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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 or
42 Match 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 Match Restricts the following declarations (up to the next Host or
59 Match keyword) to be used only when the conditions following the
60 Match keyword are satisfied. Match conditions are specified
61 using one or more keyword/criteria pairs or the single token all
62 which matches all criteria. The available keywords are: exec,
63 host, originalhost, user, and localuser.
64
65 The exec keyword executes the specified command under the user's
66 shell. If the command returns a zero exit status then the
67 condition is considered true. Commands containing whitespace
68 characters must be quoted. The following character sequences in
69 the command will be expanded prior to execution: `%L' will be
70 substituted by the first component of the local host name, `%l'
71 will be substituted by the local host name (including any domain
72 name), `%h' will be substituted by the target host name, `%n'
73 will be substituted by the original target host name specified on
74 the command-line, `%p' the destination port, `%r' by the remote
75 login username, and `%u' by the username of the user running
76 ssh(1).
77
78 The other keywords' criteria must be single entries or comma-
79 separated lists and may use the wildcard and negation operators
80 described in the PATTERNS section. The criteria for the host
81 keyword are matched against the target hostname, after any
82 substitution by the Hostname option. The originalhost keyword
83 matches against the hostname as it was specified on the command-
84 line. The user keyword matches against the target username on
85 the remote host. The localuser keyword matches against the name
86 of the local user running ssh(1) (this keyword may be useful in
87 system-wide ssh_config files).
88
89 AddressFamily
90 Specifies which address family to use when connecting. Valid
91 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6''
92 (use IPv6 only).
93
94 BatchMode
95 If set to ``yes'', passphrase/password querying will be disabled.
96 This option is useful in scripts and other batch jobs where no
97 user is present to supply the password. The argument must be
98 ``yes'' or ``no''. The default is ``no''.
99
100 BindAddress
101 Use the specified address on the local machine as the source
102 address of the connection. Only useful on systems with more than
103 one address. Note that this option does not work if
104 UsePrivilegedPort is set to ``yes''.
105
106 CanonicalDomains
107 When CanonicalizeHostname is enabled, this option specifies the
108 list of domain suffixes in which to search for the specified
109 destination host.
110
111 CanonicalizeFallbackLocal
112 Specifies whether to fail with an error when hostname
113 canonicalization fails. The default, ``yes'', will attempt to
114 look up the unqualified hostname using the system resolver's
115 search rules. A value of ``no'' will cause ssh(1) to fail
116 instantly if CanonicalizeHostname is enabled and the target
117 hostname cannot be found in any of the domains specified by
118 CanonicalDomains.
119
120 CanonicalizeHostname
121 Controls whether explicit hostname canonicalization is performed.
122 The default, ``no'', is not to perform any name rewriting and let
123 the system resolver handle all hostname lookups. If set to
124 ``yes'' then, for connections that do not use a ProxyCommand,
125 ssh(1) will attempt to canonicalize the hostname specified on the
126 command line using the CanonicalDomains suffixes and
127 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
128 set to ``always'', then canonicalization is applied to proxied
129 connections too.
130
131 CanonicalizeMaxDots
132 Specifies the maximum number of dot characters in a hostname
133 before canonicalization is disabled. The default, ``1'', allows
134 a single dot (i.e. hostname.subdomain).
135
136 CanonicalizePermittedCNAMEs
137 Specifies rules to determine whether CNAMEs should be followed
138 when canonicalizing hostnames. The rules consist of one or more
139 arguments of source_domain_list:target_domain_list, where
140 source_domain_list is a pattern-list of domains that may follow
141 CNAMEs in canonicalization, and target_domain_list is a pattern-
142 list of domains that they may resolve to.
143
144 For example, ``*.a.example.com:*.b.example.com,*.c.example.com''
145 will allow hostnames matching ``*.a.example.com'' to be
146 canonicalized to names in the ``*.b.example.com'' or
147 ``*.c.example.com'' domains.
148
149 ChallengeResponseAuthentication
150 Specifies whether to use challenge-response authentication. The
151 argument to this keyword must be ``yes'' or ``no''. The default
152 is ``yes''.
