Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.106
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.
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1.106 ! dtucker 37: .\" $OpenBSD: ssh_config.5,v 1.105 2007/10/29 07:48:19 jmc Exp $
1.105 jmc 38: .Dd $Mdocdate: October 29 2007 $
1.1 stevesk 39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
1.98 jmc 45: .Nm ~/.ssh/config
46: .Nm /etc/ssh/ssh_config
1.1 stevesk 47: .Sh DESCRIPTION
1.84 jmc 48: .Xr ssh 1
1.1 stevesk 49: obtains configuration data from the following sources in
50: the following order:
1.79 jmc 51: .Pp
1.2 stevesk 52: .Bl -enum -offset indent -compact
53: .It
54: command-line options
55: .It
56: user's configuration file
1.50 djm 57: .Pq Pa ~/.ssh/config
1.2 stevesk 58: .It
59: system-wide configuration file
60: .Pq Pa /etc/ssh/ssh_config
61: .El
1.1 stevesk 62: .Pp
63: For each parameter, the first obtained value
64: will be used.
1.41 jmc 65: The configuration files contain sections separated by
1.1 stevesk 66: .Dq Host
67: specifications, and that section is only applied for hosts that
68: match one of the patterns given in the specification.
69: The matched host name is the one given on the command line.
70: .Pp
71: Since the first obtained value for each parameter is used, more
72: host-specific declarations should be given near the beginning of the
73: file, and general defaults at the end.
1.80 jmc 74: .Pp
1.1 stevesk 75: The configuration file has the following format:
76: .Pp
77: Empty lines and lines starting with
78: .Ql #
79: are comments.
80: Otherwise a line is of the format
81: .Dq keyword arguments .
82: Configuration options may be separated by whitespace or
83: optional whitespace and exactly one
84: .Ql = ;
85: the latter format is useful to avoid the need to quote whitespace
86: when specifying configuration options using the
87: .Nm ssh ,
1.87 jmc 88: .Nm scp ,
1.1 stevesk 89: and
90: .Nm sftp
91: .Fl o
92: option.
1.88 dtucker 93: Arguments may optionally be enclosed in double quotes
94: .Pq \&"
95: in order to represent arguments containing spaces.
1.1 stevesk 96: .Pp
97: The possible
98: keywords and their meanings are as follows (note that
99: keywords are case-insensitive and arguments are case-sensitive):
100: .Bl -tag -width Ds
101: .It Cm Host
102: Restricts the following declarations (up to the next
103: .Cm Host
104: keyword) to be only for those hosts that match one of the patterns
105: given after the keyword.
1.106 ! dtucker 106: If more than one pattern is provided, they should be separated by whitepsace.
1.1 stevesk 107: A single
1.83 jmc 108: .Ql *
1.1 stevesk 109: as a pattern can be used to provide global
110: defaults for all hosts.
111: The host is the
112: .Ar hostname
1.83 jmc 113: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 114: a canonicalized host name before matching).
1.81 jmc 115: .Pp
116: See
117: .Sx PATTERNS
118: for more information on patterns.
1.10 djm 119: .It Cm AddressFamily
1.11 jmc 120: Specifies which address family to use when connecting.
121: Valid arguments are
1.10 djm 122: .Dq any ,
123: .Dq inet
1.84 jmc 124: (use IPv4 only), or
1.10 djm 125: .Dq inet6
1.40 jmc 126: (use IPv6 only).
1.1 stevesk 127: .It Cm BatchMode
128: If set to
129: .Dq yes ,
130: passphrase/password querying will be disabled.
131: This option is useful in scripts and other batch jobs where no user
132: is present to supply the password.
133: The argument must be
134: .Dq yes
135: or
136: .Dq no .
137: The default is
138: .Dq no .
139: .It Cm BindAddress
1.60 dtucker 140: Use the specified address on the local machine as the source address of
1.61 jmc 141: the connection.
142: Only useful on systems with more than one address.
1.1 stevesk 143: Note that this option does not work if
144: .Cm UsePrivilegedPort
145: is set to
146: .Dq yes .
147: .It Cm ChallengeResponseAuthentication
1.82 jmc 148: Specifies whether to use challenge-response authentication.
1.1 stevesk 149: The argument to this keyword must be
150: .Dq yes
151: or
152: .Dq no .
153: The default is
154: .Dq yes .
155: .It Cm CheckHostIP
156: If this flag is set to
157: .Dq yes ,
1.84 jmc 158: .Xr ssh 1
159: will additionally check the host IP address in the
1.1 stevesk 160: .Pa known_hosts
161: file.
162: This allows ssh to detect if a host key changed due to DNS spoofing.
163: If the option is set to
164: .Dq no ,
165: the check will not be executed.
166: The default is
167: .Dq yes .
168: .It Cm Cipher
169: Specifies the cipher to use for encrypting the session
170: in protocol version 1.
171: Currently,
172: .Dq blowfish ,
173: .Dq 3des ,
174: and
175: .Dq des
176: are supported.
