1 SSH_CONFIG(5) File Formats Manual SSH_CONFIG(5)
4 ssh_config M-bM-^@M-^S 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 M-bM-^@M-^\HostM-bM-^@M-^] specifications,
20 and that section is only applied for hosts that match one of the patterns
21 given in the specification. The matched host name is usually the one
22 given on the command line (see the CanonicalizeHostname option for
25 Since the first obtained value for each parameter is used, more host-
26 specific declarations should be given near the beginning of the file, and
27 general defaults at the end.
29 The configuration file has the following format:
31 Empty lines and lines starting with M-bM-^@M-^X#M-bM-^@M-^Y are comments. Otherwise a line
32 is of the format M-bM-^@M-^\keyword argumentsM-bM-^@M-^]. Configuration options may be
33 separated by whitespace or optional whitespace and exactly one M-bM-^@M-^X=M-bM-^@M-^Y; the
34 latter format is useful to avoid the need to quote whitespace when
35 specifying configuration options using the ssh, scp, and sftp -o option.
36 Arguments may optionally be enclosed in double quotes (") in order to
37 represent arguments containing spaces.
39 The possible keywords and their meanings are as follows (note that
40 keywords are case-insensitive and arguments are case-sensitive):
42 Host Restricts the following declarations (up to the next Host or
43 Match keyword) to be only for those hosts that match one of the
44 patterns given after the keyword. If more than one pattern is
45 provided, they should be separated by whitespace. A single M-bM-^@M-^X*M-bM-^@M-^Y
46 as a pattern can be used to provide global defaults for all
47 hosts. The host is usually the hostname argument given on the
48 command line (see the CanonicalizeHostname option for
51 A pattern entry may be negated by prefixing it with an
52 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y). If a negated entry is matched, then the
53 Host entry is ignored, regardless of whether any other patterns
54 on the line match. Negated matches are therefore useful to
55 provide exceptions for wildcard matches.
57 See PATTERNS for more information on patterns.
59 Match Restricts the following declarations (up to the next Host or
60 Match keyword) to be used only when the conditions following the
61 Match keyword are satisfied. Match conditions are specified
62 using one or more critera or the single token all which always
63 matches. The available criteria keywords are: canonical, exec,
64 host, originalhost, user, and localuser. The all criteria must
65 appear alone or immediately after canonical. Other criteria may
66 be combined arbitrarily. All criteria but all and canonical
67 require an argument. Criteria may be negated by prepending an
68 exclamation mark (M-bM-^@M-^X!M-bM-^@M-^Y).
70 The canonical keywork matches only when the configuration file is
71 being re-parsed after hostname canonicalization (see the
72 CanonicalizeHostname option.) This may be useful to specify
73 conditions that work with canonical host names only. The exec
74 keyword executes the specified command under the user's shell.
75 If the command returns a zero exit status then the condition is
76 considered true. Commands containing whitespace characters must
77 be quoted. The following character sequences in the command will
78 be expanded prior to execution: M-bM-^@M-^X%LM-bM-^@M-^Y will be substituted by the
79 first component of the local host name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted
80 by the local host name (including any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be
81 substituted by the target host name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by
82 the original target host name specified on the command-line, M-bM-^@M-^X%pM-bM-^@M-^Y
83 the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by the remote login username, and M-bM-^@M-^X%uM-bM-^@M-^Y
84 by the username of the user running ssh(1).
86 The other keywords' criteria must be single entries or comma-
87 separated lists and may use the wildcard and negation operators
88 described in the PATTERNS section. The criteria for the host
89 keyword are matched against the target hostname, after any
90 substitution by the Hostname or CanonicalizeHostname options.
91 The originalhost keyword matches against the hostname as it was
92 specified on the command-line. The user keyword matches against
93 the target username on the remote host. The localuser keyword
94 matches against the name of the local user running ssh(1) (this
95 keyword may be useful in system-wide ssh_config files).
98 Specifies which address family to use when connecting. Valid
99 arguments are M-bM-^@M-^\anyM-bM-^@M-^], M-bM-^@M-^\inetM-bM-^@M-^] (use IPv4 only), or M-bM-^@M-^\inet6M-bM-^@M-^] (use IPv6
103 If set to M-bM-^@M-^\yesM-bM-^@M-^], passphrase/password querying will be disabled.
104 This option is useful in scripts and other batch jobs where no
105 user is present to supply the password. The argument must be
106 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
109 Use the specified address on the local machine as the source
110 address of the connection. Only useful on systems with more than
111 one address. Note that this option does not work if
112 UsePrivilegedPort is set to M-bM-^@M-^\yesM-bM-^@M-^].
115 When CanonicalizeHostname is enabled, this option specifies the
116 list of domain suffixes in which to search for the specified
119 CanonicalizeFallbackLocal
120 Specifies whether to fail with an error when hostname
121 canonicalization fails. The default, M-bM-^@M-^\yesM-bM-^@M-^], will attempt to look
122 up the unqualified hostname using the system resolver's search
123 rules. A value of M-bM-^@M-^\noM-bM-^@M-^] will cause ssh(1) to fail instantly if
124 CanonicalizeHostname is enabled and the target hostname cannot be
125 found in any of the domains specified by CanonicalDomains.
128 Controls whether explicit hostname canonicalization is performed.
129 The default, M-bM-^@M-^\noM-bM-^@M-^], is not to perform any name rewriting and let
130 the system resolver handle all hostname lookups. If set to M-bM-^@M-^\yesM-bM-^@M-^]
131 then, for connections that do not use a ProxyCommand, ssh(1) will
132 attempt to canonicalize the hostname specified on the command
133 line using the CanonicalDomains suffixes and
134 CanonicalizePermittedCNAMEs rules. If CanonicalizeHostname is
135 set to M-bM-^@M-^\alwaysM-bM-^@M-^], then canonicalization is applied to proxied
138 If this option is enabled, then the configuration files are
139 processed again using the new target name to pick up any new
140 configuration in matching Host and Match stanzas.
