Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.96
1.1 stevesk 1: .\" -*- nroff -*-
2: .\"
3: .\" Author: Tatu Ylonen <ylo@cs.hut.fi>
4: .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5: .\" All rights reserved
6: .\"
7: .\" As far as I am concerned, the code I have written for this software
8: .\" can be used freely for any purpose. Any derived versions of this
9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
16: .\"
17: .\" Redistribution and use in source and binary forms, with or without
18: .\" modification, are permitted provided that the following conditions
19: .\" are met:
20: .\" 1. Redistributions of source code must retain the above copyright
21: .\" notice, this list of conditions and the following disclaimer.
22: .\" 2. Redistributions in binary form must reproduce the above copyright
23: .\" notice, this list of conditions and the following disclaimer in the
24: .\" documentation and/or other materials provided with the distribution.
25: .\"
26: .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
27: .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
28: .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
29: .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
30: .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
31: .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
32: .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
33: .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
34: .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
35: .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
36: .\"
1.96 ! markus 37: .\" $OpenBSD: ssh_config.5,v 1.95 2006/07/02 17:12:58 stevesk Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
1.50 djm 46: .It Pa ~/.ssh/config
1.1 stevesk 47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
1.84 jmc 50: .Xr ssh 1
1.1 stevesk 51: obtains configuration data from the following sources in
52: the following order:
1.79 jmc 53: .Pp
1.2 stevesk 54: .Bl -enum -offset indent -compact
55: .It
56: command-line options
57: .It
58: user's configuration file
1.50 djm 59: .Pq Pa ~/.ssh/config
1.2 stevesk 60: .It
61: system-wide configuration file
62: .Pq Pa /etc/ssh/ssh_config
63: .El
1.1 stevesk 64: .Pp
65: For each parameter, the first obtained value
66: will be used.
1.41 jmc 67: The configuration files contain sections separated by
1.1 stevesk 68: .Dq Host
69: specifications, and that section is only applied for hosts that
70: match one of the patterns given in the specification.
71: The matched host name is the one given on the command line.
72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 jmc 76: .Pp
1.1 stevesk 77: The configuration file has the following format:
78: .Pp
79: Empty lines and lines starting with
80: .Ql #
81: are comments.
82: Otherwise a line is of the format
83: .Dq keyword arguments .
84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
1.87 jmc 90: .Nm scp ,
1.1 stevesk 91: and
92: .Nm sftp
93: .Fl o
94: option.
1.88 dtucker 95: Arguments may optionally be enclosed in double quotes
96: .Pq \&"
97: in order to represent arguments containing spaces.
1.1 stevesk 98: .Pp
99: The possible
100: keywords and their meanings are as follows (note that
101: keywords are case-insensitive and arguments are case-sensitive):
102: .Bl -tag -width Ds
103: .It Cm Host
104: Restricts the following declarations (up to the next
105: .Cm Host
106: keyword) to be only for those hosts that match one of the patterns
107: given after the keyword.
108: A single
1.83 jmc 109: .Ql *
1.1 stevesk 110: as a pattern can be used to provide global
111: defaults for all hosts.
112: The host is the
113: .Ar hostname
1.83 jmc 114: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 115: a canonicalized host name before matching).
1.81 jmc 116: .Pp
117: See
118: .Sx PATTERNS
119: for more information on patterns.
1.10 djm 120: .It Cm AddressFamily
1.11 jmc 121: Specifies which address family to use when connecting.
122: Valid arguments are
1.10 djm 123: .Dq any ,
124: .Dq inet
1.84 jmc 125: (use IPv4 only), or
1.10 djm 126: .Dq inet6
1.40 jmc 127: (use IPv6 only).
1.1 stevesk 128: .It Cm BatchMode
129: If set to
130: .Dq yes ,
131: passphrase/password querying will be disabled.
132: This option is useful in scripts and other batch jobs where no user
133: is present to supply the password.
134: The argument must be
135: .Dq yes
136: or
137: .Dq no .
138: The default is
139: .Dq no .
140: .It Cm BindAddress
1.60 dtucker 141: Use the specified address on the local machine as the source address of
1.61 jmc 142: the connection.
143: Only useful on systems with more than one address.
1.1 stevesk 144: Note that this option does not work if
145: .Cm UsePrivilegedPort
146: is set to
147: .Dq yes .
148: .It Cm ChallengeResponseAuthentication
1.82 jmc 149: Specifies whether to use challenge-response authentication.
1.1 stevesk 150: The argument to this keyword must be
151: .Dq yes
152: or
153: .Dq no .
154: The default is
155: .Dq yes .
