Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.142
1.1 stevesk 1: .\"
2: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
3: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
4: .\" All rights reserved
5: .\"
6: .\" As far as I am concerned, the code I have written for this software
7: .\" can be used freely for any purpose. Any derived versions of this
8: .\" software must be clearly marked as such, and if the derived work is
9: .\" incompatible with the protocol description in the RFC file, it must be
10: .\" called by a name other than "ssh" or "Secure Shell".
11: .\"
12: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
13: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
14: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
15: .\"
16: .\" Redistribution and use in source and binary forms, with or without
17: .\" modification, are permitted provided that the following conditions
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19: .\" 1. Redistributions of source code must retain the above copyright
20: .\" notice, this list of conditions and the following disclaimer.
21: .\" 2. Redistributions in binary form must reproduce the above copyright
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25: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
26: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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1.142 ! jmc 36: .\" $OpenBSD: ssh_config.5,v 1.141 2010/09/22 08:30:08 jmc Exp $
1.141 jmc 37: .Dd $Mdocdate: September 22 2010 $
1.1 stevesk 38: .Dt SSH_CONFIG 5
39: .Os
40: .Sh NAME
41: .Nm ssh_config
42: .Nd OpenSSH SSH client configuration files
43: .Sh SYNOPSIS
1.98 jmc 44: .Nm ~/.ssh/config
45: .Nm /etc/ssh/ssh_config
1.1 stevesk 46: .Sh DESCRIPTION
1.84 jmc 47: .Xr ssh 1
1.1 stevesk 48: obtains configuration data from the following sources in
49: the following order:
1.79 jmc 50: .Pp
1.2 stevesk 51: .Bl -enum -offset indent -compact
52: .It
53: command-line options
54: .It
55: user's configuration file
1.50 djm 56: .Pq Pa ~/.ssh/config
1.2 stevesk 57: .It
58: system-wide configuration file
59: .Pq Pa /etc/ssh/ssh_config
60: .El
1.1 stevesk 61: .Pp
62: For each parameter, the first obtained value
63: will be used.
1.41 jmc 64: The configuration files contain sections separated by
1.1 stevesk 65: .Dq Host
66: specifications, and that section is only applied for hosts that
67: match one of the patterns given in the specification.
68: The matched host name is the one given on the command line.
69: .Pp
70: Since the first obtained value for each parameter is used, more
71: host-specific declarations should be given near the beginning of the
72: file, and general defaults at the end.
1.80 jmc 73: .Pp
1.1 stevesk 74: The configuration file has the following format:
75: .Pp
76: Empty lines and lines starting with
77: .Ql #
78: are comments.
79: Otherwise a line is of the format
80: .Dq keyword arguments .
81: Configuration options may be separated by whitespace or
82: optional whitespace and exactly one
83: .Ql = ;
84: the latter format is useful to avoid the need to quote whitespace
85: when specifying configuration options using the
86: .Nm ssh ,
1.87 jmc 87: .Nm scp ,
1.1 stevesk 88: and
89: .Nm sftp
90: .Fl o
91: option.
1.88 dtucker 92: Arguments may optionally be enclosed in double quotes
93: .Pq \&"
94: in order to represent arguments containing spaces.
1.1 stevesk 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.
1.112 krw 105: If more than one pattern is provided, they should be separated by whitespace.
1.1 stevesk 106: A single
1.83 jmc 107: .Ql *
1.1 stevesk 108: as a pattern can be used to provide global
109: defaults for all hosts.
110: The host is the
111: .Ar hostname
1.83 jmc 112: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 113: a canonicalized host name before matching).
1.81 jmc 114: .Pp
115: See
116: .Sx PATTERNS
117: for more information on patterns.
1.10 djm 118: .It Cm AddressFamily
1.11 jmc 119: Specifies which address family to use when connecting.
120: Valid arguments are
1.10 djm 121: .Dq any ,
122: .Dq inet
1.84 jmc 123: (use IPv4 only), or
1.10 djm 124: .Dq inet6
1.40 jmc 125: (use IPv6 only).
1.1 stevesk 126: .It Cm BatchMode
127: If set to
128: .Dq yes ,
129: passphrase/password querying will be disabled.
130: This option is useful in scripts and other batch jobs where no user
131: is present to supply the password.
132: The argument must be
133: .Dq yes
134: or
135: .Dq no .
136: The default is
137: .Dq no .
138: .It Cm BindAddress
1.60 dtucker 139: Use the specified address on the local machine as the source address of
1.61 jmc 140: the connection.
141: Only useful on systems with more than one address.
1.1 stevesk 142: Note that this option does not work if
143: .Cm UsePrivilegedPort
144: is set to
145: .Dq yes .
146: .It Cm ChallengeResponseAuthentication
1.82 jmc 147: Specifies whether to use challenge-response authentication.
1.1 stevesk 148: The argument to this keyword must be
149: .Dq yes
150: or
151: .Dq no .
152: The default is
153: .Dq yes .
154: .It Cm CheckHostIP
155: If this flag is set to
156: .Dq yes ,
1.84 jmc 157: .Xr ssh 1
158: will additionally check the host IP address in the
1.1 stevesk 159: .Pa known_hosts
160: file.
161: This allows ssh to detect if a host key changed due to DNS spoofing.
1.107 grunk 162: If the option is set to
1.1 stevesk 163: .Dq no ,
164: the check will not be executed.
165: The default is
166: .Dq yes .
167: .It Cm Cipher
168: Specifies the cipher to use for encrypting the session
169: in protocol version 1.