143 Specifies the maximum number of dot characters in a hostname
144 before canonicalization is disabled. The default, M-bM-^@M-^\1M-bM-^@M-^], allows a
145 single dot (i.e. hostname.subdomain).
147 CanonicalizePermittedCNAMEs
148 Specifies rules to determine whether CNAMEs should be followed
149 when canonicalizing hostnames. The rules consist of one or more
150 arguments of source_domain_list:target_domain_list, where
151 source_domain_list is a pattern-list of domains that may follow
152 CNAMEs in canonicalization, and target_domain_list is a pattern-
153 list of domains that they may resolve to.
155 For example, M-bM-^@M-^\*.a.example.com:*.b.example.com,*.c.example.comM-bM-^@M-^]
156 will allow hostnames matching M-bM-^@M-^\*.a.example.comM-bM-^@M-^] to be
157 canonicalized to names in the M-bM-^@M-^\*.b.example.comM-bM-^@M-^] or
158 M-bM-^@M-^\*.c.example.comM-bM-^@M-^] domains.
160 ChallengeResponseAuthentication
161 Specifies whether to use challenge-response authentication. The
162 argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
163 M-bM-^@M-^\yesM-bM-^@M-^].
166 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will additionally check the
167 host IP address in the known_hosts file. This allows ssh to
168 detect if a host key changed due to DNS spoofing. If the option
169 is set to M-bM-^@M-^\noM-bM-^@M-^], the check will not be executed. The default is
170 M-bM-^@M-^\yesM-bM-^@M-^].
172 Cipher Specifies the cipher to use for encrypting the session in
173 protocol version 1. Currently, M-bM-^@M-^\blowfishM-bM-^@M-^], M-bM-^@M-^\3desM-bM-^@M-^], and M-bM-^@M-^\desM-bM-^@M-^] are
174 supported. des is only supported in the ssh(1) client for
175 interoperability with legacy protocol 1 implementations that do
176 not support the 3des cipher. Its use is strongly discouraged due
177 to cryptographic weaknesses. The default is M-bM-^@M-^\3desM-bM-^@M-^].
180 Specifies the ciphers allowed for protocol version 2 in order of
181 preference. Multiple ciphers must be comma-separated. The
182 supported ciphers are:
191 aes128-gcm@openssh.com
192 aes256-gcm@openssh.com
198 chacha20-poly1305@openssh.com
202 aes128-ctr,aes192-ctr,aes256-ctr,
203 aes128-gcm@openssh.com,aes256-gcm@openssh.com,
204 chacha20-poly1305@openssh.com,
205 arcfour256,arcfour128,
206 aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,
207 aes192-cbc,aes256-cbc,arcfour
209 The list of available ciphers may also be obtained using the -Q
210 option of ssh(1) with an argument of M-bM-^@M-^\cipherM-bM-^@M-^].
213 Specifies that all local, remote, and dynamic port forwardings
214 specified in the configuration files or on the command line be
215 cleared. This option is primarily useful when used from the
216 ssh(1) command line to clear port forwardings set in
217 configuration files, and is automatically set by scp(1) and
218 sftp(1). The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
219 M-bM-^@M-^\noM-bM-^@M-^].
222 Specifies whether to use compression. The argument must be M-bM-^@M-^\yesM-bM-^@M-^]
223 or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
226 Specifies the compression level to use if compression is enabled.
227 The argument must be an integer from 1 (fast) to 9 (slow, best).
228 The default level is 6, which is good for most applications. The
229 meaning of the values is the same as in gzip(1). Note that this
230 option applies to protocol version 1 only.
233 Specifies the number of tries (one per second) to make before
234 exiting. The argument must be an integer. This may be useful in
235 scripts if the connection sometimes fails. The default is 1.
238 Specifies the timeout (in seconds) used when connecting to the
239 SSH server, instead of using the default system TCP timeout.
240 This value is used only when the target is down or really
241 unreachable, not when it refuses the connection.
244 Enables the sharing of multiple sessions over a single network
245 connection. When set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will listen for
246 connections on a control socket specified using the ControlPath
247 argument. Additional sessions can connect to this socket using
248 the same ControlPath with ControlMaster set to M-bM-^@M-^\noM-bM-^@M-^] (the
249 default). These sessions will try to reuse the master instance's
250 network connection rather than initiating new ones, but will fall
251 back to connecting normally if the control socket does not exist,
254 Setting this to M-bM-^@M-^\askM-bM-^@M-^] will cause ssh to listen for control
255 connections, but require confirmation using the SSH_ASKPASS
256 program before they are accepted (see ssh-add(1) for details).
257 If the ControlPath cannot be opened, ssh will continue without
258 connecting to a master instance.
260 X11 and ssh-agent(1) forwarding is supported over these
261 multiplexed connections, however the display and agent forwarded
262 will be the one belonging to the master connection i.e. it is not
263 possible to forward multiple displays or agents.
