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1SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5)
2
3NAME
4 ssh_config - OpenSSH SSH client configuration files
5
6SYNOPSIS
7 ~/.ssh/config
8 /etc/ssh/ssh_config
9
10DESCRIPTION
11 ssh(1) obtains configuration data from the following sources in the
12 following order:
13
14 1. command-line options
15 2. user's configuration file (~/.ssh/config)
16 3. system-wide configuration file (/etc/ssh/ssh_config)
17
18 For each parameter, the first obtained value will be used. The
19 configuration files contain sections separated by ``Host''
20 specifications, and that section is only applied for hosts that match one
21 of the patterns given in the specification. The matched host name is the
22 one given on the command line.
23
24 Since the first obtained value for each parameter is used, more host-
25 specific declarations should be given near the beginning of the file, and
26 general defaults at the end.
27
28 The configuration file has the following format:
29
30 Empty lines and lines starting with `#' are comments. Otherwise a line
31 is of the format ``keyword arguments''. Configuration options may be
32 separated by whitespace or optional whitespace and exactly one `='; the
33 latter format is useful to avoid the need to quote whitespace when
34 specifying configuration options using the ssh, scp, and sftp -o option.
35 Arguments may optionally be enclosed in double quotes (") in order to
36 represent arguments containing spaces.
37
38 The possible keywords and their meanings are as follows (note that
39 keywords are case-insensitive and arguments are case-sensitive):
40
41 Host Restricts the following declarations (up to the next Host
42 keyword) to be only for those hosts that match one of the
43 patterns given after the keyword. If more than one pattern is
44 provided, they should be separated by whitespace. A single `*'
45 as a pattern can be used to provide global defaults for all
46 hosts. The host is the hostname argument given on the command
47 line (i.e. the name is not converted to a canonicalized host name
48 before matching).
49
50 A pattern entry may be negated by prefixing it with an
51 exclamation mark (`!'). If a negated entry is matched, then the
52 Host entry is ignored, regardless of whether any other patterns
53 on the line match. Negated matches are therefore useful to
54 provide exceptions for wildcard matches.
55
56 See PATTERNS for more information on patterns.
57
58 AddressFamily
59 Specifies which address family to use when connecting. Valid
60 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6''
61 (use IPv6 only).
62
63 BatchMode
64 If set to ``yes'', passphrase/password querying will be disabled.
65 This option is useful in scripts and other batch jobs where no
66 user is present to supply the password. The argument must be
67 ``yes'' or ``no''. The default is ``no''.
68
69 BindAddress
70 Use the specified address on the local machine as the source
71 address of the connection. Only useful on systems with more than
72 one address. Note that this option does not work if
73 UsePrivilegedPort is set to ``yes''.
74
75 ChallengeResponseAuthentication
76 Specifies whether to use challenge-response authentication. The
77 argument to this keyword must be ``yes'' or ``no''. The default
78 is ``yes''.
79
80 CheckHostIP
81 If this flag is set to ``yes'', ssh(1) will additionally check
82 the host IP address in the known_hosts file. This allows ssh to
83 detect if a host key changed due to DNS spoofing. If the option
84 is set to ``no'', the check will not be executed. The default is
85 ``yes''.
86
87 Cipher Specifies the cipher to use for encrypting the session in
88 protocol version 1. Currently, ``blowfish'', ``3des'', and
89 ``des'' are supported. des is only supported in the ssh(1)
90 client for interoperability with legacy protocol 1
91 implementations that do not support the 3des cipher. Its use is
92 strongly discouraged due to cryptographic weaknesses. The
93 default is ``3des''.