170: Currently,
171: .Dq blowfish ,
172: .Dq 3des ,
173: and
174: .Dq des
175: are supported.
176: .Ar des
177: is only supported in the
1.84 jmc 178: .Xr ssh 1
1.1 stevesk 179: client for interoperability with legacy protocol 1 implementations
180: that do not support the
181: .Ar 3des
1.7 jmc 182: cipher.
183: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 184: The default is
185: .Dq 3des .
186: .It Cm Ciphers
187: Specifies the ciphers allowed for protocol version 2
188: in order of preference.
189: Multiple ciphers must be comma-separated.
1.35 dtucker 190: The supported ciphers are
191: .Dq 3des-cbc ,
192: .Dq aes128-cbc ,
193: .Dq aes192-cbc ,
194: .Dq aes256-cbc ,
195: .Dq aes128-ctr ,
196: .Dq aes192-ctr ,
197: .Dq aes256-ctr ,
1.54 djm 198: .Dq arcfour128 ,
199: .Dq arcfour256 ,
1.35 dtucker 200: .Dq arcfour ,
201: .Dq blowfish-cbc ,
202: and
203: .Dq cast128-cbc .
1.84 jmc 204: The default is:
205: .Bd -literal -offset 3n
1.116 naddy 206: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
207: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
208: aes256-cbc,arcfour
1.1 stevesk 209: .Ed
210: .It Cm ClearAllForwardings
1.84 jmc 211: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 212: specified in the configuration files or on the command line be
1.7 jmc 213: cleared.
214: This option is primarily useful when used from the
1.84 jmc 215: .Xr ssh 1
1.1 stevesk 216: command line to clear port forwardings set in
217: configuration files, and is automatically set by
218: .Xr scp 1
219: and
220: .Xr sftp 1 .
221: The argument must be
222: .Dq yes
223: or
224: .Dq no .
225: The default is
226: .Dq no .
227: .It Cm Compression
228: Specifies whether to use compression.
229: The argument must be
230: .Dq yes
231: or
232: .Dq no .
233: The default is
234: .Dq no .
235: .It Cm CompressionLevel
236: Specifies the compression level to use if compression is enabled.
237: The argument must be an integer from 1 (fast) to 9 (slow, best).
238: The default level is 6, which is good for most applications.
239: The meaning of the values is the same as in
240: .Xr gzip 1 .
241: Note that this option applies to protocol version 1 only.
242: .It Cm ConnectionAttempts
243: Specifies the number of tries (one per second) to make before exiting.
244: The argument must be an integer.
245: This may be useful in scripts if the connection sometimes fails.
246: The default is 1.
1.9 djm 247: .It Cm ConnectTimeout
1.84 jmc 248: Specifies the timeout (in seconds) used when connecting to the
249: SSH server, instead of using the default system TCP timeout.
1.11 jmc 250: This value is used only when the target is down or really unreachable,
251: not when it refuses the connection.
1.36 djm 252: .It Cm ControlMaster
253: Enables the sharing of multiple sessions over a single network connection.
254: When set to
1.84 jmc 255: .Dq yes ,
256: .Xr ssh 1
1.36 djm 257: will listen for connections on a control socket specified using the
258: .Cm ControlPath
259: argument.
260: Additional sessions can connect to this socket using the same
261: .Cm ControlPath
262: with
263: .Cm ControlMaster
264: set to
265: .Dq no
1.38 jmc 266: (the default).
1.64 jmc 267: These sessions will try to reuse the master instance's network connection
1.63 djm 268: rather than initiating new ones, but will fall back to connecting normally
269: if the control socket does not exist, or is not listening.
270: .Pp
1.37 djm 271: Setting this to
272: .Dq ask
1.84 jmc 273: will cause ssh
1.37 djm 274: to listen for control connections, but require confirmation using the
275: .Ev SSH_ASKPASS
276: program before they are accepted (see
277: .Xr ssh-add 1
1.38 jmc 278: for details).
1.51 jakob 279: If the
280: .Cm ControlPath
1.84 jmc 281: cannot be opened,
282: ssh will continue without connecting to a master instance.
1.58 djm 283: .Pp
284: X11 and
1.59 jmc 285: .Xr ssh-agent 1
1.58 djm 286: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 287: display and agent forwarded will be the one belonging to the master
1.59 jmc 288: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 289: .Pp
290: Two additional options allow for opportunistic multiplexing: try to use a
291: master connection but fall back to creating a new one if one does not already
292: exist.
293: These options are:
294: .Dq auto
295: and
296: .Dq autoask .
297: The latter requires confirmation like the
298: .Dq ask
299: option.
1.36 djm 300: .It Cm ControlPath
1.55 djm 301: Specify the path to the control socket used for connection sharing as described
302: in the
1.36 djm 303: .Cm ControlMaster
1.57 djm 304: section above or the string
305: .Dq none
306: to disable connection sharing.
1.55 djm 307: In the path,
1.77 djm 308: .Ql %l
309: will be substituted by the local host name,
1.55 djm 310: .Ql %h
311: will be substituted by the target host name,
312: .Ql %p
1.84 jmc 313: the port, and
1.55 djm 314: .Ql %r
315: by the remote login username.
1.56 djm 316: It is recommended that any
317: .Cm ControlPath
318: used for opportunistic connection sharing include
1.78 jmc 319: at least %h, %p, and %r.
1.56 djm 320: This ensures that shared connections are uniquely identified.