153
154 CheckHostIP
155 If this flag is set to ``yes'', ssh(1) will additionally check
156 the host IP address in the known_hosts file. This allows ssh to
157 detect if a host key changed due to DNS spoofing. If the option
158 is set to ``no'', the check will not be executed. The default is
159 ``yes''.
160
161 Cipher Specifies the cipher to use for encrypting the session in
162 protocol version 1. Currently, ``blowfish'', ``3des'', and
163 ``des'' are supported. des is only supported in the ssh(1)
164 client for interoperability with legacy protocol 1
165 implementations that do not support the 3des cipher. Its use is
166 strongly discouraged due to cryptographic weaknesses. The
167 default is ``3des''.
168
169 Ciphers
170 Specifies the ciphers allowed for protocol version 2 in order of
171 preference. Multiple ciphers must be comma-separated. The
172 supported ciphers are:
173
174 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
175 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'',
176 ``aes128-gcm@openssh.com'', ``aes256-gcm@openssh.com'',
177 ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'',
178 ``cast128-cbc'', and ``chacha20-poly1305@openssh.com''.
179
180 The default is:
181
182 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
183 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
184 chacha20-poly1305@openssh.com,
185 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
186 aes256-cbc,arcfour
187
188 The list of available ciphers may also be obtained using the -Q
189 option of ssh(1).
190
191 ClearAllForwardings
192 Specifies that all local, remote, and dynamic port forwardings
193 specified in the configuration files or on the command line be
194 cleared. This option is primarily useful when used from the
195 ssh(1) command line to clear port forwardings set in
196 configuration files, and is automatically set by scp(1) and
197 sftp(1). The argument must be ``yes'' or ``no''. The default is
198 ``no''.
199
200 Compression
201 Specifies whether to use compression. The argument must be
202 ``yes'' or ``no''. The default is ``no''.
203
204 CompressionLevel
205 Specifies the compression level to use if compression is enabled.
206 The argument must be an integer from 1 (fast) to 9 (slow, best).
207 The default level is 6, which is good for most applications. The
208 meaning of the values is the same as in gzip(1). Note that this
209 option applies to protocol version 1 only.
210
211 ConnectionAttempts
212 Specifies the number of tries (one per second) to make before
213 exiting. The argument must be an integer. This may be useful in
214 scripts if the connection sometimes fails. The default is 1.
215
216 ConnectTimeout
217 Specifies the timeout (in seconds) used when connecting to the
218 SSH server, instead of using the default system TCP timeout.
219 This value is used only when the target is down or really
220 unreachable, not when it refuses the connection.
221
222 ControlMaster
223 Enables the sharing of multiple sessions over a single network
224 connection. When set to ``yes'', ssh(1) will listen for
225 connections on a control socket specified using the ControlPath
226 argument. Additional sessions can connect to this socket using
227 the same ControlPath with ControlMaster set to ``no'' (the
228 default). These sessions will try to reuse the master instance's
229 network connection rather than initiating new ones, but will fall
230 back to connecting normally if the control socket does not exist,
231 or is not listening.
232
233 Setting this to ``ask'' will cause ssh to listen for control
234 connections, but require confirmation using the SSH_ASKPASS
235 program before they are accepted (see ssh-add(1) for details).
236 If the ControlPath cannot be opened, ssh will continue without
237 connecting to a master instance.
238
239 X11 and ssh-agent(1) forwarding is supported over these
240 multiplexed connections, however the display and agent forwarded
241 will be the one belonging to the master connection i.e. it is not
242 possible to forward multiple displays or agents.
243
244 Two additional options allow for opportunistic multiplexing: try
245 to use a master connection but fall back to creating a new one if
246 one does not already exist. These options are: ``auto'' and
247 ``autoask''. The latter requires confirmation like the ``ask''
248 option.
249
250 ControlPath
251 Specify the path to the control socket used for connection
252 sharing as described in the ControlMaster section above or the
253 string ``none'' to disable connection sharing. In the path, `%L'
254 will be substituted by the first component of the local host
255 name, `%l' will be substituted by the local host name (including
256 any domain name), `%h' will be substituted by the target host
257 name, `%n' will be substituted by the original target host name
258 specified on the command line, `%p' the destination port, `%r' by
259 the remote login username, and `%u' by the username of the user
260 running ssh(1). It is recommended that any ControlPath used for
261 opportunistic connection sharing include at least %h, %p, and %r.