94
95 Ciphers
96 Specifies the ciphers allowed for protocol version 2 in order of
97 preference. Multiple ciphers must be comma-separated. The
98 supported ciphers are ``3des-cbc'', ``aes128-cbc'',
99 ``aes192-cbc'', ``aes256-cbc'', ``aes128-ctr'', ``aes192-ctr'',
100 ``aes256-ctr'', ``arcfour128'', ``arcfour256'', ``arcfour'',
101 ``blowfish-cbc'', and ``cast128-cbc''. The default is:
102
103 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
104 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
105 aes256-cbc,arcfour
106
107 ClearAllForwardings
108 Specifies that all local, remote, and dynamic port forwardings
109 specified in the configuration files or on the command line be
110 cleared. This option is primarily useful when used from the
111 ssh(1) command line to clear port forwardings set in
112 configuration files, and is automatically set by scp(1) and
113 sftp(1). The argument must be ``yes'' or ``no''. The default is
114 ``no''.
115
116 Compression
117 Specifies whether to use compression. The argument must be
118 ``yes'' or ``no''. The default is ``no''.
119
120 CompressionLevel
121 Specifies the compression level to use if compression is enabled.
122 The argument must be an integer from 1 (fast) to 9 (slow, best).
123 The default level is 6, which is good for most applications. The
124 meaning of the values is the same as in gzip(1). Note that this
125 option applies to protocol version 1 only.
126
127 ConnectionAttempts
128 Specifies the number of tries (one per second) to make before
129 exiting. The argument must be an integer. This may be useful in
130 scripts if the connection sometimes fails. The default is 1.
131
132 ConnectTimeout
133 Specifies the timeout (in seconds) used when connecting to the
134 SSH server, instead of using the default system TCP timeout.
135 This value is used only when the target is down or really
136 unreachable, not when it refuses the connection.
137
138 ControlMaster
139 Enables the sharing of multiple sessions over a single network
140 connection. When set to ``yes'', ssh(1) will listen for
141 connections on a control socket specified using the ControlPath
142 argument. Additional sessions can connect to this socket using
143 the same ControlPath with ControlMaster set to ``no'' (the
144 default). These sessions will try to reuse the master instance's
145 network connection rather than initiating new ones, but will fall
146 back to connecting normally if the control socket does not exist,
147 or is not listening.
148
149 Setting this to ``ask'' will cause ssh to listen for control
150 connections, but require confirmation using the SSH_ASKPASS
151 program before they are accepted (see ssh-add(1) for details).
152 If the ControlPath cannot be opened, ssh will continue without
153 connecting to a master instance.
154
155 X11 and ssh-agent(1) forwarding is supported over these
156 multiplexed connections, however the display and agent forwarded
157 will be the one belonging to the master connection i.e. it is not
158 possible to forward multiple displays or agents.
159
160 Two additional options allow for opportunistic multiplexing: try
161 to use a master connection but fall back to creating a new one if
162 one does not already exist. These options are: ``auto'' and
163 ``autoask''. The latter requires confirmation like the ``ask''
164 option.
165
166 ControlPath
167 Specify the path to the control socket used for connection
168 sharing as described in the ControlMaster section above or the
169 string ``none'' to disable connection sharing. In the path, `%L'
170 will be substituted by the first component of the local host
171 name, `%l' will be substituted by the local host name (including
172 any domain name), `%h' will be substituted by the target host
173 name, `%n' will be substituted by the original target host name
174 specified on the command line, `%p' the port, `%r' by the remote
175 login username, and `%u' by the username of the user running
176 ssh(1). It is recommended that any ControlPath used for
177 opportunistic connection sharing include at least %h, %p, and %r.
178 This ensures that shared connections are uniquely identified.
179
180 ControlPersist
181 When used in conjunction with ControlMaster, specifies that the
182 master connection should remain open in the background (waiting
183 for future client connections) after the initial client
184 connection has been closed. If set to ``no'', then the master
185 connection will not be placed into the background, and will close
186 as soon as the initial client connection is closed. If set to
187 ``yes'', then the master connection will remain in the background
188 indefinitely (until killed or closed via a mechanism such as the
189 ssh(1) ``-O exit'' option). If set to a time in seconds, or a
190 time in any of the formats documented in sshd_config(5), then the
191 backgrounded master connection will automatically terminate after
192 it has remained idle (with no client connections) for the
193 specified time.