1.137 djm 321: .It Cm ControlPersist
322: When used in conjunction with
323: .Cm ControlMaster ,
324: specifies that the master connection should remain open
325: in the background (waiting for future client connections)
326: after the initial client connection has been closed.
327: If set to
328: .Dq no ,
329: then the master connection will not be placed into the background,
330: and will close as soon as the initial client connection is closed.
331: If set to
332: .Dq yes ,
333: then the master connection will remain in the background indefinitely
334: (until killed or closed via a mechanism such as the
335: .Xr ssh 1
336: .Dq Fl O No exit
337: option).
338: If set to a time in seconds, or a time in any of the formats documented in
339: .Xr sshd_config 5 ,
340: then the backgrounded master connection will automatically terminate
341: after it has remained idle (with no client connections) for the
342: specified time.
1.38 jmc 343: .It Cm DynamicForward
1.74 jmc 344: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 345: over the secure channel, and the application
346: protocol is then used to determine where to connect to from the
347: remote machine.
1.62 djm 348: .Pp
349: The argument must be
350: .Sm off
351: .Oo Ar bind_address : Oc Ar port .
352: .Sm on
1.138 djm 353: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 354: By default, the local port is bound in accordance with the
355: .Cm GatewayPorts
356: setting.
357: However, an explicit
358: .Ar bind_address
359: may be used to bind the connection to a specific address.
360: The
361: .Ar bind_address
362: of
363: .Dq localhost
364: indicates that the listening port be bound for local use only, while an
365: empty address or
366: .Sq *
367: indicates that the port should be available from all interfaces.
368: .Pp
1.38 jmc 369: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 370: .Xr ssh 1
1.38 jmc 371: will act as a SOCKS server.
372: Multiple forwardings may be specified, and
373: additional forwardings can be given on the command line.
374: Only the superuser can forward privileged ports.
1.14 markus 375: .It Cm EnableSSHKeysign
376: Setting this option to
377: .Dq yes
378: in the global client configuration file
379: .Pa /etc/ssh/ssh_config
380: enables the use of the helper program
381: .Xr ssh-keysign 8
382: during
383: .Cm HostbasedAuthentication .
384: The argument must be
385: .Dq yes
386: or
387: .Dq no .
388: The default is
389: .Dq no .
1.23 jmc 390: This option should be placed in the non-hostspecific section.
1.14 markus 391: See
392: .Xr ssh-keysign 8
393: for more information.
1.1 stevesk 394: .It Cm EscapeChar
395: Sets the escape character (default:
396: .Ql ~ ) .
397: The escape character can also
398: be set on the command line.
399: The argument should be a single character,
400: .Ql ^
401: followed by a letter, or
402: .Dq none
403: to disable the escape
404: character entirely (making the connection transparent for binary
405: data).
1.96 markus 406: .It Cm ExitOnForwardFailure
407: Specifies whether
408: .Xr ssh 1
409: should terminate the connection if it cannot set up all requested
1.102 stevesk 410: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 411: The argument must be
412: .Dq yes
413: or
414: .Dq no .
415: The default is
416: .Dq no .
1.1 stevesk 417: .It Cm ForwardAgent
418: Specifies whether the connection to the authentication agent (if any)
419: will be forwarded to the remote machine.
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: Agent forwarding should be enabled with caution.
428: Users with the ability to bypass file permissions on the remote host
429: (for the agent's Unix-domain socket)
430: can access the local agent through the forwarded connection.
431: An attacker cannot obtain key material from the agent,
1.3 stevesk 432: however they can perform operations on the keys that enable them to
433: authenticate using the identities loaded into the agent.
1.1 stevesk 434: .It Cm ForwardX11
435: Specifies whether X11 connections will be automatically redirected
436: over the secure channel and
437: .Ev DISPLAY
438: set.
439: The argument must be
440: .Dq yes
441: or
442: .Dq no .
443: The default is
444: .Dq no .
1.3 stevesk 445: .Pp
1.7 jmc 446: X11 forwarding should be enabled with caution.
447: Users with the ability to bypass file permissions on the remote host
1.22 markus 448: (for the user's X11 authorization database)
1.7 jmc 449: can access the local X11 display through the forwarded connection.
1.22 markus 450: An attacker may then be able to perform activities such as keystroke monitoring
451: if the
452: .Cm ForwardX11Trusted
453: option is also enabled.
1.134 djm 454: .It Cm ForwardX11Timeout
1.135 jmc 455: Specify a timeout for untrusted X11 forwarding
456: using the format described in the
1.134 djm 457: .Sx TIME FORMATS
458: section of
459: .Xr sshd_config 5 .
460: X11 connections received by
461: .Xr ssh 1
462: after this time will be refused.
463: The default is to disable untrusted X11 forwarding after twenty minutes has
464: elapsed.
1.22 markus 465: .It Cm ForwardX11Trusted
1.34 jmc 466: If this option is set to
1.84 jmc 467: .Dq yes ,
468: remote X11 clients will have full access to the original X11 display.
1.42 djm 469: .Pp
1.22 markus 470: If this option is set to
1.84 jmc 471: .Dq no ,
472: remote X11 clients will be considered untrusted and prevented
1.22 markus 473: from stealing or tampering with data belonging to trusted X11
474: clients.
1.42 djm 475: Furthermore, the
476: .Xr xauth 1
477: token used for the session will be set to expire after 20 minutes.
478: Remote clients will be refused access after this time.
1.22 markus 479: .Pp
480: The default is
481: .Dq no .
482: .Pp
483: See the X11 SECURITY extension specification for full details on
484: the restrictions imposed on untrusted clients.