156: .It Cm CheckHostIP
157: If this flag is set to
158: .Dq yes ,
1.84 jmc 159: .Xr ssh 1
160: will additionally check the host IP address in the
1.1 stevesk 161: .Pa known_hosts
162: file.
163: This allows ssh to detect if a host key changed due to DNS spoofing.
164: If the option is set to
165: .Dq no ,
166: the check will not be executed.
167: The default is
168: .Dq yes .
169: .It Cm Cipher
170: Specifies the cipher to use for encrypting the session
171: in protocol version 1.
172: Currently,
173: .Dq blowfish ,
174: .Dq 3des ,
175: and
176: .Dq des
177: are supported.
178: .Ar des
179: is only supported in the
1.84 jmc 180: .Xr ssh 1
1.1 stevesk 181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
1.7 jmc 184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 186: The default is
187: .Dq 3des .
188: .It Cm Ciphers
189: Specifies the ciphers allowed for protocol version 2
190: in order of preference.
191: Multiple ciphers must be comma-separated.
1.35 dtucker 192: The supported ciphers are
193: .Dq 3des-cbc ,
194: .Dq aes128-cbc ,
195: .Dq aes192-cbc ,
196: .Dq aes256-cbc ,
197: .Dq aes128-ctr ,
198: .Dq aes192-ctr ,
199: .Dq aes256-ctr ,
1.54 djm 200: .Dq arcfour128 ,
201: .Dq arcfour256 ,
1.35 dtucker 202: .Dq arcfour ,
203: .Dq blowfish-cbc ,
204: and
205: .Dq cast128-cbc .
1.84 jmc 206: The default is:
207: .Bd -literal -offset 3n
208: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
209: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
210: aes192-ctr,aes256-ctr
1.1 stevesk 211: .Ed
212: .It Cm ClearAllForwardings
1.84 jmc 213: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 214: specified in the configuration files or on the command line be
1.7 jmc 215: cleared.
216: This option is primarily useful when used from the
1.84 jmc 217: .Xr ssh 1
1.1 stevesk 218: command line to clear port forwardings set in
219: configuration files, and is automatically set by
220: .Xr scp 1
221: and
222: .Xr sftp 1 .
223: The argument must be
224: .Dq yes
225: or
226: .Dq no .
227: The default is
228: .Dq no .
229: .It Cm Compression
230: Specifies whether to use compression.
231: The argument must be
232: .Dq yes
233: or
234: .Dq no .
235: The default is
236: .Dq no .
237: .It Cm CompressionLevel
238: Specifies the compression level to use if compression is enabled.
239: The argument must be an integer from 1 (fast) to 9 (slow, best).
240: The default level is 6, which is good for most applications.
241: The meaning of the values is the same as in
242: .Xr gzip 1 .
243: Note that this option applies to protocol version 1 only.
244: .It Cm ConnectionAttempts
245: Specifies the number of tries (one per second) to make before exiting.
246: The argument must be an integer.
247: This may be useful in scripts if the connection sometimes fails.
248: The default is 1.
1.9 djm 249: .It Cm ConnectTimeout
1.84 jmc 250: Specifies the timeout (in seconds) used when connecting to the
251: SSH server, instead of using the default system TCP timeout.
1.11 jmc 252: This value is used only when the target is down or really unreachable,
253: not when it refuses the connection.
1.36 djm 254: .It Cm ControlMaster
255: Enables the sharing of multiple sessions over a single network connection.
256: When set to
1.84 jmc 257: .Dq yes ,
258: .Xr ssh 1
1.36 djm 259: will listen for connections on a control socket specified using the
260: .Cm ControlPath
261: argument.
262: Additional sessions can connect to this socket using the same
263: .Cm ControlPath
264: with
265: .Cm ControlMaster
266: set to
267: .Dq no
1.38 jmc 268: (the default).
1.64 jmc 269: These sessions will try to reuse the master instance's network connection
1.63 djm 270: rather than initiating new ones, but will fall back to connecting normally
271: if the control socket does not exist, or is not listening.
272: .Pp
1.37 djm 273: Setting this to
274: .Dq ask
1.84 jmc 275: will cause ssh
1.37 djm 276: to listen for control connections, but require confirmation using the
277: .Ev SSH_ASKPASS
278: program before they are accepted (see
279: .Xr ssh-add 1
1.38 jmc 280: for details).
1.51 jakob 281: If the
282: .Cm ControlPath
1.84 jmc 283: cannot be opened,
284: ssh will continue without connecting to a master instance.