194
195 DynamicForward
196 Specifies that a TCP port on the local machine be forwarded over
197 the secure channel, and the application protocol is then used to
198 determine where to connect to from the remote machine.
199
200 The argument must be [bind_address:]port. IPv6 addresses can be
201 specified by enclosing addresses in square brackets. By default,
202 the local port is bound in accordance with the GatewayPorts
203 setting. However, an explicit bind_address may be used to bind
204 the connection to a specific address. The bind_address of
205 ``localhost'' indicates that the listening port be bound for
206 local use only, while an empty address or `*' indicates that the
207 port should be available from all interfaces.
208
209 Currently the SOCKS4 and SOCKS5 protocols are supported, and
210 ssh(1) will act as a SOCKS server. Multiple forwardings may be
211 specified, and additional forwardings can be given on the command
212 line. Only the superuser can forward privileged ports.
213
214 EnableSSHKeysign
215 Setting this option to ``yes'' in the global client configuration
216 file /etc/ssh/ssh_config enables the use of the helper program
217 ssh-keysign(8) during HostbasedAuthentication. The argument must
218 be ``yes'' or ``no''. The default is ``no''. This option should
219 be placed in the non-hostspecific section. See ssh-keysign(8)
220 for more information.
221
222 EscapeChar
223 Sets the escape character (default: `~'). The escape character
224 can also be set on the command line. The argument should be a
225 single character, `^' followed by a letter, or ``none'' to
226 disable the escape character entirely (making the connection
227 transparent for binary data).
228
229 ExitOnForwardFailure
230 Specifies whether ssh(1) should terminate the connection if it
231 cannot set up all requested dynamic, tunnel, local, and remote
232 port forwardings. The argument must be ``yes'' or ``no''. The
233 default is ``no''.
234
235 ForwardAgent
236 Specifies whether the connection to the authentication agent (if
237 any) will be forwarded to the remote machine. The argument must
238 be ``yes'' or ``no''. The default is ``no''.
239
240 Agent forwarding should be enabled with caution. Users with the
241 ability to bypass file permissions on the remote host (for the
242 agent's Unix-domain socket) can access the local agent through
243 the forwarded connection. An attacker cannot obtain key material
244 from the agent, however they can perform operations on the keys
245 that enable them to authenticate using the identities loaded into
246 the agent.
247
248 ForwardX11
249 Specifies whether X11 connections will be automatically
250 redirected over the secure channel and DISPLAY set. The argument
251 must be ``yes'' or ``no''. The default is ``no''.
252
253 X11 forwarding should be enabled with caution. Users with the
254 ability to bypass file permissions on the remote host (for the
255 user's X11 authorization database) can access the local X11
256 display through the forwarded connection. An attacker may then
257 be able to perform activities such as keystroke monitoring if the
258 ForwardX11Trusted option is also enabled.
259
260 ForwardX11Timeout
261 Specify a timeout for untrusted X11 forwarding using the format
262 described in the TIME FORMATS section of sshd_config(5). X11
263 connections received by ssh(1) after this time will be refused.
264 The default is to disable untrusted X11 forwarding after twenty
265 minutes has elapsed.
266
267 ForwardX11Trusted
268 If this option is set to ``yes'', remote X11 clients will have
269 full access to the original X11 display.
270
271 If this option is set to ``no'', remote X11 clients will be
272 considered untrusted and prevented from stealing or tampering
273 with data belonging to trusted X11 clients. Furthermore, the
274 xauth(1) token used for the session will be set to expire after
275 20 minutes. Remote clients will be refused access after this
276 time.
277
278 The default is ``no''.
279
280 See the X11 SECURITY extension specification for full details on
281 the restrictions imposed on untrusted clients.