177: .Ar des
178: is only supported in the
1.84 jmc 179: .Xr ssh 1
1.1 stevesk 180: client for interoperability with legacy protocol 1 implementations
181: that do not support the
182: .Ar 3des
1.7 jmc 183: cipher.
184: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 185: The default is
186: .Dq 3des .
187: .It Cm Ciphers
188: Specifies the ciphers allowed for protocol version 2
189: in order of preference.
190: Multiple ciphers must be comma-separated.
1.35 dtucker 191: The supported ciphers are
192: .Dq 3des-cbc ,
193: .Dq aes128-cbc ,
194: .Dq aes192-cbc ,
195: .Dq aes256-cbc ,
196: .Dq aes128-ctr ,
197: .Dq aes192-ctr ,
198: .Dq aes256-ctr ,
1.54 djm 199: .Dq arcfour128 ,
200: .Dq arcfour256 ,
1.35 dtucker 201: .Dq arcfour ,
202: .Dq blowfish-cbc ,
203: and
204: .Dq cast128-cbc .
1.84 jmc 205: The default is:
206: .Bd -literal -offset 3n
207: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
208: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
209: aes192-ctr,aes256-ctr
1.1 stevesk 210: .Ed
211: .It Cm ClearAllForwardings
1.84 jmc 212: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 213: specified in the configuration files or on the command line be
1.7 jmc 214: cleared.
215: This option is primarily useful when used from the
1.84 jmc 216: .Xr ssh 1
1.1 stevesk 217: command line to clear port forwardings set in
218: configuration files, and is automatically set by
219: .Xr scp 1
220: and
221: .Xr sftp 1 .
222: The argument must be
223: .Dq yes
224: or
225: .Dq no .
226: The default is
227: .Dq no .
228: .It Cm Compression
229: Specifies whether to use compression.
230: The argument must be
231: .Dq yes
232: or
233: .Dq no .
234: The default is
235: .Dq no .
236: .It Cm CompressionLevel
237: Specifies the compression level to use if compression is enabled.
238: The argument must be an integer from 1 (fast) to 9 (slow, best).
239: The default level is 6, which is good for most applications.
240: The meaning of the values is the same as in
241: .Xr gzip 1 .
242: Note that this option applies to protocol version 1 only.
243: .It Cm ConnectionAttempts
244: Specifies the number of tries (one per second) to make before exiting.
245: The argument must be an integer.
246: This may be useful in scripts if the connection sometimes fails.
247: The default is 1.
1.9 djm 248: .It Cm ConnectTimeout
1.84 jmc 249: Specifies the timeout (in seconds) used when connecting to the
250: SSH server, instead of using the default system TCP timeout.
1.11 jmc 251: This value is used only when the target is down or really unreachable,
252: not when it refuses the connection.
1.36 djm 253: .It Cm ControlMaster
254: Enables the sharing of multiple sessions over a single network connection.
255: When set to
1.84 jmc 256: .Dq yes ,
257: .Xr ssh 1
1.36 djm 258: will listen for connections on a control socket specified using the
259: .Cm ControlPath
260: argument.
261: Additional sessions can connect to this socket using the same
262: .Cm ControlPath
263: with
264: .Cm ControlMaster
265: set to
266: .Dq no
1.38 jmc 267: (the default).
1.64 jmc 268: These sessions will try to reuse the master instance's network connection
1.63 djm 269: rather than initiating new ones, but will fall back to connecting normally
270: if the control socket does not exist, or is not listening.
271: .Pp
1.37 djm 272: Setting this to
273: .Dq ask
1.84 jmc 274: will cause ssh
1.37 djm 275: to listen for control connections, but require confirmation using the
276: .Ev SSH_ASKPASS
277: program before they are accepted (see
278: .Xr ssh-add 1
1.38 jmc 279: for details).
1.51 jakob 280: If the
281: .Cm ControlPath
1.84 jmc 282: cannot be opened,
283: ssh will continue without connecting to a master instance.
1.58 djm 284: .Pp
285: X11 and
1.59 jmc 286: .Xr ssh-agent 1
1.58 djm 287: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 288: display and agent forwarded will be the one belonging to the master
1.59 jmc 289: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 290: .Pp
291: Two additional options allow for opportunistic multiplexing: try to use a
292: master connection but fall back to creating a new one if one does not already
293: exist.
294: These options are:
295: .Dq auto
296: and
297: .Dq autoask .
298: The latter requires confirmation like the
299: .Dq ask
300: option.
1.36 djm 301: .It Cm ControlPath
1.55 djm 302: Specify the path to the control socket used for connection sharing as described
303: in the
1.36 djm 304: .Cm ControlMaster
1.57 djm 305: section above or the string
306: .Dq none
307: to disable connection sharing.
1.55 djm 308: In the path,
1.77 djm 309: .Ql %l
310: will be substituted by the local host name,
1.55 djm 311: .Ql %h
312: will be substituted by the target host name,
313: .Ql %p
1.84 jmc 314: the port, and
1.55 djm 315: .Ql %r
316: by the remote login username.
