Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.42
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
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9: .\" software must be clearly marked as such, and if the derived work is
10: .\" incompatible with the protocol description in the RFC file, it must be
11: .\" called by a name other than "ssh" or "Secure Shell".
12: .\"
13: .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved.
14: .\" Copyright (c) 1999 Aaron Campbell. All rights reserved.
15: .\" Copyright (c) 1999 Theo de Raadt. All rights reserved.
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1.42 ! djm 37: .\" $OpenBSD: ssh_config.5,v 1.41 2005/01/28 18:14:09 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
46: .It Pa $HOME/.ssh/config
47: .It Pa /etc/ssh/ssh_config
48: .El
49: .Sh DESCRIPTION
50: .Nm ssh
51: obtains configuration data from the following sources in
52: the following order:
1.2 stevesk 53: .Bl -enum -offset indent -compact
54: .It
55: command-line options
56: .It
57: user's configuration file
58: .Pq Pa $HOME/.ssh/config
59: .It
60: system-wide configuration file
61: .Pq Pa /etc/ssh/ssh_config
62: .El
1.1 stevesk 63: .Pp
64: For each parameter, the first obtained value
65: will be used.
1.41 jmc 66: The configuration files contain sections separated by
1.1 stevesk 67: .Dq Host
68: specifications, and that section is only applied for hosts that
69: match one of the patterns given in the specification.
70: The matched host name is the one given on the command line.
71: .Pp
72: Since the first obtained value for each parameter is used, more
73: host-specific declarations should be given near the beginning of the
74: file, and general defaults at the end.
75: .Pp
76: The configuration file has the following format:
77: .Pp
78: Empty lines and lines starting with
79: .Ql #
80: are comments.
81: .Pp
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 ,
90: .Nm scp
91: and
92: .Nm sftp
93: .Fl o
94: option.
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.
105: .Ql \&*
106: and
1.20 jmc 107: .Ql \&?
1.1 stevesk 108: can be used as wildcards in the
109: patterns.
110: A single
111: .Ql \&*
112: as a pattern can be used to provide global
113: defaults for all hosts.
114: The host is the
115: .Ar hostname
116: argument given on the command line (i.e., the name is not converted to
117: a canonicalized host name before matching).
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
1.40 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
139: Specify the interface to transmit from on machines with multiple
140: interfaces or aliased addresses.
141: Note that this option does not work if
142: .Cm UsePrivilegedPort
143: is set to
144: .Dq yes .
145: .It Cm ChallengeResponseAuthentication
146: Specifies whether to use challenge response authentication.
147: The argument to this keyword must be
148: .Dq yes
149: or
150: .Dq no .
151: The default is
152: .Dq yes .
153: .It Cm CheckHostIP
154: If this flag is set to
155: .Dq yes ,
156: ssh will additionally check the host IP address in the
157: .Pa known_hosts
158: file.
159: This allows ssh to detect if a host key changed due to DNS spoofing.
160: If the option is set to
161: .Dq no ,
162: the check will not be executed.
163: The default is
164: .Dq yes .
165: .It Cm Cipher
166: Specifies the cipher to use for encrypting the session
167: in protocol version 1.
168: Currently,
169: .Dq blowfish ,
170: .Dq 3des ,
171: and
172: .Dq des
173: are supported.
174: .Ar des
175: is only supported in the
176: .Nm ssh
177: client for interoperability with legacy protocol 1 implementations
178: that do not support the
179: .Ar 3des
1.7 jmc 180: cipher.
181: Its use is strongly discouraged due to cryptographic weaknesses.
1.1 stevesk 182: The default is
183: .Dq 3des .
184: .It Cm Ciphers
185: Specifies the ciphers allowed for protocol version 2
186: in order of preference.
187: Multiple ciphers must be comma-separated.
1.35 dtucker 188: The supported ciphers are
189: .Dq 3des-cbc ,
190: .Dq aes128-cbc ,
191: .Dq aes192-cbc ,
192: .Dq aes256-cbc ,
193: .Dq aes128-ctr ,
194: .Dq aes192-ctr ,
195: .Dq aes256-ctr ,
196: .Dq arcfour ,
197: .Dq blowfish-cbc ,
198: and
199: .Dq cast128-cbc .