282
283 GatewayPorts
284 Specifies whether remote hosts are allowed to connect to local
285 forwarded ports. By default, ssh(1) binds local port forwardings
286 to the loopback address. This prevents other remote hosts from
287 connecting to forwarded ports. GatewayPorts can be used to
288 specify that ssh should bind local port forwardings to the
289 wildcard address, thus allowing remote hosts to connect to
290 forwarded ports. The argument must be ``yes'' or ``no''. The
291 default is ``no''.
292
293 GlobalKnownHostsFile
294 Specifies one or more files to use for the global host key
295 database, separated by whitespace. The default is
296 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
297
298 GSSAPIAuthentication
299 Specifies whether user authentication based on GSSAPI is allowed.
300 The default is ``no''. Note that this option applies to protocol
301 version 2 only.
302
303 GSSAPIDelegateCredentials
304 Forward (delegate) credentials to the server. The default is
305 ``no''. Note that this option applies to protocol version 2
306 only.
307
308 HashKnownHosts
309 Indicates that ssh(1) should hash host names and addresses when
310 they are added to ~/.ssh/known_hosts. These hashed names may be
311 used normally by ssh(1) and sshd(8), but they do not reveal
312 identifying information should the file's contents be disclosed.
313 The default is ``no''. Note that existing names and addresses in
314 known hosts files will not be converted automatically, but may be
315 manually hashed using ssh-keygen(1).
316
317 HostbasedAuthentication
318 Specifies whether to try rhosts based authentication with public
319 key authentication. The argument must be ``yes'' or ``no''. The
320 default is ``no''. This option applies to protocol version 2
321 only and is similar to RhostsRSAAuthentication.
322
323 HostKeyAlgorithms
324 Specifies the protocol version 2 host key algorithms that the
325 client wants to use in order of preference. The default for this
326 option is:
327
328 ecdsa-sha2-nistp256-cert-v01@openssh.com,
329 ecdsa-sha2-nistp384-cert-v01@openssh.com,
330 ecdsa-sha2-nistp521-cert-v01@openssh.com,
331 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
332 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
333 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
334 ssh-rsa,ssh-dss
335
336 If hostkeys are known for the destination host then this default
337 is modified to prefer their algorithms.
338
339 HostKeyAlias
340 Specifies an alias that should be used instead of the real host
341 name when looking up or saving the host key in the host key
342 database files. This option is useful for tunneling SSH
343 connections or for multiple servers running on a single host.
344
345 HostName
346 Specifies the real host name to log into. This can be used to
347 specify nicknames or abbreviations for hosts. If the hostname
348 contains the character sequence `%h', then this will be replaced
349 with the host name specified on the command line (this is useful
350 for manipulating unqualified names). The default is the name
351 given on the command line. Numeric IP addresses are also
352 permitted (both on the command line and in HostName
353 specifications).
354
355 IdentitiesOnly
356 Specifies that ssh(1) should only use the authentication identity
357 files configured in the ssh_config files, even if ssh-agent(1)
358 offers more identities. The argument to this keyword must be
359 ``yes'' or ``no''. This option is intended for situations where
360 ssh-agent offers many different identities. The default is
361 ``no''.
362
363 IdentityFile
364 Specifies a file from which the user's DSA, ECDSA or DSA
365 authentication identity is read. The default is ~/.ssh/identity
366 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa and
367 ~/.ssh/id_rsa for protocol version 2. Additionally, any
368 identities represented by the authentication agent will be used
369 for authentication. ssh(1) will try to load certificate
370 information from the filename obtained by appending -cert.pub to
371 the path of a specified IdentityFile.
372
373 The file name may use the tilde syntax to refer to a user's home
374 directory or one of the following escape characters: `%d' (local
375 user's home directory), `%u' (local user name), `%l' (local host
376 name), `%h' (remote host name) or `%r' (remote user name).
377
378 It is possible to have multiple identity files specified in
379 configuration files; all these identities will be tried in
380 sequence. Multiple IdentityFile directives will add to the list
381 of identities tried (this behaviour differs from that of other
382 configuration directives).