1.1 stevesk 485: .It Cm GatewayPorts
486: Specifies whether remote hosts are allowed to connect to local
487: forwarded ports.
488: By default,
1.84 jmc 489: .Xr ssh 1
1.7 jmc 490: binds local port forwardings to the loopback address.
491: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 492: .Cm GatewayPorts
1.84 jmc 493: can be used to specify that ssh
1.1 stevesk 494: should bind local port forwardings to the wildcard address,
495: thus allowing remote hosts to connect to forwarded ports.
496: The argument must be
497: .Dq yes
498: or
499: .Dq no .
500: The default is
501: .Dq no .
502: .It Cm GlobalKnownHostsFile
503: Specifies a file to use for the global
504: host key database instead of
505: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 506: .It Cm GSSAPIAuthentication
1.27 markus 507: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 508: The default is
1.21 markus 509: .Dq no .
1.18 markus 510: Note that this option applies to protocol version 2 only.
511: .It Cm GSSAPIDelegateCredentials
512: Forward (delegate) credentials to the server.
513: The default is
514: .Dq no .
515: Note that this option applies to protocol version 2 only.
1.44 djm 516: .It Cm HashKnownHosts
517: Indicates that
1.84 jmc 518: .Xr ssh 1
1.44 djm 519: should hash host names and addresses when they are added to
1.50 djm 520: .Pa ~/.ssh/known_hosts .
1.44 djm 521: These hashed names may be used normally by
1.84 jmc 522: .Xr ssh 1
1.44 djm 523: and
1.84 jmc 524: .Xr sshd 8 ,
1.44 djm 525: but they do not reveal identifying information should the file's contents
526: be disclosed.
527: The default is
528: .Dq no .
1.97 jmc 529: Note that existing names and addresses in known hosts files
530: will not be converted automatically,
531: but may be manually hashed using
1.45 djm 532: .Xr ssh-keygen 1 .
1.1 stevesk 533: .It Cm HostbasedAuthentication
534: Specifies whether to try rhosts based authentication with public key
535: authentication.
536: The argument must be
537: .Dq yes
538: or
539: .Dq no .
540: The default is
541: .Dq no .
542: This option applies to protocol version 2 only and
543: is similar to
544: .Cm RhostsRSAAuthentication .
545: .It Cm HostKeyAlgorithms
546: Specifies the protocol version 2 host key algorithms
547: that the client wants to use in order of preference.
548: The default for this option is:
1.139 djm 549: .Bd -literal -offset 3n
550: ecdsa-sha2-nistp256-cert-v01@openssh.com,
551: ecdsa-sha2-nistp384-cert-v01@openssh.com,
552: ecdsa-sha2-nistp521-cert-v01@openssh.com,
553: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
554: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
555: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
556: ssh-rsa,ssh-dss
557: .Ed
1.1 stevesk 558: .It Cm HostKeyAlias
559: Specifies an alias that should be used instead of the
560: real host name when looking up or saving the host key
561: in the host key database files.
1.84 jmc 562: This option is useful for tunneling SSH connections
1.1 stevesk 563: or for multiple servers running on a single host.
564: .It Cm HostName
565: Specifies the real host name to log into.
566: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 567: If the hostname contains the character sequence
568: .Ql %h ,
569: then this will be replaced with the host name specified on the commandline
570: (this is useful for manipulating unqualified names).
1.84 jmc 571: The default is the name given on the command line.
1.1 stevesk 572: Numeric IP addresses are also permitted (both on the command line and in
573: .Cm HostName
574: specifications).
1.29 markus 575: .It Cm IdentitiesOnly
576: Specifies that
1.84 jmc 577: .Xr ssh 1
1.29 markus 578: should only use the authentication identity files configured in the
1.31 jmc 579: .Nm
1.29 markus 580: files,
1.84 jmc 581: even if
582: .Xr ssh-agent 1
1.29 markus 583: offers more identities.
584: The argument to this keyword must be
585: .Dq yes
586: or
587: .Dq no .
1.84 jmc 588: This option is intended for situations where ssh-agent
1.29 markus 589: offers many different identities.
590: The default is
591: .Dq no .
1.67 jmc 592: .It Cm IdentityFile
1.139 djm 593: Specifies a file from which the user's DSA, ECDSA or DSA authentication
594: identity is read.
1.67 jmc 595: The default is
596: .Pa ~/.ssh/identity
597: for protocol version 1, and
1.139 djm 598: .Pa ~/.ssh/id_dsa ,
599: .Pa ~/.ssh/id_ecdsa
600: and
1.67 jmc 601: .Pa ~/.ssh/id_rsa
602: for protocol version 2.
603: Additionally, any identities represented by the authentication agent
604: will be used for authentication.
1.129 djm 605: .Xr ssh 1
606: will try to load certificate information from the filename obtained by
607: appending
608: .Pa -cert.pub
609: to the path of a specified
610: .Cm IdentityFile .
1.90 djm 611: .Pp
1.67 jmc 612: The file name may use the tilde
1.91 jmc 613: syntax to refer to a user's home directory or one of the following
1.90 djm 614: escape characters:
615: .Ql %d
616: (local user's home directory),
617: .Ql %u
618: (local user name),
619: .Ql %l
620: (local host name),
621: .Ql %h
622: (remote host name) or
1.92 djm 623: .Ql %r
1.90 djm 624: (remote user name).
625: .Pp
1.67 jmc 626: It is possible to have
627: multiple identity files specified in configuration files; all these
628: identities will be tried in sequence.