1.58 djm 285: .Pp
286: X11 and
1.59 jmc 287: .Xr ssh-agent 1
1.58 djm 288: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 289: display and agent forwarded will be the one belonging to the master
1.59 jmc 290: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 291: .Pp
292: Two additional options allow for opportunistic multiplexing: try to use a
293: master connection but fall back to creating a new one if one does not already
294: exist.
295: These options are:
296: .Dq auto
297: and
298: .Dq autoask .
299: The latter requires confirmation like the
300: .Dq ask
301: option.
1.36 djm 302: .It Cm ControlPath
1.55 djm 303: Specify the path to the control socket used for connection sharing as described
304: in the
1.36 djm 305: .Cm ControlMaster
1.57 djm 306: section above or the string
307: .Dq none
308: to disable connection sharing.
1.55 djm 309: In the path,
1.77 djm 310: .Ql %l
311: will be substituted by the local host name,
1.55 djm 312: .Ql %h
313: will be substituted by the target host name,
314: .Ql %p
1.84 jmc 315: the port, and
1.55 djm 316: .Ql %r
317: by the remote login username.
1.56 djm 318: It is recommended that any
319: .Cm ControlPath
320: used for opportunistic connection sharing include
1.78 jmc 321: at least %h, %p, and %r.
1.56 djm 322: This ensures that shared connections are uniquely identified.
1.38 jmc 323: .It Cm DynamicForward
1.74 jmc 324: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 325: over the secure channel, and the application
326: protocol is then used to determine where to connect to from the
327: remote machine.
1.62 djm 328: .Pp
329: The argument must be
330: .Sm off
331: .Oo Ar bind_address : Oc Ar port .
332: .Sm on
333: IPv6 addresses can be specified by enclosing addresses in square brackets or
334: by using an alternative syntax:
335: .Oo Ar bind_address Ns / Oc Ns Ar port .
336: By default, the local port is bound in accordance with the
337: .Cm GatewayPorts
338: setting.
339: However, an explicit
340: .Ar bind_address
341: may be used to bind the connection to a specific address.
342: The
343: .Ar bind_address
344: of
345: .Dq localhost
346: indicates that the listening port be bound for local use only, while an
347: empty address or
348: .Sq *
349: indicates that the port should be available from all interfaces.
350: .Pp
1.38 jmc 351: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 352: .Xr ssh 1
1.38 jmc 353: will act as a SOCKS server.
354: Multiple forwardings may be specified, and
355: additional forwardings can be given on the command line.
356: Only the superuser can forward privileged ports.
1.14 markus 357: .It Cm EnableSSHKeysign
358: Setting this option to
359: .Dq yes
360: in the global client configuration file
361: .Pa /etc/ssh/ssh_config
362: enables the use of the helper program
363: .Xr ssh-keysign 8
364: during
365: .Cm HostbasedAuthentication .
366: The argument must be
367: .Dq yes
368: or
369: .Dq no .
370: The default is
371: .Dq no .
1.23 jmc 372: This option should be placed in the non-hostspecific section.
1.14 markus 373: See
374: .Xr ssh-keysign 8
375: for more information.
1.1 stevesk 376: .It Cm EscapeChar
377: Sets the escape character (default:
378: .Ql ~ ) .
379: The escape character can also
380: be set on the command line.
381: The argument should be a single character,
382: .Ql ^
383: followed by a letter, or
384: .Dq none
385: to disable the escape
386: character entirely (making the connection transparent for binary
387: data).
1.96 ! markus 388: .It Cm ExitOnForwardFailure
! 389: Specifies whether
! 390: .Xr ssh 1
! 391: should terminate the connection if it cannot set up all requested
! 392: dynamic, local, and remote port forwardings.
! 393: The argument must be
! 394: .Dq yes
! 395: or
! 396: .Dq no .
! 397: The default is
! 398: .Dq no .
1.1 stevesk 399: .It Cm ForwardAgent
400: Specifies whether the connection to the authentication agent (if any)
401: will be forwarded to the remote machine.
402: The argument must be
403: .Dq yes
404: or
405: .Dq no .
406: The default is
407: .Dq no .
1.3 stevesk 408: .Pp
1.7 jmc 409: Agent forwarding should be enabled with caution.
410: Users with the ability to bypass file permissions on the remote host
411: (for the agent's Unix-domain socket)
412: can access the local agent through the forwarded connection.
413: An attacker cannot obtain key material from the agent,
1.3 stevesk 414: however they can perform operations on the keys that enable them to
415: authenticate using the identities loaded into the agent.
1.1 stevesk 416: .It Cm ForwardX11
417: Specifies whether X11 connections will be automatically redirected
418: over the secure channel and
419: .Ev DISPLAY
420: set.
421: The argument must be
422: .Dq yes
423: or
424: .Dq no .