1.1 stevesk 200: The default is
201: .Bd -literal
202: ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
203: aes192-cbc,aes256-cbc''
204: .Ed
205: .It Cm ClearAllForwardings
206: Specifies that all local, remote and dynamic port forwardings
207: specified in the configuration files or on the command line be
1.7 jmc 208: cleared.
209: This option is primarily useful when used from the
1.1 stevesk 210: .Nm ssh
211: command line to clear port forwardings set in
212: configuration files, and is automatically set by
213: .Xr scp 1
214: and
215: .Xr sftp 1 .
216: The argument must be
217: .Dq yes
218: or
219: .Dq no .
220: The default is
221: .Dq no .
222: .It Cm Compression
223: Specifies whether to use compression.
224: The argument must be
225: .Dq yes
226: or
227: .Dq no .
228: The default is
229: .Dq no .
230: .It Cm CompressionLevel
231: Specifies the compression level to use if compression is enabled.
232: The argument must be an integer from 1 (fast) to 9 (slow, best).
233: The default level is 6, which is good for most applications.
234: The meaning of the values is the same as in
235: .Xr gzip 1 .
236: Note that this option applies to protocol version 1 only.
237: .It Cm ConnectionAttempts
238: Specifies the number of tries (one per second) to make before exiting.
239: The argument must be an integer.
240: This may be useful in scripts if the connection sometimes fails.
241: The default is 1.
1.9 djm 242: .It Cm ConnectTimeout
243: Specifies the timeout (in seconds) used when connecting to the ssh
1.11 jmc 244: server, instead of using the default system TCP timeout.
245: This value is used only when the target is down or really unreachable,
246: not when it refuses the connection.
1.36 djm 247: .It Cm ControlMaster
248: Enables the sharing of multiple sessions over a single network connection.
249: When set to
250: .Dq yes
251: .Nm ssh
252: will listen for connections on a control socket specified using the
253: .Cm ControlPath
254: argument.
255: Additional sessions can connect to this socket using the same
256: .Cm ControlPath
257: with
258: .Cm ControlMaster
259: set to
260: .Dq no
1.38 jmc 261: (the default).
1.36 djm 262: These sessions will reuse the master instance's network connection rather
263: than initiating new ones.
1.37 djm 264: Setting this to
265: .Dq ask
266: will cause
267: .Nm ssh
268: to listen for control connections, but require confirmation using the
269: .Ev SSH_ASKPASS
270: program before they are accepted (see
271: .Xr ssh-add 1
1.38 jmc 272: for details).
1.36 djm 273: .It Cm ControlPath
1.38 jmc 274: Specify the path to the control socket used for connection sharing.
1.36 djm 275: See
276: .Cm ControlMaster
277: above.
1.38 jmc 278: .It Cm DynamicForward
279: Specifies that a TCP/IP port on the local machine be forwarded
280: over the secure channel, and the application
281: protocol is then used to determine where to connect to from the
282: remote machine.
283: The argument must be a port number.
284: Currently the SOCKS4 and SOCKS5 protocols are supported, and
285: .Nm ssh
286: will act as a SOCKS server.
287: Multiple forwardings may be specified, and
288: additional forwardings can be given on the command line.
289: Only the superuser can forward privileged ports.
1.14 markus 290: .It Cm EnableSSHKeysign
291: Setting this option to
292: .Dq yes
293: in the global client configuration file
294: .Pa /etc/ssh/ssh_config
295: enables the use of the helper program
296: .Xr ssh-keysign 8
297: during
298: .Cm HostbasedAuthentication .
299: The argument must be
300: .Dq yes
301: or
302: .Dq no .
303: The default is
304: .Dq no .
1.23 jmc 305: This option should be placed in the non-hostspecific section.
1.14 markus 306: See
307: .Xr ssh-keysign 8
308: for more information.
1.1 stevesk 309: .It Cm EscapeChar
310: Sets the escape character (default:
311: .Ql ~ ) .
312: The escape character can also
313: be set on the command line.
314: The argument should be a single character,
315: .Ql ^
316: followed by a letter, or
317: .Dq none
318: to disable the escape
319: character entirely (making the connection transparent for binary
320: data).
321: .It Cm ForwardAgent
322: Specifies whether the connection to the authentication agent (if any)
323: will be forwarded to the remote machine.
324: The argument must be
325: .Dq yes
326: or
327: .Dq no .
328: The default is
329: .Dq no .
1.3 stevesk 330: .Pp
1.7 jmc 331: Agent forwarding should be enabled with caution.