1.56 djm 317: It is recommended that any
318: .Cm ControlPath
319: used for opportunistic connection sharing include
1.78 jmc 320: at least %h, %p, and %r.
1.56 djm 321: This ensures that shared connections are uniquely identified.
1.38 jmc 322: .It Cm DynamicForward
1.74 jmc 323: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 324: over the secure channel, and the application
325: protocol is then used to determine where to connect to from the
326: remote machine.
1.62 djm 327: .Pp
328: The argument must be
329: .Sm off
330: .Oo Ar bind_address : Oc Ar port .
331: .Sm on
332: IPv6 addresses can be specified by enclosing addresses in square brackets or
333: by using an alternative syntax:
334: .Oo Ar bind_address Ns / Oc Ns Ar port .
335: By default, the local port is bound in accordance with the
336: .Cm GatewayPorts
337: setting.
338: However, an explicit
339: .Ar bind_address
340: may be used to bind the connection to a specific address.
341: The
342: .Ar bind_address
343: of
344: .Dq localhost
345: indicates that the listening port be bound for local use only, while an
346: empty address or
347: .Sq *
348: indicates that the port should be available from all interfaces.
349: .Pp
1.38 jmc 350: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 351: .Xr ssh 1
1.38 jmc 352: will act as a SOCKS server.
353: Multiple forwardings may be specified, and
354: additional forwardings can be given on the command line.
355: Only the superuser can forward privileged ports.
1.14 markus 356: .It Cm EnableSSHKeysign
357: Setting this option to
358: .Dq yes
359: in the global client configuration file
360: .Pa /etc/ssh/ssh_config
361: enables the use of the helper program
362: .Xr ssh-keysign 8
363: during
364: .Cm HostbasedAuthentication .
365: The argument must be
366: .Dq yes
367: or
368: .Dq no .
369: The default is
370: .Dq no .
1.23 jmc 371: This option should be placed in the non-hostspecific section.
1.14 markus 372: See
373: .Xr ssh-keysign 8
374: for more information.
1.1 stevesk 375: .It Cm EscapeChar
376: Sets the escape character (default:
377: .Ql ~ ) .
378: The escape character can also
379: be set on the command line.
380: The argument should be a single character,
381: .Ql ^
382: followed by a letter, or
383: .Dq none
384: to disable the escape
385: character entirely (making the connection transparent for binary
386: data).
1.96 markus 387: .It Cm ExitOnForwardFailure
388: Specifies whether
389: .Xr ssh 1
390: should terminate the connection if it cannot set up all requested
1.102 stevesk 391: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 392: The argument must be
393: .Dq yes
394: or
395: .Dq no .
396: The default is
397: .Dq no .
1.1 stevesk 398: .It Cm ForwardAgent
399: Specifies whether the connection to the authentication agent (if any)
400: will be forwarded to the remote machine.
401: The argument must be
402: .Dq yes
403: or
404: .Dq no .
405: The default is
406: .Dq no .
1.3 stevesk 407: .Pp
1.7 jmc 408: Agent forwarding should be enabled with caution.
409: Users with the ability to bypass file permissions on the remote host
410: (for the agent's Unix-domain socket)
411: can access the local agent through the forwarded connection.
412: An attacker cannot obtain key material from the agent,
1.3 stevesk 413: however they can perform operations on the keys that enable them to
414: authenticate using the identities loaded into the agent.
1.1 stevesk 415: .It Cm ForwardX11
416: Specifies whether X11 connections will be automatically redirected
417: over the secure channel and
418: .Ev DISPLAY
419: set.
420: The argument must be
421: .Dq yes
422: or
423: .Dq no .
424: The default is
425: .Dq no .
1.3 stevesk 426: .Pp
1.7 jmc 427: X11 forwarding should be enabled with caution.
428: Users with the ability to bypass file permissions on the remote host
1.22 markus 429: (for the user's X11 authorization database)
1.7 jmc 430: can access the local X11 display through the forwarded connection.
1.22 markus 431: An attacker may then be able to perform activities such as keystroke monitoring
432: if the
433: .Cm ForwardX11Trusted
434: option is also enabled.
435: .It Cm ForwardX11Trusted
1.34 jmc 436: If this option is set to
1.84 jmc 437: .Dq yes ,
438: remote X11 clients will have full access to the original X11 display.
1.42 djm 439: .Pp
1.22 markus 440: If this option is set to
1.84 jmc 441: .Dq no ,
442: remote X11 clients will be considered untrusted and prevented
1.22 markus 443: from stealing or tampering with data belonging to trusted X11
444: clients.
1.42 djm 445: Furthermore, the
446: .Xr xauth 1
447: token used for the session will be set to expire after 20 minutes.
448: Remote clients will be refused access after this time.
1.22 markus 449: .Pp
450: The default is
451: .Dq no .
452: .Pp
453: See the X11 SECURITY extension specification for full details on
454: the restrictions imposed on untrusted clients.