425: The default is
426: .Dq no .
1.3 stevesk 427: .Pp
1.7 jmc 428: X11 forwarding should be enabled with caution.
429: Users with the ability to bypass file permissions on the remote host
1.22 markus 430: (for the user's X11 authorization database)
1.7 jmc 431: can access the local X11 display through the forwarded connection.
1.22 markus 432: An attacker may then be able to perform activities such as keystroke monitoring
433: if the
434: .Cm ForwardX11Trusted
435: option is also enabled.
436: .It Cm ForwardX11Trusted
1.34 jmc 437: If this option is set to
1.84 jmc 438: .Dq yes ,
439: remote X11 clients will have full access to the original X11 display.
1.42 djm 440: .Pp
1.22 markus 441: If this option is set to
1.84 jmc 442: .Dq no ,
443: remote X11 clients will be considered untrusted and prevented
1.22 markus 444: from stealing or tampering with data belonging to trusted X11
445: clients.
1.42 djm 446: Furthermore, the
447: .Xr xauth 1
448: token used for the session will be set to expire after 20 minutes.
449: Remote clients will be refused access after this time.
1.22 markus 450: .Pp
451: The default is
452: .Dq no .
453: .Pp
454: See the X11 SECURITY extension specification for full details on
455: the restrictions imposed on untrusted clients.
1.1 stevesk 456: .It Cm GatewayPorts
457: Specifies whether remote hosts are allowed to connect to local
458: forwarded ports.
459: By default,
1.84 jmc 460: .Xr ssh 1
1.7 jmc 461: binds local port forwardings to the loopback address.
462: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 463: .Cm GatewayPorts
1.84 jmc 464: can be used to specify that ssh
1.1 stevesk 465: should bind local port forwardings to the wildcard address,
466: thus allowing remote hosts to connect to forwarded ports.
467: The argument must be
468: .Dq yes
469: or
470: .Dq no .
471: The default is
472: .Dq no .
473: .It Cm GlobalKnownHostsFile
474: Specifies a file to use for the global
475: host key database instead of
476: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 477: .It Cm GSSAPIAuthentication
1.27 markus 478: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 479: The default is
1.21 markus 480: .Dq no .
1.18 markus 481: Note that this option applies to protocol version 2 only.
482: .It Cm GSSAPIDelegateCredentials
483: Forward (delegate) credentials to the server.
484: The default is
485: .Dq no .
486: Note that this option applies to protocol version 2 only.
1.44 djm 487: .It Cm HashKnownHosts
488: Indicates that
1.84 jmc 489: .Xr ssh 1
1.44 djm 490: should hash host names and addresses when they are added to
1.50 djm 491: .Pa ~/.ssh/known_hosts .
1.44 djm 492: These hashed names may be used normally by
1.84 jmc 493: .Xr ssh 1
1.44 djm 494: and
1.84 jmc 495: .Xr sshd 8 ,
1.44 djm 496: but they do not reveal identifying information should the file's contents
497: be disclosed.
498: The default is
499: .Dq no .
1.46 jmc 500: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 501: to existing known hosts files, but these may be manually hashed using
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.
1.39 djm 580: .It Cm KbdInteractiveDevices
581: Specifies the list of methods to use in keyboard-interactive authentication.
582: Multiple method names must be comma-separated.
583: The default is to use the server specified list.
1.85 jmc 584: The methods available vary depending on what the server supports.
585: For an OpenSSH server,
586: it may be zero or more of:
587: .Dq bsdauth ,
588: .Dq pam ,
589: and
590: .Dq skey .
1.65 reyk 591: .It Cm LocalCommand
592: Specifies a command to execute on the local machine after successfully
593: connecting to the server.
594: The command string extends to the end of the line, and is executed with
595: .Pa /bin/sh .
596: This directive is ignored unless
597: .Cm PermitLocalCommand
598: has been enabled.
1.1 stevesk 599: .It Cm LocalForward
1.74 jmc 600: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 601: the secure channel to the specified host and port from the remote machine.
1.49 jmc 602: The first argument must be
1.43 djm 603: .Sm off
1.49 jmc 604: .Oo Ar bind_address : Oc Ar port
1.43 djm 605: .Sm on
1.49 jmc 606: and the second argument must be
607: .Ar host : Ns Ar hostport .
1.46 jmc 608: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 609: by using an alternative syntax:
1.49 jmc 610: .Oo Ar bind_address Ns / Oc Ns Ar port
611: and
612: .Ar host Ns / Ns Ar hostport .
1.46 jmc 613: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 614: given on the command line.
1.1 stevesk 615: Only the superuser can forward privileged ports.