332: Users with the ability to bypass file permissions on the remote host
333: (for the agent's Unix-domain socket)
334: can access the local agent through the forwarded connection.
335: An attacker cannot obtain key material from the agent,
1.3 stevesk 336: however they can perform operations on the keys that enable them to
337: authenticate using the identities loaded into the agent.
1.1 stevesk 338: .It Cm ForwardX11
339: Specifies whether X11 connections will be automatically redirected
340: over the secure channel and
341: .Ev DISPLAY
342: set.
343: The argument must be
344: .Dq yes
345: or
346: .Dq no .
347: The default is
348: .Dq no .
1.3 stevesk 349: .Pp
1.7 jmc 350: X11 forwarding should be enabled with caution.
351: Users with the ability to bypass file permissions on the remote host
1.22 markus 352: (for the user's X11 authorization database)
1.7 jmc 353: can access the local X11 display through the forwarded connection.
1.22 markus 354: An attacker may then be able to perform activities such as keystroke monitoring
355: if the
356: .Cm ForwardX11Trusted
357: option is also enabled.
358: .It Cm ForwardX11Trusted
1.34 jmc 359: If this option is set to
1.22 markus 360: .Dq yes
361: then remote X11 clients will have full access to the original X11 display.
1.42 ! djm 362: .Pp
1.22 markus 363: If this option is set to
364: .Dq no
365: then remote X11 clients will be considered untrusted and prevented
366: from stealing or tampering with data belonging to trusted X11
367: clients.
1.42 ! djm 368: Furthermore, the
! 369: .Xr xauth 1
! 370: token used for the session will be set to expire after 20 minutes.
! 371: Remote clients will be refused access after this time.
1.22 markus 372: .Pp
373: The default is
374: .Dq no .
375: .Pp
376: See the X11 SECURITY extension specification for full details on
377: the restrictions imposed on untrusted clients.
1.1 stevesk 378: .It Cm GatewayPorts
379: Specifies whether remote hosts are allowed to connect to local
380: forwarded ports.
381: By default,
382: .Nm ssh
1.7 jmc 383: binds local port forwardings to the loopback address.
384: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 385: .Cm GatewayPorts
386: can be used to specify that
387: .Nm ssh
388: should bind local port forwardings to the wildcard address,
389: thus allowing remote hosts to connect to forwarded ports.
390: The argument must be
391: .Dq yes
392: or
393: .Dq no .
394: The default is
395: .Dq no .
396: .It Cm GlobalKnownHostsFile
397: Specifies a file to use for the global
398: host key database instead of
399: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 400: .It Cm GSSAPIAuthentication
1.27 markus 401: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 402: The default is
1.21 markus 403: .Dq no .
1.18 markus 404: Note that this option applies to protocol version 2 only.
405: .It Cm GSSAPIDelegateCredentials
406: Forward (delegate) credentials to the server.
407: The default is
408: .Dq no .
409: Note that this option applies to protocol version 2 only.
1.1 stevesk 410: .It Cm HostbasedAuthentication
411: Specifies whether to try rhosts based authentication with public key
412: authentication.
413: The argument must be
414: .Dq yes
415: or
416: .Dq no .
417: The default is
418: .Dq no .
419: This option applies to protocol version 2 only and
420: is similar to
421: .Cm RhostsRSAAuthentication .
422: .It Cm HostKeyAlgorithms
423: Specifies the protocol version 2 host key algorithms
424: that the client wants to use in order of preference.
425: The default for this option is:
426: .Dq ssh-rsa,ssh-dss .
427: .It Cm HostKeyAlias
428: Specifies an alias that should be used instead of the
429: real host name when looking up or saving the host key
430: in the host key database files.
431: This option is useful for tunneling ssh connections
432: or for multiple servers running on a single host.
433: .It Cm HostName
434: Specifies the real host name to log into.
435: This can be used to specify nicknames or abbreviations for hosts.
436: Default is the name given on the command line.
437: Numeric IP addresses are also permitted (both on the command line and in
438: .Cm HostName
439: specifications).
440: .It Cm IdentityFile
441: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 442: is read.
443: The default is
1.1 stevesk 444: .Pa $HOME/.ssh/identity
445: for protocol version 1, and
446: .Pa $HOME/.ssh/id_rsa
447: and
448: .Pa $HOME/.ssh/id_dsa
449: for protocol version 2.