1.1 stevesk 455: .It Cm GatewayPorts
456: Specifies whether remote hosts are allowed to connect to local
457: forwarded ports.
458: By default,
1.84 jmc 459: .Xr ssh 1
1.7 jmc 460: binds local port forwardings to the loopback address.
461: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 462: .Cm GatewayPorts
1.84 jmc 463: can be used to specify that ssh
1.1 stevesk 464: should bind local port forwardings to the wildcard address,
465: thus allowing remote hosts to connect to forwarded ports.
466: The argument must be
467: .Dq yes
468: or
469: .Dq no .
470: The default is
471: .Dq no .
472: .It Cm GlobalKnownHostsFile
473: Specifies a file to use for the global
474: host key database instead of
475: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 476: .It Cm GSSAPIAuthentication
1.27 markus 477: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 478: The default is
1.21 markus 479: .Dq no .
1.18 markus 480: Note that this option applies to protocol version 2 only.
481: .It Cm GSSAPIDelegateCredentials
482: Forward (delegate) credentials to the server.
483: The default is
484: .Dq no .
485: Note that this option applies to protocol version 2 only.
1.44 djm 486: .It Cm HashKnownHosts
487: Indicates that
1.84 jmc 488: .Xr ssh 1
1.44 djm 489: should hash host names and addresses when they are added to
1.50 djm 490: .Pa ~/.ssh/known_hosts .
1.44 djm 491: These hashed names may be used normally by
1.84 jmc 492: .Xr ssh 1
1.44 djm 493: and
1.84 jmc 494: .Xr sshd 8 ,
1.44 djm 495: but they do not reveal identifying information should the file's contents
496: be disclosed.
497: The default is
498: .Dq no .
1.97 jmc 499: Note that existing names and addresses in known hosts files
500: will not be converted automatically,
501: but may be manually hashed using
1.45 djm 502: .Xr ssh-keygen 1 .
1.1 stevesk 503: .It Cm HostbasedAuthentication
504: Specifies whether to try rhosts based authentication with public key
505: authentication.
506: The argument must be
507: .Dq yes
508: or
509: .Dq no .
510: The default is
511: .Dq no .
512: This option applies to protocol version 2 only and
513: is similar to
514: .Cm RhostsRSAAuthentication .
515: .It Cm HostKeyAlgorithms
516: Specifies the protocol version 2 host key algorithms
517: that the client wants to use in order of preference.
518: The default for this option is:
519: .Dq ssh-rsa,ssh-dss .
520: .It Cm HostKeyAlias
521: Specifies an alias that should be used instead of the
522: real host name when looking up or saving the host key
523: in the host key database files.
1.84 jmc 524: This option is useful for tunneling SSH connections
1.1 stevesk 525: or for multiple servers running on a single host.
526: .It Cm HostName
527: Specifies the real host name to log into.
528: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 529: The default is the name given on the command line.
1.1 stevesk 530: Numeric IP addresses are also permitted (both on the command line and in
531: .Cm HostName
532: specifications).
1.29 markus 533: .It Cm IdentitiesOnly
534: Specifies that
1.84 jmc 535: .Xr ssh 1
1.29 markus 536: should only use the authentication identity files configured in the
1.31 jmc 537: .Nm
1.29 markus 538: files,
1.84 jmc 539: even if
540: .Xr ssh-agent 1
1.29 markus 541: offers more identities.
542: The argument to this keyword must be
543: .Dq yes
544: or
545: .Dq no .
1.84 jmc 546: This option is intended for situations where ssh-agent
1.29 markus 547: offers many different identities.
548: The default is
549: .Dq no .
1.67 jmc 550: .It Cm IdentityFile
551: Specifies a file from which the user's RSA or DSA authentication identity
552: is read.
553: The default is
554: .Pa ~/.ssh/identity
555: for protocol version 1, and
556: .Pa ~/.ssh/id_rsa
557: and
558: .Pa ~/.ssh/id_dsa
559: for protocol version 2.
560: Additionally, any identities represented by the authentication agent
561: will be used for authentication.
1.90 djm 562: .Pp
1.67 jmc 563: The file name may use the tilde
1.91 jmc 564: syntax to refer to a user's home directory or one of the following
1.90 djm 565: escape characters:
566: .Ql %d
567: (local user's home directory),
568: .Ql %u
569: (local user name),
570: .Ql %l
571: (local host name),
572: .Ql %h
573: (remote host name) or
1.92 djm 574: .Ql %r
1.90 djm 575: (remote user name).
576: .Pp
1.67 jmc 577: It is possible to have
578: multiple identity files specified in configuration files; all these
579: identities will be tried in sequence.
1.103 djm 580: .It Cm KbdInteractiveAuthentication
581: Specifies whether to use keyboard-interactive authentication.
582: The argument to this keyword must be
583: .Dq yes
584: or
585: .Dq no .
586: The default is
587: .Dq yes .