1.43 djm 616: By default, the local port is bound in accordance with the
617: .Cm GatewayPorts
618: setting.
619: However, an explicit
620: .Ar bind_address
621: may be used to bind the connection to a specific address.
622: The
623: .Ar bind_address
624: of
625: .Dq localhost
1.46 jmc 626: indicates that the listening port be bound for local use only, while an
627: empty address or
628: .Sq *
1.43 djm 629: indicates that the port should be available from all interfaces.
1.1 stevesk 630: .It Cm LogLevel
631: Gives the verbosity level that is used when logging messages from
1.84 jmc 632: .Xr ssh 1 .
1.1 stevesk 633: The possible values are:
1.84 jmc 634: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 635: The default is INFO.
636: DEBUG and DEBUG1 are equivalent.
637: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 638: .It Cm MACs
639: Specifies the MAC (message authentication code) algorithms
640: in order of preference.
641: The MAC algorithm is used in protocol version 2
642: for data integrity protection.
643: Multiple algorithms must be comma-separated.
1.84 jmc 644: The default is:
1.1 stevesk 645: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
646: .It Cm NoHostAuthenticationForLocalhost
647: This option can be used if the home directory is shared across machines.
648: In this case localhost will refer to a different machine on each of
649: the machines and the user will get many warnings about changed host keys.
650: However, this option disables host authentication for localhost.
651: The argument to this keyword must be
652: .Dq yes
653: or
654: .Dq no .
655: The default is to check the host key for localhost.
656: .It Cm NumberOfPasswordPrompts
657: Specifies the number of password prompts before giving up.
658: The argument to this keyword must be an integer.
1.84 jmc 659: The default is 3.
1.1 stevesk 660: .It Cm PasswordAuthentication
661: Specifies whether to use password authentication.
662: The argument to this keyword must be
663: .Dq yes
664: or
665: .Dq no .
666: The default is
667: .Dq yes .
1.65 reyk 668: .It Cm PermitLocalCommand
669: Allow local command execution via the
670: .Ic LocalCommand
671: option or using the
1.66 jmc 672: .Ic !\& Ns Ar command
1.65 reyk 673: escape sequence in
674: .Xr ssh 1 .
675: The argument must be
676: .Dq yes
677: or
678: .Dq no .
679: The default is
680: .Dq no .
1.67 jmc 681: .It Cm Port
682: Specifies the port number to connect on the remote host.
1.84 jmc 683: The default is 22.
1.1 stevesk 684: .It Cm PreferredAuthentications
685: Specifies the order in which the client should try protocol 2
1.11 jmc 686: authentication methods.
1.48 jmc 687: This allows a client to prefer one method (e.g.\&
1.1 stevesk 688: .Cm keyboard-interactive )
1.48 jmc 689: over another method (e.g.\&
1.1 stevesk 690: .Cm password )
691: The default for this option is:
1.94 jmc 692: .Do gssapi-with-mic ,
693: hostbased,
694: publickey,
695: keyboard-interactive,
696: password
697: .Dc .
1.1 stevesk 698: .It Cm Protocol
699: Specifies the protocol versions
1.84 jmc 700: .Xr ssh 1
1.1 stevesk 701: should support in order of preference.
702: The possible values are
1.84 jmc 703: .Sq 1
1.1 stevesk 704: and
1.84 jmc 705: .Sq 2 .
1.1 stevesk 706: Multiple versions must be comma-separated.
707: The default is
708: .Dq 2,1 .
1.84 jmc 709: This means that ssh
1.1 stevesk 710: tries version 2 and falls back to version 1
711: if version 2 is not available.
712: .It Cm ProxyCommand
713: Specifies the command to use to connect to the server.
714: The command
715: string extends to the end of the line, and is executed with
716: .Pa /bin/sh .
717: In the command string,
718: .Ql %h
719: will be substituted by the host name to
720: connect and
721: .Ql %p
722: by the port.
723: The command can be basically anything,
724: and should read from its standard input and write to its standard output.
725: It should eventually connect an
726: .Xr sshd 8
727: server running on some machine, or execute
728: .Ic sshd -i
729: somewhere.
730: Host key management will be done using the
731: HostName of the host being connected (defaulting to the name typed by
732: the user).
1.7 jmc 733: Setting the command to
734: .Dq none
1.6 markus 735: disables this option entirely.
1.1 stevesk 736: Note that
737: .Cm CheckHostIP
738: is not available for connects with a proxy command.
1.52 djm 739: .Pp
740: This directive is useful in conjunction with
741: .Xr nc 1
742: and its proxy support.