262 This ensures that shared connections are uniquely identified.
263
264 ControlPersist
265 When used in conjunction with ControlMaster, specifies that the
266 master connection should remain open in the background (waiting
267 for future client connections) after the initial client
268 connection has been closed. If set to ``no'', then the master
269 connection will not be placed into the background, and will close
270 as soon as the initial client connection is closed. If set to
271 ``yes'', then the master connection will remain in the background
272 indefinitely (until killed or closed via a mechanism such as the
273 ssh(1) ``-O exit'' option). If set to a time in seconds, or a
274 time in any of the formats documented in sshd_config(5), then the
275 backgrounded master connection will automatically terminate after
276 it has remained idle (with no client connections) for the
277 specified time.
278
279 DynamicForward
280 Specifies that a TCP port on the local machine be forwarded over
281 the secure channel, and the application protocol is then used to
282 determine where to connect to from the remote machine.
283
284 The argument must be [bind_address:]port. IPv6 addresses can be
285 specified by enclosing addresses in square brackets. By default,
286 the local port is bound in accordance with the GatewayPorts
287 setting. However, an explicit bind_address may be used to bind
288 the connection to a specific address. The bind_address of
289 ``localhost'' indicates that the listening port be bound for
290 local use only, while an empty address or `*' indicates that the
291 port should be available from all interfaces.
292
293 Currently the SOCKS4 and SOCKS5 protocols are supported, and
294 ssh(1) will act as a SOCKS server. Multiple forwardings may be
295 specified, and additional forwardings can be given on the command
296 line. Only the superuser can forward privileged ports.
297
298 EnableSSHKeysign
299 Setting this option to ``yes'' in the global client configuration
300 file /etc/ssh/ssh_config enables the use of the helper program
301 ssh-keysign(8) during HostbasedAuthentication. The argument must
302 be ``yes'' or ``no''. The default is ``no''. This option should
303 be placed in the non-hostspecific section. See ssh-keysign(8)
304 for more information.
305
306 EscapeChar
307 Sets the escape character (default: `~'). The escape character
308 can also be set on the command line. The argument should be a
309 single character, `^' followed by a letter, or ``none'' to
310 disable the escape character entirely (making the connection
311 transparent for binary data).
312
313 ExitOnForwardFailure
314 Specifies whether ssh(1) should terminate the connection if it
315 cannot set up all requested dynamic, tunnel, local, and remote
316 port forwardings. The argument must be ``yes'' or ``no''. The
317 default is ``no''.
318
319 ForwardAgent
320 Specifies whether the connection to the authentication agent (if
321 any) will be forwarded to the remote machine. The argument must
322 be ``yes'' or ``no''. The default is ``no''.
323
324 Agent forwarding should be enabled with caution. Users with the
325 ability to bypass file permissions on the remote host (for the
326 agent's Unix-domain socket) can access the local agent through
327 the forwarded connection. An attacker cannot obtain key material
328 from the agent, however they can perform operations on the keys
329 that enable them to authenticate using the identities loaded into
330 the agent.
331
332 ForwardX11
333 Specifies whether X11 connections will be automatically
334 redirected over the secure channel and DISPLAY set. The argument
335 must be ``yes'' or ``no''. The default is ``no''.
336
337 X11 forwarding should be enabled with caution. Users with the
338 ability to bypass file permissions on the remote host (for the
339 user's X11 authorization database) can access the local X11
340 display through the forwarded connection. An attacker may then
341 be able to perform activities such as keystroke monitoring if the
342 ForwardX11Trusted option is also enabled.
343
344 ForwardX11Timeout
345 Specify a timeout for untrusted X11 forwarding using the format
346 described in the TIME FORMATS section of sshd_config(5). X11
347 connections received by ssh(1) after this time will be refused.
348 The default is to disable untrusted X11 forwarding after twenty
349 minutes has elapsed.
350
351 ForwardX11Trusted
352 If this option is set to ``yes'', remote X11 clients will have
353 full access to the original X11 display.
354
355 If this option is set to ``no'', remote X11 clients will be
356 considered untrusted and prevented from stealing or tampering
357 with data belonging to trusted X11 clients. Furthermore, the
358 xauth(1) token used for the session will be set to expire after
359 20 minutes. Remote clients will be refused access after this
360 time.