1.103 djm 629: .It Cm KbdInteractiveAuthentication
630: Specifies whether to use keyboard-interactive authentication.
631: The argument to this keyword must be
632: .Dq yes
633: or
634: .Dq no .
635: The default is
636: .Dq yes .
1.39 djm 637: .It Cm KbdInteractiveDevices
638: Specifies the list of methods to use in keyboard-interactive authentication.
639: Multiple method names must be comma-separated.
640: The default is to use the server specified list.
1.85 jmc 641: The methods available vary depending on what the server supports.
642: For an OpenSSH server,
643: it may be zero or more of:
644: .Dq bsdauth ,
645: .Dq pam ,
646: and
647: .Dq skey .
1.140 djm 648: .It Cm KexAlgorithms
649: Specifies the available KEX (Key Exchange) algorithms.
650: Multiple algorithms must be comma-separated.
1.141 jmc 651: The default is:
652: .Bd -literal -offset indent
653: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
654: diffie-hellman-group-exchange-sha256,
655: diffie-hellman-group-exchange-sha1,
656: diffie-hellman-group14-sha1,
657: diffie-hellman-group1-sha1
658: .Ed
1.65 reyk 659: .It Cm LocalCommand
660: Specifies a command to execute on the local machine after successfully
661: connecting to the server.
662: The command string extends to the end of the line, and is executed with
1.105 jmc 663: the user's shell.
1.109 dtucker 664: The following escape character substitutions will be performed:
665: .Ql %d
666: (local user's home directory),
667: .Ql %h
668: (remote host name),
669: .Ql %l
670: (local host name),
671: .Ql %n
672: (host name as provided on the command line),
673: .Ql %p
674: (remote port),
675: .Ql %r
676: (remote user name) or
677: .Ql %u
678: (local user name).
1.123 djm 679: .Pp
680: The command is run synchronously and does not have access to the
681: session of the
682: .Xr ssh 1
683: that spawned it.
684: It should not be used for interactive commands.
685: .Pp
1.65 reyk 686: This directive is ignored unless
687: .Cm PermitLocalCommand
688: has been enabled.
1.1 stevesk 689: .It Cm LocalForward
1.74 jmc 690: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 691: the secure channel to the specified host and port from the remote machine.
1.49 jmc 692: The first argument must be
1.43 djm 693: .Sm off
1.49 jmc 694: .Oo Ar bind_address : Oc Ar port
1.43 djm 695: .Sm on
1.49 jmc 696: and the second argument must be
697: .Ar host : Ns Ar hostport .
1.138 djm 698: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 699: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 700: given on the command line.
1.1 stevesk 701: Only the superuser can forward privileged ports.
1.43 djm 702: By default, the local port is bound in accordance with the
703: .Cm GatewayPorts
704: setting.
705: However, an explicit
706: .Ar bind_address
707: may be used to bind the connection to a specific address.
708: The
709: .Ar bind_address
710: of
711: .Dq localhost
1.46 jmc 712: indicates that the listening port be bound for local use only, while an
713: empty address or
714: .Sq *
1.43 djm 715: indicates that the port should be available from all interfaces.
1.1 stevesk 716: .It Cm LogLevel
717: Gives the verbosity level that is used when logging messages from
1.84 jmc 718: .Xr ssh 1 .
1.1 stevesk 719: The possible values are:
1.84 jmc 720: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 721: The default is INFO.
722: DEBUG and DEBUG1 are equivalent.
723: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 724: .It Cm MACs
725: Specifies the MAC (message authentication code) algorithms
726: in order of preference.
727: The MAC algorithm is used in protocol version 2
728: for data integrity protection.
729: Multiple algorithms must be comma-separated.
1.84 jmc 730: The default is:
1.101 jmc 731: .Bd -literal -offset indent
732: hmac-md5,hmac-sha1,umac-64@openssh.com,
733: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
734: .Ed
1.1 stevesk 735: .It Cm NoHostAuthenticationForLocalhost
736: This option can be used if the home directory is shared across machines.
737: In this case localhost will refer to a different machine on each of
738: the machines and the user will get many warnings about changed host keys.
739: However, this option disables host authentication for localhost.
740: The argument to this keyword must be
741: .Dq yes
742: or
743: .Dq no .
744: The default is to check the host key for localhost.
745: .It Cm NumberOfPasswordPrompts
746: Specifies the number of password prompts before giving up.
747: The argument to this keyword must be an integer.
1.84 jmc 748: The default is 3.
1.1 stevesk 749: .It Cm PasswordAuthentication
750: Specifies whether to use password authentication.
751: The argument to this keyword must be
752: .Dq yes
753: or
754: .Dq no .
755: The default is
756: .Dq yes .
1.65 reyk 757: .It Cm PermitLocalCommand
758: Allow local command execution via the
759: .Ic LocalCommand
760: option or using the
1.66 jmc 761: .Ic !\& Ns Ar command
1.65 reyk 762: escape sequence in
763: .Xr ssh 1 .
764: The argument must be
765: .Dq yes
766: or
767: .Dq no .
768: The default is
769: .Dq no .
1.127 markus 770: .It Cm PKCS11Provider
771: Specifies which PKCS#11 provider to use.
772: The argument to this keyword is the PKCS#11 shared libary
773: .Xr ssh 1
1.128 markus 774: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 775: private RSA key.
1.67 jmc 776: .It Cm Port
777: Specifies the port number to connect on the remote host.
1.84 jmc 778: The default is 22.
