Annotation of src/usr.bin/ssh/ssh_config.5, Revision 1.20.2.2
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.
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1.20.2.2! brad 37: .\" $OpenBSD: ssh_config.5,v 1.38 2004/06/26 09:11:14 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.
66: The configuration files contain sections bracketed by
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
123: (Use IPv4 only) or
124: .Dq inet6
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.
1.20.2.2! brad 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.
1.20.2.2! brad 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
! 261: (the default).
! 262: These sessions will reuse the master instance's network connection rather
! 263: than initiating new ones.
! 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
! 272: for details).
! 273: .It Cm ControlPath
! 274: Specify the path to the control socket used for connection sharing.
! 275: See
! 276: .Cm ControlMaster
! 277: above.
1.1 stevesk 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
1.7 jmc 282: remote machine.
283: The argument must be a port number.
1.15 markus 284: Currently the SOCKS4 and SOCKS5 protocols are supported, and
1.1 stevesk 285: .Nm ssh
1.15 markus 286: will act as a SOCKS server.
1.1 stevesk 287: Multiple forwardings may be specified, and
1.7 jmc 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 .
1.20.2.1 brad 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
1.20.2.1 brad 352: (for the user's X11 authorization database)
1.7 jmc 353: can access the local X11 display through the forwarded connection.
1.20.2.1 brad 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
1.20.2.2! brad 359: If this option is set to
1.20.2.1 brad 360: .Dq yes
361: then remote X11 clients will have full access to the original X11 display.
362: If this option is set to
363: .Dq no
364: then remote X11 clients will be considered untrusted and prevented
365: from stealing or tampering with data belonging to trusted X11
366: clients.
367: .Pp
368: The default is
369: .Dq no .
370: .Pp
371: See the X11 SECURITY extension specification for full details on
372: the restrictions imposed on untrusted clients.
1.1 stevesk 373: .It Cm GatewayPorts
374: Specifies whether remote hosts are allowed to connect to local
375: forwarded ports.
376: By default,
377: .Nm ssh
1.7 jmc 378: binds local port forwardings to the loopback address.
379: This prevents other remote hosts from connecting to forwarded ports.
1.1 stevesk 380: .Cm GatewayPorts
381: can be used to specify that
382: .Nm ssh
383: should bind local port forwardings to the wildcard address,
384: thus allowing remote hosts to connect to forwarded ports.
385: The argument must be
386: .Dq yes
387: or
388: .Dq no .
389: The default is
390: .Dq no .
391: .It Cm GlobalKnownHostsFile
392: Specifies a file to use for the global
393: host key database instead of
394: .Pa /etc/ssh/ssh_known_hosts .
1.18 markus 395: .It Cm GSSAPIAuthentication
1.20.2.1 brad 396: Specifies whether user authentication based on GSSAPI is allowed.
1.20 jmc 397: The default is
1.20.2.1 brad 398: .Dq no .
1.18 markus 399: Note that this option applies to protocol version 2 only.
400: .It Cm GSSAPIDelegateCredentials
401: Forward (delegate) credentials to the server.
402: The default is
403: .Dq no .
404: Note that this option applies to protocol version 2 only.
1.1 stevesk 405: .It Cm HostbasedAuthentication
406: Specifies whether to try rhosts based authentication with public key
407: authentication.
408: The argument must be
409: .Dq yes
410: or
411: .Dq no .
412: The default is
413: .Dq no .
414: This option applies to protocol version 2 only and
415: is similar to
416: .Cm RhostsRSAAuthentication .
417: .It Cm HostKeyAlgorithms
418: Specifies the protocol version 2 host key algorithms
419: that the client wants to use in order of preference.
420: The default for this option is:
421: .Dq ssh-rsa,ssh-dss .
422: .It Cm HostKeyAlias
423: Specifies an alias that should be used instead of the
424: real host name when looking up or saving the host key
425: in the host key database files.
426: This option is useful for tunneling ssh connections
427: or for multiple servers running on a single host.
428: .It Cm HostName
429: Specifies the real host name to log into.
430: This can be used to specify nicknames or abbreviations for hosts.
431: Default is the name given on the command line.
432: Numeric IP addresses are also permitted (both on the command line and in
433: .Cm HostName
434: specifications).
435: .It Cm IdentityFile
436: Specifies a file from which the user's RSA or DSA authentication identity
1.11 jmc 437: is read.