383
384 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
385 Accepted values are ``af11'', ``af12'', ``af13'', ``af14'',
386 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'',
387 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'',
388 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'',
389 ``reliability'', or a numeric value. This option may take one or
390 two arguments, separated by whitespace. If one argument is
391 specified, it is used as the packet class unconditionally. If
392 two values are specified, the first is automatically selected for
393 interactive sessions and the second for non-interactive sessions.
394 The default is ``lowdelay'' for interactive sessions and
395 ``throughput'' for non-interactive sessions.
396
397 KbdInteractiveAuthentication
398 Specifies whether to use keyboard-interactive authentication.
399 The argument to this keyword must be ``yes'' or ``no''. The
400 default is ``yes''.
401
402 KbdInteractiveDevices
403 Specifies the list of methods to use in keyboard-interactive
404 authentication. Multiple method names must be comma-separated.
405 The default is to use the server specified list. The methods
406 available vary depending on what the server supports. For an
407 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'',
408 and ``skey''.
409
410 KexAlgorithms
411 Specifies the available KEX (Key Exchange) algorithms. Multiple
412 algorithms must be comma-separated. The default is:
413
414 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
415 diffie-hellman-group-exchange-sha256,
416 diffie-hellman-group-exchange-sha1,
417 diffie-hellman-group14-sha1,
418 diffie-hellman-group1-sha1
419
420 LocalCommand
421 Specifies a command to execute on the local machine after
422 successfully connecting to the server. The command string
423 extends to the end of the line, and is executed with the user's
424 shell. The following escape character substitutions will be
425 performed: `%d' (local user's home directory), `%h' (remote host
426 name), `%l' (local host name), `%n' (host name as provided on the
427 command line), `%p' (remote port), `%r' (remote user name) or
428 `%u' (local user name).
429
430 The command is run synchronously and does not have access to the
431 session of the ssh(1) that spawned it. It should not be used for
432 interactive commands.
433
434 This directive is ignored unless PermitLocalCommand has been
435 enabled.
436
437 LocalForward
438 Specifies that a TCP port on the local machine be forwarded over
439 the secure channel to the specified host and port from the remote
440 machine. The first argument must be [bind_address:]port and the
441 second argument must be host:hostport. IPv6 addresses can be
442 specified by enclosing addresses in square brackets. Multiple
443 forwardings may be specified, and additional forwardings can be
444 given on the command line. Only the superuser can forward
445 privileged ports. By default, the local port is bound in
446 accordance with the GatewayPorts setting. However, an explicit
447 bind_address may be used to bind the connection to a specific
448 address. The bind_address of ``localhost'' indicates that the
449 listening port be bound for local use only, while an empty
450 address or `*' indicates that the port should be available from
451 all interfaces.
452
453 LogLevel
454 Gives the verbosity level that is used when logging messages from
455 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
456 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
457 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
458 higher levels of verbose output.
459
460 MACs Specifies the MAC (message authentication code) algorithms in
461 order of preference. The MAC algorithm is used in protocol
462 version 2 for data integrity protection. Multiple algorithms
463 must be comma-separated. The default is:
464
465 hmac-md5,hmac-sha1,umac-64@openssh.com,
466 hmac-ripemd160,hmac-sha1-96,hmac-md5-96,
467 hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,
468 hmac-sha2-512-96
469
470 NoHostAuthenticationForLocalhost
471 This option can be used if the home directory is shared across
472 machines. In this case localhost will refer to a different
473 machine on each of the machines and the user will get many
474 warnings about changed host keys. However, this option disables
475 host authentication for localhost. The argument to this keyword
476 must be ``yes'' or ``no''. The default is to check the host key
477 for localhost.
478
479 NumberOfPasswordPrompts
480 Specifies the number of password prompts before giving up. The
481 argument to this keyword must be an integer. The default is 3.