1.39 djm 588: .It Cm KbdInteractiveDevices
589: Specifies the list of methods to use in keyboard-interactive authentication.
590: Multiple method names must be comma-separated.
591: The default is to use the server specified list.
1.85 jmc 592: The methods available vary depending on what the server supports.
593: For an OpenSSH server,
594: it may be zero or more of:
595: .Dq bsdauth ,
596: .Dq pam ,
597: and
598: .Dq skey .
1.65 reyk 599: .It Cm LocalCommand
600: Specifies a command to execute on the local machine after successfully
601: connecting to the server.
602: The command string extends to the end of the line, and is executed with
1.105 jmc 603: the user's shell.
1.65 reyk 604: This directive is ignored unless
605: .Cm PermitLocalCommand
606: has been enabled.
1.1 stevesk 607: .It Cm LocalForward
1.74 jmc 608: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 609: the secure channel to the specified host and port from the remote machine.
1.49 jmc 610: The first argument must be
1.43 djm 611: .Sm off
1.49 jmc 612: .Oo Ar bind_address : Oc Ar port
1.43 djm 613: .Sm on
1.49 jmc 614: and the second argument must be
615: .Ar host : Ns Ar hostport .
1.46 jmc 616: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 617: by using an alternative syntax:
1.49 jmc 618: .Oo Ar bind_address Ns / Oc Ns Ar port
619: and
620: .Ar host Ns / Ns Ar hostport .
1.46 jmc 621: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 622: given on the command line.
1.1 stevesk 623: Only the superuser can forward privileged ports.
1.43 djm 624: By default, the local port is bound in accordance with the
625: .Cm GatewayPorts
626: setting.
627: However, an explicit
628: .Ar bind_address
629: may be used to bind the connection to a specific address.
630: The
631: .Ar bind_address
632: of
633: .Dq localhost
1.46 jmc 634: indicates that the listening port be bound for local use only, while an
635: empty address or
636: .Sq *
1.43 djm 637: indicates that the port should be available from all interfaces.
1.1 stevesk 638: .It Cm LogLevel
639: Gives the verbosity level that is used when logging messages from
1.84 jmc 640: .Xr ssh 1 .
1.1 stevesk 641: The possible values are:
1.84 jmc 642: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 643: The default is INFO.
644: DEBUG and DEBUG1 are equivalent.
645: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 646: .It Cm MACs
647: Specifies the MAC (message authentication code) algorithms
648: in order of preference.
649: The MAC algorithm is used in protocol version 2
650: for data integrity protection.
651: Multiple algorithms must be comma-separated.
1.84 jmc 652: The default is:
1.101 jmc 653: .Bd -literal -offset indent
654: hmac-md5,hmac-sha1,umac-64@openssh.com,
655: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
656: .Ed
1.1 stevesk 657: .It Cm NoHostAuthenticationForLocalhost
658: This option can be used if the home directory is shared across machines.
659: In this case localhost will refer to a different machine on each of
660: the machines and the user will get many warnings about changed host keys.
661: However, this option disables host authentication for localhost.
662: The argument to this keyword must be
663: .Dq yes
664: or
665: .Dq no .
666: The default is to check the host key for localhost.
667: .It Cm NumberOfPasswordPrompts
668: Specifies the number of password prompts before giving up.
669: The argument to this keyword must be an integer.
1.84 jmc 670: The default is 3.
1.1 stevesk 671: .It Cm PasswordAuthentication
672: Specifies whether to use password authentication.
673: The argument to this keyword must be
674: .Dq yes
675: or
676: .Dq no .
677: The default is
678: .Dq yes .
1.65 reyk 679: .It Cm PermitLocalCommand
680: Allow local command execution via the
681: .Ic LocalCommand
682: option or using the
1.66 jmc 683: .Ic !\& Ns Ar command
1.65 reyk 684: escape sequence in
685: .Xr ssh 1 .
686: The argument must be
687: .Dq yes
688: or
689: .Dq no .
690: The default is
691: .Dq no .
1.67 jmc 692: .It Cm Port
693: Specifies the port number to connect on the remote host.
1.84 jmc 694: The default is 22.
1.1 stevesk 695: .It Cm PreferredAuthentications
696: Specifies the order in which the client should try protocol 2
1.11 jmc 697: authentication methods.
1.48 jmc 698: This allows a client to prefer one method (e.g.\&
1.1 stevesk 699: .Cm keyboard-interactive )
1.48 jmc 700: over another method (e.g.\&
1.1 stevesk 701: .Cm password )
702: The default for this option is:
1.94 jmc 703: .Do gssapi-with-mic ,
704: hostbased,
705: publickey,
706: keyboard-interactive,
707: password
708: .Dc .
1.1 stevesk 709: .It Cm Protocol
710: Specifies the protocol versions
1.84 jmc 711: .Xr ssh 1
1.1 stevesk 712: should support in order of preference.
713: The possible values are
1.84 jmc 714: .Sq 1
1.1 stevesk 715: and
1.84 jmc 716: .Sq 2 .
