Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.147
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
22: .\" notice, this list of conditions and the following disclaimer in the
23: .\" documentation and/or other materials provided with the distribution.
24: .\"
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
27: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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1.147 ! djm 36: .\" $OpenBSD: ssh_config.5,v 1.146 2010/12/08 04:02:47 djm Exp $
! 37: .Dd $Mdocdate: December 8 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,
1.147 ! djm 308: .Ql %L
! 309: will be substituted by the first component of the local host name,
1.77 djm 310: .Ql %l
1.147 ! djm 311: will be substituted by the local host name (including any domain name),
1.55 djm 312: .Ql %h
313: will be substituted by the target host name,
1.147 ! djm 314: .Ql %h
! 315: will be substituted by original target host name specified on the commandline,
1.55 djm 316: .Ql %p
1.147 ! djm 317: the port,
1.55 djm 318: .Ql %r
1.147 ! djm 319: by the remote login username, and
! 320: .Ql %u
! 321: by the username of the user running
! 322: .Xr ssh 1 .
1.56 djm 323: It is recommended that any
324: .Cm ControlPath
325: used for opportunistic connection sharing include
1.78 jmc 326: at least %h, %p, and %r.
1.56 djm 327: This ensures that shared connections are uniquely identified.
1.137 djm 328: .It Cm ControlPersist
329: When used in conjunction with
330: .Cm ControlMaster ,
331: specifies that the master connection should remain open
332: in the background (waiting for future client connections)
333: after the initial client connection has been closed.
334: If set to
335: .Dq no ,
336: then the master connection will not be placed into the background,
337: and will close as soon as the initial client connection is closed.
338: If set to
339: .Dq yes ,
340: then the master connection will remain in the background indefinitely
341: (until killed or closed via a mechanism such as the
342: .Xr ssh 1
343: .Dq Fl O No exit
344: option).
345: If set to a time in seconds, or a time in any of the formats documented in
346: .Xr sshd_config 5 ,
347: then the backgrounded master connection will automatically terminate
348: after it has remained idle (with no client connections) for the
349: specified time.
1.38 jmc 350: .It Cm DynamicForward
1.74 jmc 351: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 352: over the secure channel, and the application
353: protocol is then used to determine where to connect to from the
354: remote machine.
1.62 djm 355: .Pp
356: The argument must be
357: .Sm off
358: .Oo Ar bind_address : Oc Ar port .
359: .Sm on
1.138 djm 360: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.62 djm 361: By default, the local port is bound in accordance with the
362: .Cm GatewayPorts
363: setting.
364: However, an explicit
365: .Ar bind_address
366: may be used to bind the connection to a specific address.
367: The
368: .Ar bind_address
369: of
370: .Dq localhost
371: indicates that the listening port be bound for local use only, while an
372: empty address or
373: .Sq *
374: indicates that the port should be available from all interfaces.
375: .Pp
1.38 jmc 376: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 377: .Xr ssh 1
1.38 jmc 378: will act as a SOCKS server.
379: Multiple forwardings may be specified, and
380: additional forwardings can be given on the command line.
381: Only the superuser can forward privileged ports.
1.14 markus 382: .It Cm EnableSSHKeysign
383: Setting this option to
384: .Dq yes
385: in the global client configuration file
386: .Pa /etc/ssh/ssh_config
387: enables the use of the helper program
388: .Xr ssh-keysign 8
389: during
390: .Cm HostbasedAuthentication .
391: The argument must be
392: .Dq yes
393: or
394: .Dq no .
395: The default is
396: .Dq no .
1.23 jmc 397: This option should be placed in the non-hostspecific section.
1.14 markus 398: See
399: .Xr ssh-keysign 8
400: for more information.
1.1 stevesk 401: .It Cm EscapeChar
402: Sets the escape character (default:
403: .Ql ~ ) .
404: The escape character can also
405: be set on the command line.
406: The argument should be a single character,
407: .Ql ^
408: followed by a letter, or
409: .Dq none
410: to disable the escape
411: character entirely (making the connection transparent for binary
412: data).
1.96 markus 413: .It Cm ExitOnForwardFailure
414: Specifies whether
415: .Xr ssh 1
416: should terminate the connection if it cannot set up all requested
1.102 stevesk 417: dynamic, tunnel, local, and remote port forwardings.
1.96 markus 418: The argument must be
419: .Dq yes
420: or
421: .Dq no .
422: The default is
423: .Dq no .
1.1 stevesk 424: .It Cm ForwardAgent
425: Specifies whether the connection to the authentication agent (if any)
426: will be forwarded to the remote machine.
