Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.88
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: .\"
1.88 ! dtucker 37: .\" $OpenBSD: ssh_config.5,v 1.87 2006/02/26 18:03:10 jmc Exp $
1.1 stevesk 38: .Dd September 25, 1999
39: .Dt SSH_CONFIG 5
40: .Os
41: .Sh NAME
42: .Nm ssh_config
43: .Nd OpenSSH SSH client configuration files
44: .Sh SYNOPSIS
45: .Bl -tag -width Ds -compact
1.50 djm 46: .It Pa ~/.ssh/config
1.1 stevesk 47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
1.84 jmc 50: .Xr ssh 1
1.1 stevesk 51: obtains configuration data from the following sources in
52: the following order:
1.79 jmc 53: .Pp
1.2 stevesk 54: .Bl -enum -offset indent -compact
55: .It
56: command-line options
57: .It
58: user's configuration file
1.50 djm 59: .Pq Pa ~/.ssh/config
1.2 stevesk 60: .It
61: system-wide configuration file
62: .Pq Pa /etc/ssh/ssh_config
63: .El
1.1 stevesk 64: .Pp
65: For each parameter, the first obtained value
66: will be used.
1.41 jmc 67: The configuration files contain sections separated by
1.1 stevesk 68: .Dq Host
69: specifications, and that section is only applied for hosts that
70: match one of the patterns given in the specification.
71: The matched host name is the one given on the command line.
72: .Pp
73: Since the first obtained value for each parameter is used, more
74: host-specific declarations should be given near the beginning of the
75: file, and general defaults at the end.
1.80 jmc 76: .Pp
1.1 stevesk 77: The configuration file has the following format:
78: .Pp
79: Empty lines and lines starting with
80: .Ql #
81: are comments.
82: Otherwise a line is of the format
83: .Dq keyword arguments .
84: Configuration options may be separated by whitespace or
85: optional whitespace and exactly one
86: .Ql = ;
87: the latter format is useful to avoid the need to quote whitespace
88: when specifying configuration options using the
89: .Nm ssh ,
1.87 jmc 90: .Nm scp ,
1.1 stevesk 91: and
92: .Nm sftp
93: .Fl o
94: option.
1.88 ! dtucker 95: Arguments may optionally be enclosed in double quotes
! 96: .Pq \&"
! 97: in order to represent arguments containing spaces.
1.1 stevesk 98: .Pp
99: The possible
100: keywords and their meanings are as follows (note that
101: keywords are case-insensitive and arguments are case-sensitive):
102: .Bl -tag -width Ds
103: .It Cm Host
104: Restricts the following declarations (up to the next
105: .Cm Host
106: keyword) to be only for those hosts that match one of the patterns
107: given after the keyword.
108: A single
1.83 jmc 109: .Ql *
1.1 stevesk 110: as a pattern can be used to provide global
111: defaults for all hosts.
112: The host is the
113: .Ar hostname
1.83 jmc 114: argument given on the command line (i.e. the name is not converted to
1.1 stevesk 115: a canonicalized host name before matching).
1.81 jmc 116: .Pp
117: See
118: .Sx PATTERNS
119: for more information on patterns.
1.10 djm 120: .It Cm AddressFamily
1.11 jmc 121: Specifies which address family to use when connecting.
122: Valid arguments are
1.10 djm 123: .Dq any ,
124: .Dq inet
1.84 jmc 125: (use IPv4 only), or
1.10 djm 126: .Dq inet6
1.40 jmc 127: (use IPv6 only).
1.1 stevesk 128: .It Cm BatchMode
129: If set to
130: .Dq yes ,
131: passphrase/password querying will be disabled.
132: This option is useful in scripts and other batch jobs where no user
133: is present to supply the password.
134: The argument must be
135: .Dq yes
136: or
137: .Dq no .
138: The default is
139: .Dq no .
140: .It Cm BindAddress
1.60 dtucker 141: Use the specified address on the local machine as the source address of
1.61 jmc 142: the connection.
143: Only useful on systems with more than one address.
1.1 stevesk 144: Note that this option does not work if
145: .Cm UsePrivilegedPort
146: is set to
147: .Dq yes .
148: .It Cm ChallengeResponseAuthentication
1.82 jmc 149: Specifies whether to use challenge-response authentication.
1.1 stevesk 150: The argument to this keyword must be
151: .Dq yes
152: or
153: .Dq no .
154: The default is
155: .Dq yes .
156: .It Cm CheckHostIP
157: If this flag is set to
158: .Dq yes ,
1.84 jmc 159: .Xr ssh 1
160: will additionally check the host IP address in the
1.1 stevesk 161: .Pa known_hosts
162: file.
163: This allows ssh to detect if a host key changed due to DNS spoofing.
164: If the option is set to
165: .Dq no ,
166: the check will not be executed.
167: The default is
168: .Dq yes .