1.53 jmc 743: For example, the following directive would connect via an HTTP proxy at
1.52 djm 744: 192.0.2.0:
745: .Bd -literal -offset 3n
746: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
747: .Ed
1.1 stevesk 748: .It Cm PubkeyAuthentication
749: Specifies whether to try public key authentication.
750: The argument to this keyword must be
751: .Dq yes
752: or
753: .Dq no .
754: The default is
755: .Dq yes .
756: This option applies to protocol version 2 only.
1.75 dtucker 757: .It Cm RekeyLimit
758: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 759: session key is renegotiated.
1.75 dtucker 760: The argument is the number of bytes, with an optional suffix of
1.76 jmc 761: .Sq K ,
762: .Sq M ,
1.75 dtucker 763: or
1.76 jmc 764: .Sq G
1.75 dtucker 765: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
766: The default is between
1.84 jmc 767: .Sq 1G
1.75 dtucker 768: and
1.84 jmc 769: .Sq 4G ,
1.75 dtucker 770: depending on the cipher.
1.76 jmc 771: This option applies to protocol version 2 only.
1.1 stevesk 772: .It Cm RemoteForward
1.74 jmc 773: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 774: the secure channel to the specified host and port from the local machine.
1.49 jmc 775: The first argument must be
1.43 djm 776: .Sm off
1.49 jmc 777: .Oo Ar bind_address : Oc Ar port
1.43 djm 778: .Sm on
1.49 jmc 779: and the second argument must be
780: .Ar host : Ns Ar hostport .
781: IPv6 addresses can be specified by enclosing addresses in square brackets
782: or by using an alternative syntax:
783: .Oo Ar bind_address Ns / Oc Ns Ar port
784: and
785: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 786: Multiple forwardings may be specified, and additional
787: forwardings can be given on the command line.
788: Only the superuser can forward privileged ports.
1.43 djm 789: .Pp
790: If the
791: .Ar bind_address
792: is not specified, the default is to only bind to loopback addresses.
793: If the
794: .Ar bind_address
795: is
796: .Ql *
797: or an empty string, then the forwarding is requested to listen on all
798: interfaces.
799: Specifying a remote
800: .Ar bind_address
1.46 jmc 801: will only succeed if the server's
802: .Cm GatewayPorts
1.43 djm 803: option is enabled (see
1.46 jmc 804: .Xr sshd_config 5 ) .
1.1 stevesk 805: .It Cm RhostsRSAAuthentication
806: Specifies whether to try rhosts based authentication with RSA host
807: authentication.
808: The argument must be
809: .Dq yes
810: or
811: .Dq no .
812: The default is
813: .Dq no .
814: This option applies to protocol version 1 only and requires
1.84 jmc 815: .Xr ssh 1
1.1 stevesk 816: to be setuid root.
817: .It Cm RSAAuthentication
818: Specifies whether to try RSA authentication.
819: The argument to this keyword must be
820: .Dq yes
821: or
822: .Dq no .
823: RSA authentication will only be
824: attempted if the identity file exists, or an authentication agent is
825: running.
826: The default is
827: .Dq yes .
828: Note that this option applies to protocol version 1 only.
1.32 djm 829: .It Cm SendEnv
830: Specifies what variables from the local
831: .Xr environ 7
832: should be sent to the server.
1.84 jmc 833: Note that environment passing is only supported for protocol 2.
834: The server must also support it, and the server must be configured to
1.33 djm 835: accept these environment variables.
1.32 djm 836: Refer to
837: .Cm AcceptEnv
838: in
839: .Xr sshd_config 5
840: for how to configure the server.
1.80 jmc 841: Variables are specified by name, which may contain wildcard characters.
1.33 djm 842: Multiple environment variables may be separated by whitespace or spread
1.32 djm 843: across multiple
844: .Cm SendEnv
845: directives.
846: The default is not to send any environment variables.
1.81 jmc 847: .Pp
848: See
849: .Sx PATTERNS
850: for more information on patterns.
1.28 markus 851: .It Cm ServerAliveCountMax
1.73 jmc 852: Sets the number of server alive messages (see below) which may be
1.28 markus 853: sent without
1.84 jmc 854: .Xr ssh 1
1.28 markus 855: receiving any messages back from the server.
856: If this threshold is reached while server alive messages are being sent,
1.84 jmc 857: ssh will disconnect from the server, terminating the session.
1.28 markus 858: It is important to note that the use of server alive messages is very
859: different from
860: .Cm TCPKeepAlive
861: (below).
862: The server alive messages are sent through the encrypted channel
863: and therefore will not be spoofable.
864: The TCP keepalive option enabled by
865: .Cm TCPKeepAlive
866: is spoofable.