427: The argument must be
428: .Dq yes
429: or
430: .Dq no .
431: The default is
432: .Dq no .
1.3 stevesk 433: .Pp
1.7 jmc 434: Agent forwarding should be enabled with caution.
435: Users with the ability to bypass file permissions on the remote host
436: (for the agent's Unix-domain socket)
437: can access the local agent through the forwarded connection.
438: An attacker cannot obtain key material from the agent,
1.3 stevesk 439: however they can perform operations on the keys that enable them to
440: authenticate using the identities loaded into the agent.
1.1 stevesk 441: .It Cm ForwardX11
442: Specifies whether X11 connections will be automatically redirected
443: over the secure channel and
444: .Ev DISPLAY
445: set.
446: The argument must be
447: .Dq yes
448: or
449: .Dq no .
450: The default is
451: .Dq no .
1.3 stevesk 452: .Pp
1.7 jmc 453: X11 forwarding should be enabled with caution.
454: Users with the ability to bypass file permissions on the remote host
1.22 markus 455: (for the user's X11 authorization database)
1.7 jmc 456: can access the local X11 display through the forwarded connection.
1.22 markus 457: An attacker may then be able to perform activities such as keystroke monitoring
458: if the
459: .Cm ForwardX11Trusted
460: option is also enabled.
1.134 djm 461: .It Cm ForwardX11Timeout
1.135 jmc 462: Specify a timeout for untrusted X11 forwarding
463: using the format described in the
1.134 djm 464: .Sx TIME FORMATS
465: section of
466: .Xr sshd_config 5 .
467: X11 connections received by
468: .Xr ssh 1
469: after this time will be refused.
470: The default is to disable untrusted X11 forwarding after twenty minutes has
471: elapsed.
1.22 markus 472: .It Cm ForwardX11Trusted
1.34 jmc 473: If this option is set to
1.84 jmc 474: .Dq yes ,
475: remote X11 clients will have full access to the original X11 display.
1.42 djm 476: .Pp
1.22 markus 477: If this option is set to
1.84 jmc 478: .Dq no ,
479: remote X11 clients will be considered untrusted and prevented
1.22 markus 480: from stealing or tampering with data belonging to trusted X11
481: clients.
1.42 djm 482: Furthermore, the
483: .Xr xauth 1
484: token used for the session will be set to expire after 20 minutes.
485: Remote clients will be refused access after this time.
1.22 markus 486: .Pp
487: The default is
488: .Dq no .
489: .Pp
490: See the X11 SECURITY extension specification for full details on
491: the restrictions imposed on untrusted clients.
1.1 stevesk 492: .It Cm GatewayPorts
493: Specifies whether remote hosts are allowed to connect to local
494: forwarded ports.
495: By default,
1.84 jmc 496: .Xr ssh 1
1.7 jmc 497: binds local port forwardings to the loopback address.
498: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 499: .Cm GatewayPorts
1.84 jmc 500: can be used to specify that ssh
1.1 stevesk 501: should bind local port forwardings to the wildcard address,
502: thus allowing remote hosts to connect to forwarded ports.
503: The argument must be
504: .Dq yes
505: or
506: .Dq no .
507: The default is
508: .Dq no .
509: .It Cm GlobalKnownHostsFile
510: Specifies a file to use for the global
511: host key database instead of
512: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 513: .It Cm GSSAPIAuthentication
1.27 markus 514: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 515: The default is
1.21 markus 516: .Dq no .
1.18 markus 517: Note that this option applies to protocol version 2 only.
518: .It Cm GSSAPIDelegateCredentials
519: Forward (delegate) credentials to the server.
520: The default is
521: .Dq no .
522: Note that this option applies to protocol version 2 only.
1.44 djm 523: .It Cm HashKnownHosts
524: Indicates that
1.84 jmc 525: .Xr ssh 1
1.44 djm 526: should hash host names and addresses when they are added to
1.50 djm 527: .Pa ~/.ssh/known_hosts .
1.44 djm 528: These hashed names may be used normally by
1.84 jmc 529: .Xr ssh 1
1.44 djm 530: and
1.84 jmc 531: .Xr sshd 8 ,
1.44 djm 532: but they do not reveal identifying information should the file's contents
533: be disclosed.
534: The default is
535: .Dq no .
1.97 jmc 536: Note that existing names and addresses in known hosts files
537: will not be converted automatically,
538: but may be manually hashed using
1.45 djm 539: .Xr ssh-keygen 1 .
1.1 stevesk 540: .It Cm HostbasedAuthentication
541: Specifies whether to try rhosts based authentication with public key
542: authentication.