265 Two additional options allow for opportunistic multiplexing: try
266 to use a master connection but fall back to creating a new one if
267 one does not already exist. These options are: M-bM-^@M-^\autoM-bM-^@M-^] and
268 M-bM-^@M-^\autoaskM-bM-^@M-^]. The latter requires confirmation like the M-bM-^@M-^\askM-bM-^@M-^]
272 Specify the path to the control socket used for connection
273 sharing as described in the ControlMaster section above or the
274 string M-bM-^@M-^\noneM-bM-^@M-^] to disable connection sharing. In the path, M-bM-^@M-^X%LM-bM-^@M-^Y
275 will be substituted by the first component of the local host
276 name, M-bM-^@M-^X%lM-bM-^@M-^Y will be substituted by the local host name (including
277 any domain name), M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted by the target host
278 name, M-bM-^@M-^X%nM-bM-^@M-^Y will be substituted by the original target host name
279 specified on the command line, M-bM-^@M-^X%pM-bM-^@M-^Y the destination port, M-bM-^@M-^X%rM-bM-^@M-^Y by
280 the remote login username, M-bM-^@M-^X%uM-bM-^@M-^Y by the username of the user
281 running ssh(1), and M-bM-^@M-^X%CM-bM-^@M-^Y by a hash of the concatenation:
282 %l%h%p%r. It is recommended that any ControlPath used for
283 opportunistic connection sharing include at least %h, %p, and %r
284 (or alternatively %C) and be placed in a directory that is not
285 writable by other users. This ensures that shared connections
286 are uniquely identified.
289 When used in conjunction with ControlMaster, specifies that the
290 master connection should remain open in the background (waiting
291 for future client connections) after the initial client
292 connection has been closed. If set to M-bM-^@M-^\noM-bM-^@M-^], then the master
293 connection will not be placed into the background, and will close
294 as soon as the initial client connection is closed. If set to
295 M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\0M-bM-^@M-^], then the master connection will remain in the
296 background indefinitely (until killed or closed via a mechanism
297 such as the ssh(1) M-bM-^@M-^\-O exitM-bM-^@M-^] option). If set to a time in
298 seconds, or a time in any of the formats documented in
299 sshd_config(5), then the backgrounded master connection will
300 automatically terminate after it has remained idle (with no
301 client connections) for the specified time.
304 Specifies that a TCP port on the local machine be forwarded over
305 the secure channel, and the application protocol is then used to
306 determine where to connect to from the remote machine.
308 The argument must be [bind_address:]port. IPv6 addresses can be
309 specified by enclosing addresses in square brackets. By default,
310 the local port is bound in accordance with the GatewayPorts
311 setting. However, an explicit bind_address may be used to bind
312 the connection to a specific address. The bind_address of
313 M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the listening port be bound for local
314 use only, while an empty address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port
315 should be available from all interfaces.
317 Currently the SOCKS4 and SOCKS5 protocols are supported, and
318 ssh(1) will act as a SOCKS server. Multiple forwardings may be
319 specified, and additional forwardings can be given on the command
320 line. Only the superuser can forward privileged ports.
323 Setting this option to M-bM-^@M-^\yesM-bM-^@M-^] in the global client configuration
324 file /etc/ssh/ssh_config enables the use of the helper program
325 ssh-keysign(8) during HostbasedAuthentication. The argument must
326 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^]. This option should be
327 placed in the non-hostspecific section. See ssh-keysign(8) for
331 Sets the escape character (default: M-bM-^@M-^X~M-bM-^@M-^Y). The escape character
332 can also be set on the command line. The argument should be a
333 single character, M-bM-^@M-^X^M-bM-^@M-^Y followed by a letter, or M-bM-^@M-^\noneM-bM-^@M-^] to disable
334 the escape character entirely (making the connection transparent
338 Specifies whether ssh(1) should terminate the connection if it
339 cannot set up all requested dynamic, tunnel, local, and remote
340 port forwardings. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
341 default is M-bM-^@M-^\noM-bM-^@M-^].
344 Specifies the hash algorithm used when displaying key
345 fingerprints. Valid options are: M-bM-^@M-^\md5M-bM-^@M-^] and M-bM-^@M-^\sha256M-bM-^@M-^]. The
346 default is M-bM-^@M-^\sha256M-bM-^@M-^].
349 Specifies whether the connection to the authentication agent (if
350 any) will be forwarded to the remote machine. The argument must
351 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
353 Agent forwarding should be enabled with caution. Users with the
354 ability to bypass file permissions on the remote host (for the
355 agent's Unix-domain socket) can access the local agent through
356 the forwarded connection. An attacker cannot obtain key material
357 from the agent, however they can perform operations on the keys
358 that enable them to authenticate using the identities loaded into
362 Specifies whether X11 connections will be automatically
363 redirected over the secure channel and DISPLAY set. The argument
364 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
366 X11 forwarding should be enabled with caution. Users with the
367 ability to bypass file permissions on the remote host (for the
368 user's X11 authorization database) can access the local X11
369 display through the forwarded connection. An attacker may then
370 be able to perform activities such as keystroke monitoring if the
371 ForwardX11Trusted option is also enabled.
374 Specify a timeout for untrusted X11 forwarding using the format
375 described in the TIME FORMATS section of sshd_config(5). X11
376 connections received by ssh(1) after this time will be refused.
377 The default is to disable untrusted X11 forwarding after twenty
381 If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], remote X11 clients will have full
382 access to the original X11 display.
384 If this option is set to M-bM-^@M-^\noM-bM-^@M-^], remote X11 clients will be
385 considered untrusted and prevented from stealing or tampering
386 with data belonging to trusted X11 clients. Furthermore, the
387 xauth(1) token used for the session will be set to expire after
388 20 minutes. Remote clients will be refused access after this
391 The default is M-bM-^@M-^\noM-bM-^@M-^].
393 See the X11 SECURITY extension specification for full details on
394 the restrictions imposed on untrusted clients.