169: .It Cm Cipher
170: Specifies the cipher to use for encrypting the session
171: in protocol version 1.
172: Currently,
173: .Dq blowfish ,
174: .Dq 3des ,
175: and
176: .Dq des
177: are supported.
178: .Ar des
179: is only supported in the
1.84 jmc 180: .Xr ssh 1
1.1 stevesk 181: client for interoperability with legacy protocol 1 implementations
182: that do not support the
183: .Ar 3des
1.7 jmc 184: cipher.
185: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 186: The default is
187: .Dq 3des .
188: .It Cm Ciphers
189: Specifies the ciphers allowed for protocol version 2
190: in order of preference.
191: Multiple ciphers must be comma-separated.
1.35 dtucker 192: The supported ciphers are
193: .Dq 3des-cbc ,
194: .Dq aes128-cbc ,
195: .Dq aes192-cbc ,
196: .Dq aes256-cbc ,
197: .Dq aes128-ctr ,
198: .Dq aes192-ctr ,
199: .Dq aes256-ctr ,
1.54 djm 200: .Dq arcfour128 ,
201: .Dq arcfour256 ,
1.35 dtucker 202: .Dq arcfour ,
203: .Dq blowfish-cbc ,
204: and
205: .Dq cast128-cbc .
1.84 jmc 206: The default is:
207: .Bd -literal -offset 3n
208: aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128,
209: arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr,
210: aes192-ctr,aes256-ctr
1.1 stevesk 211: .Ed
212: .It Cm ClearAllForwardings
1.84 jmc 213: Specifies that all local, remote, and dynamic port forwardings
1.1 stevesk 214: specified in the configuration files or on the command line be
1.7 jmc 215: cleared.
216: This option is primarily useful when used from the
1.84 jmc 217: .Xr ssh 1
1.1 stevesk 218: command line to clear port forwardings set in
219: configuration files, and is automatically set by
220: .Xr scp 1
221: and
222: .Xr sftp 1 .
223: The argument must be
224: .Dq yes
225: or
226: .Dq no .
227: The default is
228: .Dq no .
229: .It Cm Compression
230: Specifies whether to use compression.
231: The argument must be
232: .Dq yes
233: or
234: .Dq no .
235: The default is
236: .Dq no .
237: .It Cm CompressionLevel
238: Specifies the compression level to use if compression is enabled.
239: The argument must be an integer from 1 (fast) to 9 (slow, best).
240: The default level is 6, which is good for most applications.
241: The meaning of the values is the same as in
242: .Xr gzip 1 .
243: Note that this option applies to protocol version 1 only.
244: .It Cm ConnectionAttempts
245: Specifies the number of tries (one per second) to make before exiting.
246: The argument must be an integer.
247: This may be useful in scripts if the connection sometimes fails.
248: The default is 1.
1.9 djm 249: .It Cm ConnectTimeout
1.84 jmc 250: Specifies the timeout (in seconds) used when connecting to the
251: SSH server, instead of using the default system TCP timeout.
1.11 jmc 252: This value is used only when the target is down or really unreachable,
253: not when it refuses the connection.
1.36 djm 254: .It Cm ControlMaster
255: Enables the sharing of multiple sessions over a single network connection.
256: When set to
1.84 jmc 257: .Dq yes ,
258: .Xr ssh 1
1.36 djm 259: will listen for connections on a control socket specified using the
260: .Cm ControlPath
261: argument.
262: Additional sessions can connect to this socket using the same
263: .Cm ControlPath
264: with
265: .Cm ControlMaster
266: set to
267: .Dq no
1.38 jmc 268: (the default).
1.64 jmc 269: These sessions will try to reuse the master instance's network connection
1.63 djm 270: rather than initiating new ones, but will fall back to connecting normally
271: if the control socket does not exist, or is not listening.
272: .Pp
1.37 djm 273: Setting this to
274: .Dq ask
1.84 jmc 275: will cause ssh
1.37 djm 276: to listen for control connections, but require confirmation using the
277: .Ev SSH_ASKPASS
278: program before they are accepted (see
279: .Xr ssh-add 1
1.38 jmc 280: for details).
1.51 jakob 281: If the
282: .Cm ControlPath
1.84 jmc 283: cannot be opened,
284: ssh will continue without connecting to a master instance.
1.58 djm 285: .Pp
286: X11 and
1.59 jmc 287: .Xr ssh-agent 1
1.58 djm 288: forwarding is supported over these multiplexed connections, however the
1.70 stevesk 289: display and agent forwarded will be the one belonging to the master
1.59 jmc 290: connection i.e. it is not possible to forward multiple displays or agents.
1.56 djm 291: .Pp
292: Two additional options allow for opportunistic multiplexing: try to use a
293: master connection but fall back to creating a new one if one does not already
294: exist.
295: These options are:
296: .Dq auto
297: and
298: .Dq autoask .