543: The argument must be
544: .Dq yes
545: or
546: .Dq no .
547: The default is
548: .Dq no .
549: This option applies to protocol version 2 only and
550: is similar to
551: .Cm RhostsRSAAuthentication .
552: .It Cm HostKeyAlgorithms
553: Specifies the protocol version 2 host key algorithms
554: that the client wants to use in order of preference.
555: The default for this option is:
1.139 djm 556: .Bd -literal -offset 3n
557: ecdsa-sha2-nistp256-cert-v01@openssh.com,
558: ecdsa-sha2-nistp384-cert-v01@openssh.com,
559: ecdsa-sha2-nistp521-cert-v01@openssh.com,
560: ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
561: ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
562: ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
563: ssh-rsa,ssh-dss
564: .Ed
1.145 djm 565: .Pp
566: If hostkeys are known for the destination host then this default is modified
567: to prefer their algorithms.
1.1 stevesk 568: .It Cm HostKeyAlias
569: Specifies an alias that should be used instead of the
570: real host name when looking up or saving the host key
571: in the host key database files.
1.84 jmc 572: This option is useful for tunneling SSH connections
1.1 stevesk 573: or for multiple servers running on a single host.
574: .It Cm HostName
575: Specifies the real host name to log into.
576: This can be used to specify nicknames or abbreviations for hosts.
1.136 djm 577: If the hostname contains the character sequence
578: .Ql %h ,
579: then this will be replaced with the host name specified on the commandline
580: (this is useful for manipulating unqualified names).
1.84 jmc 581: The default is the name given on the command line.
1.1 stevesk 582: Numeric IP addresses are also permitted (both on the command line and in
583: .Cm HostName
584: specifications).
1.29 markus 585: .It Cm IdentitiesOnly
586: Specifies that
1.84 jmc 587: .Xr ssh 1
1.29 markus 588: should only use the authentication identity files configured in the
1.31 jmc 589: .Nm
1.29 markus 590: files,
1.84 jmc 591: even if
592: .Xr ssh-agent 1
1.29 markus 593: offers more identities.
594: The argument to this keyword must be
595: .Dq yes
596: or
597: .Dq no .
1.84 jmc 598: This option is intended for situations where ssh-agent
1.29 markus 599: offers many different identities.
600: The default is
601: .Dq no .
1.67 jmc 602: .It Cm IdentityFile
1.139 djm 603: Specifies a file from which the user's DSA, ECDSA or DSA authentication
604: identity is read.
1.67 jmc 605: The default is
606: .Pa ~/.ssh/identity
607: for protocol version 1, and
1.139 djm 608: .Pa ~/.ssh/id_dsa ,
609: .Pa ~/.ssh/id_ecdsa
610: and
1.67 jmc 611: .Pa ~/.ssh/id_rsa
612: for protocol version 2.
613: Additionally, any identities represented by the authentication agent
614: will be used for authentication.
1.129 djm 615: .Xr ssh 1
616: will try to load certificate information from the filename obtained by
617: appending
618: .Pa -cert.pub
619: to the path of a specified
620: .Cm IdentityFile .
1.90 djm 621: .Pp
1.67 jmc 622: The file name may use the tilde
1.91 jmc 623: syntax to refer to a user's home directory or one of the following
1.90 djm 624: escape characters:
625: .Ql %d
626: (local user's home directory),
627: .Ql %u
628: (local user name),
629: .Ql %l
630: (local host name),
631: .Ql %h
632: (remote host name) or
1.92 djm 633: .Ql %r
1.90 djm 634: (remote user name).
635: .Pp
1.67 jmc 636: It is possible to have
637: multiple identity files specified in configuration files; all these
638: identities will be tried in sequence.
1.143 djm 639: .It Cm IPQoS
640: Specifies the IPv4 type-of-service or DSCP class for connections.
641: Accepted values are
642: .Dq af11 ,
643: .Dq af12 ,
644: .Dq af13 ,
645: .Dq af14 ,
646: .Dq af22 ,
647: .Dq af23 ,
648: .Dq af31 ,
649: .Dq af32 ,
650: .Dq af33 ,
651: .Dq af41 ,
652: .Dq af42 ,
653: .Dq af43 ,
654: .Dq cs0 ,
655: .Dq cs1 ,
656: .Dq cs2 ,
657: .Dq cs3 ,
658: .Dq cs4 ,
659: .Dq cs5 ,
660: .Dq cs6 ,
661: .Dq cs7 ,
662: .Dq ef ,
663: .Dq lowdelay ,
664: .Dq throughput ,
665: .Dq reliability ,
666: or a numeric value.