867: The server alive mechanism is valuable when the client or
868: server depend on knowing when a connection has become inactive.
869: .Pp
870: The default value is 3.
871: If, for example,
872: .Cm ServerAliveInterval
1.84 jmc 873: (see below) is set to 15 and
1.28 markus 874: .Cm ServerAliveCountMax
1.84 jmc 875: is left at the default, if the server becomes unresponsive,
876: ssh will disconnect after approximately 45 seconds.
1.89 markus 877: This option applies to protocol version 2 only.
1.67 jmc 878: .It Cm ServerAliveInterval
879: Sets a timeout interval in seconds after which if no data has been received
880: from the server,
1.84 jmc 881: .Xr ssh 1
1.67 jmc 882: will send a message through the encrypted
883: channel to request a response from the server.
884: The default
885: is 0, indicating that these messages will not be sent to the server.
886: This option applies to protocol version 2 only.
1.1 stevesk 887: .It Cm SmartcardDevice
1.11 jmc 888: Specifies which smartcard device to use.
889: The argument to this keyword is the device
1.84 jmc 890: .Xr ssh 1
1.1 stevesk 891: should use to communicate with a smartcard used for storing the user's
1.11 jmc 892: private RSA key.
893: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 894: .It Cm StrictHostKeyChecking
895: If this flag is set to
896: .Dq yes ,
1.84 jmc 897: .Xr ssh 1
1.1 stevesk 898: will never automatically add host keys to the
1.50 djm 899: .Pa ~/.ssh/known_hosts
1.1 stevesk 900: file, and refuses to connect to hosts whose host key has changed.
901: This provides maximum protection against trojan horse attacks,
1.84 jmc 902: though it can be annoying when the
1.1 stevesk 903: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 904: file is poorly maintained or when connections to new hosts are
1.1 stevesk 905: frequently made.
906: This option forces the user to manually
907: add all new hosts.
908: If this flag is set to
909: .Dq no ,
1.84 jmc 910: ssh will automatically add new host keys to the
1.1 stevesk 911: user known hosts files.
912: If this flag is set to
913: .Dq ask ,
914: new host keys
915: will be added to the user known host files only after the user
916: has confirmed that is what they really want to do, and
1.84 jmc 917: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 918: The host keys of
919: known hosts will be verified automatically in all cases.
920: The argument must be
921: .Dq yes ,
1.84 jmc 922: .Dq no ,
1.1 stevesk 923: or
924: .Dq ask .
925: The default is
926: .Dq ask .
1.26 markus 927: .It Cm TCPKeepAlive
928: Specifies whether the system should send TCP keepalive messages to the
929: other side.
930: If they are sent, death of the connection or crash of one
931: of the machines will be properly noticed.
932: However, this means that
933: connections will die if the route is down temporarily, and some people
934: find it annoying.
935: .Pp
936: The default is
937: .Dq yes
938: (to send TCP keepalive messages), and the client will notice
939: if the network goes down or the remote host dies.
940: This is important in scripts, and many users want it too.
941: .Pp
942: To disable TCP keepalive messages, the value should be set to
943: .Dq no .
1.65 reyk 944: .It Cm Tunnel
1.95 stevesk 945: Request
1.65 reyk 946: .Xr tun 4
1.69 jmc 947: device forwarding between the client and the server.
1.65 reyk 948: The argument must be
1.68 reyk 949: .Dq yes ,
1.95 stevesk 950: .Dq point-to-point
951: (layer 3),
952: .Dq ethernet
953: (layer 2),
1.65 reyk 954: or
955: .Dq no .
1.95 stevesk 956: Specifying
957: .Dq yes
958: requests the default tunnel mode, which is
959: .Dq point-to-point .
1.65 reyk 960: The default is
961: .Dq no .
962: .It Cm TunnelDevice
1.95 stevesk 963: Specifies the
1.65 reyk 964: .Xr tun 4
1.95 stevesk 965: devices to open on the client
966: .Pq Ar local_tun
967: and the server
968: .Pq Ar remote_tun .
969: .Pp
970: The argument must be
971: .Sm off
972: .Ar local_tun Op : Ar remote_tun .
973: .Sm on
974: The devices may be specified by numerical ID or the keyword
975: .Dq any ,
976: which uses the next available tunnel device.
977: If
978: .Ar remote_tun
979: is not specified, it defaults to
980: .Dq any .
981: The default is
982: .Dq any:any .
1.72 jmc 983: .It Cm UsePrivilegedPort
984: Specifies whether to use a privileged port for outgoing connections.
985: The argument must be
986: .Dq yes
987: or
988: .Dq no .