1.1 stevesk 717: Multiple versions must be comma-separated.
718: The default is
719: .Dq 2,1 .
1.84 jmc 720: This means that ssh
1.1 stevesk 721: tries version 2 and falls back to version 1
722: if version 2 is not available.
723: .It Cm ProxyCommand
724: Specifies the command to use to connect to the server.
725: The command
726: string extends to the end of the line, and is executed with
1.105 jmc 727: the user's shell.
1.1 stevesk 728: In the command string,
729: .Ql %h
730: will be substituted by the host name to
731: connect and
732: .Ql %p
733: by the port.
734: The command can be basically anything,
735: and should read from its standard input and write to its standard output.
736: It should eventually connect an
737: .Xr sshd 8
738: server running on some machine, or execute
739: .Ic sshd -i
740: somewhere.
741: Host key management will be done using the
742: HostName of the host being connected (defaulting to the name typed by
743: the user).
1.7 jmc 744: Setting the command to
745: .Dq none
1.6 markus 746: disables this option entirely.
1.1 stevesk 747: Note that
748: .Cm CheckHostIP
749: is not available for connects with a proxy command.
1.52 djm 750: .Pp
751: This directive is useful in conjunction with
752: .Xr nc 1
753: and its proxy support.
1.53 jmc 754: For example, the following directive would connect via an HTTP proxy at
1.52 djm 755: 192.0.2.0:
756: .Bd -literal -offset 3n
757: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
758: .Ed
1.1 stevesk 759: .It Cm PubkeyAuthentication
760: Specifies whether to try public key authentication.
761: The argument to this keyword must be
762: .Dq yes
763: or
764: .Dq no .
765: The default is
766: .Dq yes .
767: This option applies to protocol version 2 only.
1.75 dtucker 768: .It Cm RekeyLimit
769: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 770: session key is renegotiated.
1.75 dtucker 771: The argument is the number of bytes, with an optional suffix of
1.76 jmc 772: .Sq K ,
773: .Sq M ,
1.75 dtucker 774: or
1.76 jmc 775: .Sq G
1.75 dtucker 776: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
777: The default is between
1.84 jmc 778: .Sq 1G
1.75 dtucker 779: and
1.84 jmc 780: .Sq 4G ,
1.75 dtucker 781: depending on the cipher.
1.76 jmc 782: This option applies to protocol version 2 only.
1.1 stevesk 783: .It Cm RemoteForward
1.74 jmc 784: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 785: the secure channel to the specified host and port from the local machine.
1.49 jmc 786: The first argument must be
1.43 djm 787: .Sm off
1.49 jmc 788: .Oo Ar bind_address : Oc Ar port
1.43 djm 789: .Sm on
1.49 jmc 790: and the second argument must be
791: .Ar host : Ns Ar hostport .
792: IPv6 addresses can be specified by enclosing addresses in square brackets
793: or by using an alternative syntax:
794: .Oo Ar bind_address Ns / Oc Ns Ar port
795: and
796: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 797: Multiple forwardings may be specified, and additional
798: forwardings can be given on the command line.
799: Only the superuser can forward privileged ports.
1.43 djm 800: .Pp
801: If the
802: .Ar bind_address
803: is not specified, the default is to only bind to loopback addresses.
804: If the
805: .Ar bind_address
806: is
807: .Ql *
808: or an empty string, then the forwarding is requested to listen on all
809: interfaces.
810: Specifying a remote
811: .Ar bind_address
1.46 jmc 812: will only succeed if the server's
813: .Cm GatewayPorts
1.43 djm 814: option is enabled (see
1.46 jmc 815: .Xr sshd_config 5 ) .
1.1 stevesk 816: .It Cm RhostsRSAAuthentication
817: Specifies whether to try rhosts based authentication with RSA host
818: authentication.
819: The argument must be
820: .Dq yes
821: or
822: .Dq no .
823: The default is
824: .Dq no .
825: This option applies to protocol version 1 only and requires
1.84 jmc 826: .Xr ssh 1
1.1 stevesk 827: to be setuid root.
828: .It Cm RSAAuthentication
829: Specifies whether to try RSA authentication.
830: The argument to this keyword must be
831: .Dq yes
832: or
833: .Dq no .
834: RSA authentication will only be
835: attempted if the identity file exists, or an authentication agent is
836: running.
837: The default is
838: .Dq yes .
839: Note that this option applies to protocol version 1 only.
1.32 djm 840: .It Cm SendEnv
841: Specifies what variables from the local
842: .Xr environ 7
843: should be sent to the server.
1.84 jmc 844: Note that environment passing is only supported for protocol 2.
845: The server must also support it, and the server must be configured to
1.33 djm 846: accept these environment variables.
1.32 djm 847: Refer to
848: .Cm AcceptEnv
849: in
850: .Xr sshd_config 5
851: for how to configure the server.
1.80 jmc 852: Variables are specified by name, which may contain wildcard characters.