361
362 The default is ``no''.
363
364 See the X11 SECURITY extension specification for full details on
365 the restrictions imposed on untrusted clients.
366
367 GatewayPorts
368 Specifies whether remote hosts are allowed to connect to local
369 forwarded ports. By default, ssh(1) binds local port forwardings
370 to the loopback address. This prevents other remote hosts from
371 connecting to forwarded ports. GatewayPorts can be used to
372 specify that ssh should bind local port forwardings to the
373 wildcard address, thus allowing remote hosts to connect to
374 forwarded ports. The argument must be ``yes'' or ``no''. The
375 default is ``no''.
376
377 GlobalKnownHostsFile
378 Specifies one or more files to use for the global host key
379 database, separated by whitespace. The default is
380 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
381
382 GSSAPIAuthentication
383 Specifies whether user authentication based on GSSAPI is allowed.
384 The default is ``no''. Note that this option applies to protocol
385 version 2 only.
386
387 GSSAPIDelegateCredentials
388 Forward (delegate) credentials to the server. The default is
389 ``no''. Note that this option applies to protocol version 2
390 only.
391
392 HashKnownHosts
393 Indicates that ssh(1) should hash host names and addresses when
394 they are added to ~/.ssh/known_hosts. These hashed names may be
395 used normally by ssh(1) and sshd(8), but they do not reveal
396 identifying information should the file's contents be disclosed.
397 The default is ``no''. Note that existing names and addresses in
398 known hosts files will not be converted automatically, but may be
399 manually hashed using ssh-keygen(1).
400
401 HostbasedAuthentication
402 Specifies whether to try rhosts based authentication with public
403 key authentication. The argument must be ``yes'' or ``no''. The
404 default is ``no''. This option applies to protocol version 2
405 only and is similar to RhostsRSAAuthentication.
406
407 HostKeyAlgorithms
408 Specifies the protocol version 2 host key algorithms that the
409 client wants to use in order of preference. The default for this
410 option is:
411
412 ecdsa-sha2-nistp256-cert-v01@openssh.com,
413 ecdsa-sha2-nistp384-cert-v01@openssh.com,
414 ecdsa-sha2-nistp521-cert-v01@openssh.com,
415 ssh-ed25519-cert-v01@openssh.com,
416 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
417 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
418 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
419 ssh-ed25519,ssh-rsa,ssh-dss
420
421 If hostkeys are known for the destination host then this default
422 is modified to prefer their algorithms.
423
424 HostKeyAlias
425 Specifies an alias that should be used instead of the real host
426 name when looking up or saving the host key in the host key
427 database files. This option is useful for tunneling SSH
428 connections or for multiple servers running on a single host.
429
430 HostName
431 Specifies the real host name to log into. This can be used to
432 specify nicknames or abbreviations for hosts. If the hostname
433 contains the character sequence `%h', then this will be replaced
434 with the host name specified on the command line (this is useful
435 for manipulating unqualified names). The default is the name
436 given on the command line. Numeric IP addresses are also
437 permitted (both on the command line and in HostName
438 specifications).
439
440 IdentitiesOnly
441 Specifies that ssh(1) should only use the authentication identity
442 files configured in the ssh_config files, even if ssh-agent(1) or
443 a PKCS11Provider offers more identities. The argument to this
444 keyword must be ``yes'' or ``no''. This option is intended for
445 situations where ssh-agent offers many different identities. The
446 default is ``no''.
447
448 IdentityFile
449 Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA
450 authentication identity is read. The default is ~/.ssh/identity
451 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
452 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2.
453 Additionally, any identities represented by the authentication
454 agent will be used for authentication unless IdentitiesOnly is
455 set. ssh(1) will try to load certificate information from the
456 filename obtained by appending -cert.pub to the path of a
457 specified IdentityFile.
458
459 The file name may use the tilde syntax to refer to a user's home
460 directory or one of the following escape characters: `%d' (local
461 user's home directory), `%u' (local user name), `%l' (local host
462 name), `%h' (remote host name) or `%r' (remote user name).
463
464 It is possible to have multiple identity files specified in
465 configuration files; all these identities will be tried in
466 sequence. Multiple IdentityFile directives will add to the list
467 of identities tried (this behaviour differs from that of other
468 configuration directives).