299: The latter requires confirmation like the
300: .Dq ask
301: option.
1.36 djm 302: .It Cm ControlPath
1.55 djm 303: Specify the path to the control socket used for connection sharing as described
304: in the
1.36 djm 305: .Cm ControlMaster
1.57 djm 306: section above or the string
307: .Dq none
308: to disable connection sharing.
1.55 djm 309: In the path,
1.77 djm 310: .Ql %l
311: will be substituted by the local host name,
1.55 djm 312: .Ql %h
313: will be substituted by the target host name,
314: .Ql %p
1.84 jmc 315: the port, and
1.55 djm 316: .Ql %r
317: by the remote login username.
1.56 djm 318: It is recommended that any
319: .Cm ControlPath
320: used for opportunistic connection sharing include
1.78 jmc 321: at least %h, %p, and %r.
1.56 djm 322: This ensures that shared connections are uniquely identified.
1.38 jmc 323: .It Cm DynamicForward
1.74 jmc 324: Specifies that a TCP port on the local machine be forwarded
1.38 jmc 325: over the secure channel, and the application
326: protocol is then used to determine where to connect to from the
327: remote machine.
1.62 djm 328: .Pp
329: The argument must be
330: .Sm off
331: .Oo Ar bind_address : Oc Ar port .
332: .Sm on
333: IPv6 addresses can be specified by enclosing addresses in square brackets or
334: by using an alternative syntax:
335: .Oo Ar bind_address Ns / Oc Ns Ar port .
336: By default, the local port is bound in accordance with the
337: .Cm GatewayPorts
338: setting.
339: However, an explicit
340: .Ar bind_address
341: may be used to bind the connection to a specific address.
342: The
343: .Ar bind_address
344: of
345: .Dq localhost
346: indicates that the listening port be bound for local use only, while an
347: empty address or
348: .Sq *
349: indicates that the port should be available from all interfaces.
350: .Pp
1.38 jmc 351: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.84 jmc 352: .Xr ssh 1
1.38 jmc 353: will act as a SOCKS server.
354: Multiple forwardings may be specified, and
355: additional forwardings can be given on the command line.
356: Only the superuser can forward privileged ports.
1.14 markus 357: .It Cm EnableSSHKeysign
358: Setting this option to
359: .Dq yes
360: in the global client configuration file
361: .Pa /etc/ssh/ssh_config
362: enables the use of the helper program
363: .Xr ssh-keysign 8
364: during
365: .Cm HostbasedAuthentication .
366: The argument must be
367: .Dq yes
368: or
369: .Dq no .
370: The default is
371: .Dq no .
1.23 jmc 372: This option should be placed in the non-hostspecific section.
1.14 markus 373: See
374: .Xr ssh-keysign 8
375: for more information.
1.1 stevesk 376: .It Cm EscapeChar
377: Sets the escape character (default:
378: .Ql ~ ) .
379: The escape character can also
380: be set on the command line.
381: The argument should be a single character,
382: .Ql ^
383: followed by a letter, or
384: .Dq none
385: to disable the escape
386: character entirely (making the connection transparent for binary
387: data).
388: .It Cm ForwardAgent
389: Specifies whether the connection to the authentication agent (if any)
390: will be forwarded to the remote machine.
391: The argument must be
392: .Dq yes
393: or
394: .Dq no .
395: The default is
396: .Dq no .
1.3 stevesk 397: .Pp
1.7 jmc 398: Agent forwarding should be enabled with caution.
399: Users with the ability to bypass file permissions on the remote host
400: (for the agent's Unix-domain socket)
401: can access the local agent through the forwarded connection.
402: An attacker cannot obtain key material from the agent,
1.3 stevesk 403: however they can perform operations on the keys that enable them to
404: authenticate using the identities loaded into the agent.
1.1 stevesk 405: .It Cm ForwardX11
406: Specifies whether X11 connections will be automatically redirected
407: over the secure channel and
408: .Ev DISPLAY
409: set.
410: The argument must be
411: .Dq yes
412: or
413: .Dq no .
414: The default is
415: .Dq no .
1.3 stevesk 416: .Pp
1.7 jmc 417: X11 forwarding should be enabled with caution.
418: Users with the ability to bypass file permissions on the remote host
1.22 markus 419: (for the user's X11 authorization database)
1.7 jmc 420: can access the local X11 display through the forwarded connection.
1.22 markus 421: An attacker may then be able to perform activities such as keystroke monitoring
422: if the
423: .Cm ForwardX11Trusted
424: option is also enabled.
425: .It Cm ForwardX11Trusted
1.34 jmc 426: If this option is set to
1.84 jmc 427: .Dq yes ,
428: remote X11 clients will have full access to the original X11 display.
1.42 djm 429: .Pp
1.22 markus 430: If this option is set to
1.84 jmc 431: .Dq no ,
432: remote X11 clients will be considered untrusted and prevented
1.22 markus 433: from stealing or tampering with data belonging to trusted X11
434: clients.
