1 SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5)
4 ssh_config - OpenSSH SSH client configuration files
11 ssh(1) obtains configuration data from the following sources in the
14 1. command-line options
15 2. user's configuration file (~/.ssh/config)
16 3. system-wide configuration file (/etc/ssh/ssh_config)
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.
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.
28 The configuration file has the following format:
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.
38 The possible keywords and their meanings are as follows (note that
39 keywords are case-insensitive and arguments are case-sensitive):
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
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.
56 See PATTERNS for more information on patterns.
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.
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
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).
90 Specifies which address family to use when connecting. Valid
91 arguments are ``any'', ``inet'' (use IPv4 only), or ``inet6''
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''.
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''.
107 When CanonicalizeHostname is enabled, this option specifies the
108 list of domain suffixes in which to search for the specified
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
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
131 If this option is enabled and canonicalisation results in the
132 target hostname changing, then the configuration files are
133 processed again using the new target name to pick up any new
134 configuration in matching Host stanzas.
137 Specifies the maximum number of dot characters in a hostname
138 before canonicalization is disabled. The default, ``1'', allows
139 a single dot (i.e. hostname.subdomain).
141 CanonicalizePermittedCNAMEs
142 Specifies rules to determine whether CNAMEs should be followed
143 when canonicalizing hostnames. The rules consist of one or more
144 arguments of source_domain_list:target_domain_list, where
145 source_domain_list is a pattern-list of domains that may follow
146 CNAMEs in canonicalization, and target_domain_list is a pattern-
147 list of domains that they may resolve to.
149 For example, ``*.a.example.com:*.b.example.com,*.c.example.com''
150 will allow hostnames matching ``*.a.example.com'' to be
151 canonicalized to names in the ``*.b.example.com'' or
152 ``*.c.example.com'' domains.
154 ChallengeResponseAuthentication
155 Specifies whether to use challenge-response authentication. The
156 argument to this keyword must be ``yes'' or ``no''. The default
160 If this flag is set to ``yes'', ssh(1) will additionally check
161 the host IP address in the known_hosts file. This allows ssh to
162 detect if a host key changed due to DNS spoofing. If the option
163 is set to ``no'', the check will not be executed. The default is
166 Cipher Specifies the cipher to use for encrypting the session in
167 protocol version 1. Currently, ``blowfish'', ``3des'', and
168 ``des'' are supported. des is only supported in the ssh(1)
169 client for interoperability with legacy protocol 1
170 implementations that do not support the 3des cipher. Its use is
171 strongly discouraged due to cryptographic weaknesses. The
175 Specifies the ciphers allowed for protocol version 2 in order of
176 preference. Multiple ciphers must be comma-separated. The
177 supported ciphers are:
179 ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'', ``aes256-cbc'',
180 ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'',
181 ``aes128-gcm@openssh.com'', ``aes256-gcm@openssh.com'',
182 ``arcfour128'', ``arcfour256'', ``arcfour'', ``blowfish-cbc'',
183 ``cast128-cbc'', and ``chacha20-poly1305@openssh.com''.
187 aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,
188 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
189 chacha20-poly1305@openssh.com,
190 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,
193 The list of available ciphers may also be obtained using the -Q
197 Specifies that all local, remote, and dynamic port forwardings
198 specified in the configuration files or on the command line be
199 cleared. This option is primarily useful when used from the
200 ssh(1) command line to clear port forwardings set in
201 configuration files, and is automatically set by scp(1) and
202 sftp(1). The argument must be ``yes'' or ``no''. The default is
206 Specifies whether to use compression. The argument must be
207 ``yes'' or ``no''. The default is ``no''.
210 Specifies the compression level to use if compression is enabled.
211 The argument must be an integer from 1 (fast) to 9 (slow, best).
212 The default level is 6, which is good for most applications. The
213 meaning of the values is the same as in gzip(1). Note that this
214 option applies to protocol version 1 only.
217 Specifies the number of tries (one per second) to make before
218 exiting. The argument must be an integer. This may be useful in
219 scripts if the connection sometimes fails. The default is 1.
222 Specifies the timeout (in seconds) used when connecting to the
223 SSH server, instead of using the default system TCP timeout.
224 This value is used only when the target is down or really
225 unreachable, not when it refuses the connection.