1.33 djm 853: Multiple environment variables may be separated by whitespace or spread
1.32 djm 854: across multiple
855: .Cm SendEnv
856: directives.
857: The default is not to send any environment variables.
1.81 jmc 858: .Pp
859: See
860: .Sx PATTERNS
861: for more information on patterns.
1.28 markus 862: .It Cm ServerAliveCountMax
1.73 jmc 863: Sets the number of server alive messages (see below) which may be
1.28 markus 864: sent without
1.84 jmc 865: .Xr ssh 1
1.28 markus 866: receiving any messages back from the server.
867: If this threshold is reached while server alive messages are being sent,
1.84 jmc 868: ssh will disconnect from the server, terminating the session.
1.28 markus 869: It is important to note that the use of server alive messages is very
870: different from
871: .Cm TCPKeepAlive
872: (below).
873: The server alive messages are sent through the encrypted channel
874: and therefore will not be spoofable.
875: The TCP keepalive option enabled by
876: .Cm TCPKeepAlive
877: is spoofable.
878: The server alive mechanism is valuable when the client or
879: server depend on knowing when a connection has become inactive.
880: .Pp
881: The default value is 3.
882: If, for example,
883: .Cm ServerAliveInterval
1.84 jmc 884: (see below) is set to 15 and
1.28 markus 885: .Cm ServerAliveCountMax
1.84 jmc 886: is left at the default, if the server becomes unresponsive,
887: ssh will disconnect after approximately 45 seconds.
1.89 markus 888: This option applies to protocol version 2 only.
1.67 jmc 889: .It Cm ServerAliveInterval
890: Sets a timeout interval in seconds after which if no data has been received
891: from the server,
1.84 jmc 892: .Xr ssh 1
1.67 jmc 893: will send a message through the encrypted
894: channel to request a response from the server.
895: The default
896: is 0, indicating that these messages will not be sent to the server.
897: This option applies to protocol version 2 only.
1.1 stevesk 898: .It Cm SmartcardDevice
1.11 jmc 899: Specifies which smartcard device to use.
900: The argument to this keyword is the device
1.84 jmc 901: .Xr ssh 1
1.1 stevesk 902: should use to communicate with a smartcard used for storing the user's
1.11 jmc 903: private RSA key.
904: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 905: .It Cm StrictHostKeyChecking
906: If this flag is set to
907: .Dq yes ,
1.84 jmc 908: .Xr ssh 1
1.1 stevesk 909: will never automatically add host keys to the
1.50 djm 910: .Pa ~/.ssh/known_hosts
1.1 stevesk 911: file, and refuses to connect to hosts whose host key has changed.
912: This provides maximum protection against trojan horse attacks,
1.84 jmc 913: though it can be annoying when the
1.1 stevesk 914: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 915: file is poorly maintained or when connections to new hosts are
1.1 stevesk 916: frequently made.
917: This option forces the user to manually
918: add all new hosts.
919: If this flag is set to
920: .Dq no ,
1.84 jmc 921: ssh will automatically add new host keys to the
1.1 stevesk 922: user known hosts files.
923: If this flag is set to
924: .Dq ask ,
925: new host keys
926: will be added to the user known host files only after the user
927: has confirmed that is what they really want to do, and
1.84 jmc 928: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 929: The host keys of
930: known hosts will be verified automatically in all cases.
931: The argument must be
932: .Dq yes ,
1.84 jmc 933: .Dq no ,
1.1 stevesk 934: or
935: .Dq ask .
936: The default is
937: .Dq ask .
1.26 markus 938: .It Cm TCPKeepAlive
939: Specifies whether the system should send TCP keepalive messages to the
940: other side.
941: If they are sent, death of the connection or crash of one
942: of the machines will be properly noticed.
943: However, this means that
944: connections will die if the route is down temporarily, and some people
945: find it annoying.
946: .Pp
947: The default is
948: .Dq yes
949: (to send TCP keepalive messages), and the client will notice
950: if the network goes down or the remote host dies.
951: This is important in scripts, and many users want it too.
952: .Pp
953: To disable TCP keepalive messages, the value should be set to
954: .Dq no .
1.65 reyk 955: .It Cm Tunnel
1.95 stevesk 956: Request
1.65 reyk 957: .Xr tun 4
1.69 jmc 958: device forwarding between the client and the server.
1.65 reyk 959: The argument must be
1.68 reyk 960: .Dq yes ,
1.95 stevesk 961: .Dq point-to-point
962: (layer 3),
963: .Dq ethernet
964: (layer 2),
1.65 reyk 965: or
966: .Dq no .
1.95 stevesk 967: Specifying
968: .Dq yes
969: requests the default tunnel mode, which is
970: .Dq point-to-point .
1.65 reyk 971: The default is
972: .Dq no .
973: .It Cm TunnelDevice
1.95 stevesk 974: Specifies the
1.65 reyk 975: .Xr tun 4
1.95 stevesk 976: devices to open on the client
977: .Pq Ar local_tun
978: and the server
979: .Pq Ar remote_tun .