1.146 djm 667: This option may take one or two arguments, separated by whitespace.
1.143 djm 668: If one argument is specified, it is used as the packet class unconditionally.
669: If two values are specified, the first is automatically selected for
670: interactive sessions and the second for non-interactive sessions.
671: The default is
672: .Dq lowdelay
673: for interactive sessions and
674: .Dq throughput
675: for non-interactive sessions.
1.103 djm 676: .It Cm KbdInteractiveAuthentication
677: Specifies whether to use keyboard-interactive authentication.
678: The argument to this keyword must be
679: .Dq yes
680: or
681: .Dq no .
682: The default is
683: .Dq yes .
1.39 djm 684: .It Cm KbdInteractiveDevices
685: Specifies the list of methods to use in keyboard-interactive authentication.
686: Multiple method names must be comma-separated.
687: The default is to use the server specified list.
1.85 jmc 688: The methods available vary depending on what the server supports.
689: For an OpenSSH server,
690: it may be zero or more of:
691: .Dq bsdauth ,
692: .Dq pam ,
693: and
694: .Dq skey .
1.140 djm 695: .It Cm KexAlgorithms
696: Specifies the available KEX (Key Exchange) algorithms.
697: Multiple algorithms must be comma-separated.
1.141 jmc 698: The default is:
699: .Bd -literal -offset indent
700: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
701: diffie-hellman-group-exchange-sha256,
702: diffie-hellman-group-exchange-sha1,
703: diffie-hellman-group14-sha1,
704: diffie-hellman-group1-sha1
705: .Ed
1.65 reyk 706: .It Cm LocalCommand
707: Specifies a command to execute on the local machine after successfully
708: connecting to the server.
709: The command string extends to the end of the line, and is executed with
1.105 jmc 710: the user's shell.
1.109 dtucker 711: The following escape character substitutions will be performed:
712: .Ql %d
713: (local user's home directory),
714: .Ql %h
715: (remote host name),
716: .Ql %l
717: (local host name),
718: .Ql %n
719: (host name as provided on the command line),
720: .Ql %p
721: (remote port),
722: .Ql %r
723: (remote user name) or
724: .Ql %u
725: (local user name).
1.123 djm 726: .Pp
727: The command is run synchronously and does not have access to the
728: session of the
729: .Xr ssh 1
730: that spawned it.
731: It should not be used for interactive commands.
732: .Pp
1.65 reyk 733: This directive is ignored unless
734: .Cm PermitLocalCommand
735: has been enabled.
1.1 stevesk 736: .It Cm LocalForward
1.74 jmc 737: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 738: the secure channel to the specified host and port from the remote machine.
1.49 jmc 739: The first argument must be
1.43 djm 740: .Sm off
1.49 jmc 741: .Oo Ar bind_address : Oc Ar port
1.43 djm 742: .Sm on
1.49 jmc 743: and the second argument must be
744: .Ar host : Ns Ar hostport .
1.138 djm 745: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.46 jmc 746: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 747: given on the command line.
1.1 stevesk 748: Only the superuser can forward privileged ports.
1.43 djm 749: By default, the local port is bound in accordance with the
750: .Cm GatewayPorts
751: setting.
752: However, an explicit
753: .Ar bind_address
754: may be used to bind the connection to a specific address.
755: The
756: .Ar bind_address
757: of
758: .Dq localhost
1.46 jmc 759: indicates that the listening port be bound for local use only, while an
760: empty address or
761: .Sq *
1.43 djm 762: indicates that the port should be available from all interfaces.
1.1 stevesk 763: .It Cm LogLevel
764: Gives the verbosity level that is used when logging messages from
1.84 jmc 765: .Xr ssh 1 .
1.1 stevesk 766: The possible values are:
1.84 jmc 767: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 768: The default is INFO.
769: DEBUG and DEBUG1 are equivalent.
770: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 771: .It Cm MACs
772: Specifies the MAC (message authentication code) algorithms
773: in order of preference.
774: The MAC algorithm is used in protocol version 2
775: for data integrity protection.
776: Multiple algorithms must be comma-separated.
1.84 jmc 777: The default is:
1.101 jmc 778: .Bd -literal -offset indent
779: hmac-md5,hmac-sha1,umac-64@openssh.com,
780: hmac-ripemd160,hmac-sha1-96,hmac-md5-96
781: .Ed
1.1 stevesk 782: .It Cm NoHostAuthenticationForLocalhost
783: This option can be used if the home directory is shared across machines.
784: In this case localhost will refer to a different machine on each of
785: the machines and the user will get many warnings about changed host keys.