482
483 PasswordAuthentication
484 Specifies whether to use password authentication. The argument
485 to this keyword must be ``yes'' or ``no''. The default is
486 ``yes''.
487
488 PermitLocalCommand
489 Allow local command execution via the LocalCommand option or
490 using the !command escape sequence in ssh(1). The argument must
491 be ``yes'' or ``no''. The default is ``no''.
492
493 PKCS11Provider
494 Specifies which PKCS#11 provider to use. The argument to this
495 keyword is the PKCS#11 shared library ssh(1) should use to
496 communicate with a PKCS#11 token providing the user's private RSA
497 key.
498
499 Port Specifies the port number to connect on the remote host. The
500 default is 22.
501
502 PreferredAuthentications
503 Specifies the order in which the client should try protocol 2
504 authentication methods. This allows a client to prefer one
505 method (e.g. keyboard-interactive) over another method (e.g.
506 password). The default is:
507
508 gssapi-with-mic,hostbased,publickey,
509 keyboard-interactive,password
510
511 Protocol
512 Specifies the protocol versions ssh(1) should support in order of
513 preference. The possible values are `1' and `2'. Multiple
514 versions must be comma-separated. When this option is set to
515 ``2,1'' ssh will try version 2 and fall back to version 1 if
516 version 2 is not available. The default is `2'.
517
518 ProxyCommand
519 Specifies the command to use to connect to the server. The
520 command string extends to the end of the line, and is executed
521 with the user's shell. In the command string, any occurrence of
522 `%h' will be substituted by the host name to connect, `%p' by the
523 port, and `%r' by the remote user name. The command can be
524 basically anything, and should read from its standard input and
525 write to its standard output. It should eventually connect an
526 sshd(8) server running on some machine, or execute sshd -i
527 somewhere. Host key management will be done using the HostName
528 of the host being connected (defaulting to the name typed by the
529 user). Setting the command to ``none'' disables this option
530 entirely. Note that CheckHostIP is not available for connects
531 with a proxy command.
532
533 This directive is useful in conjunction with nc(1) and its proxy
534 support. For example, the following directive would connect via
535 an HTTP proxy at 192.0.2.0:
536
537 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
538
539 PubkeyAuthentication
540 Specifies whether to try public key authentication. The argument
541 to this keyword must be ``yes'' or ``no''. The default is
542 ``yes''. This option applies to protocol version 2 only.
543
544 RekeyLimit
545 Specifies the maximum amount of data that may be transmitted
546 before the session key is renegotiated. The argument is the
547 number of bytes, with an optional suffix of `K', `M', or `G' to
548 indicate Kilobytes, Megabytes, or Gigabytes, respectively. The
549 default is between `1G' and `4G', depending on the cipher. This
550 option applies to protocol version 2 only.
551
552 RemoteForward
553 Specifies that a TCP port on the remote machine be forwarded over
554 the secure channel to the specified host and port from the local
555 machine. The first argument must be [bind_address:]port and the
556 second argument must be host:hostport. IPv6 addresses can be
557 specified by enclosing addresses in square brackets. Multiple
558 forwardings may be specified, and additional forwardings can be
559 given on the command line. Privileged ports can be forwarded
560 only when logging in as root on the remote machine.
561
562 If the port argument is `0', the listen port will be dynamically
563 allocated on the server and reported to the client at run time.
564
565 If the bind_address is not specified, the default is to only bind
566 to loopback addresses. If the bind_address is `*' or an empty
567 string, then the forwarding is requested to listen on all
568 interfaces. Specifying a remote bind_address will only succeed
569 if the server's GatewayPorts option is enabled (see
570 sshd_config(5)).
571
572 RequestTTY
573 Specifies whether to request a pseudo-tty for the session. The
574 argument may be one of: ``no'' (never request a TTY), ``yes''
575 (always request a TTY when standard input is a TTY), ``force''
576 (always request a TTY) or ``auto'' (request a TTY when opening a
577 login session). This option mirrors the -t and -T flags for
578 ssh(1).