397 Specifies whether remote hosts are allowed to connect to local
398 forwarded ports. By default, ssh(1) binds local port forwardings
399 to the loopback address. This prevents other remote hosts from
400 connecting to forwarded ports. GatewayPorts can be used to
401 specify that ssh should bind local port forwardings to the
402 wildcard address, thus allowing remote hosts to connect to
403 forwarded ports. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
404 default is M-bM-^@M-^\noM-bM-^@M-^].
407 Specifies one or more files to use for the global host key
408 database, separated by whitespace. The default is
409 /etc/ssh/ssh_known_hosts, /etc/ssh/ssh_known_hosts2.
412 Specifies whether user authentication based on GSSAPI is allowed.
413 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol
416 GSSAPIDelegateCredentials
417 Forward (delegate) credentials to the server. The default is
418 M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol version 2 only.
421 Indicates that ssh(1) should hash host names and addresses when
422 they are added to ~/.ssh/known_hosts. These hashed names may be
423 used normally by ssh(1) and sshd(8), but they do not reveal
424 identifying information should the file's contents be disclosed.
425 The default is M-bM-^@M-^\noM-bM-^@M-^]. Note that existing names and addresses in
426 known hosts files will not be converted automatically, but may be
427 manually hashed using ssh-keygen(1).
429 HostbasedAuthentication
430 Specifies whether to try rhosts based authentication with public
431 key authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
432 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 2 only
433 and is similar to RhostsRSAAuthentication.
436 Specifies the key types that will be used for hostbased
437 authentication as a comma-separated pattern list. The default
438 M-bM-^@M-^\*M-bM-^@M-^] will allow all key types. The -Q option of ssh(1) may be
439 used to list supported key types.
442 Specifies the protocol version 2 host key algorithms that the
443 client wants to use in order of preference. The default for this
446 ecdsa-sha2-nistp256-cert-v01@openssh.com,
447 ecdsa-sha2-nistp384-cert-v01@openssh.com,
448 ecdsa-sha2-nistp521-cert-v01@openssh.com,
449 ssh-ed25519-cert-v01@openssh.com,
450 ssh-rsa-cert-v01@openssh.com,ssh-dss-cert-v01@openssh.com,
451 ssh-rsa-cert-v00@openssh.com,ssh-dss-cert-v00@openssh.com,
452 ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,
453 ssh-ed25519,ssh-rsa,ssh-dss
455 If hostkeys are known for the destination host then this default
456 is modified to prefer their algorithms.
458 The list of available key types may also be obtained using the -Q
459 option of ssh(1) with an argument of M-bM-^@M-^\keyM-bM-^@M-^].
462 Specifies an alias that should be used instead of the real host
463 name when looking up or saving the host key in the host key
464 database files. This option is useful for tunneling SSH
465 connections or for multiple servers running on a single host.
468 Specifies the real host name to log into. This can be used to
469 specify nicknames or abbreviations for hosts. If the hostname
470 contains the character sequence M-bM-^@M-^X%hM-bM-^@M-^Y, then this will be replaced
471 with the host name specified on the command line (this is useful
472 for manipulating unqualified names). The character sequence M-bM-^@M-^X%%M-bM-^@M-^Y
473 will be replaced by a single M-bM-^@M-^X%M-bM-^@M-^Y character, which may be used
474 when specifying IPv6 link-local addresses.
476 The default is the name given on the command line. Numeric IP
477 addresses are also permitted (both on the command line and in
478 HostName specifications).
481 Specifies that ssh(1) should only use the authentication identity
482 files configured in the ssh_config files, even if ssh-agent(1) or
483 a PKCS11Provider offers more identities. The argument to this
484 keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. This option is intended for
485 situations where ssh-agent offers many different identities. The
486 default is M-bM-^@M-^\noM-bM-^@M-^].
489 Specifies a file from which the user's DSA, ECDSA, Ed25519 or RSA
490 authentication identity is read. The default is ~/.ssh/identity
491 for protocol version 1, and ~/.ssh/id_dsa, ~/.ssh/id_ecdsa,
492 ~/.ssh/id_ed25519 and ~/.ssh/id_rsa for protocol version 2.
493 Additionally, any identities represented by the authentication
494 agent will be used for authentication unless IdentitiesOnly is
495 set. ssh(1) will try to load certificate information from the
496 filename obtained by appending -cert.pub to the path of a
497 specified IdentityFile.
499 The file name may use the tilde syntax to refer to a user's home
500 directory or one of the following escape characters: M-bM-^@M-^X%dM-bM-^@M-^Y (local
501 user's home directory), M-bM-^@M-^X%uM-bM-^@M-^Y (local user name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host
502 name), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host name) or M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name).
504 It is possible to have multiple identity files specified in
505 configuration files; all these identities will be tried in
506 sequence. Multiple IdentityFile directives will add to the list
507 of identities tried (this behaviour differs from that of other
508 configuration directives).
510 IdentityFile may be used in conjunction with IdentitiesOnly to
511 select which identities in an agent are offered during
515 Specifies a pattern-list of unknown options to be ignored if they
516 are encountered in configuration parsing. This may be used to
517 suppress errors if ssh_config contains options that are
518 unrecognised by ssh(1). It is recommended that IgnoreUnknown be
519 listed early in the configuration file as it will not be applied
520 to unknown options that appear before it.