980: .Pp
981: The argument must be
982: .Sm off
983: .Ar local_tun Op : Ar remote_tun .
984: .Sm on
985: The devices may be specified by numerical ID or the keyword
986: .Dq any ,
987: which uses the next available tunnel device.
988: If
989: .Ar remote_tun
990: is not specified, it defaults to
991: .Dq any .
992: The default is
993: .Dq any:any .
1.72 jmc 994: .It Cm UsePrivilegedPort
995: Specifies whether to use a privileged port for outgoing connections.
996: The argument must be
997: .Dq yes
998: or
999: .Dq no .
1000: The default is
1001: .Dq no .
1002: If set to
1.84 jmc 1003: .Dq yes ,
1004: .Xr ssh 1
1.72 jmc 1005: must be setuid root.
1006: Note that this option must be set to
1007: .Dq yes
1008: for
1009: .Cm RhostsRSAAuthentication
1010: with older servers.
1.1 stevesk 1011: .It Cm User
1012: Specifies the user to log in as.
1013: This can be useful when a different user name is used on different machines.
1014: This saves the trouble of
1015: having to remember to give the user name on the command line.
1016: .It Cm UserKnownHostsFile
1017: Specifies a file to use for the user
1018: host key database instead of
1.50 djm 1019: .Pa ~/.ssh/known_hosts .
1.8 jakob 1020: .It Cm VerifyHostKeyDNS
1021: Specifies whether to verify the remote key using DNS and SSHFP resource
1022: records.
1.24 jakob 1023: If this option is set to
1024: .Dq yes ,
1.25 jmc 1025: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1026: from DNS.
1027: Insecure fingerprints will be handled as if this option was set to
1028: .Dq ask .
1029: If this option is set to
1030: .Dq ask ,
1031: information on fingerprint match will be displayed, but the user will still
1032: need to confirm new host keys according to the
1033: .Cm StrictHostKeyChecking
1034: option.
1035: The argument must be
1036: .Dq yes ,
1.84 jmc 1037: .Dq no ,
1.25 jmc 1038: or
1039: .Dq ask .
1.8 jakob 1040: The default is
1041: .Dq no .
1.12 jakob 1042: Note that this option applies to protocol version 2 only.
1.84 jmc 1043: .Pp
1044: See also
1045: .Sx VERIFYING HOST KEYS
1046: in
1047: .Xr ssh 1 .
1.1 stevesk 1048: .It Cm XAuthLocation
1.5 stevesk 1049: Specifies the full pathname of the
1.1 stevesk 1050: .Xr xauth 1
1051: program.
1052: The default is
1053: .Pa /usr/X11R6/bin/xauth .
1054: .El
1.86 jmc 1055: .Sh PATTERNS
1056: A
1057: .Em pattern
1058: consists of zero or more non-whitespace characters,
1059: .Sq *
1060: (a wildcard that matches zero or more characters),
1061: or
1062: .Sq ?\&
1063: (a wildcard that matches exactly one character).
1064: For example, to specify a set of declarations for any host in the
1065: .Dq .co.uk
1066: set of domains,
1067: the following pattern could be used:
1068: .Pp
1069: .Dl Host *.co.uk
1070: .Pp
1071: The following pattern
1072: would match any host in the 192.168.0.[0-9] network range:
1073: .Pp
1074: .Dl Host 192.168.0.?
1075: .Pp
1076: A
1077: .Em pattern-list
1078: is a comma-separated list of patterns.
1079: Patterns within pattern-lists may be negated
1080: by preceding them with an exclamation mark
1081: .Pq Sq !\& .
1082: For example,
1083: to allow a key to be used from anywhere within an organisation
1084: except from the
1085: .Dq dialup
1086: pool,
1087: the following entry (in authorized_keys) could be used:
1088: .Pp
1089: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1090: .Sh FILES
1091: .Bl -tag -width Ds
1.50 djm 1092: .It Pa ~/.ssh/config
1.1 stevesk 1093: This is the per-user configuration file.
1094: The format of this file is described above.
1.84 jmc 1095: This file is used by the SSH client.
1.30 djm 1096: Because of the potential for abuse, this file must have strict permissions:
1097: read/write for the user, and not accessible by others.
1.1 stevesk 1098: .It Pa /etc/ssh/ssh_config
1099: Systemwide configuration file.
1100: This file provides defaults for those
1101: values that are not specified in the user's configuration file, and
1102: for those users who do not have a configuration file.
1103: This file must be world-readable.
1104: .El
1.13 jmc 1105: .Sh SEE ALSO
1106: .Xr ssh 1
1.1 stevesk 1107: .Sh AUTHORS
1108: OpenSSH is a derivative of the original and free
1109: ssh 1.2.12 release by Tatu Ylonen.
1110: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1111: Theo de Raadt and Dug Song
1112: removed many bugs, re-added newer features and
1113: created OpenSSH.
1114: Markus Friedl contributed the support for SSH
1115: protocol versions 1.5 and 2.0.
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