1.1 stevesk 779: .It Cm PreferredAuthentications
780: Specifies the order in which the client should try protocol 2
1.11 jmc 781: authentication methods.
1.48 jmc 782: This allows a client to prefer one method (e.g.\&
1.1 stevesk 783: .Cm keyboard-interactive )
1.48 jmc 784: over another method (e.g.\&
1.131 jmc 785: .Cm password ) .
786: The default is:
787: .Bd -literal -offset indent
788: gssapi-with-mic,hostbased,publickey,
789: keyboard-interactive,password
790: .Ed
1.1 stevesk 791: .It Cm Protocol
792: Specifies the protocol versions
1.84 jmc 793: .Xr ssh 1
1.1 stevesk 794: should support in order of preference.
795: The possible values are
1.84 jmc 796: .Sq 1
1.1 stevesk 797: and
1.84 jmc 798: .Sq 2 .
1.1 stevesk 799: Multiple versions must be comma-separated.
1.120 markus 800: When this option is set to
1.121 jmc 801: .Dq 2,1
1.120 markus 802: .Nm ssh
803: will try version 2 and fall back to version 1
804: if version 2 is not available.
1.1 stevesk 805: The default is
1.121 jmc 806: .Sq 2 .
1.1 stevesk 807: .It Cm ProxyCommand
808: Specifies the command to use to connect to the server.
809: The command
810: string extends to the end of the line, and is executed with
1.105 jmc 811: the user's shell.
1.133 jmc 812: In the command string, any occurrence of
1.1 stevesk 813: .Ql %h
814: will be substituted by the host name to
1.132 djm 815: connect,
1.1 stevesk 816: .Ql %p
1.133 jmc 817: by the port, and
818: .Ql %r
1.132 djm 819: by the remote user name.
1.1 stevesk 820: The command can be basically anything,
821: and should read from its standard input and write to its standard output.
822: It should eventually connect an
823: .Xr sshd 8
824: server running on some machine, or execute
825: .Ic sshd -i
826: somewhere.
827: Host key management will be done using the
828: HostName of the host being connected (defaulting to the name typed by
829: the user).
1.7 jmc 830: Setting the command to
831: .Dq none
1.6 markus 832: disables this option entirely.
1.1 stevesk 833: Note that
834: .Cm CheckHostIP
835: is not available for connects with a proxy command.
1.52 djm 836: .Pp
837: This directive is useful in conjunction with
838: .Xr nc 1
839: and its proxy support.
1.53 jmc 840: For example, the following directive would connect via an HTTP proxy at
1.52 djm 841: 192.0.2.0:
842: .Bd -literal -offset 3n
843: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
844: .Ed
1.1 stevesk 845: .It Cm PubkeyAuthentication
846: Specifies whether to try public key authentication.
847: The argument to this keyword must be
848: .Dq yes
849: or
850: .Dq no .
851: The default is
852: .Dq yes .
853: This option applies to protocol version 2 only.
1.75 dtucker 854: .It Cm RekeyLimit
855: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 856: session key is renegotiated.
1.75 dtucker 857: The argument is the number of bytes, with an optional suffix of
1.76 jmc 858: .Sq K ,
859: .Sq M ,
1.75 dtucker 860: or
1.76 jmc 861: .Sq G
1.75 dtucker 862: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
863: The default is between
1.84 jmc 864: .Sq 1G
1.75 dtucker 865: and
1.84 jmc 866: .Sq 4G ,
1.75 dtucker 867: depending on the cipher.
1.76 jmc 868: This option applies to protocol version 2 only.
1.1 stevesk 869: .It Cm RemoteForward
1.74 jmc 870: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 871: the secure channel to the specified host and port from the local machine.
1.49 jmc 872: The first argument must be
1.43 djm 873: .Sm off
1.49 jmc 874: .Oo Ar bind_address : Oc Ar port
1.43 djm 875: .Sm on
1.49 jmc 876: and the second argument must be
877: .Ar host : Ns Ar hostport .
1.138 djm 878: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 879: Multiple forwardings may be specified, and additional
880: forwardings can be given on the command line.
1.113 stevesk 881: Privileged ports can be forwarded only when
882: logging in as root on the remote machine.
1.118 jmc 883: .Pp
1.117 djm 884: If the
885: .Ar port
886: argument is
887: .Ql 0 ,
888: the listen port will be dynamically allocated on the server and reported
889: to the client at run time.
1.43 djm 890: .Pp
891: If the
892: .Ar bind_address
893: is not specified, the default is to only bind to loopback addresses.
894: If the
895: .Ar bind_address
896: is
897: .Ql *
898: or an empty string, then the forwarding is requested to listen on all
899: interfaces.
900: Specifying a remote
901: .Ar bind_address
1.46 jmc 902: will only succeed if the server's
903: .Cm GatewayPorts
1.43 djm 904: option is enabled (see
1.46 jmc 905: .Xr sshd_config 5 ) .
1.1 stevesk 906: .It Cm RhostsRSAAuthentication
907: Specifies whether to try rhosts based authentication with RSA host
908: authentication.
909: The argument must be
910: .Dq yes
911: or
912: .Dq no .
913: The default is
914: .Dq no .
915: This option applies to protocol version 1 only and requires
1.84 jmc 916: .Xr ssh 1
1.1 stevesk 917: to be setuid root.
918: .It Cm RSAAuthentication
919: Specifies whether to try RSA authentication.
920: The argument to this keyword must be
921: .Dq yes
922: or
923: .Dq no .