579
580 RhostsRSAAuthentication
581 Specifies whether to try rhosts based authentication with RSA
582 host authentication. The argument must be ``yes'' or ``no''.
583 The default is ``no''. This option applies to protocol version 1
584 only and requires ssh(1) to be setuid root.
585
586 RSAAuthentication
587 Specifies whether to try RSA authentication. The argument to
588 this keyword must be ``yes'' or ``no''. RSA authentication will
589 only be attempted if the identity file exists, or an
590 authentication agent is running. The default is ``yes''. Note
591 that this option applies to protocol version 1 only.
592
593 SendEnv
594 Specifies what variables from the local environ(7) should be sent
595 to the server. Note that environment passing is only supported
596 for protocol 2. The server must also support it, and the server
597 must be configured to accept these environment variables. Refer
598 to AcceptEnv in sshd_config(5) for how to configure the server.
599 Variables are specified by name, which may contain wildcard
600 characters. Multiple environment variables may be separated by
601 whitespace or spread across multiple SendEnv directives. The
602 default is not to send any environment variables.
603
604 See PATTERNS for more information on patterns.
605
606 ServerAliveCountMax
607 Sets the number of server alive messages (see below) which may be
608 sent without ssh(1) receiving any messages back from the server.
609 If this threshold is reached while server alive messages are
610 being sent, ssh will disconnect from the server, terminating the
611 session. It is important to note that the use of server alive
612 messages is very different from TCPKeepAlive (below). The server
613 alive messages are sent through the encrypted channel and
614 therefore will not be spoofable. The TCP keepalive option
615 enabled by TCPKeepAlive is spoofable. The server alive mechanism
616 is valuable when the client or server depend on knowing when a
617 connection has become inactive.
618
619 The default value is 3. If, for example, ServerAliveInterval
620 (see below) is set to 15 and ServerAliveCountMax is left at the
621 default, if the server becomes unresponsive, ssh will disconnect
622 after approximately 45 seconds. This option applies to protocol
623 version 2 only.
624
625 ServerAliveInterval
626 Sets a timeout interval in seconds after which if no data has
627 been received from the server, ssh(1) will send a message through
628 the encrypted channel to request a response from the server. The
629 default is 0, indicating that these messages will not be sent to
630 the server. This option applies to protocol version 2 only.
631
632 StrictHostKeyChecking
633 If this flag is set to ``yes'', ssh(1) will never automatically
634 add host keys to the ~/.ssh/known_hosts file, and refuses to
635 connect to hosts whose host key has changed. This provides
636 maximum protection against trojan horse attacks, though it can be
637 annoying when the /etc/ssh/ssh_known_hosts file is poorly
638 maintained or when connections to new hosts are frequently made.
639 This option forces the user to manually add all new hosts. If
640 this flag is set to ``no'', ssh will automatically add new host
641 keys to the user known hosts files. If this flag is set to
642 ``ask'', new host keys will be added to the user known host files
643 only after the user has confirmed that is what they really want
644 to do, and ssh will refuse to connect to hosts whose host key has
645 changed. The host keys of known hosts will be verified
646 automatically in all cases. The argument must be ``yes'',
647 ``no'', or ``ask''. The default is ``ask''.
648
649 TCPKeepAlive
650 Specifies whether the system should send TCP keepalive messages
651 to the other side. If they are sent, death of the connection or
652 crash of one of the machines will be properly noticed. However,
653 this means that connections will die if the route is down
654 temporarily, and some people find it annoying.
655
656 The default is ``yes'' (to send TCP keepalive messages), and the
657 client will notice if the network goes down or the remote host
658 dies. This is important in scripts, and many users want it too.
659
660 To disable TCP keepalive messages, the value should be set to
661 ``no''.
662
663 Tunnel Request tun(4) device forwarding between the client and the
664 server. The argument must be ``yes'', ``point-to-point'' (layer
665 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes''
666 requests the default tunnel mode, which is ``point-to-point''.