450: Additionally, any identities represented by the authentication agent
451: will be used for authentication.
452: The file name may use the tilde
453: syntax to refer to a user's home directory.
454: It is possible to have
455: multiple identity files specified in configuration files; all these
456: identities will be tried in sequence.
1.29 markus 457: .It Cm IdentitiesOnly
458: Specifies that
459: .Nm ssh
460: should only use the authentication identity files configured in the
1.31 jmc 461: .Nm
1.29 markus 462: files,
463: even if the
464: .Nm ssh-agent
465: offers more identities.
466: The argument to this keyword must be
467: .Dq yes
468: or
469: .Dq no .
470: This option is intented for situations where
471: .Nm ssh-agent
472: offers many different identities.
473: The default is
474: .Dq no .
1.39 djm 475: .It Cm KbdInteractiveDevices
476: Specifies the list of methods to use in keyboard-interactive authentication.
477: Multiple method names must be comma-separated.
478: The default is to use the server specified list.
1.1 stevesk 479: .It Cm LocalForward
480: Specifies that a TCP/IP port on the local machine be forwarded over
481: the secure channel to the specified host and port from the remote machine.
482: The first argument must be a port number, and the second must be
483: .Ar host:port .
484: IPv6 addresses can be specified with an alternative syntax:
485: .Ar host/port .
486: Multiple forwardings may be specified, and additional
487: forwardings can be given on the command line.
488: Only the superuser can forward privileged ports.
489: .It Cm LogLevel
490: Gives the verbosity level that is used when logging messages from
491: .Nm ssh .
492: The possible values are:
493: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 494: The default is INFO.
495: DEBUG and DEBUG1 are equivalent.
496: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 497: .It Cm MACs
498: Specifies the MAC (message authentication code) algorithms
499: in order of preference.
500: The MAC algorithm is used in protocol version 2
501: for data integrity protection.
502: Multiple algorithms must be comma-separated.
503: The default is
504: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
505: .It Cm NoHostAuthenticationForLocalhost
506: This option can be used if the home directory is shared across machines.
507: In this case localhost will refer to a different machine on each of
508: the machines and the user will get many warnings about changed host keys.
509: However, this option disables host authentication for localhost.
510: The argument to this keyword must be
511: .Dq yes
512: or
513: .Dq no .
514: The default is to check the host key for localhost.
515: .It Cm NumberOfPasswordPrompts
516: Specifies the number of password prompts before giving up.
517: The argument to this keyword must be an integer.
518: Default is 3.
519: .It Cm PasswordAuthentication
520: Specifies whether to use password authentication.
521: The argument to this keyword must be
522: .Dq yes
523: or
524: .Dq no .
525: The default is
526: .Dq yes .
527: .It Cm Port
528: Specifies the port number to connect on the remote host.
529: Default is 22.
530: .It Cm PreferredAuthentications
531: Specifies the order in which the client should try protocol 2
1.11 jmc 532: authentication methods.
533: This allows a client to prefer one method (e.g.
1.1 stevesk 534: .Cm keyboard-interactive )
535: over another method (e.g.
536: .Cm password )
537: The default for this option is:
538: .Dq hostbased,publickey,keyboard-interactive,password .
539: .It Cm Protocol
540: Specifies the protocol versions
541: .Nm ssh
542: should support in order of preference.
543: The possible values are
544: .Dq 1
545: and
546: .Dq 2 .
547: Multiple versions must be comma-separated.
548: The default is
549: .Dq 2,1 .
550: This means that
551: .Nm ssh
552: tries version 2 and falls back to version 1
553: if version 2 is not available.
554: .It Cm ProxyCommand
555: Specifies the command to use to connect to the server.
556: The command
557: string extends to the end of the line, and is executed with
558: .Pa /bin/sh .
559: In the command string,
560: .Ql %h
561: will be substituted by the host name to
562: connect and
563: .Ql %p
564: by the port.
565: The command can be basically anything,
566: and should read from its standard input and write to its standard output.
567: It should eventually connect an
568: .Xr sshd 8
569: server running on some machine, or execute
570: .Ic sshd -i
571: somewhere.
572: Host key management will be done using the
573: HostName of the host being connected (defaulting to the name typed by
574: the user).
1.7 jmc 575: Setting the command to
576: .Dq none
1.6 markus 577: disables this option entirely.
1.1 stevesk 578: Note that
579: .Cm CheckHostIP
580: is not available for connects with a proxy command.