438: The default is
1.1 stevesk 439: .Pa $HOME/.ssh/identity
440: for protocol version 1, and
441: .Pa $HOME/.ssh/id_rsa
442: and
443: .Pa $HOME/.ssh/id_dsa
444: for protocol version 2.
445: Additionally, any identities represented by the authentication agent
446: will be used for authentication.
447: The file name may use the tilde
448: syntax to refer to a user's home directory.
449: It is possible to have
450: multiple identity files specified in configuration files; all these
451: identities will be tried in sequence.
1.20.2.2! brad 452: .It Cm IdentitiesOnly
! 453: Specifies that
! 454: .Nm ssh
! 455: should only use the authentication identity files configured in the
! 456: .Nm
! 457: files,
! 458: even if the
! 459: .Nm ssh-agent
! 460: offers more identities.
! 461: The argument to this keyword must be
! 462: .Dq yes
! 463: or
! 464: .Dq no .
! 465: This option is intented for situations where
! 466: .Nm ssh-agent
! 467: offers many different identities.
! 468: The default is
! 469: .Dq no .
1.1 stevesk 470: .It Cm LocalForward
471: Specifies that a TCP/IP port on the local machine be forwarded over
472: the secure channel to the specified host and port from the remote machine.
473: The first argument must be a port number, and the second must be
474: .Ar host:port .
475: IPv6 addresses can be specified with an alternative syntax:
476: .Ar host/port .
477: Multiple forwardings may be specified, and additional
478: forwardings can be given on the command line.
479: Only the superuser can forward privileged ports.
480: .It Cm LogLevel
481: Gives the verbosity level that is used when logging messages from
482: .Nm ssh .
483: The possible values are:
484: QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3.
1.7 jmc 485: The default is INFO.
486: DEBUG and DEBUG1 are equivalent.
487: DEBUG2 and DEBUG3 each specify higher levels of verbose output.
1.1 stevesk 488: .It Cm MACs
489: Specifies the MAC (message authentication code) algorithms
490: in order of preference.
491: The MAC algorithm is used in protocol version 2
492: for data integrity protection.
493: Multiple algorithms must be comma-separated.
494: The default is
495: .Dq hmac-md5,hmac-sha1,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 .
496: .It Cm NoHostAuthenticationForLocalhost
497: This option can be used if the home directory is shared across machines.
498: In this case localhost will refer to a different machine on each of
499: the machines and the user will get many warnings about changed host keys.
500: However, this option disables host authentication for localhost.
501: The argument to this keyword must be
502: .Dq yes
503: or
504: .Dq no .
505: The default is to check the host key for localhost.
506: .It Cm NumberOfPasswordPrompts
507: Specifies the number of password prompts before giving up.
508: The argument to this keyword must be an integer.
509: Default is 3.
510: .It Cm PasswordAuthentication
511: Specifies whether to use password authentication.
512: The argument to this keyword must be
513: .Dq yes
514: or
515: .Dq no .
516: The default is
517: .Dq yes .
518: .It Cm Port
519: Specifies the port number to connect on the remote host.
520: Default is 22.
521: .It Cm PreferredAuthentications
522: Specifies the order in which the client should try protocol 2
1.11 jmc 523: authentication methods.
524: This allows a client to prefer one method (e.g.
1.1 stevesk 525: .Cm keyboard-interactive )
526: over another method (e.g.
527: .Cm password )
528: The default for this option is:
529: .Dq hostbased,publickey,keyboard-interactive,password .
530: .It Cm Protocol
531: Specifies the protocol versions
532: .Nm ssh
533: should support in order of preference.
534: The possible values are
535: .Dq 1
536: and
537: .Dq 2 .
538: Multiple versions must be comma-separated.
539: The default is
540: .Dq 2,1 .
541: This means that
542: .Nm ssh
543: tries version 2 and falls back to version 1
544: if version 2 is not available.
545: .It Cm ProxyCommand
546: Specifies the command to use to connect to the server.
547: The command
548: string extends to the end of the line, and is executed with
549: .Pa /bin/sh .
550: In the command string,
551: .Ql %h
552: will be substituted by the host name to
553: connect and
554: .Ql %p
555: by the port.
556: The command can be basically anything,
557: and should read from its standard input and write to its standard output.
558: It should eventually connect an
559: .Xr sshd 8
560: server running on some machine, or execute
561: .Ic sshd -i
562: somewhere.
563: Host key management will be done using the
564: HostName of the host being connected (defaulting to the name typed by
565: the user).
1.7 jmc 566: Setting the command to
567: .Dq none
1.6 markus 568: disables this option entirely.