1.42 djm 435: Furthermore, the
436: .Xr xauth 1
437: token used for the session will be set to expire after 20 minutes.
438: Remote clients will be refused access after this time.
1.22 markus 439: .Pp
440: The default is
441: .Dq no .
442: .Pp
443: See the X11 SECURITY extension specification for full details on
444: the restrictions imposed on untrusted clients.
1.1 stevesk 445: .It Cm GatewayPorts
446: Specifies whether remote hosts are allowed to connect to local
447: forwarded ports.
448: By default,
1.84 jmc 449: .Xr ssh 1
1.7 jmc 450: binds local port forwardings to the loopback address.
451: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 452: .Cm GatewayPorts
1.84 jmc 453: can be used to specify that ssh
1.1 stevesk 454: should bind local port forwardings to the wildcard address,
455: thus allowing remote hosts to connect to forwarded ports.
456: The argument must be
457: .Dq yes
458: or
459: .Dq no .
460: The default is
461: .Dq no .
462: .It Cm GlobalKnownHostsFile
463: Specifies a file to use for the global
464: host key database instead of
465: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 466: .It Cm GSSAPIAuthentication
1.27 markus 467: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 468: The default is
1.21 markus 469: .Dq no .
1.18 markus 470: Note that this option applies to protocol version 2 only.
471: .It Cm GSSAPIDelegateCredentials
472: Forward (delegate) credentials to the server.
473: The default is
474: .Dq no .
475: Note that this option applies to protocol version 2 only.
1.44 djm 476: .It Cm HashKnownHosts
477: Indicates that
1.84 jmc 478: .Xr ssh 1
1.44 djm 479: should hash host names and addresses when they are added to
1.50 djm 480: .Pa ~/.ssh/known_hosts .
1.44 djm 481: These hashed names may be used normally by
1.84 jmc 482: .Xr ssh 1
1.44 djm 483: and
1.84 jmc 484: .Xr sshd 8 ,
1.44 djm 485: but they do not reveal identifying information should the file's contents
486: be disclosed.
487: The default is
488: .Dq no .
1.46 jmc 489: Note that hashing of names and addresses will not be retrospectively applied
1.45 djm 490: to existing known hosts files, but these may be manually hashed using
491: .Xr ssh-keygen 1 .
1.1 stevesk 492: .It Cm HostbasedAuthentication
493: Specifies whether to try rhosts based authentication with public key
494: authentication.
495: The argument must be
496: .Dq yes
497: or
498: .Dq no .
499: The default is
500: .Dq no .
501: This option applies to protocol version 2 only and
502: is similar to
503: .Cm RhostsRSAAuthentication .
504: .It Cm HostKeyAlgorithms
505: Specifies the protocol version 2 host key algorithms
506: that the client wants to use in order of preference.
507: The default for this option is:
508: .Dq ssh-rsa,ssh-dss .
509: .It Cm HostKeyAlias
510: Specifies an alias that should be used instead of the
511: real host name when looking up or saving the host key
512: in the host key database files.
1.84 jmc 513: This option is useful for tunneling SSH connections
1.1 stevesk 514: or for multiple servers running on a single host.
515: .It Cm HostName
516: Specifies the real host name to log into.
517: This can be used to specify nicknames or abbreviations for hosts.
1.84 jmc 518: The default is the name given on the command line.
1.1 stevesk 519: Numeric IP addresses are also permitted (both on the command line and in
520: .Cm HostName
521: specifications).
1.29 markus 522: .It Cm IdentitiesOnly
523: Specifies that
1.84 jmc 524: .Xr ssh 1
1.29 markus 525: should only use the authentication identity files configured in the
1.31 jmc 526: .Nm
1.29 markus 527: files,
1.84 jmc 528: even if
529: .Xr ssh-agent 1
1.29 markus 530: offers more identities.
531: The argument to this keyword must be
532: .Dq yes
533: or
534: .Dq no .
1.84 jmc 535: This option is intended for situations where ssh-agent
1.29 markus 536: offers many different identities.
537: The default is
538: .Dq no .
1.67 jmc 539: .It Cm IdentityFile
540: Specifies a file from which the user's RSA or DSA authentication identity
541: is read.
542: The default is
543: .Pa ~/.ssh/identity
544: for protocol version 1, and
545: .Pa ~/.ssh/id_rsa
546: and
547: .Pa ~/.ssh/id_dsa
548: for protocol version 2.
549: Additionally, any identities represented by the authentication agent
550: will be used for authentication.
551: The file name may use the tilde
552: syntax to refer to a user's home directory.
553: It is possible to have
554: multiple identity files specified in configuration files; all these
555: identities will be tried in sequence.
1.39 djm 556: .It Cm KbdInteractiveDevices
557: Specifies the list of methods to use in keyboard-interactive authentication.