924: RSA authentication will only be
925: attempted if the identity file exists, or an authentication agent is
926: running.
927: The default is
928: .Dq yes .
929: Note that this option applies to protocol version 1 only.
1.32 djm 930: .It Cm SendEnv
931: Specifies what variables from the local
932: .Xr environ 7
933: should be sent to the server.
1.84 jmc 934: Note that environment passing is only supported for protocol 2.
935: The server must also support it, and the server must be configured to
1.33 djm 936: accept these environment variables.
1.32 djm 937: Refer to
938: .Cm AcceptEnv
939: in
940: .Xr sshd_config 5
941: for how to configure the server.
1.80 jmc 942: Variables are specified by name, which may contain wildcard characters.
1.33 djm 943: Multiple environment variables may be separated by whitespace or spread
1.32 djm 944: across multiple
945: .Cm SendEnv
946: directives.
947: The default is not to send any environment variables.
1.81 jmc 948: .Pp
949: See
950: .Sx PATTERNS
951: for more information on patterns.
1.28 markus 952: .It Cm ServerAliveCountMax
1.73 jmc 953: Sets the number of server alive messages (see below) which may be
1.28 markus 954: sent without
1.84 jmc 955: .Xr ssh 1
1.28 markus 956: receiving any messages back from the server.
957: If this threshold is reached while server alive messages are being sent,
1.84 jmc 958: ssh will disconnect from the server, terminating the session.
1.28 markus 959: It is important to note that the use of server alive messages is very
960: different from
961: .Cm TCPKeepAlive
962: (below).
963: The server alive messages are sent through the encrypted channel
964: and therefore will not be spoofable.
965: The TCP keepalive option enabled by
966: .Cm TCPKeepAlive
967: is spoofable.
968: The server alive mechanism is valuable when the client or
969: server depend on knowing when a connection has become inactive.
970: .Pp
971: The default value is 3.
972: If, for example,
973: .Cm ServerAliveInterval
1.84 jmc 974: (see below) is set to 15 and
1.28 markus 975: .Cm ServerAliveCountMax
1.84 jmc 976: is left at the default, if the server becomes unresponsive,
977: ssh will disconnect after approximately 45 seconds.
1.89 markus 978: This option applies to protocol version 2 only.
1.67 jmc 979: .It Cm ServerAliveInterval
980: Sets a timeout interval in seconds after which if no data has been received
981: from the server,
1.84 jmc 982: .Xr ssh 1
1.67 jmc 983: will send a message through the encrypted
984: channel to request a response from the server.
985: The default
986: is 0, indicating that these messages will not be sent to the server.
987: This option applies to protocol version 2 only.
1.1 stevesk 988: .It Cm StrictHostKeyChecking
989: If this flag is set to
990: .Dq yes ,
1.84 jmc 991: .Xr ssh 1
1.1 stevesk 992: will never automatically add host keys to the
1.50 djm 993: .Pa ~/.ssh/known_hosts
1.1 stevesk 994: file, and refuses to connect to hosts whose host key has changed.
995: This provides maximum protection against trojan horse attacks,
1.84 jmc 996: though it can be annoying when the
1.1 stevesk 997: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 998: file is poorly maintained or when connections to new hosts are
1.1 stevesk 999: frequently made.
1000: This option forces the user to manually
1001: add all new hosts.
1002: If this flag is set to
1003: .Dq no ,
1.84 jmc 1004: ssh will automatically add new host keys to the
1.1 stevesk 1005: user known hosts files.
1006: If this flag is set to
1007: .Dq ask ,
1008: new host keys
1009: will be added to the user known host files only after the user
1010: has confirmed that is what they really want to do, and
1.84 jmc 1011: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1012: The host keys of
1013: known hosts will be verified automatically in all cases.
1014: The argument must be
1015: .Dq yes ,
1.84 jmc 1016: .Dq no ,
1.1 stevesk 1017: or
1018: .Dq ask .
1019: The default is
1020: .Dq ask .
1.26 markus 1021: .It Cm TCPKeepAlive
1022: Specifies whether the system should send TCP keepalive messages to the
1023: other side.
1024: If they are sent, death of the connection or crash of one
1025: of the machines will be properly noticed.
1026: However, this means that
1027: connections will die if the route is down temporarily, and some people
1028: find it annoying.
1029: .Pp
1030: The default is
1031: .Dq yes
1032: (to send TCP keepalive messages), and the client will notice
1033: if the network goes down or the remote host dies.
1034: This is important in scripts, and many users want it too.
1035: .Pp
1036: To disable TCP keepalive messages, the value should be set to
1037: .Dq no .
1.65 reyk 1038: .It Cm Tunnel
1.95 stevesk 1039: Request
1.65 reyk 1040: .Xr tun 4
1.69 jmc 1041: device forwarding between the client and the server.
1.65 reyk 1042: The argument must be
1.68 reyk 1043: .Dq yes ,
1.95 stevesk 1044: .Dq point-to-point
1045: (layer 3),
1046: .Dq ethernet
1047: (layer 2),
1.65 reyk 1048: or
1049: .Dq no .
1.95 stevesk 1050: Specifying
1051: .Dq yes
1052: requests the default tunnel mode, which is
1053: .Dq point-to-point .
1.65 reyk 1054: The default is
1055: .Dq no .
1056: .It Cm TunnelDevice
1.95 stevesk 1057: Specifies the
1.65 reyk 1058: .Xr tun 4
1.95 stevesk 1059: devices to open on the client
1060: .Pq Ar local_tun
1061: and the server
1062: .Pq Ar remote_tun .