469
470 IdentityFile may be used in conjunction with IdentitiesOnly to
471 select which identities in an agent are offered during
472 authentication.
473
474 IgnoreUnknown
475 Specifies a pattern-list of unknown options to be ignored if they
476 are encountered in configuration parsing. This may be used to
477 suppress errors if ssh_config contains options that are
478 unrecognised by ssh(1). It is recommended that IgnoreUnknown be
479 listed early in the configuration file as it will not be applied
480 to unknown options that appear before it.
481
482 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
483 Accepted values are ``af11'', ``af12'', ``af13'', ``af21'',
484 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'',
485 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'',
486 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'',
487 ``reliability'', or a numeric value. This option may take one or
488 two arguments, separated by whitespace. If one argument is
489 specified, it is used as the packet class unconditionally. If
490 two values are specified, the first is automatically selected for
491 interactive sessions and the second for non-interactive sessions.
492 The default is ``lowdelay'' for interactive sessions and
493 ``throughput'' for non-interactive sessions.
494
495 KbdInteractiveAuthentication
496 Specifies whether to use keyboard-interactive authentication.
497 The argument to this keyword must be ``yes'' or ``no''. The
498 default is ``yes''.
499
500 KbdInteractiveDevices
501 Specifies the list of methods to use in keyboard-interactive
502 authentication. Multiple method names must be comma-separated.
503 The default is to use the server specified list. The methods
504 available vary depending on what the server supports. For an
505 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'',
506 and ``skey''.
507
508 KexAlgorithms
509 Specifies the available KEX (Key Exchange) algorithms. Multiple
510 algorithms must be comma-separated. The default is:
511
512 curve25519-sha256@libssh.org,
513 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
514 diffie-hellman-group-exchange-sha256,
515 diffie-hellman-group-exchange-sha1,
516 diffie-hellman-group14-sha1,
517 diffie-hellman-group1-sha1
518
519 LocalCommand
520 Specifies a command to execute on the local machine after
521 successfully connecting to the server. The command string
522 extends to the end of the line, and is executed with the user's
523 shell. The following escape character substitutions will be
524 performed: `%d' (local user's home directory), `%h' (remote host
525 name), `%l' (local host name), `%n' (host name as provided on the
526 command line), `%p' (remote port), `%r' (remote user name) or
527 `%u' (local user name).
528
529 The command is run synchronously and does not have access to the
530 session of the ssh(1) that spawned it. It should not be used for
531 interactive commands.
532
533 This directive is ignored unless PermitLocalCommand has been
534 enabled.
535
536 LocalForward
537 Specifies that a TCP port on the local machine be forwarded over
538 the secure channel to the specified host and port from the remote
539 machine. The first argument must be [bind_address:]port and the
540 second argument must be host:hostport. IPv6 addresses can be
541 specified by enclosing addresses in square brackets. Multiple
542 forwardings may be specified, and additional forwardings can be
543 given on the command line. Only the superuser can forward
544 privileged ports. By default, the local port is bound in
545 accordance with the GatewayPorts setting. However, an explicit
546 bind_address may be used to bind the connection to a specific
547 address. The bind_address of ``localhost'' indicates that the
548 listening port be bound for local use only, while an empty
549 address or `*' indicates that the port should be available from
550 all interfaces.
551
552 LogLevel
553 Gives the verbosity level that is used when logging messages from
554 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
555 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
556 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
557 higher levels of verbose output.
558
559 MACs Specifies the MAC (message authentication code) algorithms in
560 order of preference. The MAC algorithm is used in protocol
561 version 2 for data integrity protection. Multiple algorithms
562 must be comma-separated. The algorithms that contain ``-etm''
563 calculate the MAC after encryption (encrypt-then-mac). These are
564 considered safer and their use recommended. The default is:
565
566 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
567 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
568 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
569 hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
570 hmac-md5-96-etm@openssh.com,
571 hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
572 hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
573 hmac-sha1-96,hmac-md5-96
574
575 NoHostAuthenticationForLocalhost
576 This option can be used if the home directory is shared across
577 machines. In this case localhost will refer to a different
578 machine on each of the machines and the user will get many
579 warnings about changed host keys. However, this option disables
580 host authentication for localhost. The argument to this keyword
581 must be ``yes'' or ``no''. The default is to check the host key
582 for localhost.