228 Enables the sharing of multiple sessions over a single network
229 connection. When set to ``yes'', ssh(1) will listen for
230 connections on a control socket specified using the ControlPath
231 argument. Additional sessions can connect to this socket using
232 the same ControlPath with ControlMaster set to ``no'' (the
233 default). These sessions will try to reuse the master instance's
234 network connection rather than initiating new ones, but will fall
235 back to connecting normally if the control socket does not exist,
238 Setting this to ``ask'' will cause ssh to listen for control
239 connections, but require confirmation using the SSH_ASKPASS
240 program before they are accepted (see ssh-add(1) for details).
241 If the ControlPath cannot be opened, ssh will continue without
242 connecting to a master instance.
244 X11 and ssh-agent(1) forwarding is supported over these
245 multiplexed connections, however the display and agent forwarded
246 will be the one belonging to the master connection i.e. it is not
247 possible to forward multiple displays or agents.
249 Two additional options allow for opportunistic multiplexing: try
250 to use a master connection but fall back to creating a new one if
251 one does not already exist. These options are: ``auto'' and
252 ``autoask''. The latter requires confirmation like the ``ask''
256 Specify the path to the control socket used for connection
257 sharing as described in the ControlMaster section above or the
258 string ``none'' to disable connection sharing. In the path, `%L'
259 will be substituted by the first component of the local host
260 name, `%l' will be substituted by the local host name (including
261 any domain name), `%h' will be substituted by the target host
262 name, `%n' will be substituted by the original target host name
263 specified on the command line, `%p' the destination port, `%r' by
264 the remote login username, and `%u' by the username of the user
265 running ssh(1). It is recommended that any ControlPath used for
266 opportunistic connection sharing include at least %h, %p, and %r.
267 This ensures that shared connections are uniquely identified.
270 When used in conjunction with ControlMaster, specifies that the
271 master connection should remain open in the background (waiting
272 for future client connections) after the initial client
273 connection has been closed. If set to ``no'', then the master
274 connection will not be placed into the background, and will close
275 as soon as the initial client connection is closed. If set to
276 ``yes'', then the master connection will remain in the background
277 indefinitely (until killed or closed via a mechanism such as the
278 ssh(1) ``-O exit'' option). If set to a time in seconds, or a
279 time in any of the formats documented in sshd_config(5), then the
280 backgrounded master connection will automatically terminate after
281 it has remained idle (with no client connections) for the
285 Specifies that a TCP port on the local machine be forwarded over
286 the secure channel, and the application protocol is then used to
287 determine where to connect to from the remote machine.
289 The argument must be [bind_address:]port. IPv6 addresses can be
290 specified by enclosing addresses in square brackets. By default,
291 the local port is bound in accordance with the GatewayPorts
292 setting. However, an explicit bind_address may be used to bind
293 the connection to a specific address. The bind_address of
294 ``localhost'' indicates that the listening port be bound for
295 local use only, while an empty address or `*' indicates that the
296 port should be available from all interfaces.
298 Currently the SOCKS4 and SOCKS5 protocols are supported, and
299 ssh(1) will act as a SOCKS server. Multiple forwardings may be
300 specified, and additional forwardings can be given on the command
301 line. Only the superuser can forward privileged ports.
304 Setting this option to ``yes'' in the global client configuration
305 file /etc/ssh/ssh_config enables the use of the helper program
306 ssh-keysign(8) during HostbasedAuthentication. The argument must
307 be ``yes'' or ``no''. The default is ``no''. This option should
308 be placed in the non-hostspecific section. See ssh-keysign(8)
309 for more information.
312 Sets the escape character (default: `~'). The escape character
313 can also be set on the command line. The argument should be a
314 single character, `^' followed by a letter, or ``none'' to
315 disable the escape character entirely (making the connection
316 transparent for binary data).
319 Specifies whether ssh(1) should terminate the connection if it
320 cannot set up all requested dynamic, tunnel, local, and remote
321 port forwardings. The argument must be ``yes'' or ``no''. The
325 Specifies whether the connection to the authentication agent (if
326 any) will be forwarded to the remote machine. The argument must
327 be ``yes'' or ``no''. The default is ``no''.