667 The default is ``no''.
668
669 TunnelDevice
670 Specifies the tun(4) devices to open on the client (local_tun)
671 and the server (remote_tun).
672
673 The argument must be local_tun[:remote_tun]. The devices may be
674 specified by numerical ID or the keyword ``any'', which uses the
675 next available tunnel device. If remote_tun is not specified, it
676 defaults to ``any''. The default is ``any:any''.
677
678 UsePrivilegedPort
679 Specifies whether to use a privileged port for outgoing
680 connections. The argument must be ``yes'' or ``no''. The
681 default is ``no''. If set to ``yes'', ssh(1) must be setuid
682 root. Note that this option must be set to ``yes'' for
683 RhostsRSAAuthentication with older servers.
684
685 User Specifies the user to log in as. This can be useful when a
686 different user name is used on different machines. This saves
687 the trouble of having to remember to give the user name on the
688 command line.
689
690 UserKnownHostsFile
691 Specifies one or more files to use for the user host key
692 database, separated by whitespace. The default is
693 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
694
695 VerifyHostKeyDNS
696 Specifies whether to verify the remote key using DNS and SSHFP
697 resource records. If this option is set to ``yes'', the client
698 will implicitly trust keys that match a secure fingerprint from
699 DNS. Insecure fingerprints will be handled as if this option was
700 set to ``ask''. If this option is set to ``ask'', information on
701 fingerprint match will be displayed, but the user will still need
702 to confirm new host keys according to the StrictHostKeyChecking
703 option. The argument must be ``yes'', ``no'', or ``ask''. The
704 default is ``no''. Note that this option applies to protocol
705 version 2 only.
706
707 See also VERIFYING HOST KEYS in ssh(1).
708
709 VisualHostKey
710 If this flag is set to ``yes'', an ASCII art representation of
711 the remote host key fingerprint is printed in addition to the hex
712 fingerprint string at login and for unknown host keys. If this
713 flag is set to ``no'', no fingerprint strings are printed at
714 login and only the hex fingerprint string will be printed for
715 unknown host keys. The default is ``no''.
716
717 XAuthLocation
718 Specifies the full pathname of the xauth(1) program. The default
719 is /usr/X11R6/bin/xauth.
720
721PATTERNS
722 A pattern consists of zero or more non-whitespace characters, `*' (a
723 wildcard that matches zero or more characters), or `?' (a wildcard that
724 matches exactly one character). For example, to specify a set of
725 declarations for any host in the ``.co.uk'' set of domains, the following
726 pattern could be used:
727
728 Host *.co.uk
729
730 The following pattern would match any host in the 192.168.0.[0-9] network
731 range:
732
733 Host 192.168.0.?
734
735 A pattern-list is a comma-separated list of patterns. Patterns within
736 pattern-lists may be negated by preceding them with an exclamation mark
737 (`!'). For example, to allow a key to be used from anywhere within an
738 organisation except from the ``dialup'' pool, the following entry (in
739 authorized_keys) could be used:
740
741 from="!*.dialup.example.com,*.example.com"
742
743FILES
744 ~/.ssh/config
745 This is the per-user configuration file. The format of this file
746 is described above. This file is used by the SSH client.
747 Because of the potential for abuse, this file must have strict
748 permissions: read/write for the user, and not accessible by
749 others.
750
751 /etc/ssh/ssh_config
752 Systemwide configuration file. This file provides defaults for
753 those values that are not specified in the user's configuration
754 file, and for those users who do not have a configuration file.
755 This file must be world-readable.
756
757SEE ALSO
758 ssh(1)
759
760AUTHORS
761 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
762 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
763 de Raadt and Dug Song removed many bugs, re-added newer features and
764 created OpenSSH. Markus Friedl contributed the support for SSH protocol
765 versions 1.5 and 2.0.
766
767OpenBSD 5.0 August 2, 2011 OpenBSD 5.0
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-11 07:08:30 +0000