1.1 stevesk 569: Note that
570: .Cm CheckHostIP
571: is not available for connects with a proxy command.
572: .Pp
573: .It Cm PubkeyAuthentication
574: Specifies whether to try public key authentication.
575: The argument to this keyword must be
576: .Dq yes
577: or
578: .Dq no .
579: The default is
580: .Dq yes .
581: This option applies to protocol version 2 only.
582: .It Cm RemoteForward
583: Specifies that a TCP/IP port on the remote machine be forwarded over
584: the secure channel to the specified host and port from the local machine.
585: The first argument must be a port number, and the second must be
586: .Ar host:port .
587: IPv6 addresses can be specified with an alternative syntax:
588: .Ar host/port .
589: Multiple forwardings may be specified, and additional
590: forwardings can be given on the command line.
591: Only the superuser can forward privileged ports.
592: .It Cm RhostsRSAAuthentication
593: Specifies whether to try rhosts based authentication with RSA host
594: authentication.
595: The argument must be
596: .Dq yes
597: or
598: .Dq no .
599: The default is
600: .Dq no .
601: This option applies to protocol version 1 only and requires
602: .Nm ssh
603: to be setuid root.
604: .It Cm RSAAuthentication
605: Specifies whether to try RSA authentication.
606: The argument to this keyword must be
607: .Dq yes
608: or
609: .Dq no .
610: RSA authentication will only be
611: attempted if the identity file exists, or an authentication agent is
612: running.
613: The default is
614: .Dq yes .
615: Note that this option applies to protocol version 1 only.
1.20.2.2! brad 616: .It Cm SendEnv
! 617: Specifies what variables from the local
! 618: .Xr environ 7
! 619: should be sent to the server.
! 620: Note that environment passing is only supported for protocol 2, the
! 621: server must also support it, and the server must be configured to
! 622: accept these environment variables.
! 623: Refer to
! 624: .Cm AcceptEnv
! 625: in
! 626: .Xr sshd_config 5
! 627: for how to configure the server.
! 628: Variables are specified by name, which may contain the wildcard characters
! 629: .Ql \&*
! 630: and
! 631: .Ql \&? .
! 632: Multiple environment variables may be separated by whitespace or spread
! 633: across multiple
! 634: .Cm SendEnv
! 635: directives.
! 636: The default is not to send any environment variables.
1.20.2.1 brad 637: .It Cm ServerAliveInterval
638: Sets a timeout interval in seconds after which if no data has been received
639: from the server,
640: .Nm ssh
641: will send a message through the encrypted
642: channel to request a response from the server.
643: The default
644: is 0, indicating that these messages will not be sent to the server.
645: This option applies to protocol version 2 only.
646: .It Cm ServerAliveCountMax
647: Sets the number of server alive messages (see above) which may be
648: sent without
649: .Nm ssh
650: receiving any messages back from the server.
651: If this threshold is reached while server alive messages are being sent,
652: .Nm ssh
653: will disconnect from the server, terminating the session.
654: It is important to note that the use of server alive messages is very
655: different from
656: .Cm TCPKeepAlive
657: (below).
658: The server alive messages are sent through the encrypted channel
659: and therefore will not be spoofable.
660: The TCP keepalive option enabled by
661: .Cm TCPKeepAlive
662: is spoofable.
663: The server alive mechanism is valuable when the client or
664: server depend on knowing when a connection has become inactive.
665: .Pp
666: The default value is 3.
667: If, for example,
668: .Cm ServerAliveInterval
669: (above) is set to 15, and
670: .Cm ServerAliveCountMax
671: is left at the default, if the server becomes unresponsive ssh
672: will disconnect after approximately 45 seconds.
1.1 stevesk 673: .It Cm SmartcardDevice
1.11 jmc 674: Specifies which smartcard device to use.
675: The argument to this keyword is the device
1.1 stevesk 676: .Nm ssh
677: should use to communicate with a smartcard used for storing the user's
1.11 jmc 678: private RSA key.
679: By default, no device is specified and smartcard support is not activated.
1.1 stevesk 680: .It Cm StrictHostKeyChecking
681: If this flag is set to
682: .Dq yes ,
683: .Nm ssh
684: will never automatically add host keys to the
685: .Pa $HOME/.ssh/known_hosts
686: file, and refuses to connect to hosts whose host key has changed.
687: This provides maximum protection against trojan horse attacks,
688: however, can be annoying when the
689: .Pa /etc/ssh/ssh_known_hosts
690: file is poorly maintained, or connections to new hosts are
691: frequently made.