329 Agent forwarding should be enabled with caution. Users with the
330 ability to bypass file permissions on the remote host (for the
331 agent's Unix-domain socket) can access the local agent through
332 the forwarded connection. An attacker cannot obtain key material
333 from the agent, however they can perform operations on the keys
334 that enable them to authenticate using the identities loaded into
338 Specifies whether X11 connections will be automatically
339 redirected over the secure channel and DISPLAY set. The argument
340 must be ``yes'' or ``no''. The default is ``no''.
342 X11 forwarding should be enabled with caution. Users with the
343 ability to bypass file permissions on the remote host (for the
344 user's X11 authorization database) can access the local X11
345 display through the forwarded connection. An attacker may then
346 be able to perform activities such as keystroke monitoring if the
347 ForwardX11Trusted option is also enabled.
350 Specify a timeout for untrusted X11 forwarding using the format
351 described in the TIME FORMATS section of sshd_config(5). X11
352 connections received by ssh(1) after this time will be refused.
353 The default is to disable untrusted X11 forwarding after twenty
357 If this option is set to ``yes'', remote X11 clients will have
358 full access to the original X11 display.
360 If this option is set to ``no'', remote X11 clients will be
361 considered untrusted and prevented from stealing or tampering
362 with data belonging to trusted X11 clients. Furthermore, the
363 xauth(1) token used for the session will be set to expire after
364 20 minutes. Remote clients will be refused access after this
367 The default is ``no''.
369 See the X11 SECURITY extension specification for full details on
370 the restrictions imposed on untrusted clients.
373 Specifies whether remote hosts are allowed to connect to local
374 forwarded ports. By default, ssh(1) binds local port forwardings
375 to the loopback address. This prevents other remote hosts from
376 connecting to forwarded ports. GatewayPorts can be used to
377 specify that ssh should bind local port forwardings to the
378 wildcard address, thus allowing remote hosts to connect to
379 forwarded ports. The argument must be ``yes'' or ``no''. The
383 Specifies one or more files to use for the global host key
384 database, separated by whitespace. The default is
385 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
388 Specifies whether user authentication based on GSSAPI is allowed.
389 The default is ``no''. Note that this option applies to protocol
392 GSSAPIDelegateCredentials
393 Forward (delegate) credentials to the server. The default is
394 ``no''. Note that this option applies to protocol version 2
398 Indicates that ssh(1) should hash host names and addresses when
399 they are added to ~/.ssh/known_hosts. These hashed names may be
400 used normally by ssh(1) and sshd(8), but they do not reveal
401 identifying information should the file's contents be disclosed.
402 The default is ``no''. Note that existing names and addresses in
403 known hosts files will not be converted automatically, but may be
404 manually hashed using ssh-keygen(1).
406 HostbasedAuthentication
407 Specifies whether to try rhosts based authentication with public
408 key authentication. The argument must be ``yes'' or ``no''. The
409 default is ``no''. This option applies to protocol version 2
410 only and is similar to RhostsRSAAuthentication.
413 Specifies the protocol version 2 host key algorithms that the
414 client wants to use in order of preference. The default for this
417 ecdsa-sha2-nistp256-cert-v01@openssh.com,
418 ecdsa-sha2-nistp384-cert-v01@openssh.com,
419 ecdsa-sha2-nistp521-cert-v01@openssh.com,
420 ssh-ed25519-cert-v01@openssh.com,
421 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
422 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
423 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
424 ssh-ed25519,ssh-rsa,ssh-dss
426 If hostkeys are known for the destination host then this default
427 is modified to prefer their algorithms.
430 Specifies an alias that should be used instead of the real host
431 name when looking up or saving the host key in the host key
432 database files. This option is useful for tunneling SSH
433 connections or for multiple servers running on a single host.
436 Specifies the real host name to log into. This can be used to
437 specify nicknames or abbreviations for hosts. If the hostname
438 contains the character sequence `%h', then this will be replaced
439 with the host name specified on the command line (this is useful
440 for manipulating unqualified names). The default is the name
441 given on the command line. Numeric IP addresses are also
442 permitted (both on the command line and in HostName
446 Specifies that ssh(1) should only use the authentication identity
447 files configured in the ssh_config files, even if ssh-agent(1) or
448 a PKCS11Provider offers more identities. The argument to this
449 keyword must be ``yes'' or ``no''. This option is intended for
450 situations where ssh-agent offers many different identities. The
454 Specifies a file from which the user's DSA, ECDSA, ED25519 or RSA
455 authentication identity is read. The default is ~/.ssh/identity
456 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
457 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2.