558: Multiple method names must be comma-separated.
559: The default is to use the server specified list.
1.85 jmc 560: The methods available vary depending on what the server supports.
561: For an OpenSSH server,
562: it may be zero or more of:
563: .Dq bsdauth ,
564: .Dq pam ,
565: and
566: .Dq skey .
1.65 reyk 567: .It Cm LocalCommand
568: Specifies a command to execute on the local machine after successfully
569: connecting to the server.
570: The command string extends to the end of the line, and is executed with
571: .Pa /bin/sh .
572: This directive is ignored unless
573: .Cm PermitLocalCommand
574: has been enabled.
1.1 stevesk 575: .It Cm LocalForward
1.74 jmc 576: Specifies that a TCP port on the local machine be forwarded over
1.1 stevesk 577: the secure channel to the specified host and port from the remote machine.
1.49 jmc 578: The first argument must be
1.43 djm 579: .Sm off
1.49 jmc 580: .Oo Ar bind_address : Oc Ar port
1.43 djm 581: .Sm on
1.49 jmc 582: and the second argument must be
583: .Ar host : Ns Ar hostport .
1.46 jmc 584: IPv6 addresses can be specified by enclosing addresses in square brackets or
1.43 djm 585: by using an alternative syntax:
1.49 jmc 586: .Oo Ar bind_address Ns / Oc Ns Ar port
587: and
588: .Ar host Ns / Ns Ar hostport .
1.46 jmc 589: Multiple forwardings may be specified, and additional forwardings can be
1.43 djm 590: given on the command line.
1.1 stevesk 591: Only the superuser can forward privileged ports.
1.43 djm 592: By default, the local port is bound in accordance with the
593: .Cm GatewayPorts
594: setting.
595: However, an explicit
596: .Ar bind_address
597: may be used to bind the connection to a specific address.
598: The
599: .Ar bind_address
600: of
601: .Dq localhost
1.46 jmc 602: indicates that the listening port be bound for local use only, while an
603: empty address or
604: .Sq *
1.43 djm 605: indicates that the port should be available from all interfaces.
1.1 stevesk 606: .It Cm LogLevel
607: Gives the verbosity level that is used when logging messages from
1.84 jmc 608: .Xr ssh 1 .
1.1 stevesk 609: The possible values are:
1.84 jmc 610: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3.
1.7 jmc 611: The default is INFO.
612: DEBUG and DEBUG1 are equivalent.
613: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 614: .It Cm MACs
615: Specifies the MAC (message authentication code) algorithms
616: in order of preference.
617: The MAC algorithm is used in protocol version 2
618: for data integrity protection.
619: Multiple algorithms must be comma-separated.
1.84 jmc 620: The default is:
1.1 stevesk 621: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
622: .It Cm NoHostAuthenticationForLocalhost
623: This option can be used if the home directory is shared across machines.
624: In this case localhost will refer to a different machine on each of
625: the machines and the user will get many warnings about changed host keys.
626: However, this option disables host authentication for localhost.
627: The argument to this keyword must be
628: .Dq yes
629: or
630: .Dq no .
631: The default is to check the host key for localhost.
632: .It Cm NumberOfPasswordPrompts
633: Specifies the number of password prompts before giving up.
634: The argument to this keyword must be an integer.
1.84 jmc 635: The default is 3.
1.1 stevesk 636: .It Cm PasswordAuthentication
637: Specifies whether to use password authentication.
638: The argument to this keyword must be
639: .Dq yes
640: or
641: .Dq no .
642: The default is
643: .Dq yes .
1.65 reyk 644: .It Cm PermitLocalCommand
645: Allow local command execution via the
646: .Ic LocalCommand
647: option or using the
1.66 jmc 648: .Ic !\& Ns Ar command
1.65 reyk 649: escape sequence in
650: .Xr ssh 1 .
651: The argument must be
652: .Dq yes
653: or
654: .Dq no .
655: The default is
656: .Dq no .
1.67 jmc 657: .It Cm Port
658: Specifies the port number to connect on the remote host.
1.84 jmc 659: The default is 22.
1.1 stevesk 660: .It Cm PreferredAuthentications
661: Specifies the order in which the client should try protocol 2
1.11 jmc 662: authentication methods.
1.48 jmc 663: This allows a client to prefer one method (e.g.\&
1.1 stevesk 664: .Cm keyboard-interactive )
1.48 jmc 665: over another method (e.g.\&
1.1 stevesk 666: .Cm password )
667: The default for this option is:
668: .Dq hostbased,publickey,keyboard-interactive,password .
669: .It Cm Protocol
670: Specifies the protocol versions
1.84 jmc 671: .Xr ssh 1
1.1 stevesk 672: should support in order of preference.
673: The possible values are
1.84 jmc 674: .Sq 1
1.1 stevesk 675: and
1.84 jmc 676: .Sq 2 .