522 IPQoS Specifies the IPv4 type-of-service or DSCP class for connections.
523 Accepted values are M-bM-^@M-^\af11M-bM-^@M-^], M-bM-^@M-^\af12M-bM-^@M-^], M-bM-^@M-^\af13M-bM-^@M-^], M-bM-^@M-^\af21M-bM-^@M-^], M-bM-^@M-^\af22M-bM-^@M-^],
524 M-bM-^@M-^\af23M-bM-^@M-^], M-bM-^@M-^\af31M-bM-^@M-^], M-bM-^@M-^\af32M-bM-^@M-^], M-bM-^@M-^\af33M-bM-^@M-^], M-bM-^@M-^\af41M-bM-^@M-^], M-bM-^@M-^\af42M-bM-^@M-^], M-bM-^@M-^\af43M-bM-^@M-^], M-bM-^@M-^\cs0M-bM-^@M-^],
525 M-bM-^@M-^\cs1M-bM-^@M-^], M-bM-^@M-^\cs2M-bM-^@M-^], M-bM-^@M-^\cs3M-bM-^@M-^], M-bM-^@M-^\cs4M-bM-^@M-^], M-bM-^@M-^\cs5M-bM-^@M-^], M-bM-^@M-^\cs6M-bM-^@M-^], M-bM-^@M-^\cs7M-bM-^@M-^], M-bM-^@M-^\efM-bM-^@M-^],
526 M-bM-^@M-^\lowdelayM-bM-^@M-^], M-bM-^@M-^\throughputM-bM-^@M-^], M-bM-^@M-^\reliabilityM-bM-^@M-^], or a numeric value.
527 This option may take one or two arguments, separated by
528 whitespace. If one argument is specified, it is used as the
529 packet class unconditionally. If two values are specified, the
530 first is automatically selected for interactive sessions and the
531 second for non-interactive sessions. The default is M-bM-^@M-^\lowdelayM-bM-^@M-^]
532 for interactive sessions and M-bM-^@M-^\throughputM-bM-^@M-^] for non-interactive
535 KbdInteractiveAuthentication
536 Specifies whether to use keyboard-interactive authentication.
537 The argument to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default
538 is M-bM-^@M-^\yesM-bM-^@M-^].
540 KbdInteractiveDevices
541 Specifies the list of methods to use in keyboard-interactive
542 authentication. Multiple method names must be comma-separated.
543 The default is to use the server specified list. The methods
544 available vary depending on what the server supports. For an
545 OpenSSH server, it may be zero or more of: M-bM-^@M-^\bsdauthM-bM-^@M-^], M-bM-^@M-^\pamM-bM-^@M-^], and
546 M-bM-^@M-^\skeyM-bM-^@M-^].
549 Specifies the available KEX (Key Exchange) algorithms. Multiple
550 algorithms must be comma-separated. The default is:
552 curve25519-sha256@libssh.org,
553 ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2-nistp521,
554 diffie-hellman-group-exchange-sha256,
555 diffie-hellman-group14-sha1,
556 diffie-hellman-group-exchange-sha1,
557 diffie-hellman-group1-sha1
559 The list of available key exchange algorithms may also be
560 obtained using the -Q option of ssh(1) with an argument of M-bM-^@M-^\kexM-bM-^@M-^].
563 Specifies a command to execute on the local machine after
564 successfully connecting to the server. The command string
565 extends to the end of the line, and is executed with the user's
566 shell. The following escape character substitutions will be
567 performed: M-bM-^@M-^X%dM-bM-^@M-^Y (local user's home directory), M-bM-^@M-^X%hM-bM-^@M-^Y (remote host
568 name), M-bM-^@M-^X%lM-bM-^@M-^Y (local host name), M-bM-^@M-^X%nM-bM-^@M-^Y (host name as provided on the
569 command line), M-bM-^@M-^X%pM-bM-^@M-^Y (remote port), M-bM-^@M-^X%rM-bM-^@M-^Y (remote user name) or
570 M-bM-^@M-^X%uM-bM-^@M-^Y (local user name) or M-bM-^@M-^X%CM-bM-^@M-^Y by a hash of the concatenation:
573 The command is run synchronously and does not have access to the
574 session of the ssh(1) that spawned it. It should not be used for
575 interactive commands.
577 This directive is ignored unless PermitLocalCommand has been
581 Specifies that a TCP port on the local machine be forwarded over
582 the secure channel to the specified host and port from the remote
583 machine. The first argument must be [bind_address:]port and the
584 second argument must be host:hostport. IPv6 addresses can be
585 specified by enclosing addresses in square brackets. Multiple
586 forwardings may be specified, and additional forwardings can be
587 given on the command line. Only the superuser can forward
588 privileged ports. By default, the local port is bound in
589 accordance with the GatewayPorts setting. However, an explicit
590 bind_address may be used to bind the connection to a specific
591 address. The bind_address of M-bM-^@M-^\localhostM-bM-^@M-^] indicates that the
592 listening port be bound for local use only, while an empty
593 address or M-bM-^@M-^X*M-bM-^@M-^Y indicates that the port should be available from
597 Gives the verbosity level that is used when logging messages from
598 ssh(1). The possible values are: QUIET, FATAL, ERROR, INFO,
599 VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. The default is INFO.
600 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
601 higher levels of verbose output.
603 MACs Specifies the MAC (message authentication code) algorithms in
604 order of preference. The MAC algorithm is used in protocol
605 version 2 for data integrity protection. Multiple algorithms
606 must be comma-separated. The algorithms that contain M-bM-^@M-^\-etmM-bM-^@M-^]
607 calculate the MAC after encryption (encrypt-then-mac). These are
608 considered safer and their use recommended. The default is:
610 umac-64-etm@openssh.com,umac-128-etm@openssh.com,
611 hmac-sha2-256-etm@openssh.com,hmac-sha2-512-etm@openssh.com,
612 umac-64@openssh.com,umac-128@openssh.com,
613 hmac-sha2-256,hmac-sha2-512,
614 hmac-md5-etm@openssh.com,hmac-sha1-etm@openssh.com,
615 hmac-ripemd160-etm@openssh.com,
616 hmac-sha1-96-etm@openssh.com,hmac-md5-96-etm@openssh.com,
617 hmac-md5,hmac-sha1,hmac-ripemd160,
618 hmac-sha1-96,hmac-md5-96
620 The list of available MAC algorithms may also be obtained using
621 the -Q option of ssh(1) with an argument of M-bM-^@M-^\macM-bM-^@M-^].