458 Additionally, any identities represented by the authentication
459 agent will be used for authentication unless IdentitiesOnly is
460 set. ssh(1) will try to load certificate information from the
461 filename obtained by appending -cert.pub to the path of a
462 specified IdentityFile.
464 The file name may use the tilde syntax to refer to a user's home
465 directory or one of the following escape characters: `%d' (local
466 user's home directory), `%u' (local user name), `%l' (local host
467 name), `%h' (remote host name) or `%r' (remote user name).
469 It is possible to have multiple identity files specified in
470 configuration files; all these identities will be tried in
471 sequence. Multiple IdentityFile directives will add to the list
472 of identities tried (this behaviour differs from that of other
473 configuration directives).
475 IdentityFile may be used in conjunction with IdentitiesOnly to
476 select which identities in an agent are offered during
480 Specifies a pattern-list of unknown options to be ignored if they
481 are encountered in configuration parsing. This may be used to
482 suppress errors if ssh_config contains options that are
483 unrecognised by ssh(1). It is recommended that IgnoreUnknown be
484 listed early in the configuration file as it will not be applied
485 to unknown options that appear before it.
487 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
488 Accepted values are ``af11'', ``af12'', ``af13'', ``af21'',
489 ``af22'', ``af23'', ``af31'', ``af32'', ``af33'', ``af41'',
490 ``af42'', ``af43'', ``cs0'', ``cs1'', ``cs2'', ``cs3'', ``cs4'',
491 ``cs5'', ``cs6'', ``cs7'', ``ef'', ``lowdelay'', ``throughput'',
492 ``reliability'', or a numeric value. This option may take one or
493 two arguments, separated by whitespace. If one argument is
494 specified, it is used as the packet class unconditionally. If
495 two values are specified, the first is automatically selected for
496 interactive sessions and the second for non-interactive sessions.
497 The default is ``lowdelay'' for interactive sessions and
498 ``throughput'' for non-interactive sessions.
500 KbdInteractiveAuthentication
501 Specifies whether to use keyboard-interactive authentication.
502 The argument to this keyword must be ``yes'' or ``no''. The
505 KbdInteractiveDevices
506 Specifies the list of methods to use in keyboard-interactive
507 authentication. Multiple method names must be comma-separated.
508 The default is to use the server specified list. The methods
509 available vary depending on what the server supports. For an
510 OpenSSH server, it may be zero or more of: ``bsdauth'', ``pam'',
514 Specifies the available KEX (Key Exchange) algorithms. Multiple
515 algorithms must be comma-separated. The default is:
517 curve25519-sha256@libssh.org,
518 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
519 diffie-hellman-group-exchange-sha256,
520 diffie-hellman-group-exchange-sha1,
521 diffie-hellman-group14-sha1,
522 diffie-hellman-group1-sha1
525 Specifies a command to execute on the local machine after
526 successfully connecting to the server. The command string
527 extends to the end of the line, and is executed with the user's
528 shell. The following escape character substitutions will be
529 performed: `%d' (local user's home directory), `%h' (remote host
530 name), `%l' (local host name), `%n' (host name as provided on the
531 command line), `%p' (remote port), `%r' (remote user name) or
532 `%u' (local user name).
534 The command is run synchronously and does not have access to the
535 session of the ssh(1) that spawned it. It should not be used for
536 interactive commands.
538 This directive is ignored unless PermitLocalCommand has been
542 Specifies that a TCP port on the local machine be forwarded over
543 the secure channel to the specified host and port from the remote
544 machine. The first argument must be [bind_address:]port and the
545 second argument must be host:hostport. IPv6 addresses can be
546 specified by enclosing addresses in square brackets. Multiple
547 forwardings may be specified, and additional forwardings can be
548 given on the command line. Only the superuser can forward
549 privileged ports. By default, the local port is bound in
550 accordance with the GatewayPorts setting. However, an explicit
551 bind_address may be used to bind the connection to a specific
552 address. The bind_address of ``localhost'' indicates that the
553 listening port be bound for local use only, while an empty
554 address or `*' indicates that the port should be available from
558 Gives the verbosity level that is used when logging messages from
559 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
560 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
561 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
562 higher levels of verbose output.