583
584 NumberOfPasswordPrompts
585 Specifies the number of password prompts before giving up. The
586 argument to this keyword must be an integer. The default is 3.
587
588 PasswordAuthentication
589 Specifies whether to use password authentication. The argument
590 to this keyword must be ``yes'' or ``no''. The default is
591 ``yes''.
592
593 PermitLocalCommand
594 Allow local command execution via the LocalCommand option or
595 using the !command escape sequence in ssh(1). The argument must
596 be ``yes'' or ``no''. The default is ``no''.
597
598 PKCS11Provider
599 Specifies which PKCS#11 provider to use. The argument to this
600 keyword is the PKCS#11 shared library ssh(1) should use to
601 communicate with a PKCS#11 token providing the user's private RSA
602 key.
603
604 Port Specifies the port number to connect on the remote host. The
605 default is 22.
606
607 PreferredAuthentications
608 Specifies the order in which the client should try protocol 2
609 authentication methods. This allows a client to prefer one
610 method (e.g. keyboard-interactive) over another method (e.g.
611 password). The default is:
612
613 gssapi-with-mic,hostbased,publickey,
614 keyboard-interactive,password
615
616 Protocol
617 Specifies the protocol versions ssh(1) should support in order of
618 preference. The possible values are `1' and `2'. Multiple
619 versions must be comma-separated. When this option is set to
620 ``2,1'' ssh will try version 2 and fall back to version 1 if
621 version 2 is not available. The default is `2'.
622
623 ProxyCommand
624 Specifies the command to use to connect to the server. The
625 command string extends to the end of the line, and is executed
626 with the user's shell. In the command string, any occurrence of
627 `%h' will be substituted by the host name to connect, `%p' by the
628 port, and `%r' by the remote user name. The command can be
629 basically anything, and should read from its standard input and
630 write to its standard output. It should eventually connect an
631 sshd(8) server running on some machine, or execute sshd -i
632 somewhere. Host key management will be done using the HostName
633 of the host being connected (defaulting to the name typed by the
634 user). Setting the command to ``none'' disables this option
635 entirely. Note that CheckHostIP is not available for connects
636 with a proxy command.
637
638 This directive is useful in conjunction with nc(1) and its proxy
639 support. For example, the following directive would connect via
640 an HTTP proxy at 192.0.2.0:
641
642 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
643
644 ProxyUseFdpass
645 Specifies that ProxyCommand will pass a connected file descriptor
646 back to ssh(1) instead of continuing to execute and pass data.
647 The default is ``no''.
648
649 PubkeyAuthentication
650 Specifies whether to try public key authentication. The argument
651 to this keyword must be ``yes'' or ``no''. The default is
652 ``yes''. This option applies to protocol version 2 only.
653
654 RekeyLimit
655 Specifies the maximum amount of data that may be transmitted
656 before the session key is renegotiated, optionally followed a
657 maximum amount of time that may pass before the session key is
658 renegotiated. The first argument is specified in bytes and may
659 have a suffix of `K', `M', or `G' to indicate Kilobytes,
660 Megabytes, or Gigabytes, respectively. The default is between
661 `1G' and `4G', depending on the cipher. The optional second
662 value is specified in seconds and may use any of the units
663 documented in the TIME FORMATS section of sshd_config(5). The
664 default value for RekeyLimit is ``default none'', which means
665 that rekeying is performed after the cipher's default amount of
666 data has been sent or received and no time based rekeying is
667 done. This option applies to protocol version 2 only.
668
669 RemoteForward
670 Specifies that a TCP port on the remote machine be forwarded over
671 the secure channel to the specified host and port from the local
672 machine. The first argument must be [bind_address:]port and the
673 second argument must be host:hostport. IPv6 addresses can be
674 specified by enclosing addresses in square brackets. Multiple
675 forwardings may be specified, and additional forwardings can be
676 given on the command line. Privileged ports can be forwarded
677 only when logging in as root on the remote machine.
678
679 If the port argument is `0', the listen port will be dynamically
680 allocated on the server and reported to the client at run time.