786: However, this option disables host authentication for localhost.
787: The argument to this keyword must be
788: .Dq yes
789: or
790: .Dq no .
791: The default is to check the host key for localhost.
792: .It Cm NumberOfPasswordPrompts
793: Specifies the number of password prompts before giving up.
794: The argument to this keyword must be an integer.
1.84 jmc 795: The default is 3.
1.1 stevesk 796: .It Cm PasswordAuthentication
797: Specifies whether to use password authentication.
798: The argument to this keyword must be
799: .Dq yes
800: or
801: .Dq no .
802: The default is
803: .Dq yes .
1.65 reyk 804: .It Cm PermitLocalCommand
805: Allow local command execution via the
806: .Ic LocalCommand
807: option or using the
1.66 jmc 808: .Ic !\& Ns Ar command
1.65 reyk 809: escape sequence in
810: .Xr ssh 1 .
811: The argument must be
812: .Dq yes
813: or
814: .Dq no .
815: The default is
816: .Dq no .
1.127 markus 817: .It Cm PKCS11Provider
818: Specifies which PKCS#11 provider to use.
1.144 jmc 819: The argument to this keyword is the PKCS#11 shared library
1.127 markus 820: .Xr ssh 1
1.128 markus 821: should use to communicate with a PKCS#11 token providing the user's
1.127 markus 822: private RSA key.
1.67 jmc 823: .It Cm Port
824: Specifies the port number to connect on the remote host.
1.84 jmc 825: The default is 22.
1.1 stevesk 826: .It Cm PreferredAuthentications
827: Specifies the order in which the client should try protocol 2
1.11 jmc 828: authentication methods.
1.48 jmc 829: This allows a client to prefer one method (e.g.\&
1.1 stevesk 830: .Cm keyboard-interactive )
1.48 jmc 831: over another method (e.g.\&
1.131 jmc 832: .Cm password ) .
833: The default is:
834: .Bd -literal -offset indent
835: gssapi-with-mic,hostbased,publickey,
836: keyboard-interactive,password
837: .Ed
1.1 stevesk 838: .It Cm Protocol
839: Specifies the protocol versions
1.84 jmc 840: .Xr ssh 1
1.1 stevesk 841: should support in order of preference.
842: The possible values are
1.84 jmc 843: .Sq 1
1.1 stevesk 844: and
1.84 jmc 845: .Sq 2 .
1.1 stevesk 846: Multiple versions must be comma-separated.
1.120 markus 847: When this option is set to
1.121 jmc 848: .Dq 2,1
1.120 markus 849: .Nm ssh
850: will try version 2 and fall back to version 1
851: if version 2 is not available.
1.1 stevesk 852: The default is
1.121 jmc 853: .Sq 2 .
1.1 stevesk 854: .It Cm ProxyCommand
855: Specifies the command to use to connect to the server.
856: The command
857: string extends to the end of the line, and is executed with
1.105 jmc 858: the user's shell.
1.133 jmc 859: In the command string, any occurrence of
1.1 stevesk 860: .Ql %h
861: will be substituted by the host name to
1.132 djm 862: connect,
1.1 stevesk 863: .Ql %p
1.133 jmc 864: by the port, and
865: .Ql %r
1.132 djm 866: by the remote user name.
1.1 stevesk 867: The command can be basically anything,
868: and should read from its standard input and write to its standard output.
869: It should eventually connect an
870: .Xr sshd 8
871: server running on some machine, or execute
872: .Ic sshd -i
873: somewhere.
874: Host key management will be done using the
875: HostName of the host being connected (defaulting to the name typed by
876: the user).
1.7 jmc 877: Setting the command to
878: .Dq none
1.6 markus 879: disables this option entirely.
1.1 stevesk 880: Note that
881: .Cm CheckHostIP
882: is not available for connects with a proxy command.
1.52 djm 883: .Pp
884: This directive is useful in conjunction with
885: .Xr nc 1
886: and its proxy support.
1.53 jmc 887: For example, the following directive would connect via an HTTP proxy at
1.52 djm 888: 192.0.2.0:
889: .Bd -literal -offset 3n
890: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
891: .Ed
1.1 stevesk 892: .It Cm PubkeyAuthentication
893: Specifies whether to try public key authentication.
894: The argument to this keyword must be
895: .Dq yes
896: or
897: .Dq no .
898: The default is
899: .Dq yes .
900: This option applies to protocol version 2 only.
1.75 dtucker 901: .It Cm RekeyLimit
902: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 903: session key is renegotiated.