564 MACs Specifies the MAC (message authentication code) algorithms in
565 order of preference. The MAC algorithm is used in protocol
566 version 2 for data integrity protection. Multiple algorithms
567 must be comma-separated. The algorithms that contain ``-etm''
568 calculate the MAC after encryption (encrypt-then-mac). These are
569 considered safer and their use recommended. The default is:
571 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
572 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
573 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
574 hmac-ripemd160-etm@openssh.com,hmac-sha1-96-etm@openssh.com,
575 hmac-md5-96-etm@openssh.com,
576 hmac-md5,hmac-sha1,umac-64@openssh.com,umac-128@openssh.com,
577 hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,
578 hmac-sha1-96,hmac-md5-96
580 NoHostAuthenticationForLocalhost
581 This option can be used if the home directory is shared across
582 machines. In this case localhost will refer to a different
583 machine on each of the machines and the user will get many
584 warnings about changed host keys. However, this option disables
585 host authentication for localhost. The argument to this keyword
586 must be ``yes'' or ``no''. The default is to check the host key
589 NumberOfPasswordPrompts
590 Specifies the number of password prompts before giving up. The
591 argument to this keyword must be an integer. The default is 3.
593 PasswordAuthentication
594 Specifies whether to use password authentication. The argument
595 to this keyword must be ``yes'' or ``no''. The default is
599 Allow local command execution via the LocalCommand option or
600 using the !command escape sequence in ssh(1). The argument must
601 be ``yes'' or ``no''. The default is ``no''.
604 Specifies which PKCS#11 provider to use. The argument to this
605 keyword is the PKCS#11 shared library ssh(1) should use to
606 communicate with a PKCS#11 token providing the user's private RSA
609 Port Specifies the port number to connect on the remote host. The
612 PreferredAuthentications
613 Specifies the order in which the client should try protocol 2
614 authentication methods. This allows a client to prefer one
615 method (e.g. keyboard-interactive) over another method (e.g.
616 password). The default is:
618 gssapi-with-mic,hostbased,publickey,
619 keyboard-interactive,password
622 Specifies the protocol versions ssh(1) should support in order of
623 preference. The possible values are `1' and `2'. Multiple
624 versions must be comma-separated. When this option is set to
625 ``2,1'' ssh will try version 2 and fall back to version 1 if
626 version 2 is not available. The default is `2'.
629 Specifies the command to use to connect to the server. The
630 command string extends to the end of the line, and is executed
631 with the user's shell. In the command string, any occurrence of
632 `%h' will be substituted by the host name to connect, `%p' by the
633 port, and `%r' by the remote user name. The command can be
634 basically anything, and should read from its standard input and
635 write to its standard output. It should eventually connect an
636 sshd(8) server running on some machine, or execute sshd -i
637 somewhere. Host key management will be done using the HostName
638 of the host being connected (defaulting to the name typed by the
639 user). Setting the command to ``none'' disables this option
640 entirely. Note that CheckHostIP is not available for connects
641 with a proxy command.
643 This directive is useful in conjunction with nc(1) and its proxy
644 support. For example, the following directive would connect via
645 an HTTP proxy at 192.0.2.0:
647 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
650 Specifies that ProxyCommand will pass a connected file descriptor
651 back to ssh(1) instead of continuing to execute and pass data.
652 The default is ``no''.
655 Specifies whether to try public key authentication. The argument
656 to this keyword must be ``yes'' or ``no''. The default is
657 ``yes''. This option applies to protocol version 2 only.
660 Specifies the maximum amount of data that may be transmitted
661 before the session key is renegotiated, optionally followed a
662 maximum amount of time that may pass before the session key is
663 renegotiated. The first argument is specified in bytes and may
664 have a suffix of `K', `M', or `G' to indicate Kilobytes,
665 Megabytes, or Gigabytes, respectively. The default is between
666 `1G' and `4G', depending on the cipher. The optional second
667 value is specified in seconds and may use any of the units
668 documented in the TIME FORMATS section of sshd_config(5). The
669 default value for RekeyLimit is ``default none'', which means
670 that rekeying is performed after the cipher's default amount of
671 data has been sent or received and no time based rekeying is
672 done. This option applies to protocol version 2 only.