1.1 stevesk 677: Multiple versions must be comma-separated.
678: The default is
679: .Dq 2,1 .
1.84 jmc 680: This means that ssh
1.1 stevesk 681: tries version 2 and falls back to version 1
682: if version 2 is not available.
683: .It Cm ProxyCommand
684: Specifies the command to use to connect to the server.
685: The command
686: string extends to the end of the line, and is executed with
687: .Pa /bin/sh .
688: In the command string,
689: .Ql %h
690: will be substituted by the host name to
691: connect and
692: .Ql %p
693: by the port.
694: The command can be basically anything,
695: and should read from its standard input and write to its standard output.
696: It should eventually connect an
697: .Xr sshd 8
698: server running on some machine, or execute
699: .Ic sshd -i
700: somewhere.
701: Host key management will be done using the
702: HostName of the host being connected (defaulting to the name typed by
703: the user).
1.7 jmc 704: Setting the command to
705: .Dq none
1.6 markus 706: disables this option entirely.
1.1 stevesk 707: Note that
708: .Cm CheckHostIP
709: is not available for connects with a proxy command.
1.52 djm 710: .Pp
711: This directive is useful in conjunction with
712: .Xr nc 1
713: and its proxy support.
1.53 jmc 714: For example, the following directive would connect via an HTTP proxy at
1.52 djm 715: 192.0.2.0:
716: .Bd -literal -offset 3n
717: ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
718: .Ed
1.1 stevesk 719: .It Cm PubkeyAuthentication
720: Specifies whether to try public key authentication.
721: The argument to this keyword must be
722: .Dq yes
723: or
724: .Dq no .
725: The default is
726: .Dq yes .
727: This option applies to protocol version 2 only.
1.75 dtucker 728: .It Cm RekeyLimit
729: Specifies the maximum amount of data that may be transmitted before the
1.76 jmc 730: session key is renegotiated.
1.75 dtucker 731: The argument is the number of bytes, with an optional suffix of
1.76 jmc 732: .Sq K ,
733: .Sq M ,
1.75 dtucker 734: or
1.76 jmc 735: .Sq G
1.75 dtucker 736: to indicate Kilobytes, Megabytes, or Gigabytes, respectively.
737: The default is between
1.84 jmc 738: .Sq 1G
1.75 dtucker 739: and
1.84 jmc 740: .Sq 4G ,
1.75 dtucker 741: depending on the cipher.
1.76 jmc 742: This option applies to protocol version 2 only.
1.1 stevesk 743: .It Cm RemoteForward
1.74 jmc 744: Specifies that a TCP port on the remote machine be forwarded over
1.1 stevesk 745: the secure channel to the specified host and port from the local machine.
1.49 jmc 746: The first argument must be
1.43 djm 747: .Sm off
1.49 jmc 748: .Oo Ar bind_address : Oc Ar port
1.43 djm 749: .Sm on
1.49 jmc 750: and the second argument must be
751: .Ar host : Ns Ar hostport .
752: IPv6 addresses can be specified by enclosing addresses in square brackets
753: or by using an alternative syntax:
754: .Oo Ar bind_address Ns / Oc Ns Ar port
755: and
756: .Ar host Ns / Ns Ar hostport .
1.1 stevesk 757: Multiple forwardings may be specified, and additional
758: forwardings can be given on the command line.
759: Only the superuser can forward privileged ports.
1.43 djm 760: .Pp
761: If the
762: .Ar bind_address
763: is not specified, the default is to only bind to loopback addresses.
764: If the
765: .Ar bind_address
766: is
767: .Ql *
768: or an empty string, then the forwarding is requested to listen on all
769: interfaces.
770: Specifying a remote
771: .Ar bind_address
1.46 jmc 772: will only succeed if the server's
773: .Cm GatewayPorts
1.43 djm 774: option is enabled (see
1.46 jmc 775: .Xr sshd_config 5 ) .
1.1 stevesk 776: .It Cm RhostsRSAAuthentication
777: Specifies whether to try rhosts based authentication with RSA host
778: authentication.
779: The argument must be
780: .Dq yes
781: or
782: .Dq no .
783: The default is
784: .Dq no .
785: This option applies to protocol version 1 only and requires
1.84 jmc 786: .Xr ssh 1
1.1 stevesk 787: to be setuid root.
788: .It Cm RSAAuthentication
789: Specifies whether to try RSA authentication.
790: The argument to this keyword must be
791: .Dq yes
792: or
793: .Dq no .
794: RSA authentication will only be
795: attempted if the identity file exists, or an authentication agent is
796: running.
797: The default is
798: .Dq yes .
799: Note that this option applies to protocol version 1 only.
1.32 djm 800: .It Cm SendEnv
801: Specifies what variables from the local
802: .Xr environ 7
803: should be sent to the server.
1.84 jmc 804: Note that environment passing is only supported for protocol 2.