623 NoHostAuthenticationForLocalhost
624 This option can be used if the home directory is shared across
625 machines. In this case localhost will refer to a different
626 machine on each of the machines and the user will get many
627 warnings about changed host keys. However, this option disables
628 host authentication for localhost. The argument to this keyword
629 must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is to check the host key for
632 NumberOfPasswordPrompts
633 Specifies the number of password prompts before giving up. The
634 argument to this keyword must be an integer. The default is 3.
636 PasswordAuthentication
637 Specifies whether to use password authentication. The argument
638 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^].
641 Allow local command execution via the LocalCommand option or
642 using the !command escape sequence in ssh(1). The argument must
643 be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
646 Specifies which PKCS#11 provider to use. The argument to this
647 keyword is the PKCS#11 shared library ssh(1) should use to
648 communicate with a PKCS#11 token providing the user's private RSA
651 Port Specifies the port number to connect on the remote host. The
654 PreferredAuthentications
655 Specifies the order in which the client should try protocol 2
656 authentication methods. This allows a client to prefer one
657 method (e.g. keyboard-interactive) over another method (e.g.
658 password). The default is:
660 gssapi-with-mic,hostbased,publickey,
661 keyboard-interactive,password
664 Specifies the protocol versions ssh(1) should support in order of
665 preference. The possible values are M-bM-^@M-^X1M-bM-^@M-^Y and M-bM-^@M-^X2M-bM-^@M-^Y. Multiple
666 versions must be comma-separated. When this option is set to
667 M-bM-^@M-^\2,1M-bM-^@M-^] ssh will try version 2 and fall back to version 1 if
668 version 2 is not available. The default is M-bM-^@M-^X2M-bM-^@M-^Y.
671 Specifies the command to use to connect to the server. The
672 command string extends to the end of the line, and is executed
673 using the user's shell M-bM-^@M-^XexecM-bM-^@M-^Y directive to avoid a lingering
676 In the command string, any occurrence of M-bM-^@M-^X%hM-bM-^@M-^Y will be substituted
677 by the host name to connect, M-bM-^@M-^X%pM-bM-^@M-^Y by the port, and M-bM-^@M-^X%rM-bM-^@M-^Y by the
678 remote user name. The command can be basically anything, and
679 should read from its standard input and write to its standard
680 output. It should eventually connect an sshd(8) server running
681 on some machine, or execute sshd -i somewhere. Host key
682 management will be done using the HostName of the host being
683 connected (defaulting to the name typed by the user). Setting
684 the command to M-bM-^@M-^\noneM-bM-^@M-^] disables this option entirely. Note that
685 CheckHostIP is not available for connects with a proxy command.
687 This directive is useful in conjunction with nc(1) and its proxy
688 support. For example, the following directive would connect via
689 an HTTP proxy at 192.0.2.0:
691 ProxyCommand /usr/bin/nc -X connect -x 192.0.2.0:8080 %h %p
694 Specifies that ProxyCommand will pass a connected file descriptor
695 back to ssh(1) instead of continuing to execute and pass data.
696 The default is M-bM-^@M-^\noM-bM-^@M-^].
699 Specifies whether to try public key authentication. The argument
700 to this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\yesM-bM-^@M-^].
701 This option applies to protocol version 2 only.
704 Specifies the maximum amount of data that may be transmitted
705 before the session key is renegotiated, optionally followed a
706 maximum amount of time that may pass before the session key is
707 renegotiated. The first argument is specified in bytes and may
708 have a suffix of M-bM-^@M-^XKM-bM-^@M-^Y, M-bM-^@M-^XMM-bM-^@M-^Y, or M-bM-^@M-^XGM-bM-^@M-^Y to indicate Kilobytes,
709 Megabytes, or Gigabytes, respectively. The default is between
710 M-bM-^@M-^X1GM-bM-^@M-^Y and M-bM-^@M-^X4GM-bM-^@M-^Y, depending on the cipher. The optional second
711 value is specified in seconds and may use any of the units
712 documented in the TIME FORMATS section of sshd_config(5). The
713 default value for RekeyLimit is M-bM-^@M-^\default noneM-bM-^@M-^], which means that
714 rekeying is performed after the cipher's default amount of data
715 has been sent or received and no time based rekeying is done.
716 This option applies to protocol version 2 only.
719 Specifies that a TCP port on the remote machine be forwarded over
720 the secure channel to the specified host and port from the local
721 machine. The first argument must be [bind_address:]port and the
722 second argument must be host:hostport. IPv6 addresses can be
723 specified by enclosing addresses in square brackets. Multiple
724 forwardings may be specified, and additional forwardings can be
725 given on the command line. Privileged ports can be forwarded
726 only when logging in as root on the remote machine.
728 If the port argument is M-bM-^@M-^X0M-bM-^@M-^Y, the listen port will be dynamically
729 allocated on the server and reported to the client at run time.