675 Specifies that a TCP port on the remote machine be forwarded over
676 the secure channel to the specified host and port from the local
677 machine. The first argument must be [bind_address:]port and the
678 second argument must be host:hostport. IPv6 addresses can be
679 specified by enclosing addresses in square brackets. Multiple
680 forwardings may be specified, and additional forwardings can be
681 given on the command line. Privileged ports can be forwarded
682 only when logging in as root on the remote machine.
684 If the port argument is `0', the listen port will be dynamically
685 allocated on the server and reported to the client at run time.
687 If the bind_address is not specified, the default is to only bind
688 to loopback addresses. If the bind_address is `*' or an empty
689 string, then the forwarding is requested to listen on all
690 interfaces. Specifying a remote bind_address will only succeed
691 if the server's GatewayPorts option is enabled (see
695 Specifies whether to request a pseudo-tty for the session. The
696 argument may be one of: ``no'' (never request a TTY), ``yes''
697 (always request a TTY when standard input is a TTY), ``force''
698 (always request a TTY) or ``auto'' (request a TTY when opening a
699 login session). This option mirrors the -t and -T flags for
702 RhostsRSAAuthentication
703 Specifies whether to try rhosts based authentication with RSA
704 host authentication. The argument must be ``yes'' or ``no''.
705 The default is ``no''. This option applies to protocol version 1
706 only and requires ssh(1) to be setuid root.
709 Specifies whether to try RSA authentication. The argument to
710 this keyword must be ``yes'' or ``no''. RSA authentication will
711 only be attempted if the identity file exists, or an
712 authentication agent is running. The default is ``yes''. Note
713 that this option applies to protocol version 1 only.
716 Specifies what variables from the local environ(7) should be sent
717 to the server. Note that environment passing is only supported
718 for protocol 2. The server must also support it, and the server
719 must be configured to accept these environment variables. Refer
720 to AcceptEnv in sshd_config(5) for how to configure the server.
721 Variables are specified by name, which may contain wildcard
722 characters. Multiple environment variables may be separated by
723 whitespace or spread across multiple SendEnv directives. The
724 default is not to send any environment variables.
726 See PATTERNS for more information on patterns.
729 Sets the number of server alive messages (see below) which may be
730 sent without ssh(1) receiving any messages back from the server.
731 If this threshold is reached while server alive messages are
732 being sent, ssh will disconnect from the server, terminating the
733 session. It is important to note that the use of server alive
734 messages is very different from TCPKeepAlive (below). The server
735 alive messages are sent through the encrypted channel and
736 therefore will not be spoofable. The TCP keepalive option
737 enabled by TCPKeepAlive is spoofable. The server alive mechanism
738 is valuable when the client or server depend on knowing when a
739 connection has become inactive.
741 The default value is 3. If, for example, ServerAliveInterval
742 (see below) is set to 15 and ServerAliveCountMax is left at the
743 default, if the server becomes unresponsive, ssh will disconnect
744 after approximately 45 seconds. This option applies to protocol
748 Sets a timeout interval in seconds after which if no data has
749 been received from the server, ssh(1) will send a message through
750 the encrypted channel to request a response from the server. The
751 default is 0, indicating that these messages will not be sent to
752 the server. This option applies to protocol version 2 only.
754 StrictHostKeyChecking
755 If this flag is set to ``yes'', ssh(1) will never automatically
756 add host keys to the ~/.ssh/known_hosts file, and refuses to
757 connect to hosts whose host key has changed. This provides
758 maximum protection against trojan horse attacks, though it can be
759 annoying when the /etc/ssh/ssh_known_hosts file is poorly
760 maintained or when connections to new hosts are frequently made.
761 This option forces the user to manually add all new hosts. If
762 this flag is set to ``no'', ssh will automatically add new host
763 keys to the user known hosts files. If this flag is set to
764 ``ask'', new host keys will be added to the user known host files
765 only after the user has confirmed that is what they really want
766 to do, and ssh will refuse to connect to hosts whose host key has
767 changed. The host keys of known hosts will be verified
768 automatically in all cases. The argument must be ``yes'',
769 ``no'', or ``ask''. The default is ``ask''.
