 7
816: should be sent to the server.
1.84 jmc 817: Note that environment passing is only supported for protocol 2.
818: The server must also support it, and the server must be configured to
1.33 djm 819: accept these environment variables.
1.32 djm 820: Refer to
821: .Cm AcceptEnv
822: in
823: .Xr sshd_config 5
824: for how to configure the server.
1.80 jmc 825: Variables are specified by name, which may contain wildcard characters.
1.33 djm 826: Multiple environment variables may be separated by whitespace or spread
1.32 djm 827: across multiple
828: .Cm SendEnv
829: directives.
830: The default is not to send any environment variables.
1.81 jmc 831: .Pp
832: See
833: .Sx PATTERNS
834: for more information on patterns.
1.28 markus 835: .It Cm ServerAliveCountMax
1.73 jmc 836: Sets the number of server alive messages (see below) which may be
1.28 markus 837: sent without
1.84 jmc 838: .Xr ssh 1
1.28 markus 839: receiving any messages back from the server.
840: If this threshold is reached while server alive messages are being sent,
1.84 jmc 841: ssh will disconnect from the server, terminating the session.
1.28 markus 842: It is important to note that the use of server alive messages is very
843: different from
844: .Cm TCPKeepAlive
845: (below).
846: The server alive messages are sent through the encrypted channel
847: and therefore will not be spoofable.
848: The TCP keepalive option enabled by
849: .Cm TCPKeepAlive
850: is spoofable.
851: The server alive mechanism is valuable when the client or
852: server depend on knowing when a connection has become inactive.
853: .Pp
854: The default value is 3.
855: If, for example,
856: .Cm ServerAliveInterval
1.84 jmc 857: (see below) is set to 15 and
1.28 markus 858: .Cm ServerAliveCountMax
1.84 jmc 859: is left at the default, if the server becomes unresponsive,
860: ssh will disconnect after approximately 45 seconds.
1.89 markus 861: This option applies to protocol version 2 only.
1.67 jmc 862: .It Cm ServerAliveInterval
863: Sets a timeout interval in seconds after which if no data has been received
864: from the server,
1.84 jmc 865: .Xr ssh 1
1.67 jmc 866: will send a message through the encrypted
867: channel to request a response from the server.
868: The default
869: is 0, indicating that these messages will not be sent to the server.
870: This option applies to protocol version 2 only.
1.1 stevesk 871: .It Cm SmartcardDevice
1.11 jmc 872: Specifies which smartcard device to use.
873: The argument to this keyword is the device
1.84 jmc 874: .Xr ssh 1
1.1 stevesk 875: should use to communicate with a smartcard used for storing the user's
1.11 jmc 876: private RSA key.
877: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 878: .It Cm StrictHostKeyChecking
879: If this flag is set to
880: .Dq yes ,
1.84 jmc 881: .Xr ssh 1
1.1 stevesk 882: will never automatically add host keys to the
1.50 djm 883: .Pa ~/.ssh/known_hosts
1.1 stevesk 884: file, and refuses to connect to hosts whose host key has changed.
885: This provides maximum protection against trojan horse attacks,
1.84 jmc 886: though it can be annoying when the
1.1 stevesk 887: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 888: file is poorly maintained or when connections to new hosts are
1.1 stevesk 889: frequently made.
890: This option forces the user to manually
891: add all new hosts.
892: If this flag is set to
893: .Dq no ,
1.84 jmc 894: ssh will automatically add new host keys to the
1.1 stevesk 895: user known hosts files.
896: If this flag is set to
897: .Dq ask ,
898: new host keys
899: will be added to the user known host files only after the user
900: has confirmed that is what they really want to do, and
1.84 jmc 901: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 902: The host keys of
903: known hosts will be verified automatically in all cases.
904: The argument must be
905: .Dq yes ,
1.84 jmc 906: .Dq no ,
1.1 stevesk 907: or
908: .Dq ask .
909: The default is
910: .Dq ask .
1.26 markus 911: .It Cm TCPKeepAlive
912: Specifies whether the system should send TCP keepalive messages to the
913: other side.
914: If they are sent, death of the connection or crash of one
915: of the machines will be properly noticed.
916: However, this means that
917: connections will die if the route is down temporarily, and some people
918: find it annoying.
919: .Pp
920: The default is
921: .Dq yes
922: (to send TCP keepalive messages), and the client will notice
923: if the network goes down or the remote host dies.
924: This is important in scripts, and many users want it too.
925: .Pp
926: To disable TCP keepalive messages, the value should be set to
927: .Dq no .
1.65 reyk 928: .It Cm Tunnel
929: Request starting
930: .Xr tun 4
1.69 jmc 931: device forwarding between the client and the server.
932: This option also allows requesting layer 2 (ethernet)
933: instead of layer 3 (point-to-point) tunneling from the server.