1.75 dtucker 904: The argument is the number of bytes, with an optional suffix of
1.76 jmc 905: .Sq K ,
906: .Sq M ,
1.75 dtucker 907: or
1.76 jmc 908: .Sq G
1.75 dtucker 909: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
910: The default is between
1.84 jmc 911: .Sq 1G
1.75 dtucker 912: and
1.84 jmc 913: .Sq 4G ,
1.75 dtucker 914: depending on the cipher.
1.76 jmc 915: This option applies to protocol version 2 only.
1.1 stevesk 916: .It Cm RemoteForward
1.74 jmc 917: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 918: the secure channel to the specified host and port from the local machine.
1.49 jmc 919: The first argument must be
1.43 djm 920: .Sm off
1.49 jmc 921: .Oo Ar bind_address : Oc Ar port
1.43 djm 922: .Sm on
1.49 jmc 923: and the second argument must be
924: .Ar host : Ns Ar hostport .
1.138 djm 925: IPv6 addresses can be specified by enclosing addresses in square brackets.
1.1 stevesk 926: Multiple forwardings may be specified, and additional
927: forwardings can be given on the command line.
1.113 stevesk 928: Privileged ports can be forwarded only when
929: logging in as root on the remote machine.
1.118 jmc 930: .Pp
1.117 djm 931: If the
932: .Ar port
933: argument is
934: .Ql 0 ,
935: the listen port will be dynamically allocated on the server and reported
936: to the client at run time.
1.43 djm 937: .Pp
938: If the
939: .Ar bind_address
940: is not specified, the default is to only bind to loopback addresses.
941: If the
942: .Ar bind_address
943: is
944: .Ql *
945: or an empty string, then the forwarding is requested to listen on all
946: interfaces.
947: Specifying a remote
948: .Ar bind_address
1.46 jmc 949: will only succeed if the server's
950: .Cm GatewayPorts
1.43 djm 951: option is enabled (see
1.46 jmc 952: .Xr sshd_config 5 ) .
1.1 stevesk 953: .It Cm RhostsRSAAuthentication
954: Specifies whether to try rhosts based authentication with RSA host
955: authentication.
956: The argument must be
957: .Dq yes
958: or
959: .Dq no .
960: The default is
961: .Dq no .
962: This option applies to protocol version 1 only and requires
1.84 jmc 963: .Xr ssh 1
1.1 stevesk 964: to be setuid root.
965: .It Cm RSAAuthentication
966: Specifies whether to try RSA authentication.
967: The argument to this keyword must be
968: .Dq yes
969: or
970: .Dq no .
971: RSA authentication will only be
972: attempted if the identity file exists, or an authentication agent is
973: running.
974: The default is
975: .Dq yes .
976: Note that this option applies to protocol version 1 only.
1.32 djm 977: .It Cm SendEnv
978: Specifies what variables from the local
979: .Xr environ 7
980: should be sent to the server.
1.84 jmc 981: Note that environment passing is only supported for protocol 2.
982: The server must also support it, and the server must be configured to
1.33 djm 983: accept these environment variables.
1.32 djm 984: Refer to
985: .Cm AcceptEnv
986: in
987: .Xr sshd_config 5
988: for how to configure the server.
1.80 jmc 989: Variables are specified by name, which may contain wildcard characters.
1.33 djm 990: Multiple environment variables may be separated by whitespace or spread
1.32 djm 991: across multiple
992: .Cm SendEnv
993: directives.
994: The default is not to send any environment variables.
1.81 jmc 995: .Pp
996: See
997: .Sx PATTERNS
998: for more information on patterns.
1.28 markus 999: .It Cm ServerAliveCountMax
1.73 jmc 1000: Sets the number of server alive messages (see below) which may be
1.28 markus 1001: sent without
1.84 jmc 1002: .Xr ssh 1
1.28 markus 1003: receiving any messages back from the server.
1004: If this threshold is reached while server alive messages are being sent,
1.84 jmc 1005: ssh will disconnect from the server, terminating the session.
1.28 markus 1006: It is important to note that the use of server alive messages is very
1007: different from
1008: .Cm TCPKeepAlive
1009: (below).
1010: The server alive messages are sent through the encrypted channel
1011: and therefore will not be spoofable.
1012: The TCP keepalive option enabled by
1013: .Cm TCPKeepAlive
1014: is spoofable.
1015: The server alive mechanism is valuable when the client or
1016: server depend on knowing when a connection has become inactive.
1017: .Pp
1018: The default value is 3.
1019: If, for example,
1020: .Cm ServerAliveInterval
1.84 jmc 1021: (see below) is set to 15 and
1.28 markus 1022: .Cm ServerAliveCountMax
1.84 jmc 1023: is left at the default, if the server becomes unresponsive,
1024: ssh will disconnect after approximately 45 seconds.