681
682 If the bind_address is not specified, the default is to only bind
683 to loopback addresses. If the bind_address is `*' or an empty
684 string, then the forwarding is requested to listen on all
685 interfaces. Specifying a remote bind_address will only succeed
686 if the server's GatewayPorts option is enabled (see
687 sshd_config(5)).
688
689 RequestTTY
690 Specifies whether to request a pseudo-tty for the session. The
691 argument may be one of: ``no'' (never request a TTY), ``yes''
692 (always request a TTY when standard input is a TTY), ``force''
693 (always request a TTY) or ``auto'' (request a TTY when opening a
694 login session). This option mirrors the -t and -T flags for
695 ssh(1).
696
697 RhostsRSAAuthentication
698 Specifies whether to try rhosts based authentication with RSA
699 host authentication. The argument must be ``yes'' or ``no''.
700 The default is ``no''. This option applies to protocol version 1
701 only and requires ssh(1) to be setuid root.
702
703 RSAAuthentication
704 Specifies whether to try RSA authentication. The argument to
705 this keyword must be ``yes'' or ``no''. RSA authentication will
706 only be attempted if the identity file exists, or an
707 authentication agent is running. The default is ``yes''. Note
708 that this option applies to protocol version 1 only.
709
710 SendEnv
711 Specifies what variables from the local environ(7) should be sent
712 to the server. Note that environment passing is only supported
713 for protocol 2. The server must also support it, and the server
714 must be configured to accept these environment variables. Refer
715 to AcceptEnv in sshd_config(5) for how to configure the server.
716 Variables are specified by name, which may contain wildcard
717 characters. Multiple environment variables may be separated by
718 whitespace or spread across multiple SendEnv directives. The
719 default is not to send any environment variables.
720
721 See PATTERNS for more information on patterns.
722
723 ServerAliveCountMax
724 Sets the number of server alive messages (see below) which may be
725 sent without ssh(1) receiving any messages back from the server.
726 If this threshold is reached while server alive messages are
727 being sent, ssh will disconnect from the server, terminating the
728 session. It is important to note that the use of server alive
729 messages is very different from TCPKeepAlive (below). The server
730 alive messages are sent through the encrypted channel and
731 therefore will not be spoofable. The TCP keepalive option
732 enabled by TCPKeepAlive is spoofable. The server alive mechanism
733 is valuable when the client or server depend on knowing when a
734 connection has become inactive.
735
736 The default value is 3. If, for example, ServerAliveInterval
737 (see below) is set to 15 and ServerAliveCountMax is left at the
738 default, if the server becomes unresponsive, ssh will disconnect
739 after approximately 45 seconds. This option applies to protocol
740 version 2 only.
741
742 ServerAliveInterval
743 Sets a timeout interval in seconds after which if no data has
744 been received from the server, ssh(1) will send a message through
745 the encrypted channel to request a response from the server. The
746 default is 0, indicating that these messages will not be sent to
747 the server. This option applies to protocol version 2 only.
748
749 StrictHostKeyChecking
750 If this flag is set to ``yes'', ssh(1) will never automatically
751 add host keys to the ~/.ssh/known_hosts file, and refuses to
752 connect to hosts whose host key has changed. This provides
753 maximum protection against trojan horse attacks, though it can be
754 annoying when the /etc/ssh/ssh_known_hosts file is poorly
755 maintained or when connections to new hosts are frequently made.
756 This option forces the user to manually add all new hosts. If
757 this flag is set to ``no'', ssh will automatically add new host
758 keys to the user known hosts files. If this flag is set to
759 ``ask'', new host keys will be added to the user known host files
760 only after the user has confirmed that is what they really want
761 to do, and ssh will refuse to connect to hosts whose host key has
762 changed. The host keys of known hosts will be verified
763 automatically in all cases. The argument must be ``yes'',
764 ``no'', or ``ask''. The default is ``ask''.
765
766 TCPKeepAlive
767 Specifies whether the system should send TCP keepalive messages
768 to the other side. If they are sent, death of the connection or
769 crash of one of the machines will be properly noticed. However,
770 this means that connections will die if the route is down
771 temporarily, and some people find it annoying.
772
773 The default is ``yes'' (to send TCP keepalive messages), and the
774 client will notice if the network goes down or the remote host
775 dies. This is important in scripts, and many users want it too.