1.65 reyk 934: The argument must be
1.68 reyk 935: .Dq yes ,
936: .Dq point-to-point ,
1.84 jmc 937: .Dq ethernet ,
1.65 reyk 938: or
939: .Dq no .
940: The default is
941: .Dq no .
942: .It Cm TunnelDevice
943: Force a specified
944: .Xr tun 4
945: device on the client.
946: Without this option, the next available device will be used.
1.72 jmc 947: .It Cm UsePrivilegedPort
948: Specifies whether to use a privileged port for outgoing connections.
949: The argument must be
950: .Dq yes
951: or
952: .Dq no .
953: The default is
954: .Dq no .
955: If set to
1.84 jmc 956: .Dq yes ,
957: .Xr ssh 1
1.72 jmc 958: must be setuid root.
959: Note that this option must be set to
960: .Dq yes
961: for
962: .Cm RhostsRSAAuthentication
963: with older servers.
1.1 stevesk 964: .It Cm User
965: Specifies the user to log in as.
966: This can be useful when a different user name is used on different machines.
967: This saves the trouble of
968: having to remember to give the user name on the command line.
969: .It Cm UserKnownHostsFile
970: Specifies a file to use for the user
971: host key database instead of
1.50 djm 972: .Pa ~/.ssh/known_hosts .
1.8 jakob 973: .It Cm VerifyHostKeyDNS
974: Specifies whether to verify the remote key using DNS and SSHFP resource
975: records.
1.24 jakob 976: If this option is set to
977: .Dq yes ,
1.25 jmc 978: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 979: from DNS.
980: Insecure fingerprints will be handled as if this option was set to
981: .Dq ask .
982: If this option is set to
983: .Dq ask ,
984: information on fingerprint match will be displayed, but the user will still
985: need to confirm new host keys according to the
986: .Cm StrictHostKeyChecking
987: option.
988: The argument must be
989: .Dq yes ,
1.84 jmc 990: .Dq no ,
1.25 jmc 991: or
992: .Dq ask .
1.8 jakob 993: The default is
994: .Dq no .
1.12 jakob 995: Note that this option applies to protocol version 2 only.
1.84 jmc 996: .Pp
997: See also
998: .Sx VERIFYING HOST KEYS
999: in
1000: .Xr ssh 1 .
1.1 stevesk 1001: .It Cm XAuthLocation
1.5 stevesk 1002: Specifies the full pathname of the
1.1 stevesk 1003: .Xr xauth 1
1004: program.
1005: The default is
1006: .Pa /usr/X11R6/bin/xauth .
1007: .El
1.86 jmc 1008: .Sh PATTERNS
1009: A
1010: .Em pattern
1011: consists of zero or more non-whitespace characters,
1012: .Sq *
1013: (a wildcard that matches zero or more characters),
1014: or
1015: .Sq ?\&
1016: (a wildcard that matches exactly one character).
1017: For example, to specify a set of declarations for any host in the
1018: .Dq .co.uk
1019: set of domains,
1020: the following pattern could be used:
1021: .Pp
1022: .Dl Host *.co.uk
1023: .Pp
1024: The following pattern
1025: would match any host in the 192.168.0.[0-9] network range:
1026: .Pp
1027: .Dl Host 192.168.0.?
1028: .Pp
1029: A
1030: .Em pattern-list
1031: is a comma-separated list of patterns.
1032: Patterns within pattern-lists may be negated
1033: by preceding them with an exclamation mark
1034: .Pq Sq !\& .
1035: For example,
1036: to allow a key to be used from anywhere within an organisation
1037: except from the
1038: .Dq dialup
1039: pool,
1040: the following entry (in authorized_keys) could be used:
1041: .Pp
1042: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1043: .Sh FILES
1044: .Bl -tag -width Ds
1.50 djm 1045: .It Pa ~/.ssh/config
1.1 stevesk 1046: This is the per-user configuration file.
1047: The format of this file is described above.
1.84 jmc 1048: This file is used by the SSH client.
1.30 djm 1049: Because of the potential for abuse, this file must have strict permissions:
1050: read/write for the user, and not accessible by others.
1.1 stevesk 1051: .It Pa /etc/ssh/ssh_config
1052: Systemwide configuration file.
1053: This file provides defaults for those
1054: values that are not specified in the user's configuration file, and
1055: for those users who do not have a configuration file.
1056: This file must be world-readable.
1057: .El
1.13 jmc 1058: .Sh SEE ALSO
1059: .Xr ssh 1
1.1 stevesk 1060: .Sh AUTHORS
1061: OpenSSH is a derivative of the original and free
1062: ssh 1.2.12 release by Tatu Ylonen.
1063: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1064: Theo de Raadt and Dug Song
1065: removed many bugs, re-added newer features and
1066: created OpenSSH.
1067: Markus Friedl contributed the support for SSH
1068: protocol versions 1.5 and 2.0.
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