805: The server must also support it, and the server must be configured to
1.33 djm 806: accept these environment variables.
1.32 djm 807: Refer to
808: .Cm AcceptEnv
809: in
810: .Xr sshd_config 5
811: for how to configure the server.
1.80 jmc 812: Variables are specified by name, which may contain wildcard characters.
1.33 djm 813: Multiple environment variables may be separated by whitespace or spread
1.32 djm 814: across multiple
815: .Cm SendEnv
816: directives.
817: The default is not to send any environment variables.
1.81 jmc 818: .Pp
819: See
820: .Sx PATTERNS
821: for more information on patterns.
1.28 markus 822: .It Cm ServerAliveCountMax
1.73 jmc 823: Sets the number of server alive messages (see below) which may be
1.28 markus 824: sent without
1.84 jmc 825: .Xr ssh 1
1.28 markus 826: receiving any messages back from the server.
827: If this threshold is reached while server alive messages are being sent,
1.84 jmc 828: ssh will disconnect from the server, terminating the session.
1.28 markus 829: It is important to note that the use of server alive messages is very
830: different from
831: .Cm TCPKeepAlive
832: (below).
833: The server alive messages are sent through the encrypted channel
834: and therefore will not be spoofable.
835: The TCP keepalive option enabled by
836: .Cm TCPKeepAlive
837: is spoofable.
838: The server alive mechanism is valuable when the client or
839: server depend on knowing when a connection has become inactive.
840: .Pp
841: The default value is 3.
842: If, for example,
843: .Cm ServerAliveInterval
1.84 jmc 844: (see below) is set to 15 and
1.28 markus 845: .Cm ServerAliveCountMax
1.84 jmc 846: is left at the default, if the server becomes unresponsive,
847: ssh will disconnect after approximately 45 seconds.
1.67 jmc 848: .It Cm ServerAliveInterval
849: Sets a timeout interval in seconds after which if no data has been received
850: from the server,
1.84 jmc 851: .Xr ssh 1
1.67 jmc 852: will send a message through the encrypted
853: channel to request a response from the server.
854: The default
855: is 0, indicating that these messages will not be sent to the server.
856: This option applies to protocol version 2 only.
1.1 stevesk 857: .It Cm SmartcardDevice
1.11 jmc 858: Specifies which smartcard device to use.
859: The argument to this keyword is the device
1.84 jmc 860: .Xr ssh 1
1.1 stevesk 861: should use to communicate with a smartcard used for storing the user's
1.11 jmc 862: private RSA key.
863: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 864: .It Cm StrictHostKeyChecking
865: If this flag is set to
866: .Dq yes ,
1.84 jmc 867: .Xr ssh 1
1.1 stevesk 868: will never automatically add host keys to the
1.50 djm 869: .Pa ~/.ssh/known_hosts
1.1 stevesk 870: file, and refuses to connect to hosts whose host key has changed.
871: This provides maximum protection against trojan horse attacks,
1.84 jmc 872: though it can be annoying when the
1.1 stevesk 873: .Pa /etc/ssh/ssh_known_hosts
1.84 jmc 874: file is poorly maintained or when connections to new hosts are
1.1 stevesk 875: frequently made.
876: This option forces the user to manually
877: add all new hosts.
878: If this flag is set to
879: .Dq no ,
1.84 jmc 880: ssh will automatically add new host keys to the
1.1 stevesk 881: user known hosts files.
882: If this flag is set to
883: .Dq ask ,
884: new host keys
885: will be added to the user known host files only after the user
886: has confirmed that is what they really want to do, and
1.84 jmc 887: ssh will refuse to connect to hosts whose host key has changed.
1.1 stevesk 888: The host keys of
889: known hosts will be verified automatically in all cases.
890: The argument must be
891: .Dq yes ,
1.84 jmc 892: .Dq no ,
1.1 stevesk 893: or
894: .Dq ask .
895: The default is
896: .Dq ask .
1.26 markus 897: .It Cm TCPKeepAlive
898: Specifies whether the system should send TCP keepalive messages to the
899: other side.
900: If they are sent, death of the connection or crash of one
901: of the machines will be properly noticed.
902: However, this means that
903: connections will die if the route is down temporarily, and some people
904: find it annoying.
905: .Pp
906: The default is
907: .Dq yes
908: (to send TCP keepalive messages), and the client will notice
909: if the network goes down or the remote host dies.
910: This is important in scripts, and many users want it too.
911: .Pp
912: To disable TCP keepalive messages, the value should be set to
913: .Dq no .
1.65 reyk 914: .It Cm Tunnel
915: Request starting
916: .Xr tun 4
1.69 jmc 917: device forwarding between the client and the server.
918: This option also allows requesting layer 2 (ethernet)
919: instead of layer 3 (point-to-point) tunneling from the server.