731 If the bind_address is not specified, the default is to only bind
732 to loopback addresses. If the bind_address is M-bM-^@M-^X*M-bM-^@M-^Y or an empty
733 string, then the forwarding is requested to listen on all
734 interfaces. Specifying a remote bind_address will only succeed
735 if the server's GatewayPorts option is enabled (see
739 Specifies whether to request a pseudo-tty for the session. The
740 argument may be one of: M-bM-^@M-^\noM-bM-^@M-^] (never request a TTY), M-bM-^@M-^\yesM-bM-^@M-^] (always
741 request a TTY when standard input is a TTY), M-bM-^@M-^\forceM-bM-^@M-^] (always
742 request a TTY) or M-bM-^@M-^\autoM-bM-^@M-^] (request a TTY when opening a login
743 session). This option mirrors the -t and -T flags for ssh(1).
746 Specifies revoked host public keys. Keys listed in this file
747 will be refused for host authentication. Note that if this file
748 does not exist or is not readable, then host authentication will
749 be refused for all hosts. Keys may be specified as a text file,
750 listing one public key per line, or as an OpenSSH Key Revocation
751 List (KRL) as generated by ssh-keygen(1). For more information
752 on KRLs, see the KEY REVOCATION LISTS section in ssh-keygen(1).
754 RhostsRSAAuthentication
755 Specifies whether to try rhosts based authentication with RSA
756 host authentication. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The
757 default is M-bM-^@M-^\noM-bM-^@M-^]. This option applies to protocol version 1 only
758 and requires ssh(1) to be setuid root.
761 Specifies whether to try RSA authentication. The argument to
762 this keyword must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. RSA authentication will only
763 be attempted if the identity file exists, or an authentication
764 agent is running. The default is M-bM-^@M-^\yesM-bM-^@M-^]. Note that this option
765 applies to protocol version 1 only.
768 Specifies what variables from the local environ(7) should be sent
769 to the server. Note that environment passing is only supported
770 for protocol 2. The server must also support it, and the server
771 must be configured to accept these environment variables. Refer
772 to AcceptEnv in sshd_config(5) for how to configure the server.
773 Variables are specified by name, which may contain wildcard
774 characters. Multiple environment variables may be separated by
775 whitespace or spread across multiple SendEnv directives. The
776 default is not to send any environment variables.
778 See PATTERNS for more information on patterns.
781 Sets the number of server alive messages (see below) which may be
782 sent without ssh(1) receiving any messages back from the server.
783 If this threshold is reached while server alive messages are
784 being sent, ssh will disconnect from the server, terminating the
785 session. It is important to note that the use of server alive
786 messages is very different from TCPKeepAlive (below). The server
787 alive messages are sent through the encrypted channel and
788 therefore will not be spoofable. The TCP keepalive option
789 enabled by TCPKeepAlive is spoofable. The server alive mechanism
790 is valuable when the client or server depend on knowing when a
791 connection has become inactive.
793 The default value is 3. If, for example, ServerAliveInterval
794 (see below) is set to 15 and ServerAliveCountMax is left at the
795 default, if the server becomes unresponsive, ssh will disconnect
796 after approximately 45 seconds. This option applies to protocol
800 Sets a timeout interval in seconds after which if no data has
801 been received from the server, ssh(1) will send a message through
802 the encrypted channel to request a response from the server. The
803 default is 0, indicating that these messages will not be sent to
804 the server. This option applies to protocol version 2 only.
807 Sets the octal file creation mode mask (umask) used when creating
808 a Unix-domain socket file for local or remote port forwarding.
809 This option is only used for port forwarding to a Unix-domain
812 The default value is 0177, which creates a Unix-domain socket
813 file that is readable and writable only by the owner. Note that
814 not all operating systems honor the file mode on Unix-domain
817 StreamLocalBindUnlink
818 Specifies whether to remove an existing Unix-domain socket file
819 for local or remote port forwarding before creating a new one.
820 If the socket file already exists and StreamLocalBindUnlink is
821 not enabled, ssh will be unable to forward the port to the Unix-
822 domain socket file. This option is only used for port forwarding
823 to a Unix-domain socket file.
825 The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is M-bM-^@M-^\noM-bM-^@M-^].
827 StrictHostKeyChecking
828 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) will never automatically add
829 host keys to the ~/.ssh/known_hosts file, and refuses to connect
830 to hosts whose host key has changed. This provides maximum
831 protection against trojan horse attacks, though it can be
832 annoying when the /etc/ssh/ssh_known_hosts file is poorly
833 maintained or when connections to new hosts are frequently made.
834 This option forces the user to manually add all new hosts. If
835 this flag is set to M-bM-^@M-^\noM-bM-^@M-^], ssh will automatically add new host
836 keys to the user known hosts files. If this flag is set to
837 M-bM-^@M-^\askM-bM-^@M-^], new host keys will be added to the user known host files
838 only after the user has confirmed that is what they really want
839 to do, and ssh will refuse to connect to hosts whose host key has
840 changed. The host keys of known hosts will be verified
841 automatically in all cases. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or
842 M-bM-^@M-^\askM-bM-^@M-^]. The default is M-bM-^@M-^\askM-bM-^@M-^].
845 Specifies whether the system should send TCP keepalive messages
846 to the other side. If they are sent, death of the connection or
847 crash of one of the machines will be properly noticed. However,
848 this means that connections will die if the route is down
849 temporarily, and some people find it annoying.
851 The default is M-bM-^@M-^\yesM-bM-^@M-^] (to send TCP keepalive messages), and the
852 client will notice if the network goes down or the remote host
853 dies. This is important in scripts, and many users want it too.
855 To disable TCP keepalive messages, the value should be set to
856 M-bM-^@M-^\noM-bM-^@M-^].
858 Tunnel Request tun(4) device forwarding between the client and the
859 server. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\point-to-pointM-bM-^@M-^] (layer 3),
860 M-bM-^@M-^\ethernetM-bM-^@M-^] (layer 2), or M-bM-^@M-^\noM-bM-^@M-^]. Specifying M-bM-^@M-^\yesM-bM-^@M-^] requests the
861 default tunnel mode, which is M-bM-^@M-^\point-to-pointM-bM-^@M-^]. The default is
862 M-bM-^@M-^\noM-bM-^@M-^].
865 Specifies the tun(4) devices to open on the client (local_tun)
866 and the server (remote_tun).