581: .Pp
582: .It Cm PubkeyAuthentication
583: Specifies whether to try public key authentication.
584: The argument to this keyword must be
585: .Dq yes
586: or
587: .Dq no .
588: The default is
589: .Dq yes .
590: This option applies to protocol version 2 only.
591: .It Cm RemoteForward
592: Specifies that a TCP/IP port on the remote machine be forwarded over
593: the secure channel to the specified host and port from the local machine.
594: The first argument must be a port number, and the second must be
595: .Ar host:port .
596: IPv6 addresses can be specified with an alternative syntax:
597: .Ar host/port .
598: Multiple forwardings may be specified, and additional
599: forwardings can be given on the command line.
600: Only the superuser can forward privileged ports.
601: .It Cm RhostsRSAAuthentication
602: Specifies whether to try rhosts based authentication with RSA host
603: authentication.
604: The argument must be
605: .Dq yes
606: or
607: .Dq no .
608: The default is
609: .Dq no .
610: This option applies to protocol version 1 only and requires
611: .Nm ssh
612: to be setuid root.
613: .It Cm RSAAuthentication
614: Specifies whether to try RSA authentication.
615: The argument to this keyword must be
616: .Dq yes
617: or
618: .Dq no .
619: RSA authentication will only be
620: attempted if the identity file exists, or an authentication agent is
621: running.
622: The default is
623: .Dq yes .
624: Note that this option applies to protocol version 1 only.
1.32 djm 625: .It Cm SendEnv
626: Specifies what variables from the local
627: .Xr environ 7
628: should be sent to the server.
629: Note that environment passing is only supported for protocol 2, the
1.33 djm 630: server must also support it, and the server must be configured to
631: accept these environment variables.
1.32 djm 632: Refer to
633: .Cm AcceptEnv
634: in
635: .Xr sshd_config 5
636: for how to configure the server.
637: Variables are specified by name, which may contain the wildcard characters
638: .Ql \&*
639: and
640: .Ql \&? .
1.33 djm 641: Multiple environment variables may be separated by whitespace or spread
1.32 djm 642: across multiple
643: .Cm SendEnv
644: directives.
645: The default is not to send any environment variables.
1.28 markus 646: .It Cm ServerAliveInterval
647: Sets a timeout interval in seconds after which if no data has been received
648: from the server,
649: .Nm ssh
650: will send a message through the encrypted
651: channel to request a response from the server.
652: The default
653: is 0, indicating that these messages will not be sent to the server.
654: This option applies to protocol version 2 only.
655: .It Cm ServerAliveCountMax
656: Sets the number of server alive messages (see above) which may be
657: sent without
658: .Nm ssh
659: receiving any messages back from the server.
660: If this threshold is reached while server alive messages are being sent,
661: .Nm ssh
662: will disconnect from the server, terminating the session.
663: It is important to note that the use of server alive messages is very
664: different from
665: .Cm TCPKeepAlive
666: (below).
667: The server alive messages are sent through the encrypted channel
668: and therefore will not be spoofable.
669: The TCP keepalive option enabled by
670: .Cm TCPKeepAlive
671: is spoofable.
672: The server alive mechanism is valuable when the client or
673: server depend on knowing when a connection has become inactive.
674: .Pp
675: The default value is 3.
676: If, for example,
677: .Cm ServerAliveInterval
678: (above) is set to 15, and
679: .Cm ServerAliveCountMax
680: is left at the default, if the server becomes unresponsive ssh
681: will disconnect after approximately 45 seconds.
1.1 stevesk 682: .It Cm SmartcardDevice
1.11 jmc 683: Specifies which smartcard device to use.
684: The argument to this keyword is the device
1.1 stevesk 685: .Nm ssh
686: should use to communicate with a smartcard used for storing the user's
1.11 jmc 687: private RSA key.
688: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 689: .It Cm StrictHostKeyChecking
690: If this flag is set to
691: .Dq yes ,
692: .Nm ssh
693: will never automatically add host keys to the
694: .Pa $HOME/.ssh/known_hosts
695: file, and refuses to connect to hosts whose host key has changed.
696: This provides maximum protection against trojan horse attacks,
697: however, can be annoying when the
698: .Pa /etc/ssh/ssh_known_hosts
699: file is poorly maintained, or connections to new hosts are
700: frequently made.
701: This option forces the user to manually
702: add all new hosts.