772 Specifies whether the system should send TCP keepalive messages
773 to the other side. If they are sent, death of the connection or
774 crash of one of the machines will be properly noticed. However,
775 this means that connections will die if the route is down
776 temporarily, and some people find it annoying.
778 The default is ``yes'' (to send TCP keepalive messages), and the
779 client will notice if the network goes down or the remote host
780 dies. This is important in scripts, and many users want it too.
782 To disable TCP keepalive messages, the value should be set to
785 Tunnel Request tun(4) device forwarding between the client and the
786 server. The argument must be ``yes'', ``point-to-point'' (layer
787 3), ``ethernet'' (layer 2), or ``no''. Specifying ``yes''
788 requests the default tunnel mode, which is ``point-to-point''.
789 The default is ``no''.
792 Specifies the tun(4) devices to open on the client (local_tun)
793 and the server (remote_tun).
795 The argument must be local_tun[:remote_tun]. The devices may be
796 specified by numerical ID or the keyword ``any'', which uses the
797 next available tunnel device. If remote_tun is not specified, it
798 defaults to ``any''. The default is ``any:any''.
801 Specifies whether to use a privileged port for outgoing
802 connections. The argument must be ``yes'' or ``no''. The
803 default is ``no''. If set to ``yes'', ssh(1) must be setuid
804 root. Note that this option must be set to ``yes'' for
805 RhostsRSAAuthentication with older servers.
807 User Specifies the user to log in as. This can be useful when a
808 different user name is used on different machines. This saves
809 the trouble of having to remember to give the user name on the
813 Specifies one or more files to use for the user host key
814 database, separated by whitespace. The default is
815 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
818 Specifies whether to verify the remote key using DNS and SSHFP
819 resource records. If this option is set to ``yes'', the client
820 will implicitly trust keys that match a secure fingerprint from
821 DNS. Insecure fingerprints will be handled as if this option was
822 set to ``ask''. If this option is set to ``ask'', information on
823 fingerprint match will be displayed, but the user will still need
824 to confirm new host keys according to the StrictHostKeyChecking
825 option. The argument must be ``yes'', ``no'', or ``ask''. The
826 default is ``no''. Note that this option applies to protocol
829 See also VERIFYING HOST KEYS in ssh(1).
832 If this flag is set to ``yes'', an ASCII art representation of
833 the remote host key fingerprint is printed in addition to the hex
834 fingerprint string at login and for unknown host keys. If this
835 flag is set to ``no'', no fingerprint strings are printed at
836 login and only the hex fingerprint string will be printed for
837 unknown host keys. The default is ``no''.
840 Specifies the full pathname of the xauth(1) program. The default
841 is /usr/X11R6/bin/xauth.
844 A pattern consists of zero or more non-whitespace characters, `*' (a
845 wildcard that matches zero or more characters), or `?' (a wildcard that
846 matches exactly one character). For example, to specify a set of
847 declarations for any host in the ``.co.uk'' set of domains, the following
848 pattern could be used:
852 The following pattern would match any host in the 192.168.0.[0-9] network
857 A pattern-list is a comma-separated list of patterns. Patterns within
858 pattern-lists may be negated by preceding them with an exclamation mark
859 (`!'). For example, to allow a key to be used from anywhere within an
860 organization except from the ``dialup'' pool, the following entry (in
861 authorized_keys) could be used:
863 from="!*.dialup.example.com,*.example.com"
867 This is the per-user configuration file. The format of this file
868 is described above. This file is used by the SSH client.
869 Because of the potential for abuse, this file must have strict
870 permissions: read/write for the user, and not accessible by
874 Systemwide configuration file. This file provides defaults for
875 those values that are not specified in the user's configuration
876 file, and for those users who do not have a configuration file.
877 This file must be world-readable.
883 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
884 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
885 de Raadt and Dug Song removed many bugs, re-added newer features and
886 created OpenSSH. Markus Friedl contributed the support for SSH protocol
887 versions 1.5 and 2.0.
889 OpenBSD 5.5 February 23, 2014 OpenBSD 5.5
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