868 The argument must be local_tun[:remote_tun]. The devices may be
869 specified by numerical ID or the keyword M-bM-^@M-^\anyM-bM-^@M-^], which uses the
870 next available tunnel device. If remote_tun is not specified, it
871 defaults to M-bM-^@M-^\anyM-bM-^@M-^]. The default is M-bM-^@M-^\any:anyM-bM-^@M-^].
874 Specifies whether ssh(1) should accept notifications of
875 additional hostkeys from the server sent after authentication has
876 completed and add them to UserKnownHostsFile. The argument must
877 be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^] (the default) or M-bM-^@M-^\askM-bM-^@M-^]. Enabling this option
878 allows learning alternate hostkeys for a server and supports
879 graceful key rotation by allowing a server to send replacement
880 public keys before old ones are removed. Additional hostkeys are
881 only accepted if the key used to authenticate the host was
882 already trusted or explicity accepted by the user. If
883 UpdateHostKeys is set to M-bM-^@M-^\askM-bM-^@M-^], then the user is asked to confirm
884 the modifications to the known_hosts file. Confirmation is
885 currently incompatible with ControlPersist, and will be disabled
888 Presently, only sshd(8) from OpenSSH 6.8 and greater support the
889 M-bM-^@M-^\hostkeys@openssh.comM-bM-^@M-^] protocol extension used to inform the
890 client of all the server's hostkeys.
893 Specifies whether to use a privileged port for outgoing
894 connections. The argument must be M-bM-^@M-^\yesM-bM-^@M-^] or M-bM-^@M-^\noM-bM-^@M-^]. The default is
895 M-bM-^@M-^\noM-bM-^@M-^]. If set to M-bM-^@M-^\yesM-bM-^@M-^], ssh(1) must be setuid root. Note that
896 this option must be set to M-bM-^@M-^\yesM-bM-^@M-^] for RhostsRSAAuthentication with
899 User Specifies the user to log in as. This can be useful when a
900 different user name is used on different machines. This saves
901 the trouble of having to remember to give the user name on the
905 Specifies one or more files to use for the user host key
906 database, separated by whitespace. The default is
907 ~/.ssh/known_hosts, ~/.ssh/known_hosts2.
910 Specifies whether to verify the remote key using DNS and SSHFP
911 resource records. If this option is set to M-bM-^@M-^\yesM-bM-^@M-^], the client
912 will implicitly trust keys that match a secure fingerprint from
913 DNS. Insecure fingerprints will be handled as if this option was
914 set to M-bM-^@M-^\askM-bM-^@M-^]. If this option is set to M-bM-^@M-^\askM-bM-^@M-^], information on
915 fingerprint match will be displayed, but the user will still need
916 to confirm new host keys according to the StrictHostKeyChecking
917 option. The argument must be M-bM-^@M-^\yesM-bM-^@M-^], M-bM-^@M-^\noM-bM-^@M-^], or M-bM-^@M-^\askM-bM-^@M-^]. The default
918 is M-bM-^@M-^\noM-bM-^@M-^]. Note that this option applies to protocol version 2
921 See also VERIFYING HOST KEYS in ssh(1).
924 If this flag is set to M-bM-^@M-^\yesM-bM-^@M-^], an ASCII art representation of the
925 remote host key fingerprint is printed in addition to the
926 fingerprint string at login and for unknown host keys. If this
927 flag is set to M-bM-^@M-^\noM-bM-^@M-^], no fingerprint strings are printed at login
928 and only the fingerprint string will be printed for unknown host
929 keys. The default is M-bM-^@M-^\noM-bM-^@M-^].
932 Specifies the full pathname of the xauth(1) program. The default
933 is /usr/X11R6/bin/xauth.
936 A pattern consists of zero or more non-whitespace characters, M-bM-^@M-^X*M-bM-^@M-^Y (a
937 wildcard that matches zero or more characters), or M-bM-^@M-^X?M-bM-^@M-^Y (a wildcard that
938 matches exactly one character). For example, to specify a set of
939 declarations for any host in the M-bM-^@M-^\.co.ukM-bM-^@M-^] set of domains, the following
940 pattern could be used:
944 The following pattern would match any host in the 192.168.0.[0-9] network
949 A pattern-list is a comma-separated list of patterns. Patterns within
950 pattern-lists may be negated by preceding them with an exclamation mark
951 (M-bM-^@M-^X!M-bM-^@M-^Y). For example, to allow a key to be used from anywhere within an
952 organization except from the M-bM-^@M-^\dialupM-bM-^@M-^] pool, the following entry (in
953 authorized_keys) could be used:
955 from="!*.dialup.example.com,*.example.com"
959 This is the per-user configuration file. The format of this file
960 is described above. This file is used by the SSH client.
961 Because of the potential for abuse, this file must have strict
962 permissions: read/write for the user, and not accessible by
966 Systemwide configuration file. This file provides defaults for
967 those values that are not specified in the user's configuration
968 file, and for those users who do not have a configuration file.
969 This file must be world-readable.
975 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
976 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
977 de Raadt and Dug Song removed many bugs, re-added newer features and
978 created OpenSSH. Markus Friedl contributed the support for SSH protocol
979 versions 1.5 and 2.0.
981 OpenBSD 5.7 February 20, 2015 OpenBSD 5.7
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