1063: .Pp
1064: The argument must be
1065: .Sm off
1066: .Ar local_tun Op : Ar remote_tun .
1067: .Sm on
1068: The devices may be specified by numerical ID or the keyword
1069: .Dq any ,
1070: which uses the next available tunnel device.
1071: If
1072: .Ar remote_tun
1073: is not specified, it defaults to
1074: .Dq any .
1075: The default is
1076: .Dq any:any .
1.72 jmc 1077: .It Cm UsePrivilegedPort
1078: Specifies whether to use a privileged port for outgoing connections.
1079: The argument must be
1080: .Dq yes
1081: or
1082: .Dq no .
1083: The default is
1084: .Dq no .
1085: If set to
1.84 jmc 1086: .Dq yes ,
1087: .Xr ssh 1
1.72 jmc 1088: must be setuid root.
1089: Note that this option must be set to
1090: .Dq yes
1091: for
1092: .Cm RhostsRSAAuthentication
1093: with older servers.
1.1 stevesk 1094: .It Cm User
1095: Specifies the user to log in as.
1096: This can be useful when a different user name is used on different machines.
1097: This saves the trouble of
1098: having to remember to give the user name on the command line.
1099: .It Cm UserKnownHostsFile
1100: Specifies a file to use for the user
1101: host key database instead of
1.50 djm 1102: .Pa ~/.ssh/known_hosts .
1.8 jakob 1103: .It Cm VerifyHostKeyDNS
1104: Specifies whether to verify the remote key using DNS and SSHFP resource
1105: records.
1.24 jakob 1106: If this option is set to
1107: .Dq yes ,
1.25 jmc 1108: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1109: from DNS.
1110: Insecure fingerprints will be handled as if this option was set to
1111: .Dq ask .
1112: If this option is set to
1113: .Dq ask ,
1114: information on fingerprint match will be displayed, but the user will still
1115: need to confirm new host keys according to the
1116: .Cm StrictHostKeyChecking
1117: option.
1118: The argument must be
1119: .Dq yes ,
1.84 jmc 1120: .Dq no ,
1.25 jmc 1121: or
1122: .Dq ask .
1.8 jakob 1123: The default is
1124: .Dq no .
1.12 jakob 1125: Note that this option applies to protocol version 2 only.
1.84 jmc 1126: .Pp
1127: See also
1128: .Sx VERIFYING HOST KEYS
1129: in
1130: .Xr ssh 1 .
1.111 grunk 1131: .It Cm VisualHostKey
1132: If this flag is set to
1133: .Dq yes ,
1134: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1135: printed in addition to the hex fingerprint string at login and
1136: for unknown host keys.
1.111 grunk 1137: If this flag is set to
1138: .Dq no ,
1.114 stevesk 1139: no fingerprint strings are printed at login and
1140: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1141: The default is
1142: .Dq no .
1.1 stevesk 1143: .It Cm XAuthLocation
1.5 stevesk 1144: Specifies the full pathname of the
1.1 stevesk 1145: .Xr xauth 1
1146: program.
1147: The default is
1148: .Pa /usr/X11R6/bin/xauth .
1149: .El
1.86 jmc 1150: .Sh PATTERNS
1151: A
1152: .Em pattern
1153: consists of zero or more non-whitespace characters,
1154: .Sq *
1155: (a wildcard that matches zero or more characters),
1156: or
1157: .Sq ?\&
1158: (a wildcard that matches exactly one character).
1159: For example, to specify a set of declarations for any host in the
1160: .Dq .co.uk
1161: set of domains,
1162: the following pattern could be used:
1163: .Pp
1164: .Dl Host *.co.uk
1165: .Pp
1166: The following pattern
1167: would match any host in the 192.168.0.[0-9] network range:
1168: .Pp
1169: .Dl Host 192.168.0.?
1170: .Pp
1171: A
1172: .Em pattern-list
1173: is a comma-separated list of patterns.
1174: Patterns within pattern-lists may be negated
1175: by preceding them with an exclamation mark
1176: .Pq Sq !\& .
1177: For example,
1178: to allow a key to be used from anywhere within an organisation
1179: except from the
1180: .Dq dialup
1181: pool,
1182: the following entry (in authorized_keys) could be used:
1183: .Pp
1184: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1185: .Sh FILES
1186: .Bl -tag -width Ds
1.50 djm 1187: .It Pa ~/.ssh/config
1.1 stevesk 1188: This is the per-user configuration file.
1189: The format of this file is described above.
1.84 jmc 1190: This file is used by the SSH client.
1.30 djm 1191: Because of the potential for abuse, this file must have strict permissions:
1192: read/write for the user, and not accessible by others.
1.1 stevesk 1193: .It Pa /etc/ssh/ssh_config
1194: Systemwide configuration file.
1195: This file provides defaults for those
1196: values that are not specified in the user's configuration file, and
1197: for those users who do not have a configuration file.
1198: This file must be world-readable.
1199: .El
1.13 jmc 1200: .Sh SEE ALSO
1201: .Xr ssh 1
1.1 stevesk 1202: .Sh AUTHORS
1203: OpenSSH is a derivative of the original and free
1204: ssh 1.2.12 release by Tatu Ylonen.
1205: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1206: Theo de Raadt and Dug Song
1207: removed many bugs, re-added newer features and
1208: created OpenSSH.
1209: Markus Friedl contributed the support for SSH
1210: protocol versions 1.5 and 2.0.
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