703: If this flag is set to
704: .Dq no ,
705: .Nm ssh
706: will automatically add new host keys to the
707: user known hosts files.
708: If this flag is set to
709: .Dq ask ,
710: new host keys
711: will be added to the user known host files only after the user
712: has confirmed that is what they really want to do, and
713: .Nm ssh
714: will refuse to connect to hosts whose host key has changed.
715: The host keys of
716: known hosts will be verified automatically in all cases.
717: The argument must be
718: .Dq yes ,
719: .Dq no
720: or
721: .Dq ask .
722: The default is
723: .Dq ask .
1.26 markus 724: .It Cm TCPKeepAlive
725: Specifies whether the system should send TCP keepalive messages to the
726: other side.
727: If they are sent, death of the connection or crash of one
728: of the machines will be properly noticed.
729: However, this means that
730: connections will die if the route is down temporarily, and some people
731: find it annoying.
732: .Pp
733: The default is
734: .Dq yes
735: (to send TCP keepalive messages), and the client will notice
736: if the network goes down or the remote host dies.
737: This is important in scripts, and many users want it too.
738: .Pp
739: To disable TCP keepalive messages, the value should be set to
740: .Dq no .
1.1 stevesk 741: .It Cm UsePrivilegedPort
742: Specifies whether to use a privileged port for outgoing connections.
743: The argument must be
744: .Dq yes
745: or
746: .Dq no .
747: The default is
748: .Dq no .
1.4 stevesk 749: If set to
750: .Dq yes
751: .Nm ssh
752: must be setuid root.
1.1 stevesk 753: Note that this option must be set to
754: .Dq yes
1.17 markus 755: for
1.1 stevesk 756: .Cm RhostsRSAAuthentication
1.17 markus 757: with older servers.
1.1 stevesk 758: .It Cm User
759: Specifies the user to log in as.
760: This can be useful when a different user name is used on different machines.
761: This saves the trouble of
762: having to remember to give the user name on the command line.
763: .It Cm UserKnownHostsFile
764: Specifies a file to use for the user
765: host key database instead of
766: .Pa $HOME/.ssh/known_hosts .
1.8 jakob 767: .It Cm VerifyHostKeyDNS
768: Specifies whether to verify the remote key using DNS and SSHFP resource
769: records.
1.24 jakob 770: If this option is set to
771: .Dq yes ,
1.25 jmc 772: the client will implicitly trust keys that match a secure fingerprint
1.24 jakob 773: from DNS.
774: Insecure fingerprints will be handled as if this option was set to
775: .Dq ask .
776: If this option is set to
777: .Dq ask ,
778: information on fingerprint match will be displayed, but the user will still
779: need to confirm new host keys according to the
780: .Cm StrictHostKeyChecking
781: option.
782: The argument must be
783: .Dq yes ,
784: .Dq no
1.25 jmc 785: or
786: .Dq ask .
1.8 jakob 787: The default is
788: .Dq no .
1.12 jakob 789: Note that this option applies to protocol version 2 only.
1.1 stevesk 790: .It Cm XAuthLocation
1.5 stevesk 791: Specifies the full pathname of the
1.1 stevesk 792: .Xr xauth 1
793: program.
794: The default is
795: .Pa /usr/X11R6/bin/xauth .
796: .El
797: .Sh FILES
798: .Bl -tag -width Ds
799: .It Pa $HOME/.ssh/config
800: This is the per-user configuration file.
801: The format of this file is described above.
802: This file is used by the
803: .Nm ssh
804: client.
1.30 djm 805: Because of the potential for abuse, this file must have strict permissions:
806: read/write for the user, and not accessible by others.
1.1 stevesk 807: .It Pa /etc/ssh/ssh_config
808: Systemwide configuration file.
809: This file provides defaults for those
810: values that are not specified in the user's configuration file, and
811: for those users who do not have a configuration file.
812: This file must be world-readable.
813: .El
1.13 jmc 814: .Sh SEE ALSO
815: .Xr ssh 1
1.1 stevesk 816: .Sh AUTHORS
817: OpenSSH is a derivative of the original and free
818: ssh 1.2.12 release by Tatu Ylonen.
819: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
820: Theo de Raadt and Dug Song
821: removed many bugs, re-added newer features and
822: created OpenSSH.
823: Markus Friedl contributed the support for SSH
824: protocol versions 1.5 and 2.0.