1.89 markus 1025: This option applies to protocol version 2 only.
1.67 jmc 1026: .It Cm ServerAliveInterval
1027: Sets a timeout interval in seconds after which if no data has been received
1028: from the server,
1.84 jmc 1029: .Xr ssh 1
1.67 jmc 1030: will send a message through the encrypted
1031: channel to request a response from the server.
1032: The default
1033: is 0, indicating that these messages will not be sent to the server.
1034: This option applies to protocol version 2 only.
1.1 stevesk 1035: .It Cm StrictHostKeyChecking
1036: If this flag is set to
1037: .Dq yes ,
1.84 jmc 1038: .Xr ssh 1
1.1 stevesk 1039: will never automatically add host keys to the
1.50 djm 1040: .Pa ~/.ssh/known_hosts
1.1 stevesk 1041: file, and refuses to connect to hosts whose host key has changed.
1042: This provides maximum protection against trojan horse attacks,
1.84 jmc 1043: though it can be annoying when the
1.1 stevesk 1044: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 1045: file is poorly maintained or when connections to new hosts are
1.1 stevesk 1046: frequently made.
1047: This option forces the user to manually
1048: add all new hosts.
1049: If this flag is set to
1050: .Dq no ,
1.84 jmc 1051: ssh will automatically add new host keys to the
1.1 stevesk 1052: user known hosts files.
1053: If this flag is set to
1054: .Dq ask ,
1055: new host keys
1056: will be added to the user known host files only after the user
1057: has confirmed that is what they really want to do, and
1.84 jmc 1058: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 1059: The host keys of
1060: known hosts will be verified automatically in all cases.
1061: The argument must be
1062: .Dq yes ,
1.84 jmc 1063: .Dq no ,
1.1 stevesk 1064: or
1065: .Dq ask .
1066: The default is
1067: .Dq ask .
1.26 markus 1068: .It Cm TCPKeepAlive
1069: Specifies whether the system should send TCP keepalive messages to the
1070: other side.
1071: If they are sent, death of the connection or crash of one
1072: of the machines will be properly noticed.
1073: However, this means that
1074: connections will die if the route is down temporarily, and some people
1075: find it annoying.
1076: .Pp
1077: The default is
1078: .Dq yes
1079: (to send TCP keepalive messages), and the client will notice
1080: if the network goes down or the remote host dies.
1081: This is important in scripts, and many users want it too.
1082: .Pp
1083: To disable TCP keepalive messages, the value should be set to
1084: .Dq no .
1.65 reyk 1085: .It Cm Tunnel
1.95 stevesk 1086: Request
1.65 reyk 1087: .Xr tun 4
1.69 jmc 1088: device forwarding between the client and the server.
1.65 reyk 1089: The argument must be
1.68 reyk 1090: .Dq yes ,
1.95 stevesk 1091: .Dq point-to-point
1092: (layer 3),
1093: .Dq ethernet
1094: (layer 2),
1.65 reyk 1095: or
1096: .Dq no .
1.95 stevesk 1097: Specifying
1098: .Dq yes
1099: requests the default tunnel mode, which is
1100: .Dq point-to-point .
1.65 reyk 1101: The default is
1102: .Dq no .
1103: .It Cm TunnelDevice
1.95 stevesk 1104: Specifies the
1.65 reyk 1105: .Xr tun 4
1.95 stevesk 1106: devices to open on the client
1107: .Pq Ar local_tun
1108: and the server
1109: .Pq Ar remote_tun .
1110: .Pp
1111: The argument must be
1112: .Sm off
1113: .Ar local_tun Op : Ar remote_tun .
1114: .Sm on
1115: The devices may be specified by numerical ID or the keyword
1116: .Dq any ,
1117: which uses the next available tunnel device.
1118: If
1119: .Ar remote_tun
1120: is not specified, it defaults to
1121: .Dq any .
1122: The default is
1123: .Dq any:any .
1.72 jmc 1124: .It Cm UsePrivilegedPort
1125: Specifies whether to use a privileged port for outgoing connections.
1126: The argument must be
1127: .Dq yes
1128: or
1129: .Dq no .
1130: The default is
1131: .Dq no .
1132: If set to
1.84 jmc 1133: .Dq yes ,
1134: .Xr ssh 1
1.72 jmc 1135: must be setuid root.
1136: Note that this option must be set to
1137: .Dq yes
1138: for
1139: .Cm RhostsRSAAuthentication
1140: with older servers.