776
777 To disable TCP keepalive messages, the value should be set to
778 ``no''.
779
780 Tunnel Request tun(4) device forwarding between the client and the
781 server. The argument must be ``yes'', ``point-to-point'' (layer
782 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes''
783 requests the default tunnel mode, which is ``point-to-point''.
784 The default is ``no''.
785
786 TunnelDevice
787 Specifies the tun(4) devices to open on the client (local_tun)
788 and the server (remote_tun).
789
790 The argument must be local_tun[:remote_tun]. The devices may be
791 specified by numerical ID or the keyword ``any'', which uses the
792 next available tunnel device. If remote_tun is not specified, it
793 defaults to ``any''. The default is ``any:any''.
794
795 UsePrivilegedPort
796 Specifies whether to use a privileged port for outgoing
797 connections. The argument must be ``yes'' or ``no''. The
798 default is ``no''. If set to ``yes'', ssh(1) must be setuid
799 root. Note that this option must be set to ``yes'' for
800 RhostsRSAAuthentication with older servers.
801
802 User Specifies the user to log in as. This can be useful when a
803 different user name is used on different machines. This saves
804 the trouble of having to remember to give the user name on the
805 command line.
806
807 UserKnownHostsFile
808 Specifies one or more files to use for the user host key
809 database, separated by whitespace. The default is
810 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
811
812 VerifyHostKeyDNS
813 Specifies whether to verify the remote key using DNS and SSHFP
814 resource records. If this option is set to ``yes'', the client
815 will implicitly trust keys that match a secure fingerprint from
816 DNS. Insecure fingerprints will be handled as if this option was
817 set to ``ask''. If this option is set to ``ask'', information on
818 fingerprint match will be displayed, but the user will still need
819 to confirm new host keys according to the StrictHostKeyChecking
820 option. The argument must be ``yes'', ``no'', or ``ask''. The
821 default is ``no''. Note that this option applies to protocol
822 version 2 only.
823
824 See also VERIFYING HOST KEYS in ssh(1).
825
826 VisualHostKey
827 If this flag is set to ``yes'', an ASCII art representation of
828 the remote host key fingerprint is printed in addition to the hex
829 fingerprint string at login and for unknown host keys. If this
830 flag is set to ``no'', no fingerprint strings are printed at
831 login and only the hex fingerprint string will be printed for
832 unknown host keys. The default is ``no''.
833
834 XAuthLocation
835 Specifies the full pathname of the xauth(1) program. The default
836 is /usr/X11R6/bin/xauth.
837
838PATTERNS
839 A pattern consists of zero or more non-whitespace characters, `*' (a
840 wildcard that matches zero or more characters), or `?' (a wildcard that
841 matches exactly one character). For example, to specify a set of
842 declarations for any host in the ``.co.uk'' set of domains, the following
843 pattern could be used:
844
845 Host *.co.uk
846
847 The following pattern would match any host in the 192.168.0.[0-9] network
848 range:
849
850 Host 192.168.0.?
851
852 A pattern-list is a comma-separated list of patterns. Patterns within
853 pattern-lists may be negated by preceding them with an exclamation mark
854 (`!'). For example, to allow a key to be used from anywhere within an
855 organization except from the ``dialup'' pool, the following entry (in
856 authorized_keys) could be used:
857
858 from="!*.dialup.example.com,*.example.com"
859
860FILES
861 ~/.ssh/config
862 This is the per-user configuration file. The format of this file
863 is described above. This file is used by the SSH client.
864 Because of the potential for abuse, this file must have strict
865 permissions: read/write for the user, and not accessible by
866 others.
867
868 /etc/ssh/ssh_config
869 Systemwide configuration file. This file provides defaults for
870 those values that are not specified in the user's configuration
871 file, and for those users who do not have a configuration file.
872 This file must be world-readable.
873
874SEE ALSO
875 ssh(1)
876
877AUTHORS
878 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
879 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
880 de Raadt and Dug Song removed many bugs, re-added newer features and
881 created OpenSSH. Markus Friedl contributed the support for SSH protocol
882 versions 1.5 and 2.0.
883
884OpenBSD 5.4 January 19, 2014 OpenBSD 5.4
generated by cgit v1.2.3 (git 2.39.1) at 2024-06-26 18:01:45 +0000