989: The default is
990: .Dq no .
991: If set to
1.84 jmc 992: .Dq yes ,
993: .Xr ssh 1
1.72 jmc 994: must be setuid root.
995: Note that this option must be set to
996: .Dq yes
997: for
998: .Cm RhostsRSAAuthentication
999: with older servers.
1.1 stevesk 1000: .It Cm User
1001: Specifies the user to log in as.
1002: This can be useful when a different user name is used on different machines.
1003: This saves the trouble of
1004: having to remember to give the user name on the command line.
1005: .It Cm UserKnownHostsFile
1006: Specifies a file to use for the user
1007: host key database instead of
1.50 djm 1008: .Pa ~/.ssh/known_hosts .
1.8 jakob 1009: .It Cm VerifyHostKeyDNS
1010: Specifies whether to verify the remote key using DNS and SSHFP resource
1011: records.
1.24 jakob 1012: If this option is set to
1013: .Dq yes ,
1.25 jmc 1014: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 1015: from DNS.
1016: Insecure fingerprints will be handled as if this option was set to
1017: .Dq ask .
1018: If this option is set to
1019: .Dq ask ,
1020: information on fingerprint match will be displayed, but the user will still
1021: need to confirm new host keys according to the
1022: .Cm StrictHostKeyChecking
1023: option.
1024: The argument must be
1025: .Dq yes ,
1.84 jmc 1026: .Dq no ,
1.25 jmc 1027: or
1028: .Dq ask .
1.8 jakob 1029: The default is
1030: .Dq no .
1.12 jakob 1031: Note that this option applies to protocol version 2 only.
1.84 jmc 1032: .Pp
1033: See also
1034: .Sx VERIFYING HOST KEYS
1035: in
1036: .Xr ssh 1 .
1.1 stevesk 1037: .It Cm XAuthLocation
1.5 stevesk 1038: Specifies the full pathname of the
1.1 stevesk 1039: .Xr xauth 1
1040: program.
1041: The default is
1042: .Pa /usr/X11R6/bin/xauth .
1043: .El
1.86 jmc 1044: .Sh PATTERNS
1045: A
1046: .Em pattern
1047: consists of zero or more non-whitespace characters,
1048: .Sq *
1049: (a wildcard that matches zero or more characters),
1050: or
1051: .Sq ?\&
1052: (a wildcard that matches exactly one character).
1053: For example, to specify a set of declarations for any host in the
1054: .Dq .co.uk
1055: set of domains,
1056: the following pattern could be used:
1057: .Pp
1058: .Dl Host *.co.uk
1059: .Pp
1060: The following pattern
1061: would match any host in the 192.168.0.[0-9] network range:
1062: .Pp
1063: .Dl Host 192.168.0.?
1064: .Pp
1065: A
1066: .Em pattern-list
1067: is a comma-separated list of patterns.
1068: Patterns within pattern-lists may be negated
1069: by preceding them with an exclamation mark
1070: .Pq Sq !\& .
1071: For example,
1072: to allow a key to be used from anywhere within an organisation
1073: except from the
1074: .Dq dialup
1075: pool,
1076: the following entry (in authorized_keys) could be used:
1077: .Pp
1078: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1079: .Sh FILES
1080: .Bl -tag -width Ds
1.50 djm 1081: .It Pa ~/.ssh/config
1.1 stevesk 1082: This is the per-user configuration file.
1083: The format of this file is described above.
1.84 jmc 1084: This file is used by the SSH client.
1.30 djm 1085: Because of the potential for abuse, this file must have strict permissions:
1086: read/write for the user, and not accessible by others.
1.1 stevesk 1087: .It Pa /etc/ssh/ssh_config
1088: Systemwide configuration file.
1089: This file provides defaults for those
1090: values that are not specified in the user's configuration file, and
1091: for those users who do not have a configuration file.
1092: This file must be world-readable.
1093: .El
1.13 jmc 1094: .Sh SEE ALSO
1095: .Xr ssh 1
1.1 stevesk 1096: .Sh AUTHORS
1097: OpenSSH is a derivative of the original and free
1098: ssh 1.2.12 release by Tatu Ylonen.
1099: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1100: Theo de Raadt and Dug Song
1101: removed many bugs, re-added newer features and
1102: created OpenSSH.
1103: Markus Friedl contributed the support for SSH
1104: protocol versions 1.5 and 2.0.
![[BACK]](/icons/back.gif){kind=icon}
Return to ssh_config.5 CVS log ![[TXT]](/icons/text.gif){kind=icon}
![[DIR]](/icons/dir.gif){kind=icon}
Up to [local] / src / usr.bin / ssh