1.1 stevesk 1141: .It Cm User
1142: Specifies the user to log in as.
1143: This can be useful when a different user name is used on different machines.
1144: This saves the trouble of
1145: having to remember to give the user name on the command line.
1146: .It Cm UserKnownHostsFile
1147: Specifies a file to use for the user
1148: host key database instead of
1.50 djm 1149: .Pa ~/.ssh/known_hosts .
1.8 jakob 1150: .It Cm VerifyHostKeyDNS
1151: Specifies whether to verify the remote key using DNS and SSHFP resource
1152: records.
1.24 jakob 1153: If this option is set to
1154: .Dq yes ,
1.25 jmc 1155: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1156: from DNS.
1157: Insecure fingerprints will be handled as if this option was set to
1158: .Dq ask .
1159: If this option is set to
1160: .Dq ask ,
1161: information on fingerprint match will be displayed, but the user will still
1162: need to confirm new host keys according to the
1163: .Cm StrictHostKeyChecking
1164: option.
1165: The argument must be
1166: .Dq yes ,
1.84 jmc 1167: .Dq no ,
1.25 jmc 1168: or
1169: .Dq ask .
1.8 jakob 1170: The default is
1171: .Dq no .
1.12 jakob 1172: Note that this option applies to protocol version 2 only.
1.84 jmc 1173: .Pp
1174: See also
1175: .Sx VERIFYING HOST KEYS
1176: in
1177: .Xr ssh 1 .
1.111 grunk 1178: .It Cm VisualHostKey
1179: If this flag is set to
1180: .Dq yes ,
1181: an ASCII art representation of the remote host key fingerprint is
1.114 stevesk 1182: printed in addition to the hex fingerprint string at login and
1183: for unknown host keys.
1.111 grunk 1184: If this flag is set to
1185: .Dq no ,
1.114 stevesk 1186: no fingerprint strings are printed at login and
1187: only the hex fingerprint string will be printed for unknown host keys.
1.111 grunk 1188: The default is
1189: .Dq no .
1.1 stevesk 1190: .It Cm XAuthLocation
1.5 stevesk 1191: Specifies the full pathname of the
1.1 stevesk 1192: .Xr xauth 1
1193: program.
1194: The default is
1195: .Pa /usr/X11R6/bin/xauth .
1196: .El
1.86 jmc 1197: .Sh PATTERNS
1198: A
1199: .Em pattern
1200: consists of zero or more non-whitespace characters,
1201: .Sq *
1202: (a wildcard that matches zero or more characters),
1203: or
1204: .Sq ?\&
1205: (a wildcard that matches exactly one character).
1206: For example, to specify a set of declarations for any host in the
1207: .Dq .co.uk
1208: set of domains,
1209: the following pattern could be used:
1210: .Pp
1211: .Dl Host *.co.uk
1212: .Pp
1213: The following pattern
1214: would match any host in the 192.168.0.[0-9] network range:
1215: .Pp
1216: .Dl Host 192.168.0.?
1217: .Pp
1218: A
1219: .Em pattern-list
1220: is a comma-separated list of patterns.
1221: Patterns within pattern-lists may be negated
1222: by preceding them with an exclamation mark
1223: .Pq Sq !\& .
1224: For example,
1225: to allow a key to be used from anywhere within an organisation
1226: except from the
1227: .Dq dialup
1228: pool,
1229: the following entry (in authorized_keys) could be used:
1230: .Pp
1231: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1232: .Sh FILES
1233: .Bl -tag -width Ds
1.50 djm 1234: .It Pa ~/.ssh/config
1.1 stevesk 1235: This is the per-user configuration file.
1236: The format of this file is described above.
1.84 jmc 1237: This file is used by the SSH client.
1.30 djm 1238: Because of the potential for abuse, this file must have strict permissions:
1239: read/write for the user, and not accessible by others.
1.1 stevesk 1240: .It Pa /etc/ssh/ssh_config
1241: Systemwide configuration file.
1242: This file provides defaults for those
1243: values that are not specified in the user's configuration file, and
1244: for those users who do not have a configuration file.
1245: This file must be world-readable.
1246: .El
1.13 jmc 1247: .Sh SEE ALSO
1248: .Xr ssh 1
1.1 stevesk 1249: .Sh AUTHORS
1250: OpenSSH is a derivative of the original and free
1251: ssh 1.2.12 release by Tatu Ylonen.
1252: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1253: Theo de Raadt and Dug Song
1254: removed many bugs, re-added newer features and
1255: created OpenSSH.
1256: Markus Friedl contributed the support for SSH
1257: protocol versions 1.5 and 2.0.
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