692: This option forces the user to manually
693: add all new hosts.
694: If this flag is set to
695: .Dq no ,
696: .Nm ssh
697: will automatically add new host keys to the
698: user known hosts files.
699: If this flag is set to
700: .Dq ask ,
701: new host keys
702: will be added to the user known host files only after the user
703: has confirmed that is what they really want to do, and
704: .Nm ssh
705: will refuse to connect to hosts whose host key has changed.
706: The host keys of
707: known hosts will be verified automatically in all cases.
708: The argument must be
709: .Dq yes ,
710: .Dq no
711: or
712: .Dq ask .
713: The default is
714: .Dq ask .
1.20.2.1 brad 715: .It Cm TCPKeepAlive
716: Specifies whether the system should send TCP keepalive messages to the
717: other side.
718: If they are sent, death of the connection or crash of one
719: of the machines will be properly noticed.
720: However, this means that
721: connections will die if the route is down temporarily, and some people
722: find it annoying.
723: .Pp
724: The default is
725: .Dq yes
726: (to send TCP keepalive messages), and the client will notice
727: if the network goes down or the remote host dies.
728: This is important in scripts, and many users want it too.
729: .Pp
730: To disable TCP keepalive messages, the value should be set to
731: .Dq no .
1.1 stevesk 732: .It Cm UsePrivilegedPort
733: Specifies whether to use a privileged port for outgoing connections.
734: The argument must be
735: .Dq yes
736: or
737: .Dq no .
738: The default is
739: .Dq no .
1.4 stevesk 740: If set to
741: .Dq yes
742: .Nm ssh
743: must be setuid root.
1.1 stevesk 744: Note that this option must be set to
745: .Dq yes
1.17 markus 746: for
1.1 stevesk 747: .Cm RhostsRSAAuthentication
1.17 markus 748: with older servers.
1.1 stevesk 749: .It Cm User
750: Specifies the user to log in as.
751: This can be useful when a different user name is used on different machines.
752: This saves the trouble of
753: having to remember to give the user name on the command line.
754: .It Cm UserKnownHostsFile
755: Specifies a file to use for the user
756: host key database instead of
757: .Pa $HOME/.ssh/known_hosts .
1.8 jakob 758: .It Cm VerifyHostKeyDNS
759: Specifies whether to verify the remote key using DNS and SSHFP resource
760: records.
1.20.2.1 brad 761: If this option is set to
762: .Dq yes ,
763: the client will implicitly trust keys that match a secure fingerprint
764: from DNS.
765: Insecure fingerprints will be handled as if this option was set to
766: .Dq ask .
767: If this option is set to
768: .Dq ask ,
769: information on fingerprint match will be displayed, but the user will still
770: need to confirm new host keys according to the
771: .Cm StrictHostKeyChecking
772: option.
773: The argument must be
774: .Dq yes ,
775: .Dq no
776: or
777: .Dq ask .
1.8 jakob 778: The default is
779: .Dq no .
1.12 jakob 780: Note that this option applies to protocol version 2 only.
1.1 stevesk 781: .It Cm XAuthLocation
1.5 stevesk 782: Specifies the full pathname of the
1.1 stevesk 783: .Xr xauth 1
784: program.
785: The default is
786: .Pa /usr/X11R6/bin/xauth .
787: .El
788: .Sh FILES
789: .Bl -tag -width Ds
790: .It Pa $HOME/.ssh/config
791: This is the per-user configuration file.
792: The format of this file is described above.
793: This file is used by the
794: .Nm ssh
795: client.
1.20.2.2! brad 796: Because of the potential for abuse, this file must have strict permissions:
! 797: read/write for the user, and not accessible by others.
1.1 stevesk 798: .It Pa /etc/ssh/ssh_config
799: Systemwide configuration file.
800: This file provides defaults for those
801: values that are not specified in the user's configuration file, and
802: for those users who do not have a configuration file.
803: This file must be world-readable.
804: .El
1.13 jmc 805: .Sh SEE ALSO
806: .Xr ssh 1
1.1 stevesk 807: .Sh AUTHORS
808: OpenSSH is a derivative of the original and free
809: ssh 1.2.12 release by Tatu Ylonen.
810: Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos,
811: Theo de Raadt and Dug Song
812: removed many bugs, re-added newer features and
813: created OpenSSH.
814: Markus Friedl contributed the support for SSH
815: protocol versions 1.5 and 2.0.
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