1.65 reyk 920: The argument must be
1.68 reyk 921: .Dq yes ,
922: .Dq point-to-point ,
1.84 jmc 923: .Dq ethernet ,
1.65 reyk 924: or
925: .Dq no .
926: The default is
927: .Dq no .
928: .It Cm TunnelDevice
929: Force a specified
930: .Xr tun 4
931: device on the client.
932: Without this option, the next available device will be used.
1.72 jmc 933: .It Cm UsePrivilegedPort
934: Specifies whether to use a privileged port for outgoing connections.
935: The argument must be
936: .Dq yes
937: or
938: .Dq no .
939: The default is
940: .Dq no .
941: If set to
1.84 jmc 942: .Dq yes ,
943: .Xr ssh 1
1.72 jmc 944: must be setuid root.
945: Note that this option must be set to
946: .Dq yes
947: for
948: .Cm RhostsRSAAuthentication
949: with older servers.
1.1 stevesk 950: .It Cm User
951: Specifies the user to log in as.
952: This can be useful when a different user name is used on different machines.
953: This saves the trouble of
954: having to remember to give the user name on the command line.
955: .It Cm UserKnownHostsFile
956: Specifies a file to use for the user
957: host key database instead of
1.50 djm 958: .Pa ~/.ssh/known_hosts .
1.8 jakob 959: .It Cm VerifyHostKeyDNS
960: Specifies whether to verify the remote key using DNS and SSHFP resource
961: records.
1.24 jakob 962: If this option is set to
963: .Dq yes ,
1.25 jmc 964: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 965: from DNS.
966: Insecure fingerprints will be handled as if this option was set to
967: .Dq ask .
968: If this option is set to
969: .Dq ask ,
970: information on fingerprint match will be displayed, but the user will still
971: need to confirm new host keys according to the
972: .Cm StrictHostKeyChecking
973: option.
974: The argument must be
975: .Dq yes ,
1.84 jmc 976: .Dq no ,
1.25 jmc 977: or
978: .Dq ask .
1.8 jakob 979: The default is
980: .Dq no .
1.12 jakob 981: Note that this option applies to protocol version 2 only.
1.84 jmc 982: .Pp
983: See also
984: .Sx VERIFYING HOST KEYS
985: in
986: .Xr ssh 1 .
1.1 stevesk 987: .It Cm XAuthLocation
1.5 stevesk 988: Specifies the full pathname of the
1.1 stevesk 989: .Xr xauth 1
990: program.
991: The default is
992: .Pa /usr/X11R6/bin/xauth .
993: .El
1.86 jmc 994: .Sh PATTERNS
995: A
996: .Em pattern
997: consists of zero or more non-whitespace characters,
998: .Sq *
999: (a wildcard that matches zero or more characters),
1000: or
1001: .Sq ?\&
1002: (a wildcard that matches exactly one character).
1003: For example, to specify a set of declarations for any host in the
1004: .Dq .co.uk
1005: set of domains,
1006: the following pattern could be used:
1007: .Pp
1008: .Dl Host *.co.uk
1009: .Pp
1010: The following pattern
1011: would match any host in the 192.168.0.[0-9] network range:
1012: .Pp
1013: .Dl Host 192.168.0.?
1014: .Pp
1015: A
1016: .Em pattern-list
1017: is a comma-separated list of patterns.
1018: Patterns within pattern-lists may be negated
1019: by preceding them with an exclamation mark
1020: .Pq Sq !\& .
1021: For example,
1022: to allow a key to be used from anywhere within an organisation
1023: except from the
1024: .Dq dialup
1025: pool,
1026: the following entry (in authorized_keys) could be used:
1027: .Pp
1028: .Dl from=\&"!*.dialup.example.com,*.example.com\&"
1.1 stevesk 1029: .Sh FILES
1030: .Bl -tag -width Ds
1.50 djm 1031: .It Pa ~/.ssh/config
1.1 stevesk 1032: This is the per-user configuration file.
1033: The format of this file is described above.
1.84 jmc 1034: This file is used by the SSH client.
1.30 djm 1035: Because of the potential for abuse, this file must have strict permissions:
1036: read/write for the user, and not accessible by others.
1.1 stevesk 1037: .It Pa /etc/ssh/ssh_config
1038: Systemwide configuration file.
1039: This file provides defaults for those
1040: values that are not specified in the user's configuration file, and
1041: for those users who do not have a configuration file.
1042: This file must be world-readable.
1043: .El
1.13 jmc 1044: .Sh SEE ALSO
1045: .Xr ssh 1
1.1 stevesk 1046: .Sh AUTHORS
1047: OpenSSH is a derivative of the original and free
1048: ssh 1.2.12 release by Tatu Ylonen.
1049: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
1050: Theo de Raadt and Dug Song
1051: removed many bugs, re-added newer features and
1052: created OpenSSH.
1053: Markus Friedl contributed the support for SSH
1054: protocol versions 1.5 and 2.0.